Optimizing the extraction of phenolic antioxidants from peanut skins using response surface methodology

Peanut skins are a byproduct of peanut blanching operations and contain high levels of phenolic antioxidants. The effect of solvent type (methanol MeOH, ethanol EtOH, and water), concentration (0, 30, 60, 90%), temperature (30, 45, 60 degrees C), and time (10, 20, 30 min) on total phenolic content (TPC), oxygen radical absorbance capacity (ORAC) level, and resveratrol content of peanut skins was investigated. Response surface methodology was used to estimate the optimum extraction conditions for each solvent. EtOH extracts had the highest TPC followed by MeOH and water. The maximum predicted TPC under the optimized conditions (30.8%, 30.9 degrees C, 12 min) was 118 mg of gallic acid equivalents (GAE)/g of skins. MeOH extracts had the highest ORAC activity of 2149 micromol of TE/g followed by EtOH and water under the optimized conditions of 30% MeOH, 52.9 degrees C and 30 min. Resveratrol was identified in MeOH extracts but was not found in samples extracted with EtOH or water.