脂肪酶交联聚集体的制备及其催化合成月桂酸淀粉酯的研究

Preparation of cross linked lipase aggregates for synthesis of starch laurate

采用交联酶聚集体(cross-linked enzyme aggregates,CLEAs)技术制备了脂肪酶CLEAs,优化了制备条件:以硫酸铵为沉淀剂,以14 mmol/L戊二醛为交联剂,交联时间1.5 h,所得脂肪酶CLEAs的相对酶活力达到41.89%;与游离酶相比,脂肪酶CLEAs的热稳定性显著增强,重复使用性显著提高,重复使用10次后相对酶活力达到50.26%。以该脂肪酶CLEAs作为催化剂,以玉米淀粉和月桂酸为原料,进行了酯化反应,得到月桂酸淀粉酯的最大取代度为0.151。此外,利用红外光谱(Fourier transform infrared spectoscopy,FT-IR)对月桂酸淀粉酯进行了分子表征,发现在1 713 cm-1处出现了羰基CO的特征吸收峰,说明月桂酸与淀粉在脂肪酶CLEAs的催化作用下合成了月桂酸淀粉酯。同时,热重分析(TGA)表明,相比于原淀粉,酯化产物的热稳定有较低趋势。

In this work, lipase-eross linked aggregates （lipase-CLEAs） were prepared and the effects of the precipitation and cross-linking on CLEAs activity were investigated. The optimum conditions for immobilization process were obtained as follows： ammonium sulfate was used as precipitant, concentration of cross-linker and enzyme respectively was 14 mmol/L and 30 mg/mL,cross-linking time was 1.5 h. The maximum activity recovery was 41.89% for the lipase-CLEAs. Compared with free enzyme, the thermal stability of CLEAs was largely enhanced and the reusability was significantly improved to 50.26% of their initial activity after 10 recycles. Then maize starch was esterified with laurate by using lipase-CLEAs as catalyst. The effects of the reaction temperature and the molar ratio of lauric acid/anhydroglueose unit （AGU） in starch on the degree of substitution （DS） of starch laurate were studied. The product with the highest DS of 0. 151 was prepared under the given conditions. Fourier transform infrared （FTIR） analysis showed that a new peak at 1 713 cm^-1 for C = O stretching in the ester group was observed, which confirmed the formation of starch laurate. Furthermore, decrease of thermal stability of the starch laurate was indicated by thermal gravimetric analysis （TGA）.