《冷冻食品》（英文第二版） Part 11 Microbiological hazards and safe process design.pdf_大学文库

288 Chilled foods manufacture and there was better management of retail outlets with regard to patty storage and cooking. Good m manufacturin ng practice guides are available for many sectors of the chilled food industry (e.g. IFST Guide to Food and Drink Good Manufacturing Practice: IFST 1998. UK Chilled Food Association Guidelines: CFA 1997). These guides outline responsibilities in relation to the manufacture of safe products; adherence to their principles will ensure that the product remains wholesome and safe under the expected conditions of use Product and process design will always be a compromise between the demands for safety and quality on the one hand, and cost and operational limitations on the other. Heat is the main means of ensuring product safety and the elimination of spoilage bacteria. The heating that can be applied may sometimes be limited by quality changes in the product. Usually, minimum cooking processes, either in-factory or in-home, will be designed to kill specific bacteria such as infectious pathogens or those causing spoilage. The skill of the product designer is to balance these competing demands for quality and safety and decide where an acceptable balance lies. Even so, usually more than one process step contributes to quality and safety, for example refrigerated storage is used to retard or prevent the growth of vegetative cells and spores that have survived factory heating. Hence the safety of chilled foods which have no inherent preservative properties, depends almost exclusively on suitable refrigeration temperatures being maintained throughout the supply chain including, for example, the defrosting of frozen ingredients and loading of refrigerated vehicles. Where preservation is used, for example, reduced pH/ increased acidity or vacuum packing, chilling will also contribute to the effectiveness of the preservation system and introduces the need for additional controls during processing The techniques of risk assessment, either formal or more commonly informal ay be used to guide the manufacturer in achieving a predictable and acceptabl balance between the sale of raw or undecontaminated components, cooking and the chances of pathogen survival. Successful process design must consider not only contaminants likely to be carried by the raw materials, but also the shelf- life of the food and its anticipated storage conditions with distributors, retailers or customers, CFDRA (1990). In this sense, the customer is an integral part of the safety chain and some additional level of risk attributable to consumer mishandling or mis-use is always accepted by a manufacturer when he designs products whose safety and high quality shelf-life relies on customer use(e.g cooking or chilled storage). Brackett (1992)has pointed out that chilled foods contain few, or no, antimicrobial additives to prevent growth of pathogenic micro-organisms and are susceptible to the effects of inadequate refrigeration that may allow pathogen growth. He also highlights related issues such as over reliance on shelf-life as a measure of quality and the need to consider the needs of sensitive groups(such as immunocompromised consumers)in the product design. If the product design relies on the customer carrying out a killing step to of pathogens, such as salmonellae, it is important that helpful alidated heating or cooking instructions are provided by the

manufacture and there was better management of retail outlets with regard to patty storage and cooking. Good manufacturing practice guides are available for many sectors of the chilled food industry (e.g. IFST Guide to Food and Drink Good Manufacturing Practice: IFST 1998, UK Chilled Food Association Guidelines: CFA 1997). These guides outline responsibilities in relation to the manufacture of safe products; adherence to their principles will ensure that the product remains wholesome and safe under the expected conditions of use. Product and process design will always be a compromise between the demands for safety and quality on the one hand, and cost and operational limitations on the other. Heat is the main means of ensuring product safety and the elimination of spoilage bacteria. The heating that can be applied may sometimes be limited by quality changes in the product. Usually, minimum cooking processes, either in-factory or in-home, will be designed to kill specific bacteria such as infectious pathogens or those causing spoilage. The skill of the product designer is to balance these competing demands for quality and safety and decide where an acceptable balance lies. Even so, usually more than one process step contributes to quality and safety, for example refrigerated storage is used to retard or prevent the growth of vegetative cells and spores that have survived factory heating. Hence the safety of chilled foods which have no inherent preservative properties, depends almost exclusively on suitable refrigeration temperatures being maintained throughout the supply chain including, for example, the defrosting of frozen ingredients and loading of refrigerated vehicles. Where preservation is used, for example, reduced pH/ increased acidity or vacuum packing, chilling will also contribute to the effectiveness of the preservation system and introduces the need for additional controls during processing. The techniques of risk assessment, either formal or more commonly informal, may be used to guide the manufacturer in achieving a predictable and acceptable balance between the sale of raw or undecontaminated components, cooking and the chances of pathogen survival. Successful process design must consider not only contaminants likely to be carried by the raw materials, but also the shelflife of the food and its anticipated storage conditions with distributors, retailers or customers, CFDRA (1990). In this sense, the customer is an integral part of the safety chain and some additional level of risk attributable to consumer mishandling or mis-use is always accepted by a manufacturer when he designs products whose safety and high quality shelf-life relies on customer use (e.g. cooking or chilled storage). Brackett (1992) has pointed out that chilled foods contain few, or no, antimicrobial additives to prevent growth of pathogenic micro-organisms and are susceptible to the effects of inadequate refrigeration that may allow pathogen growth. He also highlights related issues such as over reliance on shelf-life as a measure of quality and the need to consider the needs of sensitive groups (such as immunocompromised consumers) in the product design. If the product design relies on the customer carrying out a killing step to free the product of pathogens, such as salmonellae, it is important that helpful, accurate and validated heating or cooking instructions are provided by the 288 Chilled foods

