Characterization of the proteolytic activity of starter cultures of Penicillium roqueforti for production of blue veined cheeses

Thirty strains of Penicillium roqueforti used for the production of blue cheeses were examined for proteolytic activity by agar diffusion on casein agar, by the azocasein test and by capillary zone electrophoresis (CE). Distinct differences were seen between the strains by all three methods applied and the 30 strains could be subdivided in three groups being significantly different in their proteolytic activity as measured by the agar diffusion test. The quantitative differences seen in the agar diffusion test were confirmed by the azocasein test. However, a negative result on casein agar, i.e., no clearing of the agar was observed for one strain while it showed low proteolytic activity in the azocasein test. CE proved to be a valuable method for revealing qualitative differences between strains of P. roqueforti in the breakdown of casein. Three strongly proteolytic strains broke down the specific casein fractions differently: one strain broke down βA1-casein faster than βA2-casein, the second preferred α s1-casein while the last strain broke down the casein fractions at equal rates. For a strain with medium proteolytic activity, the degradation of casein was seen by the appearance of a peak with migration time similar to α s1-I casein, a peptide normally produced by chymosin.