【作者】 汪明明； 杨瑞金； 华霄； 沈秋云； 张文斌； 赵伟；

【Author】 Mingming Wang;Ruijin Yang;Xiao Hua;Qiuyun Shen;Wenbin Zhang;Wei Zhao;School of Food Science and Technology,Jiangnan University;

【机构】 江南大学食品学院；

【摘要】 Caldicellulosiruptor saccharolyticus纤维二糖差向异构酶（CsCE）能够催化单一底物乳糖异构化生成乳果糖,是目前已知的酶法合成乳果糖中最为高效的酶。而全细胞生物催化剂相较于游离酶,在很多生物转化过程中具有明显的优势。本实验旨在制备一种透性化CsCE全细胞生物催化剂,并应用于催化乳糖生产乳果糖。研究结果表明:乙醇是一种高效的细胞透化试剂,能够有效破除细胞膜对酶与底物接触的阻碍作用。经40%（v/v）乙醇处理15 min后的产CsCE细胞冻干后直接作为全细胞生物催化剂。在乳糖浓度600g/L,80℃,pH 7.5,生物催化剂添加量12.5 U/mL的条件下,在不同缓冲液中经2 h反应后,最终在Na₂HPO₄-NaH₂PO₄缓冲液中乳果糖转化效率最高,乳果糖浓度达到390.59 g/L,生产率为195.3 g/（L·h）,乳糖转化率达到65.1%。同时研究还表明,Na₂HPO₄-NaH₂PO₄缓冲液能促进乳果糖的转化,同时降低副产物依匹乳糖的生成,最终体系中依匹乳糖的含量仅为11.7 g/L,转化率小于2%。本实验为酶法制备高纯度乳果糖提供了一种新的途径,有助于工业上早日实现高产量、高转化率以及高纯度乳果糖的酶法生产。更多还原

【Abstract】 Caldicellulosiruptor saccharolyticuscellobiose 2-epimerase（CsCE） catalyzes the single substrate lactose into lactulose and is the most efficient enzyme ever found for the enzymatic synthesis of lactulose.Biocatalysts in the form of whole cells have advantages over purified enzymes in many industrial bioconversion processes.This study is concerned with the preparation of freeze dried ethanol permeabilized cells containing CsCE and their use as biocatalysts for lactulose production.The results show that ethanol was efficient for permeabilizing cells and can reduce the permeability barrier.After being treated with 40%（v/v） ethanol for 15 min,the permeabilized cells were freeze dried and stored at 4℃ before being used as a biocatalyst for lactulose production.The reaction conditions were optimized to be 600 g/L lactose,pH 7.5,80℃ and12.5 U/mL of biocatalyst.After incubated at different buffers for 2 h,the maximum lactulose production were obtained in Na₂HPO₄-NaH₂PO₄ buffer and approximately 390.59 g/L lactulose was achieved with a conversion yield of 65.1%and a productivity of 195.3 g/（L · h）.Na₂HPO₄-NaH₂PO₄ buffer can reduce epilactose yield thus increase lactulose production.The lowest production and conversion yield of epilactose in Na₂HPO₄-NaH₂PO₄ buffer were 11.7 g/L with a conversion yield less than 2%.The results represent a promising technology to attain high production and conversion yield of lactulose with a high purity on industrial scale.更多还原