Oxidative deterioration in foods

Food antioxidants in the broadest sense are all of the substances that have some effect on preventing or retarding oxidative deterioration in foods. They can be classified into a number of groups (Kochhar and Rossell 1990). 

Some volatile aldehydes formed by autoxidation of unsaturated fatty acids are listed in Table 1. The aromas of aldehydes are generally described as green, painty, metallic, beany, and rancid, and they are often responsible for the undesirable flavors in fats and oils. Hexanal has long been used as an index of oxidative deterioration in foods. Some aldehydes, particularly the unsaturated aldehydes, are very potent flavor compounds. Table 2 fists aroma characteristics of some common aldehydes found in fats and oils (8). 

Kiokias, S., Lampa, K., Tsimogiannis, D., and Oreopoulou, V., Inhibition of oxidative deterioration in food emulsions, in Proceedings of INTRAFOOD-EFFoST Conference, Valencia, Spain, Vol. 2, p. 1237,... 

Methods to measure lipid oxidation have generally been unspecific and not sufficiently sensitive to measure flavor and low levels of oxidative deterioration of food lipids. Several specific complementary methods are needed to determine the contribution of lipid oxidation products formed at different stages of the multi-step process of oxidative deterioration in foods. Since polyunsaturated hydroperoxides decompose more readily at higher temperatures to form aldehydes causing rancidity, it is important to measure both aldehydes and hydroperoxides to monitor lipid oxidation. For the reliable prediction of shelf life of foods containing polyunsaturated lipids, it is essential to use more than one specific method to determine oxidation at different levels and to store samples at several temperatures, preferably between 40 and 60°C. 

Many methods are available for determining food antioxidant capacity, which is an important topic in food and nutrition research. However, there is a great need to standardize these methods because the frequent lack of an actual substrate in the procedure, the system composition, and the method of inducing oxidation could limit their accuracy. In fact, antioxidant activities in complex systems cannot be evaluated satisfactorily using a single test, and several test procedures may be required. The search for more specific assays that can be more directly related to oxidative deterioration of foods and biological systems should be the objective of future investigations. 

As oxidation normally proceeds very slowly at the initial stage, the time to reach a sudden increase in oxidation rate is referred to as the induction period (6). Lipid hydroperoxides have been identified as primary products of autoxidation decomposition of hydroperoxides yields aldehydes, ketones, alcohols, hydrocarbons, volatile organic acids, and epoxy compounds, known as secondary oxidation products. These compounds, together with free radicals, constitute the bases for measurement of oxidative deterioration of food lipids. This chapter aims to explore current methods for measuring lipid oxidation in food lipids. 

USE Mainly in the protection of foods for the removal of glucose from egg albumin and whole eggs prior to drying. To remove oxygen from canned foods, soft drinks, beer, and stored food. In the manuf ol test papers for diabetes control and fertility tests. To stabilize ascorbic acid and vitamin B,-prepns. In combination with catalase, for treatment of food wrappers to prevent oxidative deterioration of food Sarett, Scott, U.S. pat. 2,765,233 (1956 to Ban L. Sarett). 

Schwarz, K. 19(i2. In Symposium on Foods Oxidative Deterioration of Food Lipids (If. W. iSchultz, ed.), Chapter 20. Mack Printing Co., Easton, Pennsylvania. Schwarz, K., and Foltz, C. M. 1900. Federation Froc. 19, 421. 

In actual lipid oxidation, one cannot overlook the critical role of trace metals, which complicate the kinetic sequences of initiation and decomposition of lipid hydroperoxides. These metals catalyse both initiation of free radicals and decomposition of hydroperoxides, which become particularly significant with polyunsaturated lipids containing more than two double bonds. With these polyunsaturated lipids, although the yields of hydroperoxides are reduced in the presence of metals, they produce volatile decomposition products that have a serious impact on flavor deterioration. In foods and biological systems, the mixture of trace metals and hydroperoxides is the most important initiator that plays a key part in the development of free radical oxidation and rancidity. The use of artificial azo compounds as initiators to study free radical oxidation is therefore not relevant. 

Fluorescence techniques are very sensitive. On a molar basis, the amount of malonaldehyde detected by fluorescence is 10 to 1(X) times more sensitive than the colorimetric TB A assay. However, this method is not specific, as it measures complex mixtures resulting from the interactions of oxidized lipids, unsaturated aldehydes and malonaldehyde with proteins, peptides, amino acids, phospholipids, DNA and nucleic acids. These interactions involve oxidized or polymerized species of proteins or amino acids. The fluorescence method provides a non-speciflc but sensitive measure of oxidative deterioration in complex foods such as meats and fish, which are often difficult to analyse for... 

To learn about the real effects of antioxidants, it is therefore important to obtain specific chemical information about which products of lipid oxidation are inhibited. Several specific assays are needed to elucidate how lipid oxidation products act in the complex multi-step mechanism of lipid oxidative deterioration of foods. The results of several complementary methods are required to determine lipid oxidation products formed at different stages of the free radical chain. Since antioxidants show different activities toward hydroperoxide formation and decomposition, it is important that more than one method be used to monitor Upid oxidation. 

