Introduction

Strawberry is believed to be originated from Northeast, Europe and North America but now cultivated all over the world in hilly tropics and temperate regions. It is not only relished for its desirable flavour and taste but also for being rich in vitamin C and E, phenolics, anthocyanins and β-carotene (Velde et al. 2013; Kårlund et al. 2014). Being an extremely perishable commodity, it possesses short shelf life under ambient conditions which is mainly due to textural softening, moisture loss and fungal decay (Goulas and Manganaris 2011). High respiration rate of strawberries generates water and heat which further accelerates its moisture loss (Vargas et al. 2006). Storage of strawberries under low temperature conditions, i.e. 4–5°C and >90% relative humidity, lowers respiration rate and extends its market life for as long as 10 days (Campaniello et al. 2008; Mishra and Kar 2014). It is also damaged by microbial and fungal infection and mechanical injury which results in deterioration of fruit quality and marketability (Vu et al. 2011). This generally results in 20–40% loss at postharvest level (Anwar 2016). Thus, proper postharvest management is imperative to overcome extensive losses in strawberries.

Several storage methods have been established and designed to enhance storage life of fresh horticultural commodities and expand market access. Controlled atmosphere storage, modified atmosphere packaging, refrigeration and application of fungicide and preservatives are among commonly used techniques. Some of these techniques have been shown to negatively impact fruit quality of strawberries (Holcroft and Kader 1999; Sallato et al. 2007). On the other hand, improper use of fungicide to reduce postharvest disease may negatively influence human health (Gullino and Kuijpers 1994). So, substitute technologies with ability to reduce moisture loss and fungal decay are required to maintain fruit quality during storage to distant markets.

Edible coatings make a biofilm on fruit surface and hinder gas and moisture movement, reduce microbial growth and thus enhance postharvest life of commodity (Rojas-Graü et al. 2010; Zhang et al. 2019). As safer choice, these coatings are also biodegradable, eco-friendly and non-toxic (Sánchez-González et al. 2011). Chitosan is a natural polysaccharide which consists of linear high-molecular weight polymer made of β-l, 4 linked glucosamine (GlcN) along with residues of N-acetylated GlcN (Shahidi et al. 1999). Being an anti-pathogenic but edible coating, chitosan has been implicated in developing resistance against pathogens and retain postharvest quality attributes in strawberries (Wang and Gao 2013; Zhang et al. 2014; Petriccione et al. 2015; Trevino-Garza et al. 2015; Perdones et al. 2016; Petriccione et al. 2017). Keeping in view the diversity in commercial cultivars and variation in supply chain systems of different areas, a concerted effort is needed to optimize and introduce chitosan-based coating for improving market life of strawberries. Therefore, with an objective to increase postharvest life of strawberries, effect of chitosan coatings on fruit quality of strawberries was evaluated during their cold storage at 5°C. In a recent study where efficacy of 2% chitosan, sodium alginate and Aloe vera gel was tested on refrigerated strawberries cv. Chandler, edible coating of Aloe vera gel has been shown to perform better than other edible coatings (Qamar et al. 2018). In this study, effect of chitosan on fruit decay and storage life of strawberries has been tested in relatively lower dose range (0.5, 1 and 1.5%) with an objective to investigate best concentrations of chitosan which would extend storage life of strawberries without compromising the edible and nutritional quality of strawberries cv. Chandler.

Materials and Methods

Strawberry fruits of variety Chandler (Fragaria × ananassa Duch.) were harvested from a commercial farm (31°31'13.4"N 74°11'36.0"E) near Sharaqpur, Sheikhupura district, Punjab, Pakistan. Runners of strawberry cv. Chandler had been sourced from a commercial nursery in Matta, Swat district, Khyber Pakhtunkhwa, Pakistan and transplanted on 18-inch high ridges mulched with black polythene. Strawberry production followed standard cultural practices including drip irrigation, mineral nutrition, weed management and insect/pest and disease control. This field had been under strawberry cultivation followed by bottle gourd (Lagenaria siceraria) or zucchini (Cucurbita pepo) production for the last five years.

