In vitro digestion and fermentation of sialyllactoses by infant gut microflora

• SLs were partly degraded under acidic condition of infant stomach.
• Major part of SLs can reach the large intestine thereafter.
• SLs mediate beneficial prebiotic effects in the large intestine.
• SLs are one of the important bifidogenic components in HMO.

Sialyllactoses (SLs) are acidic components of human milk oligosaccharides. To investigate their prebiotic effects in infants, their digestibility in the gastrointestinal tract and fermentability in the colon were analysed in vitro. When 2,3-SL (3'-SL) and 2,6-SL (6'-SL) were incubated under stomach and small intestinal conditions, they were slightly hydrolysed (8.21% of 3'-SL and 15.09% of 6'-SL) at pH 2.0. Meanwhile, when they were individually incubated with beneficial and harmful intestinal bacteria (24 strains), Bifidobacterium infantis, B. bifidum, and Bacteroides vulgatus utilised SLs for their growth. Furthermore, when SLs were incubated in the pH-controlled batch fermenter with an infant faecal sample, the population of the bifidobacteria significantly increased and short-chain fatty acids with lactate were synthesised. The present study demonstrates that, when infants take in mother's milk, a small fraction of SLs is hydrolysed in the stomach, whereas the majority travel to the colon to mediate beneficial prebiotic effects.