Nitrogen Dioxide Fumigation for Microbial Control on Unshelled Peanuts*

Stored peanuts often need treatments to control microbial infections as well as insects to maintain postharvest quality. Nitric oxide (NO) is a recently discovered fumigant for postharvest pest control. NO fumigation must be conducted under ultralow oxygen condition to preserve NO and always contains NO2 due to NO reaction with oxygen and NO2 has antimicrobial property. Therefore, NO fumigation has potential to control both pests and pathogens. In this study, we evaluated antimicrobial effects of NO2 fumigation on unpasteurized unshelled peanuts. Peanuts were fumigated with 0.3%, 1.0%, and 3.0% NO2 for three days at 25˚C by injecting NO gas into glass jars to react with O2 in the atmosphere. After fumigation, wash-off microbial samples were collected from intact peanut samples and, then, cracked open peanut samples with non-selective tryptic soy broth medium. The wash-off samples were then diluted with both the non-selective medium and a fungal-selective potato dextrose broth medium and were tested on GreenLight™ rapid enumeration test based on oxygen depletion on culture medium. All three NO2 fumigation treatments showed significant antibacterial and antifungal effects on intact peanuts as well as on cracked peanuts with complete inhibition with 3.0% NO2. Fumigation did not have obvious effects on appearance of skinned peanut kernels. These results suggested that NO2 fumigation has potential to control microbes on stored products, and NO fumigation with the combination of NO and NO2 has potential to control both insects and microbes on stored products.