Microbiological hazards and safe process design manufacturer and that use of these instructions results in high product quality Good control of heat processing and hygiene in the factory and the home or food service outlet are essential for product safety. The prevention of product re- contamination or cross-contamination after heating plays an even more critical role when products are sold as ready-to-eat It is essential that foods relying on chilled storage for their safety are stored at or below the specified temperature(s)(from -1 to +8C)during manufacture, distribution and storage. Storage at higher temperatures can allow the growth of any hazardous micro-organisms that may be present. Inappropriate processing in conjunction with temperature or time abuse during storage will certainly lead to the growth of spoilage micro-organisms and premature loss of quality. Labuza and Bin-Fu(1995)have proposed the use of time/temperature integrators(TTI)for monitoring the conditions and the extent of temperature abuse in the distribution chain. In conjunction with predictive microbial kinetics the impact of storage temperature on the safe shelf-life of meat and poultry products can be estimated The risks associated with any particular products can be investigated either by practical trials(such as challenge testing) or by the use of mathematical modelling The use of predictive models for microbial killing by heat (interchange of ime and temperature to calculate process lethality based on D and values)or the extent of microbial growth can improve supply chain management. In the Uk,FoodMicromodel(fmm:www.ifra.co.uk)andintheUs,thePathogen ModellingProgram(www.arserrc.gov/mfs/regform.htm)arecomputer-based predictive microbiology databases applicable to chilled products. Panisello and Quantick, (1998)used FMM to make predictions on the growth of pathogens in response to variations in the ph and salt content of a product and specifically the effect of lowering the pH of pate. Zwietering and Hasting(1997)have taken this oncept a stage further and developed a modelling approach to predict the ffects of processing on microbial growth during food production, storage and distribution. Their process models were based on mass and energy balances ogether with simple microbial growth and death kinetics and were evaluated using a meat product line and a burger processing line. Such models can predict the contribution of each individual process stage to the microbial level in a product Zwietering et al.(1991)and Zwietering et al. (1994a, b)have modelled the impact of temperature and time and shifts in temperature during processing on the growth of Lactobacillus plantarum. Such predictive models can, in principle be used for suggesting the conditions needed to control microbial growth or the extent of the microbial 'lag'phase during processing and distribution where temperature fluctuations may be common and could allow growth. Impe et al.(1992) have also built similar models describing the behaviour of bacterial populations during processing in terms of both time and temperature, but have extended their models to cover inactivation at temperatures above the maximum temperature for growth Adair and Briggs (1993)have proposed the development of expert systems, based on predictive models to assess the microbiological safety of chilled foods

