Integration of UV irradiation and chitosan coating: A powerful treatment for maintaining the postharvest quality of sweet cherry fruit

Scientia Horticulturae 264 (2020) 109197

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Integration of UV irradiation and chitosan coating: A powerful treatment for maintaining the postharvest quality of sweet cherry fruit

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Moslem Abdipoura, Parivash Sadat Malekhossinib, Mehdi Hosseinifarahic,*, Mohsen Radib a Kohgiluyeh and Boyerahmad Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization(AREEO), Yasuj, Iran b Department of Food Science, Yasooj Branch, Islamic Azad University, Yasooj, Iran c Department of Horticultural Science, Yasooj Branch, Islamic Azad University, Yasooj, Iran

A R T I C LE I N FO

A B S T R A C T

Keywords: Anthocyanin Antioxidant capacity Sweet cherry fruit Ultraviolet rays Total phenol

Sweet cherry is a non-climacteric fruit consumed more as fresh for its essential nutrients and phytochemical compounds. In this study, the single and combined effects of UV-B (21.6 kj/m2), UV-C (21.6 kj/m2) radiation, and chitosan (CS) coating 1 % treatments on fruit quality of sweet cherry were studied during 28 d at 4 °C. Sweet cherry fruit were evaluated for weight loss, firmness, total titratable acidity (TTA), pH, total soluble solids (TSS), ascorbic acid (AA), total anthocyanin content (TAC), antioxidant (AOX) capacity and total phenol compounds (TPC) every 7d. Compared with control, fruit quality was better maintained in UV/CS treated fruit. The UV/CS treatments significantly inhibited the decrease in the firmness, TAC, and AOX capacity, and the increased rate of weight loss and TSS in the sweet cherry fruit. Although both UV lights were effective in the maintenance of fruit quality, sweet cherries treated with UV-C showed higher TPC accumulation and related AOX capacity compared to UV-B treatment. Overall, the integration of UV lights (UV-B and UV-C) with CS was the best treatment that could strongly inhibit the increase in the weight loss and TSS and achieved the highest firmness, AA, TAC, AOX capacity and TPC. Our results indicate that the integrated management is a potentially effective method for preventing undesirable post-harvest changes and extending the shelf-life of sweet cherry fruit.

1. Introduction

Saracoglu et al., 2017; Yildiz et al., 2018) and post-harvest (Karagiannis et al., 2018; Tsaniklidis et al., 2017; Zhao et al., 2019) treatments can reduce quality losses in fruits throughout the storage period and prolong their shelf life. However, post-harvest treatments are more significant which is due to their preventing of fruits from potential losses during storage. In the past, synthetic fungicides have been used to control postharvest decays; however, there are grave concerns about fungicide-resistant population of pathogens and chemical residues, which necessitates the research for safer and more eco-friendly alternative control approaches (Bautista-Baños, 2014; Huang et al., 2015; Ou et al., 2016). Currently, many physical treatments including nearfreezing temperature, hydro-cooling and modified atmosphere packing are being used to prevent the postharvest quality loss in sweet cherry fruit (Tsaniklidis et al., 2017; Zhao et al., 2019). However, some of the above-mentioned physical treatments have the potential risk of storage and cause some physiological disorders, such as surface pitting and

Sweet cherry (Prunus avium) is a popular fruit among broad strata of the population for its organoleptic properties and high content of beneficial health compounds (Commisso et al., 2017; Mirto et al., 2018). Specifically, it is rich in polyphenols such as anthocyanin with high antioxidant potential to reduce the risk of several chronic degenerative diseases, including cancer and cardiovascular diseases (Habib et al., 2017; Harakotr et al., 2014). However, sweet cherry as a nonclimacteric fruit has relatively short postharvest life due to high respiratory activity, susceptibility to fungal rots, and rapid senescence (Correia et al., 2017), so the harvested fruit are highly perishable and often cannot satisfy an optimal quality for consumer (Petriccione et al., 2015). Therefore, there is a need to provide technologies to handle fresh products with minimize postharvest losses and prolong the storage duration of sweet cherries. Both pre-harvest (Dong et al., 2019;

Abbreviations: AA, ascorbic acid; ANOVA, analysis of variance; ANS, anthocyanidin synthase; AOX, antioxidant; CRD, completely randomized design; CS, chitosan; DPPH, 2,2-diphenyl-1-picrylhidrazyl; FCR, Folin-Ciocalteu reagent; GA, gallic acid; HPLC, high-performance liquid chromatography; ME, methyl esterase; PAL, phenylalanine ammonia lyase; PET, polyethylene terephthalate; PG, polygalacturonase; PME, pectin methyl esterase; RSC, radical scavenging capacity; SAS, statistical analysis system; TAC, total anthocyanin content; TPC, total phenolic compounds; TSS, total soluble solids; TTA, total titratable acidity; UV, ultraviolent ⁎ Corresponding author. E-mail address: [email protected] (M. Hosseinifarahi). https://doi.org/10.1016/j.scienta.2020.109197 Received 7 October 2019; Received in revised form 9 January 2020; Accepted 10 January 2020 0304-4238/ © 2020 Elsevier B.V. All rights reserved.

