Lectin inhibition assays for the analysis of bioactive milk sialoglycoconjugates

Assay systems were developed to determine bioactive sialylated structures in complex and crude mixtures as they occur in milk fractionation processes. The sialic acid-binding proteins Maackia amurensis lectin and Sambucus nigra agglutinin as well as Siglec-2 and Siglec-4 were used in inhibition assays. The complementary linkage specificities of these lectins allow the determination of α2,3- and α2,6-linked sialic acids even in the presence of high lactose concentrations that are common in milk products. The functionality and linkage specificity of the assays have been evaluated using oligosaccharides from human and bovine milk. Furthermore, the presence of bioactive sialoglycoconjugates has been determined in fractions from a bovine milk fractionation process like sweet buttermilk, lactose-reduced serum, skim milk proteins, caseins and glycomacropeptides.