Degradation of structurally different non-digestible oligosaccharides by intestinal bacteria: glycosylhydrolases of Bifidobacterium adolescentis = Afbraak van in structuur verschillende niet-verteerbare oligosacchariden door darmbacteriën : glycosylhydrolasen van Bifidobacterium adolescentis

<p>Non-digestible oligosaccharides (NDOs) are oligosaccharides, which resist digestion in the upper gastrointestinal tract, and which are fermented in the colon by intestinal bacteria. Some NDOs are considered bifidogenic, meaning that they selectively stimulate the growth of bifidobacteria in the colon microbiota. The degradative fermentation of structurally different oligosaccharides by intestinal bacteria was studied in this thesis, in order to establish the potentially bifidogenic effects of various types of NDOs. Structurally different oligosaccharides were produced using different routes. Arabino-, (arabino-)galacto-, (arabino-)xylo-, galacturono-, and rhamnogalacturono- oligosaccharides were derived by enzymatic hydrolysis of plant polysaccharides. Through transglycosylation reactions using glycosidases, transgalactooligosaccharides of theα- andβ-glycosyl linkage type were obtained.</p><p>The chemical structure of the oligosaccharides clearly influenced their fermentation behaviour. It was concluded that species belonging to different groups, so not only bifidobacteria, have the capability of hydrolysing these oligosaccharides. <em>Bi. adolescentis,</em> being a major bifidobacterial species of the adult intestinal microflora, was able to utilise a wide range of oligosaccharides showing its wide range of glycosidases. Two novel arabinoxylan degrading enzymes were purified from <em>Bi. adolescentis</em> and these enzymes in combination with aβ-xylosidase are involved in the complete degradation of arabinoxylooligosaccharides. For the utilisation ofα-galactooligosaccharides <em>Bi. adolescentis</em> produced anα-galactosidase. Thisα-galactosidase was characterised as a retaining glycosidase and was used for the production of new types ofα-galactooligosaccharides. Theseα-1→6 linked-galactooligosaccharides could be utilised by various strains belonging to bifidobacteria and lactobacilli. Upon growth of <em>Bi. adolescentis</em> on transgalactooligosaccharides (TOS) a novelβ-galactosidase was produced, involved in the degradation of TOS. It was speculated that this enzyme was membrane or cell wall associated. After growth of <em>Bi. adolescentis</em> on TOS or on hydrolysed arabinogalactan theβ-galactosidase production of <em>Bi. adolescentis</em> increased compared to growth on galactose and this increasedβ-galactosidase activity could be linked to increased activity towards both polymeric and oligomeric galactan. <em>In vivo</em> dietary intervention with TOS also resulted in increased levels of v-galactosidase activity in feces. Although the nature and specificity of theβ-galactosidase is not yet known it can be concluded that glycosidase activity of the intestinal bacteria might be a useful biomarker of the colonic metabolic activity.</p&gt