Comparison of Iron (III) Reducing Antioxidant Capacity (iRAC) and ABTS Radical Quenching Assays for Estimating Antioxidant Activity of Pomegranate

Abstract

Pomegranate juice (PJ) has total antioxidant capacity which is reportedly higher compared to other common beverages. This short study aimed to assess the total antioxidant capacity of commercial PJ and pomegranate fruit using a newly described method for iron (III) reducing antioxidant capacity (iRAC) and to compare with the ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid)) and Folin–Ciocalteu assays. Commercial PJ, freeze-dried pomegranate, and oven-dried pomegranate were analyzed. The calibration results for iRAC were comparable to ABTS and Folin–Ciocalteu methods in terms of linearity (R2 > 0.99), sensitivity and precision. The total antioxidant capacity for PJ expressed as trolox equivalent antioxidant capacity (TEAC) was 33.4 ± 0.5 mM with the iRAC method and 36.3 ± 2.1 mM using the ABTS method. For dried pomegranates, total antioxidant capacity on a dry weight basis (DB) was 89–110 mmol/100 g DB or 76.0 ± 4.3 mmol/100 g DB using iRAC and ABTS methods, respectively. Freeze-dried pomegranate had 15% higher total antioxidant capacity compared with oven-dried pomegranate. In conclusion, pomegranate has high total antioxidant capacity as evaluated by the iRAC and ABTS methods, though variations occur due to the type of cultivar, geographic origin, processing and other factors. The study is relevant for attempts to refine food composition data for pomegranate and other functional foods.