Protein chemical deterioration

Isolation, concentration, separation, and Identification of thermally-derived aromas 1s an Important area. These aromas are frequently associated with other non-volatile products Including pigments, fats, carbohydrates, and proteins. Techniques are required to separate the volatiles from the non-volatiles without causing chemical deterioration. 

Protein chemical modification is a problem-solving technique in research and technology. Modifications also occur in natural deteriorations. Generally these modifications are with the most reactive side chains and are predominantly oxidations, reductions, and nucleophilic and electrophilic substitutions. Deteriorations include peptide bond scissions, racemizations, fi-eliminations, and formation of products by the reaction of proteins with added chemicals. Proteins are modified intentionally for structure-function relationship studies or for development of new and improved products. Although appearing quite varied, the techniques used in pharmacological, food and feed, or other industrial areas differ more operationally than from major differences in the levels of chemical sophistication that are used. 

Overview on the Chemical Deteriorative Changes of Proteins and Their Consequences... 

Approximately 150 different amino acid residues have been reported in proteins (1 5). At least half of these could undergo chemical deteriorations under the conditions of stress usually encountered. Many of these deteriorative reactions involve hydrolytic scissions, not only of peptide bonds but of the many different nonprotein substances added covalently to proteins postribosomally. These susceptible side chain groups are indole, phenoxy, thioether, amino, imidazole, sulfhydryl, and derivatives of serine and threonine (such as 0-glycosyl or O-phosphoryl), the disulfides of cystine, and, of course, the amides (such as asparagine and glutamine). With strong acid or alkali, other residues, such as serine and threonine, also are less stable. 

When proteins are deliberately treated with chemicals in order to derivatize them, the reaction conditions may also cause chemical deteriorative side reactions. Some of the more common ones are listed in Table III. Inspection of Table III shows that many of these effects are those found in deteriorative reactions... 

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