Healthy and uniform-sized fruits weighing 20–25 g with ~75% red surface colour and free from visual signs of disease incidence, insect damage or mechanical injury were selected and immediately coated with chitosan. Chitosan coating solution was prepared as earlier described by Vargas et al. (2006). Briefly, 1% glacial acetic acid solution (v/v) was prepared and heated at 40°C before dissolving required amount of chitosan (0.5, 1 and 1.5%; w/v) under continues stirring. Wettability of solution was improved by adding 0.1% Tween-80 (v/v). After submerging fruits in solutions with or without chitosan (control) for 15 sec, fruits were taken out and air-dried under shade for 60 min. Fruits were gently packed in 500 g plastic box and transported under cool condition (13±2°C) to storage facility. At destination, fruits were stored at 5°C and 95% relative humidity for maximum period of 14 days. To determine change in postharvest quality of treated and untreated fruits, five boxes (one box per replication) of each treatment were analysed for physical and biochemical attributes before storage and then every alternate day after storage. Before every analysis, cold stored fruits were first taken out of storage and kept under ambient conditions for 30 min.

At every sampling time, percentage of marketable fruits was calculated by counting number of healthy fruits (without any visual sign of tissue softening or disease infection) in each box. Fruits were visually scored for fungal decay according to the five-point scale used by Babalar et al. (2007) and presented as fungal decay index. Scoring method was based on the percentage of surface area showing signs of fungal decay where; 1 = no decay on fruit surface, 2 = <5% of fruit surface decayed, 3 = 5–20% of fruit surface decayed, 4 = 20–50% of fruit surface decayed, and 5 = >50% of fruit surface decayed (Babalar et al., 2007). Electrolyte leakage was measured as earlier described by Huan et al. (2016). Fresh fruit weight was calculated by randomly selecting ten fruits per replication whereas fruit dry matter content, as percentage of fresh pulp weight, was calculated by drying 70 g of fresh tissue at 70°C until constant tissue weight was attained (Kamperidou and Vasilakakis 2006). For biochemical analyses, homogenous pulp of strawberry fruits was prepared and centrifuged at 5,000 rpm for 15 min at 4°C. The pH was

Fig. 1: Changes in percentage of marketable fruits, disease incidence and tissue integrity (electrolyte leakage) of strawberry fruit cv. Chandler coated with chitosan and stored at 5°C. Markers in scatter plots represent average values (control – ●; 0.5% chitosan – ■; 1.0% chitosan – ◆; 1.5% chitosan – ▲) and lines (only in right-side figure) indicate second order polynomial trendline for each treatment (control,  ; 0.5% chitosan, 1.0% chitosan, ; 1.5% chitosan, ). Error bars represent ±SD (n = 5, 30 fruits per replication)

determined with pre-calibrated pH/Temp meter (Milwaukee, MW 102, Romania) whereas total soluble solids (TSS, %) in supernatant were determined at 20°C with refractometer (ATAGO, RS-5000, Atago, Japan). Total titratable acidity (TTA) was determined by titrimetric method (Jouquand et al. 2008) where supernatant was titrated against 0.1 N NaOH to pH 8.1 end-point. Ascorbic acid was determined by titration with 2,6-dichlorophenolindophenol (Sogvar et al. 2016). Briefly, 5 mL of the filtered aliquot from homogenized solution of supernatant juice portion and 0.4% oxalic acid (1/10, v/v) was titrated against freshly prepared 2,6-dichlorophenol indophenol dye until light pink colour end-point was retained for 15 sec. Ascorbic acid content in fruit juice (mg 100 g^-1 fresh weight) was measured using different concentrations of ascorbic acid for standard curve. Sugars in centrifuged supernatant were determined as reducing sugars, non-reducing sugars and total sugars by copper titration method (Khan et al. 2009) and were expressed as percentage. For sensory analysis, strawberry fruits were divided into four pieces using sharp knife and placed in unmarked clean plates. Samples were placed in randomized sequence for organoleptic evaluation by a panel of 15 persons. Each sample was evaluated for external appearance, flavour, texture and aroma using a nine-point hedonic scale (1 = dislike extremely, 5 = neither like nor dislike, 9 = like extremely) whereas sweetness and sourness of strawberries were scored according to five-point just-right scale (1 = not sweet/sour enough, 3 = just right, 5 = too sweet/sour) (Jouquand et al. 2008; Resende et al. 2008; Schwieterman et al. 2014).

