SESSION 3 . Microbiological hazards and control measures
Abstract
From the primary production to the point of consumption, a number of single validated control measures or combinations of validated hurdles/control measures are used to insure the food prouct is safe and suitable. People acquainted with the HACCP system focus on Critical Control Points, understood as single control measures, and defined as:
«A step at which control can be applied and is essential to prevent or eliminate a food safety hazard or reduce it to an acceptable level.»
The possibility to combine control measures is not taken into account within most HACCP systems. For example, the safety of dairy products can be obtained by the use of milk pasteurization. Therefore, not one but TWO measures are needed: pasteurization AND prevention of contamination post pasteurization.
The need for more than one control measure is recognized in reference texts. According to the Codex Alimentarius, Hazard Analysis and Critical Control Point (HACCP) System and Guidelines for its Application Annex to CAC/RCP 1-1969, Rev. 3 (1997), Task 6 where Principle 1 applies:
«More than one control measure may be required to control a specific hazard(s) and more than one hazard may be controlled by a specified control measure».
Also, according to the Codex General Standard for Cheese - CODEX STAN A-6-1978, Rev. 1-1999, Amended in 2001, section 6.2:
«From raw material production to the point of consumption, the products covered by this standard should be subject to a combination of control measures, which may include, for example, pasteurization, and these should be shown to achieve the appropriate level of public health protection.»
Control measures can be combined by applying them sequentially or simultaneously. This is the Hurdle Concept of L. Leistner and W. Rodel (1976). Whereas a Hurdle can be defined as a control measure that reduces or inhibits the growth of hazards within a food, Hurdle Technology is the use of two or more hurdles to take advantage of their additivity or synergy.
Examples of individual hurdles are:
- heat treatment leading to cell injury,
- temperature of shelf life,
- increase of salt concentration/decrease of water activity,
- low acidity/pH,
- addition of preservatives, etc.
When applied in combination, the hurdles can have one or several effects on the microorganisms present, greater than if they had been applied individually, such as:
- extend the lag phase,
- slow down the exponential phase,
- lower the maximum cell number at the end of the
growth phase,
- accelerate the decline during shelf life,
- inhibit growth,
- kill/inactivate, etc.
A variety of mathematical models have been designed in order to describe accurately the growth curves as well as the survival curves and the way they are influenced by single hurdles and more importantly by the interaction between hurdles. New models describe the growth-no growth borderline when interacting hurdles/control measures are in place.
These control measures should be put in place first at the farm, and should cover all steps of the Primary Production:
- Environmental hygiene,
- Hygienic production of milk,
- Areas and premises for milk production,
- Animal health (General hygiene practice, Feeding, Pest control, Veterinary drugs),
- Hygienic milking,
- Handling, storage and transport of milk,
- Milking equipment,
- Storage equipment,
- Premises for, and storage of, milk and milking-related equipment,
- Collection, transport and delivery procedures and equipment.
As regards Control of Operation:
«The combination of control measures should effectively control the identified hazards in milk and milk products.»
Control of food hazards includes:
- Hazard identification,
- Control measure selection (pasteurization, etc.),
- Establishment of process criteria,
- Key aspects of hygiene control systems, such as temperature and time controls for incoming milk,intermediate products, time and temperature controls for heat treatment, distribution of finished products and establishment of shelf life, attention to specific process steps, the use of microbiological and other specifications, attention to microbiological cross contamination and physical and chemical contamination,
- Incoming material (other than milk) requirements,
- Packaging,
- Water.
In Annex II Guidelines for the Management of Control Measures during and after Processing it is explained:
«The combination of control measures has two main objectives: during processing, providing assurance that the levels of the pathogens (and/or spoilage organisms) of concern, where present, are kept at or reduced to acceptable levels. After processing (packaging, distribution and storage): providing assurance that the acceptable levels of the pathogens (and/or spoilage organisms) of concern that have been achieved during processing are kept under control throughout shelf life».
It is further explained that there are two types of hurdles:
«Microbiostatic treatments are control measures that minimize or prevent the growth of microorganisms present in a food»
and
«Microbiocidal treatments are control measures that substantially reduce or practically eliminate the number of microorganism present in a food.»
Examples of microbiostatic hurdles are:
- carbon dioxide (CO2),
- coatings,
- freezing,
- lactoferrins,
- lactoperoxidase system,
- modified atmosphere packaging,
- pH reduction,
- preservatives,
- pulsed high-intensity light,
- redox potential control,
- refrigeration, time (shelf life),
- water activity control.
Examples of microbiocidal hurdles are:
- bactofugation®,
- sterilization (heat),
- competitive microflora,
- cooking of cheese curd,
- electromagnetic energy treatment,
- high pressure treatment (pascalization),
- irradiation,
- microfiltration,
- pasteurization (heat),
- ripening (ageing),
- thermization,
- ultrasonication,
- warm sealed packaging.
Examples of validated hurdle technology with milk products are:
- Boiling drinking milk at home and consuming it as soon as it is cool enough,
- Making milk with long shelf life at ambient temperature that is heat sterilized and then hermetically packaged under aseptic conditions,
- Making very hard cheeses, including the heating of cheese curd, use of competitive microflora, low water activity, long ripening time and thick inedible rind.
For the making of raw milk soft cheeses, hurdles can be:
- Tuberculosis and brucellosis free herds,
- Health of udder,
- Hygiene of housing, feeding, milking,
- Sorting of farms according to microbiological status of milk (all milk should be free of pathogens),
- Acidification during first steps of cheese making,
- Hygiene of cheese making, ripening, transport,distribution,
- Short shelf life under refrigerated conditions,
- End product microbiological criteria.
Safety performance for a treatment or a combination of treatments for milk products has to be validated. This is usually done on the basis of historical evidence, or on surveys according to an appropriate sampling plan. In case of new processes, it is recommended to follow the 7-Phase Process of IDF:
- Identify all microbial hazards of concern for the intended end product,
- Among the list established at Phase 1, identify microbial hazards of specific concern to treatment or combination of treatments under study,
- For each microbial hazard identified at Phase 2, gather data on its concentration C,0 in the raw material submitted to the treatment or combination of treatments under study,
- For each microbial hazard identified at Phase 2 and the intended end product, obtain the corresponding « Microbiological Food Safety Objective » C from the public health authority,
- In consultation with the appropriate public health authority and in a transparent manner, determine if the use of a «safety factor» (SF) is appropriate and, if so, what value should be used,
- Using initial concentration C0 identified at Phase 3, final concentration C identified at Phase 4, and the safety factor SF identified at Phase 5, calculate the total efficiency that the treatment or combination of treatments has to achieve in order to meet the Microbiological Food Safety Objective. Calculation is done according to : E log,10 (C0) log,10 (C) log,10 (SF)
- Conduct experimentation and validate that the treatment or combination of treatments under study achieves the efficiency calculated at phase 6 In summary, from the primary production to the point of consumption, a number of single validated control measures or combinations of validated hurdles/control measures are used, to insure the food product is safe and suitable.
BIBLIOGRAPHY
LEISTNER, L., and RODEL, W. 1976. The stability of intermediate moisture foods with respect to microorganisms. Pages 120-137 in: Intermediate Moisture Foods. R. Davies, G.G. Birch,and K.J. Parker, eds. Applied Science Publ., London.
IDF/FAO international symposium on dairy safety and hygiene Cape Town,
March 2–5, 2004,
South Africa |
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