Effects of extraction, solvents, cold pressing, and period of storage upon oven stability of raw peanut oil

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Abstract
Keeping time (oven stability, 60 C), oleate/linoleate ratios, peroxide values, and free fatty acid numbers were determined on oils from 5 peanut varieties grown at 2 Texas locations in 1972. Cold‐pressing within polyethylene bags (bag‐pressing) resulted in increased oven stabilities and better correlations between oleate/linoleate ratios and oven keeping times in comparison to cold‐pressed oils. Average relative storage stabilities for the solvent extracted oils were: chloroform‐methanol (3:1) ≫ cyclohexane ≈ ether > acetone ≈ bag‐pressed > cold‐pressed. Correlations of oleate/linoleate ratios and keeping times were increased using low peroxide ether in place of reagent grade ether. Extracted oils from samples including skins appeared to have longer keeping times than those minus skins. Oven keeping times and correlations with oleate/linoleate ratios decreased with extended peanut storage times (11 months), but the use of chloroform‐methanol tended to compensate for this effect. For samples taken from storage after 3 and 6 months, the following average correlations were obtained: bag‐pressed, 0.27; chloroform‐methanol (without skins), 0.87; chloroform‐methanol (with skins), 0.90; ether (reagent), 0.49; ether (low peroxide), 0.89; cyclohexane, 0.87; and acetone, 0.62. Generally poor correlations were found between oven stability and peroxide and free fatty acid numbers. Differences in the degree to which minor components are extracted from the cotyledons and skins, interaction between the oils, and residual traces of solvents or trace impurities in solvents were suggested as possible factors leading to differences in keeping times of solvent extracted oils.