manufacturer and that use of these instructions results in high product quality. Good control of heat processing and hygiene in the factory and the home or food service outlet are essential for product safety. The prevention of product recontamination or cross-contamination after heating plays an even more critical role when products are sold as ready-to-eat. It is essential that foods relying on chilled storage for their safety are stored at or below the specified temperature(s) (from 1º to +8ºC) during manufacture, distribution and storage. Storage at higher temperatures can allow the growth of any hazardous micro-organisms that may be present. Inappropriate processing in conjunction with temperature or time abuse during storage will certainly lead to the growth of spoilage micro-organisms and premature loss of quality. Labuza and Bin-Fu (1995) have proposed the use of time/temperature integrators (TTI) for monitoring the conditions and the extent of temperature abuse in the distribution chain. In conjunction with predictive microbial kinetics the impact of storage temperature on the safe shelf-life of meat and poultry products can be estimated. The risks associated with any particular products can be investigated either by practical trials (such as challenge testing) or by the use of mathematical modelling. The use of predictive models for microbial killing by heat (interchange of time and temperature to calculate process lethality based on D and z values) or the extent of microbial growth can improve supply chain management. In the UK, Food MicroModel (FMM: www.lfra.co.uk) and in the US, the Pathogen Modelling Program (www.arserrc.gov/mfs/regform.htm) are computer-based predictive microbiology databases applicable to chilled products. Panisello and Quantick, (1998) used FMM to make predictions on the growth of pathogens in response to variations in the pH and salt content of a product and specifically the effect of lowering the pH of paˆte´. Zwietering and Hasting (1997) have taken this concept a stage further and developed a modelling approach to predict the effects of processing on microbial growth during food production, storage and distribution. Their process models were based on mass and energy balances together with simple microbial growth and death kinetics and were evaluated using a meat product line and a burger processing line. Such models can predict the contribution of each individual process stage to the microbial level in a product. Zwietering et al. (1991) and Zwietering et al. (1994a, b) have modelled the impact of temperature and time and shifts in temperature during processing on the growth of Lactobacillus plantarum. Such predictive models can, in principle, be used for suggesting the conditions needed to control microbial growth or indicate the extent of the microbial ‘lag’ phase during processing and distribution where temperature fluctuations may be common and could allow growth. Impe et al. (1992) have also built similar models describing the behaviour of bacterial populations during processing in terms of both time and temperature, but have extended their models to cover inactivation at temperatures above the maximum temperature for growth. Adair and Briggs (1993) have proposed the development of expert systems, based on predictive models to assess the microbiological safety of chilled foods. Microbiological hazards and safe process design 289

290 Chilled foods Such systems could be used to interpret microbiological, processing, formula- tion and usage data to predict the microbiological safety of foods. However to be realistic, the models are only as good as the data input and at present there is both uncertainty and variability associated with the data available. Betts(1997) has also discussed the practical application of microbial growth models to the determination of shelf-life of chilled foods and points out the usefulness of models in speeding up product development and the importance of validating the output of models in real products. Modelling technology can offer advantages i terms of time and cost, but is still in its infancy(Pin and Baranyi 1998). Its usefulness is limited, as there is variation not only in the microbial types present in raw materials and products but also in their activities and interactions altering growth or survival rates or the production of metabolites recognised by customers as spoilage There are, not surprisingly, major differences between manufacturers in the degree of time or temperature abuse they design their product to withstand and hence the risks they are prepared to accept on behalf of their customers. This can result in major differences in the processes, ingredients and packaging used and the shelf-lives given to apparently similar products 11.2 Definitions Definitions are given below, firstly in order to avoid misunderstanding and secondly to introduce general comments and guidance for the design of processes which control microbiological risks adequately. They are discussed in the following groups: raw materials; Chilled foods, Safety and quality control Processes 11.2.1 Raw materials Undecontaminated materials These include any food components of the final product, that have not been decontaminated so that they are effectively free of bacteria prejudicing or reducing the microbiological safety or shelf-life of the finished product. Such arting materials should be handled in the factory so that numbers of contaminants are not increased and they cannot contaminate any other components that have already been decontaminated. For example, the layout of processing areas should be designed on the forward flow principle to prever cross contamination; uncooked material should not be handled by personnel also handling finished product (except with the appropriate hygiene controls and separation), or allowed to enter high care areas(see below). If it is anticipated that these materials may contain pathogenic microbes, the severity of the risks should be assessed Their handling, processing and usage should be controlled accordingly to prevent cross contamination or manufacture of products which may be accidentally harmful to customers

