Kinetics and Metabolism of Bifidobacterium adolescentis MB 239 Growing on Glucose, Galactose, Lactose, and Galactooligosaccharides

Abstract

The kinetics and the metabolism of Bifidobacterium adolescentis MB 239 growing on galactooligosaccharides (GOS), lactose, galactose, and glucose were investigated. An unstructured unsegregated model for growth in batch cultures was developed, and kinetic parameters were calculated with a recursive algorithm. The growth rate and cellular yield were highest on galactose, followed by lactose and GOS, and were lowest on glucose. Lactate, acetate, and ethanol yields allowed the calculation of carbon fluxes toward fermentation products. Distributions between two-and three-carbon products were similar on all the carbohydrates (55 and 45%, respectively), but ethanol yields were different on glucose, GOS, lactose, and galactose, in decreasing order of production. Based on the stoichiometry of the fructose-6-phosphate shunt and on the carbon distribution among the products, the ATP yield was calculated. The highest yield was obtained on galactose, while the yields were 5, 8, and 25% lower on lactose, GOS, and glucose, respectively. Therefore, a correspondence among ethanol production, low ATP yields, and low biomass production was established, demonstrating that carbohydrate preferences may result from different distributions of carbon fluxes through the fermentative pathway. During the fermentation of a GOS mixture, substrate selectivity based on the degree of polymerization was exhibited, since lactose and the trisaccharide were the first to be consumed, while a delay was observed until longer oligosaccharides were utilized. Throughout the growth on both lactose and GOS, galactose accumulated in the cultural broth, suggesting that ␤(1-4) galactosides can be hydrolyzed before they are taken up.Many nondigestible oligosaccharides, such as fructooligosaccharides, isomaltooligosaccharides, galactooligosaccharides (GOS), and xylooligosaccharides, have been reported to beneficially affect human health. They are defined as prebiotics and are increasingly being used as functional food ingredients (18). ␤-GOS are manufactured from highly concentrated lactose solutions by the action of ␤-galactosidases (␤-Gals) which have transgalactosylation activity. In standardized large-scale production, trisaccharides to hexasaccharides are the main products; hence, commercial GOS occur as mixtures of various degrees of polymerization (DP) and glycosidic linkages and contain large amounts of glucose and unreacted lactose. The linkage between galactose moieties (mainly ␤1-4, ␤1-6, and ␤1-3), the efficiency of transgalactosylation, and the components in the final product depend upon the enzymes and the reaction conditions (3,7,25,30,34,39,41).As demonstrated in several in vitro and in vivo studies (5, 40), GOS resist hydrolysis by human digestive enzymes and are not absorbed on transit through the small intestine; therefore, they are available for fermentation by the colon-resident microflora. The utilization of GOS by the major intestinal bacteria has been investigated (25,34,46). It was shown that ␤1-4-linked oligosaccharides were selectivel...

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