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anthocyanin degradation (Correia et al., 2017; Wani et al., 2014). Ultraviolet lights (UV-B and UV-C) have been proposed as a friendly and cost-effective non-molecular tool with easy operation to maintain the quality of horticultural crops during postharvest life. The application of UV-B could highly enhance bioactive compounds and/or antioxidant enzymes (Santin et al., 2018), while UV-C radiation (100–280 nm) due to its high germicidal properties, could be used as an alternative to prevent initial microbial load (Araque et al., 2018; Ou et al., 2016). Therefore, the combination of UV-B and UV-C may improve postharvest quality through delay in fruit ripening/senescence, prevent chronic changes in firmness, water loss, and pH, enhance some great antioxidants such as phenolic compounds and reduce the incidence of post-harvest spoilage in sweet cherry fruit. However, such combined UV treatment has not already been investigated on sweet cherry. Among several edible coatings used for prolonging the shelf life of fresh fruits, chitosan as a biodegradable, non-toxic and antimicrobial compound, has attracted a lot of attention due to its excellent filmforming and biochemical properties (Han et al., 2014; Muzzarelli et al., 2012). It forms a semipermeable membrane and creates a modified internal atmosphere, thereby, slowing down respiration and transpiration, and activates defense mechanisms against a wide range of microorganisms in fruits and vegetables (Pagliarulo et al., 2016). Chitosan coating has been applied in loquat fruits (Adiletta et al., 2018), guava (Silva et al., 2018), mango (Jongsri et al., 2016) sweet cherry (Petriccione et al., 2015), and plum (Kumar et al., 2017) with successful results. The pre- and post-harvest application of UV-C combined with chitosan coating for maintaining sensory quality, and reduction of fungal decay in grapes have been reported (Freitas et al., 2015; Romanazzi et al., 2006). However, during our review, we couldn’t find any study into the effect of the combination of UV and chitosan on the shelf life and postharvest quality of sweet cherry under low-temperature storage. Therefore, we designed a study with the objective of evaluating the potential effects of a combined treatment of UV radiation and chitosan coating on the postharvest life and quality attributes of sweet cherry during low-temperature storage.

Table 1 List of UV lights and chitosan coating treatments. Treatment

Abbreviation

Control Chitosan 1 % Ultraviolet- B Ultraviolet- C Chitosan 1 % + Ultraviolet- B Chitosan 1 % + Ultraviolet- C Chitosan 1 % + Ultraviolet- B + Ultraviolet- C

C CS UV-B (21.6 kj/m2) UV-C (21.6 kj/m2) CS + UV-B CS + UV-C CS + UV-B + UV-C

Whatman No. 1 filter paper under vacuum to remove impurities and insoluble matter. Glycerol was then added as the plasticizer (at a concentration of 0.5 % of CS solution) to improve film formation on the fruit surface and reduce the brittleness of CS coating. The sweet cherry fruits were dipped into the CS solution for 1 min at 25 °C to allow the CS to create a uniform film throughout the fruit surface. The fruits were then kept for 1 h at 25 °C on a bench to be air-dried. 2.2.2. Ultraviolent radiation Sweet cherry fruits were exposed to UV-B and/or UV-C radiation according to Abdipour et al. (2019) with some modification. For this purpose, a UV chamber equipped with three UV-B (21.6 kj/m2) and three UV-C (21.6 kj/m2) lamps (30 W each/ Philips, length of 90 cm and 2.5 cm in diameter), was used. The fruits were placed at the bottom of the chamber and were treated by UV lights for 10 min. The fruit's distance from the lamps was about 50 cm. To ensure uniform irradiation of the entire fruit surface, first a side of the fruit was irradiated and then the fruits were rotated to the other side to be irradiated. The fruits kept in the dark served as the control. 2.3. Storage conditions

2. Material and methods

Treated and untreated sweet cherries were covered with a polyethylene terephthalate (PET) clamshells (140 × 128 × 30 mm) (Pars Plastic Khuzestan, Ahwaz, Iran) with four vent holes in the sides (1 mm in diameter) and were stored at 5 ∘C with 90 ± 2 % relative humidity for 28 days.

2.1. Plant materials preparation

2.4. Weight loss

The study was carried out in 2018 on sweet cherries (cv.) ‘Takdaneh Mashhad’ harvested from a local orchard in Sisakht, Kohgiluyeh and Boyer-Ahmad Province, Iran (Latitude: 30° 51′ 59.99″ N, Longitude: 51° 26′ 59.99″ E), at the commercial maturity stage in May. The cherries were transferred to the laboratory (in a cold room at 4 °C) on the day of collection. Upon arrival at the laboratory, the fruits were graded for uniformity of color, size and the absence of physical injuries or pest and disease infection.

Fruit weight loss was determined by the difference between the initial weight (Wi) and the weights measured after 7, 14, 21 and 28th d during cold storage (Wf) as follows (Eq.1). The result is expressed as percentage.

2.2. Experimental design, treatments, and sampling

A texture analyzer (CT-3 Texture Analyzer, Brookfield, USA) with a 30 mm diameter flat cylindrical probe was used to determine fruit firmness and the results were expressed in newton (mN). It measures the maximum force (mN) recorded during compression of the specimen between the base and a flat cylindrical probe. The crosshead speed was 1 mm s−1, and the data were normalized as the ratio of the force required in order to achieve 15 % fruit deformation over the fruit large diameter (Goulas et al., 2015).

WL= [(Wi − Wf)/Wi] × 100

(1)

2.5. Fruit firmness

The experiments were laid out as factorial based on a completely randomized design (CRD) with three replications. The single and combined effects of UV-B, UV-C radiation and chitosan coating were defined in seven treatments (Table 1). A total number of 1680 uniform fruit were randomly sampled and divided into seven groups. 2.2.1. Preparation and application of chitosan coating Chitosan (CS) from crab shells (Sigma Aldrich, chemicals) with 90 % deacetylation and a molecular weight of 360 kDa was used to prepare a CS solution at a concentration of 1 % (w/v) in an aqueous solution of acetic acid (1 % w/v). The solution was stirred overnight at 40 °C for the complete dissolution of CS. The solution (CS 1 %) was filtered through a

2.6. Total soluble solids (TSS), Total titratable acidity (TTA) and Ascorbic acid (AA) content For TSS, TTA and AA measurements, 50 fruits were randomly selected from each replicate and after the removal fruit stone; fruit juice was extracted with a commercial juicer (Model No. Hinari JEP311, Alba 2

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Plc., Elstree, U.K.), at about 2000×g, and was then filtered with a milk filter (Schwartz Manufacturing Co., Two Rivers, WI). The TSS was assayed using an Abbe Refractometer (Atago, NAR-3 T, Japan) and was expressed in percentage (Brix %). The TTA was determined by titrating 10 mL of sweet cherry juice to pH 8.1 with 0.1 M NaOH solution and the results were expressed as g malic acid g/kg−1 juice. The AA was determined using the DAD-HPLC analysis, following the method adopted by Liu et al. (2015) with a slight modification. For this purpose, an Agilent 1260 Infinity HPLC system (Agilent, USA) equipped with a C18 column (15 cm × 4.6 mm ID, 5 μm; Zorbax Eclipse Plus) was used. An isocratic eluting solution (90 % formic acid and 10 % methanol) at the flow rate of 0.8 mL min−1 was used and the measurements were performed at 245 nm. The measured values were qualified based on the standard curve obtained with L-ascorbic acid reference. The AA content was expressed as mg of AA per 1 kg of juice (mg/ kg−1).

