Raw material selection: dairy ingredients R. Early, Harper Adams University College 2.1 Introduction As the first food of infant mammals, milk provides an important source of fat, protein, carbohydrate, vitamins and minerals, essential to the development of tissue and bone, and the growth of young. Milk is also a substance used beneficially by humans of all ages, both as a food in its own right and as a material for the production of milk products and milk-based food ingredients The composition of milk varies significantly among species and bovine milk is most widely used world-wide for consumption as milk and for conversion into other products. Ovine and caprine milks are not without significance particularly within the realms of cheesemaking The relevance of milk to chilled foods is found in the milk products which are chilled foods in their own right and in the range of milk-based ingredients used in the manufacture of chilled foods. Many milk products such as cheese and yogurt have a long heritage. In contrast, most milk-based ingredients are relatively recent innovations. Their existence is linked to the development of the modern food market place and the presence of convenience foods and ready meals, many of which are chilled foods 2.2 Milk Water is the main component of milk and most manufacturing techniques employed by the dairy industry concern methods of water control. with a water lanie Hooper(Dairy Crest Ingredients)and Steve Timms( Fayrfield Foodtec Ltd)for tion on milk-based ingredients and their uses, and to David Jefferies(Oscar Meyer ng advice on the use of dairy products in chilled ready meals
2.1 Introduction As the first food of infant mammals, milk provides an important source of fat, protein, carbohydrate, vitamins and minerals, essential to the development of tissue and bone, and the growth of young. Milk is also a substance used beneficially by humans of all ages, both as a food in its own right and as a material for the production of milk products and milk-based food ingredients. The composition of milk varies significantly among species and bovine milk is most widely used world-wide for consumption as milk and for conversion into other products. Ovine and caprine milks are not without significance, particularly within the realms of cheesemaking. The relevance of milk to chilled foods is found in the milk products which are chilled foods in their own right and in the range of milk-based ingredients used in the manufacture of chilled foods. Many milk products such as cheese and yogurt have a long heritage. In contrast, most milk-based ingredients are relatively recent innovations. Their existence is linked to the development of the modern food market place and the presence of convenience foods and ready meals, many of which are chilled foods. 2.2 Milk composition Water is the main component of milk and most manufacturing techniques employed by the dairy industry concern methods of water control. With a water 2 Raw material selection: dairy ingredients R. Early, Harper Adams University College Thanks go to Melanie Hooper (Dairy Crest Ingredients) and Steve Timms (Fayrfield Foodtec Ltd) for providing information on milk-based ingredients and their uses, and to David Jefferies (Oscar Meyer Limited) for giving advice on the use of dairy products in chilled ready meals
38 Chilled foods Table 2.1 The major nutrients(A)and major components(B)contained in cows'whole milk, and major components on a dry basis(C) Fat(g) casein 37.9 0.75 Calcium(mg) Sodium(mg) 563 Thiamin(mg) Niacin equivalent(mg) Vitamin B12(ug) 0.41 Energy( y) Vitamin D( from Fox, P F. and McSweeney, P.L. H. 1998. Dairy chemistry Blackie Academic and Professional. London: and MAFF. I Office. London content of typically 87.5% cows'milk has a high water activity(aw)of about aw 0.993( Fox and McSweeney 1998)and is prone to rapid microbial spoilage, unless adequately heat treated, packaged and stored. The manufacture of many milk products involves the removal of water, either partially or significantly, to help generate the characteristics of products and preserve the nutritional value of he milk solids that constitute them. The nutrients in whole milk are given in Table 2. 1 along with the proportions of the major milk solids components: being ilkfat, lactose (the milk sugar), the milk proteins(casein and the whey proteins), and the minerals or ash. 2.3 Functional approach The different components of the milk solids exhibit what are termed 'functional properties, meaning that they fulfil specific roles within food systems, e.g emulsification, gelation and water binding. Disagreement exists about the logic of the term"functional properties, as all foods and food materials are functional (Anon. 1995a). With the development of so-called functional foods' or foods with health-giving/enhancing properties, the word functional when applied to food seems destined to create confusion. This said, the dairy industry and food
