Amino acids degradation during peptide hydrolysis

Peptides formed enzymically or by mineral acid hydrolysis or thermal degradation of higher molecular veight protein can also serve as flavor precursors in thermally induced reactions. The reactivity of peptides is evidenced by their behavior during pyrolysis/GC (9), heating in air (10), reactions vith mono- (11), and dicarbonyl (12, 13) compounds and reactions in hot acetic acid (1A). The types of reactions observed for peptides include side-chain thermolysis, fragmentation into amino acids, DKP formation and Halliard reaction vith ambient carbohydrates. 

Chymotrypsin specifically cleaves peptide bonds whose C-terminal amino acid is adjacent to non-polar aromatic amino acid residues or the bulky, hydrophobic methionine. Because these residues are often buried in the interior of proteins, including chymotrypsin, the self-hydrolysis of native, folded chymotrypsin is very inefficient. In fact, during digestion, chymotrypsin acts most effectively on partially degraded and denatured (unfolded) proteins. 

Hydrolysis with 6 M HCI in a sealed tube at 110°C for 24 h converts wool completely to its component amino acids for amino acid analysis. Tryptophan is destroyed by this procedure, and cystine, serine, and threonine are partially degraded. Peptide bonds on both sides of amino acid residues with acidic side-chains (aspartic and glutamic acid residues) are hydrolyzed faster than other peptide bonds [260]. Similarly, peptide bonds on both sides of cysteic acid residues hydrolyze rapidly therefore, wool oxidized during shrink-proofing is more susceptible to acid damage than untreated wool. 

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