Biodegradable Packaging and EDIBLE COATING for Fresh-Cut Fruits and Vegetables

REVIEW

Biodegradable packaging aND EDIBLE COATING for fresh-cut fruits and vegetables

F. GALGANO1*, N. CONDELLI1, F. FAVATI2, V. DI BIANCO1, G. PERRETTI3 and M.C. CARUSO1 1 School of Agricultural, Forestry, Food and Environmental Sciences, University of Basilicata, Viale dell’Ateneo Lucano 10, 85100 Potenza, Italy 2 Department of Biotechnology, University of Verona, Strada Le Grazie 15, 37134 Verona, Italy 3Department of Agriculture, Food and Environmental Sciences, University of Perugia, Via S. Costanzo n.c.n., 06126 Perugia, Italy *Corresponding author: Tel. +39 0971-205570, Fax +39 0971-205503, email: [email protected]

Abstract

This work focuses on biodegradable packaging and edible coatings applied to fresh-cut fruits and vegetables and their effects on the product quality. Practical applications are mainly limited to the use of biodegradable materials that, however, do not allow full control of the product moisture loss. Better results can be achieved by the combined use of biodegradable packagings with edible coatings and recent research has shown that enrichment with silver-montmorillonite nanoparticles may be a promising technique. However, the actual utilization of these materials is still limited, due to the high costs of the raw materials and the limited production.

- Keywords: biodegradable packaging, biopolymers, edible coating, fresh-cut fruits and vegetables, minimally processed foods, nanocomposites -

Ital. J. Food Sci., vol. 27 - 2015 1 Introduction appropriate atmosphere within packages (Smith et al., 1987). In recent years, the establishment of new Traditionally, food companies use polymeric lifestyles, characterized by a lack of time in do- films (polyethylene PE, polypropylene PP, poly- mestic preparations, has been accompanied by styrene, PS) to package fresh fruits and vegeta- an evolution of the structure of food consump- bles because of their large availability at relation and a destructuring of meals. Therefore, tively low cost and their good mechanical per- the consumption of minimally processed fruits formance, good barrier to oxygen, carbon diox- and vegetables has grown rapidly as a result of ide (Siracusa et al., 2008). Nowadays, there is the consumer trend- “rich in cash, poor in time” a growing trend in fresh fruits and vegetables (MartÍn-Diana et al., 2007; Conte et al., 2009). packaging sector to replace the petrochemi- Minimally processed fruits and vegetables cal based packaging films with more environ- were developed in the 1980s to respond to the mentally-friendly biodegradable materials (Tha- emerging consumer demand for both conve- ranathan, 2003). The extensive use of synthet- nience and high quality aspects (Del Nobile et ic packaging films has led to serious ecological al., 2008). These foodstuffs combine fresh-like problems due to their total non- biodegradabili- and healthy characteristics with a minimal time ty. Therefore, biodegradability is not only a func- of preparation before consumption (Ragaert et tional requirement but also an important envi- al., 2004). In fact, their success is also due to the ronmental attribute. Biologically-based packag- beneficial health effects for the presence of an- ing contains raw materials originated from agri- tioxidants that act as receptors of free radicals; cultural sources, produced from renewable raw in particular, ascorbic acid and β-carotene are materials such as starch and bio-derived mono- the antioxidants present in the greatest quanti- mers (Lucera et al., 2010). These materials rep- ties in fruits and vegetables (Rico et al., 2007). resent a viable alternative because: The minimal processing operations (“mild - they are obtained from renewable sources; technology”) necessary to produce fresh-cut - they are recyclable and degradable; foods, such as peeling, cutting, washing, treat- - they are an opportunity to reduce costs. ments with sanitizing agents, drying, alter the The applications range from the design of mul- physical integrity of these products, making tilayer barrier coating consisting of biopolymers, them more perishable than the original raw ma- to enrichment of the matrix of traditional plas- terials (Corbo et al., 2006). This is due to res- tics PP and PE with nanocomposite materials of piration, transpiration, enzymatic activity of the natural origin. However, bio-packaging still rep- living tissue after harvest and processing and, resents a niche market because of the cost and at the same time, to proliferation of spoilage and poor overall performance of biodegradable films pathogenic microorganisms (GALGANO et al., when compared to those of traditional plastic 2014; Nguyen-the and Carlin, 1994). The in- materials (Del Nobile et al., 2009 a). dustrial process accelerates the degradation of The present work focuses on the different the minimally processed foods and leads to biopackaging strategies for fresh-cut fruits and chemical changes such as: vegetables. In particular, the potential appli- - increasing of respiration that accelerates the cations of biodegradable materials and edible oxidation processes; coatings have been described, with their effects - degradation of cell membranes and enzy- on the quality of these products. The applica- matic browning; tion of nanotechnology, as a tool to improve the - loss of tissue texture. performance and thermal, barrier and mechani- The knowledge of factors influencing quality cal properties of bio-polymers has also been as- degradation after processing of fruits and vegeta- sessed (Azeredo, 2009). bles is essential to develop technologies for shelf- life extending and maintaining quality during processing and distribution (Corbo et al., 2006). Bio-based materials In order to reduce the microbiological, chem- FOR food packaging ical and physical spoilage, it is possible to act on processing or, more usually, on packaging The term “Bio-Based Materials” (BBM) is as- that represents a barrier to qualitative decay of signed to packaging materials and to packaging the product (GALGANO et al., 2014). The packag- produced from biological renewable raw mate- ing operation should establish inside the pack- rials (PIERGIOVANNI and MASCHERONI, 2007). aging an optimal atmosphere for the best pres- Polymers derived from renewable resources ervation of the product. Generally, low O2 and (biopolymers) are broadly classified according elevated CO2 atmospheres, associated with low to method of production, as follows: storage temperature, reduce product respira- 1. Polymers directly extracted/removed from tion rate, limiting, in this way, losses in fresh natural materials (mainly plants). Examples weight (Watada et al., 1996). Therefore, a prop- are polysaccharides, such as starch and cellu- er combination of product characteristics and lose and proteins, like casein and wheat glu- film permeability results in the evolution of an ten, and lipids.

2 Ital. J. Food Sci., vol. 27 - 2015 2. Polymers produced by “classical’’ chemi- in comparison with commercial plastic films. cal synthesis from renewable bio-derived mon- The main polysaccharides that can be includ- omers. A good example is polylactate, a biopol- ed in edible coating formulations are starch yester polymerised from lactic acid monomers. and starch derivates, cellulose derivates, alg- The monomer itself is produced via fermenta- inate, carrageenan, chitosan, pectin, and sev- tion of carbohydrate feedstock. eral gums. Based on the molecular level, pol- 3. Polymers produced by microorganisms ysaccharides vary according to their molecu- or genetically transformed bacteria. The best lar weight, degree of branching, conformation, known bio-polymer types are the polyhydroxyal- electrical charge and hydrophobicity. Variations kanoates, mainly polyhydroxy butyrates and co- in these molecular characteristics will lead to polymers of hydroxy-butyrate (HB) and hydroxy- variations in the ability of different polysaccha- valerate (HV) (Petersen et al., 1999). rides to form coatings, as well as to variations The compostability attribute is very impor- in the physicochemical properties and perfor- tant for biopolymer materials, because compost- mance of the coatings formed. For example, ing allows disposal of the packages in the soil, the linear structure of some of these polysac- which is more energy efficient than recycling. charides such as cellulose, amylose (a compo- During biological degradation water, carbon di- nent of starch), and chitosan makes their films oxide and inorganic compounds without toxic tough, flexible, transparent, and resistant to residues are produced. fats and oils (Vargas et al., 2008). According to the European Bioplastics, biopol- Starch, a storage polysaccharide of cereals ymers made with renewable resources have to and legumes, is most commonly used in the for- be biodegradable and especially compostable, so mulation of edible coatings and films because they can act as fertilizers and soil conditioners. it is inexpensive, abundant, biodegradable, and Whereas plastics based on renewable resources easy to use. Films based on starch have mod- must not necessarily be biodegradable or com- erate gas barrier properties. Their mechani- postable, the bioplastic materials do not neces- cal properties are generally inferior to synthet- sarily have to be based on renewable materials, ic polymer films. When a plasticizer, such as because the biodegradability is directly corre- water, is added starches exhibit thermoplastic lated to the chemical structure of the materials behavior (KROCHTA and MULDER-JOHNSTON, rather than the origin. In particular, the type of 1997). Starch-based thermoplastic materials chemical bond defines whether and in what time have been commercialized over the last few the microbes can biodegrade the material. Sev- years and today dominate the market of bio- eral synthetic polymers are biodegradable and based, compostable materials (CLAUS, 2000). compostable, such as starch, cellulose, which The properties of the starch-based materials are naturally carbon-based polymers. Vicever- can be improved by destructuring the native sa, the bioplastics based on natural monomer, conformation of the starch and adding syn- can lose their biodegradability through chemical thetic substances. It is common practice to modification like polymerization, such as for ex- add copious amounts of synthetic polymer to ample Nylon 9 type polymers obtained from po- the starch, such as polyvinyl alcohol (PVA) or lymerization of oleic acid monomer or Polyam- polycaprolactone. id 11 obtained from the polymerization of castor Another important polysaccharide is chi- oil monomer (SIRACUSA et al., 2008). tosan, which is mainly obtained from crab and The problems associated with renewable bi- shrimp shells (Hirano, 1999). Films and coat- opolymers are threefold: performance, process- ings based on chitosan have selective permea- ing and cost. Although these factors are some- bility to gases (CO2 and O2) and good mechan- what interrelated, problems due to “performance ical properties. However, their uses are limited and processing’’ are more pronounced with poly- mainly because of their high water vapor perme- mers extracted directly from biomass (cellulose, ability (BUTLER et al., 1996; CANER et al., 1998). starch, proteins). Conversely, polymers belong- Moreover, chitosan shows antifungal and anti- ing to categories 2 and 3 above, generally per- bacterial properties, which are believed to have form very well and are easily processed into films originated from its polycationic nature. An edi- using standard plastic techniques, but tend to ble film with innovative characteristics has been be expensive compared with synthetic analogues obtained by combining the antimicrobial prop- (Petersen et al., 1999). erties of chitosan with the property of self-sealing banana starch, variety Kluai Namwa. The Polymers directly extracted/removed presence of starch in the composite film makes from natural materials water soluble and sealable bags or wraps possible, while the presence of chitosan gives them Polysaccharides the antimicrobial property. The composite bags were found to protect asparagus, baby corn and The polysaccharides show effective gas bar- Chinese cabbage against Staphylococcus aureus rier properties although they are highly hydro- activity by serving as a good barrier and as an philic and show high water vapor permeability antimicrobial agent. The properties of composite

