Bioactive components of fermented soya beans effective against diarrhoea-associated bacteria

Tempe is a fermented food, obtained by fungal fermentation of soya beans. During the processing specific flavour, texture and nutritional properties are achieved. Previous research has indicated that tempe reduced the incidence and severity of diarrhoea. In this thesis the bioactive effects of tempe on diarrhoea-associated bacteria are described. Tempe appeared to be antibacterial against Bacillus cereus cells and spores, but not against enterotoxigenic Escherichia coli (ETEC). Nevertheless, tempe was found to inhibit the adhesion of ETEC to intestinal epithelial cells. Experiments showed that the inhibition of adhesion was caused by an interaction between ETEC and tempe extracts. A range of ETEC strains was shown to be sensitive for the anti-adhesive component, making the bioactivity of broader interest for applications in feed matrices. Furthermore, several substrates (legumes and cereals) were fermented and all fermented legumes tested were equally bioactive as the fermented soya beans, whereas the fermented cereals were not active. The use of different starter cultures showed that Bacillus spp., moulds and some yeasts were capable to release or form the bioactive component during fermentation, thus the bioactivity was not specific for one microbial species. After heating, defatting and protease treatment of the bioactive tempe extracts, they remained bioactive. On the contrary, after treatment with polysaccharide degrading enzyme mixtures the bioactivity was lost. This suggests that the bioactive component contains carbohydrates, and explains the interaction between ETEC and tempe extracts, which could indeed be established by carbohydrates of the tempe extract. Ultra-filtration revealed the bioactive component to have molecular masses >30 kDa. Further purification yielded an active fraction with an increased carbohydrate content. Monosaccharide analysis showed the importance of arabinose in the bioactive components. In conclusion, the bioactive component is released or formed during fermentation by enzymatic degradation of legumes. The bioactive component is of carbohydrate nature and contains arabinose, which originates from arabinan or arabinogalactan chains of the pectic cell wall polysaccharides of legumes.