Seed Disinfection in Sprout Production: Survey of Methods Applied, Basis for Selection and Efficacy in Controlling Human Pathogens

Introduction: Sprouted seed such as alfalfa have been implicated in high profile foodborne illness outbreaks and as such are considered a high risk food despite the perceived nutritional benefits. In addition to applying GAP during production, pathogen screening and traceability, seed disinfection is considered a key intervention to enhance microbiological safety of sprouts. Currently seed disinfection is voluntary in sprout production although proposals under FSMA would make a verified seed disinfection method mandatory in the industry.

Purpose: To undertake a survey on what seed disinfection methods are currently applied in industry and understand the reasons for selection. A second part of the study tested the efficacy of the identified seed disinfection methods to control Escherichia coli O157:H7, Salmonella and Listeria monocytogenesinoculated on alfalfa seeds.

Methods: A thirteen-question survey was sent to sprout growers in North America, Europe and Australia to identify seed disinfection applied, in addition factors influencing selection. Laboratory based trials assessed the efficacy of identified seed disinfection methods to inactivate human pathogens inoculated onto alfalfa seed. Assessment of the different seed disinfection methods was assessed on the basis of effect on seed germination, initial reduction of pathogens and potential for post-treatment recovery during the sprouting process.

Results: From the survey results it was found that 90% of respondents applied seed disinfection with hypochlorite being the most used although hot water, peroxyacetic acid, hydrogen peroxide, electrolyzed water and chlorine dioxide were also applied. The main motivation for selecting a specific seed disinfection method was based on government recommendations. From laboratory trails none of the treatments, apart from stabilized sodium chlorite, could ensure elimination of pathogens without post-treatment recovery or significant effect on germination rates.

Significance: Methods for seed disinfection should be evaluated using standard protocols taking germination rates and potential pathogen post-treatment recovery into account. Government recommendations have a strong influencing the method sprout producers used for seed disinfection.