Food contaminated with microorganisms such as bacteria, yeasts, molds or viruses may pose a risk to the consumer. In addition to the detection of pathogenic microorganisms, it is important to monitor typical spoilage organisms in order to reduce losses during production.
Microorganisms are creatures of microscopically small size, mainly organized as single-cell organisms, while some of them may occur multicellularly. They can be found everywhere in the natural environment (water, soil, air, etc.). Microorganisms may naturally be present in foods or on the surfaces of foods (e.g. fresh vegetables) or added as contamination during the manufacturing process of food products (e.g. insufficient hygiene in meat processing).
In food industry, it can be distinguished between different categories of microbiological contamination:
Pathogenic microorganisms are either not allowed at all to occur in the foodstuff or they are limited to a specified number of cells per gram food. These limits differ to the respective food matrix. (For more information please visit the DGHM Website.) If limits are exceeded, this might have tremendous consequences for consumer’s health. Therefore, a zero tolerance per 25 g of food sample is predicted for most of all common pathogens (Salmonella, Campylobacter, E. coli, etc.).
In general, you can differentiate between two methods of microbiological testing: food testing and hygiene monitoring / cleaning control.
Detection of microorganisms in the production environment
Microbiological tests for cleaning and hygiene control detect general residues of foods on insufficient cleaned surfaces in the production environment. These residues of nutrients are the basis for growth of microorganisms.
Colony counting in foods or on surfaces can be done using the ready-to-use Compact Dry plates. Compact Dry are available for 13 different parameters of analysis. General method base of examinations with Compact Dry is the cultivation of microorganisms on standard nutrient media. The test principle is based on specific chromogenic substrates which are converted into colored products by the metabolism of microorganisms. Beside examination of diluted food samples, Compact Dry is also suited for swab samples from surfaces or incubation of membrane filter samples from liquids.
Residues of foods on surfaces can be detected using protein tests (RIDA®CHECK) or ATP measurements (LuciPac™Pen). Determination of proteins roughly describes the stage of contamination by color change of the colorimetric detection reagent. However, the relative amount of ATP (Adenosintriphosphat) or AMP (Adenosinmonophosphat) respectively can be measured very precisely. A special bioluminescence reaction which requires the presence of ATP or AMP is recorded in a special luminometer instrument (Lumitester™ PD-20). Both systems are suited for consistent control of efficiency of cleaning procedures. These controls ensure maintenance of general industrial hygiene. Surfaces which are hygienically clean can reduce the risk of product contaminations.
|Compact Dry||RIDA®STAMP||RIDA®CHECK||Lumitester™ PD-30|
|Ready-to-use nutrient plates||Ready-to-use agar plates||Protein test||ATP / AMP measurement|
|Microbial count on surfaces and in diluted food samples||Microbial count on flat surfaces in the production environment and on solid foods||Swab test for the detection of food residues on surfaces||Detection of food residues on surfaces|
|Easy and safe||Easy to use and to evaluate||Rapid and reliable method||Rapid and convenient using LuciPac®Pen with integrated swab|
Detection of microorganisms in foods
Toxic residues of bacteria in food and beverage samples can be analyzed with test kits for bacterial toxins. Common test formats for microbial food testing are ELISA assays, real-time PCR tests, nutrient plates and agar plates.
For detection of pathogenic bacteria, immunological based methods (ELISA) are available. RIDASCREEN® assays are based on the sandwich technology, in which the antigen (bacterial surface protein) will be captured in the well of a microplate and detected by adding a second antibody which is marked with a special detection enzyme. The immunological detection requires suitable pre-enrichment procedures depending on the kind of pathogen bacteria.
The detection of bacterial toxins is possible directly from food samples (RIDASCREEN® SET Total and RIDASCREEN® SET A,B,C,D,E) or is used for indirect detection of toxin producing pathogenic bacteria (RIDASCREEN® Verotoxin) subsequent to appropriate pre-enrichment.
The identification of pathogenic bacteria and viruses can be performed with molecular biological systems, e.g. the highly specific real-time PCR kits of the SureFast® PATHOGEN line. The modular system consists of optimized DNA preparation via spin filter columns and the commonly used TaqMan hydrolysis probe technology linked with FAM dyes for detection. It can be performed with all commonly available types of real-time PCR thermo cyclers. The internal amplification control is integrated into all PLUS kits. The appropriate choice of amplification control dye depends on the cycler type where the reaction will be applied to.
|Immunological test (ELISA)||Molecular-biological test (real-time PCR)||Ready-to-use nutrient plates||Ready-to-use agar plates|
|For the detection of bacteria and bacterial toxins||For the detection of bacteria and viruses||Microbial count on surfaces and in diluted food samples||Microbial count on flat surfaces and on solid foods|
|Rapid and reliable method||Highly specific and fast; suitable for all standard PCR thermal cyclers||Easy and safe||Easy to use and to evaluate|
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