Study On The Preparation Of Chitosan Derivative And Its Antimicrobial Activity In Raw Milk And Yoghourt

This study took chitin as main raw materials, changed it into chitosan by chemical reaction, and then we studied on chitosan ulteriorly. After hydrolyze reaction and replace reaction, we got all water-soluble chitosan hydrolysate and o-carboxymethy chitosan. Putting the two products into raw milk and yoghourt, we studied their antimicrobial activity. The study showed that:(1) When chitosan was mixed with 55% NaOH solution in proportion of 1:10(w/v g/mL) and the reaction took place at temperature of 110℃ for 6 hours. lavaging every two hours during reaction and at last time lavaging chitosan until to pH=7. After drying it at temperature of 60℃, we got chitosan having a deacetyl percentage of 92% and viscosity of >200cp.(2) Put 3g chitosan into 50mL 1% CH3COOH solution, after dissolved completely, added 9mL H2O2 into this solution and the reaction took place at temperature of 80℃ for 3 hours. Filtrated the hydrolysate and then concentrated liquid to 20mL, neutralized liquid with 1% NaOH, added 200mL ethanol to extract hydrolyte, 3000r/min eccentricity, and then we could got all water-soluble canary yellow chitosan by vacuum-freeze drying.(3) Mixed 3g chitosan with 50mL iso-propyl alcohol, and then added 10mL NaOH to this mixture, the concentration is 12.5mol/L, 2mL every 20 minutes, after reacted about 1hour, added 5g ClCH2COOH to this mixture, 1g every 5minutes, and then reacted at the temperature of 60℃ for 8 hours, adjusted the liquid to neutralization, lavaged products. We got the nearly water-soluble o-carboxymethy chitosan by drying products at 60℃.(4) The study showed that all water-soluble chitosan with concentration >1.60% had prominent antimicrobial activity to raw milk and >0.20% all water-soluble chitosan had obvious anti-postacidification characteristic for yoghurt, meanwhile, the live lactobacillus were more than 106CFU/mL that was prescribed by national laws.(5) The study showed that the nearly water-soluble o-carboxymethy chitosan with concentration 0.80% had prominent antimicrobial activity to raw milk and 0.25% the nearly water-soluble o-carboxymethy chitosan had obvious anti-postacidification characteristic for yoghurt, meanwhile, the live lactobacillus were more than 106CFU/mL that was prescribed by national laws.The study of this dissertation showed that all water-soluble chitosan and nearly water-soluble o-carboxymethy chitosan had obviously antimicrobial activity and could be utilized to raw milk and yoghurt. On the other hand, combining with chitosan's physical activities and functional characters, chitosan will be act as an important role in the development of milk product field.