Flower Extracts and Their Essential Oils as Potential Antimicrobial Agents for Food Uses and Pharmaceutical Applications Han Ching Voon, Rajeev Bhat, and Gulam Rusul

Abstract: Plants with potential therapeutic value have been used from time immemorial to cure various ailments and infectious diseases. Secondary metabolites or the bioactive compounds (phytochemicals) present in plants have been reported to be accountable for various observed biological activities. Consumer awareness of the possible side effects of using chemical-based antimicrobial agents has forced researchers to identify and explore natural plant-based antimicrobial agents (or preservatives) that are toxicologically safe, especially when used in food applications. Of late, scientific evidence has been provided on the potential antimicrobial activities exhibited by certain traditionally used flower extracts or their essential oils (edible and wild). This review focuses on providing and updating available information on the antimicrobial activities exhibited by flowers, which are envisaged to find potential applications as natural preservatives for foods or applications in the pharmaceutical industries to develop new and economical herbal-based products for treating various diseases.

Introduction procedures has been attributed mainly to the presence of active Infectious diseases and foodborne illnesses can cause severe phytochemicals or bioactive compounds in plants (Quarenghi and health effects and can even lead to death among the residing others 2000; Ye and others 2004; Zhang and Zhang 2007; Dung population, especially in the developing regions of the world. and others 2008; Zhao and others 2009). The continual emergence of antibiotic-resistant microorganisms Given the scope of searching new antimicrobial agents, antimi- has prompted researchers’ world over to search for new antimicro- crobials derived from plant materials are often regarded as natural bial agents that are more effective against the resistant microbial and safe compared to industrial chemicals. Of late, plant-based pathogens (Nascimento and others 2000; Thaller and others 2010). medicine has become more popular due to the increasing concern Structural modification of the antimicrobials (against which mi- of consumers with regard to the use of synthetic chemical prepa- crobial resistance has been developed) is reported to improve the rations and use of artificial antimicrobial preservatives, especially effectiveness of antimicrobial agents against bacteria, fungi, and in modern food protection practices (Marino and others 2001; viruses (De Clercq 2001; Poole 2001; Jeu and others 2003; Zhang Hamedo and Abdelmigid 2009). and others 2010). However, of late, research efforts have been Some of the hoped-for advantages of using natural antimicro- put forth to improve the effectiveness of antimicrobial drugs by bials include: reducing total dependence on antibiotics, reducing developing novel and a new class of antimicrobial drugs that can development of antibiotic resistance by pathogenic microorgan- effectively work on multitargeted sites or organisms (Esterhuizen isms, controlling cross-contaminations by foodborne pathogens, and others 2006; Alka and others 2010). improvizing food preservation technology, and strengthening im- Traditionally, plants with potential therapeutic or medicinal val- mune system in humans (Abou-taleb and Kawai 2008; Fisher ues have been successfully utilized for preventing and treating var- and Phillips 2008; Tajkarimi and others 2010). Today, growing ious ailments and foodborne illnesses. Since time immemorial, market trends indicate a rapid increase in the number of natu- various plants and their products have been used in traditional ral plant-derived products (such as green tea, herbal decoctions, medicine to cure some of the common disorders and degenerative or herbal medicines) that may include aerial parts, seeds, fruits, diseases in humans as well as in animals (such as Ayurvedic and tra- roots, rhizomes, and flowers. Among these, flowers have attained ditional Chinese medicinal practices). The effectiveness of these high priority and found various applications. Floral extracts and their isolated essential oils are traditionally believed to be rich in phytochemicals exhibiting rich bioactivity. These compounds are MS 20110898 Submitted 7/26/2011, Accepted 9/26/2011. Authors are of interest to the local industry as well as to the general pop- with Food Technology Div., School of Industrial Technology, Univ. Sains Malaysia, Penang 11800, Malaysia. Direct inquiries to author Bhat (E-mail: ulation and are actively being explored for various commercial [email protected] and [email protected]). applications (such as tea, bakery products, and more). Floral ex- tracts and essential oils are also considered to be potential natural

c 2011 Institute of Food Technologists r 34 ComprehensiveReviewsinFoodScienceandFoodSafety Vol.11,2012 doi: 10.1111/j.1541-4337.2011.00169.x Flowers as potential antimicrobial agents . . . antimicrobial agents. Available reports indicate their efficacy and at reduced pressure (temperature preferably ≤ 40 ◦C) in a rotary to possess a broad spectrum of antimicrobial activity against vari- evaporator to prevent degradation of heat-sensitive compounds. ous spoilage and pathogenic microorganisms, which is attributed Solvent extractions are classified into 2 methods: continuous to their bioactive constituents (Quarenghi and others 2000; and noncontinuous. In continuous extraction method (such as Ye and others 2004; Zhang and Zhang 2007; Dung and others percolation, soxhlet extraction), solvent flow through the sample 2008; Zhao and others 2009). Based on these facts, the present re- continuously and the saturated solvent is constantly replaced with view focuses mainly on providing baseline information on explor- a less saturated solvent. In noncontinuous method (such as mac- ing some of the common and wild (edible and nonedible) flowers eration, infusion, decoction), the extraction is stopped when a possessing potential antimicrobial activities. The details on these suitable equilibrium is reached between the solute concentration aspects are hopefully expected to be useful for the commercial ex- (inside the flowers and the solvent), unless the solvent needs to be ploitation of flowers to develop natural preservative preparations replaced with a new batch of solvent (Jones and Kinghorn 2005). with applicability in the food and pharmaceutical industries. Percolation. This is an efficient method wherein a percolator is used for extraction. Percolator is comprised of a wide opening Extraction Method (at the top) to accommodate addition or removal of a sample Solvent extraction along with a valve at the bottom, designed to allow outflow of Solvent extraction is one of the most widely employed methods the solvent. With the valve held at a closed position, samples in for preparation of flower extracts. Solvent extraction (solid-liquid powdered form are added and packed into the percolator leaving extraction) involves the process of leaching (simple physical so- sufficient space to allow expansion. Then the samples are covered lution or dissolution process). Leaching is a separation technique by addition of a suitable solvent, and are allowed to soak for few that involves removal of soluble solids from a solid mixture by hours or overnight. Further, the solvent is allowed to flow out at employing a suitable solvent or solvent mixture. Various factors a controlled flow rate from the bottom of the percolator through influence the solvent extraction procedure, which includes: the the valve. Fresh solvent is added at the top to replace the saturated rate of transport of solvent into the material, rate of solubilization solvent “flow-out” from the percolator (Jones and Kinghorn 2005; of soluble constituents in the solvent, and the rate of transport Singh 2008). of solution (extract) out of the insoluble matter. Solvent polarity, Soxhlet extraction. Soxhlet extraction is a common conven- vapor pressure, and viscosity are also of importance for effective tional method used for extracting heat-stable compounds. The extraction. In case of plant materials, adequate time is required for Soxhlet extractor consists of a distillation flask, an extractor, and diffusion of solvent via plant cell walls for dissolution of soluble a condenser. The solvent in the distillation flask is heated and the constituents and for diffusion of the solution (extract) out to the resulting vapor is condensed in the condenser. The condensed sol- surface of the cell wall (Houghton and Raman 1998; Singh 2008; vent from the condenser fills into the thimble-holder containing Wijekoon and others 2011). the sample that needs to be extracted. When the solution in the Flower extracts can be prepared either from fresh or dried sam- extractor reaches the overflow level, a siphon aspirates the solution ples. Prior to extraction, flower samples are subjected to air-drying of the thimble-holder and unloads it back into the distillation flask, or freeze-drying, followed by grinding, milling, or homogeniza- carrying dissolved solute into the bulk liquid. The solute is left in tion to reduce sample particle size. These procedures are followed the distillation flask while the solvent is evaporated, condensed, in order to enhance the efficiency of extraction process and yield of and passed back into the sample solid bed. This process is repeated the resulting extract. Various solvents, such as methanol, ethanol, 3 to 5 times or until a complete extraction is achieved (Tandon hexane, acetone, ethyl acetate, chloroform are commonly used for and Rane 2008). extraction (either in the pure form or after dilution with distilled Maceration. This method is routinely employed in the labs water) (Dai and Mumper 2010). Choice of selecting a solvent wherein a conical flask covered with aluminum foil or parafilm is mainly depends on the solubility of the bioactive constituents, used to prevent evaporation of the solvent to avoid batch to batch safety aspects, and potentials involved for artifact formations (Jones variations. The powdered sample is left to macerate for a known and Kinghorn 2005). Maintaining the stability of bioactive com- period after addition of a suitable solvent. The maceration process pounds is vital while selecting an appropriate and efficient ex- is considered to be rather slow, and sometimes requires occasional traction method as some of the compounds (mainly those of or continuous shaking (or stirring), as it works by molecular dif- phenolics) tends to get oxidized and degraded at high temper- fusion. Occasional shaking ensures dispersal of saturated solution ature or on prolonging the extraction time (Robards 2003; Dai around the particle surface, bringing fresh solvent to the surface of and Mumper 2010). Besides, an optimized value of “sample-to- particle for further extraction. After maceration, the extract is fil- solvent” ratio needs to be standardized, which involves equilibrium tered through an appropriate filter or screen. In certain instances, between avoidance of saturation effects, solvent wastes, and costs the solid residues are pressed and the occluded solutions are pooled incurred (Pinelo and others 2006; Dai and Mumper 2010). Mag- with the extract before filtration (Jones and Kinghorn 2005; Singh netic stirring and continuous rotary shaking are also employed 2008). in certain cases to enhance molecular interactions during extrac- Infusion. Infusion is a dilute solution that contains readily solu- tion process. Usually, to ensure maximum extraction of bioactive ble constituents prepared by short period of maceration (steeping) compounds, the extraction process is repeated 2 or 3 times and of sample in cold or boiling water. Cold water is recommended the extracts are pooled together (Guillen´ and others 1996; Stalikas to be used for extraction of heat-sensitive compounds. It is highly 2007). Followed by this, the extracts are filtered and centrifuged crucial to dispense the infusion within 12 h of its preparation as it to remove any floating particulate matters. In order to prevent for- is liable for microbial contamination (Singh 2008). mation of artifacts and degradation or polymerization of phenolic Decoction. Decoction is the most widely used and popular tra- compounds, flower extract should not be stored in the solvent at ditional method for the preparation of aqueous extracts of medic- room temperature or exposed to direct sunlight for a long time inal plants. It is made by boiling the sample in water for a period duration. Once done, extracts are freeze dried or concentrated of fixed time duration (Tandon and Rane 2008).

r c 2011 Institute of Food Technologists Vol. 11, 2012 Comprehensive Reviews in Food Science and Food Safety 35 Flowers as potential antimicrobial agents . . .

