Study On The Molecular Modification Of Chitosan And Their Bio-coating Preservation

Chitosan is a natural, non-toxic, the biodegradable polymer compound. It displays interesting properties such as biocompatibility, biodegradability, non-toxic, non-immunogenic and non-carcinogenic. Therefore, chitosan has prospective applications in many fields such as biomedicine, waste water treatment, functional membranes and flocculation. However, the nonsolubility of chitosan limits its application as a food preservative or as bioactive materials. Therefore, several derivatives of the chitosan were synthesized to improve its solubility in water and its antimicrobial. The objectives of this study were to synthesis derivatives from chitosan. In these paper, we synsthesis several derivatives such as carboxymethylchitosan (CMC), N, N, N-trimethylated chitosan(TMC). The antimicrobial activity of chitosan and its derivatives was tested against Staphylococcus aureus and E. coli. Then, the preservation effects of CMC against Lentinus edoes and Chinese shrimp were compared to that of chitosan. The main conclusions are as follows: 1. By single-factor experiments, the optimum condition of the synthesis of CMC was obtained as follows:sodium hydroxide concentration of50%, the reaction temperature of60℃, reaction time of3h, chitosan-chloroacetic acid ratio of1:2.5(m/m). It finally gets the water-soluble CMC with substitution degree of88%, the molecular weight of3.5x10-5. A two-step method was investigated to synthesis TMC with different degree of quaternization (27.5%-91.7%) avoiding O-methylation and chain scission as side reactions. The degrees of trimethylation for TMCs increased as prolongation of the reaction time, which were42.8%,67.0%,84.1%and91.7%for24h,48h,72h and96h reaction respectively. The TMC with different degree of quaternization were studied for their solubility. It was showed that the TMC with degree of quaternization above42.8%were soluble in water and the solution was transparent. The antimicrobial activity of chitosan and its derivatives was tested against Staphylococcus aureus and E. coll. It was showed that the MIC of CMC with the substitution degree of88%against Staphylococcus aureus and E.coli was0.3906mg/mL and0.1953mg/mL respectively, and the TMC with degree of quatemization of91.7%was0.1953mg/mL,0.3906mg/mL respectively. The inhibition effect of CMC against on staphylococcus aureus is stronger than TMC. With the risement of the degree of substitution, the inhibition effect of CMC and TMC against Staphylococcus aureus and E.coli increased. 2. Mushroom(Lentinus edoes) were coated with1.0%CMC and1.0%chitosan (dissolved in0.5%lactic acid solution) as control. It was showed that the1.0%CMC coatings reduced respiration activity, thus delaying the progress of mushroom decay due to senescence. CMC coatings delayed changes in weight loss, firmness, external color, nutrient, PPO activity compared to chitosan and untreated samples. This may be due to that CMC coatings can form a layer of film, inhibiting moisture loss, invading germs, adjusting the mushrooms inside and outside gas exchange. Thus it forms an environment that low O2and high CO2concentration on the surface of mushrooms, reducing material transformation, so as to extend the storage time of mushrooms.3. Effects of different CMC on Chinese shrimp were studied compared to that of chitosan. The results showed that changes of pH, total volatile basic nitrogen (TVB-N), the other physical and chemical parameters were delayed, the growth of microbilological populations in Chinese shrimp treated by CMC were retarded. The treatment group maintained a good organoleptic quality. And the effect was significant when the CMC concentration was higher. The best concentration of CMC was1.5%, The shelf-life could be extended to five days when compared to the control group.