Inhibition of Lipase and Lipolysis in Milk

Abstract

The storage stability of milk lipase was markedly increased by the addition of glutathione, hydroquinone, and potassium thiocyanate. These results indicate that the loss of lipase activity on aging milk results mainly from oxidative changes. The greater effectiveness of glutathione in stabilizing milk lipase may indicate the importance of sulfhydryl groups for this enzyme activity. The heat inactivation of milk lipase followed first-order kinetics. The pH of optimum stability was in the range of 6.6–7.6. Milk lipase was very sensitive to photo-inactivation and to oxidizing agents. The stability of milk lipase to heat, light, hydrogen peroxide, and copper, like storage stability, was greater in whole milk than in skimmilk. It is suggested that the sulfhydryl groups in the membrane material of the fat globules are preferentially oxidized, thus protecting the lipase system. The inhibition of lipolysis was greatly decreased when inhibitors were applied after activation treatments of lipolysis. The evidence indicates that this protection of the lipase system may be due to a specific enzyme-substrate combination which results from the activation treatments. It is concluded that the lipase system is affected by the activation treatments of lipolysis. © 1959, American Dairy Science Association. All rights reserved.