Extraction of Essential Oils Floral Extracts and Their Essential Oils with Antimi- Hydrodistillation is the simplest and oldest method for obtaining crobial Activities essential oils from plants. In this method, samples are packed in a In Table 1, an overview is presented on some of the selected distillation unit with addition of water. This is brought to a boil reports on edible flowers exhibiting antimicrobial activities. A by applying mild heat (water distillation); alternatively, live steam schematic representation on the potential uses of edible flow- is injected into the sample (direct steam distillation). Essential oils ers, their antimicrobial activities, and their applications as natural are liberated from oil glands present in the plant tissues (due to antimicrobial agents is depicted in Figure 1. Additionally, some effects of hot water and steam). The vapor mixture of water and oil common flowers with reported antimicrobial activities are shown is condensed, when it is carried over to the condenser. From the in Figure 2. In the text below, the potential antimicrobial activities condenser, the distillate flows into a separator, where the essential exhibited/reported on some floral extracts (in solvents) and their oil is separated automatically from the distillate water. Laboratory- essential oil is discussed. scale isolation of essential oil from flowers is accomplished by hydrodistillation with a Clevenger apparatus. In this method, water Allium species distillation is used wherein samples loaded in the apparatus are Allium spp. belongs to the largest genus (Allium, Alliaceae family) completely immersed in water, and brought to a boil (Handa that is comprised of nearly 450 species and is found distributed 2008). widely in the northern hemisphere (Lonzotti 2006). However, However, there are also other physical methods that are used in most of the plants belonging to the Allium genus are consumed conjunction with these methods, such as ultrasound treatments, regularly in many Asia-Pacific regions. The plants and their parts radiation treatments (UV, Gamma, or electron beams), supercriti- are used in cooking because of their characteristic flavor, attributed cal carbon dioxide extraction and others, which have been found due to sulfur-based compounds (Tada and others 1988). Evaluation to be beneficial for better extraction of bioactive compounds. of antimicrobial activity has been reported to support the thera- peutic value of these species as anti-infective agents (Chehregani and others 2007). Methods for determining antimicrobial activity of floral The effective antimicrobial activities (of the aqueous extracts) extracts and essential oils of different parts of Allium spp. (bulbs, leaves, flowers, rhizomes) Various conventional methods are routinely employed for de- against pathogenic bacteria such as Shigella flexinix, Klebsiella pneu- termining the antimicrobial activity of floral extracts and essential moniae, Bacillus subtilis, Bacillus cereus, Staphylococcus aureus,andEs- oils. Generally, in vitro assays are employed. The agar diffusion cherichia coli have been reported based on agar disc diffusion and method (paper disc or well) and dilution method (agar or broth) serial dilution methods (Chehregani and others 2007). The re- are the 2 most common techniques used. ported diameter of inhibition zones for Allium atroviolaceum, Allium Agar diffusion method. The agar diffusion method is one of eriophyllum, Allium scabriscapum, Allium stamineum, Allium iranicum, the most widely employed techniques for evaluating antimicro- and Allium shelkovnikovii ranged from 8.5 to 36.2 mm, 6.4 to bial activity. In this technique, agar plates are inoculated with test 36.8 mm, 5.4 to 25.3 mm, 4.4 to 39.7 mm, 3.9 to 28.3 mm, microorganisms (usually pathogenic microbes). Floral extracts or and 0.0 to 27.8 mm. Moreover, the flower extracts of some Al- essential oils are applied directly onto paper discs, which are then lium spp. (A. scabriscapum, A. iranicum, A. shelkovnokovii) exhibited placed on the agar medium or into wells made in the agar. The much higher antibacterial activity than the bulb extracts with MIC agar plates are incubated to allow the components of floral extracts values (ranging from 0.625 to 5.00 mg/mL, 2.50 to 12.50 mg/mL, or essential oils to diffuse into the agar medium. The diameter of and 2.5 to 10.00 mg/mL), indicating that the tannin accumulated growth inhibition zones around the discs or wells is then consid- in the flowers to have played a role in exhibiting the antimicrobial ered to be an indication of the effectiveness of the material being activities. While the bulbs of Allium spp. are known for their high tested (Kalemba and Kunicka 2003; Holley and Patel 2005). antibacterial activities, the results of this study indicated that the Dilution method. In this method, agar broth cultures (in Petri floral extracts from Allium spp. also have high potential for use as dishes or test tubes) and liquid broth cultures (in conical flasks or antibacterial agents. test tubes or by microtiter plate-broth microdilution method) are used for determining antimicrobial activities. The inhibitory effect Alpinia galanga (Linn.) Swartz. (greater galangal) of the extracts or essential oils are measured based on turbidimetry Alpinia galangal (family: Zingiberaceae) is a stemless perennial or the plate count method. The obtained result is expressed as herb indigenous to South-East Asia and Indonesia. The plant bears growth inhibition index (percentage growth inhibition compared large white flowers with a pleasant fragrance (Yang and Eilerman to the control cultures without extract or essential oil) or minimum 1999). Galangal plant parts have been traditionally used in China inhibitory concentration, MIC (lowest concentrations of extract and Thailand to relieve gastrointestinal pain and to treat mal- or essential oil that can inhibit the growth of microorganisms). adies involving fungi (Yang and Eilerman 1999; Oonmetta-aree In some of the reports (Dung and others 2008; Abdoul-Latif and and others 2006). The flowers are either consumed raw or made others 2010) minimum lethality concentration (MLC, the lowest into pickles in Asian cuisine (Yang and Eilerman 1999; Raina and concentration of extract or essential oil that kills or totally inhibits others 2002; Tonwitowat 2008). The plant’s rhizome is extensively a microorganism), minimum bactericidal concentration (MBC) used in Thai cooking for its unique ginger-like flavor accompanied or minimum fungicidal concentration (MFC) is computed. The with a tinge of pungent and peppery odor (Juntachote and others microorganisms from agar broth or liquid broth where no growth 2007). Furthermore, this plant’s rhizome is also used for medicinal occurs are observed and are transferred into a new medium and purposes, which is reported to exhibit antifungal, antigardial, an- incubated for a certain fixed period of time. In some instances, tiamebic, antimicrobial, and antioxidant activities (Juntachote and MLC is considered to be a concentration that leads to >99.9% Berghofer 2005;Phongpaichit and others 2005; Oonmetta-aree reduction in the number of microorganisms originally inoculated and others 2006; Voravuthikunchai and others 2006; Juntachote (Kalemba and Kunicka 2003; Holley and Patel 2005). and others 2007; Hsu and others 2010).

r 36 Comprehensive Reviews in Food Science and Food Safety Vol. 11, 2012 c 2011 Institute of Food Technologists Flowers as potential antimicrobial agents . . . continued others (2011) others (2008) others(2010) Ignacimuthu (2007) Ignacimuthu (2010) others (2007) (2010) others (2008) (2008a) (2008b) others (2000) (2011) Sassi and others Bhalodia and Sangetha and Ebrahimabadi and Duraipandiyan and Duraipandiyan and Chehregani and Hsu and others Sangetha and Sassi and others Quarenghi and Mann and others , , B. E. , , C. E. coli , , T. S. , ulgaris E. B. v ,E. , A. clavatus S. aureus, E. , E. coli, P. and B. , spp. , , E. coli, S. aureus , S. epidermidis ., E. aerogenes, B. B. subtilis , S. aureus, E. coli S. saprophiticus T. mentagrophytes , C neoformans spp E. coli, A. niger A. niger C. albicans, A. niger , and , , S. marcescens C. , E. faecalis, P. aeruginosa B. cereus K. pneumoniae S. pyogenes , , T. mentagrophytes , S. aureus , thuringiensis, S. typhi, Micrococcus subtilis, S. sonnei, A. lipoferum,pneumoniae, K. P. aeruginosa aeruginosa C. albicans typhi, Micrococcus aerogenes, B. subtilis, S. sonnei, A. lipoferum, K. pneumoniae, P. aeruginosa aureus,K. pneumoniae, S. epidermidis, P. vulgaris, S. paratyphi-A serotype, C. albicans S. epidermidis floccosum water: Not tested Ethyl acetate: T. simii, T. rubrum, E.Scopulariopsis floccosum, spp. Rhein: simii, T. rubrum, E. floccosum, Scopulariopsis spp. cloaceae parapsilosis subtilis sonnei, S. boydii, S. dysenteriae methanol, water: subtilis 4- hydroxyl benzoic acid hydrate: T. mentagrophytes, albicans, A. niger E. coli, P. aeruginosa, P. coli, A. niger Chloroform: Distilled water: S. aureus, S. epidermidis, M. luteus, L. monocytogenes, S. aureus, S. S. flexinix S. epidermidis P. mirabilis, S. aureus S. aureus P. mirabilis, S. aureus P. aeruginosa, E. coli, B. subtilis, S. P. aeruginosa, E. faecalis, S. flexneri, Hexane, chloroform, ethyl acetate, Methanol and hexane: antifungal activity antifungal activity antifungal activity antifungal activity antifungal activity antifungal activity antifungal activity Antifungal activity Hexane, chloro-form, methanol, – Antibacterial and – Antibacterial and 8-dihydroxyanthraquinone-3- carboxylic acid) rhein (1, 4-hydroxy benzoic acid hydrate Antibacterial and – – Antibacterial and – – Antibacterial activity acetate, methanol, and water acetate, methanol, and hot water acetate, methanol, and water hexane, and distilled water Methanol – Antibacterial and Methanol – Antibacterial and Hexane, chloroform, ethyl Petroleum ether, ethyl Hexane and ethanol – Antibacterial activity WaterHexane, chloroform, ethyl – Antibacterial activity Methanol, chloroform, ) × )for × essential oil isolation Solvent used Major antimicrobial component Activity Sensitive microorganism Reference shaker (for 96 h) shaker for 96 h Clevenger apparatus for 3.5 h extraction for 48 h for organic extraction; boiling for 1 h forextraction water Clevenger apparatus for 5 h shaker at room temperature for 24 h temperature extraction for 48 h temperature (3 72 h Method of extraction/ Extraction on a rotary Soxhlet extractionExtraction on a rotary Hydro-alcohol and chloroformHydrodistillation with a –Maceration for 48 h (3 Antibacterial and Sequential solvent Hydrodistillation with a Shakingonanorbital Solvent extraction Methanol – Antibacterial activity Sequential solvent Maceration at room P (Sunshine (Linn.) (Stinking Linn. (Golden spp. (Onion) Blending at room tree) Boiss (Chervil) (Desf.) Batt. and Trab. Swartz. (Greater galangal) chamomile) shower) Beauv. (Gold Coast bombax) Cassia surattensis Chaerophyllum macropodum Chrysanthemumtrifurcatum Alpinia galangal Anthemis cotula Plant Allium Bombax buonopozense Cassia fistula Table 1–Some selected reports on antimicrobial activities of edible flowers.

r c 2011 Institute of Food Technologists Vol. 11, 2012 Comprehensive Reviews in Food Science and Food Safety 37 Flowers as potential antimicrobial agents . . . continued ´ o and others (2008) (2008) (2009) (2007) (2008) (2007) (2010) others (2000) (2009) (2009) (2007) (2002) (2010) Nakhaei and others Stonsauvapak and Bansod and Rai Dung and others Szab Shan and others Ushimaru and others Lachumy and others Zhao and others Uma Devi and others Shan and others Vahidi and others Chouhan and Singh A. A. C. ,MRSA spp., and S. typhi, , (VRE); (VRE); , (MARB) (MARB) S. aureus, S. M. luteus, E. coli , Cladosporium S. aureus, L. ., B. subtilis, C. (FB); , P. mirabilis, Proteus S. aureus S. aureus S. aureus , spp., spp E. faecium E. faecium S. aureus, S. (FS); spp. B. subtilis, P. Cladosporium B. subtilis, P. aeruginosa Nil S. aureus, S. epidermidis S. aureus, L. monocytogenes, S. aureus B. subtilis , albicans, A. niger Ethanol: epidermidis, E. coli baumannii, S. aureus baumannii, E. coli, E. cloacae,pneumoniae, K. P. aeruginosa, S. marcescens, S. aureus Ethanol: (FS); (FB); (SP); MRSA; aureus, E. coli, S. pyogenes,aeruginosa, P. B. proteus, S. sonnei aureus, E. coli, S. anatum Enterococcus monocytogenes, E. aerogenes, S. Typhimurium, S. enteritidis, E.coli, E. coli O157:H7 epidermidis, E. coli, C. albicans (SP); MRSA; Salmonella Micrococcus albicans, A. niger. aeruginosa Ethyl acetate: Methanol: Nil and S. anatum Petroleum ether: spp. aeruginosa, S. aureus, V. cholare Typhimurium, H. pylori S. Typhimurium, S. enteritidis, S. E. coli O157: H7, Y. enterocolitica S. B. cereus, L. monocytogenes, S. E. coli, K. pneumoniae, P. A. niger, A. fumigatus B. cereus, L. monocytogenes, E. coli, E. coli Ethyl acetate: S. aureus, B. thuringiensis, E. coli, antifungal activity antifungal activity – Antibacterial and – Antibacterial activity Petroleum ether: – Antibacterial activity – – Antifungal activity petroleum ether acetate, and methanol distilled water 80% methanol – Antibacterial activity 80% methanol – Antibacterial and Ethanol – Antibacterial activity Essential oil: Petroleum ether, ethyl Ethanol, chloroform, and 80% methanol – Antibacterial activity ) × ) in 8 d 40% ethanol – Antibacterial activity × ) × essential oil isolation Solvent used Major antimicrobial component Activity Sensitive microorganism Reference Clevenger apparatus for 5 h room temperature for 24 h hydrodistillation with a modified Clevenger apparatus for 4 h. Solvent extraction: ethanol extraction (3 wk at room temperature (3 48 h room temperature for 24 h Method of extraction/ Maceration (2 Maceration for 48 h Ethyl acetate, ethanol, and Hydrodistillation with a Solvent extraction 70% methanol – Antibacterial activity Solvent extraction for 48 h 95% ethanolShaking in water bath at – Antibacterial activity Essential oil isolation: Solvent extraction for 1 Soxhlet extraction for 1 h Extraction in a shaker for Shaking in water bath at Soxhlet extraction for 36 h Ethanol – Antibacterial activity Thunb. Linn. L. (Sunn (Torch Linn. (Saffron) Maceration for 3 d Water and methanol – Antibacterial activity Syzygium aromaticum (Blessed thistle) or (Clove) (Roxb.) Merr and Perry (Water fairy flower) ginger) (Dendrobium) Ramat (Chrysanthemum) hemp) Cnicus benedictus Crocus sativus Eugenia caryophyllata Cleistocalyx operculatus Etlingera elatior Crotalaria juncea Dendrobium nobile Plant Chrysanthemum morifolium Table 1–Continued.

