State Key Laboratory of Food Science & Technology and School of Food Science and Technology, Jiangnan University, 1800 Lihu Avenue, Wuxi 214122, Jinangsu, China.
Food Chem. 2012 Dec 1;135(3):1547-54. doi: 10.1016/j.foodchem.2012.05.115. Epub 2012 Jun 9.
The enzymatic transgalactosylation of lactose in the presence of fructose using β-galactosidase from Kluyveromyces lactis (KlβGal) leading to the formation of oligosaccharides was investigated in detail. The reaction mixture was analyzed by high performance liquid chromatography with differential refraction detector (HPLC-RI) and two main transgalactosylation products were discovered. To elucidate their overall structures, the products were isolated and purified using preparative liquid chromatography and analyzed by LC/MS, one-dimensional (1D) and two-dimensional (2D) NMR studies. Allo-lactulose(β-d-galactopyranosyl-(1→1)-d-fructose) with two main isomers in D(2)O was identified to be the major transgalactosylation product while lactulose(β-d-galactopyranosyl-(1→4)-d-fructose) turned out to be the minor one, indicating that KlβGal was regioselective with respect to the primary C-1 hydroxyl group of fructose. The maximum yields of allo-lactulose and lactulose were 47.5 and 15.4g/l, respectively, at 66.5% lactose conversion (200g/l initial lactose concentration).
在果糖存在的条件下，利用来源于乳糖克鲁维酵母（KlβGal）的β-半乳糖苷酶对乳糖进行酶法转半乳糖反应，生成低聚糖。详细研究了该反应。通过高效液相色谱-差示折光检测器（HPLC-RI）对反应混合物进行分析，发现了两种主要的转半乳糖反应产物。为了阐明它们的总体结构，使用制备液相色谱对产物进行分离和纯化，并通过 LC/MS、一维（1D）和二维（2D）NMR 研究进行分析。在 D（2）O 中，鉴定出两种主要异构体的异乳糖（β-d-半乳糖吡喃糖苷基-（1→1）-d-果糖）是主要的转半乳糖反应产物，而乳果糖（β-d-半乳糖吡喃糖苷基-（1→4）-d-果糖）则是次要产物，这表明 KlβGal 对果糖的 C-1 羟基具有区域选择性。在 66.5%乳糖转化率（初始乳糖浓度为 200g/l）下，异乳糖和乳果糖的最大产率分别为 47.5 和 15.4g/l。
