title: Antioxidant activity of betalains from plants of the amaranthaceae.
abstract: Antioxidant activity of betalain pigments (seven pure compounds and four combined fractions) from plants of the family Amaranthaceae was evaluated using the modified DPPH(*) (1,1-diphenyl-2-picrylhydrazyl) method. All tested betalains exhibited strong antioxidant activity. Their EC(50) values ranged from 3.4 to 8.4 microM. Gomphrenin type betacyanins (mean = 3.7 microM) and betaxanthins (mean = 4.2 microM) demonstrated the strongest antioxidant activity, 3-4-fold stronger than ascorbic acid (13.9 microM) and also stronger than rutin (6.1 microM) and catechin (7.2 microM). Antioxidant activity of the tested betalains decreased in the following order: simple gomphrenins > acylated gomphrenins > dopamine-betaxanthin > (S)-tryptophan-betaxanthin > 3-methoxytyramine-betaxanthin > betanin/isobetanin > celosianins > iresinins > amaranthine/isoamaranthine. This study also investigated and discussed the relationship between the chemical structure and the activity of the betalains. The free radical scavenging activity of the betalains usually increased with the numbers of hydroxyl/imino groups and, moreover, depended on the position of hydroxyl groups and glycosylation of aglycones in the betalain molecules.
authors.affiliation: Department of Botany, The University of Hong Kong, Pokfulam Road, Hong Kong.
authors.forename: Yizhong
authors.initials: Y
authors.lastname: Cai
authors.forename: Mei
authors.initials: M
authors.lastname: Sun
authors.forename: Harold
authors.initials: H
authors.lastname: Corke
mesh_terms: D027703:Amaranthaceae / Q000737:chemistry*; D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000494:pharmacology; D050858:Betalains; D001713:Biphenyl Compounds; D002851:Chromatography, High Pressure Liquid; D016166:Free Radical Scavengers / Q000737:chemistry; D010851:Picrates / Q000737:chemistry; D010936:Plant Extracts / Q000737:chemistry; D000644:Quaternary Ammonium Compounds / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D013329:Structure-Activity Relationship
chemical_list: D000975:Antioxidants; D001713:Biphenyl Compounds; D016166:Free Radical Scavengers; D010851:Picrates; D010936:Plant Extracts; D000644:Quaternary Ammonium Compounds; D050858:Betalains; C004931:1,1-diphenyl-2-picrylhydrazyl; D001205:Ascorbic Acid