Production and purification of fructo-oligosaccharides using an enzyme membrane bioreactor and subsequent fermentation with probiotic Bacillus coagulans

Fructo-oligosaccharides (FOS) are low-calorie sweeteners that can be synthesized by the transfructosylation of sucrose using enzymes known as fructosyltransferases. However, enzymatic conversion is inhibited by the accumulation of glucose as a byproduct, which limits the conversion rate and yield. We therefore developed a semi-continuous production process in an enzyme membrane bioreactor (EMBR) system followed by fermentation with the probiotic bacterium Bacillus coagulans. Filtration experiments were conducted in total recycle mode to evaluate membrane fouling using the resistance-in-series model. We found that fouling was predominantly caused by the accumulation of proteins at the membrane surface, which accounted for 29.6–95.5% of the total filtration resistance depending on the conditions. Using these data, we were able to achieve a stable filtration flux that fulfilled the requirements of the EMBR system by regulating the filtration parameters. The average concentration of total FOS in the products of EMBR reached 270 g·L−1, which was 4.6% higher than the batch process. Subsequently, the crude FOS preparation was treated by fed-batch fermentation with B. coagulans. The monosaccharides in the reaction mix (glucose and fructose) were completely removed, increasing the concentration of FOS to 195.9 g·L−1 and the purity to 96.6%.