The preservation performance of chitosan coating with different molecular weight on strawberry using electrostatic spraying technique

Journal Pre-proof The preservation performance of chitosan coating with different molecular weight on strawberry using electrostatic spraying technique

Yongli Jiang, Li Yu, Yunwen Hu, Zichun Zhu, Chenjun Zhuang, Yanyun Zhao, Yu Zhong PII:

S0141-8130(20)30465-7

DOI:

https://doi.org/10.1016/j.ijbiomac.2020.02.169

Reference:

BIOMAC 14786

To appear in:

International Journal of Biological Macromolecules

Received date:

15 January 2020

Revised date:

14 February 2020

Accepted date:

15 February 2020

Please cite this article as: Y. Jiang, L. Yu, Y. Hu, et al., The preservation performance of chitosan coating with different molecular weight on strawberry using electrostatic spraying technique, International Journal of Biological Macromolecules(2018), https://doi.org/ 10.1016/j.ijbiomac.2020.02.169

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© 2018 Published by Elsevier.

Journal Pre-proof The preservation performance of chitosan coating with different molecular weight on strawberry using electrostatic spraying technique

Yongli Jiang a, Li Yu a, Yunwen Hu a, Zichun Zhu a, Chenjun Zhuang a, Yanyun Zhao b, Yu Zhong a, c* a

Bor Luh Food Safety Center, Department of Food Science & Technology, Shanghai

Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China Department of Food Science and Technology, 100 Wiegand Hall, Oregon State

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b

Shanghai Food Safety and Engineering Technology Research Center, 800

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c

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University, Corvallis, OR, 97331, USA

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Dongchuan Road, Shanghai 200240, China

Dr. Yu Zhong

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*Corresponding author:

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Shanghai Jiao Tong University Shanghai, 200240, China

E-mail: [email protected]

Journal Pre-proof Abstract In this study, chitosan (CH) coating with different number-average molecular weight (MW, ca. 5, 19 and 61 kDa) was electrostatic sprayed on strawberry. The effects of MW on strawberry quality changes were evaluated during 15 days of storage at 4 °C. The qualities of strawberry included mold growth, weight loss, firmness, total soluble solids (TSS), pH, flavonoids content, superoxide dismutase (SOD) activity and malondialdehyde (MDA) content. Results showed that CH coating could significantly

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maintain the strawberry qualities during storage compared to uncoated treatment. CH

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coating with 61 kDa were more effective in retarding the increases of pH and MDA,

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and could better maintain flavonoids content. However, MW had no significant

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impact on mold growth, weight loss, firmness, SOD activity of coated strawberry. According to evaluation criteria, CH coating with 61 kDa had better performance on

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strawberry preservation with the highest synthetic value (6.93), and could be used to

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maintain quality, and prolong the shelf life of strawberry during cold storage.

storage

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Key words: Chitosan coating, Molecular weight, Electrostatic spraying, Strawberry

Journal Pre-proof 1.

Introduction Edible coatings have attracted increasing attentions due to their environment

friendly and non-toxicity [1-2]. Especially, edible coatings have been widely applied on fresh fruits such as strawberry to retard spoilage and maintain quality by creating a semi-permeable barrier to gases, water vapor, and volatile compounds [3-4]. Many researches have been carried out on application of various edible materials which mainly included polysaccharides, proteins and lipids [1,5-6]. Among these coating

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materials, chitosan (CH) is one of the most commonly used materials due to its

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biocompatibility, biodegradability and bioactivity properties [7-9].

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As a natural macromolecule polysaccharide, CH is the partially deacetylated

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product of chitin possessing different molecular weight (MW) and deacetylation degree (DD) [10-11]. Many literatures have demonstrated that the properties of the

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CH films/coatings were significantly affected by the above intrinsic characteristics.

