Identification of the gamma irradiation dose applied to ground beef that reduces Shiga toxin producing Escherichia coli but has no impact on consumer acceptance.

The aims of the present study were: a) to estimate the minimal dose of gamma irradiation required to reduce 5 log CFU/g of native O157 and non-O157 Shiga toxin-producing Escherichia coli population in ground beef samples inoculated with high inoculum; b) to assess its effectiveness in samples with low inoculum and 3) to evaluate consumer acceptance. Based on the results, 1 kGy was estimated as the minimal dose of gamma irradiation required to reduce 5 log CFU/g of STEC in ground beef. However, when samples with low inoculum level were subjected to 1 kGy, 3.9% of the samples were positive for stx and eae genes after an enrichment step. Consumer acceptance analysis was carried out with samples subjected to 2.5 kGy and no significant differences were found between irradiated and control samples. Therefore, 2.5 kGy was identified as the gama irradiation dose that reduces STEC but has no impact on consumer acceptance of ground beef.

Combination of organic acids and low-dose gamma irradiation as antimicrobial treatment to inactivate Shiga toxin-producing Escherichia coli inoculated in beef trimmings: Lack of benefits in relation to single treatments.

The aim of this study was to assess the efficacy of lactic acid (LA), caprylic acid (CA), high- (HDI) and low- (LDI) dose gamma irradiation and LDI combined with LA or CA on the inactivation of a pool of Shiga toxin-producing Escherichia coli (STEC) strains inoculated on beef trimmings. The three most efficacious treatments were selected to study their effect on meat quality parameters and sensory attributes. The inoculum included five native STEC serogroups (O26, O103, O111, O145 and O157). The treatments applied were 0.5% LA, 0.04% CA, 0.5 kGy LDI, 2 kGy HDI, LDI+LA and LDI+CA. Beef trimmings were divided into two groups; one was inoculated with high (7 log CFU/g) and the other with low (1 log CFU/g) level of inoculum. Efficacy was assessed by estimating log reduction and reduction of stx- and eae-positive samples after enrichment, respectively. Results showed that treatments with organic acids alone were not effective in reducing STEC populations. For high inoculum samples, the most effective treatment was HDI followed by LDI+LA and LDI alone or combined with CA. For low inoculum samples, the most effective treatment was HDI followed by LDI alone or combined with organic acids. Concerning meat quality parameters and sensory attributes, irradiation treatments (LDI and HDI) caused minimal changes, while LDI+LA modified them significantly compared with the control. Therefore, based on our results, no benefits were observed after combining organic acids with gamma irradiation.

Inactivation of Shiga toxin-producing Escherichia coli in lean ground beef by gamma irradiation.

In this study the radiation resistance of 40 Shiga Toxin-Producing Escherichia coli (STEC) isolates which contained various combinations of the shiga toxin 1 (stx1), shiga toxin 2 (stx2), intimin (eae), and hemolysin (ehx) genes were determined. The STEC were suspended in lean ground beef and irradiated at 4 °C. D10 values, the radiation dose needed to reduce 1 log (90%) of a microorganism, ranged from 0.16 to 0.48 kGy, with a mean of 0.31 kGy for the 40 isolates. Isolates associated with illness outbreaks had a mean D10 of 0.27 kGy, while non-outbreak isolates had a mean D10 of 0.36 kGy (p < 0.05). The presence or absence of stx1, stx2, or both stx1 and 2 had no affect on D10 (p > 0.05). The presence (0.30 kGy) or absence (0.35 kGy) of ehx had no affect on D10 (p > 0.05). However, the mean D10 of isolates lacking eae (0.37 kGy) were significantly higher than those containing eae (0.27 kGy) (p < 0.05). There was no difference in D10 for isolates lacking eae regardless of whether or not they were associated with a foodborne illness outbreak (p > 0.05). It may be possible to use some of the STEC isolates which lacked eae, ehx, or both (D10 > 0.30) as avirulent surrogates in food irradiation research. The data presented in this study provides risk assessors data for metagenomic analysis as well as food and radiation processors with valuable information to control of STEC in meat.