2.10. Sensory evaluation The sensory evaluation was conducted according to the method described by Echeverría et al. (2015) with some modifications. The tasting panel consisted of 15 semi-trained consumers. Each consumer was asked to assess all of the samples in the same session and mineral water was used as a palate cleanser between the samples. The fruit color, taste, odor, and overall acceptance were assessed using a fivepoint hedonic scale (1- Bad, 2- moderate, 3- Good, 4- Very good, 5Excellent). The whole process was performed at ambient temperature and standard lighting. 2.11. Statistical analysis A factorial experiment based on the complete randomized design (CRD) in triplicate was used for the experiment. The normality of data was checked by the Kolmogorov-Smirnov test and the percentage values were normalized using the arcsin of the square root. Statistical analyses were conducted by running one-way analysis of variance (ANOVA), using SAS (Statistical Analyses System) software, version 9.2 (SAS Institute, 2017), and the means were compared using Duncan’s multiple test range at P < 0.05.

2.7. Total anthocyanin content Total monomeric anthocyanin levels were measured according to the AOAC official method 2005.02 based on the change in the molar extinction coefficient of anthocyanins at two different pHs (1 and 4.5) (AOAC, 2005). The calculations were performed based on the absorptivity of cyanidin-3-glucoside (C3G), as follows: Anthocyanin (ε×l)

concentration

3. Results and discussion

(mg/kg−1) = (A × MW × DF × 1000)/ (2)

3.1. Weight loss Weight loss in fruits and vegetables is mainly due to water loss caused by evaporation during storage, which, in turn, is a result of transpiration and respiration processes (Zhao et al., 2019). A significant decrease (F4,110 = 98.64, p < 0.001) in fruit weight was found during storage time (Table S1). The weight loss proliferations of sweet cherries are taken in Table 2. As demonstrated in Table 2, control fruits started weight loss from the first days after being stored and reached a peak on the 28th day. No such increase was observed in UV and/or CS treated fruits with respect to weight loss. Compared with control, UV and CS treatments significantly retarded weight loses (F10,110 = 45.37, p < 0.001), and this difference increased with storage time in this study (Tables S1 and 2). As expected, at the end of cold storage (28th day) the lowest and highest weight losses were observed in the CS + UV-B + UV-C (12.11 %) and the control (29.34 %) treatments, respectively. Overall, combined treatments (UV-B or UV-C with CS) could better maintain the initial weight than single treatments (UV-B, UV-C or CS). Although no significant (p < 0.05) weight loss differences were recorded in fruits treated with UV-B or UV-C, the UV lights in combination with CS had a different effect and UV-B+CS treated fruits exhibited more decline than UV-C+CS treated fruit (Table 2). As shown in Table 2, the UV treatments (as single or in combination with CS) compared with the control could inhibit weight loss with more efficiency throughout the storage period. The role of UV lights in preventing weight loss in fruit may be associated with limiting respiration rate and transpiration, which in turn reduces water loss in treated fruits (Abdipour et al., 2019). In addition, minor weight loss in the UV treated fruit can be related to the inhibition of cell membrane dysfunctions (Promyou and Supapvanich, 2012). In the same way, a positive association between fresh weight loss and increase in electrolyte leakage of tissue in melon fruit was reported by Supapvanich and Tucker (2013). Moreover, according to the results reported in Hagen et al. (2007), the percentage of weight loss in UV-B irradiated apples was lower and their moisture was further preserved, which was due to stimulating the activity of ligninizing enzymes. These observations are in agreement with a previous study that reported UV lights in sweet cherry fruit could suppress the ripening process and maintain the fruit weight (SirooyeNejad et al., 2013). The CS coating significantly limited fruit weight loss compared with other single treatments (UVB and UVC), and the CS-fruit weight loss was 6.9 and 4.7 % lower than that of fruit treated with UVC

where A = [(Absorbance 520 nm – Absorbance 700 nm) at pH 1.0] − [(Absorbance520 nm – Absorbance 700 nm) at pH 4.5]; MW is the molecular weight of C3G = 449.2 g/mol; DF is the dilution factor; l is the path-length in cm; ε is the molar extinction coefficient of C3G = 26900 L mol−1 cm−1; and 1000 is the factor for conversion from g to mg. 2.8. Antioxidant activity Antioxidant activity was evaluated based on 2,2-diphenyl-1-picrylhidrazyl (DPPH) radical scavenging capacity (RSC) method proposed by Brand-Williams et al. (1995) with some modifications. To give an overview, a 0.1 mM solution of DPPH in methanol was prepared, and 0.1 mL of cherry juice or double-distilled water (as the control) was added to the test tubes containing 3.9 mL of DPPH solution. The mixture was shaken well and was incubated for 30 min in the dark room. A spectrophotometer (T80+, PG Instruments, UK) was used to take the absorbance of the main solution (A) and the control (B) at 517 nm. The antioxidant compounds in the samples scavenge the DPPH radicals and cause the solution to discolor from deep violet to pale yellow. The percentage of radical inhibition was calculated as follows: Antiradical activity % = [(B − A)/B] × 100

(3)

2.9. Total phenol compounds Total phenolic compounds were measured using Folin–Ciocalteu reagent (FCR) according to the method described by Singleton et al. (1999) with minor modifications. To be more specific, the juice samples and FCR were diluted 10-folds with distilled water. Then 1 mL of diluted juice was added to 7.5 mL of diluted FCR in the test tubes. After an incubation period of 5 min, 7.5 mL Na2CO3 (6 %) was added to each tube and the tubes were kept at 25 °C for 2 h. The absorbance of the solutions was measured at 725 nm, using a spectrophotometer (T80+, PG Instruments, UK). The results were calculated as the gallic acid (GA) equivalents, based on a calibration curve constructed by plotting the serial concentrations of GA versus absorbance. 3

