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In this experience, we found that the coated samples markedly decreased decay rates, and chitosan glucose complex showed the best effect on inhibiting the incidence of berry decay. Gray mold, which caused by Botrytis cinerea Pers., is a direct cause of postharvest decay for table grapes. In the previous researches, two mechanisms have been described about chitosan to control the growth of pathogens. One theory is that chitosan by interfering with the negatively charged residues of macromolecules exposed on the fungal cell surface lead to the loss of intracellular electrolytes and proteinaceous constituents (Meng et al., 2008; Xu et al., 2006). Another argument is that diffused hydrolysis products from chitosan may be to interact with the fungal DNA, thus affecting mRNA and protein synthesis (Zakrzewska et al., 2005). Liu et al. (2007) found that chitosan could significantly inhibit spore germination and mycelial growth of Botrytis cinerea by damaging the plasma membrane of the spore in vitro. In addition, chitosan preharvest spray and postharvest coating have previously been reported to have antifungal effect when applied to table grape (Meng et al., 2008). In our study, the results supported the ideas that the chitosan were effective to reduced decay of grapes. Also, the results in the experiment showed that chitosan glucose complex had a better function to reduce the natural decay incidence of grape fruit, compared with chitosan or glucose alone. The mechanism of microorganism inhibition by chitosan glucose complex is not fully understood, but it can be guessed that Maillard reaction products, from chitosan and glucose, enhanced the antimicrobial properties of chitosan. A soy protein-chitosan conjugate, produced by the Maillard reaction, has been reported to enhance antimicrobial activity (Usui et al., 2004). Similarly, Chung et al. (2005) found that the chitosan-glucosamine derivatives, formed using the Maillard reaction, had relatively high antibacterial action as compared with pure chitosan. In addition, glucose coatings showed a good function to reduce the natural decay incidence of grape fruit. It can be guessed that glucose coatings could hinder or defer pathogen infections. |