41 Detecting the Presence of Bacteria or Chemical Residue
This chapter covers outcome 9: Describe feels, smells, or visual clues that might indicate the presence of bacteria or chemical residue. (We also look for physical contaminants)
The three main types of hazards we are concerned with are biological (microbial), physical (glass, metal, wood, etc.) and chemical (allergens, excessive chemicals, etc.).
We look at ingredients and finished products. It is often referred to as organoleptic testing or sensory evaluations. These tests are done for safety and quality. We look for standard appearance, off odours, colour changes, bone fragments in meat, bruising, etc.
Lab tests are usually done to determine the presence of bacterial contamination. However, spoilage and indication of contamination can be indicated by appearance changes, as well.
Microbial testing provides the detection and quantification of pathogens and spoilage microorganisms in a variety of products. Not only do these analyses allow processors to address food safety issues if pathogenic bacteria are detected, but they also predict the shelf life of a product when evaluating spoilage microorganisms.
Culture techniques
Culture techniques, which are commonly used in microbiology, rely on the growth of microorganisms under specific conditions (ex: time, temperature, oxygen content, pH and pressure) in liquid or on solid media containing nutrients. Culture methods using standard media require between 1 to 7 days for detecting the presence of microorganisms. Often, an enrichment step and/or a confirmation procedure is required before and after microbial detection, respectively.
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Biochemical and enzymatic methods
Rapid methods for microbial testing assess the microbial population through the metabolic activity of the cells. Such techniques include chromogenic media, colorimetry, ATP (adenosine triphosphate) determination, protein detection and biochemical kits.
- Chromogenic media for culture techniques. This method relies on the detection of enzymatic activities of target microorganisms by the addition of dyes or organic compounds. Microorganisms growing in the presence of these compounds may fluoresce under UV light or produce distinctive colours. Compared to a standard media analysis, this method enables more sensitivity and rapid analysis (1) (within 24 hours). Chromogenic media to identify Listeria monocytogenes and E. coli are commercially available (ex: Bio-Rad, Weber Scientific, etc).
- Colorimetry or optical systems measure microbial growth by monitoring pH and other biochemical reactions that generate a color change as microorganisms grow and metabolize in a culture broth. Test for the detection of coliforms, E. coli, yeast, molds, lactic acid bacteria, Listeria spp., and Enterobacteriaceae are commercially available (ex: Neogen Corporation).
- ATP Bioluminescence. ATP, which is the energy source in all living cells, produces light in the presence of luciferin-luciferase, oxygen and magnesium. It is believed that the amount of light generated is related to the amount of ATP, and therefore biomass. However, ATP technique measures all organic matter on the surface, instead of only microbial contaminants (2). In other word, ATP systems could detect ATP on a food contact surface but does not identify the source. This is why this method is more used as a hygienic indicator than bacteria quantification system. ATP swaps are commercially available (ex: BioTrace Bev-Trace; Cogent MLS; Millipore Milliflex; Celsis CellScan).
- Protein detection is used to evaluate in real time (within minutes) if the cleaning operation in a food plant has been carried out to a satisfactory standard. These hygiene indicators can be used as a tool to help improve the sanitation performance in your plant. Results are evident with a change in color. Minimal training is required. (ex: BioTrace provides several kits for protein detection).
- Biochemical and enzymatic identification kits. These kits are capable of identifying microorganisms by combining a series of biochemical tests and a database developed by the kit’s manufacturer. Each media included in the test kit system is inoculated and the color reactions of each media provide data for the organism detection. A minimum of 24 hours is required for reliable results. Test kits such as API system, Enterotube II, etc are commercially available. Enterotube II (Roche Diagnostics) was developed to identify species of the Enterobacteriaceae. Advantages of this system include speed and ease of inoculation. On the other hand, API system (bioMérieux) is available for Enterobacteriaceae, as well as, gram negative non- Enterobacteriaceae, Campylobacter spp., Lactobacillus, Staphylococci, yeast, etc. This system has an excellent data base and is easy to inoculate, however, readings and interpretation of reactions require training.
