Variability of Hydrolysis of β-, α_(s1)-, and α_(s2)-Caseins by 10 Strains of Streptococcus thermophilus and Resulting Bioactive Peptides

摘要

Milk proteins contain numerous potential bioactive peptides, which may be released by digestive proteases or by the proteolytic system of lactic acid bacteria during food processing. The capacity of Streptococcus thermophilus to generate peptides, especially bioactive peptides, from bovine caseins was investigated. Strains expressing various levels of the cell envelope proteinase, PrtS, were incubated with α_(s1)-, α_(s2)-, or β-casein. Analysis of the supernatants by LC-ESI-MS/MS showed that the β-casein was preferentially hydrolyzed, followed by α_(s2)-casein and then α_(s1)-casein. Numbers and types of peptides released were strain-dependent. Hydrolysis appeared to be linked with the accessibility of different casein regions by protease. Analysis of bonds hydrolyzed in the region 1-23 of α_(s1)-casein suggests that PrtS is at least in part responsible for the peptide production. Finally, among the generated peptides, 13 peptides from β-casein, 5 from α_(s2)-casein, and 2 from α_(s1)-casein have been reported as bioactive, 15 of them being angiotensin-converting enzyme inhibitors.