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
42 Chilled foods Table 2. 5 Indicators and spoilage organisms for milk, cream, dairy products and milk roduct Organi Maximum Soft cheese(raw milk) 102 104 Processed che < Anaerobic plate count <10 Other cheeses Coliforms Enterobacteriaceae E. coli <10 Pasteurised milk Coliforms 1 Enterobacteriaceae 000 Coliforms milk produc Enterobacteriaceae E. coli <<<≤ 0000 000 Yeasts(yogurt) 0° Milk powder Aerobic plate count <10 Product dependent E. coli 103 Source: IFST Development and use of microbiological criteria for foods. Institute of Food Science and g, London Table 2.6 Descriptions of pasteurised market milks in the UK Milk type Description Natural whole milk Milk with nothing added or removed Homogenised whole milk Homogenised milk with nothing added or removed Standard ised whole milk Milk standardised to a minimum fat content of 3.5% Standardised, homogenised whole milk Milk standardised to a minimum fat content of 3. 5% and homogenised Milk with a fat content of between 1.5 and 1. 8% Skimmed milk Milk with a fat content of less than 0.1% used in the manufacture of chilled products, particularly as a base for the production of sauces, such as bechamel, cheese and white sauces used in chilled ready-meals. In the production of pasteurised milk, raw milk is centrifugally clarified to remove insoluble particles and somatic cells. In accordance with UK dairy regulations(Anon. 1995b)it is then heat treated at not less than 711C for not less than 15 seconds. A negative phosphatase test confirms adequate heat treatment and a positive peroxidase test confirms the milk has not been overheated (taken above 80oC). Semi-skimmed and skimmed milks are produced by centrifugally separating cream using a hermetic separator, as described by
used in the manufacture of chilled products, particularly as a base for the production of sauces, such as bechamel, cheese and white sauces used in chilled ready-meals. In the production of pasteurised milk, raw milk is centrifugally clarified to remove insoluble particles and somatic cells. In accordance with UK dairy regulations (Anon. 1995b) it is then heat treated at not less than 71.1ºC for not less than 15 seconds. A negative phosphatase test confirms adequate heat treatment and a positive peroxidase test confirms the milk has not been overheated (taken above 80ºC). Semi-skimmed and skimmed milks are produced by centrifugally separating cream using a hermetic separator, as described by Table 2.5 Indicators and spoilage organisms for milk, cream, dairy products and milk powders Product Organism GMP Maximum Soft cheese (raw milk) E. coli 102 104 Processed cheese Aerobic plate count 102 105 Anaerobic plate count 10 105 Other cheeses Coliforms 102 104 Enterobacteriaceae 102 104 E. coli 10 103 Pasteurised milk Coliforms 1 102 and cream Enterobacteriaceae 1 102 Other pasteurised Coliforms 10 104 milk products Enterobacteriaceae 10 104 E. coli 10 103 Yeasts (yogurt) 10 106 Milk powders Aerobic plate count 103 Product dependent Enterobacteriaceae 102 104 E. coli 10 103 Source: IFST. 1999. Development and use of microbiological criteria for foods. Institute of Food Science and Technology, London. Table 2.6 Descriptions of pasteurised market milks in the UK Milk type Description Natural whole milk Milk with nothing added or removed Homogenised whole milk Homogenised milk with nothing added or removed Standardised whole milk Milk standardised to a minimum fat content of 3.5% Standardised, homogenised whole milk Milk standardised to a minimum fat content of 3.5% and homogenised Semi-skimmed milk Milk with a fat content of between 1.5 and 1.8% Skimmed milk Milk with a fat content of less than 0.1% 42 Chilled foods
Raw material selection: dairy ingredients 43 Early(1998a)and Brennan et al.(1990). High-pressure homogenisation(Early 998a, Brennan et al. 1990)is used to reduce the size of milkfat globules from as large as 20um down to 1-2um, thereby preventing the development of a cream layer, and the possible formation of a cream plug in glass bottles. Market milk is packaged in glass bottles, laminated paperboard cartons and plastic(high-density polyethylene) containers(Paine and Paine 1992) For industrial use pasteurised milk may be delivered by stainless-steel road tanker or in 1-tonne palletised containers(pallecons). Pasteurisation does not destroy all the microbes present in raw milk and pasteurised milk must be stored 8C to retard microbial growth. The spoilage of short shelf-life dairy products is usually due to microbial activity and post-pasteurisation contamina- tion with Gram negative psychrotrophic bacteria is often of significance(Mui 1996a). Frazier and Westhoff(1988)record the possible survival of heat- resistant lactic organisms (e. g, enterococci, Streptococcus thermophilus and lactobacilli) as well as spore-forming organisms of genuses Bacillus and Clostridium. Various quality defects are possible with pasteurised milk, including lactic souring, proteolysis (which is favoured by low-temperature example, to a protease produced by Pseudomonas flourescens, which survives pasteurisation even though the organism does not, and bitty cream caused by Bacillus cereus 2. 