Ital. J. Food Sci., vol. 27 - 2015 3 films were more similar to starch films than to ic strength and heat processing. The mechani- films made solely from chitosan as the amount cal, barrier and rheological properties of galacto- of banana flour was greater than chitosan in the mannan films/coatings may be used to improve films. These composite films were cheaper and the stability, safety, and quality of food products less flexible than chitosan films. Film extensi- (CERQUEIRA et al., 2011). LIMA et al. (2010) suc- bility was improved by the addition of banana cessfully blended collagen with two galactoman- flour and glycerol. Banana flour addition en- nans from different species (A. pavonina and C. hanced WVP and solubility, although, the films pulcherrima). The composition of films/coatings were not completely smooth. The biodegrada- with different proportions of galactomannan, col- ble and hot water soluble films can be used in lagen and glycerol have been optimized based food packaging and to reduce microbial counts on the wettability of films, transport and me- thus extending shelf-life of fruit and vegetables chanical properties; these films have been sub- in convenient bags (Pitak and Rakshit, 2011). sequently used to coat mangoes and apples. The Cellulose is the most abundant natural poly- results showed that the application of the coat- mer on earth and it is an essentially linear pol- ings leads to a decrease of gas transfer rates of ymer of anhydroglucose. As a consequence of the fruits. For mangoes, a coating of A. pavoni- its chemical structure, it is highly crystalline, na galactomannan (0.5%), collagen (1.5%) and fibrous, and insoluble. Many derivatives of cel- glycerol (1.5%) decreased oxygen consumption lulose have excellent properties of film-forming, and carbon dioxide production in 28% and 11%, but are simply too expensive for use on a large respectively. For apple, the oxygen consump- scale. Finally, the similarity of cellulose and tion and carbon dioxide production decreased chitosan in primary structures has facilitated for both gases by approximately 50%, with the the formation of homogeneous composite films. utilization of a coating of C. pulcherrima galac- MÖLLER et al. (2004) reported that 1% of chi- tomannan (0.5%) and collagen (1.5%). tosan in chitosan-HPMC (hydroxypropylmethyl- cellulose) composite films is effective against L. Proteins monocytogenes. Alginates can also be used to prepare edible Proteins that have received great attention for coatings and films. Alginates are the salts of alg- their capability of forming edible films and coat- inic acid, which is a linear copolymer of D-man- ings include corn zein, wheat gluten (WG), soy nuronic and L-guluronic acid monomers. Alginate protein, whey protein, casein, collagen/gelatin, coating formation is based on the ability of algi- pea protein, rice bran protein, cottonseed pro- nates to react with di-valent and tri-valent cations tein, peanut protein, and keratin (HAN and GEN- such as calcium, ferrum or magnesium, which NADIOS, 2005). Casein based edible coatings are are added as gelling agents (CHA and CHINNAN, attractive for food applications due to their high 2004). An original study (NORAJIT et al., 2010) in- nutritional quality, excellent sensory properties, vestigated the physical and antioxidant proper- and strong potential for providing food products ties of alginate biodegradable film incorporating with adequate protection against their surround- white, red and extruded white ginseng extracts. ing environment. Whey proteins have been sub- The major pharmacologically active constituents jected to intense investigation over the past dec- of ginseng are triterpene saponins called ginseno- ade or so. With the addition of plasticizer, heat- sides. The studies demonstrate that the ginseng denatured whey proteins produce transparent extract can be successfully incorporated into bio- and flexible water-based edible coatings with degradable alginate films and retain excellent an- excellent oxygen, aroma, and oil barrier prop- tioxidant activities. The incorporation of ginseng erties at low relative humidity. However, the hy- extract into the alginate films did not cause ma- drophilic nature of whey protein coatings caus- jor changes in the moisture content values. On es them to be less effective as moisture barriers the other hand, significant reductions in tensile (VARGAS et al., 2008). The water vapor permea- strength and elastic modulus values of ginseng- bility limits their potential uses for food packag- alginate film have been found compared to those ing and justifies the interest in natural hydro- of the film without ginseng extract. phobic substances, such as lipids. Galactomannans, natural polysaccharides commonly used in the food industry, mostly as Lipids a stabilizer, thickener and emulsifier, are one of the alternative materials that can be used for Edible lipids used to develop edible coatings the production of edible films/coatings based on are: beeswax, candelilla wax, carnauba wax, tri- their edibility and biodegradability. These gums glycerides, acetylated monoglycerides, fatty ac- are mostly obtained from the endosperm of di- ids, fatty alcohols, and sucrose fatty acid es- cotyledonous seeds of numerous plants, par- ters. Lipid coatings and films are mainly used ticularly the Leguminosae. The great advantage for their hydrophobic properties, representing a of galactomannans is their ability to form very good barrier to moisture loss. This factor is ex- viscous solutions at relatively low concentra- tremely important, as a great number of stud- tions that are only slightly affected by pH, ion- ies deal with the use of coatings on fresh fruits

