Peanut skin phenolic extract attenuates hyperglycemic responses in vivo and in vitro

Authors: CHRISTMAN, LINDSEY - North Carolina State University; Dean, Lisa; ALLEN, JONATHAN - North Carolina State University; FENG GODINEZ, SOFIA - North Carolina State University; Toomer, Ondulla

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2019
Publication Date: 3/27/2019
Citation: Christman, L.M., Dean, L.L., Allen, J.C., Feng Godinez, S., Toomer, O.T. 2019. Peanut skin phenolic extract attenuates hyperglycemic responses in vivo and in vitro. PLoS One. 14(3):e0211459. https://doi.org/10.1371/journal.pone.0214591.
DOI: https://doi.org/10.1371/journal.pone.0214591

Interpretive Summary: Peanut skins are a waste product from producing peanut butter and other peanut products. They contain high levels of compounds with antioxidant properties but also have bitter flavors. The antioxidant compounds can be extracted and dried to powders that can be added to foods to increase their antioxidant strength. This study added the powder to seasoned coating mixtures for peanuts. In several sets of studies, human subjects were fed either a placebo gel cap or a gel cap containing the peanut skin powder or the subjects were fed peanuts coated with a seasoned coating containing the peanut skin powder or peanuts containing only the seasoned coating. Blood glucose levels were measured using continuous monitors attached to the abdomen. When the subjects had consumed products containing the peanut skin extract, their glycemic response was lower indicating greater glucose tolerance compared to subjects who had consumed the products without peanut skin extract. In addition, human liver cells exposed to high glucose levels were treated with the peanut skin extract. Compared to untreated cells, the peanut skin extract exposed cells were better able to survive the effects of the toxic glucose added. This work showed that a waste product from the peanut industry can be used to add value to peanuts as it has an antidiabetic effect.

Technical Abstract: Diabetes affects at least 285 million people globally, and this number continues to increase. Clinical complications include impaired glucose metabolism, hyperglycemia, dyslipidemia, atherosclerosis and non-alcoholic fatty liver disease. Evidence has shown that natural phenolics play a protective effect on both the development and management of type 2 diabetes. This study evaluated effects of the extract from peanut skins containing polyphenols on induced- hyperglycemia using in vivo and in vitro methods. A human hepatocellular liver carcinoma cell line (HepG2) was used to investigate the effect of the peanut skin extract on cell viability after exposure to high glucose concentrations. In vivo, the effect of peanut skin extract on an oral glucose tolerance was investigated in human subjects. Fifteen participants aged 21-32 underwent an oral glucose tolerance test with five treatments: 1) 50-gram glucose solution (reference); 2). 50-gram glucose solution, followed by 12 mg of vegi-capsulated maltodextrin; 3) 50-gram glucose solution, followed by 120 mg of vegi-capsulated maltodextrin-encapsulated peanut skin extract; 4). 50-gram glucose solution, followed by 28 grams of unfortified coated peanuts; 5) 50-gram glucose solution, followed by 28 grams of chili lime coated peanuts fortified with encapsulated peanut skin extract. Glucose levels were measured using a continuous monitor. Peanut skin extract was found to attenuate the decrease in cell viability in high glucose treated HepG2 cells, showing a protective effect against hyperglycemia induced cell death. No difference in the glycemic response area under the curve between any treatments using the tolerance test, but the treatment of the peanut skin extract with the glucose reference resulted in a significantly lower peak blood glucose response at 45 minutes, indicating that it was effective at reducing the glycemic response. The present study shows that the phenolic extract of peanut skins has an antidiabetic effect, further confirming their value as a functional food ingredient.