r 38 Comprehensive Reviews in Food Science and Food Safety Vol. 11, 2012 c 2011 Institute of Food Technologists Flowers as potential antimicrobial agents . . . continued (2007) (2008) Vuuren (2008) (2007) (2008) (2009) (2011) (2010) (2010) Shan and others Hamdan and others Tsai and others Tsai and others Drewes and Van Rahman and Kang Rhee and others Rajeh and others Pirbalouti and others K. , B. S. aureus, E. P. spp., , P. aeruginosa, K. S. typhi, P. mirabilis , , methicillin- and Micrococcus E. coli , , S. aureus, gentamycin-resistant coli, K. pneumoniae aeruginosa, C. neoformans, C. albicans cereus, S. aureus, S. enteritidis,Typhimurium, S. E. aerogenes and E. coli perfringenes, P. acnes, Peptostreptococci pneumoniae subtilis, B. thuringiensis, E. coli pneumoniae B. cereus S. aureus S. sanguinis B. cereus, S. aureus, S. anatum S. sanguinis B. fragilis, B. ovatus, C. difficile, C. S. aureus L. monocytogenes, B. subtilis, B. B. cereus, E. faecalis, S. epidermidis, antifungal activity Antibacterial and dibenzyloxychalcone,5,7- dibenzyloxyflavanone, 1-[2,4,6-trihydroxy-3-(2- hydroxy-3-methyl-3-butenyl)- phenyl]-1-propanone, acylphloroglucinol derivative, 3-methoxyquercetin and 4’-O-glucose derivative of 2’-hydroxy-6’-methoxy chalcone – – Antibacterial activity - butanol – Antibacterial activity Methanol – Antibacterial activity Distilled water and ethanol80% methanol –Methanol Antibacterial activity n – – Antibacterial activity Antibacterial activity Dichloromethane 2’-hydroxy-4’,6’- Ethanol – Antibacterial activity -butanol essential oil isolation Solvent used Major antimicrobial component Activity Sensitive microorganism Reference (and re- extraction overnight) at room temperature blending for 3 min room temperature for 24 h (and re- extraction overnight) at room temperature Clevenger apparatus for 3 h and partitioning with n temperature for 5 d hydrodistillation with a Clevenger apparatus for 4 h. Solvent extraction: maceration Method of extraction/ Solvent extraction for 3 h Soaking for 20 min and Shaking in water bath at Solvent extraction for 3 h Hydrodistillation with a Reflux with distilled water Solvent extraction at room Essential oil isolation: Maceration for 14 d Methanol – Antibacterial activity L. (Arabian (Horse Thunb. Linn. (Asthma jasmine/ Jasmine flower) (Rosselle) (Honeysuckle) DC. mint) weed) Jasminum sambac Lonicera japonica Hibiscus sabdariffa Mentha longifolia Helichrysum gymnocomum Plant Euphorbia hirta Table 1–Continued.

r c 2011 Institute of Food Technologists Vol. 11, 2012 Comprehensive Reviews in Food Science and Food Safety 39 Flowers as potential antimicrobial agents . . . (2007) (2011) (2010) (2010) (2010) (2010) (2004) (2009) (2010) (2009) Koday and others Ioannou and others Mostafa and others Pirbalouti and others Abe and others Zahid and others Hirulkar and Agrawal Hassan and others Pirbalouti and others Ksouri and others Talreja (2010) P. , P. B. , A. niger S. typhi , , P. aeruginosa, K. P. aeruginosa, K. , , , enterohemorrhagic K. pneumoniae C. albicans , E. coli E. coli , , , C. albicans pyogenes, S. aureus, E. coli,aeruginosa P. pneumoniae S. typhi Typhimurium, E. aerogenes, P. vulgaris, S. aureus, S. epidermidis, B.subtilis, C. freundii, P. aeruginosa epidermidis, S. faecalis, C. albicans, C. tropicalis, C. glabata, Z. rouxii, S. cerevisiae, A. fumigatus, P. frequentans pneumoniae vulgaris subtilis E. coli, P. aeruginosa, C.holmii, kefyr, C. C. albicans, C. sake,glabrata C. pneumoniae, and C. albicans aeruginosa E. coli O157 EHEC S. aureus K. pneumoniae, S. pneumoniae, S. C. macginleyi S. aureus S. aureus, B. subtilis, P. aeruginosa, E. coli, S. pneumoniae, S. S. aureus, S. lutea, B. cereus, E. coli, B. cereus, B. subtilis, S. aureus, S. S. epidermidis, S. aureus, M. luteus, B. subtilis, S. aureus, E. coli, K. MRSA, multi-drug-resistant antifungal activity antifungal activity antifungal activity antifungal activity antifungal activity – Antibacterial activity – Antibacterial activity – Antibacterial activity – – Antibacterial and – – Antibacterial activity chloroform, methanol, and ethanol methanol water Ethanol – Antibacterial activity Hexane, chloroform, and Ethanol – Antibacterial activity Methanol – Antibacterial and – Petroleum ether, ether, – Hot water and 80% ethanol – Antibacterial and essential oil isolation Solvent used Major antimicrobial component Activity Sensitive microorganism Reference modified Clevenger apparatus for 3 h hydrodistillation with a Clevenger apparatus for 4 h. Solvent extraction: maceration extraction Clevenger apparatus for 3 to 4 h hydrodistillation with a Clevenger apparatus for 4 h. Solvent extraction: maceration min Method of extraction/ Hydrodistillation with a Successive Soxhlet Blending Methanol and ethyl acetate Antibacterial and Hydrodistillation with a Essential oil isolation: Magnetic stirring for 30 Soxhlet extraction for 24 h 80% ethanol – Antibacterial and L. (Savory) Essential oil isolation: Celak L. (Bladder (Horseradish Linn. (French (Thunb.) Linn. (White (Rose flower) Soxhlet extraction Petroleum ether, alcohol, and dock) (Green lavender cotton) champa) Roscoe (Myoga) (Thyme) (Egyptian white water-lily) Tamarisk) tree) Satureja bachtiarica Santolina rosmarinifolia Tamarix gallica Rumex vesicarius Rosa spp. Zingiber mioga Plumeria alba Thymus daenensis Nymphaea lotus Plant Moringa oleifera Table 1–Continued.

r 40 Comprehensive Reviews in Food Science and Food Safety Vol. 11, 2012 c 2011 Institute of Food Technologists Flowers as potential antimicrobial agents . . .

Therapeutic values (used in treatment of gastrointestinal pain, dysentery, gout, Edible flowers fever, muscle aches, skin diseases, liver disorder, etc.)

Pharmaceutical values (exhibit analgesic, anti-inflammatory, antioxidant, anticancer, antitumor, anti-hyperglycemic, astringent activities, etc.)

Solvent extracts Essential oils (Aqueous, methanol, ethanol, (Obtained by hydro-distillation) chloroform, hexane, etc.)

Pinene, limonene, spathulenol, myrcene, Tannins, flavonoids, saponins, triterpenoids,

steroids, glycosides, anthraquinones, etc. terpinene, longifolene, cadinol, etc.

Antimicrobial activities

Spoilage microorganisms Pathogenic microorganisms

(A. niger, B. subtilis, C. kefyr, C. holmii, (C. albicans, E. coli O157:H7, L. monocytogenes, E. aerogenes, E. faecalis, H. alvei, S. aureus, S. Typhimurium, S. enteritidis, P. aeruginosa, S. marcescens, S. epidermidis, T. mentagrophytes, T. simii, T. S. cerevisiae, Z. rouxii, etc.) rubrum, Scopulariopsis spp., etc.)

- Preservatives - Antimicrobial agents - Development of antimicrobial packaging (biopolymer based edible films) for food applications

Figure 1–Schematic representation of edible flowers, their antimicrobial activities, and applications as natural antimicrobial agents.

By employing the agar disc diffusion method, antimicrobial but exhibited little or no effect against Gram-negative bacteria activity of galangal flower buds against both Gram-positive and (Salmonella spp., E. coli O157: H7, and Shigella spp.). Overall, Gram-negative bacteria have been tested. The effects of drying antimicrobial activity of galangal was the highest for oven-dried methods (oven drying and freeze-drying) and solvents (hexane samples extracted with ethanol (inhibition zone = 8.94 mm and and ethanol) on the antimicrobial activity have also been investi- MIC = 1.457 mg/mL) and the lowest for the freeze-dried sam- gated (Hsu and others 2010). Galangal was shown to be effective ples extracted with ethanol (inhibition zone = 7.05 mm and MIC against Gram-positive bacteria (Listeria monocytogenes and S. aureus) = 2.470 mg/mL). Due to its ability to inhibit the growth of

r c 2011 Institute of Food Technologists Vol. 11, 2012 Comprehensive Reviews in Food Science and Food Safety 41 Flowers as potential antimicrobial agents . . .

Figure 2–Examples of some flowers with known antimicrobial activities belonging to the species of: a = Clitoria ternatea;b= Cassia fistula;c= Dendrobium nobile;d= Hibiscus spp.; e = Nelumbo spp.; f = Chrysanthemum spp.

Gram-positive bacteria, galangal flower buds have potential to be used as food, as building materials, for extracting dye, and also as a used as natural antimicrobial agent for preservation of perishable source of clothing fiber. The decoctions prepared from leaves and foodstuffs. roots are traditionally used to treat fever, muscle aches, pains, and stomach discomforts (Akuodor and others 2011). Anthemis cotula L. (Stinking chamomile) Mann and others (2011) have evaluated antimicrobial activities Anthemis cotula (family: Asteraceae), a native of Europe and a of Bombax flowers against S. aureus, E. coli,andA. niger using weed that grows extensively in Argentina, is commonly known the disc diffusion method. The results obtained clearly demon- as Manzanilla del campo. Traditionally, A. cotula is believed strated antimicrobial activity of methanol, chloroform, hexane, to be effective for treatment of dysentery and gout. The de- and aqueous extracts against the 3 pathogens tested. However, the coctions made from the leaves and flowers are reported to chloroform extract did not exhibit any activity against S. aureus exhibit insecticidal properties (Quarenghi and others 2000). and the aqueous extract showed no activity against A. niger. The The flavonoid constituents present in this flower have been results of this study were able to provide scientific evidence to sup- reported to contain: quercetagetin, quercetagetin 7-glucoside, port the traditional uses of B. buonopozense for curing microbial quercetin, quercetin 7-glucoside, patuletin, patuletin 7-glucoside, infections. kaempferol, kaempferol 7-glucoside, and kaempferol 3-rutinoside (Quarenghi and others 2000). Cassia fistula Linn. (golden shower tree) Quarenghi and others (2000) employed the agar disc diffu- Cassia fistula (family: Leguminosae) is an ornamental tree found sion method to evaluate the antimicrobial activity of A. cotula in various parts of China, India, Mauritius, South Africa, Mexico, (methanol extract) against some of the pathogenic microbes, such the West Indies, East Africa, and Brazil. Various parts of this plant as S. aureus, Staphylococcus epidermidis, Micrococcus luteus, Streptococ- are used in the treatment of intestinal disorders, skin diseases, cus pneumoniae, E. coli, Pseudomonas aeruginosa, Proteus vulgaris, and such as leucoderma, liver problems, tuberculosis, hemetemesis, di- Salmonella spp. Owing to the flavonoid compounds present in the abetes, rheumatism, hypercholesterolemia, and diarrhea. The fruit flower, methanol extract at a concentration of 200 μg/mL was pulp is used as a laxative, purgative, antipyretic, analgesic, and an- found to exhibit rich antimicrobial activities against the bacteria timicrobial agent in Indian Ayurvedic medicine. Its flowers have tested (except for S. pneumoniae and Salmonella spp.) with diameters been reported to exhibit antifungal activities (to treat skin infec- of inhibition zones ranging from 6.0 to 9.0 mm. tion) and are used to treat nasal infections in certain tribal sects (Perumal Samy and others 1998; Prashanth Kumar and others Bombax buonopozense P. Beauv. (Gold Coast Bombax) 2006; Duraipandiyan and Ignacimuthu 2007; Bhalodia and others Bombax buonopozense (family: Bombaceae) is a large tropical tree 2011). Also, flowers have been reported to be useful in treating in Africa (found in Ghana, Uganda, and Gabon). The plant grows pruritus, burning sensation, dry cough, and bronchitis attributed up to 40-m high with large buttress roots, which are spread upto to its demulcent, lubricating, cooling, and emollient effects 6 m (Beentje and Sara 2001). This tree is also popular as “Vabga” (El-Saadany and others 1991; Duraipandiyan and Ignacimuthu in Ghana and “Kurya” in Northern Nigeria. The plant parts are 2007; Bhalodia and others 2011).

r 42 Comprehensive Reviews in Food Science and Food Safety Vol. 11, 2012 c 2011 Institute of Food Technologists Flowers as potential antimicrobial agents . . .

