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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #365083

Research Project: Methyl Bromide Replacement: Post-harvest Treatment of Perishable Commodities

Location: Crop Improvement and Protection Research

Title: Effectiveness of nitrogen dioxide fumigation for microbial control on stored almonds

item OH, SOOKYUNG - University Of California
item Liu, Yong Biao

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2019
Publication Date: 3/16/2020
Citation: Oh, S., Liu, Y.-B. 2020. Effectiveness of nitrogen dioxide fumigation for microbial control on stored almonds. Journal of Food Protection. 83(4):599–604.

Interpretive Summary: Nitric oxide (NO) is a newly discovered fumigant for postharvest pest control. NO fumigation must be conducted under ultralow oxygen conditions to prevent its reaction with oxygen to form nitrogen dioxide (NO2). Because both NO and NO2 have antimicrobial property, NO fumigation with proper levels of both NO and NO2 may have potential to control both pests and microbes on stored products. In this study, NO fumigation under ambient oxygen level to expose nonpasteurized almonds to 0.1%, 0.3%, and 1% NO2 for one and three days at 25°C to determine effects of NO2 on microbes. Wash-off samples from control and treated almonds were made with both microbial culture broth medium and fungus-selective broth medium. Diluted wash-off samples were cultured using GreenLight rapid enumeration tests to determine microbial loads in diluted samples. The results showed that NO2 exposures had significant inhibitory effects on both bacteria and fungi, and complete control of bacteria and fungi was achieved at higher NO2 concentration. This study suggests that NO fumigation with proper NO2 levels have potential to control microbes on stored almonds.

Technical Abstract: Quality of stored almonds is compromised by insect infestations and microbial contamination. Nitric oxide (NO) is a potent fumigant for postharvest pest control on fresh and stored products. NO fumigation must be conducted under ultralow oxygen (ULO) conditions and NO fumigation always produces NO2 depending on the O2 level in the fumigation chamber. NO and nitrogen dioxide (NO2) have proven antimicrobial effects, but have not been tested for efficacy against microbes in almonds. We evaluated, in this study, fumigation of nonpasteurized almonds with NO2 at different levels for inhibition of bacteria and fungi. Almonds were fumigated with 0.1%, 0.3%, or 1.0% NO under ambient O2 in order to generate 0.1%, 0.3%, or 1.0% NO2 conditions; the fumigation treatments lasted one or three days at 25°C. GreenLight™ rapid enumeration tests on diluted wash-off almond samples from NO2 fumigation treatments showed either greatly reduced microbial loads or complete control of microorganisms, depending on NO2 concentration and treatment duration. The antimicrobial effects of NO2 were more prominent when fungus-selective broth was employed for the preparation of wash-off almond samples. These results suggest that postharvest NO fumigation with proper levels of NO and NO2 can be used for insect and microorganism control on stored almonds.