Storage and analyses were conducted under Completely Randomized Design (CRD) with five replications (30 fruits per replication) per treatment. Analysis of Variance (ANOVA) technique was employed to test significance among treatments. Treatment means were further analysed with Duncan’s multiple range test with significance level at 5%. Polynomial trendlines were used to describe general pattern of change in physical or biochemical parameter. All data analyses were carried out with analytical software package ‘Statistix 8.1’.

Results

Effect of chitosan coating on marketability of strawberries is presented in Fig. 1. Control fruits started exhibiting visual quality defects after four days in cold storage and 10% strawberries lost the marketable share in control category. This loss remained consistently persistent until 12 days of storage when 87% strawberries were found marketable. Overall, chitosan-coated strawberries maintained better quality and remained >92% marketable until 12 days of storage. Percentage of marketable fruit declined with increase in chitosan concentration. Edible coating of 0.5% chitosan was more effective in preserving visual quality of fruits compared to 1 and 1.5% chitosan coatings. Strawberry fruits were also observed for visual signs of fungal infection (Fig. 1). Control fruits could be seen with signs of mycelial growth after 8 days of storage whereas chitosan-coated strawberries remained visually fungus-free for 2 more days and started showing signs of fungal infection after 12 days of storage. Though, slightly different but all concentrations of chitosan were statistically equal in effectively resisting fungal spread and extending storage life of strawberries cv. Chandler. Structural integrity of fruit tissues was measured as electrolyte leakage percentage (Fig. 1). Electric conductivity test revealed that electrolyte leakage from control fruit gradually increased after 6 days until termination of study whereas chitosan-coated fruits exhibited relatively stable electrolyte leakage percentage. Since, strawberry fruits showed steep decline in marketability after 12 days, so further study of fruit quality parameter was limited to only first 12 days.

Change in fresh and dry fruit weight of cold stored strawberries was also recorded. Though, fresh weight of both control and chitosan-coated fruits declined gradually but chitosan-coated fruits retained slightly better fruit weight during later period of storage (Fig. 2). Decline in fresh weight in both coated and control fruit categories was around 25% of initial fresh weight during first week of storage whereas, in second week, control fruits showed further 5% decline in fresh weight whereas chitosan-coated strawberries stayed fresh without further loss in fresh weight. Strawberries coated with 0.5% chitosan exhibited relatively better fresh weight compared to fruits coated with higher concentrations of chitosan. Strawberries coated with 0.5 and 1% chitosan also exhibited consistent decline in dry weight (Fig. 2).

Control fruits did not exhibit any change in pH (~3.2) during storage whereas chitosan-coated fruits, regardless of chitosan concentration, also showed consistently similar but relatively higher levels of pH (~3.4) during storage (Fig. 2). Total soluble solids in control fruits did not change much and remained around 15% during first 8 days of storage after which TSS level declined sharply to 11.4% and then 9.5% on 10^th and 12^th day, respectively (Fig. 2). In chitosan-coated fruits, TSS contents slowly but gradually declined below TSS level in control fruits during first 8 days in storage but, in contrast to further drop in control fruits, TSS levels remained unchanged during next four days. Though, TTA contents of both control and chitosan-coated fruits declined during storage but decline in chitosan-coated fruits was steeper than decline in control fruits (Fig. 2). Overall, sugar:acid ratio increased with increase in chitosan concentration in fruit coating (Fig. 2).

