Antioxidants reductones

According to Sato and Herring (39), ascorbic acid can function as an antioxidant by interfering with the free radical mechanism due to the presence of the ene-diol portion of the molecule. However, St. Angelo et al (5) reported that reductone-type compounds, such as maltol, kojic acid, 3-hydroxyflavone, etc., were effective antioxidants and suggested that the alpha ketol structure may also play an important role concerning free radical mechanisms. 

The most practical method for preventing WOF in meat products is to add antioxidants prepared from natural precursors such as sugars and amino adds by heating them to produce constituents that not only act as antioxidants but serve to enhance meaty flavor as well. The resulting Maillard products have been known to have antioxidant activity in lipid systems (6-8). It is assumed that the antioxidative property of the Maillard reaction is assodated with the formation of low molecular weight reductones and high molecular weight melanoidins (6, 7, 9-13). 

Knowledge about the chemical structure of the antioxidative MRP is very limited. Only a few attempts have been made to characterize them. Evans, et al. (12) demonstrated that pure reductones produced by the reaction between hexoses and secondary amines were effective in inhibiting oxidation of vegetable oils. The importance of reductones formed from amino acids and reducing sugars is, however, still obscure. Eichner (6) suggested that reductone-like compounds, 1,2-enaminols, formed from Amadori rearrangement products could be responsible for the antioxidative effect of MRP. The mechanism was claimed to involve inactivation of lipid hydroperoxides. 

The antioxidative mechanism of MRPs in vitro and in vivo is currently unclear. However, it is estimated that the reductone structures, the electron donor property (Kato,... 

Kirigaya, N Kato, H Fujimaki, M. Studies on antioxidant activity of nonenzymic browning reaction products. Part I. Relations of color intensity and reductones with antioxidant activity of browning reaction products Agric. Biol. Chem. 1968, 32, 287-290. 

It was also demonstrated that vanillin, in food items where its aroma is desired, plays an important role as an antioxidant. Finally, some of the Maillard reaction products, such as reductones (cf. 4.2.4.4), should be considered as naturally active antioxidants. 

As a result of the presence of an enediol structure element in the a-position to the oxo function in the open-chain structures of acetylformoin, this compound belongs to the group of substances called reductones. Substances of this type, e. g., also vitamin C (ascorbic acid), are weakly acidic (Formula 4.71), reductive (Formula 4.72) and exhibit antioxidative properties. The latter are attributed to the possible formation of resonance-stabilized radicals (Formula 4.73) and also to the disproportionation of two radicals with... 

The chemical principle behind the antioxidant properties of Maillard reaction products is currently not well understood. It is assumed that these properties show both low molecular weight products and high molecular weight melanoidins. As the structure of melanoidins has not been clarified satisfactorily, it is difficult to explain the chemical nature of their antioxidant activity. The active structures are probably reductones and aminoreductones, bound in melanoidin molecules that reduce the products of autoxidation. One of a few identified reductone structures in real food melanoidins is 2,4-dihydroxy-2,5-dimethyl-l-(5-acetamino-5-methoxycarbonylpentyl)-3-oxo-2H-pyrrole bound by a peptide bond. This so-called pronyl-L-lysine (pyrrolinone... 

In addition to reductones, structures capable of binding metal ions that act as oxidation catalysts also have significant antioxidant activities. Although amino acids can bind metals to coordination compounds (see Section 6.2.2.1), metal chelates (M +) with Amadori compounds (4-257) have considerably higher stability and therefore higher antioxidant activity. The increased stability is due to additional metal ion binding by C-2 and C-3 hydroxyl... 

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