content of typically 87.5% cows’ milk has a high water activity (aw) of about aw 0.993 (Fox and McSweeney 1998) and is prone to rapid microbial spoilage, unless adequately heat treated, packaged and stored. The manufacture of many milk products involves the removal of water, either partially or significantly, to help generate the characteristics of products and preserve the nutritional value of the milk solids that constitute them. The nutrients in whole milk are given in Table 2.1 along with the proportions of the major milk solids components: being milkfat, lactose (the milk sugar), the milk proteins (casein and the whey proteins), and the minerals or ash. 2.3 Functional approach The different components of the milk solids exhibit what are termed ‘functional properties’, meaning that they fulfil specific roles within food systems, e.g. emulsification, gelation and water binding. Disagreement exists about the logic of the term ‘functional properties’, as all foods and food materials are functional (Anon. 1995a). With the development of so-called ‘functional foods’ or foods with health-giving/enhancing properties, the word functional when applied to food seems destined to create confusion. This said, the dairy industry and food Table 2.1 The major nutrients (A) and major components (B) contained in cows’ whole milk, and major components on a dry basis (C) Component A B C per 100 ml % % Fat (g) 4.01 3.9 30.8 Protein (g) 3.29 3.2 25.3 casein 2.6 20.6 whey proteins 0.6 4.7 Lactose (g) 4.95 4.8 37.9 Ash 0.75 5.9 Calcium (mg) 119 Iron (mg) 0.05 Sodium (mg) 56.7 Vitamin A (retinol equivalent) (mg) 57.2 Thiamin (mg) 0.03 Riboflavin (mg) 0.17 Niacin equivalent (mg) 0.83 Vitamin B12 (g) 0.41 Vitamin C (mg) 1.06 Vitamin D (g) 0.03 Energy (kJ) 283.6 (kcal) 67.8 Source: Adapted from Fox, P.F. and McSweeney, P.L.H. 1998. Dairy chemistry and biochemistry. Blackie Academic and Professional, London; and MAFF. 1995. Manual of nutrition. Stationery Office, London. 38 Chilled foods
Raw material selection: dairy ingredien Table 2.2 Functional properties of the major milk components Whey proteins Milkfat Lactose Fat emulsification Foaming Air incorporation Browning Gelation Anti-staling Free-flow agent recipitation by Ca Heat denaturation Creaming Humectant recipitation by Solubility at any pH Flavour carrier Low sweetening power chymosin (27-39% of sucose) Soluble at pH>6 Gloss uppresses sucrose crystallisation Water binding Layering Shortening ource: Adapted from Early, R 1998b. Milk concentrates and milk powders. In R. Early. (ed 998b. Second edition. The Technology of dairy products. Blackie Academic and Professional manufacturers using milk-based ingredients recognise the functional propertie of milks components and dairy products and they are selected and modified ccordingly for specific applications(Kirkpatrick and Fenwick 1987). The properties of dairy products which are foods in their own right, e.g.cream butter, cheese, yogurt, are significantly a consequence of the functional properties of the milk solids of which they are comprised. The composition and proportion of milk solids varies according to the product concerned and gives rise to the characteristics that typify the product. On the other hand, the formulations of many milk-based food ingredients are regulated to maximise pecific functional properties, or concentrate the functional value of certain milk components to benefit particular applications. The functional properties of the major components of milk are given in Table 2.2 2.4 Sensory properties The sensory properties of milk and milk products are a consequence of composition, which may be manifested in ways that relate to notions of quality The components of milk products, a consequence of the chemistry of milk, give rise to the physical properties of products and both chemical and physical properties influence consumer sensory perceptions. The chemical and physical properties of milk products are influenced by raw milk quality, manufacturing processes, storage conditions and associated process controls. Manufacturers aim to assure the quality of products, and, hence, maxi acceptability. However, the actions of microbes and chemical reactions such as oxidation may(and in time usually do) adversely affect the chemical and physical properties of products, leading to the loss of quality and a reduction in consumer acceptability. Consumers judge the sensory properties of milk
manufacturers using milk-based ingredients recognise the functional properties of milk’s components and dairy products and they are selected and modified accordingly for specific applications (Kirkpatrick and Fenwick 1987). The properties of dairy products which are foods in their own right, e.g. cream, butter, cheese, yogurt, are significantly a consequence of the functional properties of the milk solids of which they are comprised. The composition and proportion of milk solids varies according to the product concerned and gives rise to the characteristics that typify the product. On the other hand, the formulations of many milk-based food ingredients are regulated to maximise specific functional properties, or concentrate the functional value of certain milk components to benefit particular applications. The functional properties of the major components of milk are given in Table 2.2. 2.4 Sensory properties The sensory properties of milk and milk products are a consequence of composition, which may be manifested in ways that relate to notions of quality. The components of milk products, a consequence of the chemistry of milk, give rise to the physical properties of products and both chemical and physical properties influence consumer sensory perceptions. The chemical and physical properties of milk products are influenced by raw milk quality, manufacturing processes, storage conditions and associated process controls. Manufacturers aim to assure the quality of products, and, hence, maximise consumer acceptability. However, the actions of microbes and chemical reactions such as oxidation may (and in time usually do) adversely affect the chemical and physical properties of products, leading to the loss of quality and a reduction in consumer acceptability. Consumers judge the sensory properties of milk Table 2.2 Functional properties of the major milk components Casein Whey proteins Milkfat Lactose Fat emulsification Foaming Air incorporation Browning Foaming Gelation Anti-staling Free-flow agent Precipitation by Ca2+ Heat denaturation Creaming Humectant Precipitation by Solubility at any pH Flavour carrier Low sweetening power chymosin (27–39% of sucose) Soluble at pH 6 Gloss Suppresses sucrose crystallisation Water binding Layering Shortening Unique flavour Source: Adapted from Early, R. 1998b. Milk concentrates and milk powders. In R. Early. (ed.). 1998b. Second edition. The Technology of dairy products. Blackie Academic and Professional, London. Raw material selection: dairy ingredients 39