Duraipandiyan and Ignacimuthu (2007) have reported antimi- antibacterial activity against Gram-positive bacteria (Durmaz and crobial activity of hexane, chloroform, ethyl acetate, methanol, others 2006). and water extracts (at 1.25, 2.5, and 5 mg/disc) of C. fistula flower The antimicrobial activity of essential oil and methanolic ex- against Gram-positive bacteria (S. aureus, S. epidermidis, B. subtilis, tracts from the flower of C. macropodum against 9 bacteria and 2 Enterococcus faecalis) and 1 Gram-negative bacterium (P. aeruginosa) fungi was determined by Ebrahimabadi and others (2010) who with the inhibition zones ranging from 7 to 23 mm. The MIC for employed agar disc diffusion and mico-well dilution assays. From the sensitive microorganisms (S. aureus, S. epidermidis, B. subtilis, gas chromatography (GC) and gas chromatography-mass spec- E. faecalis, P. aeruginosa) were found to be 0.039 to 2.5 mg/mL. trometry (GC-MS) analysis, the chemical composition of essential The compound 4-Hydroxy benzoic acid hydrate, which was ob- oil was found to be comprised of 49 components representing tained from ethyl acetate extract, showed a MIC of 0.5 mg/mL 98.3% to 99.4% of the oil with trans-β-farnesene (27.5%), trans- for fungi, such as Trichophyton mentagrophytes and Epidermophyton β-ocimene (20.9%), β-pinene (2.8%), limonene (12.0%), spathu- floccosum. The compound rhein (1, 8-dihydroxyanthraquinone-3- lenol (8.6%), and myrcene (1.3%) as the major constituents. The carboxylic acid) isolated from the ethyl acetate extract was found essential oil was found to be active against all the tested microor- to be effective against fungal pathogens, such as T. mentagrophytes, ganisms (except for Shigella dysenteriae and A. niger) with inhibition Trichophyton simii, Trichophyton rubrum, Epidermophyton floccosum, zones recorded as 8 to 26 mm and MIC recorded to be 125 to and a Scopulariopsis spp. with MIC values of 31.25, 125.00, 500 μg/mL. However, the methanol extract did not show any 62.50, 31.25, and 250.00 μg/mL, respectively (Duraipandiyan and inhibitory effects on the tested microorganisms. Ignacimuthu 2010). Sangetha and others (2008) evaluated the antimicrobial ac- Chrysanthemum morifolium Ramat. (Chrysanthemum) tivity of methanol extracts from different parts (leaves, flowers, Chrysanthemum morifolium (family: Asteraceae) is an important stems, and pods) of C. fistula and Cassia surattensis against 12 bac- medicinal herb of the Asteraceae family consisting of 8 major teria and 3 fungi by using the agar disc diffusion assay. All the varieties (Hangju, Boju, Gongju, Chuju, Qiju, Huaiju, Jiju, and bacteria and fungi studied (except E. coli and Saccharomyces cere- Hang ju). C. morifolium is traditionally used in China to protect visiae)weresusceptibletotheextractofC. fistula flowers with the cardiovascular system, to lower blood glucose and fat levels, inhibition zones ranging from 12 to 20 mm. to regulate blood pressure, excrete lead, and to scavenge free rad- Bhalodia and others (2011), in one of their studies, by em- icals. This plant has been reported to exhibit significant antibac- ploying the agar disc diffusion method, screened the antimicrobial terial, antioxidant, anti-inflammatory, and anticancer activities. activities of hydro-alcohol and chloroform extracts of C. fistula (5, The bioactive compounds of C. morifolium consist of flavonoids, 25, 50, 100, and 250 `ıg/mL) against S. aureus, Streptococcus pyo- sesquiterpenoids, chlorogenic acids, vitamins, and amino acids genes, E.coli,P.aeruginosa, A. niger, Aspergillus clavatus,andCandida (Zhang and Zhang 2007; Zhao and others 2009). albicans. Results showed both the extracts to exhibit moderate to The methanolic extract of C. morifolium (inflorescence) showed strong antibacterial and antifungal activities (inhibition zones of 12 antimicrobial activity against B. cereus, L. monocytogenes, E. coli,and to 21 mm for bacteria and 13 to 22 mm for fungi) at all the tested Salmonella anatum with inhibition zones in the range of 5.5 to concentrations, except for 5 μg/mL. Preliminary phytochemical 9.2 mm (Shan and others 2007). Besides, the antimicrobial activ- screening performed in this study showed that the chemical com- ity of petroleum ether, ethyl acetate, and methanolic extracts of 7 pounds of the hydro-alcohol extract contained tannins, flavonoids, species of C. morifolium flowers cultivated in Kaifeng, China were saponins, triterpenoids, steroids, glycosides, anthraquinones, re- tested against S. aureus and methicillin resistant S. aureus (MRSA) ducing sugars, and amino acids, while those of the chloroform by the disc diffusion assay (Zhao and others 2009). Petroleum extracts were found to contain high amount of glycosides, pheno- ether extracts of Mailang, Chunrijianshan, and Lengyan, as well lic compounds, tannins, and anthraquinones. as ethyl acetate extracts of Mailang, Chunrijianshan, Lengyan, Jianliuxiangbai, Guohuawansheng, and Changhong varieties Cassia surattensis Burm.f. (Sunshine tree) showed good antibacterial activity on S. aureus with MIC of 125, Cassia surattensis (family: Leguminosae) is a flowering plant 250, 250, 250, 250, 125, 250, and 250 μg/disc, respectively. The native to South Asia, and found growing abundantly in India, petroleum ether extracts of Mailang, Chunrijianshan, and Lengyan Myanmar, Southern Pakistan, and Sri Lanka. The plants are grown were active against MRSA with MIC of 250 μg/disc. All the ex- as ornamental trees in tropical and subtropical regions. The bark tracts of Baiyudai did not exhibit any activity against S. aureus and leaves of C. surattensis are believed to exhibit antiblenorrhagic and MRSA at the tested concentration (250 μg/disc). Also, the properties (Sangetha and others 2008). methanol extracts of all the species of C. morifolium did not show In one of the experiments conducted by Sangetha and others any antimicrobial activity. The authors have concluded that better (2008) on different parts (leaves, flowers, stems, and pods) of C. antimicrobial activity was shown by yellow flowers compared to fistula and C. surattensis, all the bacteria and fungi studied (ex- purple and white flowers. cept Bacillus thuringiensis and S. cerevisiae)weresusceptibletothe methanol extract of C. surattensis flowers with inhibition zones Chrysanthemum trifurcatum (Desf.) Batt. and Trab. ranging from 12 to 20 mm. Chrysanthemum trifurcatum (family: Asteraceae) is an herbal plant bearing small yellow flowers. This plant is widely distributed in Chaerophyllum macropodum Boiss. (Chervil) Tunisia regions and the plant parts are used for treating constipa- Chaerophyllum macropodum (family: Apiaceae) is a biennial shrub tion, intestinal transit problems, and postdelivery pains (Sassi and with hard pinnate leaves. In Iran and Turkey, the edible vegetable others 2008b). The antimicrobial activity of petroleum ether, ethyl obtained from this plant is used as food and in the preparation acetate, methanol, and hot water extracts of Tunisian Chrysanthe- of cheese (Durmaz and others 2006; Coruh and others 2007; mum species against 5 Gram-positive and 9 Gram-negative bac- Ebrahimabadi and others 2010). The organic solvent extract from teria and 4 yeasts were evaluated by Sassi and others (2008a) the aerial parts of C. macropodum have been reported to exhibit by employing agar disc diffusion and microdilution assays. The

r c 2011 Institute of Food Technologists Vol. 11, 2012 Comprehensive Reviews in Food Science and Food Safety 43 Flowers as potential antimicrobial agents . . . results obtained showed all the extracts to inhibit growth of the resistant S. aureus (MRSA) and vancomycin-resistant Enterococci tested microorganisms (inhibition zone = 7.1 to 8.5 mm; MIC = (VRE), the authors found essential oil at the MBC (8 and 16 1.25 mg/mL) except for S.aureus,E.coli, K. pneumoniae, Aeromonas μL/mL) to possess potential inhibitory effects with the exposure hydrophila, C. albicans, and Candida tropicalis. time required for complete inhibition of cell viability to range Further, the same authors have reported on the antimicro- from 10 to 40 min and 10 to 20 min, respectively. Scanning bial activity of the essential oil from C. trifurcatum flower heads electron spectroscopy on the most sensitive methicillin-resistant against 5 Gram-positive bacteria (S. epidermidis, Staphylococcus hoe- S. aureus and vancomycin-resistant Enterococcus (MRSA–P249 and molyticus, Staphylococcus hominis, Staphylococcus simulans, and B. sub- VRE–B2332) treated with essential oil at MIC (8 μL/mL) showed tilis) and 3 Gram-negative bacteria (E. coli, Hafnia alvei, and disruption and lysis of membrane integrity. The essential oil Proteus mirabilis) (Sassi and others 2008b). The broth microdi- was found to contain 55 compounds representing 93.71% of lution method was adopted for assaying antimicrobial activities. the oil with γ -terpinene (5.76%), cis-linalool oxide (5.21%), The essential oil was found to exhibit better antimicrobial ac- camphene (4.12%), trans-carveol (3.93%), α-pinene (3.45%), β- tivity against Gram-negative bacteria compared to Gram-positive pinene (3.07%), terpinen-4-ol (2.58%), and myrcene (2.4%) as the bacteria. At a concentration of 500 μg/mL, the essential oil in- major monoterpenes as well as globulol (5.61%), acorenol (5.12%), hibited the growth of S. epidermidis and B. subtilis by 66% and 64% β-himachalol (3.84%), cyclobazzanene (3.12%), 2,3-dehydro-1,4- with IC50 (concentration that inhibits 50% of growth) of 62.5 cieol (3.01%), trans-dihydrocarvone (2.58%), presilphiperfol-1- and 125 μg/mL, respectively. The authors reported the presence ene (2.48%), and γ -amorphene (2.12%) as the major sesquiter- of 56 compounds representing 97.48% of the oil with limonene penes. The authors, for the first time, concluded the use of essential (20.89%), γ -terpinene (19.13%), 1,8-cineole (10.64%), β-pinene oil and ethanolic extract of C. operculatus to have applicability for (8.77%), α-pinene (5.32%), 2-hexenal (4.85%), 4-terpenyl ac- the prevention and treatment of diseases caused by foodborne and etate (3.42%), β-myrcene (2.31%), germacrene-B (2.01%), skin-infectious pathogens, especially those of antibiotic-resistant β-spathulenol (1.62%), longifolene (1.39%), α-cadinol (1.39%), strains. α-thujene (1.23%), and β-bourbobene (1.06%) as the major con- stituents that contributed to the antibacterial activity of the essen- Clitoria ternatea Linn. (butterfly pea, Asian pigeon wings) tial oil. Clitoria ternatea (Family-Liguminoceae) is a tropical, perennial twining herb bearing blue or white colored flowers (in single). Cleistocalyx operculatus (Roxb.) Merr and Perry (water fairy This plant is extensively grown for ornamental and medicinal flower) purpose in the Asian subcontinent (India, Bangladesh, Indonesia, Cleistocalyx operculatus (family: Myrtaceae), also known as Eu- Malaysia). In Malaysia, aqueous extract of the flower is used as genia operculata or Syzygium nervosum, is a perennial tree, widely a natural coloring agent for preparing dish from glutinous rice. distributed in China, Vietnam, and other tropical countries. Tra- The plant parts have been reported to exhibit anti-inflammatory, ditionally, the leaves and flower buds of the plant have been re- antipyretic, antihyperlipidemic, analgesic, tranquilizing, and im- ported to be used as an ingredient in preparing certain beverages munomodulatory activities (Mukherjee and others 2008; Solanki (tea decoctions) for treating gastrointestinal disorders and antisepsis and Jain 2010, 2011, 2012). Root contains flavonol glycosides, (Dung and others 2008). In vivo and in vitro studies have shown the which exhibit rich antibacterial activity (Yadava and Verma2003). potentiality of C. operculatus buds to exhibit anticancer, antitumor, Cliotides (biologically active peptides) (present in flowers, seeds, antihyperglycemic, and cardiotonic properties (Anthony and oth- and nodules) have been isolated from heat-stable fractions of Clito- ers 2002; Ye and others 2005; Mai and Chuyen 2007; Dung and ria ternatea extract. These cliotides showed potential antimicrobial others 2008). Results on the phytochemicals screening of flower activity against E. coli and cytotoxicity against HeLa cells (Nguyen buds have shown the presence of sterols, flavanones, chalcones, and others 2011). triterpene acid, β- sitosterol, and ursolic acids in the buds (Ye and Uma and others (2009) have screened the flower extracts others 2004; Dung and others 2008). (by maceration technique: solvents used methanol, chloro- Dung and others (2008), by using agar disc diffusion and mi- form, petroleum ether, hexane, and aqueous) of Clitorea ter- crodilution susceptibility tests, have screened the effectiveness of natea against pathogenic microorganisms, such as uropathogenic, the essential oil and ethanol extract of C. operculatus buds against enteropathogenic, and enterotoxigenic E. coli, S. Typhimurium, 2 food spoilage bacteria (B. subtilis and P. aeruginosa), 9 foodborne S. enteritidis, K. pneumoniae, and Pseudomonas aureginosa. These pathogens (2 isolates of S. aureus, L. monocytogenes, Enterobacter aero- microorganisms were isolated from patients with urinary tract genes, Salmonella Typhimurium, Salmonella enteritidis, E. coli, and 2 infection and acute gastroenteritis. The method adopted for isolates of E. coli O157:H7), 4 skin infectious pathogens (S. aureus, determining antimicrobial activity was disc diffusion method S. epidermidis, E. coli, and C. albicans), 3 methicillin-resistant S. and minimum inhibitory concentration (two-fold serial dilu- aureus, 3 vancomycin-resistant Enterococcus faecium, and 15 multi- tion method). Results of this study revealed aqueous, methanol, antibiotic-resistant bacteria (2 isolates of Acinetobacter baumannii, and chloroform extracts to exhibit antimicrobial activity against 3 isolates of E. coli, 2 isolates of Enterobacter cloacae, 2 isolates uropathogenic, enteropathogenic, and enterotoxigenic E. coli, S. of K. pneumoniae, 3 isolates of P. a e r u g i n o s a , 2 isolates of Serratia Typhimurium, K. pneumoniae, and P. a u r e g i n o s a .However,noan- marcescens,andS. aureus). The essential oil of C. operculatus buds tibacterial activity was recorded for petroleum ether and hexane showed inhibition zones and MIC/MBC, which ranged from 8 extracts. to 16 mm and 1 to 20 μL/ mL, respectively, effective against all the tested microorganisms. The ethanol extract demonstrated an- Cnicus benedictus Linn. (blessed thistle) timicrobial activity against all the Gram-positive bacteria and 1 Cnicus benedictus (family: Asteraceae) is the single species in the food-spoilage Gram-negative bacterium (P. a e r u g i n o s a ) with inhi- genus Cnicus; it is native to the Mediterranean region. This annual bition zones and MIC/MBC in the range of 8 to 22 mm and 0.25 plant grows up to 60-cm high, and has leathery, hairy leaves (ex- to 32 mg/mL. Besides, in the cell viability assay of methicillin- tending up to 30-cm long and 8-cm broad), with minute spines

