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