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

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 maintain the strawberry qualities during storage compared to uncoated treatment. CH coating with 61 kDa was more effective in retarding the increases of pH and MDA, and could better maintain flavonoids content. However, MW had no significant 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 strawberry preservation with the highest synthetic value (6.93), and could be used to maintain quality and prolong the shelf life of strawberry during cold storage.

Electrostatic spraying of chitosan coating with different deacetylation degree for strawberry preservation.

This study used electrostatic spraying (ES) system as an efficient technique for strawberry preservation with chitosan (CH) coating. The effects of CH deacetylation degree (DD, 81.0, 88.1 and 95.2%) on the qualities (weight loss, pH, total soluble solids (TSS), firmness, flavonoids content, malondialdehyde (MDA) content and superoxide dismutase (SOD) activity and mold growth) of strawberry during cold storage were investigated. Results showed that CH coating by ES formed more continuous and uniform protective layer compared with conventional spraying (CS). CH coating effectively enhanced the overall quality and extended shelf life of strawberry at least 2 days. CH coating with 81.0% and 88.1% DD were more effective in reducing weight loss of strawberry, and CH coating with 88.1% DD could better maintain TSS content, while CH coating with 95.2% DD delayed the decline in flavonoids more obviously. However, DD had no significant impact on pH, firmness, SOD activity, MDA and mold growth of coated samples. The evaluation criteria indicated CH coating with 88.1% DD had better preservation performance with the highest synthetic value (6.17) during storage. These findings suggest that CH coating especially with 88.1% DD by ES, as a safe, cheap and efficient technique, has great potential for industrial application of fruit preservation.

Effect of molecular weight on the properties of chitosan films prepared using electrostatic spraying technique.

Chitosan (CH) films were prepared with different number-average molecular weight (MW, ca. 6.55, 12.93 and 47.70 kDa) and concentration (0.5, 0.75, and 1.0%) using electrostatic spraying (ES) technique. The effects of MW on film-forming solution properties, ES-atomization performances, and film characteristics were investigated. With increase of MW, conductivity, viscosity, surface tension, and contact angle of CH film-forming solution was raised due to the increases of proportions of amine-groups and degrees of CH chain entanglements. Spray cone angle was generally higher at 12.93 kDa, while the average median diameters of film-forming solution droplets were in the range of 6.3-12.0 µm, indicating well atomization effect. Water barrier property and tensile strength of CH films were improved along with increased MW, which was in accordance with the more completed, rougher and more crystalline microstructures implying by SEM, AFM and XRD. However, film antibacterial capacities against E.coli and L. innocua were descended with increased MW. Considering the overall properties, CH film prepared by 47.70 kDa at 0.5% possessed the best performances.