Protein breakdown and release of β-casomorphins during in vitro gastro-intestinal digestion of sterilised model systems of liquid infant formula

Protein modifications occurring during sterilisation of infant formulas can affect protein digestibility and release of bioactive peptides. The effect of glycation and cross-linking on protein breakdown and release of β-casomorphins was evaluated during in vitro gastro-intestinal digestion (GID) of six sterilised model systems of infant formula. Protein degradation during in vitro GID was evaluated by SDS-PAGE and by measuring the nitrogen content of ultrafiltration (3kDa) permeates before and after in vitro GID of model IFs. Glycation strongly hindered protein breakdown, whereas cross-linking resulting from β-elimination reactions had a negligible effect. Only β-casomorphin 7 (β-CM7) was detected (0.187-0.858mgL(-1)) at the end of the intestinal digestion in all untreated IF model systems. The level of β-CM7 in the sterilised model systems prepared without addition of sugars ranged from 0.256 to 0.655mgL(-1). The release of this peptide during GID was hindered by protein glycation.