Phenol antioxidant potency

Table 7. Antioxidant Potency of Vitamins and Phenolics Based on LDL Oxidation In Vitrei...

Comparison of various oat fractions showed the following potency of TAC pearlings (2.89-8.58 TE/g) > flour (1.00-3.54 TE/g) > trichome (1.74 TE/g) = bran (1.02-1.62 TE/g) (H7). The antioxidant activity of rye extracts was significantly correlated with their total content of monomeric and dimeric hydroxycin-namates. These data suggest that rye products may be a source of dietary phenolic antioxidants that may have potential health effects (A13, E3). 

We have prepared a number of new phenolic antioxidants by alkylating phenol, p-cresol, 2,4-xylenol, and 2,6-xylenol with a-olefins. All show appreciable antioxidant effectiveness in high temperature accelerated tests. In over-all potency, 2,6-dioctadecyl-p-cresol is the best, followed closely by 2,4,6-trioctadecylphenol. For the tests used in this study, molecular weight was found to be the controlling factor in the relationship of structure to effectiveness. 

In addition to free fatly acids and their esters as previously described, compounds with antioxidant potency were also used as acyl donors. In order to investigate the synthesis of hybrid antioxidants, the enzymatic acylation of escuhn catalyzed by immobilized CALB in the ionic liquids [bmtm]BF4 and [bmim]PF6 was investigated using several phenolic acids as well as their corresponding vinyl esters. 

The comparison of the antioxidant potency of hydroxytyrosol, tyrosol, oleuropein with respect to vitamin E and BHT and the synergistic effect with vitamin E were studied in thermal initiated oxidation of methyl linoleate in the presence of azo-compounds, in heptanol or propanohwater. The activity of the phenols was expressed as increase of induction period and extent of reaction inhibition [47]. The azo compounds initiated oxidation is a free radical chain process. Confirming the results from a previous study [43], this study showed that hydroxytyrosol and oleuropein were much more effective than BHT and vitamin E in extending the induction period. Tyrosol was devoid of activity and no synergistic effect on the preservation of methyl linoleate was foxmd when vitamin E was used together with tyrosol. 

Primary antioxidants are mono- or poly-hydroxy phenols with various ring substitutions including synthetic (BHA, BHT, PG), and natural compounds (tocopherols, carotenoids). Their antioxidant potency is determined by several factors, including chemical reactivity of the antioxidant toward the radical, concentration and mobility of the antioxidant in the microenvironment, and interaction with other antioxidants. ... 

Various proteins inhibit lipid oxidation in different lipid systems by their capacity to bind or chelate metal ions. The relative antioxidant potency of phenolic compounds in liposomes was mediated to different extents by the presence of protein. At high relative metal concentrations, however, these complexes can also promote lipid oxidation (see Chapter 10.B.2). 

Phenolic substances in red wine were shown to inhibit LDL oxidation in vitro [95]. In previous studies, red wine-derived phenolic acids [115,116], resveratrol [117], flavonols (quercetin, myricetin) [68,118,119], catechins [66,120], and the grape extract itself [121,122] have been shown to possess antioxidant properties. The finding that ethanol and wine stripped of phenols did not affect LDL oxidation further confirmed that the active antioxidant components in red wine are phenolic compounds [123]. Red wine fractionation revealed major antioxidative potency to monomeric catechins, procyanidins, monomeric anthocyanidins, and phenolic acids [123]. The flavonol quercetin and the flavonol catechin were both tested for antioxidative and antiatherogenic effects in the atherosclerotic E° mice [111]. E° mice at the age of 4 weeks were supplemented for up to 6 weeks in their drinking water with placebo (1.1% alcohol) or with catechin or quercetin (50 pg/day/mouse). The atherosclerotic lesion area was smaller by 39% or by 46%, respectively, in the treated mice than in E° mice that were treated with placebo (Fig. 4A-E). 

Green and black teas have been reported to inhibit human LDL oxidation in vitro and ex vivo (13,15-18). However, at least one study has indicated tiiat black tea is not effective to protect LDL from oxidative modification (19). Current study demonstrated that the aqueous extracts of Pu-Erh tea (PET) scavenged DPPH radical and inhibited Cu -induced LDL oxidation in vitro. The antioxidant potency of PET was similar to that of green and black tea extracts but the content of EGCG in Pu-Erh tea was lower than that of the green tea. It is suggested that the antioxidant activity of PET is due to the oligomeric phenolic compounds and theaflavins. 

Antioxidant Activity towards Human LDL. At equivalent total phenol levels (by the Folin Ciocalteau method), all samples had similar activity at 10.0 pM where inhibition was generally above 95%. At 20 pM GAE all wines inhibited more than 99% of LDL oxidation regardless of the fining agent used. However, the wines had very different antioxidant activities at 5.0 pM (Table IV). The antioxidant activity at 5.0 pM GAE increased with all fining agents and dramatically with PVPP and bentonite. Because the antioxidant activities were compared after dilutions to equivalent total phenol levels, it is important to note that the data shows which samples of phenolics have the most potency at the same concentration, not which sample has the highest antioxidant concentration. 

The aniioxidative potency of a compound is related to its structure, in particular to electron delocalization of the aromatic nucleus and is also influenced by the number of hydroxyl groups (/3). In this way, the higher antioxidative activity of rosmarinic acid with respect to that of the other phenolics tested could be related with the presence of two catechol groups on its molecule. However, since the ICj value for rosmarinic acid is less than half of that for caffeic acid (Table II), other mechanisms for superoxide anion deactivation may be involved. 

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