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Table 2 Mean values of standard quality parameters (weight loss, flesh firmness, titratable acidity, and total soluble solids) at harvest (0) and after 7, 14, 21 and 28 days of storage for chitosan and/or radiated and untreated fruits (Control). Characteristic

Storage time (days)

Control

CS1 %

UVC

UVB

CS1 %+UVB

CS1 %+UVC

CS1 %+UVB + UVC

Weight loss (%)

0 7 14 21 28 0 7 14 21 28 0 7 14 21 28 0 7 14 21 28

0 ± 0a 2.28 ± 0.04a 14.01 ± 0.11a 24.37 ± 0.18a 29.34 ± 0.64a 343.15 ± 0.18a 324.91 ± 1.62c 291.18 ± 5.04f 237.12 ± 2.02d 202.61 ± 2.09g 0.043 ± 0a 0.040 ± 0b 0.029 ± 0d 0.015 ± 0f 0.010 ± 0f 17.61 ± 0.02a 18.69 ± 0.02a 21.91 ± 0.11a 22.64 ± 0.16a 26.94 ± 0.01a

0 ± 0a 1.1 ± 0d 6.11 ± 0.24c 17.14 ± 0.43d 19.61 ± 0.37ad 343.61 ± 1.52a 341.28 ± 0.63a 312.37 ± 1.05c 250.03 ± 1.27bc 217.37 ± 3.03d 0.042 ± 0a 0.042 ± 0a 0.035 ± 0c 0.024 ± 0d 0.016 ± 0d 17.11 ± 0.10a 17.41 ± 0.27b 17.71 ± 0.13b 19.26 ± 0.07b 22.49 ± 0.91b

0 ± 0a 1.4 ± 0b 12.48 ± 0.02b 20.02 ± 0.25b 24.27 ± 0.71b 342.18 ± 0.61a 339.19 ± 5.12b 302.61 ± 0.12d 244.92 ± 2.61c 214.61 ± 1.19e 0.043 ± 0a 0.042 ± 0a 0.035 ± 0c 0.020 ± 0c 0.014 ± 0e 17.02 ± 0.62a 17.45 ± 0.37b 18.97 ± 0.92b 19.44 ± 0.19b 22.17 ± 0.37b

0 ± 0a 1.48 ± 0b 12.57 ± 0.49b 21.72 ± 0.18b 26.51 ± 0.24b 343.67 ± 2.12a 339.61 ± 2.10b 295.57 ± 2.43e 241.64 ± 3.37c 209.99 ± 2.34f 0.043 ± 0a 0.043 ± 0a 0.030 ± 0d 0.017 ± 0e 0.011 ± 0e 17.14 ± 0.32a 17.49 ± 0.61b 20.25 ± 0.08ab 21.62 ± 0.28a 25.27 ± 0.02a

0 ± 0a 1.32 ± 0c 7.08 ± 0.71c 19.34 ± 0.11c 21.07 ± 0.28c 343.37 ± 0.67a 341.64 ± 1.91a 301.67 ± 1.24d 250.11 ± 1.08bc 220.51 ± 3.12c 0.043 ± 0a 0.043 ± 0a 0.037 ± 0b 0.021 ± 0c 0.016 ± 0d 17.00 ± 0.06a 17.42 ± 0.02b 18.70 ± 0.28b 19.65 ± 0.92b 22.74 ± 0.34b

0 ± 0a 1.11 ± 0d 2.91 ± 0.22ed 10.18 ± 0.08e 15.02 ± 0.54e 343.01 ± 1.16a 342.27 ± 2.27a 310.28 ± 3.19b 254.02 ± 0.64b 224.35 ± 2.64b 0.042 ± 0a 0.043 ± 0a 0.038 ± 0b 0.024 ± 0b 0.021 ± 0c 17.07 ± 0.34a 17.39 ± 02b 18.24 ± 03b 19.07 ± 0.037b 21.12 ± 0.27c

0 ± 0a 0 ± 0e 0.4 ± 0.18e 7.02 ± 0.04f 12.11 ± 0.71f 343.92 ± 0.20a 342.16 ± 0.13a 321.27 ± 1.27a 262.81 ± 2.21a 238.01 ± 2.38a 0.043 ± 0a 0.043 ± 0a 0.042 ± 0a 0.035 ± 0a 0.030 ± 0a 17.25 ± 0a 17.40 ± 0.01b 17.72 ± 0.20c 18.01 ± 0.41c 19.81 ± 0.14d

Flesh firmness (mN)

Titratable acidity (g/ kg −1)

Total soluble solid (%)

Data represent the mean of 3 replicates ± SD. Different letters indicate significantly different values according to one-way ANOVA followed by Duncan’s multiple test range (p < 0. 05).

firmness loss (Civello et al., 2014; Stevens et al., 2005). Besides UV irradiation, as shown in Table 2, a higher retention of fruit firmness was achieved by CS coating. This might have resulted from the inhibition of carbon dioxide production in the coated cherries and hence a slower softening process (Kumar et al., 2017). The secondary mechanism for chitosan may be related to a decrease in the activity of important enzymes in cell wall degradation (Xu et al., 2007). Several research reports have indicated that UV light or CS coating can be as effective as natural inhibitors for the firmness loss during shelf life and storage (Araque et al., 2018; Jongsri et al., 2016; Koçak and Bal, 2017; Ou et al., 2016; Silva et al., 2018). However, by combining UV lights radiation and CS coating, we found a higher level of retention with respect to tissue firmness, which may make it difficult to understand the correct mechanism.

