Phenolics, selenium, vitamin C, amino acids and pungency levels and antioxidant activities of two egyptian onion varieties

Abstract

Selenium, vitamin C, pungency, amino acids, phenolics content and antioxidant activities of two Egyptian onion varieties, namely white (Giza-6) and red (Beheri) onions have been studied. Data analysis showed that the red variety presents higher values for selenium, vitamin C and sulphur-containing amino acids. Concerning pungency, white onion can be classified as intermediate pungency (8.24 μmol of Pyruvic acid/100 g fresh wt.) and red as pungent (11.37 μmol of pyruvic acid/100 g fresh wt.). The phenolic acids, flavonols, anthocyanins and total phenolics content in red variety (81.59, 70.38, 7.56 and 187.17 mg/100 g fresh wt., respectively) were higher than for white variety (72.47, 32.49, 4.90 and 131.65 mg/100 g fresh wt., respectively). Consequently, antioxidant activity was higher for the red variety. Correlation analysis indicates that phenolic compounds beside other factors including Se and sulphur-containing amino acid contents play the major role in the antioxidant activity of onion bulbs. The antioxidant capacity of freeze dried powder from both onion varieties was also tested in sunflower oil-in-water emulsions and hydroperoxide formation was monitored during storage at 40°C. In accordance with differences in Se, sulphur-containing amino acid and phenolics content, Egyptian red onions had better antioxidant activity, while white onions was only effective in the early stages of the oxidation process. These data indicates that red variety has higher potential health benefits related to the presence of antioxidant compounds. © 2009 Academic Journal Inc.