Comparison of the antioxidant properties of some onion and garlic cultivars grown in Turkey

Garlic and onions are widely consumed among the vegetables in Turkey. The objective of this study was to determine the antioxidant properties of red, yellow and white onions, and Chinese and Taşköprü garlics grown in Turkey. The color, dry matter, total soluble solids, total phenolics and antioxidant activity values of the samples were determined. Total phenolic content was studied by the Folin-Ciocalteu method expressed as mg gallic acid equivalents g-1 dry weight (mg GAE g-1 DW), while antioxidant activity was analysed using two different methods as ferric reducing antioxidant power (FRAP, mmol Fe2+ g-1 DW) and, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity. Red onions had the highest total phenolic contents ranged from 6.60 to 9.85 mg GAE g-1 DW (8.40±1.06 mg GAE g-1 DW). The total phenolic contents of yellow onions, white onions, Chinese garlics and Taşköprü garlics were found as 4.41-9.55 mg GAE g-1 DW (7.19±1.96 mg GAE g-1 DW), 1.73-3.09 mg GAE g-1 DW (2.16±0.47 mg g-1 DW), 2.05-3.34 mg GAE g-1 DW (2.64±0.45 mg g-1 DW) and 1.05 to 2.08 mg GAE g-1 DW (1.59±0.38 mg GAE g-1 DW), respectively. Also, red onions had the highest antioxidant activity at 8.50±4.85 mmol Fe2+ g-1 DW and 69.68±15.95% for FRAP and DPPH assays, respectively. FRAP values of yellow onions, white onions, Chinese garlics and Taşköprü garlics were found as 3.84±2.02 mmol Fe2+g-1 DW, 1.46±0.43 mmol Fe2+ g-1 DW, 2.03±0.57 mmol Fe2+ g-1 DW and 1.26±0.32 mmol Fe+2 g-1 DW, respectively. DPPH radical scavenging activity (the percentage of DPPH reduced by 14.3 mg mL-1 extract) of yellow onions (42.25±8.32%) was higher than white onions (11.57±0.71%). DPPH radical scavenging activity of the garlic extracts (14.3 mg mL-1) was found to be less than 2%. In the present study, the highest antioxidant activity and total phenolics were found in red onions, while the lowest values was Taşköprü garlics.