## 3 Bioactive Compounds in Peanut Skins
### Chemical Antioxidant Activity
Pure ethanol, 80% ethanol in water, pure ethyl acetate, and 80% ethyl acetate in water were used. The highest yields by both weight and total phenolic compounds were found with the ethanol in the water mixture followed by pure ethanol. Higher levels were also found in the roasted peanut skins compared to the peanut skin extracts from the raw peanuts. The roasted peanut skin extract prepared using 80% ethanol in water was found to be effective as an antioxidant when added to sunflower oil, but even at 800 ppm, the effectiveness as monitoring using the Peroxide Value assay was less than that of BHT added at 200 ppm. Using only methanol, raw peanut skins were extracted for determination of total phenolic content (TPC), antioxidant activity using the DPPH assay, and inhibition of linoleic acid peroxidation [63]. Only 91.74 mg/g of TPC were found in this study compared to 148.7 mg/g reported in another study [17]. This is an example of the variability of the levels of extractable compound present in peanut skins. The effectiveness of different solvent mixtures in terms of antioxidant activity was compared with ethanol and methanol [40; 64]. Methanol or ethanol in water (80%) were used. The lipid in the extract was removed by partitioning into chloroform. The aqueous portion was then extracted with ethyl acetate to remove the nonphenolic compounds remaining as described by the methodology developed for purifying phenolic compounds from tea [65]. The aqueous portion was freeze-dried and the resulting powder dissolved in methanol for testing. A combination of solvents was used to prepare extracts from different parts of the peanut, including the skins that contained the different classes of polyphenols [66]. The initial extraction of peanut skins from a local market was performed using equal parts of methanol and water. The skins were then extracted with 70% acetone in water and the 2 extracts were combined. This represented the extractable polyphenols in the authors' description and was used to determine the total phenolic content (TPC) using the Folin-Cocialteu assay. The non-hydrolyzable polyphenols or condensed tannins were determined after treating the extracts with acidified butanol. The extracts were then evaluated using chemical assays for antioxidant activity, anticancer activity in a cell-based assay, and as an antioxidant by the heating of oil spiked with the peanut skin extracts. The solvent mixtures and solvent-assisted extraction were used in a study of various portions of peanuts including peanut skins [67]. A mixture of acetone and water (70%/30%) was acidified and used as the solvent. Acidification was used to free phenolics from glycoside complexes. Peanuts were subjected to increasing time of roasting to produce Maillard browning products. Increased roasting was found to increase the total phenolic content as well as corresponding ORAC assay values. A methanol/water mixture (50/50 v/v) followed by a mixture of acetone and water (70/30 v/v) was used to extract peanut skins, hulls, and defatted peanut flour, both raw and roasted [66]. The extracts were evaluated using TPC, nonhydrolyzable tannins (NEPP), and oxidative stability test on flaxseed oil. The extracts from the skin tested much higher than the other parts of the peanut with the roasted samples being lower than the raw ones. The procyanidins have been found in a range of plant parts in several forms. Comparison of those found in peanut skins with those from other foods has been the subject of several studies [7; 23; 65; 68; 69]. As previously discussed, peanut skins contain primarily the A-type. One report revealed both A-type and B-type dimers showed high antioxidant potency in a dose-dependent manner in the DPPH and ABTS+ assays [70]. However, the type of system used had an effect. In general, the B-type dimers showed a higher radical scavenging potency when tested in aqueous systems, whereas in tissue or lipid systems, the A-type dimers were just as effective or had even higher antioxidant potency than B-type ones.