Part IV Safety and quality issues
Part IV Safety and quality issues
Shelf-life determination and challenge testin G. Betts and L. Everis, Campden and Chorleywood Food Research Association 10.1 Introduction All food products are susceptible to deterioration in their quality during storage Chilled foods in particular are highly perishable and the time during which the quality is maintained at a consumer acceptable standard can be termed the shelf- life. The definition of shelf-life has been given by several authors as the time between the production and packaging of the product and the point it becomes unacceptable under defined environmental conditions(Ellis 1994)or the time at which it is considered unsuitable for consumption(Singh 1994). The end of products shelf-life will be due to deleterious changes to quality caused by biological, chemical, biochemical and physiochemical means, or by food safety concerns due to the growth of food pathogens which may not necessarily cause any changes in product quality There are few reference books available which give lists of shelf-lives for chilled foods as the shelf-life of each specific product is unique and based on the particular recipe, raw ingredients and manufacturing and storage conditions used. If there are any changes to these, then the shelf-life will be liable to change (see Section 10.2). Whilst there is some guidance available in the literature for chilled foods(Ellis 1994)and MAP foods(Day 1992) the shelf-life of products should be defined scientifically during product development following the The rationale for arriving at a particular shelf-life will undoubtedly encompass safety, quality and commercial decisions. It is unlikely that all of these will be in agreement and the safety of the product must al ways assume the highest priority There are, however, many commercial and marketing pressures to consider which will put some constraints on whether the shelf-life obtained from microbiological
10.1 Introduction All food products are susceptible to deterioration in their quality during storage. Chilled foods in particular are highly perishable and the time during which the quality is maintained at a consumer acceptable standard can be termed the shelflife. The definition of shelf-life has been given by several authors as the time between the production and packaging of the product and the point it becomes unacceptable under defined environmental conditions (Ellis 1994) or the time at which it is considered unsuitable for consumption (Singh 1994). The end of a product’s shelf-life will be due to deleterious changes to quality caused by biological, chemical, biochemical and physiochemical means, or by food safety concerns due to the growth of food pathogens which may not necessarily cause any changes in product quality. There are few reference books available which give lists of shelf-lives for chilled foods as the shelf-life of each specific product is unique and based on the particular recipe, raw ingredients and manufacturing and storage conditions used. If there are any changes to these, then the shelf-life will be liable to change (see Section 10.2). Whilst there is some guidance available in the literature for chilled foods (Ellis 1994) and MAP foods (Day 1992) the shelf-life of products should be defined scientifically during product development following the procedures outlined in this chapter. The rationale for arriving at a particular shelf-life will undoubtedly encompass safety, quality and commercial decisions. It is unlikely that all of these will be in agreement and the safety of the product must always assume the highest priority. There are, however, many commercial and marketing pressures to consider which will put some constraints on whether the shelf-life obtained from microbiological 10 Shelf-life determination and challenge testing G. Betts and L. Everis, Campden and Chorleywood Food Research Association
260 Chilled foods evaluation is acceptable from a commercial viewpoint. For example, how does the shelf-life compare with that of similar competitors products? Does the shelf- life provide sufficient time for the sale of a significant proportion of the product within the shelf-life, thereby minimisingend-of-shelf-life' stock disposal? Is the shelf-life long enough to suit weekly shopping, which is the way that most chilled foods are purchased(Evans et al 1991). If there is a commercially viable minimum shelf-life, then this needs to be considered at the product development stage and the recipe altered accordingly Another constraint for chilled food manufacturers is the rapid expa the chilled foods market. Over the past ten years there has been considerable development in the number and types of products available(dennis and Stringer 2000). There are approximately 7, 458 new products per year, of which 3, 616 are chilled(CCFra 1999). The chilled foods market in 1997 was f5.1 billion (Anon. 1998). Such an active market requires rapid development of new product formats and ingredient combinations with short launch times. Traditionally, the safety and quality of new products would have been evaluated solely by the us of laboratory studies which are time consuming and expensive. Predictive mathematical modelling techniques are now available and are gaining increasing use in the development of new products. Their use in shelf-life determination will be discussed later in Section 10.3 In addition to commercial pressures for extensive and rapid product development there is a consumer pressure for fresh tasting products with less salt and preservatives which require minimum preparation( Gibson and Hocking 1997). These requirements have the potential to increase the growth of food spoilage organisms and pathogens and thus decrease the likely shelf-life attainable under chilled storage conditions. Such product changes mean that new combinations of ingredients and preservative factors need to be used to maximise shelf-life. This will also be discussed throughout this chapter Determination of the shelf-life of a product is decided by a combination safety requirements, quality and marketing issues and customer demands Arriving at the correct shelf-life is essential for product success. This chapter Ilustrates how this can be achieved 10.2 Factors affecting shelf-life 10.2.1 Product considerations Before a new product can be developed there are a number of fundamental considerations to be made which will affect the shelf-life likely to be achieved Product description The first step to take is to decide what essential product characteristics are required; for example, is it a dairy product or a tomato-based product? Is it to be a homogeneous sauce or will it contain particulate matter? The generic product type will give an initial indication of the microorganisms likely to be of concern
