Antifungal Activity And Fresh-keeping Effect Of Low Molecular Weight Chitosan

As an abundant biopolymer, chitin widely distributes in nature. Chitosan, the deacetylated derivative of chitin, possesses antimicrobial activity and biosafety. Thus, it could be developed into novel safe food additives and/or fresh-keeping agent for fruit and vegetable.In this study, the antifunal activity of low molecular weight chitosan(LMWC) against fruit pathogenic fungi and its antifungal mechanism were systematically analyzed. The physical and chemical properties of LMWC and its fresh-keeping ability for fruit were also investigated. The results were summarized as follows:1. LMWC was prepared by enzymatic degradation of chitosan. The correlate detection of physical and chemical properties of LMWC was implemented. The results showed that the deacetylation degree of LMWC is 90%, and its viscosity-average molecular weight is 50 KDa. The contents of heavy metal and ash conform to the national food safety standards.2. Two pathogenic fungi from orange and pear were separated and identified. The results showed that these two pathogenic fungi were Galactomyces citri-aurantii and Botryosphaeria sp. W-01, respectively. According to the clinical and Laboratory Standards Institute(CLSI) M38-A2 method established by American Clinical Laboratory Standards Committee(NCCLS), broth microdilution assay was performed for LMWC antifungal activity in vitro. The minimum inhibitory concentration(MIC) of LMWC against these fungi was determined to be 0.078 mg/m L. Based on MIC, the biomass of pathogenic fungi was measured. LMWC inhibited the mycelia growth of pathogenic fungi significantly.The results indicated that LMWC exhibits good antifungal effect.3. The antifungal mechanism of LMWC was also researched in the present study. The biochemical index(ergosterol content) of pear pathogenic fungi was tested. The changes of the fungal ultrastructures were observed by TEM, and archoring the site of action was determined by CLSM after FITC-labeling. The results showed that LMWC reduced the fungal ergosterol content; the integrity of cell wall and cell membrane were damaged by LMWC, and it could enter into the cell interior, damage organelle, and cause the loss of cellular content.4. The coating preservation experiments of orange and pear were carried out finally. Compared to the control, LMWC significantly reduced the rate of fruit decay, and inhibited the activities of polyphenol oxidase(PPO) and peroxidase(POD) in rotten fruit. Coating with LMWC also maintained the nutritional content of fruit. The contents of soluble solid, titratable acid, and vitamin C, in the LMWC treated groups were higher than those of the control group.