Effect of far-infrared radiation and heat treatment on the antioxidant activity of water extracts from peanut hulls

The antioxidant activities of peanut (Arachis hypogaea L.) hull extracts were evaluated after far-infrared (FIR) radiation or heat treatment. Peanut hulls in petri dishes were FIR-irradiated or heat-treated (150 °C) for 5, 10, 15, 20, 40 or 60 min. The water extracts (300 mg/10 mL) of peanut hulls (WEPH) were prepared and their total phenol contents (TPC), radical scavenging activity (RSA), and reducing power were determined. The antioxidant activities of WEPH increased as the time of heating or FIR-radiation increased. When peanut hulls were FIR-irradiated at 150 °C for 60 min, the values of TPC, RSA, and reducing power of WEPH increased from 72.9 to 141.6 μM, 2.34% to 48.83%, and 0.473 to 0.910, respectively, compared to the untreated controls. Heat treatment of peanut hull under the same conditions (150 °C for 60 min) also increased the TPC, RSA, and reducing power of WEPH from 72.9 to 90.3 μM, 1.90% to 23.69%, and from 0.471 to 0.718, respectively. The result indicated that FIR-radiation or heat treatment on peanut hulls increased the antioxidant activities of WEPH.