Profile and content of sialylated oligosaccharides in donkey milk at early lactation

Animal milk oligosaccharides can be used as bioactive ingredients in functional foods and infant milk formulas. Donkey milk is already considered a functional food and a possible substitute for human milk. The aim of this study was to identify the structure and abundance of sialylated milk oligosaccharides from five Amiata donkeys during four different stages of early lactation. Liquid chromatography combined with mass spectrometry analysis led to the identification and quantification of seven sialylated oligosaccharides: 3'-sialyllactose, 6'-sialyllactose, sialyllacto-N-tetraose a, sialyllacto-N-tetraose b, sialyllacto-N-tetraose c, Neu5Ac(α2–3) + Gal(β1–4)GlcNAc(β1–6)(Gal(β1–3))Gal(β1–4)Glc and Neu5Ac(α2–6) + Gal(β1–4)GlcNAc(β1–6)(Gal(β1–3))Gal(β1–4)Glc. The latter five oligosaccharides were identified in donkey milk for the first time. The most abundant sialylated oligosaccharide found was 6'-sialyllactose. In addition, variations in the content of four oligosaccharides were highlighted over the experimental period: the highest values were found at 15 days of lactation, and the lowest at 60 days.