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

Marked changes in the specificity of hydrolysis of alpha(s1)-, beta-, and k appa-caseins by lactocepin III from Lactococcus lactis subsp, cremoris SK11 were found in humectant systems giving the equivalent water activity (a(w) ) and salt concentration of cheddar cheese. Correlations were noted between certain peptides produced by the activity of lactocepin III in the humecta nt systems and peptides found in cheddar cheese. The stability of lactocepi n III was compared with that of lactocepin I from L. lactis subsp. cremoris HP in the humectant systems at different pHs. Significant differences betw een the stability of each of the lactocepin types were evident. The relatio nship between stability and humectant type, a(w), pH, and NaCl concentratio n was complex. Nevertheless, in those systems where a(w), pH, and NaCl conc entration were equivalent to those in cheddar cheese, lactocepin I was gene rally 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 differenc es in the peptide composition of ripened cheese.