Survival of Listeria innocua in Minas Traditional Serro cheese during ripening

Cheese produced with raw milk can be a risk to consumer health. It is known that lactic acid bacteria present in raw milk and in natural starters can produce antimicrobial compounds against some foodborne bacteria. This work aimed to evaluate the survival of Listeria innocua in Minas Traditional Serro cheese during cheese ripening. The cheeses were inoculated with 10¹, 10² or 10³ CFU mL⁻¹ of the bacterium and were analyzed for 60 days of ripening at 30 °C. It was observed that the time and the dose of bacteria inoculated affected (p < 0.05) the survival of L. innocua. Even when the lowest dose was inoculated, at the end of the 60 days, approximately 10² CFU mL⁻¹ of L. innocua was detected in the cheese. The lactic acid bacteria present in the milk and in the natural starter were not sufficient to guarantee the absence of L. innocua in Minas Traditional Serro cheese even after 60 days of storage, as is required by Brazilian legislation.     

The fate of Listeria monocytogenes during the manufacture of Camembert-type cheese: A comparison between raw milk and milk treated with high hydrostatic pressure

Camembert-type cheese was produced from: raw bovine milk; raw milk inoculated with 2 or 4 log CFU/ml Listeria monocytogenes; raw milk inoculated with L. monocytogenes and subsequently pressure-treated at 500 MPa for 10 min at 20 °C; or uninoculated raw milk pressure-treated under these conditions. Cheeses produced from both pressure-treated milk and untreated milk had the typical composition, appearance and aroma of Camembert. Curd and cheese made from inoculated, untreated milk contained large numbers of L. monocytogenes throughout production. An initial inoculum of 1.95 log CFU/ml in milk increased to 4.52 log CFU/g in the curd and remained at a high level during ripening, with 3.85 log CFU/g in the final cheese. Pressure treatment inactivated L. monocytogenes in the raw milk at both inoculum levels and the pathogen was not detected in any of the final cheeses produced from pressure-treated milk. Therefore high pressure may be useful to inactivate L. monocytogenes in raw milk that is to be used for the production of soft, mould-ripened cheese.

Industrial relevance

This paper demonstrates the potential of high pressure (HP) for treatment of raw milk to be used in the manufacture of soft cheeses. HP treatment significantly reduced the level of Listeria monocytogenes in the raw milk and so allowed the production of safer non-thermally processed camembert-like soft cheese.     

Evaluation of Changes in Listeria monocytogenes Populations on Frankfurters at Different Stages from Manufacturing to Consumption

ABSTRACT: This study evaluated the fate of inoculated Listeria monocytogenes on frankfurters stored under conditions simulating those that may be encountered between manufacturing and consumption. Frankfurters with or without 1.5% potassium lactate and 0.1% sodium diacetate (PL/SD) were inoculated (1.8 ± 0.1 log CFU/cm²) with a 10‐strain composite of L. monocytogenes, vacuum‐packaged, and stored under conditions simulating predistribution storage (24 h, 4 °C), temperature abuse during transportation (7 h, 7 °C followed by 7 h, 12 °C), and storage before purchase (60 d, 4 °C; SBP). At 0, 20, 40, and 60 d of SBP, samples were exposed to conditions simulating delivery from stores to homes or food establishments (3 h, 23 °C), and then opened or held vacuum‐packaged at 4 or 7 °C for 14 d (SHF). Pathogen counts remained relatively constant on frankfurters with PL/SD regardless of product age and storage conditions; however, they increased on product without antimicrobials. In vacuum‐packaged samples, during SHF at 4 °C, the pathogen grew faster (P < 0.05) on older product (20 d of SBP) compared to product that was fresh (0 d of SBP); a similar trend was observed in opened packages. At 7 °C, the fastest growth (0.35 ± 0.02 log CFU/cm²/d) was observed on fresh product in opened packages; in vacuum‐packages, growth rates on fresh and aged products were similar. By day 40 of SBP the pathogen reached high numbers and increased slowly or remained unchanged during SHF. This information may be valuable in L. monocytogenes risk assessments and in development of guidelines for storage of frankfurters between package opening and product consumption.     

Control of Listeria monocytogenes in ready-to-eat meats containing sodium levulinate, sodium lactate, or a combination of sodium lactate and sodium diacetate

ABSTRACT:  This study investigated the use of sodium levulinate to prevent outgrowth of Listeria monocytogenes in refrigerated ready-to-eat (RTE) meat products. Turkey breast roll and bologna were formulated to contain 1%, 2%, or 3% (w/w) sodium levulinate, 2% sodium lactate, a 2% combination of sodium lactate and sodium diacetate (1.875% sodium lactate and 0.125% sodium diacetate), or no antimicrobial (control). Samples of the RTE products were sliced, inoculated with 10² to 10³ CFU/cm² of a 5-strain cocktail of L. monocytogenes , vacuum packaged, and stored at refrigeration temperature for 0 to 12 wk. Counts reached 10⁸ CFU/cm² on control turkey roll product after 8 wk, and over 10⁷ CFU/cm² on control bologna after 12 wk. Addition of 2% or more sodium levulinate to turkey roll and 1% or more sodium levulinate to bologna completely prevented growth of L. monocytogenes during 12 wk of refrigerated storage. A consumer taste panel with pathogen-free samples found no differences in the overall liking among the preparations of turkey roll or among preparations of bologna. These results show that sodium levulinate is at least as effective at inhibiting outgrowth of L. monocytogenes in RTE meat products as the current industry standards of lactate or lactate and diacetate, and levulinate addition does not alter the overall liking of the RTE meat products.     

