plants Article The Effect of Infrared Drying on Color, Projected Area, Drying Time, and Total Phenolic Content of Rose (Rose electron) Petals Kemal Ça˘gataySelvi 1,*, Abraham Kabutey 1 , Gürkan Alp Ka˘ganGürdil 1 , David Herak 1, ¸SebnemKurhan 2 and Pavel Klouˇcek 2 1 Department of Mechanical Engineering, Czech University of Life Sciences Prague, Kamycka 129, 16521 Prague, Czech Republic; [email protected] (A.K.); [email protected] (G.A.K.G.); [email protected] (D.H.) 2 Department of Quality of Agricultural Products, Czech University of Life Sciences, Faculty of Agrobiology, Food and Natural Resources, Kamýcka 129, 16521 Prague, Czech Republic; [email protected] (¸S.K.); [email protected] (P.K.) * Correspondence: [email protected]; Tel.: +90-362-312-1919 Received: 16 December 2019; Accepted: 22 January 2020; Published: 12 February 2020 Abstract: The effects of different drying temperatures (50, 60, 70 ◦C) on the quality of rose (Rose electron) petals were evaluated in this study. Drying time decreased from 1680 s to 600 s with increased infrared temperature. The temperature and time were increased from 50 ◦C to 70 ◦C and 30 min to 60 min, respectively, and a decrease in the fruit color quality was observed. The projected area (PA) of rose petals was affected significantly from temperature. After the drying process, the 2 largest PA was observed as 33.35 cm (50 ◦C, 30 min), while the smallest achieved at 70 ◦C, 60 min 2 (27.96 cm ). Depending on the temperature values (50, 60, 70 ◦C), the average projection area of dry samples of the rose petals decreased 2.17 times compared to the projection area of fresh samples. The dried samples demonstrated an increase in the total phenolic (TP) content compared to the fresh samples. The maximum TP (44.49 mg GAE/g) was achieved at 45 min and 70 ◦C rose petals sample. The results concluded that infrared drying for 45 min at 70 ◦C could be recommended for drying rose (rosa electron) petals. Keywords: infrared drying; rose petals; drying process; total phenolic content 1. Introduction The genus Rosa has approximately 100 species that are widely spread out in Europe, Asia, the Middle East, and North America [1], and its flowers in different colors are fragrant and also elegant and beautiful in shape and size. [2]. Today, besides being economically important genera of ornamental horticulture [3], rose is rising as ornamental plants widely grown in the world. They are highly popular as garden ornamental plants and cut flowers [4]. Moreover, medicinal properties, viz. anti-HIV, antibacterial, antiseptic, antioxidant, antiviral, aphrodisiac, antitussive, hypnotic, antidiabetic, relaxant effect on tracheal chains, and a tonic for the heart, liver, stomach [5], and uterus, have been recently reported for this plant, further increasing its demand [6]. Besides, it has an important role in the cosmetics industry, as well [7]. Especially, in the food industry, organic cultured roses are known as edible flowers, and phenolic compounds extracted from this plant have been used to make tea and functional beverages that exert beneficial effects on human health [8]. Considering that medicinal aromatic plants, such as roses, which can be used as a tea, are subjected to some thermal treatments during these processes, it is important to identify optimum conditions for extracting phenolic compounds from roses, due to the use of natural and functional ingredients derived from Plants 2020, 9, 236; doi:10.3390/plants9020236 www.mdpi.com/journal/plants Plants 2020, 9, 236 2 of 13 its flowers. Also, essential oils extracted from rose flowers are important ingredients for perfumes industry [9,10]. In addition to all useful information about this plant, fresh rose flowers are very sensitive and cannot retain their beauty and fresh look for a long time in spite of using the best chemicals for enhancing vase life [11]. A considerable amount of rose flowers waits for a long time until distillation due to the short blooming period and an excessive amount of flowers. There are not only losses of essential oil yield but also losses of quality, as well, depending on the waiting time of petals [12]. Color, which is one of the quality parameters for customers, is a perceptual phenomenon that depends on the observer and the conditions. Kramer [13] stated that the appearance of the product usually determines whether a product is accepted or rejected. Thus, the color of the food surface is the first quality criteria evaluated by consumers and is critical to product acceptance [14–17]. One of the oldest methods known for food preservation is drying. This process can cause changes in some physical properties, such as color, texture, and size. Chemical changes, such as losses of flavor and nutrients, can occur during convective drying, which is commonly used to process fruits and vegetables [18]. Although the two most common methods widely used for drying are sun drying and hot-air drying, they have some disadvantages