- Electrical methods, such as the use of impedance, conductance and capacitance determine the bacterial growth. This method relies on the fact that metabolites produced by microbial metabolism during growth, increase the conductivity and decrease the resistance of the media. Results could be obtained within hours. The detection time varies depending on a few variables: the temperature at which the assay is conducted, the medium, the generation time of the bacteria and the inhibition properties of the media. Systems that measure the impedance are commercially available (ex: Bactometer, RABIT for Windows”, BacTrac, etc).
Antibody-based methods
Enzyme immunoassay (EIA), also known as enzyme-linked immunosorbent assay (ELISA), is a common technique for antibody-based detection of microorganisms. This method ensures sensitivity and specificity for pathogen detection. Results can be interpreted visually (qualitatively) or using an instrumental read-out (quantitatively). Test kits for the detection of Salmonella, Listeria, Campylobacter, E. coli 0157:H7, Pseudomonas, Staphylococcus aureus are commercially available (ex: BioControl Systems, Bio Trace, etc).
Nucleic acid-based methods
Compared to antibody-based methods, there are relatively few commercialized versions of nucleic acid-based methods.
- Hybridization. This method is based on the detection of target microorganisms by the identification and binding of specific DNA sequences unique to a particular microbial group. After the binding reaction occurs, detection is accomplished colorimetrically (2). Commercial test kits (GENE-TRACK®, AccuPROBE®) for the detection of Salmonella, Listeria, E. coli, Staphylococcus, Campylobacter and Yersinia are available (ex: Neogen Corporation, Gen-Probe).
- Polymerase Chain Reaction (PCR) is based on the identification of a very specific DNA sequence from a target microorganism, followed by amplification of the sequence for the detection of the microorganism (2). This technology offers a specific and reliable detection of pathogenic bacteria within 24 hours. Test kits for the detection of Listeria monocytogenes, E. coli 0157:H7, and Campylobacter jejuni are commercially available (ex: Applied BioSystems, BioControl).
Toxin Testing
Mycotoxins (toxins produced by certain species of mold) such as aflatoxin, deoxynivalenol (DON), fumonisin, ochratoxin, T-2 toxin, zearalenone and histamine; as well as bacterial toxins (ex: bacillus, staphylococcus enterotoxins) can be detected by ELISA based test kits. These kits are commercially available. (e.x. R-Biopharm, Biotrace International, Neogen Corporation, Elisa Technologies).
For more information on Mycotoxins, refer to the following fact sheet:
Contains information from the Government of Manitoba, licensed under the OpenMB Information and Data Use License (Manitoba.ca/OpenMB). This information can be accessed in its entirety at:
https://www.gov.mb.ca/agriculture/food-safety/at-the-food-processor/food-safety-testing.html
Organoleptic and Visual Testing
Organoleptic Inspection
Is a physical examination of a representative number of sample units (for example, cartons, carcasses, combo bins), drawn at the end of visual inspection, using the senses of touch, smell, sight to determine the wholesomeness and cleanliness of a meat product.
Visual Inspection
A visual scan of the entire lot to assess the shipping containers for evidence of damaged or stained cartons, to detect objectionable odors, to verify outer labels, and to establish a correlation between the shipment and the Official Meat Inspection Certificate (OMIC) issued by the competent authority of the exporting country.
Workers look at ingredients and finished products for safety and quality. We look for standard appearance, off odours and colour changes can be evidence of spoilage and the presence of bacterial contamination. Other physical contaminants such as bone fragments in meat, bruising, etc., can be identified visually.
Contains information from the Government of Canada referenced in accordance with the terms of use. The article can be found in its entirety at https://inspection.canada.ca/inspection-and-enforcement/guidance-for-food-inspection-activities/permission-issuance/organoleptic-evaluation-meat-products/eng/1546892808848/1546892874615
