Cenci-Goga B T, Karama M, Sechi P, Iulietto M F, Novelli S, Mattei S
Dipartimento di Medicina Veterinaria, Laboratorio di Ispezione degli Alimenti di Origine Animale, Università degli Studi di Perugia, 06126 Perugia, Italy.
Dipartimento di Medicina Veterinaria, Laboratorio di Ispezione degli Alimenti di Origine Animale, Università degli Studi di Perugia, 06126 Perugia, Italy.
J Dairy Sci. 2014 Nov;97(11):6708-18. doi: 10.3168/jds.2014-8611. Epub 2014 Sep 6.
Several widespread occurrences of anomalous blue coloration of Mozzarella cheese have been recorded in the United States and some European countries. Official laboratory analysis and health authorities have linked the occurrences to contamination of the processing water with strains of Pseudomonas fluorescens, although several experts questioned how to unequivocally link the blue color to the presence of the microorganism. To establish a method to determine whether a given Pseudomonas spp. strain is responsible for the defect and study the evolution of the coloration under different storage conditions, we developed an in vitro system for the evaluation of blue coloration of Mozzarella cheese intentionally contaminated with strains of P. fluorescens. The purpose of the system was to determine whether P.fluorescens strains, isolated from Mozzarella cheese with anomalous blue coloration, were able to reproduce the blue coloration under controlled experimental conditions. Thirty-six trials of experimental inoculation of Mozzarella cheese in different preservation liquids were conducted using various suspensions of P.fluorescens (P. fluorescens ATCC 13525, P.fluorescens CFBP 3150, and P. fluorescens 349 field strain isolated from blue-colored Mozzarella cheese) at different concentrations and incubated at different temperatures. Growth curves of all tested P.fluorescens strains demonstrated that after 3 d of incubation the concentration was generally >10(6) cfu/g of Mozzarella cheese incubated in either tryptic soy broth (control) or conditioning brine. Prolonged incubation for 5 d at either 20 °C or 8 °C led to concentrations up to 10(9) cfu/g of Mozzarella cheese incubated in tryptic soy broth and up to 10(8) cfu/g of Mozzarella cheese incubated in preservation liquid. All Mozzarella cheeses inoculated with the field strain of P. fluorescens, except those opened 1h after packaging and stored at 8 °C, showed the characteristic anomalous blue coloration, which appeared from 1 to 72 h after opening the packaging, and was proportional to colony count, duration of storage, and storage temperature. With the proposed system, which enabled a larger number of samples to be analyzed under controlled experimental conditions and a large amount of data to be generated in a short time, we described precisely how and under which conditions the presence of P. fluorescens in Mozzarella cheese is responsible for the anomalous blue coloration. The system will help producers intercept contaminated batches and help consumers avoid the conditions under which the defect can appear.
在美国和一些欧洲国家，已经记录到多起马苏里拉奶酪出现异常蓝色的情况。官方实验室分析和卫生当局已将这些情况与加工用水被荧光假单胞菌菌株污染联系起来，尽管一些专家质疑如何明确将蓝色与该微生物的存在联系起来。为了建立一种方法来确定给定的假单胞菌属菌株是否是造成这种缺陷的原因，并研究在不同储存条件下颜色变化的过程，我们开发了一种体外系统，用于评估故意被荧光假单胞菌菌株污染的马苏里拉奶酪的蓝色变化。该系统的目的是确定从出现异常蓝色的马苏里拉奶酪中分离出的荧光假单胞菌菌株是否能够在受控实验条件下重现蓝色。使用不同浓度的荧光假单胞菌（荧光假单胞菌ATCC 13525、荧光假单胞菌CFBP 3150以及从蓝色马苏里拉奶酪中分离出的荧光假单胞菌349田间菌株）的各种悬浮液，在不同的保存液中对马苏里拉奶酪进行了36次实验接种，并在不同温度下孵育。所有测试的荧光假单胞菌菌株的生长曲线表明，在胰蛋白胨大豆肉汤（对照）或调理盐水中孵育3天后，马苏里拉奶酪中的浓度一般>10⁶ cfu/g。在20℃或8℃下延长孵育5天，在胰蛋白胨大豆肉汤中孵育的马苏里拉奶酪浓度可达10⁹ cfu/g，在保存液中孵育的马苏里拉奶酪浓度可达10⁸ cfu/g。所有接种了荧光假单胞菌田间菌株的马苏里拉奶酪，除了包装后1小时打开并在8℃下储存的那些，都显示出特征性的异常蓝色，这种蓝色在打开包装后1至72小时出现，并且与菌落计数、储存时间和储存温度成正比。通过所提出的系统，能够在受控实验条件下分析更多的样品，并在短时间内生成大量数据，我们精确描述了荧光假单胞菌在马苏里拉奶酪中的存在如何以及在何种条件下导致异常蓝色。该系统将帮助生产商拦截受污染的批次，并帮助消费者避免出现这种缺陷的条件。