and UVB lights, respectively. Edible coatings such as CS are suitable barriers to gas exchange (O2 and CO2) and could prolong storage and shelf life of fruits and vegetables through reducing gas exchange and water loss (Aglar et al., 2017; Valero et al., 2015; Velickova et al., 2013). Our results are in agreement with the previous studies that have shown the postharvest application of chitosan edible coating reduces weight loss in sweet cherry (Dang et al., 2010; Ma et al., 2019; Petriccione et al., 2015). Although no study has yet been conducted on the combined effect of CS and UV radiation to prevent weight loss in sweet cheery, a combined treatment of CS and UV lights (CS + UVB + UVC) showed the highest inhibitory efficiency to weight loss. It seems CS and UV light due to complementary effect can be used as postharvest treatment to prevent weight loss during storage time. 3.2. Flesh firmness

3.3. Total titratable acidity (TTA) content Flesh firmness in all treatments significantly decreased during storage (F4,110 = 41.45, p < 0.001) (Table S1), and reached a minimum level on the 28th day (Table 2). However, such decreases in treated fruits were lower than those observed in control (F10,110 = 23.31, p < 0.001) (Table S1). As shown in Table 2, the softening process in control started from the seventh day, whereas the process was delayed until the 14th day in other treatments due to UV or/and CS. Compared with other treatments, UVB + UVC + CS treatment had the slowest rate of softening and effectively delayed fruit softening, while firmness of the control fruits decreased about 40.1 % by the end of storage. Although both UV-B and UV-C could delay the fruit softness, the better inhibitory efficiency was achieved with UV-C. In combination with CS, these two ultraviolet rays also had a different inhibitory effect on fruit softness (CS + UV-C > CS + UV-B). However, CS-treated fruits, compared with fruits under single UV treatments (i.e. UV-B and UVC), showed a higher flesh firmness at the end of the storage. In fact, fruit softening is a biochemical process that is usually related to the destruction of cell wall components including pectin hydrolysis by enzymes such as polygalacturonase (PG), pectin methylesterase (PME) and methyl esterase (ME) (Atkinson et al., 2012). Therefore, any treatment that can reduce the activity of these enzymes may help the fruit firmness retention. It has been shown that UV radiation prevents ethylene synthesis and halts the effective enzymes in the softening of fruits and reduces the rate of respiration which all lead to a delay in the

Total titratable acidity (TTA) is a significant quality parameter related to the ripening and maturity of sweet cherry fruit. The TTA values in fruit decreased gradually and continuously with storage time (F4,110 = 8.17, p < 0.001) (Table S1). In untreated fruit, decrease in TTA has occurred since 7th day, but this decrease in UV or/and CS treated fruit was delayed until 14th day (Table 2). The higher acidity loss in untreated fruit could be attributed to the use of organic acids as substrates for respiratory metabolism (Gol et al., 2015). Our results are in line with those reported by Araque et al. (2018) and Abdipour et al. (2019) where a slower decrease in TTA was observed in strawberry and peach fruits irradiated with UV lights, respectively. As shown in Table 2, UV light treatments as single (UV-B and UV-C) did not show any significant difference, but in combination with CS, a lower acidity loss was found in CS + UVC compared with CS + UVB (Table 2). It is interesting to note that TTA values varied significantly (F10,110 = 7.20, p < 0.001) between the fruit samples treated with UV and CS (Table S1), and CS-coated fruits showed higher retention of TA (Table 2). Our results are in agreement with Petriccione et al. (2015); Jongsri et al. (2016); Kumar et al. (2017); Nair et al. (2018), who observed lower acidity loss during storage in sweet cherry, mango, guava and plum coated with chitosan. The lower acidity loss in CScoated fruits suggests that chitosan treatment may play a role in delaying fruit ripening (Petriccione et al., 2015). In general, CS + UV4

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those observed for single treatments. In this sense, the combination of UV-B and UV-C with CS (CS + UV-B + UV-C) that recorded the highest content of AA throughout the storage period may be more advisable due to reduced AA changes. Our findings are in agreement with Maharaj et al. (2014), Hosseini Farahi et al. (2018), Adiletta et al. (2018), Jongsri et al. (2016), who showed that UV or CS treatments delayed the AA loss in tomato, strawberry, loquat and mango fruits, respectively.

B + UV-C treatment with the lowest acidity loss (∼30 %) compared with control (with 76.74 % acidity loss) showed the highest retention of TTA in sweet cherry fruit. The other interesting point is the trend of TTA changes in sweet cherry fruit during the storage that is concurrent with the other measured factors such as weight loss and firmness. This confirms the relation of all these factors to reduction of enzymes activities and the retardation of ripening by applying the treatments. 3.4. Total soluble solids (TSS)

3.6. Total phenol content (TPC) Being a climacteric fruit, sweet cherry tends to show an increase in the total soluble solids (TSS) levels during storage (Aglar et al., 2017). Irrespective of treatment, the TSS values of fruit markedly increased (F4,110 = 155.63, p < 0.001) during storage and reached a maximum level on the 28th day (Tables S1 and 2). The increased TSS levels may be associated with water loss, ripening or softening process which, in turn, is due to increased enzymatic activity and reduced turgor pressure (Radi et al., 2017). Depolymerization of insoluble polysaccharides in cell wall such as pectin and cellulose to low molecular weight soluble sugars, and increase in the solubility of hemicellulose and polyvinylidene in cell wall are other factors contributing to the increase in TSS (Barka et al., 2000; Khan et al., 2008; Kumar et al., 2017; Larrigaudiere et al., 2002). As shown in Table 2, increase in TSS followed a faster trend in untreated fruits, as compared with treated fruit (except UV-B) (F10,110 = 14.27, p < 0.001) (Table S1). Interestingly, UV-B light had not tangible dissuasive effect on the increase in TSS and UV-B treated fruit showed no significant (p < 0.05) difference with untreated fruit. UV-B in combination with CS coating treatment did not affect the TSS values significantly either and even UV-B irradiated fruit showed a higher level of TSS than those treated with CS (Table 2). In contrast to UV-B, UV-C and CS coating treatments controlled the TSS increment well. Such effects of the UV radiation and CS coating on the TSS of fruits may probably be due to the slowing down of the catabolic processes and respiration rate (Hosseini Farahi et al., 2018; Kumar et al., 2017). The combined effect of these two treatments (UV-C and CS) had better inhibitory efficiency than the cases where these treatments were applied individually. Although single UV-B light treatment or in combination with CS did not have a significant effect on the values of TSS, this UV light in combination with UV-C and CS significantly reduced the TSS growth rate. This difference is quite visible from the comparison of fruit treated with CS + UVB (22.74 ± 0.34) and CS + UV-B + UV-C (19.81 ± 14). These results are in conformity with those of Silva et al. (2018); Ou et al. (2016), (Kumar et al., 2017) where a slower rise in TSS was observed in guava, pineapple, and plum fruits treated with UV or CS, respectively.

