Effect of Peanut Skin Extracts on the Shelf Life of Unstabilized Peanut Butter

Peanut butter is a desirable product made from roasted peanuts that is susceptible to lipid oxidation during its shelf life. The process of lipid oxidation produces rancid aromas and flavors in peanut butter that have previously been found to be undesirable to consumers. Peanut skins, the paper-like coatings that surround peanut kernels, are a waste product of peanut processing that have been shown to contain phenolic compounds that could act as antioxidants which are able to inhibit lipid oxidation. Addition of peanut skin extracts to fresh peanut paste was evaluated for their effectiveness to retard oxidation of the lipids present. Extraction of the phenolic compounds and encapsulation with maltodextrin produced a free-flowing powder that was blended into freshly ground peanuts. The paste was packed into glass jars and incubated at 30 C and 26 % relative humidity. Control samples of peanut paste without the addition of the peanut skins extract ingredient were prepared using both blanched and unblanched peanuts from the same batch where the skins were removed after roasting. Samples were evaluated biweekly over a 24-week period for free fatty acids, peroxide value, hexanal production and with descriptive sensory analysis to determine the progression of lipid oxidation. Free fatty acids were elevated by the addition of the extracts, but the peroxide values decreased over the test period. Hexanal production was not affected. Descriptive sensory analysis showed a decrease in roast peanut flavor over time regardless of the addition. The addition of the peanut skin extracts also resulted in distinct flavors that were not considered positive attributes for peanut butter. In this study, peanut skin extracts did not function as effective antioxidant ingredients for unstabilized peanut butter.