evaluation is acceptable from a commercial viewpoint. For example, how does the shelf-life compare with that of similar competitors’ products? Does the shelflife provide sufficient time for the sale of a significant proportion of the product within the shelf-life, thereby minimising ‘end-of-shelf-life’ stock disposal? Is the shelf-life long enough to suit weekly shopping, which is the way that most chilled foods are purchased (Evans et al 1991). If there is a commercially viable minimum shelf-life, then this needs to be considered at the product development stage and the recipe altered accordingly. Another constraint for chilled food manufacturers is the rapid expansion of the chilled foods market. Over the past ten years there has been considerable development in the number and types of products available (Dennis and Stringer 2000). There are approximately 7,458 new products per year, of which 3,616 are chilled (CCFRA 1999). The chilled foods market in 1997 was £5.1 billion (Anon. 1998). Such an active market requires rapid development of new product formats and ingredient combinations with short launch times. Traditionally, the safety and quality of new products would have been evaluated solely by the use of laboratory studies which are time consuming and expensive. Predictive mathematical modelling techniques are now available and are gaining increasing use in the development of new products. Their use in shelf-life determination will be discussed later in Section 10.3. In addition to commercial pressures for extensive and rapid product development there is a consumer pressure for fresh tasting products with less salt and preservatives which require minimum preparation (Gibson and Hocking 1997). These requirements have the potential to increase the growth of food spoilage organisms and pathogens and thus decrease the likely shelf-life attainable under chilled storage conditions. Such product changes mean that new combinations of ingredients and preservative factors need to be used to maximise shelf-life. This will also be discussed throughout this chapter. Determination of the shelf-life of a product is decided by a combination of safety requirements, quality and marketing issues and customer demands. Arriving at the correct shelf-life is essential for product success. This chapter illustrates how this can be achieved. 10.2 Factors affecting shelf-life 10.2.1 Product considerations Before a new product can be developed there are a number of fundamental considerations to be made which will affect the shelf-life likely to be achieved. Product description The first step to take is to decide what essential product characteristics are required; for example, is it a dairy product or a tomato-based product? Is it to be a homogeneous sauce or will it contain particulate matter? The generic product type will give an initial indication of the microorganisms likely to be of concern 260 Chilled foods
Shelf-life determination and challenge testing 261 to the product and thus the shelf-life likely to be achieved. For example, non- acidic dairy products are more susceptible to rapid growth of microorganisms and are likely to have a shorter shelf-life than, for example, acidic products which are more inhibitory to growth For pasteurised chilled products, the heat treatment required may also be different based on these essential product characteristics( Gaze and Betts 1992) and the heat processing requirements can be decided at this stage Product packaging The desired product packaging format needs to be considered. If the product is to be pasteurised in-pack, then provided that there is no post-process contamination, there should be fewer vegetative spoilage organisms or pathogens in the product and the attainable shelf-life should be relatively long Bacterial spores will remain present in the product but these grow relatively slowly at chill temperatures( see Chapter 7). If the product is assembled after cooking, then there is a greater risk of contamination with microorganisms even in good hygienic conditions. The shelf-life of these products is likely to be horter than those for in-pack pasteurised products The gaseous atmosphere of the packaging needs to be considered. If the product is packed under normal atmospheric conditions then aerobic spoilage organisms such as Pseudomonas species can grow and rapidly spoil chilled products held at <5C. If, however, modified atmosphere conditions are used which exclude oxygen, then spoilage will be by facultative or strict anaerobes which grow more slowly under good chill conditions(see Chapter 7) Preservatives Is the product to be marketed as preservative free or low salt? Removing such ingredients will allow more rapid growth of microorganisms and thus reduce the shelf-life unless additional preservative factors are included, e.g. addition of lemon juice. The effect of removing traditional preservatives should be considered at this early stage and a list of alternatives investigated elf-life It may be the case that there is a minimum shelf-life that must be achieved to make the product commercially viable, e.g. ten days to allow storage over a weekend period. This must be defined at the beginning of the shelf-life determination in order that the product formulation and packaging specifications chosen are likely to achieve the minimum desired shelf-life. Often products have a perceived maximum shelf-life by the consumer which is shorter than that which can be achieved in reality. For example, Evans(1998)reviewed the mean actual and perceived shelf-lives of a range of chilled products and found that for pate the actual storage life was over 10 days whilst the perceived storage life was only 4 days Having formulated the specific product and packaging characteristics, it is likely that a target shelf-life will be derived based on past experience. This
