The three tiers of microbiological safety

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Good hygienic practices

This is very much a hands-on concept and involves general hygiene in production, preparation and processing of the co-product streams and of the end-products derived from them. It involves ensuring that the product remains 'microbiologically clean' throughout and that no additional microbiological contamination occurs during the processing. However, it does not quantify the initial numbers of contaminating micro-organisms, does not determine the risk presented by them, and nor does it introduce procedures capable of controlling their growth or eradication. It is a good first step and should be applied irrespective of the use of HACCP or Risk Analysis approaches.

In the context of co-products, the application of good hygiene practices would begin with the segregation of separate waste streams. This should ensure that microbiological contamination is minimised. For example, waste streams intended for co-product processing should not be channelled as if they were to be discarded, but should be identified as a specific entity. In this way their microbiological quality can be maximized and not compromised by mixing with other material that may be regarded only as 'waste'.


This is a practical, yet systematic approach to the identification, evaluation and control of hazards, and focuses on micro-organisms in the co-product streams and end-products. It designs methods into the process by which the survival and growth of micro-organisms can be controlled. HACCP is, therefore, a tool to control hazards operationally. It concerns the delivery of processing variables that might be determined as requirements for processing. For example, where a heat treatment is required, it is HACCP that controls the time and temperature to which the co-products are exposed. HACCP is based on seven principles, which define the systematic approach to the identification, evaluation and control of hazards as follows (see Table 6.1).

Principle 1. Conduct a hazard analysis

This involves an understanding of the organisms likely to be found within the co-product stream or the end-product, or that may be introduced into the stream throughout processing. Once the hazard has been identified it can be controlled.

Principle 2. To determine the Critical Control Points (CCPs) These are the methods or processes by which the hazards (micro-organisms identified as being contained within the co-product) can be controlled. For example, the micro-organisms may be susceptible to a particular pH, they may be susceptible to a particular heat and time combination, or to a particular pressure treatment or degree of dehydration. These applied processes or preservative systems contained within the process are the CCPs, and these must be attained if the hazards are to be controlled.

Table 6.1 The seven principles of HACCP

1 Conduct a Hazard Analysis

2 Determine the Critical Control Points (CCPs)

3 Establish critical limits

4 Establish monitoring procedures

5 Establish corrective actions

6 Establish verification procedures

7 Establish record-keeping and documentation procedures

122 Handbook of waste management and co-product recovery Principle 3. To establish critical limits.

This stage involves identifying the acceptable operating limits of the CCPs. For example, it may be appropriate to control the pH between 2.55 and 3. These then become the limits of the CCP. Equally, a time and temperature treatment may be defined as that required to reduce the numbers of microorganisms by between 6 and 7 orders of magnitude within the co-product or processing stream. The treatments necessary to achieve these decreases then become the limits.

Principle 4. To establish monitoring procedures

Once the CCPs have been identified and their critical limits defined, it is vital that these are monitored constantly. Preferably these should be built in as on-line measurements and monitoring such that each batch of the process or co-product should be recorded as having experienced a specific CCP regime.

Principle 5. To establish corrective actions

The monitoring of adherence to CCPs will indicate when failure to achieve the specified CCPs occurs. Ideally the monitoring procedures should contain alarms that indicate when CCPs have not been met. Corrective actions should then be applied. This might involve simply reworking the co-products or the end-products through the same process, ensuring that the CCPs are met.

Principle 6. To establish verification procedures

The procedures confirm that CCPs had been met successfully and that where corrective actions needed to be applied, these were adequate.

Principle 7. To establish record-keeping and documentation Recording and documentation should be retained as evidence that HACCP had been applied successfully to the co-product stream. This is an essential element of demonstrating that the requirement for due diligence has been met.

CCPs might involve applied processing or they might involve the use of preservative compounds, procedures or systems within the co-product stream, the co-products or the end-products themselves. Section 6.3 is an introduction to methods of preservation and deals firstly with preservation systems where agents might be included within the prepared co-products or end-products; these agents are intended to protect against microbial growth during processing, storage, distribution and sale. Secondly, it deals with applied processing, where processes are applied to a batch or continuum of co-product.

