Screening of strains of Lactococci isolated from Egyptian dairy products for their proteolytic activity

A collection of cocci isolates (293) obtained from traditional Egyptian dairy products collected from four Egyptian regions yielded 151 lactic acid bacteria (LAB) cocci isolates. Among them, 24 isolates were characterised as highly proteolytic. SDS–PAGE showed that 6 isolates were the most proteolytically active, which were classified into Enterococcus faecalis HH22 (4 isolates) and Enterococcus faecium DO623 (2 isolates). The proteolytic activity of E. faecalis was higher than that of E. faecium (particularly on β-casein). The maximal degradation of milk proteins was achieved at pH 6.5–7.2 (E. faecalis) or pH 6.5 (E. faecium) and at 42 °C for both strains. The proteolytic activities of the two strains were inhibited mostly by the presence of EDTA, showing that their proteases belong mainly to metalloproteases. A slight inhibition of proteolysis by PMSF in the case of E. faecalis HH22 suggests a limited inclusion of serine proteases in its protease system.