Peanut skin procyanidins: Composition and antioxidant activities as affected by processing

Peanut skin was removed by direct peeling, blanching, and roasting. Total phenolics (TPs), total antioxidant activity (TAA) and free radical scavenging capacity of peanut skin extracts were determined. The composition of ethanolic extracts of peanut skin obtained from each processing method was determined by LC-MS and HPLC. Peanut skin processing methods significantly affected total extractable phenolics and their composition. Roasting had limited effects on concentration of TPs while blanching caused 89% loss of TPs. TPs in directly peeled, roasted, and blanched peanut skins were 130, 124, and 14.4 mg/g dry skin, respectively. Catechins, A-type and B-type procyanidin dimers, trimers and tetramers in chemically purified peanut skin extracts were identified by LC-MS. Total catechins, procyanidin dimers, trimers and tetramers in directly peeled peanut skin were 16.1, 111.3, 221.3 and 296.1 mg/100 g, respectively, versus 8.8, 143.5, 157.5 and 203.9 mg/100 g, respectively, in roasted dry skin. TAAs and free radical scavenging capacities of peanut skin extracts were all higher than those of Trolox and Vitamin C at equivalent concentration. Peanut skin, a by-product of the peanut processing industry, was found to contain potent antioxidants and could provide an inexpensive source of antioxidants for use as functional ingredients in foods or dietary supplements.