Evaluation of Aerated Steam Treatment of Alfalfa and Mung Bean Seeds To Eliminate High Levels of Escherichia coli O157:H7 and O178:H12, Salmonella enterica, and Listeria monocytogenes

Abstract

Sprouts contaminated with human pathogens are able to cause food-borne diseases due to the favorable growth conditions for bacteria during germination and because of minimal processing steps prior to consumption. We have investigated the potential of hot humid air, i.e., aerated steam, to treat alfalfa and mung bean seeds which have been artificially contaminated with Escherichia coli O157:H7, Salmonella enterica subsp. enterica serovar Weltevreden, and Listeria monocytogenes Scott A. In addition, a recently collected E. coli O178:H12 isolate, characterized by a reduced heat sensitivity, was exposed to the treatment described. Populations of E. coli O157:H7 and S. enterica on alfalfa and mung bean seeds could be completely eliminated by a 300-s treatment with steam at 70 ؎ 1°C as revealed by enrichment studies. L. monocytogenes and E. coli O178:H12 could not be completely eliminated from artificially inoculated seeds. However, bacterial populations were reduced by more than 5 log CFU/g on alfalfa and by more than 4 log CFU/g on mung bean seeds. The germination rate of mung beans was not affected by the 300-s treatment compared to the germination rate of untreated seeds whereas that of alfalfa seeds was significantly lower by 11.9%. This chemical-free method is an effective alternative to the 20,000-ppm hypochlorite treatment presently recommended by the U.S. Food and Drug Administration (FDA).

Some Like It Hot: Heat Resistance of Escherichia coli in Food

“…Desiccated strains of E. coli and Salmonella are characterized by extreme resistance to physical and chemical stressors including heat (Beuchat and Scouten, 2002; Beuchat et al, 2013; Studer et al, 2013; Syamaladevi et al, 2016). Parameters for the heat inactivation of dry bacterial cells are comparable to the moist heat inactivation of bacterial endospores spores rather than pasteurization (Brandl et al, 2008; Du et al, 2010; Podolak et al, 2010).…”

Aerated Steam Sanitization of Whole Fresh Cantaloupes Reduces and Controls Rind‐Associated Listeria but Enhances Fruit Susceptibility to Secondary Colonization

“…They did not monitor surviving Listeria on treated cantaloupe during postexposure storage, but reported that treated whole melons and cut pieces displayed no indications of decay or color change upon storage at 5 °C. Exposure to aerated steam at an average temperature of 70 °C for a 300 s reduced L. monocytogenes on mung bean and alfalfa seeds by 4 and 5 log 10 , respectively, without significantly impacting germination (Studer et al., ). Lastly, superheated steam (200 °C, 15 s) was reported to achieve >5 log 10 reductions in L. monocytogenes on almond and pistachio nuts without any accompanying quality changes (Ban & Kang, ).…”

“…Neither group reported upon survivor outgrowth (that is, storage studies), but Studer et al. () were able to recover L. monocytogenes from steam‐treated alfalfa seeds via culture enrichment.…”

“…Steam also has been used to treat L. monocytogenes ‐contaminated seeds and nuts. Exposure of alfalfa and mung bean seeds to steam at 70 °C for 300 s and almonds and pistachios to 200 °C for 30 s yielded 4 to 5 log 10 reductions in pathogen counts (Ban & Kang, ; Studer, Heller, Hummerjohann, & Drissner, ). This approach, because it utilizes a readily diffusible, tissue penetrating, and chemically stable gaseous reagent that leaves no residue, holds promise for use in the sanitization of fresh and fresh‐cut produce (Shynkaryk, Pyatkovskyy, Mohamed, Yousef, & Sastry, ).…”

Transcriptional profile of Salmonella enterica subsp. enterica serovar Weltevreden during alfalfa sprout colonization

“…A possible explanation is increased consumption caused by enhanced recognition by the broader public of sprouts as nutritious food. However, during mass production thereof, favourable conditions are generated during germination for bacteria such as Salmonella spp., especially when hygienic standards are not followed (Studer et al, 2013). In Europe, outbreaks linked to contaminated sprouts were caused by S. enterica subsp.…”