6.2 Cream Market cream is produced for domestic use with a range of minimum fat contents,as given in Table 2.7. In the manufacture of chilled products, cream finds application in soups, sauces and toppings. The fat content of cream for manufacturing use will be determined by various factors, e.g., whippability pumping, packaging/transport and storage limitations. Cream is an oil-in-water emulsion. The milkfat globules in unhomogenised cream range in diameter from 0. lum to 20um with an average of 3-4um. They are stabilised by the milkfat globule membrane which is comprised of phospholipids, lipoproteins, cerebrosides, proteins and other minor materials. The membrane has surface active, or surfactant properties. Most of the lipid in milkfat is triacylglycerols though small amounts of diacylglycerols and monoacylglycerols may be present Table 2.7 Minimum fat contents of market creams in the uK Cream or single cream Sterilised half cream Sterilised cream Whipping cream 35% Double cream Clotted cream 55%
Early (1998a) and Brennan et al. (1990). High-pressure homogenisation (Early 1998a, Brennan et al. 1990) is used to reduce the size of milkfat globules from as large as 20m down to 1–2m, thereby preventing the development of a cream layer, and the possible formation of a cream plug in glass bottles. Market milk is packaged in glass bottles, laminated paperboard cartons and plastic (high-density polyethylene) containers (Paine and Paine 1992). For industrial use pasteurised milk may be delivered by stainless-steel road tanker or in 1-tonne palletised containers (pallecons). Pasteurisation does not destroy all the microbes present in raw milk and pasteurised milk must be stored at 8ºC to retard microbial growth. The spoilage of short shelf-life dairy products is usually due to microbial activity and post-pasteurisation contamination with Gram negative psychrotrophic bacteria is often of significance (Muir 1996a). Frazier and Westhoff (1988) record the possible survival of heatresistant lactic organisms (e.g., enterococci, Streptococcus thermophilus and lactobacilli) as well as spore-forming organisms of genuses Bacillus and Clostridium. Various quality defects are possible with pasteurised milk, including lactic souring, proteolysis (which is favoured by low-temperature storage) due, for example, to a protease produced by Pseudomonas flourescens, which survives pasteurisation even though the organism does not, and bitty cream caused by Bacillus cereus. 2.6.2 Cream Market cream is produced for domestic use with a range of minimum fat contents, as given in Table 2.7. In the manufacture of chilled products, cream finds application in soups, sauces and toppings. The fat content of cream for manufacturing use will be determined by various factors, e.g., whippability, pumping, packaging/transport and storage limitations. Cream is an oil-in-water emulsion. The milkfat globules in unhomogenised cream range in diameter from 0.1m to 20m with an average of 3–4m. They are stabilised by the milkfat globule membrane which is comprised of phospholipids, lipoproteins, cerebrocides, proteins and other minor materials. The membrane has surface active, or surfactant properties. Most of the lipid in milkfat is triacylglycerols though small amounts of diacylglycerols and monoacylglycerols may be present. Table 2.7 Minimum fat contents of market creams in the UK Half cream 12% Cream or single cream 18% Sterilised half cream 12% Sterilised cream 23% Whipped cream 35% Whipping cream 35% Double cream 48% Clotted cream 55% Raw material selection: dairy ingredients 43
