Whole Conversion of Soybean Molasses into Isomaltulose and Ethanol by Combining Enzymatic Hydrolysis and Successive Selective Fermentations

Abstract

Isomaltulose is mainly produced from sucrose by microbial fermentation, when the utilization of sucrose contributes a high production cost. To achieve a low-cost isomaltulose production, soy molasses was introduced as an alternative substrate. Firstly, α-galactosidase gene from Rhizomucor miehei was expressed in Yarrowia lipolytica, which then showed a galactosidase activity of 121.6 U/mL. Under the effects of the recombinant α-galactosidase, most of the raffinose-family oligosaccharides in soy molasses were hydrolyzed into sucrose. Then the soy molasses hydrolysate with high sucrose content (22.04%, w/w) was supplemented into the medium, with an isomaltulose production of 209.4 g/L, and the yield of 0.95 g/g. Finally, by virtue of the bioremoval process using Pichia stipitis, sugar byproducts in broth were transformed into ethanol at the end of fermentation, thus resulting in high isomaltulose purity (97.8%). The bioprocess employed in this study provides a novel strategy for low-cost and efficient isomaltulose production from soybean molasses.

Whole Conversion of Agro-Industrial Wastes Rich in Galactose-Based Carbohydrates into Lipid Using Oleaginous Yeast Aureobasidium Namibiae

“…Evaluation of lipid producers of the yeast strains from SM Apart from ra nose and stachyose, SM contained high level of conventional sugars, such as glucose, fructose, and sucrose, accounting for more than 40% of total carbohydrates (Wang et al, 2019). These conventional sugars provided enough carbon sources for lipid accumulation of L. starkey and R. toruloides, with the lipid production of 2.42 g/L and 2.51 g/L, respectively (Fig.…”

“…Overall, the carbohydrates in these raw materials above mainly rely on glucose or fructose as monosaccharide unit, which can be easily assimilated. However, some agro-industrial by-products contain plenty of galactose-based carbohydrates, such as lactose and ra nose-family oligosaccharides (RFO) (Wang et al, 2019). The galactoside bonds in the sugars are di cult to break up, thereby leading to limited applications and lowered commercial value.…”

“…The galactoside bonds in the sugars are di cult to break up, thereby leading to limited applications and lowered commercial value. Due to lacking galactosidase synthesis and intracellular galactose assimilation pathway, most oleaginous yeasts cannot naturally consume galactose and RFO (Wang et al, 2019). In addition, construction of galactose metabolic pathways in most yeast was easy to achieve (Mano et al, 2020).…”

“…In addition, construction of galactose metabolic pathways in most yeast was easy to achieve (Mano et al, 2020). The abundant agro-industrial wastes containing galactose-based carbohydrates, such as whey powder (WP) and soy molasses (SM), have not been introduced as carbon source for lipid production (Wang et al, 2019;Mano et al, 2020).…”

“…Owing to the existence of α-(1,6) glycosidic bonds in RFO, SM cannot even be e ciently utilized by nonruminant animals (Wang et al, 2019). WP is a by-product in cheese production with an annual worldwide production of about 165 million tons (Macwan et al, 2016).…”