to the product and thus the shelf-life likely to be achieved. For example, nonacidic dairy products are more susceptible to rapid growth of microorganisms and are likely to have a shorter shelf-life than, for example, acidic products which are more inhibitory to growth. For pasteurised chilled products, the heat treatment required may also be different based on these essential product characteristics (Gaze and Betts 1992) and the heat processing requirements can be decided at this stage. Product packaging The desired product packaging format needs to be considered. If the product is to be pasteurised in-pack, then provided that there is no post-process contamination, there should be fewer vegetative spoilage organisms or pathogens in the product and the attainable shelf-life should be relatively long. Bacterial spores will remain present in the product but these grow relatively slowly at chill temperatures (see Chapter 7). If the product is assembled after cooking, then there is a greater risk of contamination with microorganisms even in good hygienic conditions. The shelf-life of these products is likely to be shorter than those for in-pack pasteurised products. The gaseous atmosphere of the packaging needs to be considered. If the product is packed under normal atmospheric conditions then aerobic spoilage organisms such as Pseudomonas species can grow and rapidly spoil chilled products held at 5ºC. If, however, modified atmosphere conditions are used which exclude oxygen, then spoilage will be by facultative or strict anaerobes which grow more slowly under good chill conditions (see Chapter 7). Preservatives Is the product to be marketed as preservative free or low salt? Removing such ingredients will allow more rapid growth of microorganisms and thus reduce the shelf-life unless additional preservative factors are included, e.g. addition of lemon juice. The effect of removing traditional preservatives should be considered at this early stage and a list of alternatives investigated. Shelf-life constraints It may be the case that there is a minimum shelf-life that must be achieved to make the product commercially viable, e.g. ten days to allow storage over a weekend period. This must be defined at the beginning of the shelf-life determination in order that the product formulation and packaging specifications chosen are likely to achieve the minimum desired shelf-life. Often products have a perceived maximum shelf-life by the consumer which is shorter than that which can be achieved in reality. For example, Evans (1998) reviewed the mean actual and perceived shelf-lives of a range of chilled products and found that for paˆte´ the actual storage life was over 10 days whilst the perceived storage life was only 4 days. Having formulated the specific product and packaging characteristics, it is likely that a target shelf-life will be derived based on past experience. This Shelf-life determination and challenge testing 261
262 Chilled foods should then be confirmed by a scientific approach outlined in Section 10.4. Once the shelf-life has been determined there are a number of factors which will affect shelf-life as described below. These also need to be considered at the product development stage to ensure that they are under control during routine production of the product 10.2.2 Raw materials The raw materials used in the preparation of a product will influence the biochemistry and microbiology of the finished product. In order to achieve a consistent shelf-life, the quality of the raw materials needs to be standardised and the attributes most likely to affect product shelf-life should be laid down in specifications. Variations in the quality of raw ingredients can lead to variations in the final product which may affect product shelf-life. Variations in raw material can occur for a number of reasons: natural variation, variety change, a hange of supplier, seasonal availability or pre-processing applied to raw materials. The manufacture of coleslaw provides an example of where shelf-life can be influenced by the seasonal availability of freshly harvested cabbage which has a low yeast count, whereas cabbage from cold storage has a higher yeast count. Use of cabbage from cold stores results in coleslaw with a markedly shorter shelf-life owing to the higher starting levels of yeast introduced via the If an ingredient for a raw product does not meet an agreed specification, e.g for levels of microorganisms, it is still possible to use the ingredient for a different purpose, e.g. to be added to a product before cooking, provided there is no compromise to food safety. The likely consequences of using higher levels of organisms can be evaluated using predictive models(Section 10.3). Tolerance limits for those ingredients that exert a key preservative effect in the final product, such as the percentage of salt, need to be established during the development of the product or in challenge testing(see Section 10.6) and be stated in the product process and formulation specifications. Any variability in the levels of these ingredients due to inaccuracy in weighing ingredients during routine production will affect the shelf-life achieved. Ingredients which are crucial to product safety or stability during the assigned shelf-life should be identified using product hazard analysis(Leaper 1997) and the levels of these ngredients must be controlled during routine production. For example,for chilled MAP foods a salt level of 3.5% in the aqueous phase can be a key controlling factor for these foods and the salt level must be monitored for each batch of product manufactured(Betts 1996) Product formulation can be used to overcome natural variability of critical factors in raw materials and thereby reduce the variation of the final product. The pH is one of the most important factors affecting the degree of heat processing required to achieve sterilisation. In tomatoes there is a variability of acidity between cultivars. Product formulation can be used to overcome this variability either by blending high and low acidity cultivars or by the addition of
