Nonflavonoids

There are numerous other polyphenolic compounds possessing in vitro and in vivo antioxidative activity. Several examples of these compounds are cited below. One of nonflavonoid polyphenols of particular interest is resveratrol (3,5,4 -trihydroxy-Znmv-stilbcne, Figure 29.8), which has been identified as a potential cancer chemopreventive agent and an antimutagen [182]. It has been found that resveratrol is the efficient inhibitor of cyclooxygenase and the inhibitor of free radical-mediated cellular processes. For example, resveratrol is a better free radical scavenger than a-tocopherol or ascorbic acid but has nearly the same activity as... 

Much of the information on ANS has come not from studies on enzyme extracts but from analysis of DNA sequences and recombinant proteins. Sequences for the ANS were first isolated using transposon generated mutant lines of A. majus and Z. mays They encoded proteins of 40 to 41 kDa that were found to have similarity to 20GDs, during a study on a nonflavonoid enzyme. This sequence-based identification was confirmed by the in vitro assay of the recombinant Perilla frutescens protein, and subsequent assays on recombinant ANS from a range of species that confirmed the requirement for Fe, 20G, and ascorbate. Sequence comparisons show that ANS is more closely related to flavonol synthase (FLS), another 20GD, than to F3H. 

Only a general indication of phenotype is given, and the full changes identified may include production of anthocyanin earlier in flower development than normal, increased anthocyanin production only under stress conditions, small increases in flavonoid levels in tissues already producing flavonoids, ectopic flavonoid production, changes in levels of nonflavonoid phenylpropanoids. 

Finally, reactions of flavonoid and nonflavonoid precursors are affected by other parameters like pH, temperature, presence of metal catalysts, etc. In particular, pH values determine the relative nucleophilic and electrophilic characters of both anthocyanins and flavanols. Studies performed in model solutions showed that acetaldehyde-mediated condensation is faster at pH 2.2 than at pH 4 and limited by the rate of aldehyde protonation. The formation of flavanol-anthocyanin adducts was also limited by the rate of proanthocyanidin cleavage, which was shown to take place at pH 3.2, but not at pH 3.8. Nucleophilic addition of anthocyanins was faster at pH 3.4 than at pH 1.7, but still took place at pH values much lower than those encountered in wine, as evidenced by the formation of anthocyanin-caffeoyltartaric acid adducts, methylmethine anthocyanin-flavanol adducts,and flavanol-anthocyanin adducts. The formation of pyranoanthocyanins requiring the flavylium cation was faster under more acidic conditions, as expected, but took place in the whole wine pH range. Thus, the availability of either the flavylium or the hemiketal form does not seem to limit any of the anthocyanin reactions. 

FIGURE 4.2 Wine oxidation processes adapted from Danilewicz (2003) R = further organic groups such as the three-ring structure in the flavonoids, and further groups in nonflavonoid polyphenols. 

Figure 9. Two-dimensional cellulose TLC of flavonoids in aqueous isopropyl alcohol extracts, nonflavonoid fractions of extracts, and flavonoid fractions of extracts of LCP and glandless cottonseed flours (5)...

The glycosidic anthocyanins are almost completely precipitated with red wines of a few months age and normal tannin content. However, with young wines made from the same grapes, a ros6 wine with only 713 mg GAE/liter total phenol gave 311 mg GAE/liter as not-precipitated nonflavonoid, and with increasing levels of total phenol in red wines to... 

Table X illustrates the successful application of formaldehyde precipitation as a means of estimating the flavonoid and nonflavonoid contents in a mixture. The mixture consisted of catechin as the flavonoid and caffeic, vanillic, and syringic acids as the nonflavonoids. The catechin was 86% precipitated (lower than usual because of the low level), but the other substances were not significantly precipitated. The slight apparent loss of caffeic acid is attributable to experimental variation since in many other experiments the lack of reaction and precipitation or co-precipitation of caffeic acid or chlorgenic acid has been demonstrated. Allowing for the same slight solubility of the catechin-formalde-hyde product in the mixtures as in the single component solution, the analysis of the mixtures gave 95.7-107.6% of the calculated value. This indicates no significant co-precipitation or entrainment of the nonflavonoids as the flavonoid was removed. This result has been verified a number of times with different substances added to model solutions and wines (21, 22).

Viewing the data (Table X) as if it had been the usual assay of unknowns and subtracting the assay values after formaldehyde treatment from those before, the mixtures 1, 3, and 4 would apparently contain no flavonoid when in fact they contained 8.4 mg/liter GAE by separate assay. On the other hand, mixture 2 with 16.8 mg/liter GAE of flavonoid by separate assay gave 6.9 mg/liter by formaldehyde precipitation. If correction was made for 5.8 mg/liter GAE residual solubility of the catechin-formaldehyde product then mixures 1-4 would be indicated to have, respectively, 3.9, 12.7, 4.9, and 5.0 flavonoid and 39.6, 33.1, 41.3, and 38.4 mg/liter GAE nonflavonoid. These values are considered very close to the true content considering the results are based on differences between two assays with the attendant increase in variability. 

Table XI. Average Analysis of Nonflavonoid Phenol Content of Typical Woods Which Contact Wine (27)...

Formaldehyde analysis has been used to detect and measure oak extract in wines aged in wood cooperage and to correlate the amount of extract with the aging effect (27). Tannins and phenols of oak (and redwood and cork) are predominantly nonflavonoid-hydrolyzable tannins (Table XI), and they add to the otherwise relatively low and... 

Kramling and Singleton (41) developed an analysis that differentiated flavonoids from nonflavonoids in wine based on the ability of formaldehyde to precipitate the former but not the latter from solution under proper conditions. The total phenols (42) were determined colori-metrically before and after this precipitation. They (I, 41) also showed that the nonflavonoid content of all young wines was relatively low and constant. 

Several wines known to be free of wood contact were analyzed for nonflavonoid content. The white wines averaged 157 mg GAE/liter nonflavonoid and the reds, 271 mg. The highest value obtained for a white wine was 211 and for a red wine, 448 mg GAE nonflavonoid/liter. 

On the basis of these analyses it can be assumed that if a sample of the original wine is not available for direct comparison, white wines which exceed 200 mg/liter and red wines that exceed 450 mg GAE nonflavo-noid/liter have contacted wood or another source of extra nonflavonoid phenols. A series of 26 wines with a known history of cask aging was analyzed, and of these, nine either were known to be free of wood contact or contained little nonflavonoid, and contact was not indicated by analysis. The remaining 17 wines all were correctly indicated by analysis to have... 

Nonflavonoid Phenolic Compounds—Structure and Their Dietary Occurrence 21... 

NONFLAVONOID PHENOLIC COMPOUNDS—STRUCTURE AND THEIR DIETARY OCCURRENCE... 

Phenolics are defined as compounds possessing one or more aromatic rings to which is attached at least one hydroxyl group. Phenolic compounds can be categorized as flavonoids and nonflavonoid phenolic compounds. The main nonflavonoid phenolic compounds of dietary significance are the Q-Q... 

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