Laboratory of Food Quality Control and Hygiene, Department of Food Science & Human Nutrition, Agricultural University of Athens, Greece.
Laboratory of Food Quality Control and Hygiene, Department of Food Science & Human Nutrition, Agricultural University of Athens, Greece.
Int J Food Microbiol. 2017 Apr 4;246:50-63. doi: 10.1016/j.ijfoodmicro.2017.01.015. Epub 2017 Jan 27.
Different physicochemical and microbiological characteristics of cheeses may affect Listeria monocytogenes potential to grow, survive, or exhibit an acid adaptive response during storage and digestion. The objectives of the present study were to assess: i) the survival or growth potential of L.monocytogenes on various cheeses during storage, ii) the effect of initial indigenous microbiota on pathogen growth in comparison to expected growth curves retrieved by existing predictive models, and iii) the impact of habituation on/in cheeses surfaces on the subsequent acid resistance during simulated gastric digestion. Portions of cream (Cottage and Mascarpone), soft (Anthotyros, Camembert, Mastelo®, Manouri, Mozzarella, Ricotta), and semi-hard (Edam, Halloumi, Gouda) cheeses were inoculated with ca. 100CFU/g or cm of L.monocytogenes and stored under vacuum or aerobic conditions at 7°C (n=4). The impact of varying (initial) levels of starter culture or indigenous spoilage microbiota on pathogen growth was evaluated by purchasing cheese packages on different dates in relation to production and expiration date (subsequently reflecting to different batches) mimicking a potential situation of cheese contamination with L.monocytogenes during retail display. Values of pH and a were also monitored and used to simulate growth of L. monocytogenes by existing models and compare it with the observed data of the study. Survival in simulated gastric fluid (SGF) (pH1.5; HCl; max. 120min) was assessed at three time points during storage. Mascarpone, Ricotta, Mozzarella, Camembert, and Halloumi supported L.monocytogenes growth by 0.5-0.8logCFU/g or cmper day, since low initial levels of total viable counts (TVC) (1.8-3.8logCFU/g or cm) and high pH/a values (ca. 6.23-6.64/0.965-0.993) were recorded. On Cottage, Anthotyros, Manouri, Mastelo®, Edam, and Gouda, the pathogen survived at populations similar or lower than the inoculation level due to the high reported competition and/or low pH/a during storage. L. monocytogenes growth was significantly suppressed (p<0.05) on samples purchased close to expiration date (bearing high TVC), compared to those close to production date, regardless of cheese. Cheeses which supported growth of L.monocytogenes enabled higher survival in gastric acidity along their shelf-life compared to cheeses which did not support growth. However, even in the latter cheeses (i.e., Cottage, Mastelo®, Gouda), total elimination of a persisting low initial contamination was not always achieved. Such findings may provide useful evidence for assessing the risk posed by various cheeses types in relation to their compliance with food safety regulations.
不同的理化特性和微生物特性的奶酪可能会影响李斯特菌生长、存活或表现出适应酸性的反应能力在储存和消化过程中。本研究的目的是评估：i）不同奶酪中李斯特菌的生存或生长潜力在储存过程中，ii）初始土著微生物群对病原体生长的影响与现有预测模型中检索到的预期生长曲线相比，以及 iii）在模拟胃消化过程中，奶酪表面的适应/驯化对随后的酸抗性的影响。奶油（奶酪和乳清干酪）、软质（Anthotyros、卡门贝尔、Mastelo®、马努里、马苏里拉、乳清干酪）和半硬质（埃丹、哈罗米、高达）奶酪的部分部分被接种约 100CFU/g 或 cm 的李斯特菌，并在 7°C 下真空或有氧条件下储存（n=4）。通过购买不同日期的奶酪包装，模拟零售展示过程中李斯特菌污染的潜在情况，评估不同（初始）水平的发酵剂或土著腐败微生物群对病原体生长的影响，从而反映不同批次。还监测了 pH 和 a 值，并用于通过现有模型模拟李斯特菌的生长，并将其与研究中的观察数据进行比较。在储存过程中的三个时间点评估了在模拟胃液（SGF）（pH1.5；HCl；最大 120min）中的存活情况。乳清干酪、乳清干酪、马苏里拉、卡门贝尔和哈罗米通过 0.5-0.8logCFU/g 或 cmper 天支持李斯特菌的生长，因为初始总活菌计数（TVC）水平较低（1.8-3.8logCFU/g 或 cm）和较高的 pH/a 值（约 6.23-6.64/0.965-0.993）。在奶酪、Anthotyros、马努里、Mastelo®、埃丹和高达上，由于储存过程中报告的竞争较高和/或 pH/a 较低，病原体的存活水平与接种水平相似或更低。与生产日期较近的样本相比，临近保质期的样本（具有较高的 TVC）中李斯特菌的生长受到显著抑制（p<0.05），无论奶酪如何。与不支持生长的奶酪相比，在货架期内支持李斯特菌生长的奶酪在胃酸度下的存活能力更高。然而，即使在后者的奶酪（即奶酪、乳清干酪、高达）中，也并非总是能够完全消除初始低水平的持续污染。这些发现可能为评估各种奶酪类型与食品安全法规的符合性相关的风险提供有用的证据。