should then be confirmed by a scientific approach outlined in Section 10.4. Once the shelf-life has been determined there are a number of factors which will affect shelf-life as described below. These also need to be considered at the product development stage to ensure that they are under control during routine production of the product. 10.2.2 Raw materials The raw materials used in the preparation of a product will influence the biochemistry and microbiology of the finished product. In order to achieve a consistent shelf-life, the quality of the raw materials needs to be standardised and the attributes most likely to affect product shelf-life should be laid down in specifications. Variations in the quality of raw ingredients can lead to variations in the final product which may affect product shelf-life. Variations in raw material can occur for a number of reasons: natural variation, variety change, a change of supplier, seasonal availability or pre-processing applied to raw materials. The manufacture of coleslaw provides an example of where shelf-life can be influenced by the seasonal availability of freshly harvested cabbage which has a low yeast count, whereas cabbage from cold storage has a higher yeast count. Use of cabbage from cold stores results in coleslaw with a markedly shorter shelf-life owing to the higher starting levels of yeast introduced via the raw ingredients. If an ingredient for a raw product does not meet an agreed specification, e.g. for levels of microorganisms, it is still possible to use the ingredient for a different purpose, e.g. to be added to a product before cooking, provided there is no compromise to food safety. The likely consequences of using higher levels of organisms can be evaluated using predictive models (Section 10.3). Tolerance limits for those ingredients that exert a key preservative effect in the final product, such as the percentage of salt, need to be established during the development of the product or in challenge testing (see Section 10.6) and be stated in the product process and formulation specifications. Any variability in the levels of these ingredients due to inaccuracy in weighing ingredients during routine production will affect the shelf-life achieved. Ingredients which are crucial to product safety or stability during the assigned shelf-life should be identified using product hazard analysis (Leaper 1997) and the levels of these ingredients must be controlled during routine production. For example, for chilled MAP foods a salt level of 3.5% in the aqueous phase can be a key controlling factor for these foods and the salt level must be monitored for each batch of product manufactured (Betts 1996). Product formulation can be used to overcome natural variability of critical factors in raw materials and thereby reduce the variation of the final product. The pH is one of the most important factors affecting the degree of heat processing required to achieve sterilisation. In tomatoes there is a variability of acidity between cultivars. Product formulation can be used to overcome this variability either by blending high and low acidity cultivars or by the addition of 262 Chilled foods
Shelf-life determination and challenge testing 263 permitted organic acids. Again, it is crucial that where ph is used as a key preservative factor, the ph of each batch of product should be monitored to ensure that the target level is achieved 10.2.3 Assembly of product In complex and multi-component products, contact between components may result in migration of flavourings, colourings, moisture or oil from one component to another. This may limit shelf-life due to quality changes, e.g.in multi-layered trifles where the visual appearance is impaired by the migration of colouring components from one layer to another, and in fruit pies where migration of moisture from the filling to the pastry crust leads to a loss of texture. Alternatively, migration brings together substrates for chemical reactions, and it is the products of these reactions which influence product shelf-life. Pizza toppings containing unblanched green peppers may be susceptible to rancid off-flavours as a result of the enzyme lipoxygenase in the green peppers coming into contact with fatty acid substrates in the pizza base or in the cheese The way in which multi-component products are assembled can have major effects on the microbiological safety of the product. If components which are stable due to low Aw or low pH are placed in contact with components which are inherently unstable due to a high Aw or high pH, there will be a layer formed between the two components where the Aw and ph is now suitable for microbial growth. Any microorganisms in the stable component could grow in this layer igration or contact between components can be limited to extend shelf-life and needs to be considered during product development. Where migration and contact are detrimental to product quality, the use of edible films or packaging in eparate compartments could be considered 10.2.4 Processing Processing encompasses a wide range of treatments that may be given to food from simply chopping or washing, (e.g. ready-to-eat chilled salads), to hea processing, acidification, addition of preservatives, fermentation or salting Processing exerts a considerable effect on the microflora, chemical, biochemical and sensory properties of a food. In some cases, the purpose of food processing may be primarily intended to achieve the desired characteristics of the produc e.g. fermented salads, and can res In change reducing pH. In other cases, processing may be specifically selected to influence shelf-life limiting factors, e.g. heat processing to inactivate microorganisms and deleterious food enzymes. If a process is used to achieve product shelf-life, there should be an awareness that small changes in the processing conditions can have a marked effect on shelf-life. Any stages of product manufacture which are essential for the safe shelf-life of the product should be identified during a hazard analysis and suitably controlled during routine production
