Natural antioxidant mixtures, activity

Activity of Natural Antioxidant Mixtures against Lipid Oxidation.397... 

Natural tocopherol mixtures are used as antioxidants, usually at levels up to 500 ppm, along with ascorbyl pahnitate to extend the antioxidant activity. At higher levels (>1000 ppm), a-tocopherol is considered to act as a pro-oxidant. As vegetable oils contain tocols at 200-800 ppm, further additions show only a limited effect. The tocols are very sensitive to oxidation and are more stable in esterified form where the all-important hydroxyl group is not free. However such compounds do not show antioxidant activity until they have been hydrolyzed in vivo to the free phenolic form (11). 

During refining much of the natural antioxidant may be lost. The composition of the natural mixtures of tocols varies from source to source. a-Tocopherol shows the highest vitamin activity whilst the 8 and y tocopherols are the most... 

Odoriferous substances and their mixtures (e.g. essential oils) show a number of beneficial effects for which they have found use as pharmaceuticals, pharmaceutical ingredients and food additives. Bactericidal and anti-inflammatory effects are seen in bomeol, eugenol, pinenes, camphor, thymol and menthol, choHnolytic (spasmolytic) effects preventing a drop in blood pressure and suppressing the secretory activity of various organs are found in camphor, pinenes and camphene, and analeptic effects (stimulating activity of circulation and respiratory system) are seen in camphene. The essential oils of many spices (such as marjoram, sage, thyme and many others) exhibit antioxidant effects, and therefore find use as natural antioxidants of fats. 

Soybean tocopherols are the major source of natural fat-soluble antioxidants and Vitamin E. The Vitamin E activity of natural d-cx-tocopherol is much greater that that of synthetic Vitamin E, which is a mixture of eight stereoisomers (203). Phytosterols are used as raw materials for over 75% of the world s steroid production. The more recent application of phytosterol, phytostanol, and their fatty acid esters in margarine and table spreads is based on the blood cholesterol-lowering effect of these compounds (204,205). The recent development of functional foods containing phytosterols has been reviewed by Hollingsworth (206) and Hicks and Moreau (207). 

Natural tocopherols and tocotrienols have the 2R, 4 R, 8 R and 2R, h -trans, T-trans configurations, respectively, while synthetic products are racemic mixtures. Natural and synthetic products have similar potentials as antioxidants, but natural products have higher vitamin E activity than synthetic ones. Production capacities of natural and synthetic tocopherols and tocotrienols are enlarging (ANON, 1998). In 1991, the world production of vitamin E compounds was 6800 tons (O Leary, 1993). 

In nature, flavonoids usually occur as mixtures of several compounds rather than as pure solutions of one single polyphenol. To simulate this, attempts have been made to deduce the antioxidant capacity in fruits and berries and their products from the antioxidant capacity of their individual polyphenols. Frankel et al. (1995) calculated the antioxidant capacity of 14 red and 6 white wines from the antioxidant activity of the individual polyphenols determined in the wines. The calculated antioxidant activity accounted for only 25% of the measured value. The difference was partly ascribed to unidentified polyphenols and polyphenolic acids and their polymers. Thus, there apparently is still no complete understanding of the factors contributing to the antioxidative capacity of a product. The best strategy at present seems to be to measure the products of interest directly. 

For SWE experiments, small differences were observed among the different pre-treatments used. Considering the results as a whole, no pre-treatment of the sample was selected and a deeper study of the effect of the extracting agent on the antioxidant activity was performed based on the use of ethanol and mixtures ethanohwater to determine the effect of the reduction of dielectric constant in the nature of the compounds extracted. 

Phenolic acids occur naturally in higher plants, usually as free adds, glycosides, esters, or in insoluble-bound form in a complex mixture of other phenolic compounds. The presence of phenolic acids in food products has been associated with astringency, discoloration, inhibition of enzyme activity, and antioxidant properties, among others [15]. A major portion of phenohc acids present in almond was found in the form of soluble esters. Wijeratne et al. [16] reported that the total amounts of identified free phenolic acids were 16.3, 14[ig/g and a trace amount in skin, shell, and whole seed extracts, respectively, whereas the amounts for total esterified phenolic acids were 279.6,967.1, and 40.3 [ig/g, respectively. 

Several synergistic mixtures are used commercially including BHA and BHT, BHA and PG, BHA, BHT and TBHQ, with various levels of citric acid. PG reinforces the antioxidant activity of BHA but not that of BHT. Ascorbyl palmitate (Figure 9.1) is a weak antioxidant when used alone, but it shows synergistic activity in mixtures with natural tocopherols. 

Phospholipids are generally considered to have an antioxidant effect in foods, but this activity is confounded by the formation of reducing browning material at elevated temperatures (Chapter 9). Phosphatidylethanolamine appears to have synergistic activity in mixtures with natural tocopherols and synthetic antioxidants. This synergistic activity is often related to the metal scavenging ability of phospholipids. 

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