Biocatalysis Of Non-gallated Catechin Esters

Catechins are important polyphenol compounds in tea, possessing many bioactivities. But their poor lipophilic solubility greatly limits their industrial applications. Many researches showed that the acylation modification of catechins can not only improve their lipophilicity, but also enhance their bioactivities. Compared with chemical acylation of catechins, biocatalysis methods remained largely unexplored. In this dissertation, biocatalytic methods were investigated for synthesis of non-gallated catechin fatty acid esters. Two types of biocatalysts(immobilized lipase and whole cell biocatalyst) were tested and the influences of several key factors on catalytic efficiency of the biocatalysts were investigated and the influences of organic solvent on whole cells were also analyzed.Studies have shown that the immobilized lipases, Lipozyme IM RM and Lipozyme IM TL, can effectively catalyze the acylation of non-gallated catechins in isopropanol. The highest reaction conversion(96%) was achieved using Lipozyme IM RM under the optimum conditions: molar ratio of vinyl ester to non-gallated catechins 25:1-30:1, biocatalyst dosage 30 mg/mL, reaction temperature 50 ℃ and water content 20 μL/m L. By using MS, FT-IR and 13 C NMR analysis, the main products were confirmed as 3,5’-O-acetyl-catechins. The catalytic efficiency of whole cell biocatalyst was affected by both the strains and the culture conditions. Considering the biomass and substrate conversion, Aspergillus niger cultured in soy oil-contianing medium was selected for whole cell biocatalyst preparation. The reaction conditions for Aspergillus niger whole cells were optimized and the best molar ratio of vinyl ester to non-gallated catechins, biocatalyst dosage and reaction temperature were 30:1, 30 mg/m L and 50 ℃, respectively. Preparative-scale experiments showed the possibility for industrial production of catechin esters with Lipozyme IM RM and Aspergillus niger whole cells. The operational stabilities of Aspergillus niger whole cells, however, was much lower than lipozyme IM RM, which may be due to the toxic effect of organic solvents.The toxic effects of 11 organic solvent on microbial cell were analyzed. Methanol, acetonitrile and methylbenzene have significant toxic effects on A. niger spores, forcing spore deformation even rupture. t-Amyl alcohol changed the spore morphology, making the spores smaller and more smooth. Organic solvents also affect the mycelium morphology, the biomass and their catalytic ability. However, there was no evident relationship between solvent toxicity and their logP values.This research has high theoretic and practical values, which provide new and green strategies for production of non-gallated catechin fatty acid esters.