Shelf life extension of roasted peanuts by surface lipid removal

Removal of lipids on the surface or from a layer adjacent to the surface of a roasted peanut kernel was investigated as a means to extend the oxidative stability or shelf life of roasted peanuts. Georgia green runner-type peanut kernels were roasted at 178 °C in an electric oven for 15 min. Roasted peanuts were subjected to lipid extraction in hexane by mechanical shaking and sonication at room temperature for various durations. Peanut oil was recovered from hexane using a Soxtec lipid extraction system. The surface conditions of the peanuts before and after lipid removal were examined using a florescence microscope. Results showed that surface lipids of the roasted peanuts used in this study existed at a level of approximately 0.56% of the total peanut mass. Florescence micrographs revealed that the surface of sonicated peanut kernels was clean and almost free of oil stains, as opposed to that of freshly roasted peanut kernels, where a considerable amount of lipids remained on the surface of roasted peanuts. Statistical analysis indicated that lipid removal could significantly improve the oxidative stability of roasted peanuts, and it was possible to extend the shelf life of roasted peanuts by removing partial lipids from the roasted peanuts. The results also showed that power ultrasound could remove the lipids more effectively than mechanical shaking.