Synthesis And Enzymatic Hydrolysis Of Acetylated Starch

Starch is a kind of biodegradable polysaccharide that has a wide source, easy accessibility and low cost. It has a potential to replace synthesized polymers as an environmentally friendly material. Since the invention of aetylated starch, it has been widely applied to food packages as additives and other food related realms, such as coating the surface of the hydrophilic materials, which mitigates the deficiencies of plasticized starch. By enzymatic hydrolysis of acetylated starch, surfactants were obtained. Acetylated starch could also be utilized to enwrap perfumes. However, it is vital to degrade acetylated starch with a high efficiency without causing negative effects of accumulating pollution to the environment.Acetic anhydride with its low price, easy accessibility and good performance is a suitable acetylation agent in organic solvents. With glacial acetic acid as the solvent, methanesulphonic as the catalyst, acetylated starches are synthesized by the reaction of starch with acetic anhydride. Acid-base titration, acetone-aided acid-base titration and 1H-NMR were adopted to determine the degree of substitution. Both the acetone-aided acid-base titration and 1H-NMR are more accurate than the acid-base titration, while the acetone-aided acid-base titration is faster and more ecomonic.According to the state stardard, the enzymatic activities were determined. The enzymatic activity of porcine pancreatic lipase is 10 u/g and that of microbial lipase is 143u/g. As the content of acetone increases in the buffer solution, both the enzymatic activity of lipase from porcine pancrea and microbial source get activated with 120% higher than the initial enzymatic activity of lipase from porcine pancreas and 97% higher than the initial enzymatic activity from microbial lipase. The enzymatic activity of ?-amylase is stable in 4 hours in buffer solution at the ambient temperature, which is 3015-3220 U/g. After adding biosurfactants sorbitol (2.4% w/w) and Tween 80 (0.02% w/w), the enzymatic activity of a-amylase decreases two-thirds. Unlike the a-amylase, the enzymatic activity of glucosidase is unstable in 4 hours, so the initial activity is 50600-55850 U/g. The optimal catalysis condition of isoamylase is 55?, pH 5.5,0.3 g enzyme load/g acetylated starch in 300 mL of buffer solution.After acidic hydrolysis of acetylated starch for 1h, no reducing sugar was detected. But between the first hour and the second hour, the hydrolysis of acetylated starch accelerated. At the end of the second hour, the hydrolysis degree reached 82%. With an extra hour, the acetylated starch is hydrolyzed completely. With the extreme overdose of a-amylase, the hydrolysis degree of acetylated starch could only be no more than 9.1%. After hydrolyzing for 24 hours, the hydrolysis degree is 9.3%. With biosurfactants, or sorbitol and Tween-80, in the buffer solution, the hydrolysis degree could reach 59.7% in 3 hours at pH 6.0.After treated by the microbial lipase, the hydrolysis degree of the highly substituted acetylated waxy corn starch could achieve 22.5% with the hydrolysis of ?-amylase for 24h. After hydrolysis for 5 days, the glucosidase was added to the solution and the hydrolysis degree climbed to 63%. After another 2 days for the hydrolysis of glucosidase, the glucosidase was added again to the solution. To the 14th day, the hydrolysis degree achieved 73.1%.With the treatment of microbial lipase for 1 hour (0.4 g microbial lipase load/g acetylated starch,55?, pH 5.5,10 mL acetone,90 mL buffer solution), isoamylase was added to the solution at the its optimal catalysis condition. After 2.5 h, the hydrolysis degree is 99.3%. This processing method is the fastest way to complete the hydrolysis of acetylated starch in this work.