Effect of polymorphic composition of calcium caseinate sols on their stability to rennin

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Abstract
Five hundred and seven samples of iso-electric caseins were typed by starch-gel electrophoresis and their polymorphic compositions were determined in terms of αs1-, β- and κ-casein variants. Clotting times in minutes were determined on 50 ml of 3% casein solution in milk dialysate containing 0·02 M-Ca as CaCl2 and 2 mg commercial rennin powder at pH 6·60–6·80. The clotting times ranged from 4·06 to 7·41 min. The data indicated that the polymorphic composition of casein significantly influenced its stability to rennin. The polymorphic combinations αs1B+βA+κB and αs1B+βAC+κAB, were the most resistant to rennin action (clotting times of 7·41, 7·39 min respectively). The combinations αs1B+βB+κAB and αs1BC+βB+κB were the least resistant to rennin action (clotting times of 4·25 and 4·06 min respectively). In most cases, caseins with lower stability to rennin contained κB or βB or both in their composition.
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