Antioxidant and free radical-scavenging properties of ethanolic extracts of defatted borage (Borago officinalis L.) seeds

Borage meal exerted a concentration-dependent antioxidant activity in a meat model system. At 2% (w/w), it inhibited (p less than or equal to 0.05) 2-thiobarbituric acid-reactive substances (TBARS), hexanal and total volatile formation in meat by 26.5, 30.5 and 18.6%, respectively. Antioxidant compounds in the meal were concentrated at optimum extraction conditions (in 52% ethanol at 74 degrees C for 62 min) predicted by response surface methodology (RSM). The resulting extract inhibited (p less than or equal to 0.05) the coupled oxidation of beta-carotene and linoleate in a beta-carotene-linoleate system. The system containing extract at a level providing 200 ppm phenolics retained 81% of the initial beta-carotene after 2 h of assay whereas the control retained only 11%. Inhibition (p less than or equal to 0.05) of TEARS, hexanal and total volatile formation in a meat system containing 200 ppm extract ranged from 18.9 to 88.3%, depending upon the concentration being tested. The extract inhibited (p less than or equal to 0.05) conjugated diene, hexanal and total volatile formation in bulk corn oil (8.3-9.6% inhibition) and corn-oil-in water emulsion (5.2-32.2% inhibition). Hydrogen peroxide, hydroxyl radical and superoxide radical-scavenging properties of the extract were somewhat less than, but comparable to, those observed for trans-sinapic acid at similar concentrations of phenolics. At 200 ppm, a 100% quenching of the hydroxyl radical and superoxide radical was evident. The extract scavenged 29-75% of the hydrogen peroxide in assay media after 10 min of assay as compared to 3% reduction in the control. (C) 1999 Elsevier Science Ltd. All rights reserved.