Heat resistance examination of human pathogenic bacteria in sous-vide meat (en-US)

Friday, October 9, 2015

Authors: András S. Szabó, Katalin Vajda, Jenő Szigeti, Balázs Ásványi, Petra Szűcs


The sous-vide technology belongs to mild heat treatment technologies in which pasteurized products are prepared. Due to the low temperature (55-90 °C) of the heat treatment, products have higher nutritional values and better organoleptic properties compared to conventional technologies. The basic requirement for this technology is to find the right balance between microbiological safety and organoleptic properties.

However, ensuring high microbiological quality poses a serious challenge for professionals dealing with sous-vide technology. The goal of the authors was to improve the microbiological quality of meats made by sous-vide technology. Meat is the most expensive and the most commonly used raw material for sous-vide processes, therefore, testing its microflora is of high priority. The heat resistance of pathogenic bacteria of meat, suc

as spore-forming Clostridium perfringens and enterobacteria Salmonella Enteritidis was tested in artificially inoculated chicken meat.


During our experiments, bacterially inoculated and surface sterilized minced chicken breast was heat treated at various temperatures and hold times, at atmospheric pressure and in vacuum-packaging as well. Effective heat treatment parameters (temperature and hold time) and heat destruction parameters such as decimal reduction time (D), z-value, relative thermal death rate (RTDR) and relative thermal death time (RTDT) were determined. Based on our results, it was investigated, using a t-test, how the magnitude of the germ reducing effect of the heat treatment was influenced by the packaging.


2. Introduction and literature review

Over the past decades, dietary habits of people have changed considerably. Consumers now prefer fresher, more natural, non-seasonal, „more comfortable”, „safer” foods. The production of these types of products presents a major challenge to producers, manufacturers and distributors alike. Mild food production technologies represent a solution to this problem. The word „mild” means that „the food is preserved, while its nutritional and organoleptic properties remain the same, thus reducing the side effects of heat treatment – the main preservation method” [1]. Well-regulated, standardized cook-chill systems, including one of the technologies of molecular gastronomy, the sous-vide system, are among new (mild and novel) technologies that produce minimally processed products. The sous-vide („under vacuum”) heat treatment technology is a professional cooking method that includes not only cooking, but also preservation in an oxygen-free environment, under accurate temperature control.


It produces pasteurized products that can be used later if stored cold. During the procedure, foodstuffs are vaccum-packed, and then subjected to very mild heat treatment. The main point of the technology is to apply heat treatment parameters that take into consideration the biochemical properties of the raw material, especially the thermal denaturation points of proteins. Thus, the structure of the food matrix is preserved, and fragrances, flavors and nutrients are fully retained. Meat is the most expensive and most commonly used raw material for sous-vide processes, therefore, testing its microflora is of high priority when aiming to improve the microbiological quality of the sous-vide technology. Meat tissues are sterile in healthy animals, they can be contaminated during primary processing by saprophytic and pathogenic microorganisms, that can settle on and colonize surfaces. Clostridium perfringens can be found in soil, water, dust, spices and in the intestinal tracts of humans and animals, and it is one of the five bacteria that cause food poisoning most often. It is present in 10-80% of raw poultry meat [2]. To cause food poisoning, the pathogen has to reach a level of 106-107 cells/g food [3]. It causes food poisoning, if the food is stored inadequately after heat treatment. The temperature range between 30 °C and 50 °C is especially favorable for the rapid growth of the bacterium. Oxygen level is reduced to such an extent during the application of vacuum packaging, that it favors the proliferation of inevitable anaerobic clostridia [4].


According to the 2009 summary of the European Union, 108614 human incidents were caused by salmonellosis, the second most commonly reported infection. Salmonella remained the most common pathogen of food-related  outbreaks, the bacterium was most often detedted in chicken, turkey and pork [5]. In Hungary, when analyzing the distribution of events of microbiological origin by pathogen, it can be stated that salmonellae are in first place as pathogenic factors, with an absolute dominance of of Salmonella Enteritidis. In 2006, salmonellosis accounted for 93.0% of the total bacterial diseases, and 93.8% of these were caused by Salmonella Enteritidis [6].


Based on the infectious diseases reported in the December 15-21, 2014 period, the epidemiological situation of the country can be summarized as follows: of enteric bacterial infectious diseases, the number of salmonella illnesses  reported since the beginning of the year did not differ significantly from the median characterizing weeks 1-51 of years 2008-2012, and it exceeded the corresponding value of 2012 only slightly [7]. Ensuring microbiological quality and the prevention of the proiferation of pathogenic and saprophytic microorganisms are continuous tasks facing technology professionals.


A minimum temperature value of 65 °C is prescribed by heat treatment regulations

regarding the microbiological safety of foods pasteurized in the conventional way. Sensory properties of foods are also taken into consideration by the sous-vide technology, therefore, a core temperature of 56 °C is recommended for certai meats and fish. Because of the low pasteurization temperature and the long storage time the product is microbiologically sensitive. Therefore, the critical point of applying the sous-vide technology is the

sizing of the heat treatment. The goal of our experiments was to determine optimal heat treatment parameters and thermal death parameters for both pathogens when using the technology, in the case of chicken breast, and determine how thermal deaths of the bacteria are affected by the mode of packaging.

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