Effect of gamma radiation on the reduction of Salmonella strains, Listeria monocytogenes, and Shiga toxin-producing Escherichia coli and sensory evaluation of minimally processed spinach (Tetragonia expansa).

This study evaluated the effects of irradiation on the reduction of Shiga toxin-producing Escherichia coli (STEC), Salmonella strains, and Listeria monocytogenes, as well as on the sensory characteristics of minimally processed spinach. Spinach samples were inoculated with a cocktail of three strains each of STEC, Salmonella strains, and L. monocytogenes, separately, and were exposed to gamma radiation doses of 0, 0.2, 0.4, 0.6, 0.8, and 1.0 kGy. Samples that were exposed to 0.0, 1.0, and 1.5 kGy and kept under refrigeration (4°C) for 12 days were submitted to sensory analysis. D10 -values ranged from 0.19 to 0.20 kGy for Salmonella and from 0.20 to 0.21 for L. monocytogenes; for STEC, the value was 0.17 kGy. Spinach showed good acceptability, even after exposure to 1.5 kGy. Because gamma radiation reduced the selected pathogens without causing significant changes in the quality of spinach leaves, it may be a useful method to improve safety in the fresh produce industry.

Use of low dose e-beam irradiation to reduce E. coli O157:H7, non-O157 (VTEC) E. coli and Salmonella viability on meat surfaces.

This study determined the extent that irradiation of fresh beef surfaces with an absorbed dose of 1 kGy electron (e-) beam irradiation might reduce the viability of mixtures of O157 and non-O157 verotoxigenic Escherichia coli (VTEC) and Salmonella. These were grouped together based on similar resistances to irradiation and inoculated on beef surfaces (outside flat and inside round, top and bottom muscle cuts), and then e-beam irradiated. Salmonella serovars were most resistant to 1 kGy treatment, showing a reduction of ≤1.9 log CFU/g. This treatment reduced the viability of two groups of non-O157 E. coli mixtures by ≤4.5 and ≤3.9 log CFU/g. Log reductions of ≤4.0 log CFU/g were observed for E. coli O157:H7 cocktails. Since under normal processing conditions the levels of these pathogens on beef carcasses would be lower than the lethality caused by the treatment used, irradiation at 1 kGy would be expected to eliminate the hazard represented by VTEC E. coli.

Use of low-dose irradiation to evaluate the radiation sensitivity of Escherichia coli O157:H7, non-O157 verotoxigenic Escherichia coli, and Salmonella in phosphate-buffered saline.

Verotoxigenic Escherichia coli (VTEC) and Salmonella are major foodborne pathogens, but very little information is available on the radiation resistance of a sufficiently diverse group of these pathogens. The objective of this study was to evaluate the sensitivity of E. coli O157:H7, non-O157 VTEC, and Salmonella to a low-dose ionizing radiation treatment. Test organisms were 6 serovars of Salmonella, 5 strains of E. coli O157:H7, and 27 strains of non-O157 VTEC (representing 19 serotypes). Decimal reduction doses (D-values) for individual strains were determined in phosphate-buffered saline using an X-ray source. The viability of the bacterial cells declined with an increase in absorbed dose from 0 to 0.3 kGy. The more resistant test strains were screened at 0.5 and 0.7 kGy. All six Salmonella strains survived at 0.5 and 0.7 kGy; however, only 11 VTEC survived at 0.7 kGy. After the 0.3-kGy treatment, both E. coli O157:H7 and non-O157 VTEC had D-values with similar means and ranges (0.028 to 0.123 and 0.037 to 0.127 kGy, respectively), with no significant differences (P > 0.05). Salmonella strains had a slightly higher range of D-values (0.061 to 0.147 kGy) and a mean D-value that was significantly higher (P > 0.05) than that of both the E. coli O157:H7 and non-O157 VTEC groups.