In this study, the effectiveness of prolonged dry-heat treatment (50 degrees C) alone or in combination with chemical treatments (1% oxalic acid, 0.03% phytic acid, 50% ethanol, electrolyzed acidic water, and electrolyzed alkaline water) in eliminating Escherichia coli O157:H7 on laboratory-inoculated alfalfa, radish, broccoli, and mung bean seeds was compared with that of dry-heat treatment in combination with irradiation treatment. Dry-heat treatment for 17 or 24 h alone could reduce E. coli O157:H7 numbers to below detectable levels in radish, broccoli, and alfalfa seeds, but was unable to reduce the pathogen numbers to below the detectable level in mung bean seeds. In addition, dry-heat treatment for 17 h plus sanitizer treatments were effective in greatly reducing pathogen populations on radish, broccoli, and alfalfa seeds, without compromising the quality of the sprouts, but these treatments did not eliminate the pathogen from radish and alfalfa seeds. Seventeen hours of dry heat followed by a 1.0-kGy dose of irradiation completely eliminated E. coli O157:H7 from radish and mung bean seeds, whereas only a minimum radiation dose of 0.25 kGy was required to completely eliminate the pathogen from broccoli and alfalfa seeds. Dry heat in combination with radiation doses of up to 1.0 kGy did not negatively impact the seed germination rate or length of alfalfa, broccoli, and radish seeds or the length of alfalfa, broccoli, and radish sprouts, but did decrease the length of mung bean sprouts.

The majority of the seed sprout-related outbreaks have been associated with Escherichia coli O157:H7 and Salmonella. Therefore, an effective method for inactivating these organisms on the seeds before sprouting is needed. The current pasteurization method for mung beans in Japan (hot water treatment at 85 degrees C for 10 s) was more effective for disinfecting inoculated E. coli O157:H7, Salmonella, and nonpathogenic E. coli on mung bean seeds than was the calcium hypochlorite treatment (20,000 ppm for 20 min) recommended by the U.S. Food and Drug Administration. Hot water treatment at 85 degrees C for 40 s followed by dipping in cold water for 30 s and soaking in chlorine water (2,000 ppm) for 2 h reduced the pathogens to undetectable levels, and no viable pathogens were found in a 25-g enrichment culture and during the sprouting process. Practical tests using a working pasteurization machine with nonpathogenic E. coli as a surrogate produced similar results. The harvest yield of the treated seed was within the acceptable range. These treatments could be a viable alternative to the presently recommended 20,000-ppm chlorine treatment for mung bean seeds.

The majority of seed sprout-related outbreaks has been associated with Escherichia coli O157:H7 and Salmonella. Therefore, it is necessary to find an effective method to inactivate possible pathogenic bacterial populations on the seeds prior to sprouting. In general, sanitizing is more effective in reducing contamination on seeds than on sprouts. A successful seed decontamination treatment must inactivate microbial pathogens while preserving seed viability, germination, and vigor. Seeds vary in sensitivity to antimicrobial agents and other treatments, which determine how well they germinate and grow after treatment. In addition, a treatment that is effective for one type of seed may not be applicable to all types of seeds. Seeds vary in surface features, which may influence how well an antimicrobial agent can access and inactivate pathogens on or in the seed. The use of a number of physical, non-thermal processing technologies, alone or in combination with antimicrobial chemicals, could be useful for seed decontamination. Until now, hot water treatment at 85°C for 40 seconds followed by cooling in cold water for 30 sec and soaking in chlorine water was found effective in inactivating pathogens while preserving seed viability, germination, and vigor. Therefore, hot water treatment could be an effective seed decontamination method for mung bean seeds intended for sprout production.

The majority of seed sprout-related outbreaks have been associated with Escherichia coli O157:H7 and Salmonella. Therefore, we aimed to find an effective method to inactivate these organisms on seeds before sprouting. Treatment with 8.7% (v/v) acetic acid at 55°C for 2-3 h reduced the population of E. coli O157:H7 and Salmonella inoculated on alfalfa (Medicago sativa L.) and radish seeds (Raphanus sativus L.) by more than 5.0 log CFU/g, and a longer treatment time completely eliminated the E. coli O157:H7 population. The E. coli O157:H7 populations were reduced to an undetectable level with a gaseous acetic acid treatment for 48 h. After enrichment, no E. coli O157:H7 were found in the alfalfa and radish seeds (25 g). However, these treatments were unable to eliminate Salmonella in both seed types. No significant difference between the germination rates of treated alfalfa seeds and control seeds was found, and germination rates greater than 95% were obtained for the radish seeds. Although chlorine washing is commonly used for seed decontamination, chlorine washing at 200 and 20,000 ppm resulted in a reduction of pathogens by less than or equal to 3 log CFU/g. Therefore, these results suggested that gaseous acetic acid is more effective than chlorine washing in controlling pathogenic bacteria on sprout seeds.

Several pasteurization procedures for alfalfa (Medicago sativa) seeds were investigated to completely disinfect inoculated Escherichia coli (Migula) Castellani and Chalmers ATCC(25922). Hot-water treatments (85˚C for 9 s) were equally or more effective than 20,000 ppm calcium hypochlorite treatments, yielding a reduction of 2 log 10 CFU/g. A greater reduction (4 log) was obtained by soaking the seeds prior to the heat treatments and, in some cases, no inoculated bacteria were detected after enrichment of the seeds in peptone. No survival of inoculated bacteria was detected from the seeds or the sprouts after deeply presoaking (15˚C for 60 min) and treating the seeds with heat, but the germination decreased to 73% along with the yield which fell to 78.4% that of the control. We describe the hot-water treatment as an alternative method to hypochlorite treatments for disinfecting pathogenic bacteria in seeds for alfalfa sprout production.