4 Ital. J. Food Sci., vol. 27 - 2015 and vegetables to control their desiccation. In Poly(3-hydroxybutyrate) (PHB) is one of the addition to preventing water loss, lipid-based well-known biodegradable poly(hydroxy al- coatings have been used to reduce respiration, kanoates) (PHA). PHB is a natural thermoplas- thereby extending shelf life and to improve ap- tic polyester and has many mechanical proper- pearance by generating a shine on fruits and ties comparable to synthetically produced de- vegetables. In contrast, the hydrophobic char- gradable polyesters such as the poly-L-lactides acteristic of lipids forms thicker and more brit- (FREIER et al., 2002). Since 1925 PHB has been tle films. Consequently, they must be associat- produced by bacterial fermentation (ROSA et al., ed with film forming agents such as proteins or 2004), which takes place in the presence of a cellulose derivatives (DEBEAUFORT et al., 1993). wide variety of bacteria, as intracellular reserve material. At least 75 different genera of bacte- Polymers produced by “classical” ria have been known to accumulate PHB as in- chemical synthesis from renewable tracellular granules. This polymer is synthesized bio-derived monomers under limited culture conditions and its production has most commonly been studied with Aliphatic polyesters belong to this catego- microorganisms belonging to the genera Alca- ry and are obtained from bio-derived mono- ligenes, Azobacter, Bacillus and, Pseudomonas mers by means of classical polymerization pro- (UGUR et al., 2002). PHB films are degraded by cedures. One of the most promising biopolymer numerous microorganisms (bacteria, fungi and is the poly(lactic acid) (PLA), which is derived algae) in various ecosystems. When in contact from the controlled depolymerization of the lac- with the polymer, the microorganisms secrete tic acid monomer, obtained from the fermenta- enzymes that break it into successively small- tion of sugar feedstock, corn, etc., which are re- er segments, thereby reducing the average mo- newable resources readily biodegradable (CABE- lecular weight (BUCCI et al., 2005). These pol- DO et al., 2006). Discovered in 1932 by CAROTH- ymers, alone or in combination with synthetic ERS (JAMSHIDIAN et al., 2010), it is a versatile plastic or starch produce excellent packaging polymer, recyclable and compostable, with high films. The polyalkanoates are more hydropho- transparency, high molecular weight, good pro- bic than the polysaccharide-based materials, re- cessability and water solubility resistance. In sulting in a material with good moisture barrier comparison to other biopolymers, the produc- properties, whereas the gas barriers are inferior tion of PLA has numerous advantages including: (PETERSEN et al., 1999). PHB has been used in a) production of the lactide monomer from small disposable products and in packing ma- lactic acid, which is produced by fermentation terials. However, little is known about the ap- of a renewable agricultural source corn (usual- plication of PHB to packaging for food products. ly based on the strain of Lactobacillus); This polymer is not used in cut-fruits and vege- b) fixation of significant quantities of carbon tables, so there is no sense to have it here, un- dioxide via corn (maize) production by the corn less you write some possible uses in cut-fruits plant; and vegetables. c) significant energy savings; Another biopolymer produced from microor- d) the ability to recycle back to lactic acid by ganisms is the pullulan, extracted from cells of hydrolysis or alcoholysis; Aureobasidium pullulans, Tremella mesenterica e) the ability to tailor physical properties and Cyttaria harioti. It is characterized by high through material modification D( organ et al., resistance to fats, good barrier to gases; more- 2000). over, it is completely biodegradable and can be PLA is generally recognized as safe (GRAS) by processed with conventional techniques. Chemi- the United State Food and Drug Administration cally pullulan is a polymer of maltotriose used in (FDA). Moreover, PLA can be easily processed combination with sorbitol and fatty acids ester- by conventional processing techniques used for ified with sucrose to achieve edible coatings for thermoplastics like injection moulding, blow fruits (PIERGIOVANNI and MASCHERONI, 2007). moulding, thermoforming and extrusion. PLA In a recent study the possibility of using new bi- can be used in a wide range of applications; the odegradable material such as kefiran, a microbi- major PLA application today regards packaging al polysaccharide obtained from the flora of ke- (nearly 70%). PLA food packaging applications fir grains has been investigated G( HASEMLOU et are ideal for fresh products, such as fresh meat al., 2011). It is a water-soluble polysaccharide (GALGANO et al., 2009) or fruits and vegetables. containing approximately equal amounts of glucose and galactose (MICHELI et al., 1999), used Polymers produced by microorganisms: in the food industry as a texturing agent and polyhydroxyalkanoates (PHA) gelling agent. It could be a viable alternative to synthetic materials for food packaging, also be- In recent years poly-β-hydroxyalkanoates cause it has antibacterial and anticancer prop- (PHA) have attracted a lot of attention as biocom- erties (MAEDA et al., 2004). patible and biodegradable thermoplastic mate- The biopolymers fulfill environmental require- rials with potential applications. ments, but show some limitations in terms of

Ital. J. Food Sci., vol. 27 - 2015 5 performance, such as thermal resistance, me- cost and relative simple processability (AZERE- chanical properties and barrier properties, as- DO, 2009). The most widely studied type of clay sociated with high costs. So, more research fillers is montmorillonite (MMT), a hydrated alu- needs to be carried out on the packaging mate- mina-silicate layered clay consisting of an edge- rial with a view to introducing, for instance, in- shared octahedral sheet of aluminum hydrox- telligent molecules or inorganic material, pref- ide between two silica tetrahedral layers (WEISS erably in the form of nano-particles, in order to et al., 2006). MMT is an effective reinforcement expand the range of properties of the materials. filler, due to its high surface area and large as- The protagonist of the twenty-first century is an- pect ratio (50–1000) (UYAMA et al., 2003). Fur- other scientific innovation that is affecting the thermore, the presence of this nanoclay in pol- packaging industry: nanotechnology. ymer matrix increases its degradation rate, due to hydroxyl groups of MMT (SOUZA et al., 2013). MANGIACAPRA et al. (2005) reported that it is Nanotechnology and nanocomposites possible to reduce the oxygen permeability by adding clay montmorillonite to pectins. Also the The concept of nanotechnology was intro- combination of PLA film with MMT-layered sil- duced by Richard Feyman in 1959 at a meet- icates may be useful to create a nanocompos- ing of the American Physical Society (KHADEM- ite material with good barrier properties (SOU- HOSSEINI and LANGER, 2006). Nanotechnology ZA et al., 2013). is defined as “The design, characterization, pro- Moreover, a starch/clay nanocomposite film duction and application of structures, devices have been obtained by dispersing MMT nano- and systems by controlling the shape and size particles via polymer melt processing techniques at the nanometer scale” (Royal Society and Royal (AVELLA et al., 2005). The results related to me- Academy of Engineering, Nanoscience and Na- chanical characterization showed an increase of notechnologies, 2004). Nanotechnology and its modulus and tensile strength. application in food science have recently been Besides nano-reinforcements, nanoparticles studied by several researchers. The use of nan- can have other functions when added to a poly- oparticles, such as micelles, liposomes, nanoe- mer, such as antimicrobial activity, enzyme im- mulsions, biopolymeric nanoparticles aimed at mobilization, biosensing (AZEREDO, 2009). The ensuring food safety, are some novel nano-food incorporation of antimicrobial compounds into applications. Nanotechnology is also applica- food packaging materials has received consider- ble in the context of food packaging: however, able attention. Films with antimicrobial activi- the use of edible and biodegradable polymers ty could help control the growth of pathogenic has been limited because of problems related to and spoilage microorganisms. An antimicrobi- performance (such as brittleness, poor gas and al nanocomposite film is particularly desirable moisture barrier), processing (such as low heat due to its acceptable structural integrity and distortion temperature), and cost. The applica- barrier properties imparted by the nanocom- tion of nanotechnology to these polymers may posite matrix, and the antimicrobial properties open new possibilities for improving not only contributed by the natural antimicrobial agents the properties but also the cost-price-efficien- impregnated within (RHIM and NG, 2007). The cy (Sorrentino et al., 2007). The use of fillers most common nanocomposites used as antimi- with at least one nanoscale dimension (nano- crobial films for food packaging are based on particles) produces nanocomposites. Most re- silver, which is well known for its strong tox- inforced materials present poor matrix–filler in- icity towards a wide range of microorganisms teractions, which tend to improve with decreas- (LIAU et al., 1997), with high temperature sta- ing filler dimensions. Nanoparticles have propor- bility and low volatility (KUMAR and MÜNSTEDT, tionally a larger surface area than their micro- 2005). Some mechanisms have been proposed scale counterparts, which favors the filler–ma- for the antimicrobial property of silver nan- trix interactions and the performance of the re- oparticles (Ag-NPs): adhesion to the cell sur- sulting material. face, degrading lipopolysaccharides and form- Polymer composites are mixtures of polymers ing ‘‘pits’’ in the membranes, largely increas- with inorganic or organic fillers with certain ge- ing permeability (SONDI and SALOPEK-SONDI, ometries (fibers, flakes, spheres, particulates). 2004); penetration inside bacterial cell, dam- A uniform dispersion of nanoparticles leads to aging DNA (LI et al., 2008); and releasing anti- a very large matrix/filler interfacial area, which microbial Ag+ ions by Ag-NPs dissolution (MO- changes the molecular mobility, the relaxation RONES et al., 2005). Moreover, Ag-NPs absorbs behavior and the consequent thermal and me- and decomposes ethylene (HU and FU, 2003), chanical properties of the material. Although which may contribute to its effects on extend- several nanoparticles have been recognized as ing shelf life of fruits and vegetables. Indeed, possible additives to enhance polymer perfor- LI et al. (2009) reported that a nanocomposite mance, the packaging industry has focused its PE film with Ag-NPs can retard the senescence attention mainly on layered inorganic solid like of jujube, a Chinese fruit. AN et al. (2008) re- clay and silicates, due to their availability, low ported that a coating containing Ag-NPs is ef-