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Zhong et al. [10] found that conductivity, viscosity, and contact angle of CH film-forming solution were raised with increase of MW. It was reported that the lower

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the MW of CH the higher the color differences and film solubility [12]. Jongsri et al. [13] found that CH coating with high MW (360 kDa) could effectively delay ripening and maintain postharvest quality of mango compared to the low MW CH (270 and 40 kDa). Ruzaina et al. [14] reported that CH coating with 85% DD and 300 kDa MW had better mechanical properties and water barrier, was more effective in maintaining cherry tomato quality than CH coating with 95% DD and 100 kDa MW. Except for the intrinsic characteristics of CH, the coating methods also significantly impact the performances of CH coatings [15]. Nowadays, there has been an increased interest in using electrostatic spraying (ES) for the application of coatings in food industry due to the advantages of material saving, high efficiency and

Journal Pre-proof continuous industrial operation [15-16]. Gómez-Mascaraque et al. [16] reported that CH with the lowest MW (25 kDa) allowed the highest electrosprayable concentration (5% w/v) and thus the highest productivity. In our previous study [4], ES as an efficient technique has been applied on for strawberry preservation with CH coating. And we also investigated the effect of CH coating with different DD by ES system on the quality of strawberry found that CH with 88.1% DD had better preservation

been seldom studied, especially in fresh strawberry.

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performance. However, the preservation effect of CH coating with different MW has

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Therefore, the objective of this study was to evaluate the effect of CH coating

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with different MW (5, 19, 61 kDa) on strawberry preservation by ES system. The

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qualities of fresh strawberries uncoated or coated with different MW CH were compared in term of mold growth, weight loss, firmness, total soluble solids (TSS),

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pH, flavonoids content, superoxide dismutase (SOD) activity and malondialdehyde

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(MDA) content during 15 days of storage period at 4 °C.

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2. Materials and Methods 2.1. Materials

Fresh strawberries were purchased from Auchan market (Dongchuang Road, Shanghai, China) at the same day with the coating experiments. CH, BR, at 81.0% DD with different MW (5, 19, 61 kDa) were purchased from Shandong AK biotech Ltd (Shandong, China). All chemicals and reagents were of analytical grade and obtained from Sinopharm Chemical Reagent (Shanghai, China). 2.2. CH coating solution preparation CH coating solution was prepared as described by Jiang et al. [4]. Briefly, CH was dissolved in acetic acid solution (0.5%, w/w) to prepare a 1.2% (w/w) CH

Journal Pre-proof solution. Then 30% glycerol (w/w CH) as plasticizer and 5% tween 80 (w/w CH) as surfactant were added into the solution, followed by stirring for 1 h. Then, the solution was adjusted to pH 4.5 using glacial acetic acid and then vacuumized (10 KPa) for 1 h to remove air bubbles. 2.3. Electrostatic spraying (ES) coating and strawberry storing Fruits were randomly divided into three groups (CH coatings with three different

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MW). Approximately 3 kg of strawberries for each treatment group were selected

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with uniform size, shape, color without visible damage for further study. The operating parameters were described in a previous paper [15] to obtain a

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short-round-spray pattern for uniform surface coverage. CH solution was sprayed

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onto the surfaces of strawberries using an electrostatic sprayer (SC-ET, Electrostatic

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Spraying Systems Inc, Georgia, USA) with nozzle diameter of 3 mm for 1 min. Strawberries were placed on a metallic rack and positioned in a square shape with

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distance of 2 cm between each other. The spray gun was perpendicularly fixed ca. 50

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cm over the rack with spraying speed of 3.8 L/h. The treated samples were dried at room temperature and 50% relative humidity for 5 h. Then, each group was transferred to a PET packing box (20×15×6.5 cm) for storage at 4 °C, 85% relative humidity for 15 days. Qualities of strawberry were measured at 0, 3, 5, 7, 9, 11, 13, 15 days, respectively. 2.4. Weight loss and firmness analysis The same samples were weighed at the different sampling dates. And weight loss was calculated as percentage loss based on initial weight recorded at day 0. Firmness was determined on strawberry using a texture analyzer (TA. XTPLUS, Stable MicroSystem, UK) with a P/2 probe (diameter of 2 mm) [4].