Quantitative Microbiological Risk Assessment (QMRA)

This third tier of microbiological risk management was developed under the auspices of The Codex Alimentarius Commission. It is a broad and overarching framework that is primarily for governmental safety management. QMRA can be considered as a means of imposing safety policy and is one part of a three-part Risk Analysis approach to microbiological safety (Schlundt, 2002). QMRA is the first part of the process, and overlaps with the second and third components of risk management and risk communication, respectively.

Risk Assessments were developed in the chemical industry and in chemical toxicology, where they have been established for managing chemical risks. This was enabled by the availability of dose-response models for chemical toxicology data. However, an analogous system has recently been applied to microbiological safety. This has grown from an increasingly precise ability to model the inactivation and growth of micro-organisms, but has also benefited from the availability of dedicated software and increases in computing power. However, it cannot be overstressed that QMRA is a large-scale global approach that is intended for international application. It is derived from drivers of international trade (principally The Sanitary and Phytosanitary Measures Agreement of the World Trade Organisation), which require measures based on scientific principles that can be assessed by independent experts and that form an objective reference point for international agreement.

Although principally a global and governmental exercise, it will be beneficial to describe here activities involved in QMRA, because these can inform about the microbiological quality of a co-product stream and end-product. The concepts are extremely complex, although worthy of discussion because Risk Assessment provides an estimation of health risk. However, it can equally be applied to an estimation of the risk of microbiological spoilage and provide decision support relating to the need for product recalls. It should not be confused with HACCP, and although both concepts use similar terminology, they are used for different purposes (see Fig. 6.1).

In principle, HACCP is a tool to control hazards operationally. For example, the definitions above show how HACCP involves the control of time and temperature. These are the CCPs. However, it is the role of Risk Assessments to define what extent of control should be imposed, and hence designed into a process. For example, the Risk Assessment might necessitate that to control the safety of a product globally it is necessary to reduce the numbers of micro-organisms by a number of orders of magnitude. The Risk Assessment therefore dictates, as a matter of policy, that a time and temperature should be built into the process to ensure such a decrease in numbers of micro-organisms. It is HACCP that ensures that this requirement is built into the process in a practical way in the form of appropriate CCPs.

The broad application of QMRA (see Table 6.2) to co-products or end-products necessitates an understanding of the types of micro-organism in the co-product, their numbers and fate, and the consumption or use pattern of that co-product or end-product.


A global, overarching process that assesses the safety and stability of products using internationally agreed science and opinion. It can be used to inform HACCP.

Waste stream

Application of HACCP locally will identify Critical Control Points that will enable the control of microbiological hazards during a process.

Process Process Process nm Co-product 1 Hfll Co-product 2 AHl ^>etc.

variable variable variable

Fig. 6.1 A scheme to describe the difference between the global, overarching process of QMRA and the application of HACCP, which will identify CCPs that will enable the control of microbiological hazards locally at each stage throughout a process.

Table 6.2 The component stages of QMRA

Hazard identification Hazard characterisation Exposure assessment Risk characterisation

Methodology of QMRA

1 Hazard identification. This can be either reactive or proactive. Reactive hazard identification is our response to a microbiological hazard that has been identified as a consequence either of an outbreak of disease or of spoilage. It is a response to a problem and to cases where the micro-organisms have been identified and confirmed as the causal agent.

Proactive hazard identification is preferable. It arises where the presence of a microbiological hazard in a particular product may be suspected, but where a link between the product and disease or spoilage has not definitely been established. Nevertheless, this gives us an opportunity to anticipate and control that hazard. The information needed for hazard identification might be derived from databases developed for the purposes of epidemiology or food spoilage, where micro-organisms associated with a particular commodity or co-product derived from that commodity are well documented. The raw materials may thus be used to inform the hazard identification because they might classically be associated with particular spoilage or food-borne pathogenic micro-organisms. Equally, expert information may be used in order to obtain additional data about the likelihood of occurrence of particular micro-organisms in the waste stream or the end-product. The micro-organisms can then be prioritised: some pathogens or spoilage organisms will be more important than others and therefore require urgent control. Pathogenic or spoilage micro-organisms that might emerge given novel marketing strategies must also be anticipated. For example, co-products intended to be stored or marketed in a chilled distribution chain could be susceptible to growth of psychrotrophic bacteria whose involvement in the product had not been anticipated.

