Surfactant-coated Lipase Catalyzed Synthesis Of Sucrose-6-acetate

Sucrose-6-acetate is the key intermediates in the preparation of sucralose.Enzyme-catalyzed transesterification reaction has been the focus based on its advantages,such as mild reaction,high catalytic efficiency and regioselectivity.Candida rugosa lipase catalyzed synthesis of sucrose-6-acetate was studied in this article.Through modifying enzyme with coating agents or changing the reaction medium,the esterified yield and regioselectivity of the transesterification reaction improved.First,we studied lipase-catalyzed synthesis of sucrose-6-acetate in aqueous-organic two-phase system with surfactant.The addition of surfactant in two-phase system would be the formation of micelles.We found that Hexadecyl trimethyl ammonium Bromide(CTAB)was the optimum surfactant.Compared to two-phase system,the esterified yield of lipase-catalyzed synthesis of sucrose-6-acetate in micelles was increased by 20%.Regioselectivity has also improved.Under optimal conditions,the esterified yield reached up to 70.2%,and 6-regioselectivity achieved 54.0%.Secondly,we coated lipase with surfactant,and then immobilized on sol-gel supports.Polysorbate(Tween-80)was chosen as a coating agent and the sol-gel precursor was modified with glycerol.We optimized the preparation process of surfactant-coated lipase and the procedures for sol-gel immobilization of surfactant-coated lipase.In addition,the transesterification conditions were also investigated.As a result,compared to native lipase,the surfactant-coated lipase immobilized on sol-gel supports greatly increased the esterified yield by about 10 times,reached up to 73.9%.Regioselectivity achieved 96.2%.The catalytic activity of immobilized surfactant-coated enzyme still kept high after 5 cycles of reactions.Finally,surfactant-coated lipase immobilized on sol-gel supports catalyzed synthesis of sucrose-6-acetate in microaqueous system was investigated.Three kinds of reaction mediums were investigated:1)tert-amyl alcohol with dimethyl sulfoxide microaqueous system,2)tert-amyl alcohol microaqueous system,3)sec-butyl alcohol microaqueous system.Compared to the pure organic phase,the amount of sucrose dissolved in microaqueous system was greatly increased,and the catalytic activity of immobilized surfactant-coated enzyme as well.The reaction system could be widely applied in the industry.