Effects of mechanical agitation of raw milk on the milk-fat globule in relation to the level of induced lipolysis

Abstract

SummaryThe amount of damage caused to the milk-fat globule by mechanical agitation of raw milk was assessed by several methods and related to the level of induced lipolysis resulting from the agitation. The results obtained by measuring the amount of ‘free’ fat formed, the percentage of fat in the skim-milk phase after separation, and the increase in the proportion of alkaline phosphatase associated with the skim-milk phase, showed little correlation with the level of lipolysis induced by agitation over a range of conditions. However, the level of induced lipolysis showed good correlation with the amount of lipolysis caused by addition of an exogenous lipase (from Candida cylindraceae) to the agitated milk. It is concluded that classical methods of assessing milk-fat globule damage are unsuitable for predicting the amount of fat available for lipase action and the lipolytic potential of raw milk subjected to mechanical agitation.

The milkfat globule membrane—compositional and structural changes post secretion by the mammary secretory cell

“…Temperature and stability of fat globules. Cooling of milk can have a pronounced effect on the stability of the fat globules (Ismail, El-ghanam, & Sirry, 1972;Anderson & Cheeseman, 1975;Deeth & Fitz-Gerald, 1978;Fl . uckiger & H. anni, 1980;Miller & Puhan, 1986;Kirst, 1996).…”

The milkfat globule membrane—methodologies for measuring milkfat globule (membrane) damage

“…Reports in the literature often use the term ''fat globule damage'' to denote that changes have occurred (2) solvent extraction Deeth and Fitz-Gerald (1978); Halter, Puhan, and Schmutz (1978); Fink and Kessler (1983); Evers, Crawford, Robinson, Harding, and McCarthy (2001a) Not recommended. Methods produce highly variable results…”

“…However, the term is ambiguous and various definitions of what constitutes ''free fat'' have been given. These include: (1) fat inside damaged globules (Fink & Kessler, 1983), or fat that is insufficiently enclosed by an undamaged membrane 1 (Kessler & Fink, 1992); (2) fat that has leaked out of damaged globules (Fink & Kessler, 1983); (3) ''the proportion of fat extracted by centrifugation at 60 C'', when a centrifugation method was used (Te Whaiti & Fryer, 1975); and (4) ''solvent-extractable fat'' when an extraction method was used (Deeth & Fitz-Gerald, 1978). The last two definitions define free fat as a method-dependent parameter.…”

“…ahlen, 1984). However, the performance of the method has been reported to be unsatisfactory in some studies; using fresh milk from a Friesian herd, Deeth and Fitz-Gerald (1978) could not obtain meaningful results with this method. For cream, free fat centrifugation methods have been used to determine the degree of fat globule damage occurring in cream crystallising silos (Palfreyman, 1988), or to identify points in a cream processing line where fat globule damage occurred (Williams, 1986).…”

“…Lagoni and Peters (1959) and Kirst (1980a) extracted the sample three times with a mixture of diethyl ether and petroleum ether, and thus essentially used the R . ose Gottlieb principle (Gottlieb, 1892) except for the digestion step, whereas Aule and Worstorff (1975), Deeth and Fitz-Gerald (1978) and Lehman (1988b) used either hexane or petroleum ether as the solvent. Furthermore, significant variations in sample size, solvent volume and other conditions were used.…”