Initial TPC of the control cherry was 440.01 ± 0 mg kg_1 (Table 3). TPC of all samples progressively decreased throughout the storage (F4,110 = 5.88, p < 0.001) and reached a minimum level in the control samples on the 28th day (Tables S1 and 3). However, these decreases were lower in UV- or/and CS-treated fruit than those observed in control fruit. Such retention of TPC has been attributed to the increase PAL activity (Singh, 2016) which is involved in phenol synthesis in fruits. It has been considered as the first enzyme in the phenylpropanoid pathway and key-point in the biosynthesis of phenolic compounds (Kim and Hwang, 2014). Although the application of both UV lights could significantly prevent TPC changes, UV-C irradiated fruits showed a higher retention level of TPC than that observed in UV-B irradiated fruit. Koçak and Bal (2017) reported the same trend with respect to TPC in UV irradiated cherry. On the other hand, single CS treatment showed 17.95 % higher TPC than the control samples after the 28th day (Table 3). Similar observation in TPC retention was reported from a similar study with CS-coated fruits (Petriccione et al., 2015). Interestingly, the application of UV-C or CS did not have a different effect on the TPC of the cherry fruit, since no significant (p < 0.05) differences were found between UV-C and CS at the end of storage time (Table 3). According to the hereby-reported data, the use of the UV-C treatment in combination with CS significantly (p < 0.01) affected TPC, compared with UV-B treatment. In general, UV-B and UV-C treatment in combination with CS coating achieved the highest TPC retention (366.61 ± 3.71) at the end of storage time, which is 30.64 % higher than the TPC retention reached by the control samples (Table 3). 3.7. Total anthocyanin content (TAC) Anthocyanins are colored water-soluble pigments belonging to the phenolic compounds group. These pigments are responsible for the red color in sweet cherry fruit, which is the most important indicator of maturity and quality (Chockchaisawasdee et al., 2016). A sharp decrease was observed in TAC for the control fruit from the beginning until the end of storage (F4,110 = 1069.15, p < 0.001) (Table S1). Such a decrease in TAC may be attributed to the decrease in the activity of enzymes involved in anthocyanin synthesis i.e. phenylalanine ammonia-lyase (PAL) and anthocyanidin synthase (ANS) (Severo et al., 2015). Compared with the non-treated fruits, the UV irradiated or/and CS-coated fruit showed higher retention of TAC during storage (Table 3). This delay in TAC loss might have resulted from the induction of anthocyanin biosynthesis by UV light or inhibitory effect of CS on reducing anthocyanin synthesis (Chiabrando and Giacalone, 2015; Santin et al., 2018). Contrary to the observed high retention of TAC after UV radiation or/and CS coating treatments in this study, Liu et al. (2014) and Sripong et al. (2019) reported that UV treatment inhibited anthocyanin accumulation. This may be due to different in applied UV dosage and cultivar of the fruit (Erkan et al., 2008). As shown in Table 3, TAC retention was not the same for the fruit treated with CS or UV lights (F10,110 = 36.58, p < 0.001), and we found the following retention order: UV-B < UV-C < CS (Table 3), which might be due to barrier properties of the CS coating. Such a trend has not been reported in the literature. The higher values of the TAC were obtained when we combined CS with UV-B and/orUV-C. As shown in Table 3, increases of 32.20 %, 35.54 % and 50.25 % for TAC were observed in CS + UVB,

3.5. Ascorbic acid (AA) content The initial AA content for the fruit (96.2 mg / kg −1) gradually decreased during storage (F4,110 = 14.40, p < 0.001) (Table S1) and at the end of 28 days of storage, the reduction in AA content was more than 31 % (65.9 mg / kg −1 FW) in control fruit (Table 3). The reduction in AA content might have occurred due to chemical oxidation and/or thermal degradation (Li et al., 2017; Zhao et al., 2019). However, this reduction in AA content was significantly (F10,110 = 1.96, p < 0.001) retarded by the application of irradiation and/or CS (Table 3). Compared with the control fruit, the fruit treated by UV-B, UV-C or CS (∼4.7, 14.4 and 14.8 %) maintained better AA content throughout the storage period, respectively. Higher retention of AA content in irradiated and CS-coated fruits could be due to low oxygen permeability which led to inhibition of the enzyme activity and thereby reduction in ascorbic acid oxidation (Liu et al., 2014). Although the application of single treatments (UV-B, UV-C or CS) could significantly prevent AA changes, combined treatments (CS + UV-B, CS + UV-C or CS + UV-B + UV-C) maintained a better AA content on the 28th than 5

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Table 3 Mean values of health-promoting properties (vitamin C, anthocyanin, antioxidant, and total phenolic compounds) and sensory attributes at harvest (0) and after 7, 14, 21 and 28 days of storage for chitosan and/or radiated and untreated fruits (Control). Characteristic

Storage time (days)

Control

CS1 %

UVC

UVB

CS1 %+UVB

CS1 %+UVC

CS1 %+UVB + UVC

Ascorbic acid (mg/kg −1)

