Protein Racemization

Racemization is a conversion of an L amino acid into a D amino acid. Amino acids are asymmetric, so L amino acids can be deprotonated by creating a very unstable charged carbon ion (flat structure, so the proton can either come from front or back). Out of the carbon ion, alanine and cysteine (they can be kicked out) and can produce hydrogen gas and H2S, and produce an intermediated (dehydroalanine). The enzymes cannot work on the R amino acids so the proteins stay there undigested. R amino acids in very high concentrations can be toxic.

It occurs when we are heating foods, It can occur during sterilization experiments (such as boiling).  Since we are losing essential amino acids, nutritional value is reduced. Since it is on protein structure, not amino acid, the body might not recognize the protein, so will not recognize it and will have a problem digesting it, thus has an impact on bioavailability. R amino acids can also be toxic.

In cysteine rich food it can be smell (H2s), for example in milk pasteurization (dehydroalanine). This reaction is produced under high temperatures, however alkaline environments enhance this reaction (enhance formation of dehydroalanine). Soy proteins are extracted in alkaline environment, so during production of soy milk will produce some of these degradation products. So in proteins extracted in alkaline environments, there will be higher concentrations of R amino acids and Dehydroalanine.