6 Ital. J. Food Sci., vol. 27 - 2015 fective in decreasing microbial growth and in- tween coated fruits and the environment (OLIVAS creasing shelf life of asparagus. and BARBOSA-CÁNOVAS, 2005). High CO2 con- The three new requirements of food packaging centration within fruit tissues also delays rip- are the following: “Bioactive, Biodegradable and ening by decreasing the synthesis of ethylene, a Bionanocomposite”. However, there are many hormone essential for ripening (SALTVEIT, 2003). safety concerns about nanomaterials, as their LEE et al. (2003) demonstrated that the respi- size may allow them to penetrate into cells and ration rate of apple slices decreases 20% when eventually remain in the system. One can as- coated with a film based on whey protein.E d- sume that the application of nanoparticles with ible coating based on aloe vera reduced respi- an antimicrobial function (the nanoparticles of ration rate and microbial spoilage in sliced ki- silver or copper) poses the risk the consumer’s wifruit (Benítez et al., 2013). Fresh-cut prod- direct exposure to metals. Although the migra- ucts are characterized by high water transpiration of metals from biodegradable nanocom- tion rates and the creation of a moisture and gas posite film of starch / clay applied to vegetable barrier may lead to weight loss and respiration products is considered to be minimal (AVELLA rate reduction, with a consequent general delay et al., 2005), it is necessary to have more accu- of produce senescence (Valencia-Chamorro et rate information about the likely impact on hu- al., 2011). Coating apple slices with a carbohy- man health. In fact, many studies and experi- drate/lipid bilayer film reduces water loss dur- ments relating to the use of nanoparticles are ing storage between 12 to 14 times when com- still in progress in order to avoid premature gen- pared to the water loss suffered by uncoated ap- eralizations that could undermine the potential ple slices in similar storage conditions (WONG et benefits obtainable from this technology. In the al., 1994). Alginate coatings prevented water loss next section, the potential applications of this on fresh-cut apple (LEE et al., 2003; FONTES et new category of materials (biodegradable, edible al., 2007), papaya (TAPIA et al., 2007), pear (OMS- coating and nanocomposites) and their possible OLIU et al., 2008a), and melon (OMS-OLIU et al., effects on the quality characteristics of fresh-cut 2008b). Chitosan coatings reduced water loss in fruit and vegetables is discussed. sliced mango (CHIEN et al., 2007) and carrageenan coatings prevented water loss on sliced banana (BICO et al., 2009). The cassava starch ed- Edible films and coatingS ible coating with or without the calcium lactate for FRESH-CUT fruits and vegetables was able to reduce weight loss in fresh-cut pineapple (BIERHALS et al., 2011), while the cassava Consumers usually judge the quality of fresh- starch edible coating with or without potassium cut fruit on the basis of appearance and fresh- sorbate decreased the respiration rate in freshness at the time of purchase (KADER, 2002). cut strawberries (GARCIA et al., 2010). Minimally However, minimal processing operations alter processed pummelo (Citrus Maxima Merr.), coat- the integrity of fruits, with negative effects on ed with starch-based coatings (derived from cas- product quality, such as browning, off-flavour sava and rice) had a lower weight loss of 4.8– development and texture breakdown. Also, the 7.7% compared to the control (non-coated min- presence of microorganisms on the fruit surface imally processed pummelo) (KERDCHOECHUEN may compromise the safety of fresh-cut fruit. et al., 2011). Moreover, the combination of citric Traditionally, edible coatings have been used acid dipping and cassava starch or sodium algi- in the fresh-cut industry as a strategy to reduce nate edible coatings was able to delay the qual- the deleterious effects that minimal processing ity deterioration of fresh-cut mangoes, decreas- imposes on intact vegetable tissues. ing the respiration rate of fruits with value up to An edible coating may be defined as a thin 41% lower than the control fruit. Although the layer of material that covers the surface of the citric acid increases the weight loss of the prod- food and can be eaten as part of the whole product, causing a partial dehydration of the vege- uct. Therefore, the composition of edible coat- table tissue, the use of cassava starch and algi- ings must be conform to the regulation that ap- nate coatings was able to hinder this undesira- ply to the food product concerned (GUILBERT et ble effect of citric acid, presenting a lower weight al., 1995; VARGAS et al., 2008). loss than the coated samples (CHIUMARELLI et Edible coatings may contribute to extend the al., 2011). In a previous work, CHIUMMARELLI et shelf-life of fresh-cut fruits by reducing mois- al. (2010) reported that this treatment provided ture and solute migration, gas exchange, respi- a better maintenance of colour characteristics, ration and oxidative reaction rates, as well as by due to the combined effect of citric acid dipping reducing or even suppressing physiological dis- and cassava starch coating. Citric acid delayed orders (BALDWIN et al., 1996; PARK, 1999). Ed- browning along the storage and the edible coat- ible coatings are capable of producing a modi- ings acted as a gas barrier, decreasing the res- fied atmosphere on coated fruits by isolating the piration rate of mango pieces and, consequent- coated product from the environment. Coatings ly the formation of carotenoids. with selective permeability to gases are capable Moreover, another important advantage of ed- of decreasing the interchange of O2 and CO2 be- ible coating is the reduction of synthetic packag-

Ital. J. Food Sci., vol. 27 - 2015 7 ing waste, because these coatings are composed edible coatings to fresh-cut fruits must address of biodegradable raw material (DHALL, 2013). the problem regarding the difficult adhesion of The properties of edible coating depend pri- materials to the hydrophilic surface of the sliced marily on molecular structure rather than mo- fruit. The layer-by-layer (LbL) electrodeposition lecular size and chemical constitution. Specific can solve this problem (WEISS et al., 2006). LbL requirements for edible films and coatings are assembly, which is performed by alternating the as follows (ARVANITOYANNIS and GORRIS, 1999): immersion of substrates in solutions of opposite- - the coating should be water-resistant so that ly charged polyelectrolytes with rinsing steps, it remains intact and covers a product adequate- produces ultrathin polyelectrolyte multilayers ly, when applied; on charged surfaces. A requirement for multi- - it should not deplete oxygen or build up ex- layer formation is that the addition of an oppo- cessive carbon dioxide. A minimum of 1–3% ox- site charged polyelectrolyte to a charged sur- ygen is required around a commodity to avoid face results in a charge reversal, which permits a shift from aerobic to anaerobic respiration; the successive deposition of oppositely charge - it should reduce water vapor permeability; polyelectrolytes. Chitosan, poly-L-lysine, pec- - it should melt above 40°C without decom- tin, and alginate are the most common biopoly- position; mers that can be used in the formation of these - it should be easily emulsifiable, non-sticky multilayered structures (MARUDOVA et al., 2005; or should not be tacky, and have efficient dry- KRZEMISKI et al., 2006; BERNABÉ et al., 2005). ing performance; In a study of MANTILLA et al. (2013), an alginate- - it should never interfere with the quality of based multilayered coating (developed using the fresh fruit or vegetable and not impart undesir- layer-by-layer technique) enhanced the quality able order; and shelf-life of fresh-cut pineapple extending - it should have low viscosity and be econom- its shelf-life to 15 days at 4°C. ical; The main advantage of using edible films and - it should be translucent to opaque but not coatings is that several active ingredients (such like glass and capable of tolerating slight pres- as antimicrobials, antibrownings, texture ensure. hancer and nutraceuticals) can be incorporat- The ability of edible coatings to preserve the ed into the polymer matrix and consumed with quality of fresh-cut products may vary from the food, thus enhancing safety or even nutri- product to product, then it is necessary to con- tional and sensory attributes (ROJAS-GRAÜ et sider the variety and maturity of the prod- al., 2009). uct, food surface coverage, storage conditions and composition and thickness of the coating Antimicrobial agents (GONZÁLEZ-AGUILAR et al., 2010). According to their components, edible films Fresh-cut fruits are more perishable than and coatings can be divided into three catego- their corresponding whole uncut commodities ries: hydrocolloids, lipids, and composites. Hy- due to wounding during preparation (Brecht, drocolloids include proteins and polysaccha- 1995). The physical and chemical barrier pro- rides, while lipids include waxes, acylglycerols, vided by the epidermis, which prevents the de- and fatty acids. Composites contain both hydr- velopment of microbes on the fruit surface, is ocolloid components and lipids. Their presence removed during processing. and abundance determine the barrier proper- There are several categories of antimicrobi- ties of material with regard to water vapor, ox- als that can be potentially incorporated into ed- ygen, carbon dioxide, and lipid transfer in food ible films and coatings, including organic acids systems. However, none of the three constitu- (acetic, benzoic, lactic, propionic, sorbic), fat- ents can provide the needed protection by them- ty acid esters (glyceryl monolaurate), polypep- selves and so are usually used in a combination tides (lysozyme, peroxidase, lactoferrin, nisin). for best results (MCHUGH et al.,1994; GUILBERT ESWARANANDAM et al. (2006) incorporated mal- et al., 1996). The main objective of producing ic and lactic acid into soy protein coatings aim- composite films is to improve the permeability ing to evaluate its effect on the sensory quali- or mechanical properties according to specific ty of fresh-cut cantaloupe melon, without stud- applications. These heterogeneous films are ap- ying the antimicrobial effect of the coating. In plied either in the form of an emulsion, suspen- general, organic acids incorporated in films did sion, or dispersion of the non miscible constitu- not adversely affect the sensory properties of ents, or in successive layers (multilayer coating coated fruit. or films), or in the form of a solution in a com- With reference to the use of natural antimi- mon solvent. Several other compounds such as crobials, the development of coatings which use plasticizers and emulsifiers may be added to ed- inherently antimicrobial polymers as a support ible films and coatings to improve their mechan- matrix is very promising. For example, chitosan, ical properties and form stable emulsions when produced from the deacetylation of crustacean lipids and hydrocolloids are combined (VALEN- chitin (poly-β-(1→4)-N-acetyl-D-glucosamine), CIA-CHAMORRO et al., 2011). The application of is one of the most effective antimicrobial film

