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Specificity of Lactococcus lactis subsp.cremoris SK11 Proteinase, Lactocepin III, in Low-Water-Activity, High-Salt-Concentration Humectant Systems and Its Stability Compared with That of Lactocepin I

ABSTRACT Marked changes in the specificity of hydrolysis of αs1-, β-, and κ-caseins by lactocepin III fromLactococcus lactis subsp. cremoris SK11 were found in humectant systems giving the equivalent water activity (aw) and salt concentration of cheddar cheese. Correlations were noted between certain peptides produced by the activity of lactocepin III in the humectant systems and peptides found in cheddar cheese. The stability of lactocepin III was compared with that of lactocepin I from L. lactis subsp. cremoris HP in the humectant systems at different pHs. Significant differences between the stability of each of the lactocepin types were evident. The relationship between stability and humectant type, aw, pH, and NaCl concentration was complex. Nevertheless, in those systems where aw, pH, and NaCl concentration were equivalent to those in cheddar cheese, lactocepin I was generally more stable than lactocepin III. It was concluded that differences in the specificity and/or stability of various lactocepin types are likely to persist in cheese itself and therefore potentially contribute to differences in the peptide composition of ripened cheese.