permitted organic acids. Again, it is crucial that where pH is used as a key preservative factor, the pH of each batch of product should be monitored to ensure that the target level is achieved. 10.2.3 Assembly of product In complex and multi-component products, contact between components may result in migration of flavourings, colourings, moisture or oil from one component to another. This may limit shelf-life due to quality changes, e.g. in multi-layered trifles where the visual appearance is impaired by the migration of colouring components from one layer to another, and in fruit pies where migration of moisture from the filling to the pastry crust leads to a loss of texture. Alternatively, migration brings together substrates for chemical reactions, and it is the products of these reactions which influence product shelf-life. Pizza toppings containing unblanched green peppers may be susceptible to rancid off-flavours as a result of the enzyme lipoxygenase in the green peppers coming into contact with fatty acid substrates in the pizza base or in the cheese. The way in which multi-component products are assembled can have major effects on the microbiological safety of the product. If components which are stable due to low Aw or low pH are placed in contact with components which are inherently unstable due to a high Aw or high pH, there will be a layer formed between the two components where the Aw and pH is now suitable for microbial growth. Any microorganisms in the stable component could grow in this layer. Migration or contact between components can be limited to extend shelf-life and needs to be considered during product development. Where migration and contact are detrimental to product quality, the use of edible films or packaging in separate compartments could be considered. 10.2.4 Processing Processing encompasses a wide range of treatments that may be given to food from simply chopping or washing, (e.g. ready-to-eat chilled salads), to heat processing, acidification, addition of preservatives, fermentation or salting. Processing exerts a considerable effect on the microflora, chemical, biochemical and sensory properties of a food. In some cases, the purpose of food processing may be primarily intended to achieve the desired characteristics of the product, e.g. fermented salads, and can result in changes that extend the shelf-life by reducing pH. In other cases, processing may be specifically selected to influence shelf-life limiting factors, e.g. heat processing to inactivate microorganisms and deleterious food enzymes. If a process is used to achieve product shelf-life, there should be an awareness that small changes in the processing conditions can have a marked effect on shelf-life. Any stages of product manufacture which are essential for the safe shelf-life of the product should be identified during a hazard analysis and suitably controlled during routine production. Shelf-life determination and challenge testing 263
64 Chilled foods 10. 2.5 Hygiene Poor hygienic control during preparation, processing and packaging can result in a high level of organisms being introduced into the product; for example, poor cleaning of meat slicing equipment results in an increase in the microbiological count. This may have adverse effects on the safety and quality of the product, which would affect shelf-life. The shelf-life for a particular product can only of variables that were included in th Consistent hygienic control during subsequent production runs is essential if product with the assigned shelf-life is to be produced(see Chapters 13 and 14) 10.2.6 Packaging Packaging prevents contamination by microorganisms, protects against physical damage and can be used to isolate the product from adverse environmental factors such as light, atmospheric oxygen or humidity. Packaging materials can be used to filter out light of specific wavelengths to prevent or reduce photocatalysed reactions that would result in oxidation or nutrient degradation Products sensitive to oxidation by atmospheric oxygen can be protected by selection of packaging materials with the appropriate barrier properties oxygen ingress and, similarly, selection of barrier properties with respect to moisture can be used to prevent the product from drying out or retain the humidity within the pack Modified atmosphere packaging extends the shelf-life of meats and vegetables either by directly affecting the critical quality factor(as in the case of fresh red meat, where the bright red colour is maintained by a high oxygen atmosphere), or by influencing the rate at which reactions leading to adverse quality changes proceed. In addition, active packaging, e.g. O2/CO2/H2O absorbers, or ethanol emitters may extend shelf-life(see Chapter 6) Where the atmosphere within the package is modified, i.e. is not the normal atmospheric composition, then the effects on microorganisms should be considered. Excluding oxygen from packs will prevent the normal growth of poilage organisms of air-packed chilled foods, i.e. Pseudomonas spi Therefore, foods may become unsafe due to growth of anaerobic pathogens such as C. botulinum(Anon. 1992), but these products may appear to be organoleptically stable(Betts 1996) 10.2.7 Storage and distribution The conditions applied to the final product during storage and distribution can ave a marked effect on shelf-life. Temperature, lighting and humidity influence which microorganisms grow, which biochemical reactions and physical changes take place and the rate they occur. To make an assessment of the shelf-life of the final product, the conditions that the product is likely to encounter and the effects that they will have on the product need to be known or determined Limited numbers of time-temperature surveys of chilled products during storage
