State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi 214122, China.
Department of Microbiology, College of Life Sciences, Key Laboratory for Microbiological Engineering of Agricultural Environment of the Ministry of Agriculture, Nanjing Agricultural University, 6 Tongwei Road, Nanjing, Jiangsu 210095, China.
J Dairy Sci. 2018 Mar;101(3):1872-1882. doi: 10.3168/jds.2017-12936. Epub 2017 Dec 28.
Lactose is a main by-product in the cheese industry. Many attempts have been made to convert the lactose to high value-added products, including epilactose. Epilactose is a valuable prebiotic and can be epimerized from lactose with cellobiose 2-epimerase (CEase). The objective of the present work was to construct a food-grade recombinant Bacillus subtilis that produces CEase from Thermoanaerobacterium saccharolyticum. The CEase was expressed in B. subtilis without antibiotic resistance genes. After fermentation, the maximum volumetric activity of the fermented broth was more than 7 U/mL. The activity of the recombinant B. subtilis was increased by up to 3.7 fold after ethanol permeabilization. Then, 66.9 ± 0.7 g/L of epilactose was produced from 300 g/L of whey powder solution in 1 h with 13.3 U/mL of permeabilized biocatalyst. In addition, an enzymatic route including degradation of the lactose, yeast fermentation, and cation exchange chromatography was described to further purify the produced epilactose from lactose. Finally, epilactose with a purity >98% was produced from 300 g/L of lactose with a yield of 24.0%. In conclusion, neither antibiotics nor pathogenic bacteria were used throughout the epilactose production and purification procedure.
乳糖是奶酪工业的主要副产物。人们已经尝试了许多方法将乳糖转化为高附加值产品，包括表乳糖。表乳糖是一种有价值的益生元，可以通过纤维二糖 2-差向异构酶（CEase）从乳糖中差向异构化得到。本工作的目的是构建一种能够从热解糖丝菌生产 CEase 的食品级重组枯草芽孢杆菌。CEase 在不含有抗生素抗性基因的枯草芽孢杆菌中表达。发酵后，发酵液的最大比体积酶活超过 7 U/mL。经过乙醇渗透处理后，重组枯草芽孢杆菌的酶活提高了 3.7 倍。然后，在 1 小时内，用 13.3 U/mL 的渗透生物催化剂从 300 g/L 的乳清粉溶液中生产出 66.9±0.7 g/L 的表乳糖。此外，还描述了一种包括乳糖降解、酵母发酵和阳离子交换色谱的酶法途径，以进一步从乳糖中纯化所产生的表乳糖。最终，从 300 g/L 的乳糖中以 24.0%的收率生产出纯度>98%的表乳糖。总之，在表乳糖的生产和纯化过程中既不使用抗生素也不使用致病菌。