44 Chilled foods The fat soluble vitamins A, D, E and K are also present. Cream is separated from less than 72C for not less than 15 seconds (or equivale eur: hich are milk by centrifugal separation, nowadays using hermetic separators pable of producing product in excess of 70% fat. Cream is pas nd must be phosphatase negative and peroxidase positive. Half and single cream require high-pressure homogenisation to prevent phase separation and double cream may be homogenised at low pressure to increase viscosity. Whipping cream remains un-homogenised in order to assure its functionality. Clotted cream is a traditional product of the south-western counties of England. A number of methods of production exist, as described by Wilbey and Young(1989). In general they involve the heating of milk(from which clotted cream is skimmed) or 55% fat cream at moderately high temperatures (usually 75-95oC)to cause he cream to form a solid material. or 'clot' Market cream is commonly packaged in injection moulded polystyrene flat- topped round containers. Cloake and Ashton(1982)note that in the packaging of cream it is important to exclude light, which may promote auto-oxidation of the milkfat, and prevent tainting and the absorption of water. For manufacturing use, pasteurized cream is delivered in bulk stainless-steel road tankers or one-tonne pallecons. Both market and industrial pasteurised creams require chilled storage It-8oC. Rothwell et al. (1989)review a number of quality defects possible with cream. Poor microbiological quality can reduce shelf-life below 10-14 days and lipolysis, due to indigenous or microbial lipases, can result in rancidity. Physical defects concern poor viscosity, serum separation and poor whipping character 2. 6.3 Sour cream Sour cream is used both domestically and industrially, mainly in the preparation of sauces. It is produced by the lactic fermentation of single cream(not less than 18% fat)with organisms such as Lactococcus lactis subsp. lactis, Lactococcu lactis subsp. cremoris and Leuconostoc mesenteroides subsp. cremoris Fermentation causes the precipitation of casein at its isoelectric point(pH 4.6) and the formation of a set product. Market sour cream can be fermented in the pot but for industrial use agitation is necessary to produce a pumpable product which can be transported in 20kg lined buckets or one-tonne pallecons Pasteurisation of the cream prior to fermentation and the presence of lactic acid serve as preservation factors for the product, but chilled storage is also necessary and storage at-5oC will enable a 20-day shelf-life. Creme fraiche is a variant of sour cream made by culturing homogenised cream with a fat content of 18-35% with LAB such as Lactococcus lactis subsp. lactis, Lactococcus lactis subsp cremoris and Lactococcus lactis subsp. lactis var diacetylactis. Incubation at 30-32C for 5-6 hours gives a set product with a pH in the range 4.3-4.7. Stirred or set creme fraiche is supplied to the retail market to be eaten as a chilled dessert, though for industrial use in dips, sauces, desserts and ready meals, it is suppled in various forms including 20 kg pergals and one-tonne pallecons
The fat soluble vitamins A, D, E and K are also present. Cream is separated from milk by centrifugal separation, nowadays using hermetic separators which are capable of producing product in excess of 70% fat. Cream is pasteurised at not less than 72ºC for not less than 15 seconds (or equivalent) and must be phosphatase negative and peroxidase positive. Half and single cream require high-pressure homogenisation to prevent phase separation and double cream may be homogenised at low pressure to increase viscosity. Whipping cream remains un-homogenised in order to assure its functionality. Clotted cream is a traditional product of the south-western counties of England. A number of methods of production exist, as described by Wilbey and Young (1989). In general they involve the heating of milk (from which clotted cream is skimmed) or 55% fat cream at moderately high temperatures (usually 75–95ºC) to cause the cream to form a solid material, or ‘clot’. Market cream is commonly packaged in injection moulded polystyrene flattopped round containers. Cloake and Ashton (1982) note that in the packaging of cream it is important to exclude light, which may promote auto-oxidation of the milkfat, and prevent tainting and the absorption of water. For manufacturing use, pasteurized cream is delivered in bulk stainless-steel road tankers or one-tonne pallecons. Both market and industrial pasteurised creams require chilled storage at 8ºC. Rothwell et al. (1989) review a number of quality defects possible with cream. Poor microbiological quality can reduce shelf-life below 10–14 days and lipolysis, due to indigenous or microbial lipases, can result in rancidity. Physical defects concern poor viscosity, serum separation and poor whipping characteristics. 