Journal Pre-proof 2.5. Mold analysis The mold counts experiment was performed as described by Jesmin et al. [5]. Briefly, fruit samples were mashed on aseptic console and the sample (2 g) was dissociated in saline water (50 mL), followed by shaking at 35 °C with 120 r/min for 15 min. Then, supernatant (1 mL) was added in saline water (9 mL), and 10 μL of mixture solution was spread in PDA plates. The plates were incubated for 48 h in

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37 °C and colony forming units (CFU) were counted.

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2.6. pH and total soluble solids (TSS)

Three strawberries from each group were homogenized in a mortar and filtered

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[17]. Then filtrates were used for measurements of pH and TSS with a pH meter

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(Mettler-Toledo MP 220, Schwerzenbach, Switzerland) and a digital refractometer

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2.7. Flavonoids content

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(RHB-32 model Refractometer, JDSU, CA, USA) respectively.

The flavonoid content was measured as described by He et al. [18]. Briefly, fruit

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sample was homogenized with 95% ethyl alcohol (1:8, w/v). The mixture was treated by ultrasonic extraction (S-10H, ZEALWAY, Xia, China) for 45 min at 360 W and filtered to obtain strawberry extract. Then, one-milliliter extract and 0.3 mL of 5% sodium nitrite were added in 4 mL of 30% ethyl alcohol. After 5 min, 0.3 mL of 10% aluminum nitrate was added and allowed to stand for 6 min. Subsequently, 2 mL of 4% sodium hydroxide was added and allowed to stand for 10 min. Finally, the absorbance was measured at 510 nm with a microplate reader (Type 1510, Thermo Fisher Scientific, USA). Comparisons were made with standards of known rutin concentrations. 2.8. Superoxide dismutase (SOD) activity

Journal Pre-proof SOD activity was determined as described by Obianom et al. [19]. Briefly, fruit sample was homogenized with 0.1 M potassium phosphate buffer (1:9, w/v; pH 7.2), followed by centrifuging (Z-326 K, Hermle, Wehingen, GmbH) for 10 min at 5000 ×g. The supernatant was used for measurement of SOD activity using a commercial SOD kit (Jiancheng Bioengineering Institute, Nanjing, China) as described by the suggested procedures.

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2.9. Malondialdehyde (MDA) content

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MDA content was determined as described by Pasquariello et al. [20]. Briefly, fruit sample was homogenized with 10% trichloroacetic acid (1:5, w/v), followed by

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centrifuging for 20 min at 12000 ×g. The supernatant was added in 0.67%

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thiobarbituric acid (1:1, v/v) and heated at 100 °C for 20 min with a water bath

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(THM-2865, Thermo Fisher Scientific, UN). After quickly cooling, the mixture was centrifuged at 6000 ×g for 10 min. Finally, the absorbance of supernatant at 450, 532

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and 600 nm were measured respectively. The MDA content was calculated as follows:

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𝑀𝐷𝐴 = 6.45 (𝐴532 − 𝐴600 ) − 0.56 𝐴450

where A450, A532, and A600 are the absorbance of supernatant at 450, 532 and 600 nm respectively. 2.10.

Performance evaluation criteria

Fuzzy comprehensive evaluation was used to investigate the comprehensive effect of CH coating with different MW by ES on strawberry preservation. A synthetic evaluation index (S) was calculated as the cumulative weighted value of all the parameters as follows [11]: 𝑠 = ∑7𝑖 𝜆𝑖 𝑀𝑖𝑗 where Mi is the membership degree of a parameter, and λi is the weighted assignment

Journal Pre-proof of the parameter. The parameters with positive effect included firmness, TSS, flavonoids content and SOD activity. Other parameters including mold counts, weight loss, pH, MDA content were identified with negative effect. And the subset of λi corresponding to the listed parameter was {0.10, 0.10, 0.10, 0.10, 0.20, 0.20, 0.10, 0.10}. The membership degree was calculated as follows [11]: 𝑀=𝑋

𝑋𝑖 −𝑋𝑚𝑖𝑛

positive effect

𝑀 = 1−𝑋

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𝑚𝑎𝑥 −𝑋𝑚𝑖𝑛

𝑋𝑖 −𝑋𝑚𝑖𝑛

negative effect

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𝑚𝑎𝑥 −𝑋𝑚𝑖𝑛

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where Xi is the value of the parameter; Xmax is the maximum value of the parameter; Xmin is the minimum value of the parameter.

