Fresh-cut iceberg lettuce inoculated with Escherichia coli O157:H7 was submitted to chlorine washing
(150 mg/mL) and modified atmosphere packaging on laboratory scale. Populations of E. coli O157:H7
were assessed in fresh-cut lettuce stored at 4, 8, 13 and 16 C using 6e8 replicates in each analysis point
in order to capture experimental variability. The pathogen was able to grow at temperatures 8 C,
although at low temperatures, growth data presented a high variability between replicates. Indeed, at
8 C after 15 days, some replicates did not show growth while other replicates did present an increase. A
growth primary model was fitted to the raw growth data to estimate lag time and maximum growth rate.
The prediction and confidence bands for the fitted growth models were estimated based on Monte-Carlo
method. The estimated maximum growth rates (log cfu/day) corresponded to 0.14 (95% CI: 0.06e0.31),
0.55 (95% CI: 0.17e1.20) and 1.43 (95% CI: 0.82e2.15) for 8, 13 and 16 C, respectively. A square-root
secondary model was satisfactorily derived from the estimated growth rates (R2 > 0.80; Bf ¼ 0.97;
Af ¼ 1.46). Predictive models and data obtained in this study are intended to improve quantitative risk
assessment studies for E. coli O157:H7 in leafy green products.
Fresh-cut iceberg lettuce inoculated with Escherichia coli O157:H7 was submitted to chlorine washing(150 mg/mL) and modified atmosphere packaging on laboratory scale. Populations of E. coli O157:H7were assessed in fresh-cut lettuce stored at 4, 8, 13 and 16 C using 6e8 replicates in each analysis pointin order to capture experimental variability. The pathogen was able to grow at temperatures 8 C,although at low temperatures, growth data presented a high variability between replicates. Indeed, at8 C after 15 days, some replicates did not show growth while other replicates did present an increase. Agrowth primary model was fitted to the raw growth data to estimate lag time and maximum growth rate.The prediction and confidence bands for the fitted growth models were estimated based on Monte-Carlomethod. The estimated maximum growth rates (log cfu/day) corresponded to 0.14 (95% CI: 0.06e0.31),0.55 (95% CI: 0.17e1.20) and 1.43 (95% CI: 0.82e2.15) for 8, 13 and 16 C, respectively. A square-rootsecondary model was satisfactorily derived from the estimated growth rates (R2 > 0.80; Bf ¼ 0.97;Af ¼ 1.46). Predictive models and data obtained in this study are intended to improve quantitative riskassessment studies for E. coli O157:H7 in leafy green products.
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Fresh-cut iceberg lettuce inoculated with Escherichia coli O157:H7 was submitted to chlorine washing
(150 mg/mL) and modified atmosphere packaging on laboratory scale. Populations of E. coli O157:H7
were assessed in fresh-cut lettuce stored at 4, 8, 13 and 16 C using 6e8 replicates in each analysis point
in order to capture experimental variability. The pathogen was able to grow at temperatures 8 C,
although at low temperatures, growth data presented a high variability between replicates. Indeed, at
8 C after 15 days, some replicates did not show growth while other replicates did present an increase. A
growth primary model was fitted to the raw growth data to estimate lag time and maximum growth rate.
The prediction and confidence bands for the fitted growth models were estimated based on Monte-Carlo
method. The estimated maximum growth rates (log cfu/day) corresponded to 0.14 (95% CI: 0.06e0.31),
0.55 (95% CI: 0.17e1.20) and 1.43 (95% CI: 0.82e2.15) for 8, 13 and 16 C, respectively. A square-root
secondary model was satisfactorily derived from the estimated growth rates (R2 > 0.80; Bf ¼ 0.97;
Af ¼ 1.46). Predictive models and data obtained in this study are intended to improve quantitative risk
assessment studies for E. coli O157:H7 in leafy green products.
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