In vitro digestion of prebiotic carbohydrates added to milk using a rat intestinal enzyme preparation

Resumen del trabajo presentado a la 10th NIZO Dairy Conference: "Innovations in Dairy Ingredients", celebrada en Papendal (Netherlands) del 1 al 3 de octubre de 2017.Given the huge interest towards the gastrointestinal function and prebiotics, new oligosaccharides with improved properties are being explored, such as those derived from lactulose (OsLu), recently characterized and evaluated. Assays in rats have showed their significantly higher resistance when compared with galactooligosaccharides (GOS), probably ascribed to the terminal monosaccharide (fructose vs glucose). However, no in vitro studies have been done on the digestion of OsLu within a real food. Thus, our aim was to study the effect of a rat small intestinal extract (RSIE) on the hydrolysis of lactose, lactulose (Duphalac®), commercial GOS and OsLu in samples of milk after their gastric digestion in a semi-dynamic model. OsLu and commercial prebiotics were added to milk at the prebiotic dose (5%) and the products were firstly subjected to a gastric digestion. The resulting mixtures were freeze-dried. Samples (5 mg) were later added to 100 mg of RSIE together with 1 mL of distilled water, the reaction was kept at 37' for 2 h taking aliquots after 0, 0.5, 1 and 2 h. Trimethyl-silylated oximes of carbohydrates were determined by GC-FID. Results showed that, under the assayed conditions, lactulose was more resistant than lactose due to the presence of fructose in the molecule. Hydrolysis of oligosaccharides (di-, tri- and tetrasaccharides) from OsLu was lower (15%) as compared to present oligosaccharides in GOS (35%) after 2 h, probably due to the linkage type and the terminal monosaccharide. These finding support a prebiotic role of galactosyl-fructose derivatives (OsLu) in foods, remarking their resistance to digestion not only as a free-ingredient but also as a part of a real food.Peer Reviewe