40 Chilled foods products and products incorporating milk based ingredients by sight, smell, taste and feel(texture). Product attributes which stimulate a particular sense, or senses, are often regarded as the characterising attributes of a product. For example, blue Stilton cheese is judged by appearance, aroma, texture and flavour, whereas the flavour of butter is of critical importance to its acceptability and yogurt is judged principally by its clean, sharp acid flavour and smoothness on the palate The whiteness of liquid milk is caused by the light scattering of milkfat globules, colloidal calcium caseinate and colloidal calcium phosphate (Johnson 1974)though the presence of carotenes is important to the yellow colour of milkfat. The flavour of milk is a consequence of the major milk constituents as well as minor components. The milkfat globule, comprising lipids, phospho- lipids and caseins, is significant in creating the characteristic flavour of milk The flavour of butter is a composite of the milkfat and serum(McDowall 1953) though its flavour is attributed to the relatively high proportions of short chain fatty acids that constitute butter triacylglycerols. Unfermented milk products are often described as having characteristic, clean, milky flavours, whereas the flavours of fermented products are mainly attributed to the conversion of lactose to lactic acid. The use of homofermentative bacteria gives rise to a clean, lactic taste, while heterofermentative bacteria produce aldehydes, ketones and alcohol in addition to lactic acid, causing a wide variety of flavour notes. The aromas of milk products are due mainly to short chain fatty acids with fewer than 12 carbon atoms, conventionally known as volatile fatty acids' Berk 1986) Butyric acid, a C4 fatty acid with a melting point of-79C, constitutes 5-6% of milkfat and is significant in creating the unique flavour and aroma of butter The flavours and aromas of milk products may be influenced intentionally unintentionally (on the part of man) by microbial activity. The biochemical activity of bacteria and, in some instances, the action of moulds and yeasts gives rise to the wide variety of flavours and aromas of cheese. This is evidenced, for example, by ripe Camembert, the smell and taste of which arises partly from the hydrolysis of triacylglycerols and the liberation of short chain fatty acids, as well as the breakdown of proteins to ammonia and other products. The textures of milk products are influenced by moisture and fat contents, as well as factors such as pH where, as in yogurt, acidification to the isoelectric point of casein causes the formation of a gel. In the case of cheese the lower the moisture content the harder the product. Fat content and chemistry influence directly texture perceptions and'mouth-feel, because the fatty acid profile of milkfat is subject to seasonal variation, with summer milkfat generally softer and yellower than winter milkfat. This is commonly experienced when butter is used as a spread, but the effect can also be important with other products though it may not be so obvious. There is not the space here to review fully the factors affecting the sensory perception of milk products, and reference to standard dairy chemistry texts is advised. a detailed consideration of the sensory judging of dairy products is made by Bodyfelt et al.(1988)
products and products incorporating milk based ingredients by sight, smell, taste and feel (texture). Product attributes which stimulate a particular sense, or senses, are often regarded as the characterising attributes of a product. For example, blue Stilton cheese is judged by appearance, aroma, texture and flavour, whereas the flavour of butter is of critical importance to its acceptability and yogurt is judged principally by its clean, sharp acid flavour and smoothness on the palate. The whiteness of liquid milk is caused by the light scattering of milkfat globules, colloidal calcium caseinate and colloidal calcium phosphate (Johnson 1974) though the presence of carotenes is important to the yellow colour of milkfat. The flavour of milk is a consequence of the major milk constituents as well as minor components. The milkfat globule, comprising lipids, phospholipids and caseins, is significant in creating the characteristic flavour of milk. The flavour of butter is a composite of the milkfat and serum (McDowall 1953), though its flavour is attributed to the relatively high proportions of short chain fatty acids that constitute butter triacylglycerols. Unfermented milk products are often described as having characteristic, clean, milky flavours, whereas the flavours of fermented products are mainly attributed to the conversion of lactose to lactic acid. The use of homofermentative bacteria gives rise to a clean, lactic taste, while heterofermentative bacteria produce aldehydes, ketones and alcohol in