Food microbiology is the study of microorganisms present in the food, The challenge about the food microbiology industry is that the microorganisms in the food are not distributed evenly. Some of the microorganisms grow on the surface of the food while others grow inside the food product. In fact, each ingredient of the food has its own microbiological loading.
Because of this uneven distribution of microorganisms and the conditions affecting their growth, the results of microbiology testing will have different results every time a food product is sampled.
The main cause of variability is that two similar samples give two different results. Also, Laboratory results are only representative of the sample at the time of testing only. This makes it even difficult as the same results are sometimes obtained with two seemingly different samples.
The microbiology testing performs many functions as a means to follow the methodology of the test. These tests include weighing the sample, adding diluents, pipetting volumes and incubation of the samples at specific temperatures. Microbiological testing stages have weight/volume/temperature and time tolerances. The effect of one specific difference will be minimal, the cumulative effect of all these differences will be noticeable. Thus it is possible for two similar samples to have different results when all the manipulations have been performed.
The assurances of the results of these tests rely on the application of statistical techniques of sampling and the number of samples taken. A well-planned sampling plan will provide assurance of the microbiological burden of the product and will provide an insight into the likely impact of the manufacturing processes and food safety.
In case of the presence of pathogens, they are relatively lower in number compared to other bacteria. We employ a selective enrichment step which in fact is designed to promote the growth of the target pathogen while making it difficult for other strains of bacteria to grow. Screening methods then filters all negative microorganisms and alerts us about the target pathogen. But sometimes the screening tests are not specific to a target pathogen. The reason being these pathogens that are desirable might be destroyed in certain manufacturing processes because they are exposed to many factors such as cooking, chilling, low moisture, low pH, and fermentation processes.
Once the presumptive stage has arrived more specific identification and confirmation steps can be employed to see if the presumptive pathogen is the target organism. In the lab, this assessment is done by different microbiology testing such as serology, mass spectrometry and the analysis of bacterial genetic material. Each sample is different so it is not right to assume that the results of presumptive notification will be based on historical data. Just because the presumptive tests failed to confirm the product previously the same thing will happen even this time. The recent advantage is the adoption of rapid confirmation techniques such as MALDI-TOF and PCR which make the conformation tests quicker and reduce the waiting time.
To summarize, typical reasons for microbiology testing is;
1) Look for loss of microorganisms during the manufacturing process
2) Identify risk factors
3) Process verification
4) Identification of microorganisms
Although these tests are a component of food safety, this system does not guarantee product safety. These tests can outline information about the manufacturing process.
Common test methods include;
1) Culture media: This refers to the growing of microorganisms in a special medium to identify different types of microorganisms, also known as culturing. The medium comprises different nutrients to enhance microbial growth. They are used to test both ready-to-eat foods and fresh produce. However, today immunoassay and PCR are more accepted methods than these culturing methods because culture methods are not always suitable for all the food groups. Microscopes are usually used to detect the microorganisms in the culture. Both qualitative and quantitative results of microorganisms can be obtained using culture methods. The results are typically obtained between the ranges from twelve hours to a week
2) Immunoassay: In this technique, the concentration of macromolecules in a solution is measured via antibody or immunoglobulin. The detected macromolecule in a solution in many cases is a protein and is termed as an “analyte”. Even for immunoassay qualitative and quantitative tests can be used. This method is only sensitive if paired with cultural enrichment. The results are obtained between the ranges of 24 to 48 hours.
3) Polymerase Chain Reaction: PCR is a recent method developed by Dr. Kary Mullis in 1983. PCR can recognize DNA or RNA which are expected to be unique to the target pathogen or microorganism. Selected sections of DNS or RNS can be reproduced using PCR. The tests are obtained within 24 to 48 hours.