PROTEOLYSIS AND ITS ROLE IN RELATION TO TEXTURE OF FETA CHEESE MADE FROM ULTRAFILTERED MILK WITH DIFFERENT AMOUNTS OF RENNET

The relationship between proteolysis and texture in Feta-type cheese m ade from ultrafiltered cows; milk was studied using capillary electrop horesis, chemical analysis and uniaxial compression. For this purpose cheeses were made with almost identical gross chemical compositions, b ut wide variations in texture, obtained by varying the amount of renne t and the coagulation conditions. alpha(s1)-Casein (CN) 8P, alpha(s1)- CN 9P and alpha(s1)-CN 8P-I were degraded during ripening, while beta- CN A(1). beta-CN A(2) and para-kappa-CN were slightly degraded at the highest rennet additions and longest storage time tested (39 weeks), a lpha(s1)-CN 8P: alpha(s1)-CN 9P and alpha(s1)-CN 8P-I were degraded ev en in cheeses made without rennet, and this was ascribed to cathepsin D activity. alpha(s1)-CN 9P disappeared faster than alpha(s1)-CN 8P, w hich suggests that milk acid phosphatase was active during storage. Du ring ripening: stress at fracture (sigma(f)), strain at fracture (epsi lon(f)), the deformability modulus (E) and work to fracture (W-f) all decreased. Since the gross chemical composition was essentially consta nt during storage, these changes could be ascribed purely to proteolys is. Although epsilon(f) could be predicted fairly well from capillary electrophoresis results (correlation coefficient 0.85), there were no unique relationships between degradation of casein components and sigm a(f) when both storage time and the amount of rennet used were varied. In the young cheese a high level of proteolysis could coexist with hi gh values of sigma(f). This suggests that high levels of rennet caused sigma(f) to increase, via an effect unrelated to general proteolysis, whereas general proteolysis caused the reverse effect.