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The Specificity of Milk Lipase. IV. Partition of the Lipase System in Milk

1957; Elsevier BV; Volume: 40; Issue: 4 Linguagem: Inglês

10.3168/jds.s0022-0302(57)94496-x

1529-9066

N.P. Tarassuk, E. N. Frankel,

Amino Acid Enzymes and Metabolism

Cow's milk contains at least two lipases that are present in the plasma of warm, freshly drawn milk.One, the membrane lipase, is irreversibly adsorbed on the fat globules as milk is cooled.It is abundant and active in milk from cows late in their lactation.The other one, plasma lipase, is associated with the caseinate system and it can be activated to produce lipolysis in milk.Editor.In the previous papers of this series (6, 7) evidence was presented that indicates the presence in milk of nmltiple lipolytic enzymes that include both lipase and simple esterases.Since milk contains no simple esters to serve as substrate, and the use of esters other than milk fat for lipase deternfination in milk can not be justified (6, 7), the presence of esterases is of only theoretical interest.Hydrolytic rancidity in milk results from hydrolysis of milk fat.A study of the lipase system itself in milk is, therefore, of fundamental and practical importance.A knowledge of the distribution of milk lipase or lipases among various fractions of milk is essential both for the isolation of the enzymes and an understanding of the mechanism of action of this enzyme system.The present paper deals with the identifying of different lipases on the basis of their partition among some milk components.At present, the development of hydrolytic rancidity in milk is generally associated with certain "activation" treatments of raw milk: homogenization(2), temperature changes (13), shaking (14), or agitation by air (22), as in pipeline milking systems.However, in the early literature (11,12,16,17,20) and during recent years (28), lipase activity has been reported in the milk of individual cows--especially those in late lactation and on dry feed--without the milk's being subjected to any apparent activation treatment other than aging.Milk susceptible to this lipolysis has been designated naturally rancid(2), bitter milk of late lactation (16), naturally active or naturally lipolytically active (14,20,21,23), and normally active (28).Tarassuk et al. (21,23) have referred to this lipolysis as "spontaneous," to distinguish it from "induced" lipolysis which requires activation.In this paper, milk that exhibits spontaneous lipolysis is referred to as "naturally active" or "spontaneous" milk.