Lipase cows’ milk

Luhtala, A. 1969. Studies on lipase activity, lipases and glyceride synthesis in Finnish cows milk. Meijertiet Aikakauskirja 29, 7-65. 

Two other practical applications of enzyme technology used in dairy industry are the modification of proteins with proteases to reduce possible allergens in cow milk products fed to infants, and the hydrolysis of milk with lipases for the development of lipolytic flavors in speciality cheeses. 

Human milk differs from cows milk in that it contains two lipases, a lipoprotein lipase and a bile salt-stimulated lipase. The ability of the latter to cause considerable hydrolysis of ingested milk lipids has important nutritional implications. 

There were several new developments during the 1970s. Of particular importance was the purification and characterization of a lipoprotein lipase (LPL) and the acceptance of the postulate that this was the major, if not the only, lipase in cows milk (Olivecrona, 1980). Similarly, the elucidation of the lipase system in human milk as consisting of an LPL and a bile salt-stimulated lipase, and the possible role of the latter in infant nutrition, were noteworthy (Fredrikzon et al, 1978). Also, microbial lipolysis assumed substantial significance with the widespread use of low-temperature storage of raw milk and the recognition that heat-stable lipases produced by psychrotrophic bacteria were a major cause of flavor problems in stored dairy products (Law, 1979). 

Early research on lipolytic enzymes in cows milk suggested that at least two major lipases were present a plasma lipase in the skim portion and a membrane lipase associated with the milk fat globule membrane (Tarassuk and Frankel, 1957) while later research indicated that there might be up to six different molecular species with lipase activity (Downey and Andrews, 1969). However, work by Korn (1962) showed that milk contained a lipoprotein lipase (EC 3.1.1.34) (LPL) with properties very similar to those of post-heparin plasma, adipose tissue and heart LPLs, particularly the enhancement of its activity on emulsified triglycerides by blood serum lipoproteins. It is now accepted that LPL is the major, if not the only, lipase in cows milk. Its properties have been reviewed by Olivecrona et al. (2003). 

Human milk differs from cows milk in that it contains, in addition to an LPL similar to that in cows milk, a bile salt-stimulated lipase (BSSL), which appears to have no counterpart in cows milk (Hernell and Blackberg, 1994). In addition, a third lipase known as platelet-activating factor acet-ylhydrolase activity (PAF-AH) has been demonstrated in human milk the activity is absent, or extremely low in cows milk (Furukawa, et al., 1994). 

In addition to the now well-documented lipase system, cows milk contains several other carboxyl ester hydrolases, collectively referred to as esterases. These are distinguished from lipases by their ability to act on ester substrates in solution rather than in an emulsified form (Jaeger et al., 1994) and/or by their preference for hydrolysing esters of short-chain rather than long-chain acids (Okuda and Fujii, 1968). 

Compared with the total lipase activity on emulsified milk fat or tributyrin (0.25-2.5 pmol/ml/min), the esterase activity (on soluble tribu-tyrin) is quite low, about one tenth (Downey, 1974). This may not be so for some abnormal milks where esterase levels are markedly elevated [10-12 times (Marquardt and Forster, 1962) and up to 37 times (Deeth, 1978)]. The significance of these esterases in cows milk and their relationship to each other, to LPL, and to esterases of other tissues remain to be determined. 

Cows milk LPL has phospholipase Ai activity (Scow and Egelrud, 1976), but its action on milk phospholipids has not been recorded. Freshly secreted goats milk has been shown to have phospholipase A activity (Long and Patton, 1978) but it is not known whether this can be attributed to the LPL of that milk. Human milk contains an acid sphingomylinase C, as well as ceramidase activity provided by the bile salt-stimulated lipase present (Nyberg et al., 1998). 

Raw cows milk contains a relatively large amount of lipase activity, but seldom undergoes sufficient lipolysis to cause an olf-flavor. Under optimal conditions, the lipase (milk LPL) can catalyze the hydrolysis of up to ca. 

