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Elegant and Efficient Biotransformation for Dual Production of d-Tagatose and Bioethanol from Cheese Whey Powder

Zheng, Zhaojuan, Xie, Jiaxiao, Liu, Peng, Li, Xin, Ouyang, Jia
Journal of agricultural and food chemistry 2019 v.67 no.3 pp. 829-835
Escherichia coli, Saccharomyces cerevisiae, arabinose, beta-galactosidase, bioethanol, bioprocessing, biosynthesis, biotransformation, byproducts, cheese whey, ethanol fermentation, galactose, glucose, heat tolerance, hydrolysis, isomerases, isomerization, lactose, syrups, tagatose, temperature, whey, whey powder
In this study, the dual production of valuable d-tagatose and bioethanol from lactose and cheese whey powder is presented. First, a one-pot biosynthesis involving lactose hydrolysis and d-galactose isomerization for d-tagatose production was established using crude enzymes of recombinant Escherichia coli with l-arabinose isomerase (L-AI) at 50 °C. Compared to the current enzymatic system, only L-AI was overexpressed, because of the unexpectedly thermotolerant β-galactosidase in E. coli BL21(DE3). Moreover, this high temperature rendered the d-glucose catabolism of E. coli inactive, while retaining all fermentable sugars for bioethanol fermentation. Thereafter, the mixed sugar syrup was fermented by Saccharomyces cerevisiae NL22. A total of 23.5 g/L d-tagatose and 26.9 g/L bioethanol was achieved from cheese whey powder containing 100 g/L lactose. This bioprocess not only provides an efficient method for the functionalization of byproduct whey, but also offsets the high production cost of d-tagatose and bioethanol.