Effects of peanut skin extracts on the shelf life of unstabilized peanut butter

Authors: MOHEBPOUR, DAVID - North Carolina State University; Dean, Lisa; Harding, Ronald; Hendrix, Keith

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2023
Publication Date: 6/30/2023
Citation: Mohebpour, D.A., Dean, L.L., Harding, R.O., Hendrix, K. 2023. Effects of peanut skin extracts on the shelf life of unstabilized peanut butter. Peanut Science. 50(1):8-21. https://doi.org/10.3146/0095-3679-501-PS22-8.
DOI: https://doi.org/10.3146/0095-3679-501-PS22-8

Interpretive Summary: Peanut butter is a popular food in the American diet. The high fat content makes it susceptible to rancidity which causes unpleasant odors and flavors. Peanut skins are a waste product from the peanut roasting process. Peanut skins contain high levels of compounds which have been shown to be antioxidants. These compounds were extracted from peanut skins and then added to peanut butter to determine if they could protect the peanut butter from oxidation, which leads to rancidity. In this study, freshly roasted peanuts were ground to create peanut butters. To the peanut butter, different levels of the peanut skin extracts were added. Control samples were prepared from the same roasted peanuts by grinding with and without the peanut skins. The samples were stored over a period of 24 weeks at elevated temperatures to accelerate the oxidation. The samples were tested every two weeks to evaluate the degree of oxidation. The samples were also evaluated by a trained descriptive sensory panel for changes in flavor. The testing did not show any protective effects from the additives. Negative changes in flavor were attributed to the addition of the extracts and the oxidation of the naturally occurring fats in the peanut butter samples. The results of this study suggest that peanut skin extracts would not be effective as antioxidants for peanut butter.

Technical Abstract: 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.