Descripción de puestos

Muscle foods pose considerably more challenges than other foods for development and successful application of spoilage detection methods. These include a highly complex food tissue matrix in which the microorganisms may be embedded and strongly attached, and from which they must be detached to detect and enumerate the microorganisms. This means the food must generally be placed in a liquid diluent and then physically manipulated to release the microorganisms into the liquid. This dilution effect obviously creates a need for a more sensitive detection method than a sample to which the method could be applied directly, such as a liquid food (i.e., milk). In addi-tion, the microflora is generally quite diverse and the dominant flora is very much dependent on the storage environment. At the early stage of the food process the levels of microorganisms on the raw muscle food may be as low as log 2.0 CFU g⁻¹, thus posing additional challenges for the sensitivity of the detection method.

The gold standard method to predict spoilage remains the aerobic SPC, but it is still required by the industry that alternative methods are validated against this method. However, as previ-ously described in this chapter, the SPC is far from perfect and more rapid methods to predict spoilage are urgently needed by the muscle foods sector (fish, meat, and poultry industries). These alternative spoilage methods must generally give results that are comparable and validated against

“gold standard” cultural microbial methods. The methods must be sensitive, rapid, suited to online use, and at least semiautomated. They must be suited to routine use, without the need for highly skilled operators, as high staff turnover is often a major issue in the muscle food industry, and it is neither practical nor possible to keep retraining staff to carry out a test that is highly complex.

The muscle food sector has undoubtedly been the slowest sector in the food industry to take on board alternative technologies for spoilage prediction. However, they are now being com-pelled by their customers, regulatory authorities, and consumers to more accurately predict shelf life. This is even more pertinent with the continued market move toward chilled prepared foods with minimal preservatives and a short shelf life. Although there has been much research and development in the area of rapid spoilage detection methods, recent research on rapid microbial methods has tended to focus more on methods for identification of specific species of microor-ganisms rather than on the total microbial load. However, some of the emerging technologies developed, albeit for other applications, have enormous potential to be further developed for enumeration of the total microbial load and to predict spoilage. More research efforts should now be refocused in this direction using the newer technologies to overcome the hurdles that have to date prevented the widespread uptake of rapid methods to predict spoilage by the muscle food sector.

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21

Microbial Foodborne Pathogens

Marios Mataragas and Eleftherios H. Drosinos

Contents

2.1 Introduction ... 22 2.2 Cultural Methods ... 22 2.2.1 Enumeration Methods ... 23 2.2.1.1 Plate Count... 23 2.2.1.2 Most Probable Number ... 24 2.2.2 Detection Methods ... 24 2.3 Alternative or Rapid Microbiological Methods ... 24 2.3.1 Methods with a Concentration Step ...25 2.3.2 Detection and Enumeration Methods ...25 2.4 Listeria monocytogenes ... 27 2.4.1 Detection of Listeria monocytogenes ... 27 2.4.2 Enumeration of Listeria monocytogenes ... 29 2.4.3 Confirmation of Listeria monocytogenes ... 30 2.5 Escherichia coli O157:H7 ... 32 2.5.1 Detection of Escherichia coli O157:H7... 32 2.5.2 Enumeration of Escherichia coli O157:H7 ... 34 2.5.3 Confirmation of Escherichia coli O157:H7... 34 2.6 Salmonella spp. ...35 2.6.1 Detection and Confirmation of Salmonella spp. ... 36 2.7 Staphylococcus aureus... 38 2.7.1 Enumeration and Confirmation of Staphylococcus aureus ... 38

2.8 Yersinia enterocolitica ... 40 2.8.1 Detection and Confirmation of Yersinia enterocolitica ... 40 2.9 Bacillus cereus ... 42 2.9.1 Enumeration and Confirmation of Bacillus cereus ... 42 2.10 Clostridium perfringens ... 44 2.10.1 Enumeration and Confirmation of Clostridium perfringens ...45 2.11 Campylobacter jejuni ...47 2.11.1 Detection and Confirmation of Campylobacter jejuni ...47 References ... 49

2.1 Introduction

Prevention of foodborne infections and intoxications are of paramount importance today. Hazard analysis and critical control point (HACCP)-type food safety management systems are applied by food enterprises to achieve this goal. Validation of all control measures requires, among other activities, microbiological testing of food and environmental samples. The presence of pathogenic bacteria on raw meat (beef, lamb, and pork) and poultry is the result of their contamination from the live animal, equipment, employees, and environment. Salmonella, Listeria monocytogenes, Staphylococcus aureus, Yersinia enterocolitica, Escherichia coli (mainly E. coli O157:H7), Campylo-bacter jejuni, and Clostridium perfringens often occur on raw meat and poultry. These pathogens have been implicated in foodborne outbreaks associated with the consumption of meat and poul-try. C. jejuni frequently occurs on poultry meat, whereas E. coli is rarely found on this type of meat. However, beef has been implicated in many foodborne outbreaks associated with E. coli.

Salmonella and L. monocytogenes may be found on all types of meat, including beef, lamb, pork, and poultry, and Y. enterocolitica is usually present on pork meat surfaces [1,2]. Psychrotrophic pathogens such as L. monocytogenes and Y. enterocolitica are of great concern because they are able to reach high numbers at refrigerated temperatures, especially when products are kept under

Salmonella and L. monocytogenes may be found on all types of meat, including beef, lamb, pork, and poultry, and Y. enterocolitica is usually present on pork meat surfaces [1,2]. Psychrotrophic pathogens such as L. monocytogenes and Y. enterocolitica are of great concern because they are able to reach high numbers at refrigerated temperatures, especially when products are kept under

In document Optimización del control de inventarios y control de almacén para la reducción de costos e implementación de simulación de sistemas en el almacén de refacciones del taller de la planta central de Grupo Bimbo. (página 41-44)