Absolute quantification of bovine lactadherin to screen the anti-rotavirus activity of dairy ingredients

The anti-rotavirus components in breast milk and infant formulas play an important role in the prevention of rotavirus infection. The present study examined whether the levels of phospholipids and bovine lactadherin, which are the major components and proteins of the milk fat globule membrane complex, are useful indices of the anti-rotavirus activity of dairy ingredients used in infant formulas. We compared anti-rotavirus activity of two kinds of dairy ingredients enriched in the milk fat globule membrane complex, high-fat whey protein concentrate (high-fat WPC) and butter milk powder (BMP), using 50% inhibition concentration (IC50) and linear inhibition activity for the levels of solid contents, total proteins, phospholipids and bovine lactadherin. Here, we developed a quantification method of bovine lactadherin using full-length isotope-labeled proteins to measure bovine lactadherin levels in these dairy ingredients. The evaluation of anti-rotavirus activity showed that the difference in IC50 was the smallest when the two dairy ingredients were compared at bovine lactadherin level among other indices in this study. Additionally, no significant difference was observed between the inhibition linearity of two dairy ingredients when evaluating only the bovine lactadherin levels. These results indicated that the level of bovine lactadherin was more strongly associated with anti-rotavirus activity than the level of phospholipids. Our results suggest that bovine lactadherin levels easily estimate the anti-rotavirus activity of dairy ingredients, and it can be one of the criteria used in selecting ingredients for infant formulas.