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 20
m down to 1–2
m, 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 contamina￾tion with Gram negative psychrotrophic bacteria is often of significance (Muir 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 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 0.1
m to 20
m with an average of 3–4
m. 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