초록
<P>In this study, the dual production of valuable <SMALL>D</SMALL>-tagatose and bioethanol from lactose and cheese whey powder is presented. First, a one-pot biosynthesis involving lactose hydrolysis and <SMALL>D</SMALL>-galactose isomerization for <SMALL>D</SMALL>-tagatose production was established using crude enzymes of recombinant <I>Escherichia coli</I> with <SMALL>L</SMALL>-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 <I>E. coli</I> BL21(DE3). Moreover, this high temperature rendered the <SMALL>D</SMALL>-glucose catabolism of <I>E. coli</I> inactive, while retaining all fermentable sugars for bioethanol fermentation. Thereafter, the mixed sugar syrup was fermented by <I>Saccharomyces cerevisiae</I> NL22. A total of 23.5 g/L <SMALL>D</SMALL>-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 <SMALL>D</SMALL>-tagatose and bioethanol.</P><BR>[FIG OMISSION]</BR>