Elegant and Efficient Biotransformation for Dual Production of d-Tagatose and Bioethanol from Cheese 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 degrees C. Compared to the current enzymatic system, only L-AI was overexpressed, because of the unexpectedly thermotolerant fi-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.