Efficient and economical biosynthesis of high-purity isomaltulose from sugar industrial waste molasses using an engineered Corynebacterium glutamicum strain

Abstract

Isomaltulose is attracting interest due to its unique health properties, making it an ideal substitute for sucrose. Nevertheless, the industrial production of isomaltulose from sucrose is currently expensive, thus limiting its application. Molasses is an industrial by-product of sugar refining and contains abundant sucrose, which suggests it could be a cost-effective feedstock for manufacturing isomaltulose. Although isomaltulose can be obtained successfully from molasses, the yield and purity reported in previous studies are insufficient for industrial-scale application. To overcome previous disadvantages, a new strategy was devised in this study considering the molasses composition features, where the sucrose component is used for isomaltulose biosynthesis, while the monosaccharides (glucose and fructose) are used as the energy source for strain growth. Further elements of this strategy involved a series of metabolic engineering steps to construct a recombinant Corynebacterium glutamicum strain IS7 with redirected metabolic flux and fine-tuned sucrose isomerase (SIase) activity. Under the optimum conditions, the maximum production of isomaltulose using the engineered strain IS7 was 170.1 g L⁻¹ with a yield of 0.97 g/g with cane molasses as substrate, and 167.0 g L⁻¹ with a yield of 0.97 g/g with beet molasses as substrate, after 72 h fermentation. Moreover, isomaltulose purity was 98% using either cane or beet molasses as substrate. Therefore, this study may provide a robust foundation for efficient industrial-scale bioproduction of high-purity isomaltulose from low-cost cane and beet molasses using the recombinant strain IS7. Moreover, it validates the concept of the sustainable conversion of agricultural residues by biosynthesis to high-value-added products.