State Key Laboratory of Materials-Oriented Chemical Engineering, College of Food Science and Light Industry, Nanjing University of Technology , 30 Puzhu South Road, Nanjing 211816, People's Republic of China.
J Agric Food Chem. 2014 Mar 19;62(11):2412-7. doi: 10.1021/jf4042485. Epub 2014 Mar 5.
The functional sweetener, d-tagatose, is commonly transformed from galactose by l-arabinose isomerase. To make use of a much cheaper starting material, lactose, hydrolization, and isomerization are required to take place collaboratively. Therefore, a single-step method involving β-d-galactosidase was explored for d-tagatose production. The two vital genes, β-d-galactosidase gene (lacZ) and l-arabinose isomerase mutant gene (araA') were extracted separately from Escherichia coli strains and incorporated into E. coli simultaneously. This gave us E. coli-ZY, a recombinant producing strain capable of coexpressing the two key enzymes. The resulted cells exhibited maximum d-tagatose producing activity at 34 °C and pH 6.5 and in the presence of borate, 10 mM Fe(2+), and 1 mM Mn(2+). Further monitoring showed that the recombinant cells could hydrolyze more than 95% lactose and convert 43% d-galactose into d-tagatose. This research has verified the feasibility of single-step d-tagatose fermentation, thereby laying down the foundation for industrial usage of lactose.
功能甜味剂 D-塔格糖通常由 L-阿拉伯糖异构酶将半乳糖转化而来。为了利用更便宜的起始原料乳糖，需要协同进行水解和异构化。因此，探索了一种涉及β-D-半乳糖苷酶的一步法生产 D-塔格糖。从大肠杆菌菌株中分别提取了两个关键基因，β-D-半乳糖苷酶基因（lacZ）和 L-阿拉伯糖异构酶突变体基因（araA'），并同时将它们整合到大肠杆菌中。这给了我们 E. coli-ZY，一种能够共表达两种关键酶的重组生产菌株。所得细胞在 34°C 和 pH6.5 以及硼酸盐、10mMFe（2+）和 1mM Mn（2+）存在下表现出最大的 D-塔格糖生产活性。进一步的监测表明，重组细胞可以水解超过 95%的乳糖，并将 43%的 D-半乳糖转化为 D-塔格糖。这项研究验证了一步法 D-塔格糖发酵的可行性，为乳糖的工业应用奠定了基础。
