Heating at high temperatures (like boiling ) cause denaturation of whey proteins and their interactions with K-casein .Beside that heating cause deamination and dephosphorylation of casein .
Dear Patil, As per your answer and the reply by Jasim, effect of Heat on casein protein is clear.
In case of A1 or A2 type milk:
The single amino acid difference between the A1 and A2 type of β-casein is due to the naturally occurring "single nucleotide polymorphism" (SNP) in the DNA of β-casein genes of the cow. Theoretically, this difference in amino acid sequence suggests a conformational difference in the secondary structure (folding of the amino acid chain) of the expressed protein, which subsequently may have ramifications on the physical properties of the respective casein micelles, further affecting digestion and nutritional properties of the caseins.
In vitro studies have shown that, the peptide β-casomorphin-7 (BCM‐7) is produced by the successive gastrointestinal proteolytic digestion of β-casein A1, but such cases were not seen in β-casein A2 type milk, may be this results in differential levels of bioactivities.
It is clear that -when A1 milk is heated/boiled, it wont alter or denature or effect the release of BCM-7. this peptide is produced only by digestive enzymatic hydrolysis. Heat denaturation wont be a solution to reduce the A1 milk effect.
Different proteolytic systems involved in fermented milk or cheese manufacture can potentially hydrolyze β-casein to BCM-7 or other BCMs and further degrade these peptides to shorter-chain peptides and even amino acids (EFSA Scientific Report, 2009).
Heating milk for microbial destruction has very little affect on A1 and A2 Beta Casein. The pasteurization time is not long enough to denature this protein. However, longer heating times above 72 C/15s will denature the A1 and A2. This is typical for yogurt manufacturing. In this case, the term "pasteurization" is redundant, because the yogurt mass is not "more pasteurized", the extended heating time is only needed for denaturation, and not for microbial destruction.
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