Total phenolics and antioxidant capacity of heat-treated peanut skins

Total phenolics and antioxidant capacities of heat-treated skins from Runner, Virginia and Spanish peanut types were evaluated. Peanut skin extracts were evaluated for total phenolics (TP), Trolox equivalent antioxidant capacity (TEAC) and peroxyl-radical trapping capacity (PRTC) assay. Factors studied were temperature (90, 112, 135, 158 and 180 °C), time (5, 15 and 25 min) and peanut types. Runners significantly (P < 0.05) contained more total phenolics and had higher TEAC and PRTC values than Virginia and Spanish types. Maximum values for total phenolics (280 mgGAE/g), TEAC value (2.56 mM TEAC/g) and PRTC value (31 μM Trolox/g) were obtained with Runners heated at 135 °C for 5 min. Regression analysis showed that temperature and time were not related to total phenolics in all three peanut types. TEAC values could be predicted by temperature and time for Runner, Virginia and Spanish, but PRTC values could be predicted for Runner and Virginia samples only. Generally, only mild heat treatments (<135 °C, 15 min) could further enhance the antioxidant capacity of peanut skins.