Ascorbic acid level in pre-treated strawberry fruits was 81.59 mg/100 g FW before storage (Fig. 3). Un-coated fruits (control) did not exhibit any change in ascorbic acid contents until 6^th day in storage and after which ascorbic acid content gradually dropped to 36.48 mg/100 g FW on 12^th day in storage. Chitosan-coated fruits also exhibited an early decline in ascorbic acid and the decline was noticeable even on 2^nd day in storage which was much earlier than decline observed in control fruits. Magnitude of this trend was dependent on percentage of chitosan coating. Control fruits did not exhibit significant change in reducing sugars whereas chitosan-coated fruits exhibited slight increase in first half and then decreased back to initial levels in second half of storage (Fig. 3). Magnitude of increase was inversely proportional to concentration of chitosan in fruit coating as strawberry fruits

Fig. 3: Changes in ascorbic acid and sugars (reducing, non-reducing and total constituents) in strawberry fruit cv. Chandler coated with chitosan and stored at 5°C. Markers in scatter plot represent average values (control – ●; 0.5% chitosan – ■; 1.0% chitosan – ◆; 1.5% chitosan – ▲) and lines indicate second order polynomial trendline for each treatment (control, ; 0.5% chitosan, ; 1.0% chitosan, ; 1.5% chitosan, ). Error bars represent ±SD (n = 5, 30 fruits per replication)

Fig. 2: Changes in fresh fruit weight, dry weight percentage, pH, total soluble solids (TSS), total titratable acidity as percent citric acid and TSS/TTA ratio of strawberry fruit cv. Chandler coated with chitosan and stored at 5°C. Markers in scatter plot represent average values (control – ●; 0.5% chitosan – ■; 1.0% chitosan – ◆; 1.5% chitosan – ▲) and lines indicate second order polynomial trendline for each treatment (control, ; 0.5% chitosan, ; 1.0% chitosan, ; 1.5% chitosan, ). Error bars represent ±SD (n = 5, 30 fruits per replication)

coated with 0.5% chitosan exhibited highest increase followed by fruits coated with 1% and then 1.5% chitosan. Non-reducing sugar percentage in control fruits reduced during storage whereas its trend in chitosan-coated fruits was opposite to that in reducing sugars (Fig. 3). During first half of storage, reduction in non-reducing sugars was least in 0.5% chitosan-coated fruits whereas the trend was reverse in second half of storage. Pattern of change in total sugars seems to be more influenced by non-reducing sugars (Fig. 3). Control fruits exhibited 2.6% decline in total sugars after 12 days in storage.

Overall, coating of fruits with chitosan enhanced consumer acceptance for strawberries during long-term cold storage (Fig. 4). After six days of storage, control fruits started losing high scores for appearance, flavour, texture and aroma. After 12 days in storage, control fruit category received least acceptance for appearance (5.3 score), flavour (4.0 score), texture (5.0 score) and aroma (4.7 score). Chitosan-coated fruits maintained these sensory descriptors at negligible loss of score until 10 days in storage. Changes in appearance, flavour and aroma of chitosan-coated fruits were not affected by the concentration of chitosan in coating solution. Overall, fruits coated with 0.5% chitosan were found better in maintaining fruit texture (8.0 score) than other coatings. In contrast, control fruits gained sweetness and lost sourness score during storage whereas chitosan-coated fruits, especially treated with 0.5% chitosan, maintained sweetness score during the study period.

Fig. 4: Effect of chitosan coating on sensory attribute of strawberries cv. Chandler during cold storage at 5°C. Clockwise axis values represent storage period (0, 2, 4, 6, 8, 10 and 12 days). Values on vertical axis represent average organoleptic score assigned to each treatment (control, ; 0.5% chitosan, ; 1.0% chitosan, ; 1.5% chitosan, ) on a given day. Fruit slices from each treatment were evaluated by fifteen panellists

Discussion

Strawberry is a delicate fruit with very short shelf life. Increase in demand for scrumptious strawberries in consumer-driven markets has invoked researchers to develop technologies that may help to retain its textural delicacies and unique nutritional attributes in diverse value chains. Though, low-temperature storage has been proven successful in slowing down nutritional decline (Kårlund et al. 2014; Barbieri et al. 2015) and is being widely used to increase market life of strawberry but emerging postharvest technologies seem promising in further extending the storage period by preserving quality attributes. In this perspective, chitosan has been found to be an ideal preservative coating material for fresh berries due to its antifungal and film‐forming properties (Han et al. 2005; Rahman et al. 2014). Since, cultivars vary significantly in terms of ripening physiology and postharvest metabolic activities related to nutritional quality (Sturm et al. 2003; Capocasa et al. 2008; Goulas and Manganaris 2011; Kårlund et al. 2014; Mishra and Kar 2014; Nankali et al. 2014), there was a need to optimize concentration of chitosan in coating solution with respect to its effect on the mycelial growth on fruit surface and various physical, biochemical and sensorial attributes of strawberry cv. Chandler. In a recent study, efficacy of 2% chitosan alone or in combination with sodium alginate and Aloe vera gel was tested on refrigerated strawberries cv. Chandler which showed edible coating of Aloe vera gel performing better than 2% chitosan alone (Qamar et al. 2018). So, this study was initiated to determine effect of chitosan in relatively lower dose range (0.5, 1 and 1.5%) and find out best concentrations of chitosan which would extend storage life of strawberries without compromising the edible and nutritional quality of strawberries cv. Chandler.

