178. A lipase (tributyrinase) of cows' milk. I. Occurrence, method of estimation and relationship to lactation cycle

Abstract

An enzyme which hydrolyses tributyrin is present in all samples of fresh cows' milk examined. A method has been developed for the determination of the tributyrinase activity of a given milk or fluid.In milk the enzyme is present in the aqueous rather than the fatty portion. Its optimal range of activity is in the region pH 8·2–8·7. It is rather more thermolabile than phosphatase.Its concentration in milk varies considerably from cow to cow, and in individual healthy cows there is a fairly regular variation throughout the lactation cycle. It is highest in concentration in colostrum, then the concentration falls to a minimum at about 10 days, rising later to a figure intermediate between this minimum and the colostral value. It shows no sign of increase towards the end of the lactation period.Its relationship to the “true lipase” of milk is discussed.

Studies on the properties of cow's-milk tributyrinases and their interaction with milk proteins

“…Our experiments confirm that most of the tributyrinase activity in milk is associated with the casein micelles (Sjostr6m, 1959;Jensen, 1964;Chandan & Shahani, 1964). The higher tributyrinase activity of skim milk as compared with that of whole milk is probably not an activation effect resulting from the process of cream separation because Mattick & Kay (1938) found the same thing occurred when the cream was allowed to rise of its own accord. A likely explanation is that the enzymes have kinetic properties and substrate affinities that result in the acid liberation from tributyrin alone being more rapid than that from a mixture of tributyrin and milk fat.…”

Section C. Dairy Chemistry

“…The presence in fresh clean milk of a preformed triglyceride-splitting enzyme has been verified by Mattick & Kay (61), who, rightly, were not satisfied that previous work had been sufficiently rigidly controlled to obviate lipolysis by micro-organisms or by enzymes secreted by them. A reliable method has been developed for the estimation of lipase (tributyrinase), and its occurrence and relationship to the lactation cycle have been studied.…”