Recently, there has been growing interest in research into the role of plant-derived antioxidants in food and human health. The beneficial influence of many foodstuffs and beverages including fruits, vegetables, tea, coffee, and cacao on human health has been recently recognized to originate from their antioxidant activity. For this purpose, the most commonly methods used in vitro determination of antioxidant capacity of food constituents are reviewed and presented. Also, the general chemistry underlying the assays in the present paper was clarified. Hence, this overview provides a basis and rationale for developing standardized antioxidant capacity methods for the food, nutraceutical, and dietary supplement industries. In addition, the most important advantages and shortcomings of each method were detected and highlighted. The chemical principles of these methods are outlined and critically discussed. The chemical principles of methods of 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonate) radical (ABTS·+) scavenging, 1,1-diphenyl-2-picrylhydrazyl (DPPH·) radical scavenging, Fe3+–Fe2+ transformation assay, ferric reducing antioxidant power (FRAP) assay, cupric ions (Cu2+) reducing power assay (Cuprac), Folin-Ciocalteu reducing capacity (FCR assay), peroxyl radical scavenging, superoxide anion radical (O
 2
 ·−
 ) scavenging, hydrogen peroxide (H2O2) scavenging, hydroxyl radical (OH·) scavenging, singlet oxygen (1O2) quenching assay and nitric oxide radical (NO·) scavenging assay are outlined and critically discussed. Also, the general antioxidant aspects of main food components were discussed by a number of methods which are currently used for detection of antioxidant properties food components. This review consists of two main sections. The first section is devoted to main components in the foodstuffs and beverages. The second general section is some definitions of the main antioxidant methods commonly used for determination of antioxidant activity of components in the foodstuffs and beverages. In addition, there are given some chemical and kinetic basis and technical details of the used methods.

Antioxidant activity of food constituents: an overview

Effects of sewage sludge amendment on heavy metal accumulation and consequent responses of Beta vulgaris plants

Improvement of quality and shelf-life of strawberries with edible coatings enriched with chitosan

The enzyme 4-hydroxyphenylacetate, NAD(P)H:oxygen oxidoreductase (1-hydroxylating) (EC 11413 ; 4-hydroxyphenylacetate 1-monooxygenase; referred to here as 4-HPA 1-hydroxylase) was induced in Pseudomonas acidovorans when 4-hydroxyphenylacetate (4-PHA) was utilized as carbon source for growth; homogentisate and maleylacetoacetate were intermediates in the degradation of 4-HPA A preparation of the hydroxylase that was free from homogentisate dioxygenase and could be stored at 4 C in the presence of dithioerythritol with little loss of activity was obtained by ultracentrifuging cell extracts; but when purified 18-fold by affinity chromatography the enzyme became unstable Flavin adenine dinucleotide and Mg2+ ions were required for full activity 4-HPA 1-hydrocylase was inhibited by KCl, which was uncompetitive with 4-HPA Values of Ki determined for inhibitors competitive with 4-HPA were 17 muM dl-4-hydroxymandelic acid, 43 muM 3,4-dihydroxyphenylacetic acid, 87 muM 4-hydroxy-3-methylphenylacetic acid, and 440 muM 4-hydroxyphenylpropionic acid Apparent Km values for substrates of 4-HPA 1-hydroxylase were 31 muM 4-HPA, 67 muM oxygen, 95 muM reduced nicotinamide adenine dinucleotide (NADH); AND 250 muM reduced nicotinamide adenine dinucleotide phosphate (NADPH) The same maximum velocity was given by NADH and NADPH A chemical synthesis is described for 2-deutero-4-hydroxyphenylacetic acid This compound was enzymatically hydroxylated with retention of half the deuterium in the homogentisic acid formed Activity as substrate or inhibitor of 4-HPA 1-hydroxylase was shown only by those analogues of 4-HPA that possessed a hydroxyl group substituent at C-4 of the benze nucleus A mechanism is suggested that accounts for this structural requirement and also for the observation that when 4-hydroxyphenoxyacetic acid was attacked by the enzyme, hydroquinone was formed by release of the side chain, probably as glycolic acid Only one enantiometer of racemic 4-hydroxyhydratropic acid was attacked by 4-HPA 1-hydroxylase; the product, alpha-methylhomogentisic acid (2-(2,5-dihydroxyphenyl)-propionic acid), exhibited optical activity This observation suggests that, during its shift from C-1 to C-2 of the nucleus, the side chain of the substrate remains bound to a site on the enzyme while a conformational change of the protein permits the necessary movement of the benzene ring

Metabolic function and properties of 4-hydroxyphenylacetic acid 1-hydroxylase from Pseudomonas acidovorans.

1. The metabolism of a group of polyphenols related in structure to myricetin (3,5,7,3′,4′,5′-hexahydroxyflavone), including myricetin, myricitrin, 3,4,5-trihydroxyphenylacetic acid, delphinidin, robinetin, tricetin, tricin, malvin and 5,7-dihydroxy-3′,4′,5′-trimethoxyflavone, has been studied both in vivo after oral administration to the rat and in vitro in cultures of micro-organisms derived from the intestine of the rat. 2. It was shown that the rat intestinal microflora are able to degrade compounds of this group to the ring-fission products observed in urine after oral administration of the specific flavonoid. 3. All flavones and flavonols possessing free 5- and 7-hydroxyl groups in the A ring and a free 4′-hydroxyl group in the B ring gave rise to ring-fission products that included 3′,5′-dihydroxyphenylacyl derivatives. 4. The metabolites 3,5-dihydroxyphenylacetic acid, 3-hydroxyphenylacetic acid, 3,5-dihydroxyphenylpropionic acid and 3-hydroxyphenylpropionic acid were isolated and identified by chromatographic and spectral methods. 5. On anaerobic incubation in a thioglycollate medium it was shown that intestinal micro-organisms can effect cleavage of glycosidic bonds, ring fission of certain flavonoid molecules showing 3′,4′,5′-trihydroxyphenyl substitution and dehydroxylation of certain flavonoid metabolites. 6. The urinary excretion of the metabolites 3,5-dihydroxyphenylacetic acid and 3-hydroxyphenylacetic acid was completely abolished when neomycin-treated rats were used.

H G Bray

Papers

Analysis of phenolic compounds of interest in metabolism.