2.6.3 Sour cream Sour cream is used both domestically and industrially, mainly in the preparation of sauces. It is produced by the lactic fermentation of single cream (not less than 18% fat) with organisms such as Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris and Leuconostoc mesenteroides subsp. cremoris. Fermentation causes the precipitation of casein at its isoelectric point (pH 4.6) and the formation of a set product. Market sour cream can be fermented in the pot but for industrial use agitation is necessary to produce a pumpable product which can be transported in 20kg lined buckets or one-tonne pallecons. Pasteurisation of the cream prior to fermentation and the presence of lactic acid serve as preservation factors for the product, but chilled storage is also necessary and storage at 5ºC will enable a 20-day shelf-life. Cre`me fraıˆche is a variant of sour cream made by culturing homogenised cream with a fat content of 18–35% with LAB such as Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris and Lactococcus lactis subsp. lactis var diacetylactis. Incubation at 30–32ºC for 5–6 hours gives a set product with a pH in the range 4.3–4.7. Stirred or set cre`me fraıˆche is supplied to the retail market to be eaten as a chilled dessert, though for industrial use in dips, sauces, desserts and ready meals, it is suppled in various forms including 20 kg pergals and one-tonne pallecons. 44 Chilled foods
Raw material selection: dairy ingredients 45 2. 6.4 Butter The domestic use of butter is well known, but as an industrial ingredient used chilled foods manufacture it finds application in soups and sauces. It is a constituent of roux, along with flour, used in the preparation of sauces. Garlic butters and herb butters are used as garnishes in chilled ready meals and savour ishes, fillings for garlic bread and as toppings for cooked meats, e.g., steak, chicken and fish. The production of sweet-cream butter involves inducing phase inversion of the oil-in-water emulsion of cream to create a water-in-oil mulsion, or butter. A number of methods exist, as reviewed by Lane(1998).A commonly used method is the fritz and senn method, which involves rapidly cooling 42% fat cream to 8C and holding for 2 hours, then raising the temperature to 20-21C for 2 hours and cooling to 16C, or the churning temperature. The tempering process reduces the level of mixed fat crystals in the milkfat globules, ensuring that the high melting point triacylglycerols crystallise s pure fat crystals. This improves the spreadability of the butter, particularly when the milkfat has a low iodine value and it is hard Tempered cream is processed in a continuous buttermaker with four sections the churning cylinder beats the cream and causes the milkfat globule membrane to rupture, whereupon the fat crystals coalesce, the separation section drains buttermilk from the butter; the squeeze-drying section expels remaining buttermilk; the working section smooths the product. In the production of salted butter, salt is added in the working section. It dissolves in the aqueous, discontinuous phase of butter, and at a rate of 1. 6-2.0% results in a salt-in-water content of around 11%- sufficient to inhibit microbial activity. Microbial activity is not the sole cause of quality deterioration in butter. Evaporation causing surface colour faults and the development of oxidative rancidity causee by exposure to light are cited as possible problems(Richards 1982). Market butter is packed in tubs or foil which exclude light and possess high moisture arrier properties. Butter as an industrial ingredient is supplied in 25kg units packed in corrugated fibreboard cases lined with polyethylene film. Lactic butter may be made by the fermentation of cream with lactic acid bacteria, though the flavour of cultured butter may be replicated by the addition of certain pounds to sweet cream used for butter making(Nursten 1997). Garlic and herb butters are made by blending butter with the relevant ingredient and extruding to produce the required portion shape and size 2.6.5 Skimmed milk concentrate and skimmed milk powder Skimmed milk concentrate and skimmed milk powder find application in custards, toppings, soups, sauces, dips and desserts. Skimmed milk is the by roduct of cream separation and contains around 91% water. The skimmed milk solids are the milk proteins, lactose and minerals, with a trace of fat. Skimmed milk concentrates are made by vacuum evaporation and products of 35-40% total solids are common for bulk supply to food manufacturers. Higher solids levels give rise to problems of viscosity, age gelation and lactose crystallisation