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There were two important factors (i.e. storage time and MW) played significant

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effects on qualities of strawberry. Thus, the performance evaluation should by divided into two respects. As for the impact of time, Xmax was taken as the maximum value

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during the storage period for certain group, Xmin was taken as the minimum value

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during the storage period for certain group, and S value was recorded as S1. As for the impact of MW, Xmax was taken as the maximum value within different group at certain time, Xmin was taken as the minimum value within different group at certain time, and S value was recorded as S2 [4]. 2.11.

Statistical analysis

Experimental data were analyzed by ANOVA and significant differences at P < 0.05 were determined using Duncan’ s multiple range tests in the SPSS 21.0 statistical data analytical software (IBM, NY, NY, USA). In order to enhance the identification of similarities or differences among all treatments, all data were imported into Simca 14.1 (Umea, Sweden) for multivariate statistical analysis.

Journal Pre-proof 3. Results and discussion 3.1. Mold growth of strawberry Changes of the mold counts of strawberry during storage were presented in Fig. 1A. The mold counts of samples sustainably increased with time, and the trend was anticipated in good agreement with our previous study [4]. The samples coated by CH presented lower values for log (CFU/g) of molds, indicating that CH coating had antibacterial effects when applied in strawberry fruits. According to Dotto et al. [21],

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these antibacterial effects were associated with the cationic nature of CH and the

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composition of cell membrane of the microorganism, affecting the integrity and

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permeability of bacteria. In addition, CH could cause the decrease in respiratory

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activity of the microorganism and inhibit bacterial growth [22]. As shown in Fig. 1A, the CH coating with 19 kDa MW displayed stronger inhibitory of mold growth within

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the initial 5 days. A count of 106 CFU/g for yeast, mold or total bacteria is considered

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to be the limit of acceptance for fruit-based products [22]. As shown in Fig.1A, after 11 days, mold counts of uncoated samples reached 6.65 log CFU/g, and thus the

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quality parameters of uncoated samples were no longer measured after 11 days. The mold counts of coated samples were less than 6.17 log CFU/g within 13 days. After 15 days, the mold counts increased to 6.31-6.48 log CFU/g for treated samples, but no significant (P > 0.05) differences were observed among the samples. Romanazzi et al. [23] also reported that commercial CH could effectively reduce gray mold, Rhizopus rot and blue mold of strawberries stored 7 days at 0±1 °C and then exposed to 3 days shelf-life. Our previous study indicated that CH film with lower MW exhibited a higher antibacterial activity [10], but in this study, MW had no significant (P > 0.05) impact on the antibacterial effect for strawberry samples. The reason might be that the antibacterial effect of CH coating was also influenced by many other factors such as

Journal Pre-proof the homogeneity, roughness and the degree of hydrophilicity of the coating, accessibility of amine groups in CH, and acetic acid dosage [24-25]. 3.2. Weight loss and firmness of strawberry The weight loss of strawberry is an important index that reflects respiration rate and moisture evaporation between the fruit tissue and surrounding air. As shown in Fig. 1B, CH coatings on strawberry could significantly retard the weight loss

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compared to the uncoated samples. Moreover, weight loss of all coating samples

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showed a linear increased trend during storage. Strawberry fruits are highly susceptible to a rapid loss of water due to the extremely thin skins of the fruits [2,26].

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CH coating on strawberry surface acted as a semipermeable barrier against gas and

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water, and thus reduced respiration and water loss and counteracted the dehydration

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and shrinkage of the fruit [13]. The weight loss values of strawberries coated by CH with 5, 19 and 61 kDa were 5.26%, 5.66% and 5.28%, respectively, after 15 days of

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loss [4].