8 Ital. J. Food Sci., vol. 27 - 2015 forming biopolymers. Chitosan is a cationic pol- fresh-cut melon from both the microbiological ysaccharide, which, among other antimicrobial and physicochemical points of view in compar- mechanisms, promotes cell adhesion by the in- ison with non-coated fresh-cut melon samples. teraction of the positive-charged amines with the The incorporation of the essential oils or their negative charges in the cell membranes, causing active compounds into the coating prolonged the leakage of intracellular constituents (HELAND- microbiological shelf-life by more than 21 days ER et al., 2001). Chitosan based coatings were in some cases, probably due to an enhanced an- shown to protect highly perishable fruits like timicrobial effect of malic acid and the essential strawberries, raspberries, grapes and fresh-cut- oils. However, some physicochemical character- green pepper from fungal decay. (VARGAS et al., istics, such as firmness and color, and also some 2006; EL GAOUTH et al., 1991; ZHANG and QUAN- sensory quality attributes were adversely affect- TICK, 1998; ROMANAZZI et al., 2002; DEVLIEGHE- ed, causing a significant reduction of fresh-cut RE et al., 2004; PARK et al., 2005, RAYMOND et melon shelf-life. In contrast, when malic or lactic al., 2012). organic acids incorporated in soy protein coat- The application of chitosan edible coating ings were applied to fresh-cut cantaloupe, they on fresh-cut broccoli (MOREIRA et al., 2011a) did not adversely affect the sensory properties significantly reduced mesophilic and psychro- of the fruit after cold storage (ESWARANANDAM et trophic counts and inhibited the growth of to- al., 2006). AYALA-ZAVALA et al. (2013), developed tal coliform with respect to the control samples, an edible pectin film enriched with the essential throughout the whole storage period. Similar re- oil from cinnamon leaves and proved that this sults were reported by GERALDINE et al. (2008) application can increase the antioxidant status working with minimally processed garlic. At the and reduce bacterial growth of fresh-cut peach. end of the storage, yeasts and molds were the Chitosan coatings enriched with bioactive com- most dominant flora and represented the larg- pounds (bee pollen, ethanolic extract of propo- est part of the total aerobic count in broccoli. lis, pomegranate dried extract, resveratrol)/es- On the contrary, DURANGO et al. (2006) found- sential oils (tea tree, rosemary, clove, oreganum, ed an important fungicidal action of chitosan lemon aloe vera calendula) could be a good al- applied on minimally processed carrot. Moreo- ternative for controlling not only the microor- ver, the application of mild heat shock enhanced ganisms present in broccoli, but also the sur- the chitosan inhibition action (MOREIRA et al., vival of E. coli and L. monocytogenes inoculat- 2011b). From a sensory point of view, the chi- ed in the product, without introducing delete- tosan inhibited the yellowing and opening florets rious effects on the sensory attributes of mini- of fresh-cut broccoli. Moreover, chitosan-based mally processed broccoli (ALVAREZ et al., 2013). edible coatings can also be used to carry other ROJAS-GRAU et al. (2006, 2007a) have stud- antimicrobial compounds such as organic ac- ied the effects of oregano, cinnamon, and lemon- ids (OUTTARA et al., 2000), essential oils (ZIVA- grass oils and their active compounds (carvacrol, NOVIC et al., 2005), spice extracts (PRANOTO et cinnamaldehyde and citral) incorporated into ap- al., 2005), lysozyme (PARK et al., 2004) and nisin ple puree and alginate apple puree edible films (PRANOTO et al., 2005; CHA et al., 2003). Essen- against Escherichia coli O157:H7. In these works, tial oils (EOs) (cinnamon, oregano, lemongrass) oregano oil or its active compound, carvacrol, stand out as an alternative to chemical preserv- was most effective against E. coli O157:H7. In atives and their use in foods meets the demands line with these preliminary studies, ROJAS-GRAU of consumers for natural products. BURT (2004) et al. (2007b) combined the efficacy of alginate reported that hydrophobicity is an important and gellan edible coatings with the antimicro- characteristic of EOs, which makes them able bial effect of EOs (lemongrass, oregano oil and to pass through cell membranes and enter mi- vanillin) to prolong the shelf-life of fresh-cut ap- tochondria, disturbing the internal structures ples. A 4 log reduction of the inoculated popu- and rendering the membranes more permeable. lation of Listeria innocua in fresh-cut apple was Yet the application of EOs in foods is limited observed when lemongrass or oregano oils were due to their impact on organoleptic food prop- incorporated into an apple puree alginate edi- erties, variability of their composition, and their ble coating. In addition, the coating reduced res- variable activity in foods due to interactions with piration rate and ethylene production of coat- food components. Nevertheless, the use of EOs ed fresh-cut apples. In a later work (RAYBAU- to control microbial growth in foods has been DI-MASSILIA et al., 2008a), the addition of cin- proposed for several products including fresh- namon, clove and lemongrass essential oils or cut fruits and vegetables. their active compounds, cinnamaldehyde, euge- RAYBAUDI-MASSILIA et al. (2008b) studied the nol and citral into an alginate-based coating in- effect of malic acid and essential oils of cinna- creased their antimicrobial effect, reduced the mon, palmarosa and lemongrass as natural an- population of E. coli 0157:H7 by more than 4 log timicrobial substances incorporated into an al- CFU/g and extended the microbiological shelf- ginate-based edible coating on the shelf-life of life of “Fuji” apples for at least 30 days. Accord- fresh-cut melon. The coating containing malic ing to these studies, AZARAKHSH et al. (2014), acid was effective in improving the shelf-life of observed that the lemongrass incorporated into

Ital. J. Food Sci., vol. 27 - 2015 9 an alginate-based coating for fresh-cut pineap- 1992). For example, the antioxidants citric and ple, reduces the microbial growth of the prod- ascorbic acid were incorporated into methyl- uct during storage time. According to the Insti- cellulose-based edible coatings in order to con- tute of Food Science and Technology (IFST), 106 trol oxygen permeability and reduce vitamin C CFU/g is considered the limit of acceptance for losses in apricots during storage (AYRANCI and shelf-life of fruit-based products (BIERHALS et TUNC, 2004). The combination of chitosan coat- al., 2011). In fact, the coated samples with 0.3% ing and sodium chlorite dip treatment on pear and 0.5% lemongrass reached 106 CFU/g after slices adversely affected the quality of the fruit, 12 and 16 days, respectively. On the contrary, accelerating the discoloration of cut surfaces the application of tapioca starch/decolorized and increasing the PPO activity. On the con- hsian-tsao leaf gum coatings on minimally pro- trary, coating sodium chlorite-treated samples cessed carrots with antimicrobial agents (cinna- with carboxymethyl chitosan significantly pre- mon oil and grape seed extract) had no benefi- vented the browning reaction and inhibited PPO cial effect on controlling the mesophile aerobics activity. (XIAO et al., 2011). The effect of coat- and psychrophiles. As a result, the respiration ings in combination with anti-browning agents rate of the product increased (LAI et al., 2013). (1% chitosan; 2% ascorbic acid + 0.5% CaCl2) Instead, in the case of fresh-cut “Fuji” apples, on minimally processed apple slices has been cinnamon oil incorporated in tapioca starch/de- studied during storage by HAIPING et al. (2011). colorized hsian-tsao leaf gum (dHG) based edi- Chitosan-coating treatments effectively retard- ble coatings, significantly reduced the growth of ed enzymatic browning on minimally processed microorganisms, respiration rate, CO2 and eth- apples during storage and effectively retarded ylene production (PAN et al., 2013). MANTILLA et tissue softening. al. (2013) studied the effects of a multilayered As an alternative to ascorbic acid, several thi- edible coating with a microencapsulated anti- ol-containing compounds, such as cysteine, N- microbial complex (beta-cyclodextrin and trans- acetylcysteine, reduced glutathione and 4-hex- cinnamaldehyde) on the quality and shelf-life of ylresorcinol have been investigated as inhibitors fresh-cut pineapple. They reported that trans- of enzymatic browning (GORNY et al., 2002; SON cinnamaldehyde affects the pineapple flavour. et al., 2001). These compounds react with qui- However, the application of this antimicrobial nones formed during the initial phase of enzy- coating extended the shelf-life of samples to 15 matic browning reactions to yield colorless ad- days at 4°C by inhibiting microbial growth. The ditional products or to reduce o-quinones to o- same edible coating was applied on fresh-cut diphenols (RICHARD et al., 1992). 4-hexylres- watermelon (SIPAHI et al., 2013) and similar re- orcinol, in combination with sodium erythor- sults were obtained: this type of alginate coat- bate, was effective in maintaining the color of ings extended the shelf life of fresh-cut water- pear slices “Anjou” (COLELLI and ELIA, 2009). melon from 7 (control) to 12-15 days. A micro- Furthermore, carboxylic acids (citric acid and encapsulated beta-cyclodextrin and trans-cinna- oxalic acid) have also been suggested as effec- maldehyde complex was also incorporated into tive antioxidant agents in fresh-cut fruits (JI- a multilayered edible coating made of chitosan ANG et al., 2004; PIZZOCARO et al., 1993; SON and pectin. This coating extended the shelf life et al., 2001). The incorporation of antibrowning of fresh-cut papaya up to 15 days at 4°C while agents into edible coatings applied on fresh-cut uncoated fruits did not last this long (< 7days). fruits has been studied by various authors. The Moreover, the coating reduced the losses of vi- application of alginate edible coating in con- tamin C and the total carotenoid content (BRA- junction with antibrowning agents (ascorbic SIL et al., 2012). and citric acid) to mango cubes increased vitamin C content compared to mango cubes treat- Antibrowning agents ed only with alginate coating or control cubes, preserving the color of fresh-cut mangoes and Fresh-cut fruit processing operations can in- increasing the antioxidant potential of cubes duce undesirable changes in colour and appear- (ROBLES-SÁNCHEZ et al., 2013). Moreover, PE- ance of these products during storage and mar- REZ-GAGO et al., (2006) reported a substan- keting. The phenomena is usually caused by tial reduction in browning of fresh-cut apples the enzyme polyphenol oxidase (PPO), which in when using a whey protein concentrate-bees- the presence of oxygen, converts phenolic com- wax coating containing ascorbic acid, cysteine pounds into dark colored pigments (ZAWISTOWS- or 4-hexylresorcinol. They observed a signifi- KI et al., 1991). Application of antioxidant treat- cant improvement of the efficiency of antioxi- ments such as dipping after peeling and/or cut- dant agents when incorporated into the coating ting is the most common way to control brown- formulation, being the most effective treatment ing of fresh-cut fruits. Ascorbic acid is the most with 0.5% cysteine. BRANCOLI and BARBOSA-CÁ- extensively used to avoid enzymatic browning NOVAS (2000) decreased surface discoloration of of fruit due to the reduction of the o-quinones, apple slices with maltodextrin and methylcel- generated by the action of the PPO enzymes, lulose coatings including ascorbic acid. BALD- back to the phenolic substrates (MCEVILY et al., WIN et al. (1996) found that a carboxymethyl

