Effect of processing on the total antioxidant capacity and total phenol content of Indian green leafy vegetables

Green leafy vegetables are identified as a rich source of beta carotene. Apart from carotenoids, they contain many bioactive components and are found to have the highest antioxidant capacity than some fruits and root vegetables. There are many green leafy vegetables conventionally used in Indian households and data on the Total Antioxidant Capacity (TAC) and Total Phenols (TP) of these greens is scarce. Nine commonly used green leafy vegetables, namely, Amaranthus G. (Amaranthus Gangeticus), Amaranthus T. (Amaranthus Tristis), Fenugreek leaves(Trigonella Foenum-graecum), Coriander leaves(Coriandrum Sativum Linn.), Mint leaves(Mentha Sativa), Curry leaves(Coriandrum Sativum Linn), Spinach(Spinach oleracea Linn), Solanum leaves(Solanum Nigrum) and Drumstick leaves(Moringa Oleifera) were selected and assessed for TAC by Oxygen Radical Absorbance Capacity (ORAC) assay and Ferric Reducing Antioxidant Power (FRAP) assay and TP by Folin Ciocalteau method. The leaves were subjected to steaming and drying and the effects of the processes on TAC and TP were analysed. The TAC of fresh leaves ranged from 496.72 μmol TE/100g in spinach to 5248.98 μmol TE/100g in curry leaves by ORAC assay. Fresh curry leaves had the highest antioxidant capacity in both assays and also the highest total phenolic content of 703.42 mg GAE/100g. Steamed and dried leaves had higher values than fresh leaves. In evaluating the effect of processing, after adjusting for moisture gain or loss, steaming increased while drying decreased the TAC and TP content of green leaves with few exceptions. Phenols contributed a higher percentage to TAC in fresh leaves, but their contribution decreased after steaming and drying.