Monitoring the degradation of individual dietary fibres in pig models

In this thesis, the degradation of dietary fibres in the gastrointestinal tract, especially in the large intestine, is monitored using in vitroand in vivostudies. First, an in vitromethod to simulate the conditions in the mouth, stomach and small intestine was adapted for food products, which were used in an in vivosatiation study as well. Alginate, a dietary fibre that is able to form a gel under stomach conditions, was found to be more satiating than cellulose and guar gum. Next, in vitrofermentation were performed in addition to in vivostudies using pigs as models for humans. The rates and products of dietary fibre fermentation depend on the constituent monosaccharide and linkage compositions, degree of polymerisation and molecular conformation of the dietary fibres, as well as on the adaptability of the microbiota to the dietary fibres. The dietary fibres investigated in the in vivopig studies included resistant starch, alginate and non-starch polysaccharides (NSPs) from other feed components. The large intestinal digesta and faecal samples were analysed to study how dietary fibres are degraded in the large intestine. Resistant starch was found to be preferred by the microbiota over NSPs. Hence, the utilisation of NSPs was delayed in the presence of resistant starch. The alginate used in the study was not fully utilised by the microbiota and more than 40 %(w/w) of the alginate intake was excreted in the faeces. The degradation products of alginate included an insoluble alginate fraction with increased guluronic acid content compared to the parental alginate. In addition, alginate oligosaccharides were formed. The time needed by the microbiota to adapt to different dietary fibres varied. For resistant starch, two weeks of adaptation was sufficient, but more than 39 days was required to adapt to alginate. The fermentability differences among diverse dietary fibres led to the conclusion that consumption of a changing diet containing various dietary fibres may ensure that fermentation occurs throughout the colon.