10 Ital. J. Food Sci., vol. 27 - 2015 cellulose-based coating with addition of several quantities. TAPIA et al. (2008) reported that the antioxidants, including ascorbic acid, reduced addition of ascorbic acid (1% w/v) to the algi- browning and retarded water loss of cut ap- nate and gellan based edible coatings helped to ple more effectively than an aqueous solution preserve the natural ascorbic acid content in of antioxidants. Furthermore, ROJAS-GRAÜ et fresh-cut papaya, thus helping to maintain its al. (2008) observed that both alginate and gel- nutritional quality throughout storage. In the lan edible coatings containing N-acetylcysteine last few years, attention has been paid to the prevented apple wedges from browning during addition of probiotics to obtain functional edi- 21 days of storage. More recently, the applica- ble films and coatings.T APIA et al. (2007) devel- tion of konjac glucomann (polysaccharide de- oped the first edible films for probiotic coatings rived from the tuber of konjac, Amorphophallus on fresh-cut apple and papaya, observing that konjac) with pineapple fruit extract represents both fruits were successfully coated with algi- an effective alternative to prevent browning of nate or gellan film-forming solutions contain- fresh-cut Taaptimjaan rose apple fruit during ing viable bifidobacteria. In fact, values high- storage. This coating enhanced total phenols er than 106 cfu/g Bifidobacterium lactis Bb-12 and inhibited both PPO and peroxidase (POD) were maintained for 10 days during refrigerated activities (SUPAPVANICH et al., 2012). Or even, storage of both papaya and apple pieces, dem- pullulan-based coating treatments in combina- onstrating the feasibility of these polysaccha- tion with antibrowning and antibacterial agents ride coatings to carry and support viable pro- (1% pullulan; 0.8% glutathione + 1% chitooli- biotics on fresh-cut fruits. gosaccharides) effectively inhibited enzymatic Alginate offers the possibility of formulating browning, retarded tissue softening, inhibited a broad range of functional and innovative food microbial growth, decreased weight loss and products, increasing the nutritional properties of respiration rate of the minimally processed ap- foods. Recently, an edible alginate coating con- ple slices (WU and CHEN, 2013). taining prebiotics such as oligofructose and inulin has been applied on fresh-cut apples wedg- Nutraceuticals es. Fructan analysis showed that all prebiotics remained stable over the 14 day storage period Nutraceuticals can also be incorporated into and sensory and visual assessment indicated the formulation of edible coatings. Despite the acceptable quality of apple wedges coated with growing interest in incorporating nutraceuti- prebiotics (RÖßLE et al., 2011). The addition of cal compounds into food products, few stud- prebiotics could be especially appealing to con- ies have suggested their integration into edible sumers as they are essential to human nutrition films or coatings. In this sense, the concentra- in the context of dietary guidelines. tion of nutrients added to the films/coatings However, more studies are necessary to un- must be carefully studied since it is important derstand the interactions among active ingre- to know the effects on their basic functionality, dients and coating materials when developing namely on their barrier and mechanical prop- new edible film and coating, before they are ap- erties. Some studies have reported the effect of plied to the surface of a real food system (RO- the addition of active compounds in the func- JAS-GRAÜ et al., 2009). tionality of edible films. For instance,M EI and Further progress comes from nanotechnolo- ZHAO (2003) evaluated the feasibility of milk gy, a science that could provide new techniques protein-based edible films to carry high con- for extending the shelf-life of foods. Among the centrations of calcium (5 or 10% w/v) and vi- inorganic agents, silver nanoparticles have re- tamin E (0.1% or 0.2% w/v). They concluded ceived great attention from the scientific world, that protein-based edible films can carry active due to the high biocidal effects towards many compounds, although the film functionality can species of microorganisms (KIM et al., 2007). In a be compromised. In contrast, PARK and ZHAO study by COSTA et al. (2012), the effects of both (2004) reported that the water barrier proper- active calcium-alginate coating loaded with sil- ty of the chitosan-based films was improved by ver-montmorillonite (Ag-MMT) nanoparticles and increasing the concentration of mineral (5and film barrier properties on the shelf-life of fresh- 20% w/v zinc lactate) or vitamin E in the film cut carrots were assessed. The results of this matrix. Nevertheless, the tensile strength of study suggest that the active coating is the best the films was affected by the incorporation of treatment and could be used to control both de- high concentrations of calcium or vitamin E, hydration and microbial spoilage of minimally although other mechanical properties, such as processed carrots. Moreover, the combination film elongation, puncture strength, and punc- of coating with Ag-MMT controlled the microbi- ture deformation, were not affected. Several al growth better than the sole coating treatment. researchers have endeavoured to incorporate The combined use of proper packaging and ac- minerals, vitamins and fatty acids into edible tive coating allowed the carrots to be kept in a film and coating formulations to enhance the good state of preservation thus prolonging the nutritional value of some fruits and vegetables, shelf-life to about 70 days, with respect to the where these micronutrients are present in low uncoated samples (about 4 days). However, the

Ital. J. Food Sci., vol. 27 - 2015 11 toxicological aspects of silver nanoparticles are The application of edible coating either on well known (KIRUBA et al., 2010; LU et al., 2010); fresh-cut apples or on fruits and vegetables are EU safety regulation limits the silver amount to respectively summarized in Table 1 and in Ta- 0.05 mg Ag/kg of food (FERNANDEZ et al., 2009). ble 2 (a and b).

Table 1 - Application of edible coating on fresh-cut apple.

