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

Zhi-Peng Wang,Song Liu,Xin-Jun Yu,Xiao-Yan Liu,Lin-Lin Zhang

doi:10.3390/biom9080353

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.

Highlights

Isomaltulose is a kind of structural isomer of sucrose and natural reducing disaccharide
After the treatments by P. stipitis, isomaltulose accounted for 97.8% of the total sugars, much higher than the proportions of generally below 90% in other isomaltulose productions
The sucrose content in the soy molasses was increased to 22.04% (w/w) by α-galactosidase hydrolysis

Summary

Introduction

Isomaltulose is a kind of structural isomer of sucrose and natural reducing disaccharide. Isomaltulose shares similar physical and organoleptic properties with sucrose, it has been approved as a safer sucrose substitute with advantages including slower release and absorption, higher stability, lower plasma glucose and insulin concentrations [1,2,3]. Due to low hygroscopicity, acid stability and reducing properties, isomaltulose can be used to produce food and industrial products, like instant powder products, sports beverages, and isomaltitol [4,5,6]. Since chemical synthesis of isomaltulose is accompanied with some byproducts that are difficult to remove, bacterial fermentation became the primary technology adopted in industrial isomaltulose synthesis [7,8]. Bacterial fermentation faced two weaknesses: strain safety and low production efficiency. Expressing SIase genes in food-grade hosts previously received more attention in order to solve the weaknesses [9]. Some non-invasive and non-pathogenic microbes, like Lactococcus lactis, Bacillus subtilis, Saccharomyces cerevisiae, and Yarrowia lipolytica, have

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Conclusion