Chitosan coatings delayed fungal decay and prolonged marketable life of strawberries (Fig. 1). These results support the antifungal properties of chitosan. Han et al. (2004) also reported 33 and 40% decrease in mold growth on strawberries cvs. Driscoll’s and Puget Reliance, respectively when coated with chitosan and stored at 2°C and 88% relative humidity for 14 days. Chito-oligosaccharide, an enzymatically produced chitosan, has not only been shown to significantly inhibit growth of Botrytis cinerea but has also been shown to synergistically enhance antifungal activity of synthetic fungicides even when used in low doses (Rahman et al. 2014). Recently, use of 2% chitosan as an edible coating on strawberries cv. Chandler has been reported to extend storage life of refrigerated strawberries by four more days partly due to inhibition in decay incidence (Qamar et al. 2018). Chitosan coating elicits expression of defence-associated proteins in strawberry (Petriccione et al. 2017). In vitro studies have shown that application of 5 mg/L chitosan upregulates expression of pathogenesis-related proteins and antioxidant genes in tomato which results in inhibition of radial mycelial growth by 54.8% (Chun and Chandrasekaran 2019). Decrease in percentage of electrolyte leakage from chitosan-coated strawberries gives a scientific justification of resistance in these strawberries against fungal infection (Fig. 1). Chitosan-coated fruits remained structurally stable for longer period than control fruits. Increased leakage of cellular electrolyte indicates loss in structural integrity which might have favoured mycelial growth leading to early fungal infection on control fruits whereas film-coating properties of chitosan maintained structural integrity and resisted electrolyte leakage and thereby delayed fungal infection in concentration-dependent manner (Fig. 1). Overall results suggest that application of chitosan in relatively lower concentration i.e. 0.5% is more effective in maintaining membrane integrity and inhibiting fungal decay thereby increasing market life of strawberries.

Strawberries coated with 0.5 and 1% chitosan also exhibited relatively better fresh weight but lower dry weight under long-term cold storage (Fig. 2) which suggests that carbon metabolism in these fruit tissues may be relatively more active to uphold respiration and other cellular activities whereas lower concentration of chitosan may have acted as low-density polymer coating allowing reasonable exchange of water and respiratory gases. Further research is required to explore and validate such chitosan-mediated regulations. Total soluble solids, total titratable acids and sugar:acid ratio (TSS/TTA) are the basic fruit quality parameters which are often employed to infer metabolic changes in fruit tissues and to indirectly measure consumer acceptability (Sturm et al. 2003; Rutkowski et al. 2006; Testoni et al. 2006; Testoni and Nuzzi 2006). Fruits coated with 0.5 or 1% chitosan had least TSS (2–3% lower than control) and TSS level slightly increased (1% higher) as concentration of chitosan in edible coating increased from 1 to 1.5%. Overall, chitosan-coated fruits maintained TSS for at least four days more than control fruits (Fig. 2). Moreover, steeper decline in TTA of chitosan-coated fruits compared to control fruits indicates that chitosan may have role in regulation of total titratable acid pools in strawberry fruits cv. Chandler and this effect is independent of the concentration range used in this study. Altogether, the proposed phenomenon may be involved in improving ripening index (sugar:acid ratio) of the chitosan-coated strawberries (Fig. 2). Secondly, concentration range of chitosan in coating solutions seems equally effective in altering these biochemical attributes (Fig. 2).

