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Effect of Certain Factors upon Lipolysis in Homogenized Raw Milk and Cream

1941; Elsevier BV; Volume: 24; Issue: 9 Linguagem: Inglês

10.3168/jds.s0022-0302(41)95456-5

1529-9066

I.A. Gould,

Animal Diversity and Health Studies

The acceleration of lipase action in raw milk by homogenization is now generally accepted.This acceleration has been attributed by some to increased surface area afforded the lipase by the breakdown of the fat globules and by others to a re-surfacing of the fat globules by material more susceptible to lipolytic action.Irrespective of the actual cause for the enormous and rapid rate of lipolysis in homogenized milk, evidence is accumulating which indicates that factors which affect lipase action in normal milk may not have the same effect on lipase activity in the homogenized product.A limited amount of information illustrating these differences has already been published.Additional evidence is presented in this paper.Lipolytic action on fat in homogenized milk has been previously studied (3, 4, 7).Gould and Trout (4) found the acid degree of the fat (expressed in milliliters of N/1 NaOH per 100 grams of fat) to increase four-fold to six-fold within a few minutes after homogenization, and to increase on an average of 1,652 per cent within 24 hours.The author (3) observed considerable lipolysis to have occurred in fat obtained from milk homogenized at temperatures of 105 to 135 ° F., whereas slight fat splitting occurred in milk homogenized at 145 ° F. These temperatures are considerably above those which have been found to be effective in greatly inhibiting lipase action in normal unhomogenized milk (9,10,11,12).Lipase action in homogenized milk is apparently not affected by temperature activation which brings about marked changes in normal milk (6, 7).Krukovsky and Sharp (7) believe the difference is due to the fact that in the homogenized product the "lipase is already in the active state as a result of the resurfaeing of the milk fat .... "Another point of difference between lipase activity of normal and homogenized milk pertains to the temperature coefficient.Krukovsky and Sharp (7) found the temperature coefficient of the lipase action to differ depending upon whether the fat globules were normal or whether they had been "resurfaced."Fat globules with natural surfaces showed more rapid lipolysis with lower temperature whereas a reverse condition occurred with the emulsified fat.A relationship between oxidative changes in the fat and lipolysis in normal milk is indicated by Davies (1) and Krukovsky and Sharp (8).Davies found peroxide formation to occur simultaneously with lipase action; the