Characterization of bacteriocin-coated antimicrobial polyethylene films by atomic force microscopy

Antimicrobial agents can be used to give antimicrobial properties to polymeric materials used to envelope foods for packaging purposes. In this study, we exploited an atomic force microscopy (AFM) analysis for the characterization of plastic films activated with antimicrobial agents. The aim was to acquire information on the distribution of the antimicrobials on plastic materials with the ultimate scope of understanding the mechanisms of interaction between antimicrobials and materials to be used for food packaging. Four polyethylene films differing in linear, EVA, and erucamide content were activated by 3 different bacteriocins as antimicrobials, namely, nisin and bacteriocins Bac162W from Lactobacillus curvatus and BacAM09 from Lactobacillus plantarum. The spectrum of activity of the bacteriocins was assayed and shown to include several strains of Listeria monocytogenes. The plastic films were activated by a previously developed coating procedure and the surfaces of the active films were examined by AFM. In addition, roughness parameters related to the single surfaces were investigated by an appropriate software. Significant differences were found between the bacteriocin activated and control (nonactivated) films and the activated surfaces showed lower values of average roughness and surface area ratio. It was not always possible to obtain a homogeneous distribution of the bacteriocin preparation following the coating procedure. This result was dependent on the bacteriocin used and its distribution on the different plastic films. Overall, the bacteriocin Bac162W showed the most homogeneous distribution while surfaces treated with nisin, showing a sort of microtexturing, always gave the highest roughness values. Although the issue needs further investigation, the connection between AFM imaging, roughness, and antimicrobial distribution on active packaging showed the potential to improve the understanding of the interactions between plastic films and antimicrobial preparations that can be important for the innovation in food packaging and science.     

基于MALDI-TOF MS技术对李斯特氏菌属两种细菌的快速鉴定

为提高基质辅助激光解析电离飞行时间质谱技术(MALDI-TOF MS)在李斯特氏菌属鉴定中的分辨能力,建立快速准确鉴定单增和英诺克李斯特氏菌的质谱学方法。通过采集79株单增和57株英诺克李斯特氏菌的指纹图谱,利用Clin Pro tools软件对数据进行统计学分析,建立数学判别模型并验证其准确性。峰统计结果显示,两组数据峰强度差异显著的特征峰有16个,推测出单增李斯特氏菌生物标志物6个,英诺克李斯特氏菌10个,发现在单增李斯特氏菌中质量峰3985/7970 u和3972/7942 u是独立且连锁存在。基于遗传算法的判别模型交叉验证率和检测识别能力最强,分别为99.44%和100.00%,经验证准确率达到96%以上,可实现对单增和英诺克李斯特氏菌的快速准确鉴定。同时,利用Bruker Biotyper软件将以上菌株建库形成了实验室内部李斯特氏菌谱库,对8株未测李斯特氏菌进行搜库鉴定,匹配分数均高于商品化数据库,提升了MALDI-TOF MS对李斯特菌属的自动鉴定能力。     

沙门氏菌和单增李斯特菌诱导性耐酸响应机制的研究进展

沙门氏菌和单增李斯特菌被认为是肉制品中最重要的食源性致病菌。它们在弱酸环境下会发生强烈的诱导性耐酸响应,同时诱导产生高毒、耐酸、耐渗透压的高危菌株,是影响消费者健康安全的重大隐患。本文主要从沙门氏菌和单增李斯特菌产生诱导耐酸的发现过程、诱导耐酸响应的危害、产生诱导耐酸的影响因素方面进行概述,进一步从pH值稳态系统、应激蛋白分子的调控及细胞膜组成和流动性调控的角度分析了产生诱导耐酸响应的分子机制。     

食品中微生物检测能力验证结果与分析

目的提高实验室检验人员微生物检测能力和水平,增强实验室竞争力。方法实验室参加中国检验检疫科学研究院测试评价中心组织的食品中单核细胞增生李斯特氏菌、副溶血性弧菌2项检验能力验证。按照盲样作业指导书的要求对样品进行前处理后,依据GB4789.30-2016《食品安全国家标准食品微生物学检验单核细胞增生李斯特氏菌检验》和GB 4789.7-2013《食品安全国家标准食品微生物学检验副溶血性弧菌检验》进行定性检测。结果样品17-P842鉴定出单核细胞增生李斯特氏菌,样品18-E886鉴定出副溶血性弧菌。结论本次能力验证结果满意,为今后实验室检测实际样品提供参考经验。