Food product Coating Composition Main results References Low weight loss; “Gala” apple Alginate low enxymatic browning; great- OLIVAS et al. (2007) er firmness

Cinnamon, clove, lemongrass essential oil or their 4 log reduction of the E.coli RAYBAUDI-MASSIL- Fresh-cut “Fuji” Alginate their active compound O157:H7population; shelf-life ex- IA et al. (2008) apple cinnamaldehyde, eugenol tension at least 30 days and citral

All prebiotics remained stable RÖßLE et al. (2011) Fresh-cut apple Prebiotics, such as oligo- over the 14 days; good sensory wedges fructose and inulin characteristics

4 log reduction of the inoculated ROJAS-GRAÜ et al. Fresh-cut “Fuji” Essential oils: lemongrass, population of Listeria innocua; (2007b) apple oregano oil and vanillin lower respiration rate and ethylene production

Alginate and gellan Alginate or gellan film-form- Higher values higher than 10^6 TAPIA et al. (2007) Fresh-cut apple ing solution contai- cfu/g of Bifidobacterium lactis ning viable Bifidobacteria Bb-12 were maintained for 10 days during refrigerate storage N-acetylcysteine Enzymatic browning prevention ROJAS-GRAÜ et al. Fresh-cut apple during 21 days of storage (2008)

Methylcellulose Maltodextrin Decreased surface BRANCOLI et al. Apple slices coatings and ascorbic acids. discoloration of apples slices (2000)

Substantial reduction of brown- Ascorbic acid, cysteine PEREZ-GAGO et al. Fresh-cut apple ing Whey protein or 4-hexyl-hexylresorcinol (2006) Concentrate beeswax Apple “Fuji” slic- Ascorbic acid 20% decrease of the respira- LEE et al. (2003) es and citric acid tion rate; shelf-life extension to 2 weeks. Apple slices Carbohydrate/lipid Carbohydrate/lipid bilay- Water loss reduction WONG et al. (1994) bilayer film er film Reduction of microbial growth, Fresh-cut “Fuji” Tapioca starch/de- Cinnamon oil respiration rate, CO2 and eth- PAN et al. (2013) apple colorized hsian-tsao ylene production leaf gum

Increase of total phenols; in- SUPAPVANICH et al. Fresh-cut Taap- Konjac glucomannan Pineapple fruit extract hibi-tion of PPO and POD (2012) tijaan rose apple activities. WU and CHEN Delay of tissue softening, Fresh-cut apple Pullulan Pullulan; glutathione (2013) inhibition of microbial growth, slices and chitooligosaccharides decrease of weight loss and respiration rate.

Fresh-cut apple Ascorbic acid and CaCl Delay of enzymatic browning HAIPING et al. (2011) Chitosan 2 slices and tissue softening

12 Ital. J. Food Sci., vol. 27 - 2015 Biodegradable packaging to reduce the effects of microbiological, chemi- and minimally processed fruits cal and physical events, it is possible to act on and vegetables processing or, more usually, on packaging. The packaging operation should allow to establish Fruits and vegetables are living organisms inside the packaging an optimal atmosphere which continue to respire and transpire after for the best preservation of the product. Gen- harvesting, being characterized by a respira- erally, low and elevated atmospheres, together tion rate; respiration and transpiration rates of with low storage temperature, reduce the prod- fresh fruits and vegetables are often good indi- uct respiration rate limiting, in this way, loss- cators of their storage life; the higher the rate, es in fresh weight (WATADA et al., 1996). The at- the shorter the shelf-life (FLOROS, 1993). More- mosphere that is established is the resultant of over, the shelf-life of fresh-cut products is limit- oxygen and carbon dioxide permeation through ed by microbiological deterioration and in order the walls of the packaging and of respiration

Table 2a - Application of edible coating on fresh-cut fruits and vegetables.

Food product Coating Composition Main results References

Sliced kiwifruit “Hai- Aloe vera Aloe vera Reduced O2 consumption BENÍTEZ et al. (2013) ward” and CO2 production; reduction of microbial spoilage Sliced mango Chitosan Chitosan Reduction of water loss BICO et al. (2009)

Fresh-cut mango Alginate and Ascorbic acid Increase of Vitamin C ROBLES-SÁNCHEZ et gellan al. (2013) Reduction of weight loss Fresh-cut mango Cassava and respiration rate; better CHIUMARELLI et al. Cassava starch-edible coating (pre-treated with starch-edi- maintenance of colour char- (2010, 2011) citric acid dipping) ble coating acteristics

Carrageenan Sliced banana Carrageenan Reduction of water loss BICO et al. (2009) Soy protein Soy protein, glycerol, malic Good sensory character- ESWARANANDAM et acid, lactic acid istics al. (2006)

Cantaloupe melon Alginate Malic acid and essential oils Microbiological shelf-life ex- RAYBAUDI-MASSILIA cube of cinnamon, palmarosa and tension. et al. (2008) lemongrass

Fresh-cut papaya Alginate and Ascorbic acid Preservation of the natu- MANTILLA et al. (2013); gellan ral ascorbic acid content in papaya SIPAHI et al. (2013) Microencapsulated anti-micro- Shelf-life extension to 15 Chitosan bial complex (beta-cyclodex- days; reduction of vitamin and pectin trin and trans-cinnamaldehyde) C and total carotenoid content loss

Fresh-cut apple, pa- Alginate Alginate Shelf-life extension paya, pear, melon to 15 days FONTES et al. (2007); TAPIA et al. (2007); OMS-OLIU et al. (2008)

FONTES et al. (2007); Fresh-cut pineapple, Multilayered Microencapsulated antimicro- Prevention of TAPIA et al. (2007); fresh-cut melon Sodium algi- bial complex (beta-cyclodex- water loss OMS-OLIU et al. (2008) nate coating trin and trans-cinnamaldehyde) BIERHALS et al. (2011) Reduction of weight loss Fresh-cut pineapple; Cassava Calcium lactate/ potassium starch-edi- Fresh-cut strawber- sorbate ble coating ries Reduction of respiration rate GARCIA et al. (2010)

Ital. J. Food Sci., vol. 27 - 2015 13 Table 2b - Application of edible coating on fresh-cut fruits and vegetables.

Food product Coating Composition Main results References Minimally processed Cassava Cassava or rice starch Lower weight loss of 4.8– KERD- pummel or rice starch 7.7% than the control CHOECHUEN et al. (2011) Fresh-cut peach Pectin Essential oil from cinna- Reduction of bacterial growth; AYALA-ZAVALA et mon leaves better antioxidant status al. (2013) Pear slices Chitosan Increase of PPO activity XIAO et al. (2011) Carboxymethyl chitosan Sodium chlorite Inhibition of PPO activity Fresh-cut pineapple Alginate Lemongrass oil Reduction of microbial growth AZARAKHSH et al. (2014) Fresh-cut brocco- Chitosan Chitosan Reduction of mesophilic and MOREIRA et al. li, garlic psychrotrophic counts; inhi- (2011) bition of the yellowing and opening florets of fresh-cut GERALDINE et al. broccoli (2008)

Fresh-cut broccoli Chitosan Bioactive compounds Better control of microorgan- ALVAREZ et al. (bee pollen, ethanol- isms (E. coli and L. monocy- (2013) ic extract of propo- togenes); good sensory at- lis, pomegranatedried tributes extract,resveratrol)/essential oils (tea tree, rosemary, clove, oreganum, lemon aloe vera calendula) Tapioca starch/decolor- Cinnamon oil No beneficial effect on con- LAI et al. (2013) ized hsian-tsao leaf gum trolling the meso- phyles aer- Fresh-cut carrots Active calcium-alginate obics and psychrophiles coating loaded with sil- lver montmori-llonite (Ag MMTT) nanoparticles High biocidal effects Good control of dehy- dra- COSTA et al. tion and microbial spoilage; (2012) of shelf-life extension to about 70 days, with respect to the uncoated samples

by the cells, until reaching an equilibrium con- materials, possibly combined with coating tech- dition aimed to slow the senescence and avoid nique, to minimally processed fruits and vegeta- sensorial defects to the packaged product. Ei- bles are not lacking. Results obtained by using ther high CO2 or low O2 concentrations could in- biodegradable films for samples of Iceberg let- directly induce off-flavours by stimulating the tuce are interesting: the film that is traditional- growth of homo- and hetero-fermentative bac- ly used to package fresh-cut salads is the bi-ori- teria and yeast, which produce organic acids, ented polypropylene, which is associated with a ethanol and volatile esters (CARLIN et al., 1989; level of senescence, linked to the metabolic ac- KAKIOMENOU et al., 1996). Therefore, a proper tivity of the vegetable, which is always higher combination of product characteristics and film than that achieved by salads packaged in bio- permeability, which is a fundamental character- degradable film. So, the potential application of istic of the packaging materials, results in the biopolymers for the packaging of fresh-cut let- evolution of an appropriate atmosphere with- tuce is justified (DEL NOBILE et al., 2008). Also in packages (SMITH et al., 1987). Moreover, the the rate of quality loss of minimally processed packaged food actually interacts with the pack- grapes in relationship with packaging film bar- aging material, changing the initial mechanical rier properties has been assessed (DEL NOBILE and barrier properties of the packaging materi- et al., 2009a). In earlier work, DEL NOBILE et al. als (PETERSEN et al., 1999). (2008b) investigated the influence of posthar- In alternative to the traditional polymeric ma- vest treatments (ethanol, chlorinated water and terials, biodegradable films and coatings could hot water) on the quality loss kinetics of fresh- be used. In fact, studies and experiments re- ly processed grapes packaged in biodegradable lating to possible applications of biodegradable films. The results suggested that ethanol is the