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storage. However, our previous study found that DD had negative impact on weight

Firmness is a visible change that occurs during fruit maturation, storage and distribution as a consequence of metabolic changes and water loss [3]. Generally, firmness of all samples decreased during storage (Fig. 3C), mainly due to the degradation of pectin and other cell wall components [27]. In addition, a consistent increase in weight loss led to fruit wilting as well [13]. At day 11, the loss of firmness in uncoated strawberry was 49.47%, while the values for strawberry coated by CH with 5, 19 and 61 MW were 28.47%, 27.81% and 17.97%, respectively (Fig. 1C). The data demonstrated that CH coating significantly inhibited the softening of strawberry, which was mainly due to the oxygen and water vapor barrier abilities of CH that retarded the metabolic activity and water loss [18]. Furthermore, CH coating itself had

Journal Pre-proof good mechanical strength on the surface of strawberry and could slow down the texture degradation [26]. As shown in Fig. 1C, no obvious (P > 0.05) differences of firmness were observed among coated strawberries with different MW at the end of storage. 3.3. Total soluble solids (TSS) and pH value of strawberry TSS is one of the most important parameter affecting fruit quality and consumer

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acceptability, and a higher TSS value is preferred [28]. Changes of TSS of strawberry

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during storage were presented in Fig. 2A. TSS in all samples showed slight and fluctuant increasing within 9 days. And then, the values rapidly decreased with time

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going, which was consistent with our previous study [4]. The slight increase might be

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attribute to the cell wall disassembly, the decrease in respiration rate and the increase

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in dry matter due to water loss [29]. Compared to the uncoated samples, strawberry coated by CH could effectively delay the decrease of TSS. TSS value of uncoated

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strawberry reached to 6.72% at day 11, while the values were still over 8.0% for

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coated strawberries (Fig. 2A). The results were consistent with the above analysis, which showed that CH coating could slow down respiration rate and metabolic activity and therefore retard the decay of TSS [17]. Furthermore, strawberries treated by CH with 19 and 61 kDa had significantly (P < 0.05) higher TSS values at the later period of storage than those treated by CH with 5 kDa, implying that CH with higher MW was more suitable for maintaining the TSS during storage. pH reflects the changes of organic acid content in fresh fruit during storage. As shown in Fig. 2B, the pH values showed a fluctuating increasing which was correlated to the fruit senescence [4]. At day 11, the pH value of uncoated sample increased to 4.62, while the values of coated strawberry varied from 4.07 to 4.12 (Fig. 2B), which were in agreement with previous literatures [4, 30]. Moreover, at the end of storage,

Journal Pre-proof the pH values of strawberry coated by CH with 5 and 19 kDa rapidly increased 4.57, while CH with 61 kDa effectively maintained the pH value (4.05). This behavior could be explained by that higher MW of CH coating exhibited lower water vapor permeability due to the development of a more compact structure by higher polymerization degree CH chains [12]. The TSS/pH ratio is an important index to determine the fruit flavor harmony and consumer acceptability [26]. As shown in Fig. 2C, TSS/pH ratio showed a similar

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trend with the change of TSS at initial. But after 9 days, CH coating with higher MW

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exhibited higher TSS/pH ratio, reflecting more effective in reduced ripening of

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strawberries. The results were evidently linked to the reduced rate of ethylene

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suitable for strawberry preservation.

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production and respiration [17], indicating that CH with higher MW was more

3.4. Flavonoids content of strawberry

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Flavonoids are a major group in the family of phenolic compounds with

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antioxidant and biological activity, and changes of flavonoids content of strawberry during storage were presented in Fig. 3A. Although some fluctuations in flavonoids contents were observed, the values were gradually decreased after 5 days. The decrease in flavonoids could be attributed that flavonoids converted to other secondary phenolic compounds or were substrates of some enzymes during storage [31]. CH coating could delay the reduction of flavonoids of strawberry during storage compared to the uncoated samples (Fig. 3A). After 11 days, the flavonoids content of uncoated strawberry decreased by 40.18%, while the values of CH coated samples decreased by 18.24 to 30.92% with higher MW seeming more effective. This might be explained by that the increased MW resulted in the formation of smaller droplet during ES and dense coating on strawberry surface, thereby enhanced the oxygen