Such systems could be used to interpret microbiological, processing, formulation and usage data to predict the microbiological safety of foods. However to be realistic, the models are only as good as the data input and at present there is both uncertainty and variability associated with the data available. Betts (1997) has also discussed the practical application of microbial growth models to the determination of shelf-life of chilled foods and points out the usefulness of models in speeding up product development and the importance of validating the output of models in real products. Modelling technology can offer advantages in terms of time and cost, but is still in its infancy (Pin and Baranyi 1998). Its usefulness is limited, as there is variation not only in the microbial types present in raw materials and products but also in their activities and interactions altering growth or survival rates or the production of metabolites recognised by customers as spoilage. There are, not surprisingly, major differences between manufacturers in the degree of time or temperature abuse they design their product to withstand and hence the risks they are prepared to accept on behalf of their customers. This can result in major differences in the processes, ingredients and packaging used and the shelf-lives given to apparently similar products. 11.2 Definitions Definitions are given below, firstly in order to avoid misunderstanding and secondly to introduce general comments and guidance for the design of processes which control microbiological risks adequately. They are discussed in the following groups: raw materials; Chilled foods; Safety and quality control; Processes. 11.2.1 Raw materials Undecontaminated materials These include any food components of the final product, that have not been decontaminated so that they are effectively free of bacteria prejudicing or reducing the microbiological safety or shelf-life of the finished product. Such starting materials should be handled in the factory so that numbers of contaminants are not increased and they cannot contaminate any other components that have already been decontaminated. For example, the layout of processing areas should be designed on the forward flow principle to prevent cross contamination; uncooked material should not be handled by personnel also handling finished product (except with the appropriate hygiene controls and separation), or allowed to enter high care areas (see below). If it is anticipated that these materials may contain pathogenic microbes, the severity of the risks should be assessed. Their handling, processing and usage should be controlled accordingly to prevent cross contamination or the manufacture of products which may be accidentally harmful to customers (see below). 290 Chilled foods

Microbiological hazards and ocess desig These materials will have been treated, usually with heat, to reduce their microbial load. If they are intended for direct incorporation into ready-to-eat products then the heat treatment used in their preparation should be sufficient to ensure the safety of the product(i.e. predictable absence of pathogens)depending on whether it is of short or long shelf-life(see " Safe process design' below) Suitable precautions must be taken to prevent their recontamination after treatment and during handling in the factory. Hence primary packaging should be emoved from decontaminated materials only in high-hygiene areas 11.2.2 Chilled foods This broad group covers all foods which rely on chilled storage(originally defined as from-1 to +8C(Anon. 1982)but see below)as a component of their preservation system. It may therefore include foods made entirely from raw or uncooked ingredients. Some such foods may require cooking prior to consumption in order to make them edible, e.g. raw fish and meat products, and it is accepted that such foods may unavoidably contain pathogenic micro- organisms from time to time prepared chilled or ready-to-eat foods These chilled foods may contain raw or uncooked ingredients(Risk Classes I and 2, see Risk classes below and Table 11.1), such as salad or cheese components But their preparation by the manufacturer is such that the food is either obviously eady-to-eat or only requires re-heating, rather than full cooking, prior to use. The manufacturer should do his best to ensure that such foods are free of hazardous pathogens or hazardous levels of pathogens at the end of their shelf-life, and gredients should be sourced with this objective in view. a scheme for the layout of process lines used in their manufacture is given in Figs 11. 1 and 11.2 Cooked ready-to-eat foods Such foods(Risk Classes 3 and 4, see below, ' Risk classes and Table 1)are made entirely from cooked ingredients and therefore should be freed of infectious pathogens during processing. Cooking procedures during production should be resigned to ensure this and handling procedures after cooking, including cooling should be designed to prevent recontamination of the product or its components, such as primary packaging materials. Often, the appearance of such foods makes it obvious to the customer that no heating, or mild re-heat, is all that are required before eating. Heating requirements should be made clear by any instructions Typical process line layouts are shown in Figs 11.3 and 11.4 REPFEDS For the wider range of in-pack pasteurised foods, Mossel et al.(1987) and Notermans et al. (1990)have proposed the more informative name: refrigerated teurised foods of extended durability'(or REPFED), which includes sous-

