Production and characterization of bacterial coagulants as calf rennet replacer for Egyptian cheese making.

ABSTRACT

The bacterial coagulant as calf rennet replacer was aimed to evaluate. The productivity and milk clotting activity [MCA] of coagulants of 12 strains of B. subtilis and 9 strains of B. megaterium were screened. Specific activities of coagulants were tested whether in the crude or in the purified form. The chemical, physical, microbial and organoleptic properties of Ras cheese slurry, coagulum and Domiati cheese [from conventionally salted milk] made with bacterial rennet [concentrated by dialysis against polyethelenglycol 40%] were investigated. Five strains of B.subtilis and three strains of B.megaterium produced milk clotting enzyme [MCE] with MCA> 100 SU/mI, after incubation for 7 days at 30°. The max. relative MCA was recorded at milk temperature of 65° for both types of bacterial rennet in the crude form and increased to 75° [B.subtilis] or 80° [B.megaterium] when purified. While the purification did not change the sensitivity of bacterial coagulants to NaCI or CaC1[2] concentration, where the former salt inhibited while the latter one improved the MCA. The purified enzyme of B.megaterium exhibited higher km and lower Vmax than those occurred by that of B.subtilis.Ras cheese slurry made with B.subtilis rennet matured after 5 days of incubation at 37° and was slightly higher in the flavour score than that of B.megaterium. Both slurries of bacterial rennet possessed a stimulating effect on the growth of the starter cultures added. Bacterial rennet coagulum was softer and synersed lower whey amount than that of calf rennet. Bacterial rennet had also an accelerating effect on Domiati cheese ripening as appeared from the ripening indices determined. Some weakness in the consistenôy associated with Domiati cheese made with bacterial rennet but the flavour score was better after one month and then slightly lowered after two months than the control pickled for the same period