Ascorbic acid is one of the reactive compounds in fruits (Kårlund et al. 2014). Extent of its progressive loss during storage is positively correlated with storage temperature (Nunes et al. 1998). Chitosan coating reduced ascorbic acid levels in strawberries in percentage-dependent manner. Pattern of ascorbic acid profile in fruits coated with 0.5% chitosan was relatively closer to control fruits whereas higher percentage of chitosan enhanced ascorbic acid loss which resulted in low level of ascorbic acid in chitosan-coated fruits (Fig. 3). Mishra and Kar (2014) also reported decrease in total soluble solids, ascorbic acid and total sugars in Chandler strawberries with the advent of storage at 5°C for 9 days. Aligned with this study, decline in ascorbic acid and titratable acid has also been reported in other cultivars harvested at fully matured stage and stored at ambient temperature (Rahman et al. 2016). Though, chitosan-coated fruit exhibited slight dip in total sugars during mid-period of storage but, overall, total sugar percentage at the start and end of study remained almost same (Fig. 3).

Coating of fruits with chitosan enhanced consumer acceptance for strawberries for longer period (Fig. 4). Change in appearance, flavour and aroma of chitosan-coated fruits were not affected by the concentration of chitosan in coating solution whereas fruits coated with 0.5% chitosan were found better in maintaining fruit texture (8.0 score) than other coatings. Han et al. (2005) evaluated organoleptic changes in cold stored strawberries applied with 1% chitosan-based edible coatings and concluded that chitosan coatings increased consumer acceptance but did not change consumer acceptability for flavour, sweetness or firmness. In another study, chitosan coating has been reported to alter fruit aroma composition without effecting sensorial perception of strawberries (Perdones et al. 2016). These findings suggest that film-formation of chitosan over strawberries was helpful in maintaining organoleptic properties of fruits during storage.

Conclusion

Edible coating of chitosan can be a safer option to inhibit fungal decay and maintain overall fruit quality during cold storage. Pre-storage coating of strawberries with 0.5% chitosan may help maintain fruit physical attributes whereas 1.0% chitosan coating helps strawberries retain biochemical attributes followed by 1.5% chitosan treatment. The study was designed to assess impact of chitosan-based coatings on physical, biochemical and sensorial properties of strawberries mostly reflecting consumer preferences. Comprehensive nutritional profiling of strawberries coated with 0.5% chitosan, concentration optimized in this study, may further help to comprehend its effect on human health. Further biochemical, enzymatic and molecular studies may further delineate chitosan-mediated regulatory mechanisms that inhibit fungal decay and delay deterioration in quality attributes of strawberry fruit cv. Chandler. It would also be intriguing to investigate enhanced capabilities of chitosan when combined with essential oils, natural extracts and hormones.

Acknowledgement

R. Anwar conceived the idea and J. Hassan conducted the research studies. All authors equally contributed in editing, commenting, revising and approving the manuscript without conflict of interest. Research study was partly funded by the Higher Education Commission, Pakistan (Project No. 21-668SRGP) to R. Anwar.

References

Anwar R (2016). Strawberry packaging in plastic punnets: An economical and effective technology to improve food safety and profitability, In: 101 Innovation Catalogue: Technologies for Commercialization 2016, pp:19‒21. Khan IA, ZA Zahir, M Naveed, A Rashid (Eds.). University of Agriculture Faisalabad Press, Faisalabad, Pakistan

Babalar M, M Asghari, A Talaei, A Khosroshahi (2007). Effect of pre- and postharvest salicylic on ethylene production, fungal decay acid treatment and overall quality of selva strawberry fruit. Food Chem 105:449‒453

Barbieri G, E Colonna, Y Rouphael, SD Pascale (2015). Effect of the farming system and postharvest frozen storage on quality attributes of two strawberry cultivars. Fruits 70:351‒360

Campaniello D, A Bevilacqua, M Sinigaglia, MR Corbo (2008). Chitosan: Antimicrobial activity and potential applications for preserving minimally processed strawberries. Food Microbiol 25:992‒1000

Capocasa F, J Scalzo, B Mezzetti, M Battino (2008). Combining quality and antioxidant attributes in the strawberry: The role of genotype. Food Chem 111:872‒878

