Abbreviations
GDH, galactitol dehydrogenase; GRAS, generally recognized as safe;
GS-linker, glycine–serine linker; IPTG,
isopropyl-beta-D-thiogalactopyranoside; NAD(H), nicotinamide adenine
dinucleotide; NADP(H), nicotinamide adenine dinucleotide phosphate;
non-GMO, nongenetically modified organism; Pd PDH, polyol
dehydrogenase from Paracoccus denitrificans ; WP, whey powder; XR,
aldose reductase.
Abstract:
We designed and constructed a green, sustainable, and nongenetically
modified organism (non-GMO) bioprocess to efficiently coproduceD-tagatose, bioethanol, and microbial protein from whey
powder. First, a one-pot biosynthesis process involving lactose
hydrolysis and D-galactose redox reactions forD-tagatose production was established in vitrovia a three-enzyme cascade. Second, a nicotinamide adenine dinucleotide
phosphate-dependent galactitol dehydrogenase mutant, D36A/I37R, based on
the nicotinamide adenine dinucleotide-dependent polyol dehydrogenase
from Paracoccus denitrificans was created through
rational design and screening.
Moreover, an NADPH recycling module was created in the oxidoreductive
pathway, and the tagatose yield increased by 3.35-fold compared with
that achieved through the pathway without the cofactor cycle. The
reaction process was accelerated using an enzyme assembly with a
glycine–serine linker, and the tagatose production rate was 9.28-fold
higher than the initial yield. Finally, Saccharomyces cerevisiaewas introduced into the reaction solution, and 266.5 g ofD-tagatose, 371.3 g of bioethanol, and 215.4 g of dry
yeast (including 38% protein) were obtained from 1 kg of whey powder
(including 810 g lactose). This study provides a promising non-GMO
process for functional food (D-tagatose) production.
Moreover, this process fully utilized whey powder, demonstrating good
atom economy.