addition to lactic acid, causing a wide variety of flavour notes. The aromas of milk products are due mainly to short chain fatty acids with fewer than 12 carbon atoms, conventionally known as ‘volatile fatty acids’ (Berk 1986). Butyric acid, a C4 fatty acid with a melting point of 7.9ºC, constitutes 5–6% of milkfat and is significant in creating the unique flavour and aroma of butter. The flavours and aromas of milk products may be influenced intentionally or unintentionally (on the part of man) by microbial activity. The biochemical activity of bacteria and, in some instances, the action of moulds and yeasts gives rise to the wide variety of flavours and aromas of cheese. This is evidenced, for example, by ripe Camembert, the smell and taste of which arises partly from the hydrolysis of triacylglycerols and the liberation of short chain fatty acids, as well as the breakdown of proteins to ammonia and other products. The textures of milk products are influenced by moisture and fat contents, as well as factors such as pH where, as in yogurt, acidification to the isoelectric point of casein causes the formation of a gel. In the case of cheese the lower the moisture content the harder the product. Fat content and chemistry influence directly texture perceptions and ‘mouth-feel’, because the fatty acid profile of milkfat is subject to seasonal variation, with summer milkfat generally softer and yellower than winter milkfat. This is commonly experienced when butter is used as a spread, but the effect can also be important with other products though it may not be so obvious. There is not the space here to review fully the factors affecting the sensory perception of milk products, and reference to standard dairy chemistry texts is advised. A detailed consideration of the sensory judging of dairy products is made by Bodyfelt et al. (1988). 40 Chilled foods
Raw material selection: dairy ingredients 41 2.5 Microbiological criteria for milk products Dairy products manufacturers provide microbiological criteria within their product specifications. Although manufacturers may have derived their own product standards, the microbiological criteria for dairy products are generally accepted, as defined by IFST (1999). Table 2.3 lists the IFST recommendations for milk, cream and dairy products, while Table 2. 4 addresses requirements for milk powders. The indicators and spoilage organisms for milk cream, dairy products and milk powders are given in Table 2.5 2.6 Chilled dairy products and milk-based ingredients used in chiled foods The dairy industry makes many dairy products which exist as chilled foods in their own right and numerous milk-based ingredients which find application in chilled foods. It is not possible to consider all chilled dairy products and milk-based ngredients in detail here, though the principal products are briefly reviewed 2.6.1 Pasteurised milk Pasteurised milk is consumed widely as market milk. The fat contents of products are legally defined in the UK and descriptions are given in Table 2.6. It is also Table 2.3 Microbiological criteria for milk, cream and dairy products Organism GMP Maximum ND in 25 ml or g ND in 25 ml or g allogenes ND in 25 ml or g 0 per g 0 per g E. coli o157 ND in 25 ml or g ND in 25 ml or g Source: IFST. 1999. Development and use of microbiological criteria for foods. Institute of Food Raw milk-based products Table 2.4 Microbiological criteria for powders Organism GMP Maximum ND in 25 ml or g ND in 25 ml or g S. aureus <20 per g er g B. cereus <10- per g l0 per g Source: IFST. 1999. Development and use of microbiological criteria for foods. Institute of Food Science and Technology, London
2.5 Microbiological criteria for milk products Dairy products manufacturers provide microbiological criteria within their product specifications. Although manufacturers may have derived their own product standards, the microbiological criteria for some dairy products are generally accepted, as defined by IFST (1999). Table 2.3 lists the IFST recommendations for milk, cream and dairy products, while Table 2.4 addresses requirements for milk powders. The indicators and spoilage organisms for milk, cream, dairy products and milk powders are given in Table 2.5. 2.6 Chilled dairy products and milk-based ingredients used in chilled foods The dairy industry makes many dairy products which exist as chilled foods in their own right and numerous milk-based ingredients which find application in chilled foods. It is not possible to consider all chilled dairy products and milk-based ingredients in detail here, though the principal products are briefly reviewed. 2.6.1 Pasteurised milk Pasteurised milk is consumed widely as market milk. The fat contents of products are legally defined in the UK and descriptions are given in Table 2.6. It is also Table 2.3 Microbiological criteria for milk, cream and dairy products Organism GMP Maximum Salmonella spp. ND in 25 ml or g ND in 25 ml or g L. monocytogenes ND in 25 ml or g 103 per g S. aureus 20 per g 103 per g E. coli O157* ND in 25 ml or g ND in 25 ml or g Source: IFST. 1999. Development and use of microbiological criteria for foods. Institute of Food Science and Technology, London. * Raw milk-based products. Table 2.4 Microbiological criteria for powders Organism GMP Maximum Salmonella spp. ND in 25 ml or g ND in 25 ml or g S. aureus 20 per g 103 per g B. cereus 102 per g 104 per g C. perfringens 102 per g 103 per g Source: IFST. 1999. Development and use of microbiological criteria for foods. Institute of Food Science and Technology, London. Raw material selection: dairy ingredients 41