2 Hazard characterisation. This is the evaluation of the nature of the adverse effects resulting from the presence of micro-organisms in the co-product. It may be qualitative or quantitative. The hazard characterisation can be influenced by the composition of the co-product stream. For example, a co-product stream that contains nutrients and water will promote the growth of micro-organisms, whereas an alcoholic solution or suspension will not. An additional factor is the numbers of organisms present. This is termed the dose and its importance is a function of the status of the consumer or the co-product which might render each more vulnerable to disease in the case of the consumer, or spoilage in the case of the co-product. The dose of organisms depends in part on the initial number contaminating the waste stream. However, it is influenced by the ability of the waste stream to support multiplication. This will increase the number of micro-organisms within the waste stream during processing. Equally important as an influence on dose, is the effect of any final preparation. For example, where the co-product is intended for inclusion within a food, any influence of treatment by the consumer (such as time and temperature of storage) should also be included in the dose-response, and an estimate made of the effects of such variables on numbers of spoilage or potentially pathogenic micro-organisms.

An additional concept that must be included in hazard characterisation is the status of the consumer. Consumers may be considered to be either normal populations who are fit and well, or susceptible individuals. These susceptible individuals are defined as the young, the old and the diseased; those who are pregnant, immuno-compromised or malnourished; and additionally include tourists who move from one culture and dietary regime to another, which might make them vulnerable to infection. Vulnerability to infection is described by dose-response curves, which express the sensitivity of individuals. These, of course, will differ between the susceptible individuals and the normal population, and the correct relationship must be used for any assessment of the vulnerability of that part of the population. Dose-response curves essentially define the likelihood that ingestion of a given number of potentially pathogenic micro-organisms will result in disease.

However, it could be proposed that a dose-response concept can be developed to inform about the likelihood that spoilage micro-organisms in a product could result in spoilage of that product or products into which it is incorporated. This necessitates a simpler information stream than is required for a disease dose-response curve. Essentially, it can be generally assumed that numbers of bacteria or yeasts in excess of 106 colony-forming units per gramme could result in microbiological spoilage.

3 Exposure assessment. This description can also be qualitative or quantitative, and is an assessment of the likely intake by a consumer of the hazard in the co-product. Equally, it could assess the likely presence of micro-organisms able to cause spoilage within that co-product. Exposure assessment can be regarded as a function of the prevalence of the hazard in the raw materials or the co-product stream, and its survival during the processing, but also the potential for re-contamination by organisms likely to cause spoilage or ill health. It includes the potential for the survival or growth of those organisms, or contamination and growth after the co-products have been processed, but prior to the consumption by a consumer.

4 Risk characterisation. This final aspect of QMRA is an integration of all that has gone before. It is thus an integration of hazard identification, hazard characterisation and exposure assessment. It may again be quantitative or qualitative and it is an estimate of the probability of an occurrence and the severity of the potential adverse effects derived from processing of the co-products or from consumption of the co-products. Therefore risk characterisation combines the identification of the microorganism concerned and its virulence, either in terms of the risk to the consumer or its ability to cause spoilage. The specific dose-response information about how many organisms are required to either cause spoilage of a product or cause disease by consumption of that product, should then be related to the consumption habits (if the material being produced from the co-product is to be consumed) and, of course, the fate of micro-organisms during the production of the co-products or the storage, distribution, preparation, sale and use of the end-products.

Risk Assessments might be deterministic or probabilistic. Deterministic assessments calculate the risks as a function of a single value and generate a point estimate of risk. This is typically regarded as somewhat conservative and does not take into account variability and uncertainty.

Probabilistic methods for determining risk are more complex, and involve extensive mathematical computation. Software to calculate these effects is widely available. They fall into two major categories: those that calculate risk using Monte Carlo simulations (e.g. @Risk software), and those that combine individual probabilities using Bayesian belief networks (e.g. Hugin software).

Provided that the correct micro-organisms are targeted, it should be possible for the outcome of QMRA to be the likelihood of (a) spoilage of a co-product stream due to the presence of specific organisms or (b) illness due to the consumption of a specific end-product. The estimated number of spoilage incidences or illnesses, and the outcome, may also provide risk estimates for processing, distribution and consumer-use scenarios. For example, it should be possible to assess the risk associated with an entire processing route and to determine the influence of each stage of that route on the overall risk. In this way it will be possible to minimise risk, and hence to substitute routes or processes of high risk with lower risk alternatives.

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