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Oven, microwave, combination roasting all inhibit peanut bacterial growth.

Peanut safety is important, especially since there have been quite a few Salmonella outbreaks in tree nut and peanut products in recent years.

Peanuts are particularly susceptible to contamination during their growth and storage phases. The improper storage of peanuts also can lead to an infection by the mold fungus Aspergillus flavus, releasing carcinogenic aflatoxin. These molds may produce aflatoxin in peanuts when conditions are favorable for fungal growth.

Scientists at The Ohio State University evaluated the safety and quality of peanuts using a variety of roasting technologies. Shelled raw peanuts were roasted using an oven at 163 C to 204 C, microwave or oven-microwave combinations. The researchers examined the lethal effect of these treatments on peanuts that had been inoculated with the Salmonella surrogate, Enterococcus faecium, and stored at room temperature for 1 hour, 24 hours or seven days before they were roasted.

The scientists determined roasted peanut color, odor activity values, free fatty acid content and peroxide values. Color and odor activity values were also analyzed on two commercial peanut butters. The values were calculated using volatile levels that had been quantified with selected ion flow tube mass spectrometry and known odor thresholds.

All of the treatments resulted in a minimum of a 3-log reduction of the inoculated bacterial population. Bacterial resistance was not influenced by storing the inoculated peanuts before they underwent treatment.

It turns out that roasting the peanuts using the different techniques produced equivalent, commercially ideal L* color values. Based on the odor activity values, the treated samples had similar volatiles important to flavor, compared to the commercial samples. Descriptive sensory analysis showed no significant difference among the roasting treatments for most sensory attributes.

The extent of lipid oxidation was not significantly different among the roasting methods. There was no evidence that roasting time or temperature affected the extent of lipid oxidation, when the ideal color was produced.

So it appears that oven, microwave or combination roasting should be sufficient to mitigate the threat of Salmonella contamination, and produce similar color, odor activity values, sensory attributes and lipid oxidation rates.

Further information. Sheryl A. Barringer, Department of Food Science and Technology, The Ohio State University, 317 Parker Food Science and Technology Building, 2015 Fyffe Rd., Columbus, OH 43210; phone: 614-688-3642; email:

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Publication:Emerging Food R&D Report
Date:Jan 1, 2015
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