Deteriorative reactions, beneficial

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. 

As is the case with some chemical changes occurring in biological systems, such as the blood-clotting cascade system, deteriorative reactions considered to have a beneficial effect are found in foods. For example, the Maillard reaction (lJ7,lj3) is used to produce flavors and colors in such foods as beverages and baked goods. Heat treatment (involving denaturation) has been found to increase the nutritional value of raw soybean meal by... 

The enormous scope of the subject of corrosion follows from the definition which has been adopted in the present work. Corrosion will include all reactions at a metal/environment interface irrespective of whether the reaction is beneficial or detrimental to the metal concerned —no distinction is made between chemical or electropolishing of a metal in an acid and the adventitious deterioration of metal plant by acid attack. It follows, therefore, that a comprehensive work on the subject of corrosion should include an account of batteries, electrorefining, chemical machining, chemical and electrochemical polishing, etc. 

These reactions, whether occurring in vivo or in vitro, unintentionally or deliberately, result in chemical and physical deterioration of the proteins. As noted by the examples above, chemical deterioration may be essential or nonessential, beneficial or detrimental. The same reaction can be detrimental in one case and beneficial in another. The purpose of this volume is to explore these reactions in detail in order to maximize their benefits in the processing and formulation of our food. 

The unsaturated fatty acids in all fats and oils are subject to oxidation, a chemical reaction which occurs with exposure to air. The eventual result is the development of an objectionable flavor and odor. The double bonds and the adjacent allylic functions are the sites of this chemical activity. Oil oxidation rate is roughly proportional to the degree of unsaturation for example, linolenic fatty acid (18 3) with three double bonds is more susceptible to oxidation than linoleic (18 2) with only two double bonds, which is ten or more times as susceptible as oleic (18 1) with only one double bond. Oxidative deterioration results in the formation of hydroperoxides, which decompose into carbonyls, and dimerized and polymerized gums. It is accelerated by a rise in temperature, oxygen pressure, prior oxidation, metal ions, lipoxygenases, hematin compounds, loss of natural antioxidant, absence of metal deactivators, time and ultraviolet or visible light. Extensive oxidation will eventually destroy the beneficial components contained in many fats and oils, such as the carotenoids (vitamin A), the essential fatty acids (linoleic and linolenic), and the tocopherols (vitamin E). 

Physical vapor deposition with shadow masks is known for its simplicity for creating defined areas of thin-film catalytic material in microreactors. This technique was used to deposit silver in the reaction manifolds of microreactors for small-scale synthesis of valuable fine chemicals (Figure 1.4a). The manifolds consisted of a network of 16 parallel channels (19 mm x 600(im x 60-220 tm), in which the oxidative dehydrogenation of 3-methyl-2-buten-l-ol to aldehyde was carried out successfully for temperatures up to 464 °C [31]. The conversion increased smoothly with temperature and low oxygen and high alcohol concentrations were beneficial for selectivity, in addition to less deep channels (higher catalyst surface area to reaction channel volume). For temperatures >400°C, the selectivity deteriorated due to CO and CO2 formation. 

Sulfate attack. Soluble sulfate species can cause deterioration of concrete as a result of expansive reactions between sulfate and calcium aluminates in the cement paste. Sulfate ions are ubiquitous they are foimd in soils, seawater, groundwater, and effluent solutions. Use of cement with a low tricalcium aluminate content is beneficial for reducing the severity of attack. 

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