r 44 Comprehensive Reviews in Food Science and Food Safety Vol. 11, 2012 c 2011 Institute of Food Technologists Flowers as potential antimicrobial agents . . . on the leaf margins. The flowers are yellow, which are produced Nakhaei and others (2008) screened the anti-Helicobacter pylori in a dense flower head of 3 to 4 cm dia. The entire plant of C. activity of stigmata of C. sativus against 45 clinical isolates. Based benedictus possesses astringent, bitter, diaphoretic, diuretic, emetic, on the results obtained from the agar disc diffusion method, the emmenagogue, galactogogue, stimulant, stomachic, and contra- aqueous and methanol extracts of saffron exhibited antibacterial ceptive properties. An aqueous infusion of the entire plant is activity against all the isolates with inhibition zones being in the reported to be used for the treatment of liver and gall bladder range of 10 to 23.5 mm. Based on the agar dilution method, the problems. The flowers, leaves, and stem of C. benedictus are tra- MIC of the methanol extract for all the isolates was 677 μg/mL. ditionally used as a health drink (tonic) or used in other prepa- There was no significant difference in the activity of methanol rations taken orally to improve appetite and digestion (extracts extract at 80 and 121 ◦C, in comparison to the control, indicating are believed to stimulate gastric juices). This plant is known to that high temperature not to have any effect on the activity of the contain ample amounts of sesquiterpene lactones, alkaloids, tan- extract. The results on pH stability of the methanol extract in this nins, and volatile oil. Besides this, anti-infective, anticancer, and study indicated that active compounds of C. sativus were stable at anti-inflammatory activities of C. benedictus have been reported pH 5, 6, 7, and 8. through laboratory studies by Szabo´ and others (2009). In addition, the chemical constituents (such as cnicin and polyacetylene) have Crotalaria juncea Linn. (sunn hemp) been reported to exhibit antibacterial activity (Szabo´ and others Crotalaria juncea (family: Leguminoceae) plant parts (flowers, 2009). buds, pods, and seeds) are commonly used as medicine and for The effects of ethanol extracts of C. benedictus flowers against culinary purposes (Bhatt and others 2009). The plant is widely American Type Culture Collection (ATCC) bacterial strains (S. distributed in tropical and subtropical regions, such as in India, Typhimurium, S. enteritidis, S. aureus, E. coli, S. pyogenes, P. aerug- Nepal, Sri Lanka, and Southern Africa. In Ayurvedic medicine, C. inosa, Bacillus proteus,andShigella sonnei) and pathogens obtained juncea has been used as an astringent, abortifacient, blood purifier, from hospitalized patients (S. aureus, S. pyogenes,andE. coli)were demulcent, emetic, purgative, and for curing anemia, impetigo, assessed by using the agar disc diffusion assay (Szabo´ and oth- menorrhagia, and psoriasis (Sharma and others 2001; Chouhan ers 2009). The antimicrobial activity of the C. benedictus flowers and Singh 2010). The seeds of C. juncea have been reported to ex- against all the tested bacteria were observed with inhibition zones hibit significant antispermatogenic, anti-ovulatory, and contracep- of approximately the same values at different concentrations of tive activities (Vijaykumar and others 2004; Malashetty and Patil the extracts (10% and 20%, respectively). The diameters of inhi- 2007). The chemical compounds isolated from the seeds of this bition zones shown by C. benedictus mature flowers (16 to 30 mm) plant were riddelline, seneciphylline, senecionine, trichodesmine, on ATCC bacterial strains were significantly different from those chodesmine alkaloids, galactose-specific lectin, and cardiogenin r shown by immature flowers (18 to 32 mm). The test results on the 3-O-[ ]-d-xylopyranoside (Adams and Gianturco 1956; Chouhan microorganisms harvested from hospitalized patients treated with and Singh 2010). the extract of mature flowers showed diameters of inhibition zones Chouhan and Singh (2010) have reported antibacterial activity to range between 10 and 24 mm. of the ethanolic extract of C. juncea flowers against both Gram- positive and Gram-negative bacteria by employing the agar disc Crocus sativus Linn. (saffron) diffusion assay. The extracts were found to be effective against Crocus sativus (family: Iridaceae) has been used traditionally as E. coli, K. pneumoniae, P. aeruginosa, S. aureus, and Vibrio cholare a spice and as a food colorant in most of the countries over the (inhibition zone = 13, 14, 10, 13, and 8 mm). However, the world. Saffron, the world’s most expensive spice is obtained from extracts did not exhibit any activity against Citrobacter freundi, E. the flower (mainly the stigmata) of the C. sativus plant. In folk faecalis, Shigella flexneri,andS. dysenteriae. Further, the authors medicine, saffron has been used as aphrodisiac, antispasmodic, and have reported on the presence of steroids, triterpenes, flavonoids, expectorant (Nakhaei and others 2008). Saffron is also used to treat phenolics, and glycosides in the ethanol extract. flatulence, colic, and abdominal pains, as well as to improve ap- petite and memory (Zhang and others 1994; Nakhaei and others Dendrobium nobile Lindl. (dendrobium orchid) 2008). Antitumor, radical scavenging, hyperlipemic, anticonvul- Dendrobium nobile (family: Orchidaceae) is a flowering orna- sant, cytotoxic, antigenotoxic, and anti-ulcerogenic activities have mental plant encompassing nearly 35000 species. The flowers been reported for C. sativus extracts or their chemical constituents are very attractive and appear in various colors and forms. The (Nair and others 1995; Hosseinzadeh and Khosravan 2001; opened flowers mimic bees, wasps, butterflies, moths, frogs, lizards, Abdullaev and others 2003; Al- mofleh and others 2006; Nakhaei and even humans. Native inhabitants of the Eastern Himalayas and others 2008). The biological properties of C. sativus are mainly (in India) believed that dendrobium flowers can cure eye dis- attributed to crocin and saffranal, which are isolated from stigmata, eases (Uma Devi and others 2009). Gigantel and moscatilin of D. leaves, petal, and pollen. Other isolated chemical constituents in- nobile have been reported to exhibit antimutagenic activity and its clude crocetin, picrotoxin, quercetin, and kaempferol (Nakhaei 2-phenanthrenes to exhibit anticancer activity (Kong and others and others 2008). 2003; Uma Devi and others 2009). According to Vahidi and others (2002), significant antimicrobial Uma Devi and others (2009) used the “strip plate method” to activity was observed against S. epidermidis, C. albicans, Cladosporium evaluate the antimicrobial activities of different solvent (methanol, spp., and A. niger when an ethyl acetate extract of stigmata of C. chloroform, and water) extracts of flowers and stems of D. nobile sativus was used. The inhibition zones and MIC ranged from 12 against pathogenic bacteria, such as E. coli, B. subtilis, Proteus spp., to 19 mm and 6.25 to 50 mg/mL, respectively. The ethyl acetate S. Typhimurium, and S. aureus. The extent of inhibition of floral extract of stamens exhibited antimicrobial activity against S. aureus, extracts was high in the aqueous extract than in the other 2 extracts. S. epidermidis, E. coli, M. luteus, Cladosporium spp., and A. niger with The authors recorded the inhibition zones as 0.6 to 1.0 mm for inhibition zones and MIC ranging from 15 to 21 mm and 12.5 to ethanol extract, 0.3 to 1.0 mm for chloroform extract, and 0.53 50 mg/mL, respectively. to 1.2 mm for aqueous extract. Also, in aqueous extracts, the

r c 2011 Institute of Food Technologists Vol. 11, 2012 Comprehensive Reviews in Food Science and Food Safety 45 Flowers as potential antimicrobial agents . . . inhibitory activity was found to be significantly higher in flowers Bansod and Rai (2008), reporting on the antifungal (against than that of stems. Aspergillus fumigatus and A. niger) assays of some Indian medicinal plants isolated from patients with pulmonary tuberculosis noted Etlingera elatior (Jack) R.M. Smith (torch ginger) E. caryophyllata to exhibit antifungal activity. Based on the disc Etlingera elatior (family: Zingiberaceae) is a perennial herbal plant diffusion assay, the essential oil of E. caryophyllata was found to (height of 3.6 to 4.7 m) found growing abundantly in parts of exhibit moderate antifungal activity with inhibition zones ranging Malaysia, Indonesia, Vietnam, Sri Lanka, and Thailand. The flower from 8 to 15 mm. The MIC, determined by the agar dilution (bud or inflorescence) is used both ornamentally and as a spice for method, was found to be 0.12% (v/v) for both of the fungi, culinary use. Rhizome and flowers of this plant are extensively while the MIC/MLC (determined by the broth microdilution used as a natural ingredient in cosmetics (as an ingredient of soap, method) was found to be 0.06%/0.12% (v/v) for A. fumigatus and shampoo, perfume) and also as a therapeutic agent for treating 0.12%/0.06% (v/v) for A. niger, respectively. The authors have common ailments. Fruits of the torch ginger plant are traditionally concluded that the essential oil of E. caryophyllata might play a used to treat ear ache, while leaves find use to clean wounds and pivotal role in treating mycotic infections. to remove body odor (Chan and others 2007). Flowers and the mature inflorescence of torch ginger are used to prepare such Euphorbia hirta Linn. (asthma weed) popular dishes as asam laksa, nasi kerabu, nasi ulam (in Malaysia), Euphorbia hirta (familiy: Euphorbiaceae) is a small perennial herb arisk ikan mas (in North Sumatra, Indonesia), and sayur asam (in that is found widely spread in tropical regions of the world. The Thailand) (Lachumy and others 2010; Wijekoon and others 2011). plant is erect, bears a slender hairy stem, and grows up to 80 cm Torch ginger inflorescence is reported to possess strong antioxidant in height. Occasionally, the plant is also witnessed to grow as a activities (Wijekoon and others 2011). semicreeper. The leaves are broad, elliptical, oblong, and lanceo- Lachumy and others (2010) evaluated the antimicrobial activity late, darker on the upper surface with slightly toothed margins. (by agar disc diffusion and serial dilution methods) of an 80% Flowers of this plant are small, numerous, and crowded together methanolic extract of torch ginger flowers against 7 strains of in dense cymes (about 1 cm in diameter). bacteria, 1 strain of yeast, and 1 strain of mold. Results of this study The stems and leaves contain milky-white latex. Rajeh and oth- showed methanol extract of the flowers to possess high amounts of ers (2010) have reported on the traditional use of E. hirta plant flavonoids, terpenoids, saponins, tannins, and carbohydrates. Floral decoctions to treat amebic dysentery,diarrhea, peptic ulcers, heart- extracts were found to be active against the tested microorganisms burn, vomiting, respiratory problems (bronchitis, coughs, colds), (inhibition zone = 12 to 23 mm; MIC = 1.563 to 50.000 mg/mL). kidney stones, and fertility-related problems (menstrual problems, Results from the brine shrimp lethality test revealed absence of sterility, and venereal disease). In certain instances, the plant parts toxicity of the flower extract (LC50 = 2.52 mg/mL against Artemia have been recommended to be used as an antidote and to relieve salina), and therefore are nontoxic to humans. pain from scorpion stings or snake bites. Methanolic extracts from different parts of E. hirta (leaves, flow- Eugenia caryophyllata Thunb. (synonym, Syzygium aro- ers, stems, and roots) were evaluated by Rajeh and others (2010) for maticum) (clove) antimicrobial activities against 4 Gram-positive bacteria (S. aureus, Eugenia caryophyllata (family: Myrtaceae) is commonly found a Micrococcus spp., B. subtilis,andB. thuringiensis), 4 Gram-negative growing in warm and humid climatic conditions, such as bacteria (E. coli, K. pneumoniae, Salmonella typhi,andP. mirabilis) those encountered in tropical Asia (India, Sri Lanka, Malaysia, and 1 yeast species (C. albicans). Results of this study, which were Indonesia). The handpicked, unopened, air- or sun-dried flower based on the agar disc diffusion method, revealed all the tested buds are used as spice. Traditionally, the floral buds have been used microorganisms, except C. albicans, to be sensitive to the flower to treat tooth aches. The essential oil obtained from buds are ex- extract, with inhibition zones formed ranging from 9 to 28 mm. tensively used as an ingredient of dental formulations, toothpastes, The LC50 value (0.033 mg/mL) against Artemia salina, which was breath fresheners, mouthwashes, cosmetics, soaps, and insect re- obtained from the brine shrimp lethality test, demonstrated that pellents (Politeo and others 2010). The essential oils have been E. hirta flower extract might be toxic to humans. reported to exhibit good antibacterial, antifungal, cytotoxic, and antioxidative activities (Baratta and others 1998; Gayoso and others Helichrysum gymnocomum DC. 2005; Prashar and others 2006). Helichrysum gymnocomum (family: Asteraceae) is a perennial herb Stonsaovapak and others (2000) have reported on the inhibitory with long flowering seasons commonly encountered in regions of effects of ethanolic extracts of E. caryophyllata flowers against Kwazulu-Natal Drakensburg, Africa. The pleasant scented flowers pathogenic E. coli O157:H7 and Yersinia enterocolitica with inhi- and leaves are burnt by the indigenous people of this region to bition zones of 17.75 and 18.00 mm. At 3.0 × 104 CFU/mL, fumigate sick rooms and to invoke the goodwill of ancestors. H. the MIC for E. coli O157: H7 was 1250 μg/mL, while at 3.0 × gymnocomum has also been traditionally used for the treatment of 106 CFU/mL, the MIC was 2500 μg/mL. For Y. enterocolitica,the wounds, coughs, and colds (Drewes and Van Vuuren 2008). MIC was 625 μg/ mL at 6.0 × 104 CFU/mL and 1250 μg/mL The antimicrobial activities of H. gymnocomum dichloromethane 6 at 6.0 × 10 CFU/ mL. (CH2Cl2/MeOH) extract and isolated compounds against 5 Shan and others (2007) have reported effectiveness of methanol Gram-positive bacteria, 3 Gram-negative bacteria, and 2 yeasts extracts of E. caryophyllata against B. cereus, L. monocytogenes, S. were evaluated by Drewes and Van Vuuren (2008) by the serial di- aureus, E. coli, and S. anatum with inhibition zones being in the lution method. From the results, it was noteworthy that the crude range of 10.1 to 21.3 mm. And Ushimaru and others (2007) have extracts demonstrated antimicrobial activities with MIC ranging reported methanol extract of E. caryophyllata to effectively inhibit from 312.5 to 1000 μg/mL. the growth of S. Typhimurium, S. aureus, Enterococcus spp. and E. All the isolated compounds (2-hydroxy-4,6-dibenzyloxy- coli (MIC 50% = 0.41% to 1.60% v/v and 0.39 to 1.52 mg/mL; chalcone; 5,7-dibenzyloxyflavanone; an acylphloroglucinol MIC 90% = 0.49% to 1.76% v/v and 0.46 to 1.67 mg/mL). derivative; 1-[2,4,6-trihydroxy-3-(2-hydroxy-3-methyl-3-

