Role of <i>Penicillium roqueforti</i> proteinases during blue cheese ripening

Abstract

Summary The hydrolysis of isolated α s1 - and β-caseins by Penicillium roqueforti aspartyl proteinase produced comparable quantities of pH 4·6 soluble N. The amount of non-protein nitrogen obtained with β-casein was clearly lower than that obtained with α s1 -casein, showing that few low molecular weight peptides were released when this casein was hydrolysed. Electrophoresis of α s1 -casein hydrolysates produced by aspartyl proteinase showed 5 bands of mobility close to or higher than that of α s1 -casein. β-Casein hydrolysates gave 4 bands, 2 of which (βPrapl and βPrap2) showed low electrophoretic mobility. The products corresponding to βPrapl and βPrap2 were purified from a β-casein hydrolysate and identified as fragments Val 98 -Val 209 and Glu 100 -Val 209 of β-casein respectively. The occurrence of the βPrapl and βPrap2 bands in electrophoretic patterns obtained from sterile curd with aspartyl proteinase and controlled-flora curd, where P. roqueforti was the only micro-organism developing, showed the presence of aspartyl proteinase synthesis and activity in cheese. A band of very low electrophoretic mobility (βPrmpl) was present in electrophoregrams of controlled-flora curd inoculated with P. roqueforti . This band, resulting from the action of the metalloproteinase on β-casein, revealed that this enzyme was both synthesized in and active in cheese.