14 Ital. J. Food Sci., vol. 27 - 2015 best solution to preserve the microbial stability egy to preserve the quality of artichokes, also of the fresh produce without affecting its respi- from a microbiological point of view. Interest- ration rate to any great extent. Based on these ing results also came from a study of fresh-cut results, clusters of table grapes (Vitis vinifera cactus-pear: the shelf life of the minimally pro- cv. Italia) were treated in ethanol solution pri- cessed fruit, coated with an alginate and then or to packaging in different bags made of two packed with monolayer film (based on a blend types of commercially available films (a multi- of biodegradable polyesters), was prolonged to layer film obtained by laminating nylon and a about 13 days, corresponding to an shelf-life in- polyolefin layer (NP); an oriented polypropylene crease of about 40%, compared to the control film (OPP)) and in three biodegradable polyester- sample (untreated sample); on the contrary, pro- based films (NVT-100, NVT-50, NVT-35). Results duce immersion into either agar or fish protein suggest that the respiratory activity of packed strongly reduced the shelf life, most probably minimally processed produce is the main rea- due to water migration from the surrounding son for its quality loss during storage. In fact, hydro-gel to the fresh-cut produce (DEL NOBI- the best results in terms of grape quality were LE et al., 2009 c). obtained using grapes with lower respiratory Also PLA has been tested for fresh-cut fruits activity and high barrier films, such as NP and and vegetables packaging; the coating of PLA NVT-100. From a sensory point of view, no un- silicon oxide (SiOx) improved the barrier oxy- desirable after-taste developed within the fruit, gene and water vapor properties (PEELMAN et when the grapes were packaged in the thicker al., 2013). In particular, the use of PLA contain- film (NP and NVT-100). ers with lids and pouches composed of VC999 Also PLA has been tested for fresh-cut fruits Biopack PLA films coated with a barrier of pure and vegetables packaging; the coating of PLA SiOx to preserve quality of fresh-cut pears af- silicon oxide (SiOx) improved the barrier oxy- ter 9 days of storage in comparison with con- gen and water vapor properties (PEELMAN et al., ventional polyethylene PE material, has been 2013). In particular, the use of PLA containers investigated. The results showed that color and with lids and pouches composed of VC999 Bi- firmness color of fresh-cut pears is better main- opack PLA films coated with a barrier of pure tained with biodegradable packaging materials SiOx to preserve quality of fresh-cut pears af- (KRASNOVA et al., 2013) ter 9 days of storage in comparison with con- PLA is also been used in combination with sil- ventional polyethylene PE material, has been ver; silver ions have been incorporated into poly- investigated. The results showed that color and lactic film, in order to evaluate the silver-infused firmness color of fresh-cut pears is better main- PLA films for inactivation of Salmonella and fe- tained with biodegradable packaging materials line calicivirus in vitro and on fresh-cut vegeta- (KRASNOVA et al., 2013) bles (MARTÍNEZ-ABAD et al., 2013). The results Biodegradable materials do not always ful- showed that in vitro the antibacterial and anti- fill the physiological requirements of the specif- viral activity is more efficient than on food sam- ic fruit and/or vegetable packaged in them: in ples. Anyway, in lettuce samples incubated a fact, poor moisture barrier properties, linked to 4°C at 6 days of storage, 4 log CFU of Salmonel- the hydrophilic character that marks most of the la was inactivated for film with 0.1% wt of silver bio-based-materials, is sometimes responsible ions and no viral infection has been found in the for higher percentages of weight loss in prod- same conditions (MARTÍNEZ-ABAD et al., 2013). ucts, such as zucchini (LUCERA et al., 2010), The results of the case studies on biodegrad- artichokes (DEL NOBILE et al., 2009b) lampas- able packaging applied to fresh-cut fruits and cioni (Muscari comosum) (CONTE et al., 2009c) vegetables and in some cases combined with ed- and melon (CONTE et al., 2009b). ible coating are summarized in Table 3. Often in several experiments, the technique of coating is used as a pretreatment to improve the performance of biodegradable materials and ConclusionS its effects on product quality. The coating treatment, containing sodium alginates, has been Foodstuffs are dynamic systems with a limited more effective than the dipping in delaying the shelf-life and specific requirements in terms of metabolic activity associated to respiration rate packaging. In order to ensure the highest stan- in samples of lampascioni, subsequently pack- dards of product quality, the right combination aged in NTV2, a film based biodegradable poly- of product characteristics and packaging film ester (CONTE et al., 2009c). Moreover, the brown- is the basis for the development of appropriate ing process decreased, as well as, the microbial storage conditions. growth, since the availability of oxygen on the This work focuses on the potential applica- surface of the product was reduced. The same tions of biodegradable packaging and edible type of coating was also applied to fresh-cut ar- coating for minimally processed foods. The re- tichokes (DEL NOBILE et al., 2009 b): also in this sults highlight how the biodegradable films may case, the coating together with packaging in have a more or less advantageous performance NTV2 film seems to represent the better strat- in relation to the physiological characteristics of

Ital. J. Food Sci., vol. 27 - 2015 15 Table 3 - Application and combination of biopolymer with coating for fresh-cut fruits and vegetables packaging.

Food product Biopackaging Property Main results Reference of materials Polyester-based Good gas barrier prop- Shelf-life extension DEL NOBILE Iceberg lettuce biodegradable film erties et al. (2008)

Polyester-based biodegradable film /nylon and polyole- High gas barrier Good microbiological stability; DEL NOBILE Table grape fin layer good sensory characteristics et al. (2009) (Vitis vinifera) (ethanol pre-treatment before packaging) Zucchini (Cucurbi- Biodegradable co-extruded High permeability to wa- High percentage LUCERA et al. ta pepo) polyesters ter vapor of weight loss (2010) Biodegradable monolay- Permeability to water High percentage of weight loss; er film based on a blend of vapor good microbiological stability DEL NOBILE Artichoke biodegradable polyesters et al.( 2009) Coating with sodium algi- Barrier to water vapour Shelf-life extension (200%) nate (pre-treatment before low water loss packaging) Polyester-based High permeability to wa- High percentage Lampascioni biodegradable film ter vapor of weight loss CONTE et al. (Muscari comosum) Lower water loss; low micro- (2009) Coating with sodium algi- Barrier to water vapour bial growth. reduced brown- nate (pre-treatment before and oxygen ing process packaging)

Monolayer film, based on High permeability to wa- High percentage DEL NOBILE Cactus pear a blend of biodegradable ter vapour of weight loss. et al. (2009) polyesters Shelf-life extension Coating with alginates Barrier to water vapour to about 13 days (pre-treatment before pack- and other agents aging) Improved barrier prop- Better maintenance of color an KRASNOVA Fresh-cut pears PLA films coated with a erties firmness with respect to con- et al. (2013) (Pyrus communis) barrier of pure silicon ox- ventional PE packaging ide (SiOx) Melon Blend of biodegradable pol- High permeability to wa- High percentage CONTE et al. yester ter vapor of weight loss (2009)

complex matrices, such as fruit and vegetables, ible coatings can keep product characteristics, characterized by an active metabolism which sig- such as texture and hydration intact, and they nificantly affects their conservation. Certainly, can provide significant fruit senescence retarda- biopolymers fulfill the environmental require- tion. Moreover, they serve as a carrier for a wide ments but they have some limitations in terms range of food additives, including anti-browning of performance, like thermal resistance, barri- or antimicrobial agents. er and mechanical properties. Better results can New challenges should focus on the devel- be achieved by the combined use of biodegrad- opment of tailor-made coatings, containing the able packagings with edible coatings. most appropriate film forming constituents and The use of edible films and coatings represents active ingredients for fresh and minimally pro- an environmentally-friendly technology that of- cessed fruits and vegetables, according to spe- fers substantial advantages for shelf-life prolon- cific industrial needs. New trends have shown gation of many food products, including fruits that enrichment of biodegradable materials with and vegetables. The development of new natu- silver-montmorillonite nanoparticles may be a ral edible films and coatings with either inher- promising technique. ent microbicidal activity or the addition of anti- Undoubtedly, biodegradation offers an at- fungal ingredients (food preservatives, essential tractive route to environmental waste manage- oils, antagonistic microorganisms, etc.) to im- ment. However, the actual application of these prove the quality of fresh-cut fruits and vegeta- packaging solutions to food is still limited, due bles is a technological challenge for the industry to the high cost of raw materials and the small- and a very active field of research worldwide. Ed- scale production. In the future, when the quan-

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Paper Received January 20, 2014 Accepted May 22, 2014

20 Ital. J. Food Sci., vol. 27 - 2015