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To address the concern for recovery of injured Listeria monocytogenes on natural and organic processed meats where many conventional antimicrobials cannot be used, a series of compounds with antimicrobial potential for use in these products combined with different post-lethality treatments will be evaluated for the most effective combinations. <P> The primary objective will be to find the treatment with greatest initial lethality that also achieves sustained suppression of growth of injured and uninjured L. monocytogenes when combined with a compound or compounds that has potential application to natural and organic products. <P> Frankfurters and hams will be manufactured using natural product formulations and with antimicrobial treatments including variable nitrite concentrations, cranberry powder, a buffered vinegar (DV-WTI, Inc.), vinegar and lemon juice concentrate (MOstatin LV1X-WTI, Inc.) or a lime/cherry/vinegar blend (VegStable 507-Florida Food Products). Products will be inoculated with 3 log CFU/g of a 5 strain mixture of L. monocytogenes and subjected to one of four post-lethality treatments combined with the antimicrobials listed. The post-lethality treatments will include high pressure processing, lauric arginate, octanoic acid or thermal pasteurization. Packaged products will be stored at 4.5°C, and both injured and uninjured L. monocytogenes counted during storage for at least 90 days, or longer if necessary to observe treatment differences.
Status (As of October 2012)<br/>
At this point in project, investigators have completed trials to evaluate the effectiveness of the thin agar layer (TAL) method at recovering sublethally injured L. monocytogenes. To assess the effectiveness of the TAL method, a 5-strain cocktail of L. monocytogenes was subjected to heat (60°C for varying lengths of time) and high hydrostatic pressure (400 or 600 MPa at 10°C for varying lengths of time) and survival rates were assessed by monitoring growth/recovery on TSAYE, MOX and TAL media. While the data has not yet been statistically analyzed, growth on MOX seems to be lower than on either TSAYE or TAL regardless of type of injury (heat or high hydrostatic pressure) and time of exposure.
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Secondly, preliminary trials to evaluate the effects of nitrite concentration (0, 50 and 100 ppm nitrite from VegStable 504) and high hydrostatic pressure (400 or 600 MPa for 4 min at 10°C) on the growth/recovery of L. monocytogenes in inoculated uncured ham by monitoring growth on MOX and TAL have also been conducted.
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Thirdly, trials to evaluate the effects of high hydrostatic pressure (400 or 600 MPa for 4 min at 10°C), post-lethality interventions (post-packaging thermal treatment, lauric arginate, and octanoic acid), and natural antimicrobials (1% cranberry powder, 1% dried vinegar, and 2.5% MOstatin LV1X) on the growth/recovery of L. monocytogenes in inoculated uncured ham and frankfurter-style cooked sausages (50 ppm nitrite from VegStable 504) by monitoring growth on MOX and TAL have also been conducted.
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Each of the 6 trials described above were evaluated during 98 days of storage at 4°C. Sampling was conducted on days 1, 14, 28, 42, 56, 70, 84 and 98 of each trial. Additionally, for the uncured ham and frankfurter-style cooked sausage trials, we also monitored residual nitrite levels, surface color (both products) and internal color (frankfurter-style cooked sausages only) on un-inoculated product. Data is being analyzed for comparison of results.
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Lastly, additional trials to evaluate the effects of nitrite concentration (0, 50 and 100 ppm nitrite from VegStable 504) and high hydrostatic pressure (600 MPa for 1 min at 10°C) on the growth/recovery of L. monocytogenes in inoculated uncured ham by monitoring growth on MOX and TAL are in progress. Simultaneously, trials to evaluate the effects of high hydrostatic pressure (400 MPa for 4 min at 10°C) and post-lethality interventions (post-packaging thermal treatment, lauric arginate, and octanoic acid) in combination with natural antimicrobials (1% cranberry powder, 1% dried vinegar, and 2.5% MOstatin LV1X) on the growth/recovery of L. monocytogenes in inoculated uncured ham (50 ppm nitrite from VegStable 504) by monitoring growth on MOX and TAL are underway (day 7 of 98). Sampling for this last set of trials is scheduled to take place on days 1, 14, 28, 42, 56, 70, 84 and 98 of each trial.