2.6.4 Butter The domestic use of butter is well known, but as an industrial ingredient used in chilled foods manufacture it finds application in soups and sauces. It is a constituent of roux, along with flour, used in the preparation of sauces. Garlic butters and herb butters are used as garnishes in chilled ready meals and savoury dishes, fillings for garlic bread and as toppings for cooked meats, e.g., steak, chicken and fish. The production of sweet-cream butter involves inducing phase inversion of the oil-in-water emulsion of cream to create a water-in-oil emulsion, or butter. A number of methods exist, as reviewed by Lane (1998). A commonly used method is the Fritz and Senn method, which involves rapidly cooling 42% fat cream to 8ºC and holding for 2 hours, then raising the temperature to 20–21ºC for 2 hours and cooling to 16ºC, or the churning temperature. The tempering process reduces the level of mixed fat crystals in the milkfat globules, ensuring that the high melting point triacylglycerols crystallise as pure fat crystals. This improves the spreadability of the butter, particularly when the milkfat has a low iodine value and it is hard. Tempered cream is processed in a continuous buttermaker with four sections: the churning cylinder beats the cream and causes the milkfat globule membrane to rupture, whereupon the fat crystals coalesce; the separation section drains buttermilk from the butter; the squeeze-drying section expels remaining buttermilk; the working section smooths the product. In the production of salted butter, salt is added in the working section. It dissolves in the aqueous, or discontinuous phase of butter, and at a rate of 1.6–2.0% results in a salt-in-water content of around 11% – sufficient to inhibit microbial activity. Microbial activity is not the sole cause of quality deterioration in butter. Evaporation causing surface colour faults and the development of oxidative rancidity caused by exposure to light are cited as possible problems (Richards 1982). Market butter is packed in tubs or foil which exclude light and possess high moisture barrier properties. Butter as an industrial ingredient is supplied in 25kg units, packed in corrugated fibreboard cases lined with polyethylene film. Lactic butter may be made by the fermentation of cream with lactic acid bacteria, though the flavour of cultured butter may be replicated by the addition of certain compounds to sweet cream used for butter making (Nursten 1997). Garlic and herb butters are made by blending butter with the relevant ingredient and extruding to produce the required portion shape and size. 2.6.5 Skimmed milk concentrate and skimmed milk powder Skimmed milk concentrate and skimmed milk powder find application in custards, toppings, soups, sauces, dips and desserts. Skimmed milk is the byproduct of cream separation and contains around 91% water. The skimmed milk solids are the milk proteins, lactose and minerals, with a trace of fat. Skimmed milk concentrates are made by vacuum evaporation and products of 35–40% total solids are common for bulk supply to food manufacturers. Higher solids levels give rise to problems of viscosity, age gelation and lactose crystallisation. Raw material selection: dairy ingredients 45
6 Chilled foods Pasteurised skimmed milk concentrate requires chilled storage. Skimmed milk powder is made by spray drying skimmed milk concentrate from around 60% total solids. Milk powder quality is influenced by the solids content of the dryer feed. A high solids level gives a high bulk density, and densities of >0.65 kg I give the best handling properties with least tendency to create dust. Skimmed milk powder has a moisture content of less than 3. 5% and a water activity of around 0. 2. It can be stored for many months at ambient temperature without experiencing a deterioration in quality. Agglomerated skimmed milk powder with good water dispersion characteristics can be made using two-stage drying processes, often in spray dryers with integrated fluid beds, and the pre-heat treatment of the milk before evaporation and drying can be important to the heat stability of the milk proteins(Early 1998b) 2.6.6 Whey concentrate and whey powder Whey concentrate is used in the production of margarine and non-dairy spreads, while whey powder may be used in the formulation of soups, sauces and desserts Sweet whey is the by-product of enzyme-coagulated cheese production. The material has a pH of 5.8-6.6 and a titratable acidity(TA)of 0. 1-0. 