Chun S-C, M Chandrasekaran (2019). Chitosan and chitosan nanoparticles induced expression of pathogenesis-related proteins genes enhances biotic stress tolerance in tomato. Intl J Biol Macromol 125:948‒954

Goulas V, GA Manganaris (2011). The effect of postharvest ripening on strawberry bioactive composition and antioxidant potential. J Sci Food Agric 91:1907‒1914

Gullino ML, LAM Kuijpers (1994). Social and political implications of managing plant diseases with restricted fungicides in europe. Annu Rev Phytopathol 32:559‒581

Han C, C Lederer, M McDaniel, Y Zhao (2005). Sensory evaluation of fresh strawberries (Fragaria ananassa) coated with chitosan-based edible coatings. J Food Sci 70:S172‒S178

Han C, Y Zhao, SW Leonard, MG Traber (2004). Edible coatings to improve storability and enhance nutritional value of fresh and frozen strawberries (fragaria × ananassa) and raspberries (Rubus ideaus). Postharv Biol Technol 33:67‒78

Holcroft DM, AA Kader (1999). Carbon dioxide–induced changes in color and anthocyanin synthesis of stored strawberry fruit. HortScience 34:1244‒1248

Huan C, L Jiang, X An, M Yu, Y Xu, R Ma, Z Yu (2016). Potential role of reactive oxygen species and antioxidant genes in the regulation of peach fruit development and ripening. Plant Physiol Biochem 104:294‒303

Jouquand C, C Chandler, A Plotto, K Goodner (2008). A sensory and chemical analysis of fresh strawberries over harvest dates and seasons reveals factors that affect eating quality. J Amer Soc Hortic Sci 133:859‒867

Kamperidou I, M Vasilakakis (2006). Effect of propagation material on some quality attributes of strawberry fruit (Fragaria x ananassa, var. Selva). Sci Hortic 107:137‒142

Kårlund A, U Moor, M Sandell, R Karjalainen (2014). The impact of harvesting, storage and processing factors on health-promoting phytochemicals in berries and fruits. Processes 2:596‒624

Khan AS, AU Malik, MA Pervez, BA Saleem, IA Rajwana, T Shaheen, R Anwar (2009). Foliar application of low-biuret urea and fruit canopy position in the tree influence the leaf nitrogen status and physico-chemical characteristics of kinnow mandarin (Citrus reticulata Blanco). Pak J Bot 41:73‒85

Mishra R, A Kar (2014). Effect of storage on the physicochemical and flavour attributes of two cultivars of strawberry cultivated in northern India. Sci World J 2014:794926

Nankali A, F Karami, M Sarseifi (2014). Evaluation of new strawberry cultivars for Iran. Acta Hortic 1049:423‒430

Nunes MCN, JK Brecht, AMMB Morais, SA Sargent, (1998). Controlling temperature and water loss to maintain ascorbic acid levels in strawberries during postharvest handling. J Food Sci 63:1033‒1036

Perdones A, I Escriche, A Chiralt, M Vargas (2016). Effect of chitosan-lemon essential oil coatings on volatile profile of strawberries during storage. Food Chem 197:979‒986

Petriccione M, F Mastrobuoni, MS Pasquariello, L Zampella, E Nobis, G Capriolo, M Scortichini (2015). Effect of chitosan coating on the postharvest quality and antioxidant enzyme system response of strawberry fruit during cold storage. Foods 4:501‒523

Petriccione M, F Mastrobuoni, L Zampella, E Nobis, G Capriolo, M Scortichini (2017). Effect of chitosan treatment on strawberry allergen-related gene expression during ripening stages. J Food Sci Technol 54:1340‒1345

Qamar J, S Ejaz, MA Anjum, A Nawaz, S Hussain, S Ali, S Saleem (2018). Effect of aloe vera gel, chitosan and sodium alginate based edible coatings on postharvest quality of refrigerated strawberry fruits of cv. Chandler. J Hortic Sci Technol 1:8‒16

Rahman MH, LR Shovan, LG Hjeljord, BB Aam, VGH Eijsink, M Sørlie, A Tronsmo (2014). Inhibition of fungal plant pathogens by synergistic action of chito-oligosaccharides and commercially available fungicides. PLoS One 9; Article e93192

