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

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

Effect of milk contamination with yeast or spore formers on the quality of Domiati cheese

Domiati cheese was made from pasteurized milk which was inoculated prior to salting with Saccharomyces lactis to have a count approximately of 18 X 10[5], 89 X 10[3] and 650 cells/ml or with Bacillus polymyxa spores to give approximately counts of 18 X 10[4], 75 X 10[2] and 60 spores/ml. Presense of such organisms markedly increased the pressure in cheese tins and decreased moisture, pH, total volatile fatty acids and the rate of proteolysis in the resultant Domiati cheese. In addition, cheeses containing B. polymyxa or Sacch. Lactis showed less population of lactic acid bacteria as well as the total bacterial counts

Effect of adding some gas formers inhibiting salts to cheese milk on the chemical properties and bacteriological quality of domiati cheese

Damietta cheese was made from pasteurized milk inoculated with B. polymyxa [1.8 multiplies 105 cells/ml] with the addition of some inhibiting salts solely, or for the first time in this field as mixtures containing two or three different types. That addition markedly increased the rate of proteolysis and lipolysis in the resultant cheese during pickling as indicated by the tryptophane, tyrosine and total volatile fatty acids contents. Moreover, cheese containing inhibiting salts had the most smooth body with no holes, close textures and good bacteriological quality. These effects seemed to be more obvious in cheese containing potassium sorbate or a mixture of potassium sorbate and sodium benzoate

Chemical characteristics and bacteriological quality of Domiati cheese containing gasformers inhibiting salts

Domiati cheese was made from milk inoculated with E. cola type I [44+] with the addition of some inhibiting salts individually or for the first time in this field as mixtures containing two or three different types. The presence of the gas inhibiting salts solely or in a mixture markedly accelerated the rate of proteolysis and lipolysis in the resultant cheese throughout pickling, as indicated by the tyrosine, tryptophan and TVFA contents of the cheese. Also, cheese containing inhibiting salts had smooth body, compact texture without any gas holes and good bacteriological quality. These effects seemed to be more obvious in cheese containing potassium sorbate or a mixture of potassium sorbate and sodium benzoate