2%. Medium- acid whey and acid whey are respectively, the products of fresh acid cheese and acid casein manufacture. Sweet whey is most commonly used for the production of whey concentrate and whey powder. With a water content of over 94%and the presence of lactic acid bacteria whey is very perishable. It Is pasteurised immediately after production to allow storage without deterioration. The solids content of sweet whey is 5.75% of which 75% is lactose. Whey concentrate is produced by vacuum evaporation and the low solubility of lactose sets the practical tal solids limit to around 30%. The bulk product, delivered by road tanker, has a short shelf-life and is stable for 2-3 days at <8C. Non-hygroscopic whey powde is made by crystallising the lactose in whey at temperatures below 93.5.C to ensure ae-lactose monohydrate predominates. Lactose crystallisation allows the dryer feed o be concentrated to 58-62% total solids to achieve a dense powder Demineralised whey powders can be made by ion-exchange and electrodyalysis (Houldsworth 1980)and nanofiltration techniques. Like skimmed milk powder whey powder can be stored for many months at ambient temperature 2.6.7 Lactose Lactose, the milk sugar, can be used in the formulation of soups and sauces Lactose yields the monosaccharides, D-glucose and D-galactose on hydrolysis with the enzyme B-galactosidase, and is designated as 4-0-B-D-galac ctopyr- anosyl-D-glucopyranose. It occurs in alpha and beta crystalline forms, though an amorphous form is also possible. The carbohydrate is less sweet than sucrose and as a reducing sugar it is used in some foods to provide colour in the form of Maillard browning. For industrial food uses, anhydrous a-lactose monohydrate is preferred as it is a free-flowing, non-hygroscopic material and is easy to store
Pasteurised skimmed milk concentrate requires chilled storage. Skimmed milk powder is made by spray drying skimmed milk concentrate from around 60% total solids. Milk powder quality is influenced by the solids content of the dryer feed. A high solids level gives a high bulk density, and densities of 0.65 kg 11 give the best handling properties with least tendency to create dust. Skimmed milk powder has a moisture content of less than 3.5% and a water activity of around 0.2. It can be stored for many months at ambient temperature without experiencing a deterioration in quality. Agglomerated skimmed milk powder with good water dispersion characteristics can be made using two-stage drying processes, often in spray dryers with integrated fluid beds, and the pre-heat treatment of the milk before evaporation and drying can be important to the heat stability of the milk proteins (Early 1998b). 2.6.6 Whey concentrate and whey powder Whey concentrate is used in the production of margarine and non-dairy spreads, while whey powder may be used in the formulation of soups, sauces and desserts. Sweet whey is the by-product of enzyme-coagulated cheese production. The material has a pH of 5.8–6.6 and a titrateable acidity (TA) of 0.1–0.2%. Mediumacid whey and acid whey are respectively, the products of fresh acid cheese and acid casein manufacture. Sweet whey is most commonly used for the production of whey concentrate and whey powder. With a water content of over 94% and the presence of lactic acid bacteria whey is very perishable. It is pasteurised immediately after production to allow storage without deterioration. The solids content of sweet whey is 5.75% of which 75% is lactose. Whey concentrate is produced by vacuum evaporation and the low solubility of lactose sets the practical total solids limit to around 30%. The bulk product, delivered by road tanker, has a short shelf-life and is stable for 2–3 days at 8ºC. Non-hygroscopic whey powder is made by crystallising the lactose in whey at temperatures below 93.5ºC to ensure -lactose monohydrate predominates. Lactose crystallisation allows the dryer feed to be concentrated to 58–62% total solids to achieve a dense powder. Demineralised whey powders can be made by ion-exchange and electrodyalysis (Houldsworth 1980) and nanofiltration techniques. Like skimmed milk powder, whey powder can be stored for many months at ambient temperature. 2.6.7 Lactose Lactose, the milk sugar, can be used in the formulation of soups and sauces. Lactose yields the monosaccharides, D-glucose and D-galactose on hydrolysis with the enzyme -galactosidase, and is designated as 4-0--D-galactopyranosyl-D-glucopyranose. It occurs in alpha and beta crystalline forms, though an amorphous form is also possible. The carbohydrate is less sweet than sucrose, and as a reducing sugar it is used in some foods to provide colour in the form of Maillard browning. For industrial food uses, anhydrous -lactose monohydrate is preferred as it is a free-flowing, non-hygroscopic material and is easy to store 46 Chilled foods
