Shelf‐life studies in ready‐to‐eat (RTE) modified atmosphere packaged (MAP) precut iceberg lettuce (minimally processed) were carried out in order to evaluate the natural microflora of the product and survival or multiplication of Listeria monocytogenes (L. monocytogenes), taking into consideration the impact of the production steps resulting in a reduction of the shelf life of the fresh‐cut produce, due to the accelerated enzymatic activity, moisture loss, and microbial proliferation. The research first aimed to evaluate the characteristics of the natural microflora of the product, and then, L. monocytogenes dynamics were studied via challenge tests. L. monocytogenes concentration was studied at 8 and 12°C storage temperature for 10 days, 6 days longer than their shelf life. The number of L. monocytogenes in samples stored both at 8°C and 12°C increased gradually, more evidently in samples stored at 12°C. L. monocytogenes dynamics were studied to define maximum growth rate (μmax) at 8°C (0.0104 log₁₀CFU/g/h) and 12°C (0.0183 log₁₀CFU/g/h). Data obtained from the study were used to develop and validate a specific predictive model able to predict the behavior of L. monocytogenes in RTE MAP iceberg lettuce. According to the model, an increase in storage temperature of 6°C (e.g., from 8 to 14°C) would lead to an increase in L. monocytogenes concentration of more than 6 log₁₀CFU/g at the 10th day of the challenge test (12th days of shelf life). Storage at 4°C allowed to increase L. monocytogenes enumeration from 3.30 log₁₀CFU/g at D0 to 3.60 log₁₀CFU/g at D10. The model could be applied to microorganisms other than L. monocytogenes, modifying the coefficients of the polynomial equation on which it is based.

中文翻译：

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即食卷心生菜中单增李斯特菌的挑战试验研究。

对即食 (RTE) 气调包装 (MAP) 预切卷心生菜（最低限度加工）进行了保质期研究，以评估产品的天然微生物群落以及单核细胞增生李斯特菌 (L. monocytogenes) 的存活或增殖），考虑到生产步骤的影响，由于酶活性加速、水分流失和微生物增殖，导致鲜切产品保质期缩短。该研究首先旨在评估产品的天然微生物群的特征，然后通过激发试验研究单核细胞增生李斯特氏菌的动态。在 8 和 12°C 储存温度下研究单核细胞增生李斯特菌浓度 10 天，比保质期长 6 天。8℃和12℃保存的样品中单核细胞增生李斯特菌的数量逐渐增加，12℃保存的样品中更明显。研究了单增李斯特氏菌动力学，以确定 8°C (0.0104 log ₁₀ CFU/g/h) 和 12°C (0.0183 log ₁₀ CFU/g/h) 时的最大生长速率 (μmax)。从研究中获得的数据用于开发和验证特定的预测模型，该模型能够预测RTE MAP 卷心生菜中单核细胞增生李斯特菌的行为。根据该模型，储存温度增加 6°C（例如，从 8°C 至 14°C）将导致攻击第 10 天单核细胞增生利斯特氏菌浓度增加超过6 log 10 _CFU /g测试（保质期第 12 天）。4°C 储存可使单核细胞增生李斯特氏菌计数从 D0 时的 3.30 log ₁₀ CFU/g 增加到 D10 时的 3.60 log ₁₀ CFU/g。该模型可以应用于单核细胞增生李斯特氏菌以外的微生物，修改其所基于的多项式方程的系数。