The following article will guide you about how to ensure the microbiological quality of foods.
Quality and Criteria:
We all feel we know what is meant by quality and the difference between good quality and poor quality. One dictionary defines quality as the ‘degree of excellence’ possessed by a product, that is to say how good it is at serving its purpose.
In terms of the microbiology of foods, quality comprises three aspects:
A food must not contain levels of a pathogen or its toxin likely to cause illness when the food is consumed.
A food must not contain levels of micro-organisms sufficient to render it organoleptically spoiled in an unacceptably short time.
A food must be of consistent quality both with respect to safety and to shelf-life. The consumer will not accept products which display large batch-to-batch variations in shelf-life and is certainly not prepared to play Russian roulette with illness every time he or she eats a particular product.
Regulatory bodies and the food industry are the two groups most actively interested in determining and controlling the microbiological quality of foods. The regulatory authorities must do so to fulfill their statutory responsibility to protect the public from hazardous or inferior goods.
The extent to which they intervene in food production and supply will depend of course upon the food laws of the country in which they operate. Commercial companies, both food producers and retailers, also have a major interest, since their association with products that are consistently good and safe will protect and enhance their good name and their market.
To distinguish food of acceptable quality from food of unacceptable quality requires the application of what are known as microbiological criteria.
Three different types of microbiological criterion have been defined by The International Commission on Microbiological Specifications for Foods (ICMSF):
(1) A microbiological standard is a criterion specified in a law or regulation. It is a legal requirement that foods must meet and is enforceable by the appropriate regulatory agency.
(2) A microbiological specification is a criterion applied in commerce. It is a contractual condition of acceptance that is applied by a purchaser attempting to define the microbiological quality of a product or ingredient. Failure of the supplier to meet the specification will result in rejection of the batch or a lower price.
(3) A microbiological guideline is used to monitor the microbiological acceptability of a product or process. It differs from the standard and specification in that it is more often advisory than mandatory.
The ICMSF have also specified what should be included in a microbiological criterion as set out below:
(1) A statement of the food to which the criterion applies. Clearly foods differ in their origin, composition, and processing; will present different microbial habitats; and will therefore pose different spoilage and public health problems.
(2) A statement of the micro-organisms or toxins of concern. These may cover both spoilage and health aspects, but decisions on what to include must be realistic and based on a sound understanding of the microbial ecology of the food in question.
(3) Details of the analytical methods to be used to detect and quantify the micro-organisms/toxins. Preferred methods for standards or specifications would be those elaborated by international bodies, although less sensitive or less reproducible methods may be used for simplicity and speed in confirming compliance with guidelines.
(4) The number and size of samples to be taken from a batch of food or from a source of concern such as a point in a processing line.
(5) The microbiological limits appropriate to the product and the number of sample results which must conform with these limits for the product to be acceptable (n, c, m, and M, see Section 11.2).
In this regard, it should be remembered that for certain foodborne pathogens such as Staphylococcus aureus or Clostridium perfringens, their mere presence does not necessarily indicate a hazard and specification of some numerical limits is necessary.
These last two points can present the greatest problem. In applying the microbiological criterion it is assumed that the results obtained are an accurate reflection of the microbiological quality of the whole batch of food. How justified that extrapolation is will depend upon the accuracy and precision of the tests used and on how representative the samples were that were tested.
Micro-organisms are rarely distributed uniformly throughout a food, nor in fact are they usually distributed randomly. When micro-organisms are dispersed in a food material in the course of its production, some may die, some may be unable to grow and others may find themselves in micro-environments in which they can multiply.
The resulting distribution, containing aggregates of cells, is described as a contagious distribution (Figure 11.1).
As the number of samples tested increases, so does our confidence in the result but so too does the cost of testing. To be sure of the quality of the batch or lot we would have to test it all, but since microbiological testing is destructive, this would result in almost absolute confidence in the product quality but none left to sell.
A compromise must therefore be struck between what is practicable and what gives the best estimate of lot quality.