10.2.5 Hygiene Poor hygienic control during preparation, processing and packaging can result in a high level of organisms being introduced into the product; for example, poor cleaning of meat slicing equipment results in an increase in the microbiological count. This may have adverse effects on the safety and quality of the product, which would affect shelf-life. The shelf-life for a particular product can only reflect the range of variables that were included in the testing procedures. Consistent hygienic control during subsequent production runs is essential if product with the assigned shelf-life is to be produced (see Chapters 13 and 14). 10.2.6 Packaging Packaging prevents contamination by microorganisms, protects against physical damage and can be used to isolate the product from adverse environmental factors such as light, atmospheric oxygen or humidity. Packaging materials can be used to filter out light of specific wavelengths to prevent or reduce photocatalysed reactions that would result in oxidation or nutrient degradation. Products sensitive to oxidation by atmospheric oxygen can be protected by selection of packaging materials with the appropriate barrier properties to oxygen ingress and, similarly, selection of barrier properties with respect to moisture can be used to prevent the product from drying out or retain the humidity within the pack. Modified atmosphere packaging extends the shelf-life of meats and vegetables either by directly affecting the critical quality factor (as in the case of fresh red meat, where the bright red colour is maintained by a high oxygen atmosphere), or by influencing the rate at which reactions leading to adverse quality changes proceed. In addition, active packaging, e.g. O2/CO2/H2O absorbers, or ethanol emitters may extend shelf-life (see Chapter 6). Where the atmosphere within the package is modified, i.e. is not the normal atmospheric composition, then the effects on microorganisms should be considered. Excluding oxygen from packs will prevent the normal growth of spoilage organisms of air-packed chilled foods, i.e. Pseudomonas spp. Therefore, foods may become unsafe due to growth of anaerobic pathogens such as C. botulinum (Anon. 1992), but these products may appear to be organoleptically stable (Betts 1996). 10.2.7 Storage and distribution The conditions applied to the final product during storage and distribution can have a marked effect on shelf-life. Temperature, lighting and humidity influence which microorganisms grow, which biochemical reactions and physical changes take place and the rate they occur. To make an assessment of the shelf-life of the final product, the conditions that the product is likely to encounter and the effects that they will have on the product need to be known or determined. Limited numbers of time-temperature surveys of chilled products during storage, 264 Chilled foods
Shelf-life determination and challenge testing 265 transportation, retailing and handling in the home have been performed, some of which have been summarised by Bogh-Soresen and Olsson(1990) Currently, the UK Food Safety Temperature Regulations (Food Safety Temperature Control) Regulations 1995 SI No 2200)allow a maximum of 8C during distribution and retail display of chilled products. It is important that this is considered when the shelf-life of products is determined, as any assessments done at lower temperatures will be affected by use of a higher temperature(see Section 10.4). 10.2.8 Consumer handling Consumer handling of chilled products can affect the quality and the safety of the product. Factors such as the time taken to carry the product home, consumer perceptions of chilled foods and domestic storage conditions need to be taken into consideration when setting up the time and temperature regime to be used in storage trials. This is perhaps the part of the chill chain that is most variable and over which the manufacturer has least influence and control. A survey of consumer handling of chilled foods in the UK(Evans 1998)indicated that most consumers shopped at least once a week for quantities of chilled foods. In the majority of cases, transport to the home was by car or foot(83%), taking an average of 43 minutes to get food from the retail store into the home refrigerator The temperature of the foods generally ranged from 4-20oC. Domestic efrigerator temperatures were found to have an overall mean temperature of 6.C with a range of -l"C to +llC On average, only 30% of refrigerators were operating below 5C. Of the refrigerators included in the survey, 7.3%were running at average temperatures of greater than 9oC, though positional temperature differences, particularly in fridge-freezers and larder freezers, indicate this figure to be higher if product is stored in the top of these refriger ators. Evans(1998)has also provided additional data on consumer practices Whilst such information gives an indication of the temperatures and times that are likely to be needed in shelf-life trials to simulate consumer handling, there is still the decision to be made with respect to what is a reasonable worst case to use. If theworst case temperatures and holding times that have been recorded were used in shelf-life tests, few of the products currently in the market-place would achieve the target shelf-life. The manufacturer has to estimate where reasonable abuse ends and unreasonable' abuse begins Consumer handling of products may not be as intended or envisaged by the manufacturer. Many chilled products are purchased on the basis of the fresh image, but then frozen at home. Opening and partial use of vacuum or modified atmosphere packaged products invalidates the shelf-life information with respect to the remaining product. A survey of consumer perceptions of the shelf-life of chilled foods has indicated that whilst consumers believe that most chilled foods should be stored for two days or less, in reality the same householders were storing certain chilled foods for considerably longer periods of time(Evans et al
