Oven, Microwave, and Combination Roasting of Peanuts: Comparison of Inactivation of Salmonella Surrogate Enterococcus faecium, Color, Volatiles, Flavor, and Lipid Oxidation



Peanut safety and quality were evaluated for different roasting technologies. Shelled raw peanuts were roasted using an oven at 163 to 204 °C, microwave, or oven and microwave combinations. The lethal effect of these treatments was investigated on peanuts inoculated with the Salmonella surrogate, Enterococcus faecium and stored at room temperature for 1 h, 24 h, or 7 d before roasting. Roasted peanut color, odor activity values (OAVs), descriptive sensory panel analysis, free fatty acid, and peroxide values were determined. Color and OAVs were also analyzed on 2 commercial peanut butters. OAVs were calculated using volatile levels quantified with selected ion flow tube mass spectrometry and known odor thresholds. All treatments resulted in a minimum of 3 log reduction of inoculated bacterial population. Resistance to the process was not influenced by storage of inoculated peanuts prior to treatment. Roasting by different methods produced equivalent, commercially ideal L* color. Based on the OAVs, treatments had similar volatiles important to flavor compared to the commercial samples. Descriptive sensory analysis showed no significant difference between the roasting treatments for most of the sensory attributes. Lipid oxidation was not significantly different between the roasting methods, displaying no evidence that roasting time or temperature affected lipid oxidation, when ideal color was produced. These results suggest that oven, microwave, or combination roasting should be sufficient to mitigate the threat of Salmonella contamination and produce similar color, OAVs, sensory attributes, and lipid oxidation results.

Practical Application

Peanut safety is important especially since Salmonella outbreaks in tree nut and peanut products have been numerous in recent years. Roasted peanut color, odor activity values, lipid oxidation, and sensory attributes are quality parameters used to evaluate roasted peanuts. Based on the evaluated safety and quality parameters, microwave or microwave and oven combination roasting technologies may be used as alternative roasting methods to produce peanut butter potentially decreasing the production costs.