0 7 14 21 28 0

96.2 ± 0a 89.2 ± 0a 74.1 ± 0.07c 71.4 ± 0.46d 65.9 ± 0.11f 440.01 ± 0a

96.4 ± 0a 95.2 ± 0.02b 89.2 ± 0.52b 88.0 ± 0.37b 80.1 ± 2.62c 442.43 ± 0.01a

96.2 ± 0.31a 95.0 ± 0.11b 88.8 ± 0.18b 87.4 ± 0.16b 79.7 ± 0.16d 440.61 ± 0.01a

96.7 ± 0.10a 95.0 ± 0.01b 80.4 ± 0.02b 79.1 ± 0.27c 70.4 ± 2.27e 441.92 ± 0.42a

96.5 ± 0.11a 96.0 ± 0.07b 89.2 ± 0.72b 88.0 ± 0.02b 82.4 ± 0.02bc 441.61 ± 0.27a

96.2 ± 0.0a 95.9 ± 0.11b 89.8 ± 0.0b 88.7 ± 0.12b 83.7 ± 2.41b 440.37 ± 0a

96.2 ± 0.31a 96.1 ± 0.14a 92.6 ± 0.01a 90.7 ± 0.40a 87.6 ± 0.07a 440.04 ± 0.02a

7 14 21 28 0 7 14 21 28 0 7 14 21 28 28 28 28 28

379.02 ± 0.02d 346.34 ± 0.17e 300.17 ± 0.10e 280.62 ± 1.02f 443.1 ± 0.30a 391.1 ± 0.45e 333.6 ± 0.60g 292.8 ± 0.81g 254.3 ± 0.38g 48.90 ± 0.11a 43.02 ± 0.02b 39.34 ± 0.07e 38.48 ± 2.19e 34.92 ± 2.11e 1.72 ± 0.13d 1.72 ± 0.27d 1.3 ± 0.33f 1.5 ± 0.11f

426.08 ± 1.25c 394.56 ± 4.12c 351.91 ± 0.52c 331.01 ± 0.82d 440.8 ± 0.31a 430.1 ± 0.28b 411.0 ± 0.43d 380.6 ± 0.0.24d 365.8 ± 00.31d 47.33 ± 0.20a 45.91 ± 0.18a 42.95 ± 0.92d 42.24 ± 1.37c 40.13 ± 1.0b 2.77 ± 0.31b 3.8 ± 0.20ab 3 ± 0.16b 3 ± 0.22c

420.19 ± 1.12c 388.02 ± 0.28d 347.34 ± 1.37c 328.0 ± 3.12d 449.2 ± 0a 422.1 ± 0.32c 402.5 ± 0.49e 363.8 ± 0.62e 345.2 ± 0.28e 48.37 ± 0a 45.91 ± 0.34a 42.67 ± 2.17d 42.02 ± 0.11c 39.07 ± 0c 3 ± 0.15b 3.7 ± 0.18b 3.78 ± 0.25a 2.7 ± 0.34d

384.0 ± 3.32d 372.41 ± 0.34d 338.82 ± 0.12d 297.31 ± 0.18e 444.5 ± 0a 410.5 ± 0.01d 393.1 ± 0.02f 338.4 ± 0.10f 314.1 ± 0.61f 48.91 ± 0a 45.71 ± 0.19a 41.04 ± 0.64e 40.88 ± 0.37d 36.44 ± 0.80d 2.77 ± 0.22b 2 ± 0.42c 2.5 ± 0.17d 2 ± 0.14e

430.21 ± 1.25b 399.58 ± 0.82c 362.01 ± 1.82b 341.19 ± 0.71c 443.7 ± 0.08a 432.4 ± 0.92b 419.5 ± 0.14c 397.4 ± 0.37c 374.2 ± 0.92c 48.18 ± 0a 45.90 ± 0.37a 43.90 ± 0.17c 43.39 ± 0.91b 40.21 ± 0.71b 2.5 ± 0.27c 3.9 ± 0.19ab 2 ± 0.11e 3.9 ± 0.28b

430.67 ± 2.12b 402.01 ± 1.34b 367.18 ± 0.12b 349.46 ± 0.37b 449.1 ± 0.11a 437.4 ± 0.34b 423.7 ± 0.60b 406.4 ± 0.28b 397.0 ± 0.27b 48.34 ± 0a 45.90 ± 0.22a 44.04 ± 0.12b 43.34 ± 0b 40.94 ± 0.54b 3.47 ± 0.20a 3.7 ± 0.34b 3 ± 0.31b 4.1 ± 0.19b

437.95 ± 0.12a 415.51 ± 1.46a 392.08 ± 0.15a 366.61 ± 3.71a 441.9 ± 0.01a 439.0 ± 0.01a 430.5 ± 0.08a 420.5 ± 0.61a 414.7 ± 0.10a 48.91 ± 0a 45.94 ± 1.07a 45.17 ± 1.91a 44.90 ± 0.82a 43.27 ± 0.37a 3.5 ± 0.12a 4.1 ± 0.21a 3.9 ± 0.23a 4.4 ± 0.16a

Total phenolic compounds (mg/kg −1)

Anthocyanin) (mg/kg −1) (mg/l)

Antioxidant activitya (% inhibition)

Taste Smell Color Overall acceptance

Data represent the mean of 3 replicates ± SD. Different letters indicate significantly different values according to one-way ANOVA followed by Duncan’s multiple test range (p < 0. 05). a The DPPH free radical scavenging capacity was measured and was reported as the percent inhibition (%) of free radicals of DPPH.

lower degree of AOX compounds in the UV-C irradiated fruit comparison to UV-B. As shown in Table 3, CS coated fruit showed the highest AOX retention with levels of 2.7 and 10.1 % higher than UV-C and UV-B irradiated fruit. Interestingly, no significant (P < 0.05) differences were noted when CS treatment was combined with UV-B or UV-C lights. On the contrary, CS treatment in combination with UV-B and UV-C showed the lowest AOX loss regarding its initial content with 2.97, 3.74, 4.01 and 5.64 % after 7, 14, 21 and 28 days, respectively, which is 23.91 % lower than the AOX loss reached by the control fruit.

