Antioxidants biological

Biological Antioxidant Models. Tea extracts, tea polyphenol fractions, and purified catechins have all been shown to be effective antioxidants in biologically-based model systems. A balance between oxidants and antioxidants is critical for maintenance of homeostasis. Imbalances between free radicals and antioxidants may be caused by an increased production of free radicals or decreased effectiveness of the antioxidants within the reaction system. These imbalances can be caused by the radicals overwhelming the antioxidants within the system, or by an excess of antioxidants leading to a prooxidant functionaHty (105—118). When antioxidant defense systems are consistently overwhelmed by oxidative reactions, significant damage can... 

Another approach to safer stabilization is to use a biological antioxidant such as vitamin E (a-tocopherol is the active form of vitamin E, AO-9, Table la). It is essentially a hindered phenol which acts as an effective chain breaking donor antioxidant, donating a hydrogen to ROO to yield a very stable tocopheroxyl radical, a-Tocopherol is a very effective melt stabilizer in polyolefins that offers high protection to the polymer at very low concentration [41], (Table 2). 

FRANKEL E N and MEYER A s (2000) The problems of using one-dimensional methods to evaluate multifunctional food and biological antioxidants, JSci FoodAgric, 80,1925-41. 

HAGERMAN A E, RIEDL K M, JONES G A, SOVIK K N, RITCHARD N T, HARTZFELD P W and RIECHEL T L (1998) High molecular weight plant polyphenohcs (tannins) as biological antioxidants, J Agric Food Chem, 46, 1887-92. 

MacDonald-Wicks LK, Wood LG and Garg ML. 2006. Methodology for the determination of biological antioxidant capacity in vitro A review. J Sci Food Agric 86(13) 2046-2056. 

The best known and undoubtedly most important natural antioxidants are a-tocopherol (vitamin E) and ascorbic acid (vitamin C), which are major biological antioxidants in lipid... 

Biological antioxidants such as a-tocopherol (65, vitamin E) serve to inhibit free radical chain oxidation, and the mechanisms of their reactions have attracted close attention. The chain-breaking reaction of such phenols with peroxyl radicals is by hydrogen transfer (equation 101). 

Das KC. 2005. Thioredoxin and its role in premature newborn biology. Antioxid Redox Signal 7 1740-1743. 

L-Ascorbic acid serves as a reductant for several important enzymatic biotransformations. These characteristic biological activities result from its enediol structure, which confers a strong electron-donating ability. In addition, there is considerable evidence that biological antioxidants, including ascorbic acid, play an important role in the prevention of a large number of chronic diseases such as cancer, cerebral apoplexy, diabetes, myocardial damage, and AIDS.367,368... 

To address the question of whether the biological antioxidant would withstand the high melt processing temperatures, dl-a-tocopherol (synthetic vitamin E) was extruded at different concentrations in PE and PP under different processing temperatures ranging from 210 °C to 285 °C. Similar experi-... 

The outstanding melt stabilising efficiency of tocopherol in polyolefins, coupled with the safety aspect associated with the use of such a biological antioxidant, should improve its future position in the antioxidant market and encourage its wide-spread use in many applications, especially those related to medical and other human-contact applications. 

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