Istituto Zooprofilattico Sperimentale dell' Abruzzo e del Molise "G. Caporale", National Reference Laboratory for Listeria monocytogenes, via Campo Boario, 64100 Teramo, Italy.
Istituto Zooprofilattico Sperimentale dell' Abruzzo e del Molise "G. Caporale", National Reference Laboratory for Listeria monocytogenes, via Campo Boario, 64100 Teramo, Italy.
Int J Food Microbiol. 2020 Sep 16;329:108690. doi: 10.1016/j.ijfoodmicro.2020.108690. Epub 2020 May 28.
Pecorino di Farindola is a typical cheese produced in the area surrounding the village of Farindola, located in the Abruzzo Region (central Italy), unique among Italian cheese because only raw ewe milk and pig rennet are used for its production. In the literature it is well documented that raw milk is able to support the growth of pathogenic microorganisms such as Listeria monocytogenes. Predictive microbiology can be useful in order to predict growth-death kinetics of pathogenic bacteria, on the basis of known environmental conditions. Aim of this study was to compare predictions obtained from a model, originally designed to predict the kinetics of L. monocytogenes in the dynamic growth-death environment of drying fresh sausage, with the results of challenge tests performed during the ripening of Pecorino di Farindola produced from artificially contaminated raw ewe milk. A challenge test was carried out using ewe raw milk inoculated with L. monocytogenes, in order to produce Pecorino di Farindola cheese stored at 18 °C for 149 days of ripening. During the ripening period, pH and a values decreased in all samples analysed; lactic acid bacteria become the prevailing microbial population, while for L. monocytogenes a period of stability (neither growth nor death) followed the initial situation. The growth inhibition and the following inactivation may mostly be due to competition with the autochthonous microbiota and to the reduction of water activity. Mathematical modelling was used in order to predict microbial kinetics in the dynamic ripening environment, joining growth and death patterns in a continuous way, and including the highly uncertain growth/no growth range separating the two regions. The effect of lactic acid bacteria on the growth of pathogens was also included. Predicted microbial kinetics were satisfactory, as confirmed by the absence of statistically significant difference between observed and predicted values (p > 0.05). The present study proved, via challenge tests, that a dynamic growth/death model, previously used for a meat product, can be fruitfully used in cheese characterized by active competitive microbiota and progressive drying during ripening.
佩科里诺·迪·法林多拉奶酪是一种产自意大利中部阿布鲁佐地区法林多拉村周边地区的特色奶酪，因其只使用生羊奶和猪凝乳酶生产而在意大利奶酪中独具特色。文献中记载，生奶能够为李斯特菌等致病菌的生长提供支持。基于已知的环境条件，预测微生物学可用于预测致病菌的生长-死亡动力学。本研究旨在比较基于动态生长-死亡环境中预测鲜香肠干燥过程中李斯特菌动力学的模型预测结果，与在人工污染生羊奶制成的佩科里诺·迪·法林多拉奶酪成熟过程中进行的挑战试验结果。使用接种了李斯特菌的生羊奶进行了挑战试验，以生产在 18°C 下成熟 149 天的佩科里诺·迪·法林多拉奶酪。在成熟期间，所有分析样本的 pH 值和 a 值均降低；乳酸菌成为主要的微生物种群，而李斯特菌则在初始状态后经历了一个稳定期（既不生长也不死亡）。生长抑制和随后的失活可能主要归因于与土著微生物群的竞争以及水活度的降低。数学模型用于预测动态成熟环境中的微生物动力学，以连续的方式结合生长和死亡模式，并包括将两个区域分开的高度不确定的生长/不生长范围。还包括了乳酸菌对病原体生长的影响。预测的微生物动力学结果令人满意，因为观察值和预测值之间不存在统计学上的显著差异（p＞0.05）。通过挑战试验证明，先前用于肉类产品的动态生长/死亡模型可以成功用于在成熟过程中具有活跃竞争微生物群和逐渐干燥的奶酪。