CS + UVC and, CS + UVB + UVC, compared with non-treated fruits, demonstrating that the combination of CS and UV radiation successfully improved anthocyanin content of sweet cherry and maintained their quality during storage for a longer time. 3.8. Total antioxidant capacity Antioxidant (AOX) capacity in sweet cherry fruits gradually decreased during storage (F4,110 = 101.86, p < 0.001) and this reduction was effectively inhibited by CS and/or VU treatments (Tables S1 and 3). As shown in Table 3, fruits treated with CS and/or UV lights retained AOX capacity, compared with the control during the whole storage and significant differences were found between them throughout the storage time (F10,110 = 7.04, p < 0.001) (Table S1). The lower loss of AOX observed in UV-irradiated fruits, compared with control, may have resulted from higher extraction of AOX compounds of sweet cherry fruit (Formica-Oliveira et al., 2017). Compared with UV radiation treatments, CS-coating treatment had better inhibitory efficiency for control of AOX loss throughout storage time. This finding is in line with the observed AA loss inhibition in treatments including UV radiation or/ and CS coating treatments as previously discussed. The maintenance of AOX capacity in CS-coated fruits may be related to the modification of the internal atmosphere in the fruits coated by chitosan, leading to reduction of the gas exchange like oxygen and delay in antioxidant degradation process (Silva et al., 2018). Similar phenomena of AOX loss reduction due to UV treatment have been earlier reported by Ou et al. (2016), Formica-Oliveira et al. (2017), Santin et al. (2018) respectively in pineapple, carrot, and peach. Our results are also in tune with those reported by Adiletta et al. (2018) who reported that AOX retention in loquat fruit was significantly enhanced by the application of CS coating. Although the better AOX retention was achieved by the application of UV-C, compared with UV-B, no significant (P < 0.05) differences were noted when the UV lights (UV-B or UV-C) were combined with the CS treatment. On the contrary, Formica-Oliveira et al. (2017) reported a

3.9. Sensory analysis A sensory test approach was used to evaluate the effect of UV lights radiation and CS coating on the sweet cherry fruit during storage time. Some important properties of sweet cherry fruit including taste, odor, color, and general acceptance were characterized using a quantitative descriptive analysis. The taste of fruits was significantly affected by storage time, where the control fruit exhibited unfavorable value (1.72) at the end of storage (Table 3). However, we found a slight decrease in UV or/and CS treatments and a significant difference was found among the treatments (F10,22 = 18.82, p < 0.001) (Tables S1 and 3). Such decreases in taste are most likely due to a decrease in the acid content because sweetness and sourness in sweet cherry fruits were strongly affected by soluble sugar and organic acid composition (Petriccione et al., 2015). Although no significant differences (P < 0.05) were shown for taste among single treatments (UV-B, UV-C, and CS), UV-C in combination with CS (CS + UV-B) exhibited more preferred taste values, compared with UV-B (CS + UV-B) (Table 3). Compared with control, CS + UVC and CS + UV-B + UV-C treatment could maintain the best taste values during storage. Smell is conjugation of sugars, acids, and aromatic materials within the fruit that has been considered as the most sensory attributes of fruits (Zhang et al., 2008). At the end of 28 days of storage, the reduction in smell was more pronounced in control samples while UV or/and CS 6

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treated samples retained higher values of smell (Table 3). Such a decrease may be attributed to the unfavorable relation between TSS and TA or low amounts of aromatic compounds (Petriccione et al., 2015). The highest aroma was recorded in case of CS + UV-B + UV-C samples (4.1) at the end of the storage period. The fruit color is one of the most sensory attributes because it shows the overall quality of fruit and affects consumer attention (Abdipour et al., 2019; Pan and Zu, 2012). Compared with control samples, UV or/ and CS treatments could better maintain the initial fruit color by decreasing the darkening process and improving TAC content (Table 3). Latter data is also in accordance with those found by Zhao et al. (2019). In this study, CS + UV-B + UV-C treatment with a 200 % advantage over the control was recognized as the best treatment.

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4. Conclusion In conclusion, the experiment conducted here indicated that the application of chitosan combined with UV radiation inhibited fruit ripening and maintained its quality. These treatments could retard weight loss, maintain fruit firmness, delay changes in ascorbic acid, titratable acidity, anthocyanin, total antioxidant, and total phenol content and improved sensory quality in sweet cherry fruit. In general, a combination of CS with both UV lights (CS + UV-B + UV-C) was recorded as the optimal values for quality attributes. Thus, CS + UVB + UV-C treatment could be a promising strategy to improve the quality of sweet cherry fruit during storage time and can provide a particular perspective for further biological analysis. Declaration of Competing Interest The authors declare that they have no conflicts of interest regarding the publication of this paper. Ethical standards The experiments were performed according to the current laws of the Islamic Republic of Iran. Acknowledgments The writers thank Mr. Ehsan Jamshidi and Dr. Foroud Bagheri for their cooperation in conducting some tests in the present study, and Dr. Ali Kazemi for editing the manuscript's grammar. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.scienta.2020.109197. References Abdipour, M., Hosseinifarahi, M., Naseri, N., 2019. Combination method of UV-B and UVC prevents post-harvest decay and improves organoleptic quality of peach fruit. Sci. Hortic. 256, 108564. Adiletta, G., Pasquariello, M., Zampella, L., Mastrobuoni, F., Scortichini, M., Petriccione, M., 2018. Chitosan coating: a postharvest treatment to delay oxidative stress in loquat fruits during cold storage. Agronomy 8, 54. Aglar, E., Ozturk, B., Guler, S.K., Karakaya, O., Uzun, S., Saracoglu, O., 2017. Effect of modified atmosphere packaging and ‘Parka’treatments on fruit quality characteristics of sweet cherry fruits (Prunus avium L. ‘0900 Ziraat’) during cold storage and shelf life. Sci. Hortic. 222, 162–168. AOAC, 2005. AOAC Official Methods Program Manual. Official Method 2005.02. 17th edn. AOAC International, Washington, DC. www.aoac.org/vmeth/omamanual/ omamanual.htm. Araque, L.C.O., Rodoni, L.M., Darré, M., Ortiz, C.M., Civello, P.M., Vicente, A.R., 2018. Cyclic low dose UV-C treatments retain strawberry fruit quality more effectively than conventional pre-storage single high fluence applications. LWT 92, 304–311. Atkinson, R.G., Sutherland, P.W., Johnston, S.L., Gunaseelan, K., Hallett, I.C., Mitra, D., Brummell, D.A., Schröder, R., Johnston, J.W., Schaffer, R.J., 2012. Down-regulation of POLYGALACTURONASE1 alters firmness, tensile strength and water loss in apple

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