Antioxidants synergists, types

It is important to recognize that different types of inhibitors often function by different mechanisms, and that a given antioxidant may react in more than one way. Thus, a material that acts as an antioxidant under one set of conditions may become a pro-oxidant in another simation. The search for possible synergistic combinations of antioxidants can be conducted more logically and efficiently if we seek to combine the effects of different modes of action. Five general modes of oxidation inhibition are commonly recognized ... 

There has been some evidence of a higher antioxidant effect when both flavonoids and a-tocopherol are present in systems like LDL, low-density lipoproteins (Jia et al., 1998 Zhu et al, 1999). LDL will incorporate a-tocopherol, while flavonoids will be present on the outside in the aqueous surroundings. A similar distribution is to be expected for oil-in-water emulsion type foods. In the aqueous environment, the rate of the inhibition reaction for the flavonoid is low due to hydrogen bonding and the flavonoid will not behave as a chain-breaking antioxidant. Likewise, in beer, none of the polyphenols present in barley showed any protective effect on radical processes involved in beer staling, which is an oxidative process (Andersen et al, 2000). The polyphenols have, however, been found to act synergistically... 

Chelators. The type of positive synergistic effects described above are not to be confused with synergism as referred to when an antioxidant is added with an add chelator, such as citric acid. Acid chelators, or sequestrants, are referred... 

When acid chelators are combined with one of the phenolic-type antioxidants, they can act synergistically. This type of synergism has been referred to as acid synergism (S). In this case, the primary role of a chelator is to bind metals, or metalloproteins that promote oxidation and thus, allow the antioxidant to perform its function and capture free radicals. In this manner, acid synergism is different than the BHA/BHT system. 

The aryloxyl radicals formed in the initial antioxidant reaction of phenols (equation 1) may undergo several different kinds of secondary reactions, including Type (1), rapid combination (termination) with the initiating oxygen-centered radicals (equation 11) Type (2), self-reactions Type (3), initiation of new oxidation chains by H-atom abstraction from the substrate, the so-called prooxidant effect and Type (4), reduction or regeneration by other H-atom donors resulting in synergistic inhibition. The relative importance of these secondary reactions will be considered briefly here, since they may affect the overall efficiency of the antioxidant, which includes the antioxidant activity, as measured by the rate constant, (equation 10), and the number of radicals trapped, n. 

Because primary and secondary antioxidants differ in their mechanism of attack to prevent oxidative degradation, in practice both type of antioxidants are often used together to obtain the best results. Often such combinations provide a synergistic effect, where the combined antioxidant package provides greater protection than the sum of the two alone. However, antioxidants can also interact in an antagonistic fashion, so proper pairing is needed. 

It is possible to prepare well-defined food grade microemulsions from extracted cereal lipids. Their structure is similar to that of the sponge or Lj phase. The other main type of microemulsion formed by food lipids has the L2 structure, and it can be prepared from liquid mixtures of mono- and triglycerides. An important application of microemulsions is to provide improved antioxidation effectiveness because of the possibility of a synergistic effect between hydrophilic and lipophilic antioxidants, as was illustrated in systems with soybean oil and fish oils. 

Recent studies have demonstrated the synergistic effect of phenolic phytochemicals and milk or soymilk fermentation systems for type 2 diabetes and related hypertension management in vitro (Apostolidis et al. 2007 Kwon etal. 2006). In this spirit the a random selection of dairy and soy yogurts with fruit enrichment for phenolic antioxidant-linked a-amylase, a-glucosidase, and ACE inhibitory activities was evaluated (Apostolidis etal 2006). 

In combination with primary antioxidants, secondary antioxidants delay the consumption of the former by decomposing hydroperoxides to non-radical compounds and by preventing the formation of new radical decomposition products. Many stabilizer types supplement each other, thus protecting against too rapid consumption and increasing their effectiveness multiple times. That is why secondary antioxidants are very often called synergists or co-stabilizers . Detailed descriptions of the secondary antioxidants mechanisms can be found in [518], [519], and [523]. 

The high efficiency of the antioxidant mixtures is due to their synergistic effect. Table 1 fists several types of synergistic mixtures of antioxidants [11, 12]. 

Yatchigo S, Sasaki M, Kojima F. Studies on polymer stabilizers. Part II a new concept of a synergistic mechanism between phenolic and thiopropionate type antioxidants. Polym Degrad Stab 1992 35 105-13. 

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