Lipolysis temperature activation

Wang, L. and Randolph, H. E. 1978. Activation of lipolysis. I. Distribution of lipase activity in temperature activated milk. J. Dairy Sci. 61, 874-880. 

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 practice, temperature activation can occur if a small amount of cooled milk or cream is mixed with a larger amount of warm milk and then recooled (McDowell, 1969 Nielsen, 1978). Separation of previously cooled milk at a temperature around 30°C can lead to lipolysis if the cream is held in cold storage before pasteurization. 

Fleming, M.G. 1979. Lipolysis in bovine milk as affected by mechanical and temperature activation—a review. Irish J. Food Sci. Technol. 3, 111-130. 

Kon, H., Saito, Z. 1997. Factors causing temperature activation of lipolysis in cow s milk. Milchwissenschaft 52, 435-440. 

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. 

The second way in which fats deteriorate is oxidative lipolysis. This is an entirely different process in which oxygen free radicals add across double bonds. Oxidative rancidity can be prevented or reduced by several different routes. One way is to ensure that no double bonds are present. Another is to use anti-oxidants that act as free radical traps. Exposure to oxygen and ultraviolet light should be avoided. Reducing the temperature has no effect since free radical processes have a zero activation energy. 

Most, if not all, milks contain sufficient amounts of lipase to cause rancidity. However, in practice, lipolysis does not occur in milk because the substrate (triglycerides) and enzymes are well partitioned and a multiplicity of factors affect enzyme activity. Unlike most enzymatic reactions, lipolysis takes place at an oil-water interface. This rather unique situation gives rise to variables not ordinarily encountered in enzyme reactions. Factors such as the amount of surface area available, the permeability of the emulsion, the type of glyceride employed, the physical state of the substrate (complete solid, complete liquid, or liquid-solid), and the degree of agitation of the reaction medium must be taken into account for the results to be meaningful. Other variables common to all enzymatic reactions—such as pH, temperature, the presence of inhibitors and activators, the concentration of the enzyme and substrate, light, and the duration of the incubation period—will affect the activity and the subsequent interpretation of the results. 

The freezing of raw milk followed by thawing to 4°C causes an increase in lipolysis compared to that of unfrozen control milk stored at 4°C, but the increase in activity varies considerably. Repeated freezing and thawing also causes a notable increase in lipolytic activity. The temperature of freezing has a marked effect, the increase in lipolysis being most pronounced when the temperature is lowered from —10 to... 

The data of Nilsson and Willart (1960) indicate that heating at 80°C for 20 sec is sufficient to destroy all lipases in normal milk. Their studies included assays after 48 hr of incubation following heat treatment. At lower temperatures for 20 sec, some lipolysis was detected after the 48-hr incubation period after heating. Thus, 10% residual activity remained at 73 °C. Below the temperature of 68°C the amount of residual activity was enough to render the milk rancid in 3 hr temperatures below 60 °C had no appreciable effect on lipolysis. With holding times of 30 min, 40°C produced only slight inactivation, and at 55°C 80% inactivation was reported. 

The extent of lipolysis in raw milk or cream following activation is determined by the temperature and duration of storage. Rapid cooling to, and storage at, a low temperature (without freezing) minimizes lipolysis. The rate of lipolysis falls off with time but can be accelerated by further activation treatments (Downey, 1980). 

Both proteolysis and lipolysis are involved in the cheese ripening process. The rate and extent of their interactions are influenced by the rennet preparation used, characteristics of the starter culture, pH, moisture range, salting practices, temperature, and the activity of adventitious microorganisms present in or on the cheese. 

At natural moisture levels, the FFA content of wholemeal increases with storage temperature, and no inactivation of lipolysis is evident, even when heated at 80 C for 7 days. However, at higher moisture contents, the enzyme is inactivated relatively rapidly. For example, at 80 C and 50% moisture, the lipase activity is inactivated within 15 min. Autoclaving (110 C, 10 min) gives adequate stabilisation. ... 

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