Abstract
This work highlights the utility of brush border membrane vesicles (BBMV) from the pig small intestine as a reliable model for gathering information about the reaction mechanisms involved in the human digestion of dietary carbohydrates. Concretely, the elucidation of the transgalactosylation mechanism of pig BBMV to synthesize prebiotic galacto-oligosaccharides (GOS) is provided, unravelling the catalytic activity of mammalian small intestinal β-galactosidase towards the hydrolysis of GOS. This study reveals that pig BBMV preferably synthesizes GOS linked by β-(1 → 3) bonds, since major tri- and disaccharide were produced by the transfer of a galactose unit to the C-3 of the non-reducing moiety of lactose and to the C-3 of glucose, respectively. Therefore, these results point out that dietary GOS having β-(1 → 3) as predominant glycosidic linkages could be more prone to hydrolysis by mammalian intestinal digestive enzymes as compared to those linked by β-(1 → 2), β-(1 → 4), β-(1 ↔ 1) or β-(1 → 6). Given that these data are the first evidence on the transglycosylation activity of mammalian small intestinal glycosidases, findings contained in this work could be crucial for future studies investigating the structure-small intestinal digestibility relationship of a great variety of available prebiotics, as well as for designing tailored fully non-digestible GOS.
Highlights
Since prebiotics were first defined as “non-digestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, improving host health”[1], a considerable number of carbohydrates varying in monosaccharides composition and order, configuration and position of glycosidic linkages have been proposed as potential prebiotics
Especially β-galactosidase, gradually decrease during aging of mammals, the high physiological and anatomical similarity of the pig and human digestive tracts[13,14] makes the use of brush border membrane vesicles (BBMV) of the pig small intestine an ideal model for gathering information about the reaction mechanisms involved in the human digestion of GOS as it has been previously demonstrated for the digestion of HMOs15
The three isolated individual pig small intestinal BBMV showed a considerable transgalactosylation activity under the experimental conditions used in this study, allowing the efficient synthesis of GOS with degree of polymerization (DP) 2 and 3 (Fig. 1B–D)
Summary
Since prebiotics were first defined as “non-digestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, improving host health”[1], a considerable number of carbohydrates varying in monosaccharides composition and order, configuration and position of glycosidic linkages have been proposed as potential prebiotics. There are some in vivo studies performed with neonatal and growing rats showing that GOS are selectively digested in the small intestine[7,8], challenging the assumption that GOS reach the colon with their original structure fully intact. Especially β-galactosidase, gradually decrease during aging of mammals, the high physiological and anatomical similarity of the pig and human digestive tracts[13,14] makes the use of brush border membrane vesicles (BBMV) of the pig small intestine an ideal model for gathering information about the reaction mechanisms involved in the human digestion of GOS as it has been previously demonstrated for the digestion of HMOs15. The structure-function information obtained in this study may lead to a predictive understanding about specific GOS structures that can resist the small intestinal digestion
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