Hydroxycinnamates as well as their conjugates may act as powerful antioxidants. In edible plants they have received much attention as protecting agents against oxidative deterioration of food. Antioxidant mechanism studies on ferulic acid and its coupling products with linoleate on the molecular level have been conducted recently. A radical scavenging reaction occurred at the 3 -position of the ferulate radical with four types of peroxyl radicals of ethyl linoleate. The produced peroxides subsequently underwent intramolecular rearrangement to afford stable tricyclic peroxides (Masuda et al. 2006). 

Figure 1. A schematic of die potential reaction pathways that intact the oxidative deterioration of foods. Mn and Mn " are transition metals in their reduced and oxidized states RH, ROOH and AOH are an unsaturated fatty acid, lipid hydroperoxide and chain breaking antioxidant and R , RO ROO are alkyl, alkoxyl and peroxyl radicals, and Oj and LOX are singlet oxygen and lipoxygenase, respectively.

Plants are a rich source of phenolic and polyphenolic confounds that serve as secondary metabolites to protect them from oxidative stress of photos3mdiesis and wound and also as antifeedant against herbivores. In addition, diese phenolics serve as good filters against UV light. The mixture of compounds present in different plant sources provides an excellent opportunity for exploitation to control oxidative deterioration of food lipids. The type, concentration and complexity of phenolics in different plants present a challenge for dieir isolation, identification and application. Examples will be provided to demonstrate the isolation, testing, and activity determination of a number of natural extracts finm selected oilseeds. 

Unsaturated lipid substrates are the prime compounds of deterioration in food and cosmetics. They are constituted of mixtures of tri-, di-, and monoacylglycerols, free fatty acids, glycolipids, phospholipids, sterols, and other substances (Chen et ah, 2011). Hydrolysis, polymerization, and isomerization reactions can cause the deterioration of food, and the resulting compounds are harmful to health (Chen et ah, 2011 Ng et ah, 2014). However, the most important reaction that occurs with lipids is oxidation, because lipids are easily oxidized, even by atmospheric oxygen. This process results in the destruction of essential triglycerides and fat-soluble vitamins (A, D, E, and K), which leads to the formation of aldehydes, ketones, and free fatty acids. This is undesirable because the palatability, odor, texture, consistency, appearance, and nutritional value of the food are altered (Takemoto et ah, 2009 Andre et al., 2010). 

Lipid peroxidation occurring in food products causes some deterioration in food quality such as rancid flavor, bad taste and shortening of shelf life. The intake of oxidative foods is thought to cause serious diseases such as enlargement of liver (I) or necrosis of epithelium tissue. The factors involved in these diseases were lipidperoxidants and low-molecular conqjounds produced at the latter stage of oxidative reaction (2). Furthermore, cancer, coronary heart diseases and Alzheimer s diseases were also reported to be partially responsible for oxidation or free-radical reaction (5-6). In order to prevent foods from these deterioration and prevent us from serious diseases, it is very inq>ortant to inhibit... 

The evaluation of the degree of deterioration in food has been developed recently [56]. Almost all the loss of quality (changes in flavour particularly) is the result of oxidation. This is exemplified by the effect of molecular oxygen on the chemiluminescence intensity of a commercial salad oil at 45° as seen in Fig. 21. 

One disadvantage of fats contained within foodstuffs is the deterioration of the fat through oxidative rancidity. Many consumers find the aroma and flavor of deteriorated fats in foods repulsive, while others are fond of country ham and butter which owe thek aroma and flavor to fat rancidity and other breakdown products. The use of antioxidants (qv) makes such products commercially viable. 

JACOBSEN C, HARTVIGSEN K, THOMSEN M K, HANSEN L F, LUND P, SKIBSTED L H, H0LMER G, ADLER-NissEN J and MEYER A s (2001) Lipid oxidation in fish oil enriched mayonnaise calcimn disodium ethylenediaminetetraacetate, but not gallic acid, strongly inhibited oxidative deterioration, J Agric Food Chem, 49, 1009-19. 

The development of nontransmittable chronic illnesses is associated with the presence of oxidative agents in the body. These agents are found in air, water, or food or can be produced in the body s cells. Their high content in body cells causes an imbalance that results in oxidative stress damaging proteins, DNA, and others. As a result of this deterioration, an increase in the risk of nontransmittable chronic illnesses has been noted. In order to prevent or decrease oxidative stress, the consumption of foods rich in antioxidants, such as fruits and vegetables, is recommended (van Dokkum and others 2008 Liu 2003). 

Flavor is one of the major characteristics that restricts the use of legume flours and proteins in foods. Processing of soybeans, peas and other legumes often results in a wide variety of volatile compounds that contribute flavor notes, such as grassy, beany and rancid flavors. Many of the objectionable flavors come from oxidative deterioration of the unsaturated lipids. The lipoxygenase-catalyzed conversion of unsaturated fatty acids to hydroperoxides, followed by their degradation to volatile and non-volatile compounds, has been identified as one of the important sources of flavor and aroma components of fruits and vegetables. An enzyme-active system, such as raw pea flour, may have most of the necessary enzymes to produce short chain carbonyl compounds. 

From the legal point of view, antioxidants are substances which prolong the shelf-life of foodstuffs by protecting them against deterioration caused by oxidation, such as fat rancidity, colour changes and loss of nutrient value. Hundreds of compounds, both natural and synthesised, have been reported to possess antioxidant properties. Their use in food, however, is limited by certain obvious requirements, not the least of which is adequate proof of safety. 

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