Decontaminated materials These materials will have been treated, usually with heat, to reduce their microbial load. If they are intended for direct incorporation into ready-to-eat products then the heat treatment used in their preparation should be sufficient to ensure the safety of the product (i.e. predictable absence of pathogens) depending on whether it is of short or long shelf-life (see ‘Safe process design’ below). Suitable precautions must be taken to prevent their recontamination after treatment and during handling in the factory. Hence primary packaging should be removed from decontaminated materials only in high-hygiene areas. 11.2.2 Chilled foods This broad group covers all foods which rely on chilled storage (originally defined as from 1º to +8ºC (Anon. 1982) but see below) as a component of their preservation system. It may therefore include foods made entirely from raw or uncooked ingredients. Some such foods may require cooking prior to consumption in order to make them edible, e.g. raw fish and meat products, and it is accepted that such foods may unavoidably contain pathogenic microorganisms from time to time. Prepared chilled or ready-to-eat foods These chilled foods may contain raw or uncooked ingredients (Risk Classes 1 and 2, see ‘Risk classes’ below and Table 11.1), such as salad or cheese components. But their preparation by the manufacturer is such that the food is either obviously ready-to-eat or only requires re-heating, rather than full cooking, prior to use. The manufacturer should do his best to ensure that such foods are free of hazardous pathogens or hazardous levels of pathogens at the end of their shelf-life, and ingredients should be sourced with this objective in view. A scheme for the layout of process lines used in their manufacture is given in Figs 11.1 and 11.2. Cooked ready-to-eat foods Such foods (Risk Classes 3 and 4, see below, ‘Risk classes’ and Table 1) are made entirely from cooked ingredients and therefore should be freed of infectious pathogens during processing. Cooking procedures during production should be designed to ensure this and handling procedures after cooking, including cooling, should be designed to prevent recontamination of the product or its components, such as primary packaging materials. Often, the appearance of such foods makes it obvious to the customer that no heating, or mild re-heat, is all that are required before eating. Heating requirements should be made clear by any instructions. Typical process line layouts are shown in Figs 11.3 and 11.4. REPFEDS For the wider range of in-pack pasteurised foods, Mossel et al. (1987) and Notermans et al. (1990) have proposed the more informative name: ‘refrigerated pasteurised foods of extended durability’ (or ‘REPFED’), which includes sousMicrobiological hazards and safe process design 291

vide and other foods with preservation and pasteurisation combinations that ensure long shelf-lives under chill conditions. These products are processed to free them of spoilage bacteria and pathogens capable of growth at chill temperatures, and hence allow very long shelf-lives (42 days or so). Therefore processing, handling and packaging must specifically ensure that they are free of infectious pathogens and the spore-forming pathogens capable of growing under chilled conditions. There is still a lack of knowledge on realistic safety boundaries and the risks associated with these products, with respect to the most severe hazard non-proteolytic Clostridium botulinum (Peck 1997). The determinants of effectiveness of complex combination preservation systems that rely on mild heating and chilled storage are not fully understood. 11.2.3 Safety and quality control Good manufacturing practice Good manufacturing practice (GMP) covers the boundaries and fundamental principles, procedures and means needed to design an environment suitable for the production of food of acceptable quality. Good hygienic practice (GHP) describes the basic hygienic measures that establishments should meet and Table 11.1 Risk classes of chilled foods Risk Typical Critical Relative Required minimum Required manufacturing classa shelf-life hazard risk heat treatment classb MA HA HCA 1 1 week Infectious High Customer cook ✓ (✓) pathogens (minimum 70ºC, 2 min.) 2 1–2 weeks Infectious Low Pasteurization by ✓ ✓✓ pathogens manufacturer (minimum 70ºC, 2 min.) 3 2 weeks Infectious Low Pasteurization by ✓ ✓ pathogens manufacturer and spore- (minimum 90ºC, formers 10 min.) 4 2 weeks Spore- Low Pasteurization by ✓ ✓ formers manufacturer (minimum 90ºC, 10 min.) Notes a Class 1: Raw chill-stable foods, e.g. meat, fish etc.; Class 2: Products made from a mixture of cooked and low-risk raw components; Class 3: Products cooked or baked and assembled or primary packaged in a high-care area; Class 4: Products cooked in-pack. b MA: Manufacturing area; HA: Hygienic area; HCA: High-care area. 292 Chilled foods