Rahman MM, M Moniruzzaman, MR Ahmad, BC Sarker, MK Alam (2016). Maturity stages affect the postharvest quality and shelf-life of fruits of strawberry genotypes growing in subtropical regions. J Saudi Soc Agric Sci 15:28‒37

Resende JTVd, LK Camargo, EJ Argandoña, A Marchese, CK Camargo (2008). Sensory analysis and chemical characterization of strawberry fruits. Hortic Brasileira 26:371‒374

Rojas-Graü MA, R Soliva-Fortuny, O Martín-Belloso (2010). Edible coatings: Past, present and future. Stewart Postharv Rev 6; Article 1

Rutkowski KP, DE Kruczynska, E Zurawicz (2006). Quality and shelf life of strawberry cultivars in poland. Acta Hortic 708:329‒332

Sallato BV, R Torres, JP Zoffoli, BA Latorre (2007). Effect of boscalid on postharvest decay of strawberry caused by Botrytis cinerea and Rhizopus stolonifer. Span J Agric Res 5:67‒78

Sánchez-González L, M Cháfer, M Hernández, A Chiralt, C González-Martínez (2011). Antimicrobial activity of polysaccharide films containing essential oils. Food Cont 22:1302‒1310

Schwieterman ML, TA Colquhoun, EA Jaworski, LM Bartoshuk, JL Gilbert, DM Tieman, AZ Odabasi, HR Moskowitz, KM Folta, HJ Klee, CA Sims, VM Whitaker, DG Clark (2014). Strawberry flavor: Diverse chemical compositions, a seasonal influence, and effects on sensory perception. PLoS One 9; Article e88446

Shahidi F, JKV Arachchi, Y-J Jeon (1999). Food applications of chitin and chitosans. Trends Food Sci Technol 10:37‒51

Sogvar OB, M Koushesh Saba, A Emamifar (2016). Aloe vera and ascorbic acid coatings maintain postharvest quality and reduce microbial load of strawberry fruit. Postharv Biol Technol 114:29‒35

Sturm K, D Koron, F Stampar (2003). The composition of fruit of different strawberry varieties depending on maturity stage. Food Chem 83:417‒422

Testoni A, F Lovati, M Nuzzi (2006). Evaluation of postharvest quality of strawberries in italy. Acta Hortic 708:355‒358

Testoni A, M Nuzzi (2006). Analytical and sensory evaluation of two strawberry cultivars to improve market acceptability. Acta Hortic 708:349‒354

Trevino-Garza MZ, S Garcia, M del Socorro Flores-Gonzalez, K Arevalo-Nino (2015). Edible active coatings based on pectin, pullulan and chitosan increase quality and shelf life of strawberries (Fragaria ananassa). J Food Sci 80:M1823‒1830

Vargas M, A Albors, A Chiralt, C González-Martínez (2006). Quality of cold-stored strawberries as affected by chitosan-oleic acid edible coatings. Posthar Biol Technol 41:164‒171

Velde FVD, AM Tarola, D Guemes, ME Pirovani (2013). Bioactive compounds and antioxidant capacity of camarosa and selva strawberries (Fragaria x ananassa duch.). Foods 2:120‒131

Vu KD, RG Hollingsworth, E Leroux, S Salmieri, M Lacroix (2011). Development of edible bioactive coating based on modified chitosan for increasing the shelf life of strawberries. Food Res Intl 44:198‒203

Wang SY, HY Gao (2013). Effect of chitosan-based edible coating on antioxidants, antioxidant enzyme system, and postharvest fruit quality of strawberries (Fragaria x aranassa Duch.). LWT-Food Sci Technol 52:71‒79

Zhang, H., H. Yin and G. Jin, 2019. Function of nitric oxide in chitosan oligosaccharide-induced resistance to tobacco mosaic virus. Intl J Agric Biol 21:85‒92

Zhang H, L Ge, K Chen, L Zhao, X Zhang (2014). Enhanced biocontrol activity of Rhodotorula mucilaginosa cultured in media containing chitosan against postharvest diseases in strawberries: Possible mechanisms underlying the effect. J Agric Food Chem 62:4214‒4224