Bridging the immune gap between human milk and infant formula : non-digestible oligosaccharides

Cow-milk based infant formulas are commonly supplemented with non-digestible carbohydrates (NDCs) to resemble the functional properties of oligosaccharides present in human milk. NDCs support the development of a balanced immune system through their direct interaction with immune cells, but also through their fermentation by the gut microbiota. In this thesis, it was investigated how the structure of the NDCs affects the fermentability and the microbiota-dependent immune effects of the NDCs. First, the use of pooled infant faecal inoculum in in vitro fermentation experiments was validated. This fermentation set-up enabled us to efficiently judge the fermentability of 7 structurally different NDCs by faecal microbiota of 2- and 8-week-old infants; galacto-oligosaccharides (GOS), fructo-oligosaccharides, native inulin, enzyme-treated and native oat β-glucan, isomaltose-oligosaccharides (IMO) and isomalto/malto-polysaccharides. The fermentability was dependent on the age of the infants and was negatively correlated with the size of the NDCs. In addition, a characterization method was developed based on ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS) with a stationary phase of porous graphitic carbon (PGC) to study the fate of individual isomers in the infant gut. The application of this method to digesta of GOS and IMO fermentation indicated that e.g. the type of glycosidic linkage, anomeric configuration, monomer composition and substitution of the terminal reducing residue all affect the fermentability of these complex NDCs by infant faecal microbiota. Finally, the incubation of the fermentation digesta with dendritic cells derived from the umbilical vein demonstrated the immune-attenuating effects of the NDCs, which could be linked to the bacteria-derived components and metabolites. The extent of attenuation by the NDCs depended on the age and consequent microbiota composition of the infants as well as the structure of the NDCs. These findings support the use of tailored NDC mixtures for substitution of infant formula to meet the needs of infants of different age