Denaturation lipid oxidation

Meat products have to be stabilised in some cases, as meat lipids contain no natural antioxidants or only traces of tocopherols. Most muscle foods contain, however, an efficient multi-component antioxidant defence system based on enzymes, but the balance changes adversely on storage. The denaturation of muscle proteins is the main cause of the inbalance as iron may be released from its complexes, catalysing the lipid oxidation. Salting contributes to the negative effects of storage, as it enhances oxidation. Using encapsulated salt eliminates the deleterious effect of sodium chloride. 

Denaturation of hemoproteins in cooked meats leads to liberation of the heme and oxidation of the porphyrin ring. Nonheme iron is less available nutritionally than heme iron and affects lipid oxidation more. In methemoglo-bin and metmyoglobin solutions heated for one hour at 78°C and 100°C the degradation of heme was about 22 to 26%, while after two hours at 120°C it increased to about 85 to 95% (Oellingrath, 1988). In meat cookery, however, such severe conditions do not apply. 

Adams, J.B., Harvey, A., and Dempsey, C.E. 1996. Regenerated and denatured peroxidase as potential lipid oxidation catalysts. Food Chem. 57 505-514. 

In native state, proteins exist as either fibrous or globular form. Protein should be denatured and unfolded to produce an extended chain structure to form film. Extended protein chains can interact through hydrogen, ionic, and hydrophobic bonds to form a three-dimensional stmcture (24). Protein films are excellent gas barriers but poor moisture barriers because of their hydrophilic nature. Mechanical properties and gas permeability depend on the relative humidity (1). Al-ameri (25) smdied the antioxidant and mechanical properties of soy, whey and wheat protein, and carrageenan and carboxymethyl cellulose films with incorporated tertiary-butylhy-droquinone (TBHQ), butylated hydroxytoluene (BHT), fenugreek, and rosemary extracts. Armitage et al. (26) studied egg albumin film as a carrier of natural antioxidants to reduce lipid oxidation in cooked and uncooked poultry. 

Biochemical Degradation Biochemical degradation is another harmful transformation that occurs with most biological products. There are four key reactions to consider lipid oxidation, Maillard browning, protein denaturation, and various enzyme reactions. These reactions are both heat- and moisture-dependent such that control of temperature and moisture profiles can be very important during drying. 

Freezing is one of the most common preservation methods to maintain the quality of fish and shellfish. Although freezing or frozen storage is able to prevent microbial spoilage effectively, it cannot terminate chemical deteriorations, which mainly involve protein denaturation and lipid oxidation of the products. 

Another important factor affecting storage stability of dehydrated foods is temperature and period of storage. Generally, the storage stability bears an inverse relationship to storage temperature, which affects not only the rate of deteriorative reaction (enzyme hydrolysis, lipid oxidation, NEB, protein denaturation), but also the kind of spoilage mechanism. 

The ferry 1-Fe" is slowly reduced to the met-form. If the globin structures of deoxy-, oxy-or met-forms of myoglobin are disturbed, they are reversibly or irreversibly converted into hemochrome-Fe + or hemichrome-Fe. The role of these denatured species in lipid oxidation of meat is not clear. When ferric hemin is detached from the globin, the ferryl ion can initiate lipid oxidation by hydrogen abstraction to produce a lipid radical plus a proton. Iron can also be released from hemin in the presence of hydroperoxides to participate in lipid oxidation processes. Ascorbic acid and other reducing compounds in muscle cytosol effectively inhibit lipid oxidation promoted by ferryl ions in membranes. 

Although the free iron is catalytically active, the relative importance of protein-bound iron is being debated. Lipid oxidation in cooked meat is not only attributed to changes in iron distribution by protein denaturation and the release of catalytically active non-heme iron, but also to the disruption of cell membranes in meat that brings the polyunsaturated hpids in close contact to the catalysts. Unfortunately, in many studies using the TBA test to determine the effects of different forms of iron on lipid oxidation in meats, the results must be interpreted with caution, because the TBA reaction is significantly affected by iron and other metals, and is subject to serious interference by other factors. In addition to products of lipid oxidation, TB ARS are also formed from proteins and nucleic acids and other non-lipid components in meat tissues that confound the results of the TBA test. 

However, before reaching the consumer, food emulsions undergo a variety of processes including chemical reactions such as denaturation, polymerization of protein, interface aging and lipid oxidation[2,9]. The latter has an appreciable influence on the technological, sensory and nutritional qualities of the products[3, 9, 10]. 

WOF is a problem associated with the use of precooked meat products such as roasts and steaks. The term WOF was first used by Tims and Watts (2) to describe the rapid development of oxidized flavors in refiigerated cooked meats. Published evidence indicates that the predominant oxidation catalyst is iron from ntyoglobin and hemoglobin, which becomes available following heat denaturation of the protein moiety of these complexes. The oxidation of the lipids results in the formation of low molecular weight components such as aldehydes, adds, ketones and hydrocarbons which may contribute to undesirable flavor. 

The aim is to extract protein molecules as pure as possible. Detergents generally help membrane proteins to dissolve and separate from lipids. Reductants are used to reduce disulfide bonds or prevent oxidation. Denaturing agents alter ionic strength... 

LPO causes non-enzymic oxidation of unsaturated lipids, probably acting through its haem group the heat-denatured enzyme is more active than the native enzyme. 

Irritant dermatitis does not involve an immune response and is typically caused by contact with corrosive substances that exhibit extremes of pH, oxidizing capability, dehydrating action, or tendency to dissolve skin lipids. In extreme cases of exposure, skin cells are destroyed and a permanent scar results. This condition is known as a chemical burn. Exposure to concentrated sulfuric acid, which exhibits extreme acidity, or to concentrated nitric acid, which denatures skin protein, can cause bad chemical bums. The strong oxidant action of 30% hydrogen peroxide likewise causes a chemical bum. Other chemicals causing chemical bums include ammonia, quicklime (CaO), chlorine, ethylene oxide, hydrogen halides, methyl bromide, nitrogen oxides, elemental white phosporous, phenol, alkali metal hydroxides (NaOH, KOH), and toluene diisocyanate. 

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