Effects of chitosan combined with chitosan-montmorillonite nanocomposites coating on postharvest quality of 'Hom Thong' banana fruit

Abstract

Chitosan (CTS) has been widely applied as a fruit coating in commercial fruit crops to prolong their shelf-life. In the present research, chitosan coatings were applied on ‘Hom Thong’ banana fruit, an important exported cultivar of Thailand. Postharvest qualities of ‘Hom Thong’ banana were measured after coating with 1% (w/v) low molecular weight (LMW-CTS: 65 kDa), medium molecular weight (MMW-CTS: 265 kDa), and high molecular weight (HMW-CTS: 540 kDa) chitosan for 1 min. The application of HMW-CTS showed the thickest of coated film and had effectiveness as a barrier of water vapor and O2 transmission. HMW-CTS treatment could retard fruit respiration and ethylene production, thus delaying fruit softening, reducing weight loss, peel color change, and TSS content. Moreover, HMW-CTS coated fruit exhibited reduced cell wall hydrolase enzyme activities, including polygalacturonase (PG) and pectate lyase (PL). Furthermore, HMW-CTS could enhance the antioxidant capacity, reduce cell membrane injury and disease severity of fruit. These results suggested that HMW-CTS was the most effective treatment in delaying fruit softening and exhibited a longer shelf life of ‘Hom Thong’ banana. The development of chitosan-montmorillonite nanocomposites (CTS-MMT) nanocomposites combined with chitosan solution was further investigated. The CTS solution combined with CTS-MMT nanocomposites was casted as free-standing films and neutralized with 4% (w/v) NaOH. The combination of 2% CTS-MMT in CTS thin film had a higher water resistance ability by increasing the degree of water contact angle and lowering water absorption and water solubility values compared to CTS film. The CTS solution combined with CTS-MMT nanocomposites at 1%, 2%, or 4% (w/v) were applied as banana fruit coating. Fruit was dipped in the solution for 1 min and then stored at 25 °C for 15 days. The 2% CTS-MMT coating reduced the respiration rate and ethylene production, retarded peel color change and inhibited electrolyte leakage and malondialdehyde content of bananas, indicating a decrease in membrane leakage. Taken together, the 2% CTS-MMT could delay banana fruit ripening due to the increase in the oxygen barrier property of the film, which is an important parameter for maintaining the postharvest quality of ‘Hom Thong’ banana fruit. To evaluate the effect of CTS and CTS-MMT on the development of postharvest disease, banana fruit were inoculated with Colletotrichum musae, which caused anthracnose in bananas. CTS and 2% CTS-MMT treatments significantly reduced the incidence and severity of the disease during storage at 25 °C. In addition, both treatments markedly increased the contents of phenolic content (TPC), ascorbic acid (AsA), and reduced glutathione (GSH) in bananas. Moreover, CTS and 2% CTS-MMT treatments had the ability to reinforce the microbial defense mechanism of bananas by enhancing the activities of antioxidant enzymes, including ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), and dehydroascorbate reductase (DHAR). Therefore, the CTS and 2% CTS treatments could mitigate the disease severity in ‘Hom Thong’ banana fruit.