r 46 Comprehensive Reviews in Food Science and Food Safety Vol. 11, 2012 c 2011 Institute of Food Technologists Flowers as potential antimicrobial agents . . . butenyl)-phenyl]-1-propanone; 3-methoxyquercetin; a 4-O- Lonicera japonica Thunb. (honeysuckle) glucose derivative of 2-hydroxy-6-methoxy chalcone) were Lonicera japonica (family: Caprifoliaceae) is a native plant of east- good inhibitors against the tested microorganisms with MIC ern Asia and is widely seen in parts of Japan, Korea, northern values below 64 μg/mL. The findings of this study showed and eastern China, and Taiwan. Flower buds of this plant pos- acylphloroglucinol derivative to be the most potent inhibitor for sess anticancer, antimicrobial, and anti-inflammatory properties 8 of the 10 tested microorganisms (MIC = 6.3 to 45 μg/mL), (Zhang and others 2008). Results on the phytochemical screening including S. aureus (MIC = 6.3 μg/mL) and methicillin- have reported the presence of iridoid glucosides and polyphenolic and gentamycin-resistant S. aureus (MIC = 7.8 μg/mL). The compounds in the flower buds (Kakuda and others 2000). results also revealed highest sensitivity of P. a e r u g i n o s a to all the Based on the results obtained by the agar well diffusion method, compounds (except 5, 7-dibenzyloxyflavanone) with MIC being methanol extracts of the flower showed inhibitory activities against in the range of 45 to 63 μg/mL. According to the authors, the B. cereus, S. aureus,andS. anatum with the diameters of inhibition traditional use of H. gymnocomum in healing wound infections zones ranging from 5.5 to 7.2 mm (Shan and others 2007). On was supported by the notable antimicrobial activity of the plant, another note, Tsai and others (2008), screening on the methano- particularly against S. aureus and P. aeruginosa. lic extract of different herbs against growth of S. mutan and S. Hibiscus sabdariffa Linn. (roselle) sanguinis, found MIC of L. japonica to be 4 mg/mL for S. sangui- nis, while MIC for S. mutan was >8 mg/mL (no activity). Hibiscus sabdariffa (family: Malvaceae) is a small shrub native In another study reported by Rahman and Kang (2009), the to Africa and is cultivated in parts of Sudan and Eastern Tai- essential oil of L. japonica flower demonstrated inhibitory activ- wan (Lin and others 2007). The plant parts are used in the treat- ities against L. monocytogenes, B. subtilis, B. cereus, S. aureus, S. ment of hypertention, pyrexia, and liver disorders (Wang and oth- enteritidis, S. Typhimurium, E. aerogenes, and E. coli with inhibition ers 2000; Odigie and others 2003). In vitro and in vivo studies zones recorded in the range of 12.1 to 20.3 mm and MIC in have demonstrated cardio-protective (Odigie and others 2003), the range of 62.5 to 500 μg/mL. The authors used the agar hypo-cholesterolemic (Chen and others 2003), antioxidative, and disc diffusion and broth dilution assays for the analysis. Their hepatoprotective (Wang and others 2000; Liu and others 2002) results of a GC-MS analysis showed the essential oil to con- properties of the anthocyanins and protocatechuic acid, which tain 39 compounds wherein 92.34% of the oil was composed of were isolated from dried flowers of H. sabdariffa. trans-nerolidol (16.31%), caryophyllene oxide (11.15%), linalool The floral extract (water and ethanol) of H. sabdariffa has been (8.61%), p-cymene (7.43%), hexadecanoic acid (6.39%), eugenol reported to show high inhibitory effects against B. cereus (Hamdan (6.13%), geraniol (5.01%), trans-linalool oxide (3.75%), globulol and others 2007). The inhibition zones against B. cereus were (2.34%), pentadecanoic acid (2.25%), veridiflorol (1.83%),>br/> 2, 6, and 16 mm and 4, 9, and 12 mm at 1, 2, and 4 mg/mL for benzyl alcohol (1.63%), and phenylethyl alcohol (1.25%) as major water and ethanol extracts, respectively. The authors also noted components. However, antimicrobial activity results on the essen- that as the content of water and ethanol extract increased (from tial oil did not reveal any effects of the oil against E. coli O157: H7 0.82 to 4.12 mg/mL), a corresponding increase in the inhibition and P. a e r u g i n o s a . on the growth of B. cereus occurred with complete inhibition Recently, Rhee and Lee (2011) reported the antimicrobial ac- (100%) attained at a concentration of 3.45 and 4.12 mg/mL, re- ◦ tivity of butanol extract from L. japonica flower against 104 clinical spectively. Besides, heat treatment at 70 C for 3 min did not isolates of anaerobic bacteria (Bacteroides fragilis, Bacteroides ovatus, significantly affect the antibacterial activity of H. sabdariffa extract Clostridium difficile, C. perfringens, Propionibacterium acnes, and Pep- against B. cereus. tostreptococci) (based on the agar dilution method). The butanol Jasminum sambac (Arabian jasmine/jasmine flower) extract showed antimicrobial activity against all the tested bacteria Jasminum sambac (family: Oleaceae) originated in India and with MIC ranging from 0.032 to 2.0 mg/L. Burma and is widely grown in Ambouli (Republic of Djibouti) for producing perfume. This plant is a perennial twining shrub Mentha longifolia L. (horse mint) (attaining height of 5 to 6 feet) and bearing small, white-colored Mentha longifolia (family: Lamiaceae) is a perennial herb scented flowers. The flowers are used ornamentally as well as to commonly found growing in a hot and humid climate. Mint is decorate hair. Skin care products are also formulated by using the widely distributed throughout South Africa, Botswana, Namibia, essential oil extracted from the flowers. The essential oil of the and Zimbabwe. The rhizomes creep below the ground and flower is used to reduce skin inflammation, tone the skin, and the erect flowering stems can grow up to 8-m high. The plant lift up mood (Abdoul-Latif and others 2010). Extracts of flowers bears small white or pale purple flowers borne in elongated are also used to prepare herbal tea decoctions. The floral extract clusters on the tips of the stems. The entire plant exudes a is reported to possess analgesic, anti-inflammatory, antidepressant, unique mint aroma. The leaves are the most widely used parts aphrodisiac, antiseptic, expectorant, sedative, and tonic properties. of this plant. Leaf and stem decoctions are prescribed to cure Besides, flowers and plant parts have been reported to have an- common colds, cough, bronchial ailments, headache, fever, ticancer properties (Houghton and others 2007; Alka and others indigestion, flatulence, painful menstruation, urinary tract infec- 2010). tions, diseases of the gastrointestinal tract, and bleeding problems Tsai and others (2008) have reported on the inhibitory ac- (http://www.plantzafrica.com/medmonographs/menthlong.pdf, tivities of methanolic extract of the flowers against Streptococcus accessed on Jul 25, 2011). mutans and Streptococcus sanguinis. They adopted the broth microdi- In one of the experiments conducted by Pirbalouti and others lution method for evaluating the antimicrobial/inhibitory activ- (2010) on Iranian folklore herbs, the extract and essential oil from ities. From their study, they reported the MIC to be 1 mg/mL flowers of M. longifolia have been reported to exhibit strong an- for S. sanguinis. However, the MIC of the extract for S. mutan tibacterial activity against all the tested bacteria (S. aureus, E. coli, was >8 mg/mL, which is an indication of “no activity” against S. P. aeruginosa, and K. pneumoniae) with inhibition zones and MIC mutans. values ranging from 9 to 17 mm and 0.156 to 10.00 mg/mL,

