## 2 Extraction of Peanut Skins
### Extraction Optimization
The main savings in this procedure is the time involved was less without compromising the activity of the extracts. Optimization of extraction using responsive surface methodology was also used to find the most effective conditions to extend oil shelf life [48]. Using ethanol in water over a range of 20% to 100% with a variation of time from 5 to 150 min and temperature from 25\({}^{\circ}\) to 90 \({}^{\circ}\)C, the study used both the DPPH and the 2,2\({}^{\prime}\)-Azino-bis(3-ethylbenzothazoline-6-sulfonic acid (ABTS+) assays to determine the optimal conditions. It was found that length of time was not of significance but that temperatures above 60 \({}^{\circ}\)C with 75% ethanol in water were optimum. In addition, soybean oil with the optimized extract added at 25 to 1000 mg/kg was subjected to accelerated conditions of agitation at 60 \({}^{\circ}\)C and compared to the addition of 200 mg/kg of butylated hydroxytlouene (BHT), a syntheticantioxidant compound. It required 750 mg/kg of the optimal extract to produce the same antioxidant effect of 200 mg/kg of BHT, the synthetic chemical antioxidant. Isolation of specific proanthocyanidins was performed using preparative HPLC [49]. This allowed for more automated separation of peanut skin extracts. Using earlier work as a guide [21; 32], acetone in water (60%) that had been acidified was used as the extractant. An initial purification was performed using Amberlite resin eluted with methanol. This was followed by fractionation on Sephadex LH-20. The fractions were evaluated using the DPPH assay and the most active fraction was further purified using preparative HPLC. This allowed for the isolation of proanthocyanidins A1 and A2 with the major portion of the isolate being the A1 form. The most recent study of the composition of peanut skin extracts compared them to grape skin extracts [50]. The skins were extracted using 80% ethanol in water following a procedure previously published [44]. The extracts were purified using AB-8 resin to purify the procyanidins. The extracts were then evaluated using ORAC, DPPH, ABTS+, and the Ferric Reducing Antioxidant Power (FRAP) assays as well as a cell assay using Human hepatocellular carcinoma (HepG2 cells). Both the A- and the B-type of the procyanidins were identified by HPLC-MS with the A-type predominating as found by others. In most of the assays, the peanut skin extracts had slightly higher values than the grape skin extracts, with the exception of the cell-based assay where the grape skin extracts scored higher. To release the phenolics from peanut skins by the degradation of the actual cell walls for the skins, enzymatic digestion was used [51]. Cellulase was used at an incubation temperature of 55 \({}^{\circ}\)C followed by extraction with aqueous ethanol at 45%. The yield of proanthocyanidins was 16.17%. An exploration of the effectiveness of heat in increasing the solubility and thus the extraction efficiency of solvent in removing phenolic compounds from peanut skins was performed. As many of these compounds are found to be bound into sugars and other cellular structures, the authors theorized that heat treatment of the skins before extraction would increase the yield [52]. Using temperatures from 90 \({}^{\circ}\)C to 180 \({}^{\circ}\)C, peanut skins from the market types, runner, Virginia, and Spanish were extracted using 70% ethanol in water solutions. TPC and antioxidant activity using the Trolox equivalent antioxidant capacity (TEAC) and the Peroxy-radical trapping capacity assays were compared. Heating to 135 \({}^{\circ}\)C resulted in the highest TPC in the runner peanuts (280 mg/g). Both the Virginia and Spanish peanuts did not show any significant change in TPC with heating within the tested range and were both lower (149 mg/g for the Virginia type and 137 mg/g for the Spanish type) than the runner type.