Antioxidants function/nature

There are numerous synthetic and natural compounds called antioxidants which regulate or block oxidative reactions by quenching free radicals or by preventing free-radical formation. Vitamins A, C, and E and the mineral selenium are common antioxidants occurring naturally in foods (104,105). A broad range of flavonoid or phenoHc compounds have been found to be functional antioxidants in numerous test systems (106—108). The antioxidant properties of tea flavonoids have been characterized using models of chemical and biological oxidation reactions. 

Sunda WG, Kieber D, Kiene R, Huntsman S (2002) An antioxidant function for DMSP and DMS in marine algae. Nature 418 317-320... 

Non-polymerisable monofunctional antioxidants were subsequently used to avoid the problem of homopolymerisation of the antioxidant. For example, melt grafting of the two maleated antioxidants, BPM and APM, on PP was shown to lead to high grafting efficiencies (up to 75% in the former and >90% in the latter) which were attributed to the non-polymerisable nature of the maleate (maleimide) functions [57, 59, 60]. The performance of these antioxidants, especially under extractive organic solvent conditions, was also shown to far exceed that of conventional antioxidants with similar antioxidant functions. Table 2, for example, shows the advantages of the grafted... 

Chromatography techniques with different detectors followed by skillful sample preparation are usually applied to quantify these antioxidants in natural sources. These techniques offer sensitive and specific analysis methods for most of the antioxidants. This is the first book that particularly covers and summarizes the details of sample preparation procedures and methods developed to identify and quantify various types of natural antioxidants in plants and food products. In the book, the principle of quantification methods for natural antioxidant-rich phytochemicals is introduced and current methods used in the determination of antioxidants in different sources are reviewed and summarized by experts in the field. As a handbook of analysis of natural antioxidant-rich phytochemicals, the book provides useful information for many researchers in this area to learn ideal analysis methods for the antioxidants they are examining. The book may also serve as a lecture resource for courses in food analysis, functional foods, and nutrition. 

Natural phenolic antioxidative activity is an additional benefit in the use of these smoke flavourings. The higher boiling point phenolics, in particular, possess antioxidative functionality similar to that of commercially used synthetic phenolic antioxidants. 

Vitamin E (a-tocopherol), the most widely distributed antioxidant in nature, is a lipid-soluble antioxidant vitamin that functions principally to protect against lipid peroxidation in membranes (see Fig. 24.13). Vitamin E comprises a number of tocopherols that differ in their methylation pattern. Among these, a-tocopherol is the most potent antioxidant and present in the highest amount in our diet (Fig. 24.18). 

Pokomy, J. and Schmidt, S. (2001) Natural antioxidant functionality during food processing, in Antioxidants in Food, Pokomy, J., Yanishlieva, N., and Gordon, M., Eds., CRC Press, Boca Raton, EL, 331. 

Beutner, S., Bloedom, B., Frixel, S., Blanco, L, Hoffmann, T., Martin, H., Mayer, B., Noack, P, Ruck, C., Schmidt, M., Schulke, L, Sell, S., Ernst, H., Haremza, S., Seybold, G., Sies, H., Stahl, W., and Walsh, R. 2001. Quantitative assessment of antioxidant properties of natural colorants and phytochemicals carotenoids, flavonoids, phenols and indigoids. The role of P- carotene in antioxidants functions, J. Sci. Food Agric., 81, 559. 

Beutner, S. et al. Quantitative assessment of antioxidant properties of natural colorants and phytochemicals carotenoids, flavonoids, phenols and indigoids the role of P-carotene in antioxidant functions, J. Set Food Agric., 81, 559,2001. 

The methods by which antioxidants function were outlined in Section 9.2. Subsequent sections however amply demonstrated that the behaviour of an antioxidant in an accelerated-sulphur cured diene rubber vulcanizate can be very different from its behaviour in a simple hydrocarbon like petrol or polyethylene or even a peroxide-cured natural rubber. Antioxidant combinations which in some circumstances behave synergistically may in other cases be antagonistic to each other. As was demonstrated in Fig. 9.1 an increase in the antioxidant loading may decrease the degree of pro-... 

Many of these compounds are being analysed for antioxidant activity. Antioxidants are an important and growing area in functional foods and the potential for novel antioxidants from plant sources has not gone unnoticed. Tocopherol and ascorbic acid, either synthetic or natural are the most widely used biological antioxidants most natural tocopherols are isolated from soybean oil whereas ascorbic acid is prepared through a double fermentation process. The antioxidant activity of rosmarinic acid is well known... 

