Disinfection of Alfalfa and Radish Sprouting Seed Using Oxidizing Agents and Treatments Compliant with Organic Food Production Principles

Antimicrobial seed treatments recommended by Canadian guidance for sprouted vegetable production (2,000 ppm of hypochlorite for 15 to 20 min or 6 to 10% hydrogen peroxide for 10 min at room temperature) are not fully compliant with organic production principles. We investigated the effect of a sequential treatment consisting of a 10-min soak at 50°C in water followed by exposure to a 2.0% H2O2 plus 0.1% AcOH sanitizing solution against Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica inoculated onto alfalfa and radish seed. The sequential treatment was as effective as the recommended treatments and could reduce populations of all three species by a minimum of 3 log CFU/g using a reduced (1:2) ratio of seed to sanitizing solution and low concentrations of sanitizers approved for use in organic food production. However, the efficacy of all the treatments examined in this work was considerably reduced by storage of the seed for 4 weeks at either 11 or 75% relative humidity prior to treatment and assessment. None of the treatments could eradicate the target pathogens from seed, irrespective of time elapsed since inoculation. The results of this work suggest that the effect of storage should be considered in the assessment of antimicrobial treatments for sprouting vegetable seed. Recommended antimicrobial treatments for sprouting seed are not organic compliant. Alternatives based on mild heat and low chemical concentrations were investigated. Treatments were effective against three human pathogens on alfalfa and radish seed.