Portal de Periódicos da CAPES

Inhibition of Lipase and Lipolysis in Milk

1959; Elsevier BV; Volume: 42; Issue: 3 Linguagem: Inglês

10.3168/jds.s0022-0302(59)90593-4

1529-9066

E. N. Frankel, N.P. Tarassuk,

Milk Quality and Mastitis in Dairy Cows

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.Basic information on the stability of milk lipase is of practical and fundamental importance.Thus far, heat treatments have been used exclusively to inactivate milk lipase.Other inactivation treatments might be useful in dairy processes where milder heat treatments are desirable.Work on the isolation and purification of lipase from milk requires a knowledge of conditions for maximum stability.The inhibition of different activation treatments used to induce lipolysis in milk also may shed further light on the mechanism involved in the activation of lipolysis in milk.Studies on the inactivation of milk lipase were reviewed by Herrington (7).The results o'f those studies were complicated by uncertainties involved in the methods used to-determine this enzyme system.A previous discussion of this problem led to standardization of a procedure to measure the lipolytie activity of milk toward milk fat (5).Failure to consider the effect of the instability of the lipase system on the aging of milk prior to activation (17) may have resulted in additional complications.In a previous study (6), using milk fat and simpler esters as substrates, we have shown that lipase is more stable to aging, heat, acid, alkali, light, oxidizing agents, and formaldehyde than the simple esterases of the same milk.It was also observed that tipase was more stable to aging in whole milk than inskimmilk.Therefore, the presence or absence of milk fat may be an impo'rtant variable in studies on milk lipase stability.The mechanism by which different activation treatments induce lipolysis in normal milk is not well understood.There is controversy as to whether the