Milk lipases, consequences

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 ... 

Lipolysis in raw milk can be readily initiated by vigorous agitation, causing foaming. Such treatment disrupts the milk fat globule membrane and renders the milk triglycerides more accessible to milk lipase. Incorporation of air (or other gas) and consequent foam formation are essential for damage... 

Chemical Inhibition. A large variety of chemical compounds have been added to milk or purified lipase. The conditions under which the inhibitor is studied are very important. Factors such as pH, temperature, time of addition of the chemical, sequence of addition of reactants, and the presence or absence of substrate are undoubtedly involved. The presence of substrate appears to offer some degree of protection to the enzymes. Consequently, in lipase studies, the surface area of the emulsified substrate is probably also important. 

Safari et al. (1993) examined the interesterification of milk fat by the lipase from Rhizomucor miehei in various organic solvents (hexane, hexane-choloroform (70 30, v/v), and hexane-ethylacetate (70 30, v/v)). The addition of chloroform or ethyl acetate to hexane increased lipase activity. It was suggested that the polarity of the solvent influences the partitioning of water in the system with consequent effects on enzymic activity. Bornaz et al. 

In this chapter, the lipolytic enzymes in milk and milk products and the causes, consequences and assessment of their action are discussed. The significance of lipases in human nutrition and in the production of characteristic flavors in certain dairy products is also covered. 

Unlike milk LPL, microbial lipases do not require a fatty acid acceptor such as BSA (Bengtsson and Olivecrona, 1980). Blood serum has been found to activate some of these enzymes (Fitz-Gerald and Deeth, 1983), including P. fluorescens lipases, and these have, consequently, been designated lipoprotein lipases (Aisaka and Tarada, 1979 Stepaniak and Sorhaug, 1989). 

---