Enzymatic synthesis of lactulose in fed-batch operation

Abstract

Lactulose can be synthesized by a kinetically controlled reaction of fructose transgalactosylation with lactose, catalyzed by food-grade β-galactosidase; however the enzyme catalyzes also the synthesis of other transgalactosylated oligosaccharides (TOS), namely galactooligosaccharides (GOS) and fructosylgalactooligosaccharides (fGOS), besides catalyzing the hydrolysis of lactose. Proposed reaction scheme for lactulose and TOS synthesis is in Figure 1. v Productivity not lower than 80% of the one obtained in batch and selectivity higher by at least 10% with respect to batch operation were defined as criteria for selecting fedbatch operation conditions. Then, according to results summarized in Table 1, best conditions for lactulose synthesis within the ranges of variables considered were F/ L=8 and FFR=6 mL/min. Conclusions Acknowledgement Fed-batch synthesis of lactulose from fructose and lactose appears as a plausible strategy that allows maintaining the concentration of substrates under control by proper feeding, which may improve enzyme performance. A high fructose/lactose ratio can be obtained in the reactor by feeding low amounts of lactose so that lactulose synthesis should prevail over TOS, increasing process selectivity (Guerrero et al., Biores Technol 237:126, 2017). This work evaluates the effect of fructose/lactose molar (F/L) and feed flow-rate (FFR) on the enzymatic synthesis of lactulose in fed-batch operation. Results are compared with those obtained in conventional batch operation.