Comparative control of the bioactivity of some frequently consumed vegetables subjected to different processing conditions

The main aim of this investigation was to find processing conditions and to control them, which maximally preserve bioactive compounds and antioxidant activity of garlic and onions. Garlic, white and red onions were subjected to bleaching and boiling. The contents of polyphenols, flavonoids, flavanols, tannins, corresponding antioxidant activities and their correlation coefficients were determined in various methanol and acetone extracts. The antioxidant activity was determined by 2, 2-azino-bis(3-ethyl-benzthiazoline-6-sulfonic acid) (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH), Ferric-reducing/antioxidant power (FRAP) and Cupric reducing antioxidant capacity (CUPRAC) antioxid ant assays. It was found that bleaching for 90 most fully preserves polyphenols (8.25, 9.75 and 11.98 vs. 9.00, 10.52 and 15.87 mg GAE/g DW and the level of antioxidant activity - 8.82, 22.50 and 23.90 vs. 9.00, 23.05 and 24.30 mu M TE/g DW of DPPH in extracts of treated samples with 100% of methanol vs. raw garlic, white and red onions, respectively. In conclusion, comparative control shows that bleaching for 90 of all studied vegetables most fully preserves contents of bioactive compounds and the level of antioxidant activity. Extraction of bioactive compounds with 100% methanol was more effective than with 50% methanol anol 100% acetone. (c) 2008 Elsevier Ltd. All rights reserved.