Study On Effects Of Chitosan And Its Derivatives Coating Preservation On Agaricus Bisporus

Agaricus bisporus is a mushroom which is the most widely cultivated, the maximum yield and has the most widespread consumption in the world. But because of the high moisture content, the soft organization, the surface without the protection of the structure and the intense respiration and transpiration, Agaricus bisporus is prone to decompose caused by bacteria infection and mechanical damage, usually at room temperature and 2 days after harvest, Agaricus bisporus will be discolored, metamorphic and cap opening. It is a great pressure for the fresh produce to stored and transport, either it’s unable to meet the market demand for fresh produce. Taking Agaricus bisporus as the object of the research and adopting chitosan and its group modified derivatives as the main film-forming agent, this thesis had a coating preservation experiment with compounded coatings complex preservative by adding a certain proportion of the preparation of film-forming additives. The aim is to research the physiological and biochemical changes of Agaricus bisporus after picking, also to provide a more comprehensive theory and practice thereunder for the application of chitosan and its derivatives coating preservation on Agaricus bisporus. At the same time, through this research, we are in the hope of effectively extending the storage period. The conclusions of this thesis as follows:1. The research about the harvesting period and storage temperature of Agaricus bisporus. According to evaluation of post-harvest physiological and biochemical index, the result of the research is that the most storage effect will appear when the size of harvest is controlled in cap diameter about 50-60 mm, and the appropriate storage temperature is 4℃.2. The exploratory research of chitosan coating preservation. Through the single-factor and orthogonal test, this thesis obtained the formulation of chitosan coating complex preservative is A₃B₂C₁D₂（chitosan 1.2%, ascorbic acid 0.2%, glycerin 2%, tween 20 0.01%）. although the result of acid-soluble chitosan coating caused the acid injury on the surface of Agaricus bisporus, However, some other indicators reflect preservation properties of polymer coating, it is necessary to modify Chitosan.3. According to the water insoluble and the low physiological activity of chitosan, modification was studied. We prepared carboxymethyl chitosan with high degree of substitution （DS=1.71） and prepared chitosan Schiff-base, N-substituted chitosan, quaternary ammonium salt of chitosan, carboxymethyl chitosan, N-substituted carboxymethyl chitosan and carboxymethyl chitosan quaternary ammonium salt based on chitosan and carboxymethyl chitosan respectively. 4. Through comparing the antibacterial activity of chitosan derivatives between conventional bacteria and fungi, this thesis obtained the chitosan quaternary ammonium salt displays higher antibacterial activity toward staphylococcus aureus, Escherichia coli, bacillus subtilis and saccharomyces cerevisiae. The antibacterial activity increased with the concentration. N-substituted carboxymethyl chitosan has high antibacterial activity to aspergillus niger, saccharomyces cerevisiae, embodying out good effect in inhibition growth of pathogenic fungi on the fruits and vegetables’ surface. Though the antibacterial activity of carboxymethyl chitosan is not very good, because of its good water-soluble, film-forming ability and Hygroscopicity and Retention Characteristic, carboxymethyl chitosan has a great success in the field of fruit and vegetable coating preservation. But the technology for coating preservations of carboxymethyl chitosan on Agaricus bisporus is unprecedented.5. On the basis of preclinical experimental research and application research of Chitosan, the suitable chitosan derivatives is used to research coating preservation of Agaricus bisporus. At he end, the N-substituted carboxymethyl chitosan was selected as the main film-forming agent, glycerin and tween20 as film-forming additives. Through the single-factor and orthogonal test, this thesis obtained the formulation that N-substituted carboxymethyl chitosan coatings complex preservative is A₁B₂C₃.6. Through the verification test of N-substituted carboxymethyl chitosan coating complex preservative under different storage temperature （4℃, 17℃, room temperature（15±2℃）） , this thesis obtained that comparing with the control group, N-substituted carboxymethyl chitosan coating complex preservative shows the best effect to each index the group, reaches a certain effect on the preservation. Under different storage temperature every physiological indexes of Agaricus bisporus has obvious difference. The higher the temperature is, the stronger physiological metabolism is, and the faster the quality decrease. Therefore, the combination of low temperature refrigeration and N-substituted carboxymethyl chitosan coating preservation is feasible to achieve a better preservation effect.