Peanut skin phenolics: Extraction, identification, antioxidant activity, and potential applications

Extraction and determination of total phenolics (TP) in peanut skins obtained from various processing methods was conducted. Total antioxidant activity (TAA) of peanut skin extracts was determined in order to identify and quantify different classes of phenolics in peanut skin. Peanut skins were removed by direct peeling, blanching, and roasting. TP and TAA of peanut skin extracts were determined using Folin-Ciocalteu and free radical scavenging methods, respectively. The composition of peanut skin extracts was determined by LC-MS. Peanut skin processing significantly affected total extractable phenolics and their composition. Roasting had limited effects on TP while blanching caused 89% loss of TP. TP in directly peeled, roasted, and blanched peanut skins were 130, 124, and 14.4 mg/g, respectively. TAA of all purified peanut skin extracts were higher than those of Trolox and Vitamin C at equivalent concentrations. LC-MS analysis of purified peanut skin extracts revealed the presence of catechins, A-type and B-type procyanidin dimers, trimers and tetramers. Total catechins, procyanidin dimers, trimers and tetramers in directly peeled peanut skin were 16.1, 111.3, 221.3 and 316.1 mg/100g, respectively, versus 8.8, 143.5, 157.5 and 203.9 mg/100 g, respectively, in roasted skin.