Journal Pre-proof barrier ability which was benefit for retarding the decrease of flavonoids [14]. However, there were no significant (P > 0.05) differences of flavonoids contents among the coated samples at day 15. 3.5. Superoxide dismutase (SOD) activity of strawberry SOD activity plays an important role in scavenging active oxygen species, being the first ROS scavenging enzyme that catalyzes the dismutation of toxic oxygen

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(radical superoxide) to hydrogen peroxide and molecular oxygen [32]. As shown in

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Fig. 3B, SOD activity firstly increased and maintained a stable value, and then gradually decreased with time. Compared to the uncoated samples (Fig. 3B),

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strawberry coated with CH delayed the decreases of SOD activity. At day 11, the SOD

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activity of uncoated samples was 1.78 U/g, while the values of coated samples still

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maintained higher (1.83-1.99 U/g). The results were consistent with previous literatures reported that CH coating could induce hosts to increase the activity of SOD

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in fresh fruits, delaying postharvest senescence by ROS elimination [19,32]. In

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addition, as for the impact of MW, no significant (P > 0.05) differences were observed among coated strawberries with different MW. 3.6. Malondialdehyde (MDA) content of strawberry MDA is used as measurement of the loss of membrane integrity in response to postharvest oxidative stress [20]. As shown in Fig. 3C, the MDA content of all samples increased during storage due to dioxygenation of polyunsaturated fatty acids producing toxic hydroperoxy fatty acids and consequent membrane damage [20]. At the early stage of storage, there were no significant (P > 0.05) differences for the MDA contents among the samples (Fig. 3C). However, after 9 days, CH coating could significantly retard the production of MDA of strawberry. For instance, at day 11, the

Journal Pre-proof MDA of uncoated samples increased by 162%, while the values of coated samples with 5, 19 and 61 kDa increased by 108%, 114% and 96%, respectively. The reduced accumulation of MDA in coated samples suggested that CH could be promising to prevent oxidative damage during cold storage just like reported [4,26,33]. CH coating induced less alteration of the fruit and helped to maintain membrane integrity because it created a barrier to the oxygen responsible for lipid peroxidation [33]. Moreover, CH reduced MDA content by regulating the activities of antioxidant enzymes such as

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SOD, therefore decreasing lipid peroxidation [34]. This was confirmed by the results

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of SOD (Fig. 3B). As for the impact of MW, at the early period of storage, there

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seemed no obvious differences among the coated strawberries. However, after 11 days,

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the MDA content of samples coated with 61 kDa CH was lower than that of strawberries coated with 5 and 19 kDa CH. Zhong et al. [10] reported that gas barrier

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property and tensile strength of CH films were improved along with increased MW,

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which was in accordance with better preservation effect.

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3.7. Principal component analysis (PCA) and correlation analysis In this study, PCA was applied to evaluate the effectiveness of CH coating with different MW on strawberry during cold storage. Multivariate treatment of the data obtained for the samples allowed these variables to be reduced to two principal components that explained 81.00% of the total variability, where PC1 accounts for 68.00% and PC2 for 13.00% (Fig. 4A). The proximity of different samples on the scoring plots indicated similar behaviors of their effects on the strawberry properties. These analyses allowed us to separate the strawberry samples into different groups. As shown in Fig. 4A, the strawberry properties were positively correlated with PC1 scores. Control samples at 11 days and the coated samples at 15 days were located in the fourth quadrant, indicated CH coating showed better preservation for strawberry.

