6'-Sialyllactose (6'-SL) is a sialylated trisaccharide composed of a lactose core (galactose linked β-1,4 to glucose) with a sialic acid residue (N-acetylneuraminic acid) attached via an α-2,6 glycosidic linkage to the galactose unit. Its molecular formula is C₂₃H₃₉NO₁₉, with a molecular weight of approximately 633.55 g/mol, similar to its isomer 3'-sialyllactose but differing in the position of the sialic acid attachment.

Chemically, 6'-SL appears as a white to off-white powder, soluble in water with moderate hygroscopicity. It is stable under physiological and processing conditions. Its structure is denoted as O-(N-acetyl-α-neuraminosyl)-(2→6)-O-β-D-galactopyranosyl-(1→4)-D-glucose. Like other sialylated human milk oligosaccharides (HMOs), this compound is resistant to digestion in the upper gastrointestinal tract, allowing it to reach the colon where it functions as a prebiotic promoting beneficial gut microbiota such as Bifidobacterium and Lactobacillus species.

Biological Functions of 6'-Sialyllactose

Biologically, 6'-Sialyllactose exhibits multiple important functions. It contributes to shaping the infant gut microbiome by supporting the growth of commensal bacteria and inhibiting pathogenic organisms. Additionally, it is associated with immune modulation, anti-inflammatory effects, and potential antiviral activity through inhibition of viral binding to host cell receptors. Due to these properties, 6'-SL is incorporated into infant formulas and functional foods to mimic the health benefits of human milk and support both gut and immune function.

In summary, 6'-Sialyllactose is a key human milk oligosaccharide characterized by its unique α-2,6 sialic acid linkage, which confers distinctive biological and prebiotic properties. Its chemical stability, bioactivity, and safety profile make it valuable for nutritional and therapeutic applications aimed at promoting gastrointestinal and immune health.