transportation, retailing and handling in the home have been performed, some of which have been summarised by Bøgh-Søresen and Olsson (1990). Currently, the UK Food Safety Temperature Regulations (Food Safety (Temperature Control) Regulations 1995 SI No. 2200) allow a maximum of 8ºC during distribution and retail display of chilled products. It is important that this is considered when the shelf-life of products is determined, as any assessments done at lower temperatures will be affected by use of a higher temperature (see Section 10.4). 10.2.8 Consumer handling Consumer handling of chilled products can affect the quality and the safety of the product. Factors such as the time taken to carry the product home, consumer perceptions of chilled foods and domestic storage conditions need to be taken into consideration when setting up the time and temperature regime to be used in storage trials. This is perhaps the part of the chill chain that is most variable and over which the manufacturer has least influence and control. A survey of consumer handling of chilled foods in the UK (Evans 1998) indicated that most consumers shopped at least once a week for quantities of chilled foods. In the majority of cases, transport to the home was by car or foot (83%), taking an average of 43 minutes to get food from the retail store into the home refrigerator. The temperature of the foods generally ranged from 4–20ºC. Domestic refrigerator temperatures were found to have an overall mean temperature of 6ºC with a range of 1ºC to +11ºC. On average, only 30% of refrigerators were operating below 5ºC. Of the refrigerators included in the survey, 7.3% were running at average temperatures of greater than 9ºC, though positional temperature differences, particularly in fridge-freezers and larder freezers, indicate this figure to be higher if product is stored in the top of these refrigerators. Evans (1998) has also provided additional data on consumer practices. Whilst such information gives an indication of the temperatures and times that are likely to be needed in shelf-life trials to simulate consumer handling, there is still the decision to be made with respect to what is a reasonable worst case to use. If the ‘worst case’ temperatures and holding times that have been recorded were used in shelf-life tests, few of the products currently in the market-place would achieve the target shelf-life. The manufacturer has to estimate where ‘reasonable’ abuse ends and ‘unreasonable’ abuse begins. Consumer handling of products may not be as intended or envisaged by the manufacturer. Many chilled products are purchased on the basis of the ‘fresh image’, but then frozen at home. Opening and partial use of vacuum or modified atmosphere packaged products invalidates the shelf-life information with respect to the remaining product. A survey of consumer perceptions of the shelf-life of chilled foods has indicated that whilst consumers believe that most chilled foods should be stored for two days or less, in reality the same householders were storing certain chilled foods for considerably longer periods of time (Evans et al. 1991). Shelf-life determination and challenge testing 265
266 Chilled foods 10.2.9 Legislative requirements Legislative responsibilities for the chilled food manufacturer are described fully in Chapter 2. The main legislative restrictions for chilled foods in relation to shelf-life are the distribution and storage temperatures which can be used. In the UK, chilled foods can be stored at temperatures up to 8C and this should be taken into consideration when defining the shelf-life during product develop- ment. It may be possible that a product would be able to be stored at lower temperatures throughout much of its shelf-life during retail distribution and storage,however, with the maximum temperature specification of 8%C, it is possible that on occasion a batch of the product would be stored at 8C throughout its shelf-life and therefore it should be able to withstand this time and mperature regime whilst maintaining product quality and safety In addition, if the chilled product is to be exported to other EU countries, there will be different chilled temperature restrictions. These will also need to be considered during product development. There are many different requirements for chilled products throughout the EU and a working document, first draft of proposal for a European parliament and council regulation on the hygiene of foodstuffs, is being circulated which would harmonise temperature regulations throughout the EU(Anon. 1997) With respect to MAP chilled foods, there are guidelines whic shelf-life of these products to ten days or less at chill temperatures of <8C, unless specific controlling factors are in place to minimise the potential for growth of psychrotrophic C. botulinum(Anon. 1992, Betts 1996) Any deviations from these guidelines should be made only after scientific evidence that the alternative preservation systems in the products will prevent the growth of, or toxin production by, C. botulinum 10.2.10 Effects of intrinsic/extrinsic factors The factors discussed above, namely the type and source of ingredients and the subsequent processing and packaging, will influence the types and levels of microorganisms that will be present, and the chemical and biochemical reactions that can occur, in the final product. The ability of organisms to grow or cause problems, or for chemical reactions to proceed in the final product, will be dependent on the properties of the final product, i.e. pH, Aw(known as intrinsic factors), and on the external factors that the final product encounters, such as temperature(known as extrinsic factors). Intrinsic factors include water activity(Aw)(available water) · pH/total acidity type of acid preservatives, including salt and spices nutrients natural microflora redox potential(Eh)
