Casein phosphopeptides released by simulated gastrointestinal digestion of infant formulas and their potential role in mineral binding

Adapted and follow-up milk-based infant formulas were subjected to gastrointestinal digestion simulating physiological conditions. The naturally occurring casein phosphopeptides (CPPs) generated were fractionated by anion exchange high-performance liquid chromatography and sequenced by tandem mass spectrometry. In both infant formula digests, a total of 19 CCPs from bovine casein were identified, of which 7 corresponded to αs1-casein and 12 to αs2-casein. Most CPPs had the cluster sequence SpSpSpEE, representing the binding sites for minerals. The distribution of calcium, iron and zinc content in CPP fractions eluted from the anion exchange column was also studied. The results obtained suggest that calcium could be preferably bound to CPPs with the cluster sequence SpSpSpEE, whereas iron and zinc could be bound to CPPs containing the phosphorylated cluster and phosphoserine residues.