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

Acta Alimentaria, Vol. 9 (l),pp. 1—10 (1980) DEGRADATION OF WHOLE CASEINS FROM RAW, PASTEURIZED AND HYDROGEN PEROXIDE TREATED MILKS BY CALF RENNIN AND A MICROBIAL COAGULANT L. VÁMOS-VIGYÁZÓ, M. EL-HAWARY and E. Kiss (Received 29 August 1978; accepted 30 September 1978) The actions of crystalline calf rennin (CR) and of a microbial milk clotting enzyme derived from Endothia parasitica (MR) on whole caseins prepared from raw, pasteurized (65 °C, 30 min) and hydrogen peroxide-treated skim milks (caseins Nos. I, II and III, resp.) were compared by Polyacrylamide gel electro­phoresis. The enzyme reaction was continued at 35 °C for 22 h in 2.7% (w/v), pH 6.0 casein solutions. The amount of enzyme added was sufficient to coagulate 100 ml of fresh skim milk in 30 min at 35 °C and pH 6.0. Samples for electro­phoresis were taken at intervals. Caseins prepared from the three kinds of milk gave 11, 12 and 13 protein bands, resp., in the electrophoretic system applied. The x-fraction of casein I was entirely transformed by CR to para-x-casein within 30 min. With MR the degradation product of x-casein was more strongly shifted to the cathode than in the case of CR. Changes in the electrophoretic behaviour of as- and /S-caseins were most marked and most different with the two enzymes after 22 h of incubation. With MR the breakdown of ^-casein was nearly complete by the end of this period and as-casein was split into several faint, fast moving bands. With CR, the main fractions of both as- and ^-casein were still discernible, although of reduced mobilities. The decomposition, by either enzyme, of the protein bands in the region of the x-component of casein II occurred in a somewhat different way than with casein I, however, no retardation could be observed. Pasteurization was found to increase the accessibility of as- and /S-casein to CR, while the action of MR on these proteins was less marked. With CR as clotting agent, the degradation of the x-fraction of casein III progressed considerably during the first 30 min of the reaction and was complete in 60 min, whereas the action of MR on this component was greatly retarded. During the first 60 min the decomposition of as- and /?-casein was equally found to proceed at a lower rate with MR. However, after 22 h of incubation, hydrolysis of the above fractions to low molecular weight components was nearly complete, while 15 protein bands were present in the electrophoretogram of casein III treated with CR. The majority of the results obtained with casein L were in agreement with findings of others. No data were found as to the changes in the electrophoretic behaviour of caseins from pasteurized or hydrogen peroxide-treated milks as caused by different coagulants. The experiments reported here clearly demonstrate the differences between the actions of the two milk-clotting enzymes. However, these show only after rather prolonged incubation and might play but an inferior role, if any, in cheese­making practice. During experiments aimed at the utilization, in cheese-making, of a microbial rennet derived from Endothia parasitica, hydrogen peroxide - cata­lase treatment of milk was found to reduce clotting rate as compared to that obtained with calf rennet. Since an earlier study (VÁMOS-VIGYÁZÓ et al., Acta Alimentaria 9, 1980

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