10.2.9 Legislative requirements Legislative responsibilities for the chilled food manufacturer are described fully in Chapter 2. The main legislative restrictions for chilled foods in relation to shelf-life are the distribution and storage temperatures which can be used. In the UK, chilled foods can be stored at temperatures up to 8ºC and this should be taken into consideration when defining the shelf-life during product development. It may be possible that a product would be able to be stored at lower temperatures throughout much of its shelf-life during retail distribution and storage, however, with the maximum temperature specification of 8ºC, it is possible that on occasion a batch of the product would be stored at 8ºC throughout its shelf-life and therefore it should be able to withstand this time and temperature regime whilst maintaining product quality and safety. In addition, if the chilled product is to be exported to other EU countries, there will be different chilled temperature restrictions. These will also need to be considered during product development. There are many different requirements for chilled products throughout the EU and a working document, first draft of a proposal for a European parliament and council regulation on the hygiene of foodstuffs, is being circulated which would harmonise temperature regulations throughout the EU (Anon. 1997). With respect to MAP chilled foods, there are guidelines which restrict the shelf-life of these products to ten days or less at chill temperatures of 8ºC, unless specific controlling factors are in place to minimise the potential for growth of psychrotrophic C. botulinum (Anon. 1992, Betts 1996). Any deviations from these guidelines should be made only after scientific evidence that the alternative preservation systems in the products will prevent the growth of, or toxin production by, C. botulinum. 10.2.10 Effects of intrinsic/extrinsic factors The factors discussed above, namely the type and source of ingredients and the subsequent processing and packaging, will influence the types and levels of microorganisms that will be present, and the chemical and biochemical reactions that can occur, in the final product. The ability of organisms to grow or cause problems, or for chemical reactions to proceed in the final product, will be dependent on the properties of the final product, i.e. pH, Aw (known as intrinsic factors), and on the external factors that the final product encounters, such as temperature (known as extrinsic factors). Intrinsic factors include: • water activity (Aw) (available water) • pH/total acidity • type of acid • preservatives, including salt and spices • nutrients • natural microflora • redox potential (Eh) 266 Chilled foods
Shelf-life determination and challenge testing 267 · available oxygen natural biochemistry (enzymes, chemical reactants) Extrinsic factors include heat treatment (processing, cooking or reheating of the food prior to adspace gas composition temperature throughout storage and distribution lative humidity(Rh) Table 10. 1 gives examples of minimum growth conditions for pathogenic and spoilage organisms of concern to chilled foods. It must be stressed that such Table 10. 1 Minimum growth conditions for microorganisms which may be associated with chilled food Type of microorganism Minimum pH Minimum Aw Anaerobic Minimum for growth for growth gro growth temp °C) Staphylococcus aureus (4.5 for toxin)(0.90 for toxin (10 for toxin 0.91 (psychrotrophic) Clostridium botulinum proteolytic A, B, F Non-proteolytic B, E, F Escherichia coli Vibrio parahaemolyticus Yersinia enterocolitica 95 poilage organisms a) 5.5 Enterobacter aerogenes 3.8 Microcode 5.6 9 ssos0 <2.0 0.6 44- Notes: The table lists various species and indicates approximate growth and survival limits with the arious factors acting alone. Interactions between factors are likely to considerably alter these values For example, in vacuum pack. mperatures are for growth in typical neutral pH, high water activity, chilled Anon.1997. aken from Brown 1991
• available oxygen • natural biochemistry (enzymes, chemical reactants). Extrinsic factors include: • heat treatment (processing, cooking or reheating of the food prior to consumption) • headspace gas composition • temperature throughout storage and distribution • relative humidity (Rh) • light (UV and IR). Table 10.1 gives examples of minimum growth conditions for pathogenic and spoilage organisms of concern to chilled foods. It must be stressed that such Table 10.1 Minimum growth conditions for microorganisms which may be associated with chilled food Type of microorganism Minimum pH Minimum Aw Anaerobic Minimum for growth for growth growtha growth tempb (ºC) Pathogens (c) Salmonella 4.0 0.94 Yes 7 Staphylococcus aureus 4.0 0.83 Yes 6 (4.5 for toxin) (0.90 for toxin) (10 for toxin) Bacillus cereus 4.4 0.91 Yes 4 (psychrotrophic) Clostridium botulinum 4.6 0.93 Yes 10 proteolytic A, B, F Non-proteolytic B, E, F 5.0 0.97 Yes 3.3 Listeria monocytogenes 4.3 0.92 Yes 0 Escherichia coli 4.4 0.95 Yes 7.0 Vibrio parahaemolyticus 4.8 0.94 Yes 5 Yersinia enterocolitica 4.2 0.96 Yes 2 E. coli O157 4.5 0.95 Yes 6.5 Spoilage organisms (d) Pseudomonas 5.5 0.97 No 0 Enterobacter aerogenes 4.4 0.94 Yes 2 Lactic acid bacteria 3.8 0.94 Yes 4 Micrococci 5.6 0.9 No 4 Yeasts 1–5 0.8 Yes 5 Moulds 2.0 0.6 No 0 Notes: The table lists various species and indicates approximate growth and survival limits with the various factors acting alone. Interactions between factors are likely to considerably alter these values. a For example, in vacuum pack. b Minimum growth temperatures are for growth in typical neutral pH, high water activity, chilled foods. c Data for pathogens taken from Anon. 1997. d Data for spoilage organisms taken from Brown 1991. Shelf-life determination and challenge testing 267
