Combined Effect of Low-Dose Irradiation and Acidified Sodium Chlorite Washing onEscherichia coliO157:H7 Inoculated on Mung Bean Seeds

Abstract

The effect of low-dose irradiation (0.75 and 1.5 kGy) in combination with acidified sodium chlorite (ASC) on the reduction of Escherichia coli O157:H7 on mung bean seeds was examined. Washing with ASC (0.2, 0.5, 0.8, and 1.2 g/L sodium chlorite and 1.0 g/L citric acid) for 2 h reduced the E. coli O157:H7 population from 5.2 to 2.3-3.3 log CFU/g, depending on the concentrations of sodium chlorite. Gamma ray irradiation at 0.75 and 1.5 kGy resulted in reductions of about 1.8 and 2.8 log CFU/g, respectively. Therefore, a single treatment with ASC washing or gamma ray irradiation at 0.75 or 1.5 kGy could not achieve the complete elimination of E. coli O157:H7 on mung bean seeds. Conversely, low-dose irradiation (0.75 and 1.5 kGy) followed by washing with ASC (0.5-1.2 g/L) reduced the population of E. coli O157:H7 to below the detection limit (<1 log CFU/g). However, E. coli O157:H7 was detected in most samples in the enrichment and germination studies. When the treatment order was reversed (ASC washing followed by low-dose irradiation), the E. coli O157:H7 population was also observed to be below the detection limit. Under this treatment, fewer samples (16.7%) were shown to be positive in the enrichment and germination studies, and complete elimination was not achieved. The germination rates of mung bean seeds were not affected by ASC washing and gamma irradiation; however, the yield and length of sprouts were decreased by gamma irradiation.

Microbial Contamination in Sprouts: How Effective Is Seed Disinfection Treatment?

“…Although the maximal dose for seed treatment approved by the FDA is 8 kGy (U.S. Food and Drug Administration Memorandum ), the majority of studies targeted 2 kGy or below as a generally acceptable practice for the treatments of seeds destined for sprouting with desirable germination and quality. Since there are relatively few studies available, we combined studies conducted at 2.0 kGy with those conducted at 1.5 kGy to summarize treatment efficacy for this review (Rajkowski and Thayer ; Schoeller and others ; Thayer and others ; Bari and others ; Saroj and others ; Nei and others ). Irradiation at this dose range can consistently produce an average of 3.18 log CFU/g reduction in microbial contamination (Figure ), and it is almost equally effective in seeds and final sprout products (data not shown); however, its impact on length, yield, and appearance of sprouts (Rajkowski and others ) and potential nutrient loss (that is, vitamin C, Bari and others ) are issues that currently prevent this method from becoming widely acceptable as a disinfection treatment.…”

Overview of Recent Events in the Microbiological Safety of Sprouts and New Intervention Technologies

“…Combination of low‐dose irradiation (0.75 and 1.5 kGy) with acidified sodium chlorite (ASC) was more effective than either treatment alone in reducing E. coli O157:H7 to below the detection limit (<1 log CFU/g) on mung bean seeds. However, E. coli O157:H7 was detected in most samples in the enrichment and after germination, and the yield and sprout length were decreased by gamma‐irradiation (Nei and others ). Saroj and others () also observed the same phenomenon that the survived S .…”

Current Intervention Strategies for the Microbial Safety of Sprouts

“…The 3% oxalic acid treatment on radish seeds was equally effective for reducing E. coli 0157:H7 by > 5 log CFU/g but had detrimental effects on germination (61%) (14). Peroxyacetic acid, an organic peroxide formed by acetic acid and hydrogen peroxide, has minimal effects (~l-lo g reduction) on E. coli 0157:H7 and Salmonella on alfalfa and mung bean seeds (23,96,120,133). However, the use of acetic acid as a gas has greater antimicrobial effects.…”

“…These authors therefore recommended these sequential treatments for future studies on C102 for seed treatment before sprout production. ASC (commercially known as Germin-8-or) alone has not achieved a >5-log reduction of E. coli 0157:H7 or Salmonella on alfalfa and mung bean seeds (96,120). Treatment with 800 ppm of ASC for 45 min reduced Salmonella on alfalfa seeds by 3.9 log units (96), and 1,200 ppm of ASC for 2 h reduced E. coli 0157:H7 on mung bean seeds by 2.7 log units (120).…”