Codes of Good Manufacturing Practice:
The features of control at source outlined above are often enshrined in official regulations or codes of Good Manufacturing Practice (GMP). GMP is defined as those procedures in a food-processing plant which consistently yield products of acceptable microbiological quality suitably monitored by laboratory and in-line tests.
A code of GMP must define details of the process that are necessary to achieve this goal such as times, temperatures etc., details of equipment, plant layout, disinfection (sanitation) and hygiene practices and laboratory tests.
Codes of GMP have been produced by a variety of organizations including national regulatory bodies, international organizations such as the Codex Alimentarius Commission as well as trade associations and professional bodies. They can be used by manufacturers as the basis for producing good quality product but may also be used by inspectors from regulatory bodies.
While they can be very useful, a frequent limitation is that in their desire to be widely applicable they tend to be imprecise. This leads to the use of phrases such as ‘appropriate cleaning procedures’, without specifying what these may be; ‘cleaning as frequently as possible’, without specifying a required frequency; ‘undesirable organisms’, without specifying what these may be.
They also often fail to identify which are the most important requirements affecting food quality and which are of lesser importance. As a result, someone conducting, supervising or inspecting an operation is left uncertain as to what specifically is required to ensure that the operation is conducted in compliance with GMP.
This sort of information is often only available based on a detailed analysis of an individual processing operation.
The Hazard Analysis and Critical Control Point (HACCP) Concept:
In the food industry today approaches based on Good Manufacturing Practice are being largely replaced by application of the Hazard Analysis Critical Control Point (HACCP) concept. This has improved on traditional practices by introducing a more systematic, rule-based approach for applying our knowledge of food microbiology to the control of microbiological quality.
The same system can also be adopted with physical and chemical factors affecting food safety or acceptability, but here we will confine ourselves to microbiological hazards. It should also be remembered that HACCP is primarily a preventative approach to quality assurance and as such it is not just a tool to control quality during processing but can be used to design quality into new products during their development.
HACCP was originally developed as part of the United States space programme by the Pillsbury Company, the National Aeronautics and Space Administration (NASA) and the US Army Natick Laboratories who used it to apply the same zero defects philosophy to food for astronauts as to other items of their equipment.
It is based on an engineering system known as the Failure Modes Analysis Scheme which examines a product and all its components asking the question ‘What can go wrong?’.
In 1973 it was adopted by the US Food and Drug Administration for the inspection of low-acid canned food. It has since been more and more widely applied to all aspects of food production, food processing and food service, and to all scales of operation from large industrial concerns, through to cottage industries and even domestic food preparation.
The meaning of the terms hazard and risk in the HACCP system differs from their common everyday usage as synonyms. In HACCP, a hazard is a source of danger; defined as the unacceptable contamination, growth or survival of a micro-organism which can affect safety or shelf-life, and/or the unacceptable production or persistence in food of microbial metabolites affecting safety or shelf-life.
Individual hazards can be assessed in terms of their severity and risk. Clearly a threat to food safety is more severe than one to shelf-life, and botulism is a far more severe hazard than say Staphylococcus aureus food poisoning. Risk is an estimate of the likely occurrence of a hazard so, although C. botulinum is a more severe hazard, epidemiological evidence shows that the risk it poses is generally very low.
A HACCP study is best conducted by a multidisciplinary team comprising a microbiologist, a process supervisor, an engineer and a quality assurance manager, all of whom will be able to bring their own particular expertise and experience to bear on the problem. Involvement of production personnel will also ensure identification with the plan by those who will have to implement it.
Experience suggests that best results are obtained when the study’s terms of reference specify particular microbial hazards for consideration since this will allow the team to define specific controls. The choice of hazard considered will depend on whether there is epidemiological evidence linking a particular micro-organism with the food in question.
In the absence of such evidence, factors such as the product’s physical and chemical characteristics and the way it is eventually used by the consumer must provide the basis for selection.