Modification chemical side reactions during

Table III. Possible Chemical Side Reactions during Protein Modification...

Fiber Whiteness and Thermal Stability. The most effective route to improved whiteness and thermal stability is modification of the polymerization. The polymer must be linear and free of conjugated or unstable chemical structures formed by side reactions during Ihe polymerization process. 

Although this approach has been widely developed, there are certain shortcomings of this approach as follows (i) the limitation in chemical backbone structure, (ii) the random distribution of ionic function (iii) the side reactions during the modification, i.e. sulfonation may lead to main-chain brealdng and reticulation (iv) the reaction reproducibility. 

Most ester-forming reactions are reversible. Depending on circumstances, these reactions may be either undesirable side reactions, for example hydrolytic chain scissions occurring during processing, or useful reactions when chemical modification or polymer recycling is considered. 

Scratch resistance depends on the hardness of the added particles. The problem of a lack of this property can be addressed by adding chemically identical particles of different crystal modification and Mohs hardness. The preferred additives are silica, alumina, layered silicates such as kaolin, titania, barium sulfate and calcium carbonate. The latter is only suitable for the DMT process owing to side reaction caused by acidity during the terephthalic acid (TPA) route. 

In general, reactive extrusion is the term applied to chemical modification of polymers in the presence of an initiator such as peroxides. During chemical modification, there can be other undesired side reactions taking place, for example, cross-linking, degradation into low MW fractions and so on. Good process control is an essential requisite for attaining a balance of desired properties. 

During the processing of foods, several chemical reactions affect the structure of some amino acids reactions with reducing sugars and polyphenols, interaction of the side chains of the amino acids, oxidation, etc. In some cases, these chemical modifications do not seem to change the nutritional availability of the amino acids involved, while in other cases, they do. In all cases, the presence of the newly formed molecules induces biochemical and physiological changes. 

Such chemical changes may lead to compounds that are not hydrolyzable by intestinal enzymes or to modifications of the peptide side chains that render certain amino acids unavailable. Mild heat treatments in the presence of water can significantly improve the protein s nutritional value in some cases. Sulfur-containing amino acids may become more available and certain antinutritional factors such as the trypsin inhibitors of soybeans may be deactivated. Excessive heat in the absence of water can be detrimental to protein quality for example, in fish proteins, tryptophan, arginine, methionine, and lysine may be damaged. A number of chemical reactions may take place during heat treatment including decomposition, dehydration of serine and threonine, loss of sulfur from cysteine, oxidation of cysteine and methio-... 

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