Journal Pre-proof The load of each index on the principal component was further studied to determine which index had the greatest impact on the strawberry properties (Fig. 4B). In detail, mold, weight loss, MDA and pH were positively correlated with PC1 whereas SOD, TSS, firmness and flavonoids were negatively correlated. The results were consistent with the above analysis that mold, weight loss, MDA and pH were considered as the negative parameters during performance evaluation criteria. To further evaluate the associations among quality parameters, a correlation-

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based approach using the Pearson coefficient was adopted in this study, and the results

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were presented in Table 1. The pH and firmness had significant correlation with TSS,

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flavonoids and MDA content, indicating that the production of MDA, the decrease of

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TSS and the changes of flavonoids had significant effects on the acidity and texture quality of strawberry during storage. Weight loss was significantly positive correlated

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with pH (r = 0.583, P < 0.05), MDA content (r = 0.944, P < 0.01) and mold counts (r

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= 0.962, P < 0.01), while was negative correlated with firmness, TSS and flavonoids. CH coating formed a semipermeable barrier on strawberry surfaces to retard the

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weight loss, and thus maintained the quality of strawberry [4]. Moreover, mold counts showed significant correlations with other 6 parameters except for TSS content. Therefore, CH coating was effective for strawberry preservation due to the antibacterial activity. Accordingly, the correlation results showed weight loss and mold counts had significant effect on other parameters of strawberry. Therefore, it was suitable that the weighted assignment of the two parameters was set as the highest values, i.e. 0.2. 3.8. Performance evaluation criteria The above results indicated that CH coating with different MW had different impact on strawberry preservation and this made it difficult to evaluate which MW

Journal Pre-proof was more suitable. Therefore, we used a fuzzy evaluation to investigate the comprehensive performance. As shown in Table 2, the synthetic evaluation index (S) values were continuously decreased during storage. At day 11, the S1 values of uncoated samples already decreased from 0.80 to 0.14, while the values of coated samples were all over 0.42. Especially, the S1 values of coated samples with 61 kDa at day 15 were two times than that of uncoated samples at day 11. As for the S2 values which reflected the differences among coated samples at same time, the CH coating

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with 61 kDa generally showed the highest S2 values during the whole storage and at

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the end of storage, the difference was more obvious (Table 2). The results suggested

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that CH with higher MW had more excellent performance on strawberry preservation,

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which was consistent with Jongsri et al. [13] who found that CH with higher MW could delay mango fruit ripening and thus maintain fruit quality during storage.

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According to our previous study, the probability of molecular interaction and

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self-entanglement of CH chains were enhanced with MW increase, and thus more complete and self-aggregate coatings were formed after electrostatic spraying [10],

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which might lead to the better preservation effect. 4. Conclusion

CH coating was an effectively postharvest treatment that mitigated the physiological and biochemical changes of fresh strawberry to prolong the shelf-life. MW of CH had no significant (P > 0.05) influences on mold growth, weight loss, firmness, SOD activity of coated strawberries. But CH with 61 kDa MW could better maintain flavonoids content, and retard the increases of pH and MDA. According to the fuzzy evaluation, CH coating with 61 kDa had better performance on strawberry preservation with the highest synthetic value (6.93) during storage.

Journal Pre-proof Conflict of interest All authors have no competing interests to disclose. Acknowledgements This work was supported by the National Natural Science Foundation of China [Nos. 31501533], and Shanghai Food Safety and Engineering Technology Research Center

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[16DZ2281400].

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Table 1 Correlation analysis of strawberry quality parameters during storage.

pH 0.583* 1

Firmness -0.747** -0.329 1

TSS -0.501* -0.475* 0.644** 1

Flavonoids -0.875** -0.593** 0.709** 0.508* 1

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Weight loss 1

MDA 0.944** 0.642** -0.805** -0.626** -0.848** 1

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Significant at *P < 0.05; **P < 0.01. TSS: total soluble solids, MDA: malondialdehyde, SOD: superoxide dismutase.

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Weight loss pH Firmness TSS Flavonoids MDA SOD Mold

SOD 0.243 -0.238 -0.026 0.517** -0.101 0.057 1

Mold 0.962** 0.511* -0.659** -0.322 -0.832** 0.877** 0.354** 1

Journal Pre-proof Table 2 Comprehension evaluation of strawberry quality parameter during storage.

