Oxidative deterioration of food

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. 

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. 

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. 

TAPPEL A L (1956) Freeze-dried meat. 2. The mechanism of oxidative deterioration of freeze-dried beef, Food Res, 21, 195-206. 

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. 

One of the factors responsible for the quality deterioration of foods is lipid oxidation. All foods containing fat are susceptible to oxidative rancidity, which can render the food unacceptable to the senses and also reduce nutritional quality. 

The major cause of deterioration of food products is lipid oxidation, from which low-molecular-weight, off-flavor compounds are formed. This deterioration is often caused by the oxidation of the unsaturated lipids present in foods. Off-flavor compounds are created when the hydroperoxides, formed during the initial oxidation, are degraded into secondary reaction compounds. Free radicals are also formed which can participate in reactions with secondary products and with proteins. Interactions with the latter can result in carbonyl amino... 

Autoxidation can lead to deterioration of food, drugs, cosmetics, or polymers, and inhibition of this reaction is therefore an important technical issue. The most important classes of autoxidation inhibitors are radical scavengers (phenols, sterically demanding amines [65, 66]), oxygen scavengers (e.g. ascorbic acid), UV-light absorbers, and chelators such as EDTA (to stabilize high oxidation states of metals and thereby suppress the metal-catalyzed conversion of peroxides to alkoxyl radicals) [67]. 

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). 

The thiobarbituric acid (TBA) test was proposed over 40 years ago and is now one of the most extensively used methods to detect oxidative deterioration of fat-containing foods (41). During lipid oxidation, malonaldehyde (MA), a minor component of fatty acids with 3 or more double bonds, is formed as a result of the degradation of polyunsaturated fatty acids. It is usually used as an indicator of the lipid oxidation process, both for the early appearance as oxidation occurs and for the sensitivity of the analytical method (42). In this assay, the MA is reacted with thiobarbituric acid (TBA) to form a pink MA-TBA complex that is measured spectrophotometrically at its absorption maximum at 530-535 nm (Figure 2) (9,43,44). The extent of oxidation is reported as the TBA value and is expressed as milligrams... 

Other carbonyl compounds, including propanal, pentanal, decadienal, etc., are also used for evaluating lipid oxidation in foods. For instance, propanal is a recommended indicator for lipid oxidation in foods that are high in 0)3 fatty acids, such as marine oils (67, 68). In general, it is essential to use appropriate indicators when assessing the oxidative deterioration of different food systems. 

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). 

Deterioration of food lipids by fi ee radical chain reaction and lipid peroxidation is a major problem for food manufacturers. The main route of deterioration of vegetable oils is rancidity deriving fi-om the oxidation taking place at the insaturation sites of the fatty acids in the triglyceride molecules. In general the higher the number of double bonds, the easier is... 

Usuki R, Kaneda T, Yamagishi A, Takyu C, Inaba H. Estimation of oxidative deterioration of oils and foods by measuring of ultra-weak chemiluminescence. JFoodSci 1979 44 1573-6. 

Autoxidation is the process in foods and bulk lipids, which leads to rancidity. Rancidity is the spoiled off-flavor obtained by subjective organoleptic appraisal of food. Autoxidation is the oxidative deterioration of unsaturated fatty acids via an autocatalytic process consisting of a free radical mechanism. This indicates that the intermediates are radicals (odd electron species) and that the reaction involves an initiation step and a propagation sequence, which continues until the operation of one or more termination steps. Autoxidation of lipid molecules is briefly described by reactions 1-3. ... 

Shin, M.G., Yoon, S.H., Rhee, J.B., and Kwon, T.-W., Correlation between oxidative deterioration of unsaturated hpid and normal-hexanal during storage of brown lice, J. Food Sci., 51, 460, 1986. 

Lipid antioxidants can be broadly defined as any compounds serving to inhibit oxidative processes that cause deterioration of food lipids thereby improving the quality and extending the shelf life of the food products. It has been widely accepted that antioxidants for use in food systems must satisfy the following criteria ... 

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