Uyttendaele M, Rajkovic A, Benos G, François K, Devlieghere F, Debevere J
Laboratory of Food Microbiology and Food Preservation, Faculty of Agricultural and Applied Biological Sciences, Gent University, Coupure Links 653, B-9000, Ghent, Belgium.
Int J Food Microbiol. 2004 Jan 15;90(2):219-36. doi: 10.1016/s0168-1605(03)00305-2.
Challenge testing of ready-to-eat (RTE) foods with Listeria monocytogenes is recommended to assess the potential for growth. The present study was undertaken to evaluate a protocol for challenge testing applied to RTE cooked meat products. In order to choose L. monocytogenes strains with a representative behaviour, initially, the variability of the response of multiple L. monocytogenes strains of human and food origin to different stress and growth conditions was established. The strains were not inhibited in their growth at moderate acid pH (5.25) and the four strains tested in particular showed a similar acid-adaptive response. Growth of the various strains under four different combined stress conditions indicated that no L. monocytogenes strain had consistently significant longer or shorter lag phase or higher or lower maximum specific growth rates. The effect of choice of strain and history (pre-incubation temperature 7 or 30 degrees C) on growth of L. monocytogenes under optimum conditions (Brain Heart Infusion, BHI) and modified BHI simulating conditions of cooked ham and paté was studied. In general, all four L. monocytogenes strains behaved similarly. In BHI, no difference in lag phase was observed for the cold-adapted and standard inoculum, whereas in BHI adjusted to ham and pâté conditions, a ca. 40-h reduction of the lag phase was noted for the cold-adapted inoculum. Subsequently, microbial challenge testing of L. monocytogenes in modified atmosphere packaged sliced cooked ham and paté was performed. A mixed inoculum of four L. monocytogenes strains and an inoculum level of ca. 1-10 cfu/g was used. On vacuum packed sliced cooked ham, the concentration of 100 cfu/g, the safety limit considered as low risk for causing listeriosis, was exceeded after 5 days whereas ca. 10(5) cfu/g were obtained after 14 days when also LAB spoilers reached unacceptable numbers (ca. 10(7) cfu/g) whether standard or cold-adapted inoculum was used. The concentration of sodium lactate determined the opportunities for growth of L. monocytogenes in pâté. If growth of L. monocytogenes in pâté was noticed, the threshold of 100 cfu/ml was crossed earlier for the cold-adapted inoculum compared to the standard inoculum.
建议对即食（RTE）食品进行单核细胞增生李斯特菌挑战试验，以评估其生长潜力。本研究旨在评估一种应用于即食熟肉制品的挑战试验方案。为了选择具有代表性行为的单核细胞增生李斯特菌菌株，首先确定了多株来源于人和食品的单核细胞增生李斯特菌菌株对不同应激和生长条件的反应变异性。这些菌株在中等酸性pH值（5.25）下生长未受抑制，特别是所测试的四株菌株表现出相似的酸适应性反应。在四种不同的复合应激条件下，各菌株的生长情况表明，没有一株单核细胞增生李斯特菌菌株的延迟期始终显著更长或更短，最大比生长速率也没有始终更高或更低。研究了菌株选择和培养历史（预培养温度7或30摄氏度）对单核细胞增生李斯特菌在最佳条件（脑心浸液，BHI）以及模拟熟火腿和肉酱条件的改良BHI中的生长的影响。总体而言，所有四株单核细胞增生李斯特菌菌株的表现相似。在BHI中，冷适应接种物和标准接种物的延迟期没有差异，而在调整为火腿和肉酱条件的BHI中，冷适应接种物的延迟期减少了约40小时。随后，对气调包装切片熟火腿和肉酱中的单核细胞增生李斯特菌进行了微生物挑战试验。使用了四株单核细胞增生李斯特菌菌株的混合接种物，接种水平约为1-10 cfu/g。在真空包装切片熟火腿上，100 cfu/g的浓度在5天后超过了被视为引起李斯特菌病低风险的安全限值，而在14天后达到约10⁵ cfu/g，此时无论是使用标准接种物还是冷适应接种物，乳酸菌腐败菌数量也达到了不可接受的水平（约10⁷ cfu/g）。乳酸钠的浓度决定了肉酱中单核细胞增生李斯特菌的生长机会。如果注意到肉酱中单核细胞增生李斯特菌的生长，与标准接种物相比，冷适应接种物更早达到每毫升100 cfu的阈值。
