␤-Galactosidase enzymes were extracted from pure cultures of Bifidobacterium angulatum, B. bifidum BB-12, B. adolescentis ANB-7, B. infantis DSM-20088, and B. pseudolongum DSM-20099 and used in glycosyl transfer reactions to synthesize oligosaccharides from lactose. At a lactose concentration of 30% (wt/wt) oligosaccharide yields of 24.7 to 47.6% occurred within 7 h. Examination of the products by thin-layer chromatography and methylation analysis revealed distinct product derived spectra from each enzyme. These were found to be different to that of Oligomate 55, a commercial prebiotic galacto-oligosaccharide. Fermentation testing of the oligosaccharides showed an increase in growth rate, compared to Oligomate 55, with products derived from B. angulatum, B. bifidum, B. infantis, and B. pseudolongum. However B. adolescentis had a lower growth rates on its oligosaccharide compared with Oligomate 55. Mixed culture testing of the B. bifidum BS-4 oligosaccharide showed that the overall prebiotic effect was equivalent to that of Oligomate 55.Oligosaccharides are increasingly being recognized as useful dietary tools for the modulation of the colonic microflora toward a healthy balance (8). This usually involves selectively increasing the levels of gut bifidobacteria and lactobacilli at the expense of less-desirable organisms such as Escherichia coli, clostridia, and proteolytic bacteroides. This selective fermentation is known as the prebiotic concept defined by Gibson and Roberfroid (9).Although many oligosaccharide preparations are used in functional foods in Japan (17), two general classes are widely used in Europe. These are fructans, such as inulin and fructooligosaccharides, and ␤-galacto-oligosaccharides (17, 18, 22). The latter are manufactured from lactose by glycosyl transfer catalyzed by ␤-galactosidase and occur as complex mixtures with various glycosidic linkages (7). The commercial products are made using ␤-galactosidases isolated from several sources such as bacteria and fungi (5, 7). The prebiotic properties of these galacto-oligosaccharides have been established in several studies, both in vitro (21) and in vivo (11). The consensus is that the substrates have a selective stimulatory effect on bifidobacteria.Despite the interest in galacto-oligosaccharides as prebiotics, there has been very little effort made to study the relative effects of products synthesized by different glycosidases. Given that the ␤-galactosidase enzymes from different micro-organisms display differing rate constants for hydrolysis for specific glycosidic linkages and that synthesis of galacto-oligosaccharides is kinetically controlled, synthetic product mixtures made with different enzymes are likely to contain differing profiles of FIG. 1. pH optima of cell-associated ␤-galactosidase and lactase activities of Bifidobacterium angulatum. Cells were harvested after 18 h of growth on 10 g of lactose liter Ϫ1 ; lactase activity (s) was determined using lactose as the substrate (1 mol of glucose released min Ϫ1 mg of protein Ϫ1 ), an...

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The human large intestine is recognised as a physiologically important organ responsible for the conservation of water and salts. Through its resident bacteria, it is also capable of complex, enzyme catalysed, hydrolytic-digestive functions that have a high biological impact on the host. These microorganisms metabolise dietary components, principally complex carbohydrates that are not hydrolysed or absorbed in the upper gastrointestinal tract, and in this way, sequester energy for the host, through fermentation. This process involves a series of anaerobic, energy-yielding, catabolic reactions which complete digestive processes in the gut, resulting in end products that in turn influence the distribution of microbial species present as well as having some systemic effects. Some of the bacteria are thought to possess important health-promoting activities, especially with respect to their influence on mucosal and systemic immune responses to disease. These bioactivities can be modulated by substrates that support and influence microbial development, growth and survival. For these reasons, it is necessary to review dietary factors that may delimit bacterial diversity, to be able to predict responses and sensitivities to various environmental pressures and manipulations that occur in this area of human microbiology.

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