Functional components in peanut skins
Francisco, Maria Leonora Lotis De Leon
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The functionality of peanut skins as a functional food and antioxidant ingredient was studied. The effect of heat treatment on total phenolics, antioxidant capacity (AOC) and concentration of phenolic compounds of peanut skins from Runner, Virginia and Spanish peanut types were analyzed. Heated Runners significantly (P<0.05) contained more total phenolics and had higher AOC values than heated Virginia and Spanish types. Mild heat treatments (<135C, 15 min) further enhanced the antioxidant capacity of raw peanut skins. An improved reversed-phase high performance liquid chromatography method was developed and validated for simultaneous determination of 15 phenolic compounds. Three phenolic acids, 3 flavonoids and 1 stilbene were identified and quantified in all peanut skin extracts from all peanut types. The effect of brewing conditions on the AOC, sensory attributes and consumer preference for peanut skin infusions was evaluated. Peanut skin infusions prepared from all 3 peanut skin types are rich in phenolics and have high AOC, which contributed to the different sensory attributes of the skin infusions. Consumer acceptance was low due to increased intensity in bitterness and astringency. Significant formulation issues in achieving consumer acceptability are needed to deliver beneficial effects to humans in beverage formulations. Storage stability of peanut skin extracts and skins was likewise evaluated. AOC decreased when extracts and skins were stored at different temperatures (23, 30, 35 and 40C) and followed a first order kinetic model. Infusions prepared from stored skins with 50% less AOC revealed minor differences in sensory attributes compared with the control. Finally, the antioxidant effectiveness of peanut skin extracts were evaluated in bulk soybean oil, mayonnaise and cooked, refrigerated beef patty applications. Natural antioxidant activity of peanut skin extract was observed in bulk soybean oil and cooked beef patties but not in mayonnaise. There is substantial evidence that peanut skins are packed with bioactive compounds. Peanut skin extract has antioxidant activity in multiple food systems suggesting that the extract has diverse chemical composition. More efficient use of peanut skins in high value products as dietary antioxidant ingredients and in beverages is encouraged and this will benefit the peanut industry, the economy and human health.