The effect of lysosomal proteinases and plasmin on the rennet coagulation properties of skim milk

During mastitis, there is a significant increase in activity of the alkaline milk proteinase, plasmin, and also in levels of white blood (somatic) cells, which contain many active proteinases, including elastase and cathepsins B and D. This study investigated the influence of lysosomal enzymes and plasmin on the rennet coagulation properties of milk. Elastase rapidly coagulated skim milk at high enzyme levels, but with concomitant proteolysis of casein. Both elastase and cathepsin B influenced the rheology of rennet (chymosin)-induced gels. Whole somatic cells did not affect the rennet coagulation properties of skim milk, when added at levels < 1,000,000/ml. Hydrolysis of casein by plasmin had no clear effect on the rheology of rennet gels nor on the rennet coagulation time of skim milk.