Abstract
Human milk oligosaccharides (HMOs) are the third most abundant solid component after lactose and lipids of breast milk. All mammal milk contains soluble oligosaccharides, including neutral milk oligosaccharides (NMOs) without sialic acid (Sia) moieties and acidic oligosaccharides or sialylated milk oligosaccharides (SMOs) with Sia residues at the end of sugar chains. The structural, biological diversity, and concentration of milk oligosaccharides in mammalian milk are significantly different among species. HMOs have multiple health benefits for newborns, including development of immune system, modification of the intestinal microbiota, anti-adhesive effect against pathogens, and brain development. Most infant formulas lack oligosaccharides which resemble HMOs. Formula-fed infants perform poorly across physical and psychological wellbeing measures and suffer health disadvantages compared to breast-fed infants due to the differences in the nutritional composition of breast milk and infant formula. Of these milk oligosaccharides, SMOs are coming to the forefront of research due to the beneficial nature of Sia. This review aims to critically discuss the current state of knowledge of the biology and role of SMOs in human milk, infant formula milks, and milk from several other species on gut and brain health of human and animal offspring.
Highlights
Up until the point of weaning, the milk is the most important, and often sole, source of nutrients for the neonate
Approximately 57% of N-glycans and most glycolipids in human milk are sialylated glycoconjugates [20], which are involved in numerous developmental processes; for instance, they work as building block of brain gangliosides and sialoglycoproteins and have immunomodulatory and immunostimulatory properties [42] and neurodevelopment and cognition [18,35]
13 oligosaccharides were identified in bovine milk, which were significantly influenced by breed, where most of these structures were abundant in the milk of the Jersey cattle compared to the Holstein-Friesian cattle [53]
Summary
Up until the point of weaning, the milk is the most important, and often sole, source of nutrients for the neonate. One promising nutrient is human milk oligosaccharides (HMOs), which is the third most abundant component of human breast milk after lactose and lipids [12,13,14]. Human milk oligosaccharides are reported to benefit the neonate in infection protection, brain maturation, growth, and development of infants, and microbiome establishment and maintenance [15]. Human breast milk has a far greater diversity and quantity of oligosaccharides than other reported species, with about 50–70% being neutral HMOs, commonly fucosylated (containing fucose) and non-fucosylated oligosaccharides; and 10–30% being acidic HMOs containing one or more Sia residues, so-called sialylated milk oligosaccharides (SMOs) [14,23]. SMOs are left out of the infant formula [12,29,30,31,32] because of the unavailability of food grade SMOs in the market for manufacturing infant formula
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