Antioxidant potential of beans

Waisooriya Mudiyanselage, Terrence Madhujith (2002) Antioxidant potential of beans. Masters thesis, Memorial University of Newfoundland.

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Abstract

Four different bean varieties with different coat colours (red, brown, black and white) were dehulled and the antioxidant compounds in the hulls and whole seeds extracted separately with 80 % acetone. The total phenolic content of the red, brown and black were higher than that of white beans both in the hull and in the whole seed extracts. Total phenolic contents of red and brown hulls were 2.3 times higher than those of whole seeds while that of the hulls of black beans were 7 times higher than black bean whole extract. Total antioxidant capacity of the extracts was evaluated using Trolox equivalent antioxidative capacity (TEAC) assay, β-carotene-linoleate and bulk stripped corn oil model systems. Extracts were used at 50 and 100 ppm phenolics as catechin equivalents. Scavenging efficacies of the whole bean extracts for reactive oxygen species (ROS) were evaluated using hydrogen peroxide, superoxide and 2,2-diphenyl-l-picrylhydrazyl (DPPH) radicals. Furthermore, inhibition of DNA-supercoiled strand scission and prevention of human low density lipoprotein (hLDL) oxidation by the extracts were evaluated. TEAC values of red whole bean extract (RWE), brown whole bean extract (BWE) and black whole bean extract (LWE) were 8.84, 7.46 and 4.64 while those of red bean hull extract (RHE), brown bean hull extract (BHE) and black bean hull extract (LHE) were 46.68 42.90, and 40.74, respectively. TEAC assay revealed that the antioxidant capacity of red, brown, and black bean hulls were in the same order of magnitude with little variation. Retention of β-carotene in a β-carotene-linoleate model system in the presence of RWE, BWE and LWE after 2 h of the assay was 46, 45, and 28% at 50 ppm and 52, 51, and 33% at 100 ppm, respectively, as compared to 2% in the control devoid of any extract. In a bulk corn oil model system, the order of efficacies of the extracts and reference antioxidants as measured by the formation of conjugated dienes (CD) was catechin > BHA > RWE = BWE = LWE > α-tocopherol. Inhibition of formation of hexanal in corn oil after 7 days was catechin > RWE = BWE = BHA > LWE > α-tocopherol. The efficacy of RWE, BWE and LWE at 100 ppm in scavenging hydrogen peroxide was 76, 73 and 65%, respectively. The corresponding values for superoxide radical scavenging were 54, 53 and 60%. Red, brown and black whole and hull seed extracts showed total scavenging of DPPH radical when used at 100 ppm. The Fe²+ chelation capacities of RWE, BWE and LWE were 58, 56 and 39% at 50 ppm and 72, 69, and 60% at 100 ppm, respectively. Red, brown and black whole seed extracts exhibited total inhibition of hLDL oxidation when used at 25 and 50 ppm. Red, brown and black whole seed extracts exerted total protection against peroxyl-induced DNA scission at 50 and 100 ppm levels while they did not show any protection towards hydroxyl radical induced-DNA scission. HPLC analyses revealed the presence of cyanidin in LHE while RHE and BHE contained both cyanidin and delphinidin. White bean hull extracts did not contain any of the two anthocyanidins. Ferulic, caffeic, sinapic, ρ-coumaric and vanillic acids were identified as major phenolic acids in bean hull extracts.

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