Interrelationships of chemical composition and coagulating properties of renneted milks from dairy cows grazing ryegrass or white clover

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Abstract
The chemical composition and rennet coagulation properties at pH 6·4 of bulked milks from two groups of dairy cows grazing ryegrass or white clover swards were monitored over a period of 14 weeks commencing at the fifth week of lactation. There was considerable variation in the concentrations of many components and large variations in the rennet clotting time (RCT), coagulum strength and rate of syneresis. The relative proportions of αs-, β- and κ-casein were also subject to considerable variation. Many statistically significant correlations were found between concentrations of protein fractions, minerals and citrate, some of which may be of physiological significance whereas others may be incidental. The coagulum strength displayed significant correlations with concentrations of total casein, αs-casein, inorganic phosphate (Pi), whey protein and RCT, but not with β-casein or η-casein. The syneresis time was significantly related to the concentrations of fat, citrate, η-casein and the original milk pH. RCT displayed a significant correlation with the concentration of Pi.