r c 2011 Institute of Food Technologists Vol. 11, 2012 Comprehensive Reviews in Food Science and Food Safety 47 Flowers as potential antimicrobial agents . . . respectively. Results of this study showed the essential oil of M. fruits are edible, the seeds possess hemostatic properties, while longifolia to exhibit stronger antibacterial activity than the ethanol the sap of the stem and leaves are often applied to heal ulcers, extract. herpes, and scabies. The bark is bruised and applied as a plaster over hard tumors, which is also used as a purgative, cardiotonic, Moringa oleifera (horseradish tree) diuretic, and hypotensive agent (Radha and others 2008; Zahid Moringa oleifera (family: Moringaceae) is a perennial timber and others 2010). The methanolic extract of the flowers of P. yielding softwood tree. It is native to the sub-Himalayan tracts alba have shown antimicrobial activity against Bacillus anthracis and of India, Pakistan, Bangladesh, and Afghanistan. The plant is also P. a e r u g i n o s a (Syakira and Brenda 2010; Zahid and others 2010). found to be widely distributed in parts of Ethiopia, the Philippines, Different parts of the plant are traditionally used in the treatment Africa, Latin America, the Caribbean, Florida, and the Pacific of malaria, leprosy, rheumatism, and abdominal tumors (Syakira Islands (Fahey 2005). The whole plant is edible and possesses an- and Brenda 2010). tispasmodic, anti-inflammatory, diuretic, obortifacient, emmena- The essential oils isolated from flowers of P. alba have been gogue, and ecbolic properties. The plant parts have been reported evaluated against Gram-positive S. aureus, B. subtilis, and Gram to possess therapeutic value and are used in the treatment of hys- negative E.coli,P.aeruginosa,and S. typhi by the agar well diffu- teria, tumors, leucoderma, and biliousness (Fahey 2005; Talreja sion method (Zahid and others 2010); Gram-positive bacteria (S. 2010). aureus and B. subtilis) were found to be more sensitive to essential The potential antimicrobial activity of ethanolic extracts of its oils. The sensitivity has been attributed to the absence of an outer flowers against B. subtilis, S. aureus, E. coli, K. pneumoniae, and membrane surrounding the bacterial cell wall that restricts the dif- C. albicans has been reported by Talreja (2010). Results based fusion of hydrophobic components of P. alba essential oil through on the agar disc diffusion assay showed the floral extract to have the lipopolysaccharide covering. both antibacterial and antifungal activity with zones of inhibition formed in the range of 8 to 10.5 mm for bacteria and 6.5 mm for Rosa spp. (rose flower) C. albicans. Roses are indigenous to central Asia and are grown as ornamen- tal plants. Rose flowers have been traditionally used as a medicine, Lotus (Nymphaea lotus Linn., Egyptian white waterlily; and for culinary purposes, and in the preparation of perfumes (due to a Nelumbo nucifera L., Indian lotus, sacred lotus) warm, intense, rich, and rosy fragrance). Rose flowers were used as Nymphaea lotus (family: Nymphaeaceae) is an aquatic plant, medicine in ancient Assyria, China, Egypt, Greece, India, Persia, widely seen in tropical Africa and in parts of Asia. It is a peren- and Rome. The flower has 5 petals (or multiples of 5) with nu- nial herb growing about 10- to 60-cm high. The entire plant is merous stamens. Rose petals are aromatic and have various shapes reported to possesses therapeutic value and is used as an anticancer and colors. They enclose androecium and gynoecium, which apart and antiviral agent and as an antioxidant (Saleem and others 2001; from facilitating pollination, possess antibacterial activity as a pro- Esimone and others 2006; Sowemimo and others 2007a, 2007b). tection system. Perfumes prepared from rose petals are economi- The antimicrobial activity of hot water and ethanolic ex- cally valuable and also have soothing effects (Hirulkar and Agrawal tracts of 6 plants, utilized in Pakistan for the treatment of liver 2010). Rose petal jam (prepared in parts of Asia from Rosa indica damage, against 7 bacterial strains (methicillin-resistant S. aureus, L.) is considered to provide a cooling effect on mind and body. Oil multidrug-resistant P. a e r u g i n o s a , enterohemorrhagic E. coli 0157 obtained from rose flowers has been reported to reduce blood lipid EHEC, S. typhi, P. vulgaris, K. pneumoniae, B. subtilis and 2 fungal levels in rats. The hydrating and anti-inflammatory properties of species (C. albicans and A. niger), was determined by agar well natural acids present in rose water are considered to be useful for diffusion and broth microdilution assays (Hassan and others 2009). skin and eye care. Rose petals are also recommended to be used Both extracts of N. lotus were active against all the microorganisms as mouthwash. The tea decoction prepared from rose petals is rec- tested with zones of inhibition in the range of 16 to 36 mm and ommended to heal breast pain, mastitis, menstrual difficulties, and MIC/MBC in the range of 23.3/ 27.3 to 35.3/ 41.7 mg/mL. restless fetus (Hirulkar and Agrawal 2010). The antioxidant and Antimicrobial activity of N. lotus was the stronger in ethanol ex- antimicrobial properties and the chemical compounds present in tract than in water extract. This observation has been attributed rose essential oil have been extensively published (Arıdogan˘ and to the enhanced nature of bioactive compounds in the presence others 2002; Basim and Basim 2003; Hirulkar and Agrawal 2010). of ethanol and the stronger extraction power of ethanol. The tra- Petal extract of Rosa canina L. is reported to enhance the effec- ditional use of both water and ethanol extracts of N. lotus against tiveness of several antibiotics against methicillin-resistant S. aureus liver damage was supported by the results of this study. as well as to have strong inhibitory activity against C. albicans With regard to Nelumbo nucifera, the entire plant has been re- (Rossnagel and Willich 2001; Hirulkar and Agrawal 2010). An- ported to possess rich nutraceutical value (Sridhar and Bhat 2007). thocyanins and proanthocyanidins, tellimagrandin I and rugosin B, Flowers are white to pink, sweet-scented, single, and are 10 to carotenoids, plant acids, and essential oils are present in rose petals. 25 cm in diameter. Flowers are reported to be useful to treat bleed- Rose oil is reported to contain economically valuable alcohol, ing disorders and to promote conception. Additionally, flowers are such as geraniol (a major constituent) and 1-citronellol (Hirulkar reported to be useful to treat diarrhea, cholera, fever, hepatopa- and Agrawal 2010). thy, and hyperdipsia. However, to our knowledge no reports are Hirulkar and Agrawal (2010) used the agar disc diffusion method available on the antmicrobial activity of this flower or its extracts. to study the antimicrobial activity of alcoholic, petroleum ether, and aqueous extracts of rose petals against various pathogenic bac- Plumeria alba Linn. (white champa) teria. All the dilutions (1:1, 1:2, 1:3) of the 3 types of extracts Plumeria alba (family: Apocynaceae) is a small laticiferous tree showed inhibition against all the tested bacteria with inhibition that is a native of tropical America. The plant has also been found zone diameters ranging from 12 to 30 mm. Among the tested growing in India where it is popularly called Peru. The plant bacteria, P. a e r u g i n o s a was the most sensitive to the petroleum ether grows up to 4.5-m high bearing white and fragrant flowers. The extract of rose petals with an inhibition zone of 29 mm. Results of

r 48 Comprehensive Reviews in Food Science and Food Safety Vol. 11, 2012 c 2011 Institute of Food Technologists Flowers as potential antimicrobial agents . . . this study showed higher inhibitory activity of alcoholic extracts ing from 8 to 23 mm. From the broth dilution assay performed against S. pneumoniae (30 mm), E. aerogenes (28 mm), S. epidermidis on S. aureus, the MIC and MBC of 0.3 and 0.6 μL/mL were (25 mm), B. subtilis (30 mm), and P. aeruginosa (32 mm) as com- recorded indicating strong action of the flower head essential oil pared to other bacterial strains. Aqueous extract showed higher against this particular bacterium. The chemical composition of inhibitory activity against E.coli (21 mm), E. aerogens (25mm), and essential oil from flower heads of S. rosmarinifolia (assessed by GC- B. subtilis (28 mm) as compared to other bacterial strains. It was MS) was shown to be comprised of 42 components represent- found that alcoholic extract showed higher average antimicrobial ing 92.3% to 94.0% of the oil, with β-eudesmol (13.5%), 1,8- activity (25 mm) when compared to aqueous extract (19 mm) and cineole (12.9%), camphor (8.0%), borneol (5.1%), ar-curcumene petroleum ether extract (18 mm). The authors concluded by stat- (4.8%), terpinen- 4-ol (4.5%), and spathulenol (4.4%) as the main ing that rose petals can be potentially used to treat diarrhea, oppor- constituents. tunistic infection, and skin infections caused by various pathogenic bacteria. Satureja bachtiarica Bunge. (savory) Koday and others (2010) have reported on the bactericidal The genus Satureja (family: Lamiaceae) contains more than 200 properties of methanol, chloroform, and hexane extracts of 40 species of herbs and shrubs that are widely distributed in the different medicinal plants against Corynebacterium macginleyi using Mediterranean region. Aerial parts of Satureja species are used as the agar well diffusion assay. From their study, the authors found flavoring agents in a variety of food products as well as for herbal methanolic extract of R. indica petal to possess better antimicrobial medicine preparations to treat gastrointestinal disorders (Sonboli activity against C. macginleyi compared to chloroform and hexane and others 2004). extracts. Pirbalouti and others (2010), by employing agar disc diffusion and serial dilution assays, determined the antimicrobial activities Rumex vesicarius Linn. (bladder dock) of some of the Iranian folklore herbs against S. aureus, E. coli, Rumex vesicarius (family: Polygonaceae) is a wild edible plant P. a e r u g i n o s a ,andKlebsiella pneumonia. From the results of their that grows during spring time (Al- Quran 2009). It is native to screening tests, the ethanolic extract and essential oils of flowers southwest Asia and North Africa and is cultivated in India, espe- of S. bachtiarica showed strong antibacterial activity against all the cially in regions of Tripura, West Bengal, and Bihar (Khare 2007). tested bacteria with the zone of inhibitions ranging from 12 to The plant parts are used traditionally in the treatment of various 23 mm. The MIC values ranged from 0.039 to 10.00 mg/mL. diseases, such as tumors, hepatic diseases, indigestion, constipation, This study showed essential oils to exhibit stronger antibacterial heart diseases, pains, spleen disorder, hiccough, flatulence, asthma, activity than the ethanol extract. bronchitis, dyspepsia, piles, scabies, leucoderma, toothache, nau- sea, and dysentery. The plant also has cooling, laxative, tonic, Tamarix gallica L. (French tamarisk) antibacterial, analgesic, stomachic, appertizer, diuretic, astringent, Tamarix gallica (family: Tamaricaceae) is a halophytic tree found purgative, and antispasmodic properties. Besides, this plant is growing in natural habitats ranging from coastal regions up to used to reduce biliary disorders and to control cholesterol levels deserts. This plant is known to tolerate a wide range of harsh (Elegami and others 2001; Atiqur Rahman and others 2004; environmental conditions and can resist abiotic stress, such as salt, Lakshmi and others 2009; Mostafa and others 2011). high temperature, and dryness (SaIdana¨ and others 2008; Ksouri Antimicrobial activity of different plant parts of this plant against and others 2009). In certain parts of Asia, the leaves, flowers, K. pneumoniae, S. pneumoniae, S. pyogenes, S. aureus, E. coli, and P. and galls of T. gallica are used as therapeutic agents, particularly as aeruginosa was performed using the agar disc diffusion method by anti-inflammatory, antidiarrheic, cicatrizing, and antiseptic agents. Mostafa and others (2011). Results of this study demonstrated They are also used for treating leucoderma, spleen trouble, and potential antibacterial activity (K. pneumoniae, Streptococcus pneu- eye diseases (Ksouri and others 2009). Besides, the plant parts are monia, S. pyogenes, S. aureus, E. coli,andP. a e r u g i n o s a ) of the flow- used as astringent, aperitif, stimulant of perspiration, and diuretic ers extracted in different solvent extracts (petroleum ether, ether, (SaIdana¨ and others 2008; Ksouri and others 2009). chloroform, methanol, and ethanol). Chemical analysis of flower Based on the inhibition zone measured by the disc diffusion assay extracts revealed variations in the presence and amount of active (Ksouri and others 2009), the methanolic floral extracts (2, 4, and compounds (flavonoids, anthraquinones, alkaloids, tannins, sterols 100 mg/mL) of this plant exhibited antibacterial activities against and/or triterpenoids, carbohydrates and/or glycosides, chlorides, S. epidermidis, S. aureus, M. luteus, E. coli,andP. a e r u g i n o s a . The flo- sulfates, and sublimable substances). ral extracts also showed antifungal activity against Candida spp. with inhibition zones of 6 to 15 mm and 6 to 8.66 mm, respectively. Santolina rosmarinifolia Linn. (green lavender cotton) The bioactive compounds present in the flowers were identified Santolina rosmarinifolia (family: Asteraceae) is a perennial shrub as phenolic acids (gallic, sinapic, chlorogenic, syringic, vanillic, found in the Iberian peninsula and southern France (Ioannou and p-coumaric, and trans-cinnamic acids) and flavonoids (catechin, others 2007). The infusions from flower heads are reported to be isoquercetin, quercetin, apigenin, amentoflavone, and flavone). used as an antipyretic and have been shown to posses hepatoprotec- tive, antihypertensive, and intestinal anti-inflammatory properties Thymus daenensis Celak (thyme) (Novais and others 2004). The genus Thymus (family: Lamiaceae), is a perennial herb that The antimicrobial activity of flower heads and leaves of S. has its origin in the Mediterranean region. Leaves and flowers of rosmarinifolia against S. aureus, S. lutea, B. cereus, E. coli,andC. Thymus species are traditionally used in Iran as tonic and herbal albicans was determined by Ioannou and others (2007) based on tea, antitussive, antiseptic, carminative, and a treatment for the agar disc diffusion and broth dilution assays. From their study, common cold. Thymus oil and extracts (leaves and flowers) are the antimicrobial activity of essential oil from flower heads of S. widely used by the pharmaceutical, perfume, cosmetic, and food rosmarinifolia at doses of 1, 5, and 10 μL was found to be stronger industries (Nejad Ebrahimi and others 2008; Pirbalouti and others than those from the leaves, with inhibition zone diameters rang- 2010).

r c 2011 Institute of Food Technologists Vol. 11, 2012 Comprehensive Reviews in Food Science and Food Safety 49 Flowers as potential antimicrobial agents . . .

