Protein deteriorative changes

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

The deteriorations and the deteriorative reactions of proteins have been studied by scientists in many different fields for many centuries. In order to give proper tribute to the almost ancient importance of proteins, it would be necessary to summarize the history of agriculture, medicine, food processing, and much of industry. Scientists and technologists have long recognized both the adverse and beneficial facets of deteriorative changes in proteins. 

This review focuses upon the post-translational modification and chemical changes that occur in elastin. Outlined are the steps currently recognized as important in the assembly of pro-fibrillar elastin subunits into mature fibers. Descriptions of some of the proposed mechanisms that appear important to the process are also presented. It will be emphasized that from the standpoint of protein deterioration, elastin is a very novel protein. Under normal circumstances, the final product of elastin metabolism, the elastin fiber does not undergo degradation that is easily measured. Unlike the metabolism of many other proteins, deterioration or degradation is most evident biochemically in the initial stages of synthesis rather than as a consequence of maturation. Since the presence of crosslinks is an essential component of mature elastin, a section of this review also addresses important features of crosslink formation. 

Deteriorative Changes of Proteins During Soybean Food Processing and Their Use in Foods... 

There is another phenomenon, regarded as a deteriorative change in the protein of soy milk, caused also by the evaporation of water. This is a film formation on the surface of soy milk, which occurs when heated soy milk is kept open to the air. This phenomenon is observed not only in heated soy milk but also in heated cow s milk. Film formation of soy milk occurs only when the soy milk is heated above 60°C and there is evaporation of water from the surface of the soy milk. The mechanism of protein insolubilization is basically the same as that of soy milk powder produced from heated soy milk (10. When water is removed from the surface of heated soy milk by evaporation, the molecular concentration of protein near the surface increases locally and the exposed reactive groups of the denatured molecules come close enough to interact intermolecularly both by hydrophobic interactions and through the sulfhydryl/disulfide interchange reaction to form a polymerization (film) on the surface. The upper side of the film contains more hydrophobic amino acids because of orientation of the hydrophobic portions of the unfolded molecules to the atmosphere rather than into the aqueous solution. 

Deteriorative Changes of Soybean Protein After Freezing and Their Use for Foods... 

Effect of Deteriorative Changes of Soybean Protein During Heating on Enzyme Digestibility... 

A very short time treatment minimized the other deteriorative changes. Therefore the yield of soy sauce, based on weight of protein of the starting soybean, has increased from 65 of 20 years ago to almost 905 at the present. 

Deterioration of the physical properties of proteins during food processing or food storage can be ascribed primarily to an irreversible insolubilization of proteins. However, a deteriorative change for one purpose can be a favorable one for another purpose. In Japan, for instance, the irreversible insolubilization of soybean proteins has been utilized effectively for production of soybean protein foods, such as tofu, kori-tofu, and yuba. 

Fats and Oils. Foods are complex structures of proteins, carbohydrates, fats, enzymes, vitamins and minerals. Fatty components or lipids are responsible in many foods for deteriorative changes during... 

There are several sources of food contamination by microorganisms that, on contact with food, may promote its deterioration, changing its appearance, flavor, odor, and texture. These changes occur due to the intake of chemical substances, such as carbohydrates, proteins, and lipids, by microorganisms for use as an energy source. 

This outcome was consistent with a hypothesis that structural deterioration could have been a byproduct of microorganism activity. The higher lipid content in the poorly preserved tissue suggests that those lipids are primarily extrinsic, that is, that they were produced by bacteria and/or fungi. As the food source for such microorganisms, the protein within the bone may have been substantially altered in concert with the microstructure deterioration. The quantification of the changes to the organic fraction became our next focus of research. 

The term ageing of polymers is usually reserved for long-term changes in properties of polymers exposed to weathering conditions. It may involve any of the above processes and include physical processes of polymer recrystallization and denaturation of, for example, protein structure in biopolymer chemistry. The term corrosion, used essentially for the deterioration (ageing) of metal... 

Abiotic spoilage is produced by different physical and chemical changes such as hydrolytic action of enzymes, oxidation of fats, breakdown of proteins, and a browning reaction between proteins and sugars. However, in this chapter we focus on microbial deterioration and their effects on bioactive compounds. 

The formation of free radicals after lipid oxidation is known to play a key role in the deterioration of meat flavor 8, 23), Since proteins constitute a major portion of the muscle s composition, the relationship between chemically active radical species and decomposition of food flavor proteins and peptides needs to be studied in detail. Data has been presented showing the correlation of proteins with flavor (Figures 5 and 6). Data is now presented showing how soluble meat proteins change in an environment where free radicals are induced by a free-radical oxidation generating system or FROG (Figure 10). 

Postirradiation reactions are well known in photo and radiation chemistry. Some of the reactions which occur in polymers are of interest here. Of note also are postirradiation-induced changes which occur in proteins. These include deamination, dephosphorylation, and gelation. That radiation-treated food may either improve or deteriorate during storage is therefore a distinct possibility. 

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