Bovine blood serum is lipolytically active, but cows producing milk which goes rancid quickly do not have sera that are more lipolytically active than those producing normal milk. Leukocytes, which are present in large numbers in milk, are especially high in mastitic milk they are the source of milk catalase but are apparently not the source of milk lipases (Nelson and Jezeski 1955). 

The effect of the estrous period on rancidity has also been investigated. According to Wells et al. (1969), who studied lipase activity in the milk and blood of cows throughout their lactation period, the peak blood plasma lipase values occur about 24 hr before the onset of observed estrous. Changes in blood lipase activity were reflected and magnified in the milk, although it was noted that the increase in milk lipase level occurred 9 to 15 hr after it was observed in the blood. Bachmann (1961) also has indicated that hormonal disturbances are linked to rancidity. He differentiates between rancidity produced by cows in late lactation and rancidity due to hormonal disturbances on the basis of an increased in lipase concentration in the latter. 

Irradiation by ionizing radiation and its effect on milk lipase activity have also been studied (Tsugo and Hayashi 1962). Irradiation doses of 6.6 x 104 rads destroyed 70% of the activity. The udders of lactating cows, when exposed to 60 Co gamma rays, gave milk with decreased lipase and esterase activity (Luick and Mazrimas 1966). 

Guthrie, E. S. and Herrington, B. L. 1960. Further studies of lipase activity in the milk of individual cows. J. Dairy Sci. 43, 843. 

Super, D. M., Palmquist, D. L. and Schanbacher, F. L. 1976. Relative activation of milk lipoprotein lipase by serum of cows fed varying amounts of fat. J. Dairy Sci. 59, 1409-1413. 

Other factors. A cow s hormonal balance can affect the susceptibility of her milk to spontaneous lipolysis (Fredeen et al., 1951 Kastli et al., 1967 Bachman et al., 1988). The oestrus cycle appears to have little effect on spontaneous lipolysis (Fredeen et al, 1951) but may affect lipase activity in the milk (Kelly, 1945). In contrast, treatment of cows with oestradiol and progesterone has been shown to lead to increased lipolysis in the milk (Bachman, 1982 Heo, 1983 Bachmann eta/., 1985) but no change (Bachman, 1982) or a transient increase (Bachmann et al., 1985) in total lipase activity. It appears that the increased lipolysis in milk following hormonal treatment, or in milk from cows with ovarian cysts, may not be typical spontaneous lipolysis as cooling is not needed to initiate it (Bachman, 1982) a lipase other than lipoprotein lipase, possibly a bile salt-stimulated lipase, may be responsible for such lipolysis (Heo, 1983 Bachmann et al., 1985). Treatment of cows with bovine somatotropin has been reported to have no significant effect on milk lipoprotein lipase activity (Azzara et al., 1987). 

Azzara, C.D., Dimick, P.S. 1985b. Lipoprotein lipase activity of milk from cows with prolonged subclinical mastitis. J. Dairy Sci. 68, 3171-3175. 

Kastli, P., Padrutt, O., Baumgartner, H. 1967. Will the milk of cows treated with hormones acquire a rancid flavor due to increased lipase content Schweiz. Milchztg. 93, 197. 

Saito, Z., Kim, G.Y. 1995. Effects of lactation stage on temperature-activated lipolysis and lipase activity in cow s milk. Jap. J. Dairy Food Sci. 44, A139-A145. 

Functions.—Heparin fractionated by gel filtration appeared to bind to two sites on antithrombin III (association constants 0.6 x 10 and 0.2 x 10 moll" ), whereas heparin prepared by affinity chromatography on matrix-bound antithrombin III appeared to bind to only one site (association constant 2.3 x 10 moll ). These results suggest that one of the binding sites on antithrombin III does not bind the most active heparin components, but accommodates heparin-like molecules which, although similar in size to the active heparin components, have little or no anticoagulant activity. Heparins with high or low affinities for antithrombin III exhibited no differences in their abilities to bind lipoprotein lipase. Studies of the interaction between the lipoprotein lipase from cow s milk and Sepharose-immobilized heparin have shown that heparin is poly-disperse. Whereas heparin facilitated complex formation between a-thrombin and antithrombin III, it had little effect on the interaction between p-thrombin and antithrombin III. ... 

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