Ultrasonication and Edible Coating Effects on Lipid Oxidation of Roasted Peanuts

Lipid oxidation is an important factor affecting the quality of roasted peanuts. Coatings applied to the peanuts can enhance oxygen barriers to reduce rancidity. Ultrasonication was used to remove lipids from the peanuts prior to applying the coating to improve attachment of the coating on the peanut surface. Peanuts were roasted at 178°C for 15 min and then sonicated in hexane for 10 min. Whey protein isolate (WPI) 11%, corn protein (Zein) 15%, and carboxymethyl cellulose (CMC) 0.5% were used as coating materials. Sample treatments were: (1) roasted–coated with CMC (RCMC), WPI (RWPI), and Zein (RZEIN); (2) roasted–sonicated–coated with CMC (SCMC), WPI (SWPI), and Zein (SZEIN); (3) roasted–uncoated (R) as a control. Oxidative stability was investigated by gas chromatography–mass spectrometry (GC–MS) to detect formation of volatile compounds. The GC–MS indicated an eightfold, fivefold, and fourfold increase in hexanal formation in R, RZEIN, and SZEIN samples, respectively. But there was 80%, 91%, 18%, and 66% decrease in hexanal formation in RCMC, SCMC, RWPI, and SWPI samples, respectively, as compared to R. Sonication increased capability of coatings to delay hexanal formation by 11% and 48% for CMC and WPI, respectively, as compared to nonsonicated samples. Thus, the coating in combination with ultrasonication treatment was an effective method in delaying formation of oxidative volatile compounds and hence inhibiting rancidity of roasted peanuts.