like the inability to handle large quantities to achieve consistent quality standards, contamination problems, and low energy efficiency, which is not a desirable situation for the food industry [19,20]. While sun and hot-air drying have such disadvantages, infrared heating has advantages over conventional drying under similar drying conditions. Infrared (IR) heating is a potential energy-saving up to 50% [21] and high-efficiency technology, whose application in the food processing field is still progressing [22]. Studies comparing infrared drying with techniques based on air convection showed that the infrared radiation (IR) method is quicker than convection methods [23–25]. Various heating studies have been carried out to evaluate the effects of its application for rose drying with solar drying [26], sun drying [11], hot air drying [27], and microwave vacuum drying [28]. Hence, when we look at the rose plant, in particular, it is observed that the studies discussing the effects of thin layer infrared drying method, especially, are very limited or even negligible. The aims of this study were (1) to observe the effects of different drying temperatures, (2) to determine the color and projected area changing of rose petals and, (3) to find the temperature effects on total phenolic content of the rose petals. 2. Materials and Methods 2.1. Materials Petals of rose (Rose electron), which is a particularly luminous hybrid tea rose, with very large across (12 cm), full (32-40 petals), high-centered, bright cherry pink flowers were used in this study. Petals were gathered from a botanical garden of the Technical Faculty of CULS University in Prague (Czech Republic, 50◦05016.94” N–14◦25014.74” E) and cleaned by removing undesired leaves, sepals, and waste materials. The excess water was removed with the help of a blotter. Only rose petals with healthy structure and appearance were carefully selected and put into the dryer as a thin layer (2.5 g), and the damaged petals were separated manually before putting them into the dryer. Fresh petals were stored in the refrigerator at 4 ◦C until the drying experiment. 2.2. Drying Experiment MA.R infrared dryer and moisture analyzer (Radwag balances and scales, Warsaw, POLAND) was used as drying equipment (Figure1). The drying temperatures were 50, 60, 70 ◦C in each experiment. The amount of evaporated water was determined during drying at about 2-min intervals at each drying temperature. Tests were replicated three times, and the average weight loss was reported. Plants 2020, 9, 236 3 of 13 Plants 2020, 9, 236 3 of 12 1. Drying chamber base insert 2. Drying pan shield 3. Drying pan handle 4. Cross-shaped holder 5. Disposable pan Figure 1. MA.RMA.R infrared infrared basic basic moisture moisture analyzer. 2.3. Color Color MeasurementsMeasurements Rose petalpetal color color (fresh (fresh and and dried dried samples) samples) was measuredwas measured using ausing Voltcraft a Voltcraft Plus RGB-2000 Plus RGB-2000 (Voltcraft, (Voltcraft,Lindenweg Lindenweg 15, D-92242 15, Hirschau D-92242/GERMANY) Hirschau/GERMANY) color analyzer color and describedanalyzer and in terms described of “L” in (Lightness), terms of “a”“L” (redness),(Lightness), and “a” “b” (redness), (blueness) and values. “b” (blueness) The instrument values. wasThe instrument calibrated againstwas calibrated a white standard.against a whiteThe average standard. values The ofaverage color parametersvalues of color and parame standardters deviations and standard were deviations calculated were (L*, calculated a*, b*, C*, and(L*, a*,H). b*, The C*, color and valueH). The of L*color showed value the of brightness,L* showed the and brightness, it ranged from and 0it toranged 100. Thefrom values 0 to 100. of color The valuescoordinates of color a* andcoordinates b* did not a* haveand b* a specificdid not measurementhave a specific range. measurement The sample range. color The meant sample red color if a* meantvalue wasred positive,if a* value and was it positive, reflected and green it colorreflect whened green a* value color waswhen negative. a* value Besides, was negative. if b* value Besides, was ifpositive, b* value the was color positive, was yellow; the color if itwas was negative, yellow; if the it colorwas negative, was described the color as blue. was Metric described color as chrome blue. MetricC* and color hue H* chrome values C* were and calculatedhue H* values using were the measuredcalculatedL*a*b* using the values measured [29]. L*a*b* values [29]. CC= =(a (a22 ++ b2)1/21/2 (1)(1) o −1 ho = tan 1 (b/a) (2) h = tan− (b/a) (2) According to Adak, N., et al. [18], total color difference (∆E) was determined as follows: According to Adak, N., et al. [18], total color difference (DE) was determined as follows: ∆E = [(L − Lo)2 + (a − ao )2 + ( b − bo )2]1/2 (3) 2 2 2 1/2 DE = [(L Lo) + (a ao ) + (b bo ) ] (3) where Lo, ao, and bo indicate the brightness,− redness,− and yellowness− of dried samples, respectively.