Antioxidant activity of extracts of defatted seeds of niger (Guizotia abyssinica)

• Published in: Journal of the American Oil Chemists' Society 2003-05, Vol.80 (5), p.443-450
• Main Authors: Shahidi, Fereidoon, Desilva, Cyril, Amarowicz, Ryszard
• Format: Article
• Language: English
• Subjects: Antioxidant activity; Biological and medical sciences; chlorogenic acid; electron paramagnetic resonance; Fat industries; Food industries; Fundamental and applied biological sciences. Psychology; niger (Guizotia abyssinica); niger seed extracts
• ISSN: 0003-021X; 1558-9331
• DOI: 10.1007/s11746-003-0718-9

Niger (Guizotia abyssinica) seed was ground and then defatted with hexane. The meal remaining after oil extraction was tested as a source of antioxidants. Three solvent systems, A [80∶20 (vol/vol) ethanol/water], B [80∶20 (vol/vol) acetone/water], and C (water) were evaluated as extraction media. Crude extracts were examined for their antioxidant activity in a β‐carotene‐linoleate and a meat model system. Extract A exhibited superior antioxidant activity, compared to extracts B and C, and its composition was studied further by using column chromatography and HPLC. Four fractions (I–IV) were obtained, of which fractions III and IV showed activity in the β‐carotene‐linoleate model system. Fraction IV was also highly effective in scavenging the 2,2‐diphenyl‐1‐picrylhydrazyl radical but was less active when used in a bulk oil model system. Preparative TLC showed fraction IV as consisting of two components. UV spectroscopy suggested that the major active component pressent was a chlorogenic acid‐related compound. Furthermore, HPLC analysis established that chlorogenic acid was dominant in the free phenolics fraction (2.6 mg/g). Upon hydrolysis, however, a substantial amount of caffeic acid (42.8 mg/g) was released, presumably from esterified and glycosylated chlorogenic acid. Thus, niger extracts derive their antioxidant activity, at least in part, from the chlorogenic acid‐related compounds.