The action of rennet on whole milk

Abstract

Summary: The release, by the action of rennet, of peptides which are soluble in trichloroacetic acid (TCA) has been studied using milk samples from individual cows. This release showed an initial marked increase with time of rennet action. After the milk clotted there was no further increase for at least 30 min. There was considerable variation in the total amount of N and of sialic acid released from milk samples taken from individual animals at different times during the lactation.For a given milk sample treated with rennet, the amount of sialic acid in the filtrate obtained after precipitation with 2% TCA was similar to that obtained with 10% TCA, whereas the amount of nitrogen was much greater with the 2 % TCA. It appeared that the peptides containing sialic acid were released at a slower rate.On average, about half the total sialic acid in the casein was recovered in the TCA filtrate after rennet action, which suggests that either a proportion of the κ-casein was not accessible to enzyme action or the technique used did not permit full recovery of the sialic acid-containing peptides.