Almond as a source of natural antioxidants

Siriwardhana, Subhashinee Samudra Kumari Wijeratne (2001) Almond as a source of natural antioxidants. Masters thesis, Memorial University of Newfoundland.

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Abstract

Antioxidant efficacy of defatted almond whole seed, brown skin and green shell cover were investigated using a cooked comminuted pork model system. The inhibition of 2-thiobarbituric acid reactive substances (TBARS), total volatiles and hexanal by defatted almond at 2% (w/w) during a 7- day storage period ranged from 8-88, 38-90 and 57-90%, respectively. Since defatted almond products exhibited antioxidant properties, their crude extracts in ethanol were prepared at 70°C for 30 min. The total phenolic contents of ethanolic extracts of brown skin and green shell extracts were 10- and 9-times higher than that of the whole seed. Antioxidant activities of whole seed extract (WSE), brown skin extract (BSE) and green shell extract (GSE) of almond were evaluated using Trolox equivalent antioxidant capacity (TEAC) assay, β-carotene-linoleate model and bulk stripped corn oil systems. Furthermore, inhibition of DNA scission and human low-density lipoprotein (LDL) oxidation by WSE, BSE and GSE was monitored. Different free radical trapping assays were used to investigate the free radical-scavenging activity of the extracts. TEAC assay revealed that the antioxidant capacities of BSE and GSE were 13- and 10- times greater than that of seed extracts at the same extract concentration. These extracts were then tested at 100 and 200 ppm phenolics as quercetin equivalents. Retention of β-carotene in a β-carotene-linoleate model system by WSE, BSE and GSE was 84-96, 74-83 and 71-93% respectively, as compared to 2% retention in the control. In a bulk stripped corn oil system, GSE performed better than BSE and WSE in inhibiting the formation of both primary and secondary oxidation products. In a cooked comminuted pork model system GSE and BSE inhibited formation of TBARS, total volatiles and hexanal more effectively than WSE. The scavenging activity of the superoxide radical by almond seed, skin and shell cover extracts at 100 and 200 ppm was 76, 89 and 97% (100ppm), and 85, 95 and 99% (200 ppm), respectively. The corresponding reduction of hydrogen peroxide concentration was 59, 63 and 66% (100 ppm), and 86, 91 and 91% (200 ppm), respectively. The hydroxyl radical-scavenging capacities at 100 and 200 ppm were 16 and 42% for WSE, 57 and 100% for BSE and 40 and 56% for GSE, respectively. A 100% scavenging activity of the DPPH radical was achieved by both BSE and GSE at 100 and 200 ppm levels. WSE scavenged 21 and 73% of the DPPH radical at 100 and 200ppm, respectively. A total DNA retention was given by GSE at 50 ppm level against peroxyl-induced strand scission, whereas BSE and WSE reached the same at 100 ppm. On the other hand, for hydroxyl radical induced DNA strand scission, a total protection was exerted by all three almond extracts at 50 ppm level against both non-site specific and site-specific strand scission. BSE performed effectively in preventing copper-induced oxidation of human LDL cholesterol compared to WSE and GSE. All three almond extracts exhibited excellent metal chelating efficacies. High performance liquid chromatographic (HPLC) analysis revealed the presence of quercetin, isorhamnetin, quercitrin, astragalin, kaempferol-3-O-rutinoside, isorhamnetin-3-O-β-D-glucoside and morin as the major flovonoids, and caffeic, ferulic, ρ-coumaric, sinapic and gallic acids as the major phenolic acids in all three almond extracts.

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