Nitrogen dioxide fumigation for microbial control on unshelled peanuts

Authors: Oh, Sookyung; Singh, Rippy; Liu, Yong Biao

Submitted to: Agricultural Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2020
Publication Date: 12/21/2020
Citation: Oh, S., Singh, R., Liu, Y.-B. 2020. Nitrogen dioxide fumigation for microbial control on unshelled peanuts. Agricultural Sciences. 11(12):1159-1169. https://doi.org/10.4236/as.2020.1112076.
DOI: https://doi.org/10.4236/as.2020.1112076

Interpretive Summary: Nitric oxide (NO) is a recently discovered fumigant for postharvest pest control. Because NO reacts with oxygen to form nitrogen dioxide (NO2), NO fumigation must be conducted under ultralow oxygen condition and NO fumigation always contains nitrogen dioxide (NO2) as it is impractical to remove all oxygen from fumigation chamber. However, NO2 has antimicrobial effects. Therefore, NO fumigation conducted under certain low oxygen levels has potential to control both pests and pathogens. Stored peanuts have both pest infestation and microbial infection problems. In this study, we evaluated microbicidal 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. 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. Microbial contamination of wash-off samples was analyzed using a rapid enumeration test to determine microbial loads. All three NO2 fumigation treatments had significant antibacterial and antifungal effects on whole peanuts, as well as on cracked peanuts with complete inhibition by 3.0% NO2. Fumigation did not have obvious effects on appearance of skinned peanut kernels. The results of this study 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 peanuts.

Technical Abstract: 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.