It has been recognized for many years that chemical modification of NR can be utilized to produce new materials. Chlorinated, hydrochlorinated and cyclized NR have all been produced commercially and poly(methyl methacrylate) grafted" and depolymerized NR are still available. More recent chemical reactions have been restricted to limited levels of modification to change selected properties while retaining the overall rubbery nature of the polymer. These modifications have also been utilized for antioxidant functions, vulcanization sites and coupling to silica fillers. ... 

Tocotrienols differ from tocopherols by the presence of three isolated double bonds in the branched alkyl side chain. Oxidation of tocopherol leads to ring opening and the formation of tocoquinones that show an intense red color. This species is a significant contributor to color quaUty problems in oils that have been abused. Tocopherols function as natural antioxidants (qv). An important factor in their activity is their slow reaction rate with oxygen relative to combination with other free radicals (11). 

Antioxidants (qv) have a positive effect on oils when present in the proper concentration. Sterols and tocopherols, which are natural antioxidants, may be analy2ed by gas-Hquid chromatography (glc), high performance Hquid chromatography (hplc), or thin-layer chromatography (tic). Synthetic antioxidants maybe added by processors to improve the performance or shelf life of products. These compounds include butylatedhydroxyanisole (BHA), butylated hydroxytoluene (BHT), / fZ-butyUiydroquinone (TBHQ), and propyl gallate. These materials may likewise be analy2ed by glc, hplc, or tic. Citric acid (qv), which functions as a metal chelator, may also be deterrnined by glc. 

Eor antioxidant activity, the reaction of aminyl radicals with peroxy radicals is very beneficial. The nitroxyl radicals formed in this reaction are extremely effective oxidation inhibitors. Nitroxides function by trapping chain-propagating alkyl radicals to give hydroxylamine ethers. These ethers, in turn, quench chain propagating peroxy radicals and in the process regenerate the original nitroxides. The cycHc nature of this process accounts for the superlative antioxidant activity of nitroxides (see Antioxidants). Thus, antioxidant activity improves with an increase in stabiUty of the aminyl and nitroxyl radicals. Consequendy, commercial DPA antioxidants are alkylated in the ortho and para positions to prevent undesirable coupling reactions. 

Vitamin C occurs as L-ascorbic acid and dihydroascorbic acid in fruits, vegetables and potatoes, as well as in processed foods to which it has been added as an antioxidant. The only wholly undisputed function of vitamin C is the prevention of scurvy. Although this is the physiological rationale for the currently recommended intake levels, there is growing evidence that vitamin C may provide additional protective effects against other diseases including cancer, and the recommended dietary allowance (RDA) may be increased in the near future. Scurvy develops in adults whose habitual intake of vitamin C falls below 1 mg/d, and under experimental conditions 10 mg/d is sufficient to prevent or alleviate symptoms (Bartley et al., 1953). The RDA is 60 mg per day in the USA, but plasma levels of ascorbate do not achieve saturation until daily intakes reach around 100 mg (Bates et al., 1979). Most of the ascorbate in human diets is derived from natural sources, and consumers who eat five portions, or about 400-500 g, of fruits and vegetables per day could obtain as much as 200 mg of ascorbate. 

SRB contains high-quality protein, oil, dietary fiber, polysaccharides, fat-soluble phytochemicals (plant derived bioactive compounds) and other bran nutrients. Rice bran and germ are the richest natural sources of B complex vitamins as well as E vitamins, polyphenols, several antioxidants and minerals. It is now available in the commercial food ingredient market as a safe and effective functional food and dietary supplement. 

Natural products have been noted for their potential health benefits from time immemorial and are the basis of Ayurveda, an ancient Indian medical practice (Bushkin and Bushkin, 2002). However, the potential benefits of several natural products reside in one or two active ingredients. For example green tea stands for polyphenols, soy for soy estrogens, broccoli for isothiocyanates and grape seed for polyphenols. The beauty of rice bran is that there are more than 100 antioxidants, several categories of bioactive phytonutrients, such as IP6, polyphenols, phytosterols, tocotrienols, y-oryzanol, B vitamins, minerals and trace minerals in addition to fat, protein, fiber, polysaccharides and other nutrients. These phytonutrients and antioxidants of rice bran are believed to act at the cellular level, and their synergestic function is responsible for the positive health benefits. 

---