ACTA ALIMENTARIA VOL. 9 (A QUARTERLY OF THE COMMITTEE ON FOOD SCIENCE OF THE HUNGARIAN ACADEMY OF SCIENCES, 1980)
1980 / 1. sz. - VÁMOS-VIGYÁZÓ, L.-EL-HAWARY, M.-KISS, E.: Degradation of whole caseins from raw, pasteurized and hydrogen peroxide treated milks by calf rennin and a microbial coagulant
VÁMOS -VIGYÁZÓ et al.: DEGRADATION OF PROCESSED CASEINS BY RENNETS 2 1978) had revealed distinct differences in the electrophoretic protein patterns of raw, pasteurized and hydrogen peroxide treated milks, it was thought promising to compare, by a similar method, the action of calf rennet and of the microbial coagulant on caseins prepared from above milks. A better knowledge of the mechanism of action of the microbial enzyme might contribute to establish optimum conditions of its utilization. 1. Materials and methods 1.1. Materials 1.1.1. The milk. - Raw skim milk was supplied by a Budapest dairy plant. Pasteurization was carried out at 65 °C during 30 min and was followed by rapid cooling to 20 °C. Hydrogen peroxide treatment as used in this country in Emmental cheese production has been described in detail in the paper cited (VÁMOS-VIGYÁZÓ et al., 1978). 1.1.2. Casein. — Casein was obtained from raw (I), pasteurized (II) and hydrogen peroxide treated (III) milk essentially by the method of VANDERPOORTEN and WECKX (1972) with slight modifications as described in the paper cited (VÁMOS-VIGYÁZÓ et al., 1978). 1.1.3. Enzyme preparations. - Crystalline calf rennin (CR) was purchased from SIGMA (U.S.A.). Its clotting activity on raw skim milk was found to be 830,000 SUg-1 (SU = Soxhlet unit; 1 SU = the amount of milk in ml, coagulated by 1 g or 1 ml of enzyme preparation in 40 min at 35 °C). The microbial coagulant (MR) was purified from an industrial-scale experimental preparation of the E. parasitica enzyme by two gel filtration steps on Sephadex G 10 and G 100, resp., and was subsequently concentrated by vacuum evaporation to a specific clotting activity of 240,000 SU per g protein. For activity measurements 0.5 ml of a suitable dilution of the enzyme preparations were added to 10 ml of fresh skim milk, both preheated to 35 °C. 1.2. Methods 1.2.1. Enzymatic degradation of casein. - The enzyme reaction was carried out in a 2.7% casein solution (w/v) in distilled water, the pH of which was adjusted with 1 N NaOH to 6.0 as checked in a Radiometer PHM 4 type pH meter. The solution was then filtered. The concentration of the solution corresponded to the casein content of milk. 1* Acta Alimentaria 9,1980