Lipolysis in milk

Lipases catalyse the development of hydrolytic rancidity in milk, and, consequently, lipases and lipolysis in milk have been studied extensively. Milk contains three types of esterase ... 

Brathen, G. 1980. Lipolysis in milk. Automated determination of the acidity value with the autoanalyzer and assessment of results. Meierposten 69 (13), 345-352. (Norwegian). 

Downey, W. K. 1980A. Review of the progress of dairy science Flavour impairment from pre- and post-manufacture lipolysis in milk and dairy products. J. Dairy Res. 47, 237-252. 

Pillay, V. T., Myhr, A. N. and Gray, J. L. 1980. Lipolysis in milk. I. Determination of free fatty acid and threshold value for lipolyzed flavor detection. J. Dairy Sci. 63, 1213-1218. 

Lipolysis in milk is affected by inhibiting and activating factors. As discussed above, proteose peptone fraction of milk can inhibit milk LPL while apolipoproteins stimulate the enzyme. This is particularly important in spontaneous lipolysis however, proteose peptone 3 has been shown to inhibit lipolysis induced by homogenization, sonication, and temperature activation (Arora and Joshi, 1994), while protein components of the milk fat globule membrane inhibit lipolysis caused by bacterial lipase (Danthine et al., 2000). Several exogenous chemical agents can also inhibit lipolysis (Collomb and Spahni, 1995). For example, polysaccharides such as X-carrageenan at 0.3 g/1 effectively inhibits lipolysis in milk activated by mechanical means or temperature manipulation (Shipe et al., 1982) and lipolysis caused by the lipase from P. fluorescens (Stern et al., 1988). 

In feeding trials with lipid supplements, Astrup et al. (1980) observed that palmitic or myristic acid significantly enhanced spontaneous lipolysis but stearic acid and fatty acids with a chain length shorter than myristic acid had no effect. These workers found that feeding rapeseed oil to underfed cows reduced the susceptibility of their milk to lipolysis, while Chazal and Chilliard (1985) reported that supplementation with non-protected lipids, particularly highly unsaturated oils such as rapeseed, increased the level of FFAs in milk. Protected oil supplements have been found to lead to reduced lipolysis in milk (Astrup et al., 1979) or to have little effect on FFA level (Urquhart et al., 1984). 

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). 

Detrimental Effects of Lipolysis in Milk and Milk Products... 

In milk with a normal pH of 6.7, most of the acids are in the salt form and have much less flavor than if they were completely in the acid form (Kuzdzal-Savoie, 1980). In fact, acidification of milk greatly enhances the sensitivity of organoleptic detection of lipolysis in milk (Tuckey and Stad-houders, 1967). The detection of rancidity is reduced by the association of the FFAs with certain proteins in milk (Parks and Allen, 1979 Keenan et al., 1982) and by heating of milk (Kintner and Day, 1965). The phase in which the fatty acids are soluble also influences their flavor threshold, since the short-chain acids have much lower thresholds in fat than in water, while the opposite applies to the long-chain acids (Patton, 1964). For example, butyric acid (C o) has a flavor threshold of 7 mg/kg in water, but only of 0.6 mg/kg in oil (Delahunty and Piggott, 1995). 

Brathen, G. 1984. Lipolysis in milk and factors responsible for its development. In Challenges to Contemporary Dairy Analytical Techniques, pp. 279-292, The Royal Society of Chemistry, London. 

Chazal, M.P., Chilliard, Y. 1987a. Effect of breed of cow Friesian and Montbeliarde on spontaneous and induced lipolysis in milk. J. Dairy Res. 54, 7-11. 

Downey, W.K. 1975. Lipolysis in milk and dairy products. Definition of problem. Document 86, International Dairy Federation, Brussels, pp. ii-iv. 

Jensen, R.G., Gander, G.W., Duthie, A.H. 1960. Spontaneous and induced lipolysis in milk during alternate feeding of two winter rations and of a winter ration and pasture. J. Dairy Sci. 43, 762-768. 

Koops, J., Klomp, H. 1977. Rapid colorimetric determination of free fatty acids lipolysis in milk by the copper soap method. Neth. Milk Dairy J. 31, 56-74. 

Stobbs, T.H., Deeth, H.C., Fitz-Gerald, C.H. 1973. Effects of energy intake on spontaneous lipolysis in milk from cows in late lactation. Aust. J. Dairy Technol. 28, 170-172. 

Sundheim, G., Bengtsson-Olivecrona, G. 1985. Lipolysis in milk induced by cooling or by heparin comparisons of amount of lipoprotein lipase in the cream fraction and degree of lipolysis. 1. Dairy Sci. 68, 589-593. 

---