fair enough

milk proteins are classified in two major categories, the concentration of which in bovine milk is The first and most abundant is the casein family, which consists of several fractions (mainly alpha s1, alpha s2, beta, kappa)

and most of them exist in a colloidal particle known as the casein micelle. The second protein groupinmilk is the whey proteins which include heat-sensitive, globular, water soluble proteins and enzymes

Heat treatment affects the molecular structure of milk proteins at the interfaces of oil-in-water emulsions

and in aqueous media. Experimental evidence of the impact of thermal processing on milk protein

structure is presented and the contribution of whey proteins and caseins at film formation during

emulsification is discussed. Recent advances in understanding the effect of heat treatment in milk

protein functionality at emulsion interfaces are reviewed with particular emphasis on the emulsifying

ability of whey proteins with or without the presence of the casein fraction. The major findings regarding

the destabilizing mechanisms of oil-in-water emulsions brought about by heat-induced denaturation of

milk proteins are presented.

I agree with Dr.  Khetam

Each enzyme has a specific site of action on its target molecule, and optimal conditions (pH and temperature). There are a large number of enzymes in milk and the functions of many are not well-defined. It should be noted that the enzymes in milk do not make a major contribution to the digestion of milk in humans, which is accomplished by enzymes in the human stomach and small intestine.

Lipases are enzymes that degrade fats. The major lipase in milk is lipoprotein lipase. It is associated with the casein micelle. Agitation during processing may bring the lipase into contact with the milk fat resulting in fat degradation and off-flavors. Pasteurization will inactivate the lipase in milk and increase shelf life.

Proteases are enzymes that degrade proteins. The major protease in milk is plasmin. Some proteases are inactivated by heat and some are not. Protein degradation can be undesirable and result in bitter off-flavors, or it may provide a desirable texture to cheese during ripening. Proteases are important in cheese manufacture, and a considerable amount of information is available in the cheese literature.

Alkaline phosphatase is a heat sensitive enzyme in milk that is used as indicator of pasteurization. If milk is properly pasteurized, alkaline phosphatase is inactivated.

Dear Dr. B. Jasim

this link may help you

http://jfoodprotection.org/doi/pdf/10.4315/0022-2747-33.12.377?code=fopr-site

Dear Dr.Bassima

  All enzymes are protein in nature ,so ,Kindly look in link can help you

depa.fquim.unam.mx/amyd/archivero/24Leche_14240.pdf

Dear Dr. Bassima 

this paper may help you

Article Ribonucleosides: Interesting nucleo compounds and chemical p...

Dear Dr. Basima

Since enzymes are proteins in its chemical nature, I think that any heating above 60 C will denaturant proteins and so it for enzymes. 

Regards

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwir-J2U0NvTAhVPYlAKHdspD08QFgg2MAE&url=http%3A%2F%2Fdepa.fquim.unam.mx%2Famyd%2Farchivero%2F24Leche_14240.pdf&usg=AFQjCNFIwwwmGX9WcR-iWnuFHX2vGgXDPQ&sig2=StoLXgGizwc8mb2F9nsuVQ

hi. according to temp , if high lead to breakdown

Thanks for all answers

Heat treatment (pasteurisation) inactivates enzymes like protease and lipase but these enzymes have no physiological role in human digestion. Heat treatment may lower the activity of some enzymes minimally.

Hallo Dear Abbas

The highest denaturation of enzyme and whey proteins was found in samples subjected to ultrasound and heat. At 61, 70, and 75.5 °C a synergistic effect between ultrasound and heat was observed for the inactivation of alkaline phosphatase, γ-glutamyltranspeptidase, and lactoperoxidase, respectively. A noticeable synergism between ultrasound and heat was detected for α-lactalbumin and β-lactoglobulin denaturation.

http://pubs.acs.org/doi/abs/10.1021/jf990181s

fair enough

Hi

I think because all the enzymes are proteins in nature, I think that any heating above 60 C will effect these proteins and lead to denaturation of these enzymes .

Regards

Dear Dr.

I think the heating lead to denaturantion of milk proteins and so it for enzymes. 

Best wishes

I gree with Dr. Jabbar