Rancidity hydrolytic

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 ... 

Deeth, H.C. and Fitz-Gerald, C.H. (1995) Lipolytic enzymes and hydrolytic rancidity in milk and milk products, in Advanced Dairy Chemistry, Vol. 2 Lipids, 2nd edn (ed. P.F. Fox), Chapman Hall, London, pp. 247-308. 

To increase the stability of milk products. Lipoprotein lipase is probably the most important in this regard as its activity leads to hydrolytic rancidity. It is extensively inactivated by HTST pasteurization but heating at 78°C x 10 s is required to prevent lipolysis. Plasmin activity is actually increased by HTST pasteurization due to inactivation of inhibitors of plasmin and/or of plasminogen activators. 

The flavor defect commonly referred to as rancidity or, more specifically, as hydrolytic rancidity is caused primarily by the presence in milk of a single enzyme which was proposed to be designated as... 

Richter, R. 1981. Hydrolytic rancidity Its prevalence, measurement and significance. Am. Dairy Rev. 43, 18DD, 18HH. 

Free fatty acids released by lipolysis of milk fat greatly depress the surface tension of milk. In fact, surface tension has been used to some extent as an objective index of the development of hydrolytic rancidity (Dunkley 1951 Herrington 1954 Hetrick and Tracy 1948 Tarassuk and Smith 1940). Its value for this purpose is somewhat limited by... 

Dunkley, W. L. 1951. Hydrolytic rancidity in milk. I. Surface tension and fat acidity as measures of rancidity. J. Dairy Sci. 34, 515-520. 

Homogenized milk is generally not used for cheesemaking because of the cost and potential increase in hydrolytic rancidity in cheese. There are a few major exceptions cheese spreads, cream, Neufch tel, and blue cheese (Kosikowski 1977). 

Hydrolytic rancidity flavor defects in Swiss, brick, and Cheddar cheeses have been linked to high concentrations of individual short chain free fatty acids (Woo et al 1984). Lipases from psychrotrophic bacteria have been implicated in causing rancidity in cheese (Cousin 1982 Kuzdzal-Savoie 1980), although most starter streptococci and lactobacilli isolated from cheese are also capable of hydrolyzing milk fat (Paulsen et al. 1980 Umemoto and Sato 1975). Growth of Clostridium tyrobutyricum in Swiss cheese causes the release of butyric acid and subsequent rancid-off flavors (Langsrud and Reinbold 1974). The endogenous lipoprotein lipase is also responsible for hydrolytic rancidity in nonpasteurized milk. 

Butter consistency can also be adjusted by manipulating its air and moisture contents (Kulkarni and Rama Murthy, 1985). When the moisture content of butter was increased from 12 to 15%, a softer texture was observed at both 5 and 15°C. Further increases in moisture content (up to 35%), however, drastically changed the rheological properties of butter (Kulkarni and Rama Murthy, 1985). The disadvantages of adding moisture to soften the texture of butter include structural stability, increased potential for microbial growth and hydrolytic rancidity, and violating standards of identity. 

In addition to positive aspects, numerous flavor and textural defects may be associated with the fat phase of ice cream. Such flavor defects are usually related to either autoxidation of the fat, resulting in oxidized flavors (cardboardy, painty, metallic) or, especially in the case of milk-fat, lipolysis of free fatty acids from triglycerides by the action of lipases (referred to as hydrolytic rancidity). A significant content of free butyric acid gives rise to very undesirable rancid flavors. These defects tend to be present in the raw ingredients used in ice cream manufacture, rather than promoted by the ice cream manufacturing process itself. However, processing... 

Hydrolytic rancidity in milk and milk products has been a concern to the dairy industry of most countries (Downey, 1975). Although it is not... 

Hydrolytic rancidity results from the hydrolytic degradation of milk lipids. The hydrolysis is catalyzed by lipases and produces free fatty acids (FFAs), some of which have a low flavor threshold and can cause unpleasant flavors in milk and milk products. These flavors are variously described as rancid, butyric, bitter, unclean, soapy or astringent. The lipases involved are of two types indigenous milk enzyme(s) and enzymes of microbial origin. 

Causes of Hydrolytic Rancidity in Milk and Milk Products... 

Mastitis and microbial contamination can also contribute to hydrolytic rancidity. In general, lipolysis caused by indigenous milk lipase accounts for most of the rancidity in raw milk and cream microbial lipolysis is of minor practical importance as little if any lipolysis occurs before the bacterial population reaches 106—107 cfu/ml (Suhren and Reichmuth, 1990). However, in stored milk products, lipolysis by microbial lipases is of greatest significance. Short shelf-life products such as pasteurized milks may be affected by pre-pasteurization lipolysis caused by milk lipase but may be affected by bacterial lipolysis at the end of their shelf-life (Deeth et al., 2002). 

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