19 kDa

61 kDa

0.80 0.72 0.61 0.42 0.27 0.14

0.80 0.81 0.74 0.61 0.55 0.42 0.33 0.13 1.00 0.68 0.64 0.74 0.81 0.70 0.55 0.30 5.42

0.80 0.80 0.77 0.69 0.53 0.46 0.33 0.14 1.00 0.58 0.87 0.82 0.74 0.77 0.61 0.46 5.85

0.80 0.79 0.74 0.70 0.62 0.51 0.39 0.28 1.00 0.69 0.67 0.79 0.96 0.94 0.90 0.99 6.93

1.61

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1.00 0.30 0.14 0.18 0.00 0.00

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5 kDa

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S2

Control

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S1

Storage time (Days) 0 3 5 7 9 11 13 15 0 3 5 7 9 11 13 15 Total score

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S1: synthetic evaluation index calculated at different time; S2: synthetic evaluation index calculated among different treatment

Journal Pre-proof Figure legends Fig. 1. The changes of (A) mold growth, (B) weight loss and (C) firmness of strawberries coated by CH with different MW. Data of control samples were referred to our previous study [4] Fig. 2. The changes of (A) TSS, (B) pH and (C) TSS/pH of strawberries coated by CH with different MW. TSS, total soluble solids. Data of control samples were referred to our previous study

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Fig. 3. The changes of (A) flavonoids content, (B) SOD activity and (C) MDA content

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of strawberries coated by CH with different MW.

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SOD, superoxide dismutase activity; MDA, malondialdehyde. Data of control samples were referred to our previous study [4]

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Fig. 4. The PCA analysis. (A) PCA scores and (B) loading plots.

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TSS, total soluble solids; SOD, superoxide dismutase activity; MDA,

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malondialdehyde. Data of control samples were referred to our previous study [4]

Journal Pre-proof A

5 kDa

19 kDa

61 kDa

Control

7

log CUF/g

6

5

4

3 4

8

6

5 kDa

8 10 Storage time (Days)

19 kDa

61 kDa

7

4 3

1 0

Firmness (g)

6

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4

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2

100

Control

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2

120

16

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5

140

14

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Weight loss (%)

6

C

12

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B

2

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0

5 kDa

8 10 Storage time (Days)

19 kDa

12

14

61 kDa

16

Control

80

60

40 0

2

4

6 8 10 Storage time (Days)

Fig. 1.

12

14

16

Journal Pre-proof A

5 kDa

19 kDa

61 kDa

Control

10

TSS (%)

9

8

7

6 2

4

6

8 10 Storage time (Days)

12

14

16

14

16

5 kDa

B

19 kDa

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pH

4.4 4.2

3.8 2

4

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0

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4

6 8 10 Storage time (Days)

5 kDa

2.5

Control

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4.6

C

61 kDa

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4.8

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of

0

19 kDa

12

61 kDa

Control

TSS/pH

2.0

1.5

1.0 0

2

4

6

8 10 Storage time (Days)

Fig. 2.

12

14

16

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A

5 kDa

19 kDa

61 kDa

Control

Flavonoids Content (μg/mL)

50 45 40 35 30 25 2

4

6

8 10 Storage time (Days)

12

14

16

B

2.2 2.0

1.2 1.0

MDA (μmol/L)

2

4

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0

5

Control

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1.4

6

61 kDa

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1.6

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SOD activity (U/g)

1.8

C

19 kDa

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5 kDa

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of

0

5 kDa

6 8 10 Storage time (Days)

19 kDa

61 kDa

12

14

16

Control

4

3

2

1 0

2

4

6 8 10 Storage time (Days)

Fig. 3.

12

14

16

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A

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B

Fig. 4.

Journal Pre-proof Author Statement

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Yongli Jiang: Software, Investigation, Formal analysis, Data Curation, Writing - Original Draft, Writing - Review & Editing Li Yu: Software, Investigation, Formal analysis, Data Curation, Writing - Original Draft Zichun Zhu: Investigation, Formal analysis, Data Curation, Resources Yunwen Hu: Investigation, Resources Chenjun Zhuang: Investigation, Resources Yanyun Zhao: Supervision Yu Zhong: Conceptualization, Methodology, Writing - Original Draft, Writing - Review & Editing, Supervision