An efficient process for obtaining prebiotic oligosaccharides derived from lactulose using isomerized and purified whey permeate

Abstract

[Background]: One of the most promising uses of whey permeate (WP) is the synthesis of prebiotic oligosaccharides. Herein, commercial WP was submitted to chemical isomerization catalysed by sodium borate at an alkaline pH and subsequent purification using anion-exchange resins to remove boron. Subsequently, purified mixtures were used to synthesize prebiotic oligosaccharides using β-galactosidase from Bacillus circulans. [Results]: Isomerization of concentrated WP (200 g L−1 lactose) gave rise to levels of lactulose up to 155.5 g L−1 after 30 min of reaction (molar ratio of boron/lactose, 1/1; pH 12; 70 °C). Boron was removed from the isomerized WP (IWP) using the combination of a strong acid (IR-120, H+) and a weak base (IRA-743) anion-exchange resins, reducing its level to <1 ppm, without loss of lactulose. During the transglycosylation reaction of purified IWP (lactose/lactulose ratio, 1/2.4) maximum content of prebiotic compounds was achieved, i.e. 690 g kg−1 WP after 3 h of reaction. [Conclusion]: This study shows that combined chemical–enzymatic reactions together with the purification of IWP results in an efficient synthesis of prebiotic oligosaccharides.