Chemical And Microbiological Testing Methods For Maintaining Food Safety

A wide range of testing methods is available to food producers to assess the safety of their products. For chemical testing, different analytical techniques are commonly used. These include traditional, so-called ‘wet chemical’ techniques, and advanced approaches such as infrared spectroscopy, gas and liquid chromatography and mass spectrometry.

Used in combination with liquid or gas chromatography, mass spectrometry is the most frequently used chemical test since it permits the detection of low concentrations of analytes in highlycomplex food matrices.

Conventional microbiological testing of food typically encompasses culture-based techniques with selective agars, or other biochemical assay techniques. However, DNA-based and biomolecular techniques are increasingly becoming essential analytical tools in the testing of the safety of foods. These techniques can help identify the presence of potentially harmful microorganisms, food allergens and other substances.

In addition, DNA-based and biomolecular testing are also effective means of validating product claims regarding the source of species of animal or fish-based foods, thereby helping to support efforts to combat food counterfeiting and food fraud worldwide.

As scientists and researchers discover more efficient and less time-intensive methods and technologies, the number and type of available chemical and microbiological methods applicable to food safety testing continue to expand.

For example, advancements in chemical contaminants analysis is being furthered by the speed, sensitivity and selectivity of innovative testing instruments that enable many compounds to be analysed in a single test run. In addition, methods of sample preparation, such as QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe; pronounced as ‘catchers’) do not involve any pre-concentration steps and require minimum extract clean up.

These qualities make QuEChERS-based preparations easier to automate, and has helped to make it the preferred sample preparation technique for the chemical evaluation of pesticide residues in fruits and vegetables. And the use of this technique has also rapidly expanded to include testing of other contaminants, including antibiotics and compounds found in a wide variety of food matrices, such as meat, fish and wine.

At the same time, innovations in gas chromatography high-resolution mass spectrometry instruments, along with the development of related software tools, have shown great potential. This makes it feasible to use in food testing laboratories, for non-targeted testing and identification of known and even unknown chemical contaminants and environmental pollutants that exist in the food supply chain.

In preventing and controlling the spread of foodborne pathogens, accuracy and speed in microbiological testing are among the most demanded criteria by the food industry. As a result, these factors are the primary qualities of many scientific techniques for microbiological analysis, and represent the focus of continued innovation and improvement.

For example, obtaining real-time results regarding the presence of potentially-harmful microbiological contaminants in food matrices has become a reality in recent years, albeit with some limitations. This is in contrast with conventional, culture-based techniques, which often require several days to process, thereby delaying decisions regarding the safety of food products and whether further investigations are required.

Some of the other advances that will continue to have a significant impact on microbiological testing for food safety include:

• Culture-based tests, such as enzyme-linked immunosorbent assay (ELISA) methods and diagnostic test kits for bacterial pathogens and microbial toxins. These immunological assay techniques rely primarily on antigen-antibody binding which offers a high degree of specificity and accuracy. They have dramatically reduced the time needed to obtain results, especially when compared to conventional enrichment and plating techniques (or ‘culture techniques’).
• Biosensor-based techniques: the state of these microbiological testing methods also reflects important achievements in the area of real-time testing. Biosensors are devices for pathogen detection that typically incorporate three essential elements, including a biological capture molecule, a method of converting the captured molecule-target interaction into a signal, and a data output mechanism. Although biosensor-based techniques are currently seeing only limited use in food safety testing, they offer the advantages of real-time detection, portability and multi-pathogen detection in both laboratory and field environments.
• DNA-based fingerprinting techniques for assessing the safety of food have made tremendous progress and will continue to become even more sophisticated over time. One of the principle advantages of DNA-based assays in the detection of foodborne pathogens is their high degree of specificity; they detect specific, nucleic acid sequences in the target microorganism by hybridising them into short synthetic oligonucleotides that complement the specific nucleic acid based assay. Automated polymerase chain reaction (PCR)-based technology represents one of the fastest developing DNA-based analytical approaches used in the detection of foodborne pathogens. Techniques based on PCR technology offer high specificity and extremely rapid turnaround times, making them potentially more popular as less expensive test methods and instruments are introduced for commercial use.

Continued improvements in PCR and other DNA fingerprinting technologies will add to the pool of scientific techniques which are available to identify foodborne pathogens and microbial toxins. These and other advanced techniques can facilitate the more rapid determination of whether microbiological hazards exist, as well as at what point they may have been introduced into the food supply chain.

The use of chemical and microbiological testing in food safety testing also presents a number of challenges. For example, in the area of chemical testing, some environmental pollutants that enter the food chain, such as dioxin and PCBs, have been found to be toxic at levels as low as one part per trillion (ppt), the equivalent of looking for a needle in a haystack. The sensitivity required to detect such minute levels makes the current methods for the analysis of these compounds difficult and expensive to perform.

Analysing dioxin and its isomers also requires the use of high resolution mass spectrometry detection, and few testing laboratories have the requisite equipment or technical expertise to meet the stringent quality control parameters required to conduct such testing.

Even for those testing laboratories that are properly equipped, an additional challenge is the extraction and separation of dioxins and PCBs from other compounds found in the food matrix. There are significant differences in the techniques required to conduct extraction and clean up for fruits, vegetables, dairy products, fish and meat. And processed foods have multiple ingredients that can infiltrate the matrix with chemical additives, further complicating the analysis.

For microbiological testing, research shows that some rapid techniques may perform better with some food matrices than others. These performance differences can typically be attributed to interferences such as microflora in the food matrix or the presence of certain inhibitors. All assays available for these techniques require some degree of sample preparation and pre-concentration in order to enhance their sensitivity. Care should also be taken to assess whether a particular rapid method is specifically designed for preliminary screening; in such cases, negative results are regarded as definitive, but positive results are considered preliminary and must be confirmed.

When choosing an appropriate rapid method, consideration should also be given to how the results will be validated. Any newly-adopted method must yield results equivalent to or better than the method it is intended to replace.

Therefore, it is a good practice to conduct in parallel assays based on both a new rapid method and the method targeted for replacement in order to facilitate an effective comparison of the two methods. Such validation should also focus on an assessment on the food matrix to ensure that the target microorganisms can be recovered from the matrix under test using the available equipment, and be mindful of the potential for false positive or false negative results.

Whether conducting chemical or biological testing, it is important to keep a number of factors in mind when selecting the appropriate testing technique. At a minimum, the list of considerations should include:

• Purpose of the food safety analysis (is it for research purposes or to control unsafe foods?)
• Complexity of the food sample matrix for the food product to be tested
• Timeframe within which test results are required
• Initial capital outlay for the required test equipment
• Simplicity and ease of use of the selected testing technique(s)
• Availability of technical personnel specifically trained in the testing technique

Chemical and microbiological testing are essential tools in the effort to combat foodborne illnesses as well as food fraud. Recent technical advances now provide the food industry with a variety of advanced analytical tools that offer more accurate results in less time, helping to speed the movement of safe food to the market.

However, selecting the right testing technique depends on evaluating a number of factors to ensure a balance between timeliness, accuracy and cost.