Variation of Antioxidant Capacity in Different Layers of Onion (Allium cepa L.) At Two Different Stages of Maturation

Onion (Allium cepa L.) is one of the oldest cultivated plants with tremendous therapeutic properties. They are a rich source of flavonoids, consisting mainly of the major flavonols quercetin-3,4’-O-diglucoside (QDG) and quercetin-4’- O-monoglucoside (QMG). Outer layer which is the transitional layer with the first living cells below the dry onion peel and innermost layers from two different sizes of onion were studied for their total phenolic contents (TPC) and free radical scavenging activities (FRSA). Outer layers had greatest TPC content (ranging in between 84.4 to 97.8 mg GAE/100g fresh weight vs. 48.6 to 52.5 mg GAE/100g fresh weight), and FRSA than the innermost layers. The outermost layers showed better H2O2 scavenging activity and increased reducing power. The results were more pronounced for the layers of smaller onion having lesser moisture content than larger onion. The antioxidant assays were found to be correlated with the phenolic content. Our results demonstrate that the outermost living layers had higher antioxidant activities than the innermost layers indicating higher flavonoid content in outer layers.