Several peptides were isolated from the diafiltration retentate, prepared
using 10 kDa membranes, of the water-soluble extract from a commercial mature
Cheddar cheese and identified by amino acid sequencing and mass spectrometry.
Most of the peptides were from the N-terminal half of β-casein,
but peptides from αs1-
and αs2-caseins were also identified; the extract also
contained α-lactalbumin.
Identified peptides showed the important role played by lactococcal cell envelope
proteinases in the degradation of primary proteolytic products from
αs1- and β-
caseins, produced by chymosin and plasmin respectively. Plasmin seemed to be
involved in the hydrolysis of αs2-casein. Several
phosphopeptides were identified and
the action of phosphatase on these peptides was evident.