In one of the experiments conducted by Pirbalouti and oth- Flavonols, flavones, isoflavones, flavanones flavan-3-ols (cate- ers (2010) on Iranian folklore herbs, the extract and essential oil chins and proanthocyanidins), and anthocyanins, are some of from flowers of T. daenensis have been shown to exhibit strong the subcategories of flavonoids (Toda and others 1989; Cowan antibacterial activity against all the test bacteria (S. aureus, E. coli, 1999; Grotewold 2006). Anthocyanins are responsible for the P.aeruginosa, K. pneumoniae) with inhibition zones ranging from 8 characteristic red, blue, or purple colors of flowers. Flavonols to 22 mm. The MIC values of flower extracts ranged from 0.039 (quercetin, kaempferol, and myricetin) are widespread flavonoids to 10.00 mg/mL. The results of this study clearly showed essential found in plants, which have potential antimutagenic, anticar- oil to have stronger antibacterial activity than the solvent (ethanol) cinogenic, and antihypertensive activities. Flavanones are found extracts. in abundance in citrus fruits, which impart bitter flavor to the fruit peels (Denny and Buttriss 2007; Bernhoft 2010). The ma- Zingiber mioga (Thunb.) Roscoe (Myoga) jor flavonoid constituents reported in flower extracts includes: Zingiber mioga (family: Zingiberaceae), a native to eastern Asia, quercetin, kaempferol, catechins, proanthocyanidins, apigenin, is widely cultivated in Japan as a perennial herb. The stalks of and anthocyanins (Quarenghi and others 2000; Drewes and Van this plant extend up to 1 m, with slender leaves reaching 30 cm Vuuren 2008; Dung and others 2008; Nakhaei and others 2008; having pine-cone-like flower buds ranging up to 7 to 10 cm in Ksouri and others 2009; Zhao and others 2009; Chouhan and length. In Japan, “myogabochi,” a traditional food (buns filled with Singh 2010; Hirulkar and Agrawal 2010; Lachumy and others sweetened bean paste) is wrapped with the leaves of this plant to 2010; Bhalodia and others, 2011; Mostafa and others 2011). be preserved for a long period. Flower buds have a unique and pungent flavor, attributed to the presence of diterpene dialde- Phenolic acids and quinones hyde compound, 2-alkyl-3-methoxypyrazine and (E)-8-β-(17)- Phenolic compounds as phenolic acids (gallic, sinapic, chloro- epoxylabd-12-ene-15, 16 dial (myogadial). Due to their pungent genic, syringic, vanillic, p-coumaric, and trans-cinnamic acids) are flavor, the flower buds have been used as a spice and to pre- also found in flower extracts (Ksouri and others 2009). pare pickles in Japan (Sakakibara and others 1991; Abe and others Quinones are highly reactive compounds that have aromatic 2002). rings with 2 ketone substitutions. The antimicrobial activity of Abe and others (2004) screened for the potential antimicrobial quinones involve forming of complex with proteins (surface- activities of the flower buds against a wide range of bacteria, yeasts, exposed adhesins), cell wall polypeptides, and membrane-bound and molds by employing the agar disc diffusion assay. The results enzymes, leading to inactivation of function of the proteins (Stern of their study revealed ethyl acetate extracts of flower buds to and others 1996; Cowan 1999). Besides, quinones are capable of exhibit appreciable antimicrobial activity with an inhibition zone rendering a substrate unavailable to microorganisms, thus inhibit- of 8 mm, while the methanol extract showed minimal activity with ing their growth. Mostafa and others (2011) described the pres- an inhibition zone of 2 mm. Additionally, MICs of the 3 diterpene ence of anthraquinones in various extracts of R. vesicarius flowers, dialdehydes (myogadial, galanal A, and galanal B) isolated from which served as one of the antimicrobial compounds against the the ethyl acetate extract were measured using the serial dilution tested microorganisms (K. pneumonia, S. pneumoniae, S. pyogenes, S. method. From the results, myogadial, galanal A, and galanal B aureus, E. coli and P. a e r u g i n o s a ). In one of the experiments con- were found to be effective against Gram-positive bacteria and ducted by Bhalodia and others (2011) on hydro-alcohol and chlo- yeast with myogadial (MIC = 25 to 125 μg/mL) showing higher roform extracts of C. fistula flowers, anthraquinones present in the activity compared to galanal A and B (MIC = 200 to 500 μg/mL). extracts was found to exhibit rich antimicrobial activities, which The reason for the antimicrobial activity has been attributed by were found to be active against some sensitive bacteria and fungi the authors to the presence of galanal A and B that were present (S. aureus, S. pyogenes, E. coli, P.aeruginosa, A. niger, A. clavatus, and in the 1, 6 positions of the aldehyde groups, with the introduction C. albicians). of a hydroxyl group in their molecules. Tannins Major Bioactive Compounds in Flower Extracts Tannins are a group of polymeric phenolic compounds Bioactive compounds isolated from flowers and their extracts widespread in plants. Tannins are known to exhibit astringent have shown potential antimicrobial activities. The isolated com- properties and are synthesized by condensation of flavan deriva- pounds are classified into different groups, such as phenolics, ter- tives or polymerization of quinone units (Haslam 1996; Cowan penoids, essential oils, glycosides, and alkaloids. A few of these are 1999). Tannins form complex with microbial adhesins, enzymes, discussed in the preceding text below. and cell envelope transport proteins, leading to inactivation of these proteins and inhibition of microbial growth (Haslam 1996; Phenolics Stern and others 1996). Scientific evidences showed tannins to be Among the various phenolic compounds, flavonoids are found effective against filamentous fungi, yeasts, and bacteria (Brownlee abundantly in plant-derived foods (Denny and Buttriss 2007). and others 1990; Scalbert 1991; Cowan 1999). Some examples of Flavonoids (consisting of a central 3-ring structure), are major flowers with presence of high tannin include: Allium spp. (Chehre- phenolic compounds that play a pivotal role in plants, such as gani and others 2007), C. fistula (Bhalodia and others 2011), E. protection against UV, pigmentation, stimulation of nitrogen fix- elatior (Lachumy and others 2010) and R. vesicarius (Mostafa and ing nodules, and disease resistance (Pierpoint 2000; Denny and others 2011). Buttriss 2007). This group of compounds can occur as glycosides too. Flavonoids are known to exhibit rich antioxidant, anticar- Terpenoids and essential oils cinogenic, and anti-inflammatory properties. Besides, flavonoids Essential oils are secondary metabolites containing a mixture of are known to possess antimicrobial activities due to their ability to compounds that are based on 5 carbon isoprene structure (ter- form complexes with extracellular and soluble proteins and micro- penes) occurring as diterpenes, triterpenes, tetraterpenes (C20, bial cell wall (Tsuchiya and others 1996; Cowan 1999; Grotewold C30, and C40), hemiterpenes (C5), and sesquiterpenes (C15) 2006). (Cowan 1999). The antimicrobial activity of terpenes involves

r 50 Comprehensive Reviews in Food Science and Food Safety Vol. 11, 2012 c 2011 Institute of Food Technologists Flowers as potential antimicrobial agents . . . disruption of cell membrane by their lipophilic constituents. Pre- flower extracts and their essential oils have been proven to possess liminary phytochemical screening on essential oils extracted from antimicrobial activities, these can be incorporated into develop- the flowers of C. macropodum (Ebrahimabadi and others 2010), C. ing new and novel biopolymer-based edible films, especially for trifurcatum (Sassi and others 2008b), C. operculatus (Dung and others preserving fresh produce. 2008), L. japonica (Rahman and Kang 2009), and S. rosmarinifolia Based on the reports available from in vitro studies conducted (Ioannou and others 2007) have shown monoterpenes, sesquiter- till date, high extraction yields and strong antimicrobial activities penes, and their oxygenated derivatives to be major constituents, have been demonstrated by plant materials extracted in methanol which contribute substantially to antimicrobial activities. (Quarenghi and others 2000; Annegowda and others 2011; Mann Terpenes (comprising of >30000 different compounds) are and others 2011). However, methanol can be highly toxic to hu- termed terpenoids when they contain additional elements, typ- mans and livestock and cannot be considered as a food grade ically oxygen. Reports are available wherein bacteria and fungi solvent. In comparison to methanol, solvents such as ethanol have been shown to be sensitive to terpenoids (Tassou and others and water, which have also exhibited appreciable antimicrobial 1995; Taylor and others 1996; Cowan 1999). Terpenoids present activities, can be considered safe and results generated by us- in essential oils were effective against L. monocytogenes (Aureli and ing these solvents can be beneficial for food and pharmaceutical others 1992; Cowan 1999). Terpenoid contents reported in flower applications. extracts might contribute to the observed antimicrobial activities Flower extracts and their essential oils have many traditional of the flower extracts as observed for C. fistula (Bhalodia and others uses, such as in the preparation of foods and herbal remedies, 2011), C. morifolium (Zhao and others 2009), E. elatior (Lachumy with minimal known “side-effects” on human health. Being nat- and others 2010), and Rosa spp. (Hirulkar and Agrawal 2010). ural, they are accepted to be highly safe for consumption. Of late, Plant sterols (also terpenoids), have the ability to reduce total edible flowers are extensively being explored for commercial ap- and low-density lipoprotein cholesterol level in plasma (Denny plications in food industries such as for development of floral teas, and Buttriss 2007). Flowers of C.operculatus and R. vesicarius are beverages, functional foods, and bakery products. However, to reported to contain sterols (Dung and others 2008; Mostafa and date, research works undertaken on issues pertaining toward safety others 2011). However, not much research reports are available on and toxicity of flower extracts and their essential oils are scarce. these aspects. The effectiveness of flower extracts against a wider spectrum of pathogenic microorganisms needs to be investigated before being Glycosides used for food preservation or medicinal purposes. In addition, Glycosides are composed of a variety of secondary metabolites clinical effects of the floral extracts and their essential oils under bound to a mono- or oligosaccharide or to uronic acid. The part “in vivo” conditions as well as in food systems need to be studied of saccharide or uronic acid is known as glycone, and the backbone to evaluate in detail their potential effectiveness as antimicrobial is known as aglycone. Cardiac glycosides, cyanogenic glycosides, agents as well as presence of any acute or chronic effects. glucosinolates, saponins, and anthraquinone glycosides, being dif- The sensory qualities of a foodstuff are related to consumers’ ac- ferent in their aglycone structures, are the main groups of glyco- ceptance. With regard to flowers, sensory qualities are attributable sides (Bernhoft 2010). Investigations carried out on the flowers of to chemical constituents, particularly the volatile and colored com- C.fistula,C.Juncea,and R. vesicarius have clearly demonstrated the pounds. The chemical compounds will affect the organoleptical presence of glycosides in their extracts (Chouhan and Singh 2010; attributes (desirable or undesirable with regard to appearance, col- Bhalodia and others 2011; Mostafa and others 2011). ors, tastes, and odors) of food into which the flower extract or essential oil are being incorporated. The flowers with intense char- Alkaloids acteristic colors or pleasant aroma may be feasible to be exploited Alkaloids are heterocyclic, nitrogen-containing compounds, as a food colorant or food fragrance. with potential clinical properties. Alkaloids have bitter taste and Based on the available literature, it is evident that still a wide are present in threshold level in plants (Bernhoft 2010). Flowers of gap persists in the scientific knowledge with regard to many other C. juncea and R. vesicarius have been reported to contain alkaloids indigenous flowers (common and wild flowers) used for culinary (Chouhan and Singh 2010; Mostafa and others 2011). and therapeutic purposes, which include: banana flowers, coconut Even though a wide range of bioactive compounds might be flowers, cheddar pink, rosebay willowherb, champika, chickweed, present in flowers, still there is a lack of detailed investigations Dutch clover, sweet snow, and others (just to name a few). This carried out on these aspects. These needs to be explored further merits further investigation to search for potential antimicrobial to confirm the antimicrobial activities exhibited. activities and for prospective food industry applications.

Conclusion and Outlook Acknowledgments Edible flowers from ornamental, cultivated, as well as wild plants The authors gratefully acknowledge anonymous referees and have high potential to be explored as natural resources of antimi- Scientific Editor (Prof. Dr. Manfred Kroger) for comments and crobial agents. Exploring these underutilized flowers by providing constructive suggestions provided for improving the quality of this adequate scientific evidence might enhance the chances of devel- manuscript. First author thanks Inst. of Postgraduate Studies, Univ. oping new conventional and natural antimicrobial agents (drugs Sains Malysia for the fellowship provided. Individual research fund as well as food preservatives) and be good alternatives to synthetic provided as an RU grant (Nr 1001/PTEKIND/814139,USM) for chemicals. Screening for the potential bioactive compounds ca- the corresponding author is also gratefully acknowledged. pable of exhibiting antimicrobial activities might provide more in-depth details. Further studies are warranted to identify various mechanisms involved in the antimicrobial actions exhibited by the References bioactive compounds present in flowers (as to how they interact Abdoul-Latif F, Edou P, Eba F, Mohamed N, Ali A, Djama S, Obame L, with a microorganism to cause inhibitory or lethal effects). As Bassole´ I, Dicko D. 2010. Antimicrobial and antioxidant activities of

r c 2011 Institute of Food Technologists Vol. 11, 2012 Comprehensive Reviews in Food Science and Food Safety 51 Flowers as potential antimicrobial agents . . .

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