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.
content of typically 87.5% cows’ milk has a high water activity (a
w
) of about a
w
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 B
12
(C22g) 0.41
Vitamin C (mg) 1.06
Vitamin D (C22g) 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
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 Ca
2+
Heat denaturation Creaming Humectant
Precipitation by Solubility at any pH Flavour carrier Low sweetening power
chymosin (27–39% of sucose)
Soluble at pHC626 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
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 C07.9oC, 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
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 10
3
per g
S. aureus C6020 per g 10
3
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 C6020 per g 10
3
per g
B. cereus C6010
2
per g 10
4
per g
C. perfringens C6010
2
per g 10
3
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
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 C6010
2
10
4
Processed cheese Aerobic plate count C6010
2
10
5
Anaerobic plate count C6010 10
5
Other cheeses Coliforms C6010
2
10
4
Enterobacteriaceae C6010
2
10
4
E. coli C6010 10
3
Pasteurised milk Coliforms C60110
2
and cream Enterobacteriaceae C60
2
Other pasteurised Coliforms C6010 10
4
milk products Enterobacteriaceae C6010 10
4
E. coli C6010 10
3
Yeasts (yogurt) C6010 10
6
Milk powders Aerobic plate count C6010
3
Product dependent
Enterobacteriaceae C6010
2
10
4
E. coli C6010 10
3
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
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 20C22m down to 1–2C22m, 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 C608oC 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
0.1C22mto20C22m with an average of 3–4C22m. 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
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 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
at C08oC. 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-
istics.
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 C05oC will enable a 20-day shelf-life. Cre`me fra??che 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 fra??che 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
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 by-
product 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
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 C620.65 kg 1
C01
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%. 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
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 C608oC. Non-hygroscopic whey powder
is made by crystallising the lactose in whey at temperatures below 93.5oC to ensure
C11-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 C12-galactosidase, and is designated as 4-0-C12-D-galactopyr-
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 C11-lactose monohydrate
is preferred as it is a free-flowing, non-hygroscopic material and is easy to store
46 Chilled foods
without a deterioration in quality. To ensure the formation of C11-lactose
monohydrate crystals, whey is concentrated to about 65% total solids to form a
supersaturated lactose solution at a temperature not exceeding 93.5oC. During
step-wise cooling C11-lactose monohydrate crystals are formed. Seed lactose is
used to control crystal size below 25C22m, or the threshold of detection by the
palate. Lactose crystals are commonly separated from whey concentrate by
decanter centrifuge, washed, dried in a fluid-bed dryer and packaged in multi-
ply paper sacks lined with a heat sealed polyethylene bag.
2.6.8 Yogurt and Greek-style yogurt
Yogurt is a very popular chilled dairy product, and numerous brands and
flavours can be found in supermarket chiller cabinets. A number of variants of
yogurt also exist, including Greek-style yogurt. Industrial uses of yogurt include
chilled dips, sauces, soups, desserts, toppings and ready meals such as curries
and other ethnic dishes. Yogurt is made by the lactic fermentation of whole,
standardised and skimmed milks. The pH of normal milk is 6.5–6.7, however the
fermentation of lactose to lactic acid by lactic acid bacteria (LAB) reduces the
pH to 2.6 causing the formation of an acid set gel. By the time fermentation is
arrested the pH is often in the range 3.8–4.2. The organisms Lactobacillus
delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus
have traditionally been used in yogurt production, though retail yogurts also
incorporate other organisms such as Lactobacillus acidophilus, Lactobacillus
casei subsp. casei and Bifidobacterium species to give mellow, fruity and less
acid flavours. For industrial use yogurt may be based on milks of varying fat
content, though retail products tend to be either skimmed milk or full cream
milk varieties. In the production of yogurt skimmed milk powder is added to
increase product viscosity and the non-fat milk solids level is raised from around
8.5% to 12–14%. However, gelatin and hydrocolloids such as modified starch,
guar and pectin may also be added to influence viscosity and texture. Yogurt is
made by heating milk which has been standardised for milk solids non-fat
(MSNF)and fat levels, typically to 90–95oC for five minutes. The heat treatment
kills vegetative contaminant bacteria, though higher heat treatments are required
to kill spore-forming organisms. Bacteriophage which can retard or prevent
LAB activity are destroyed and the whey proteins are denatured to the benefit of
viscosity. The milk is cooled to around 42oC, starter is added at a rate of around
2% and fermentation occurs in a closed vessel. The starter may be a culture of
LAB or a direct vat inoculation (DVI) freeze-dried or frozen concentrate
(Stanley 1998). Following incubation the pH drop is arrested by striking
(stirring) and cooling the coagulum, which may then be mechanically smoothed
to form a base material for the production of plain yogurt, fruited yogurt or for
use as an industrial ingredient. When destined for industrial use, yogurt is
usually pasteurised to kill LAB and prevent a further, gradual change in acidity.
Often supplied in 20 kg pergal containers, pasteurised yogurt has a shelf-life of
some ten weeks stored at C6016oC.
Raw material selection: dairy ingredients 47
Market yogurts vary widely in style and include solid set yogurts fermented
in the pot, to stirred and fruited products, and products which contain separate
portions of yogurt and fruit or cereal in the now ubiquitous twin-pot format. The
fat contents of the yogurt base of retail products also varies, from zero fat to high
fat products. Greek-style yogurt is, conventionally, a strained yogurt. Whey is
removed to increase the solids content to 22–26% to give a thick product,
resembling cream cheese in texture. In recent years the market for biofermented
yogurts has increased with increasing interest in health foods. Products
fermented with organisms such as Lactobacillus acidophilus and Bifidobacter-
ium spp. possess apparent probiotic properties and various starter cultures are
used to effect specific textures and flavours, as considered by Marshall and
Tamime (1997).
2.6.9 Cheese
As a product group, cheese presents many widely different types within the
retail market-place. A number of products used domestically also find
application in the manufacture of chilled foods, and particularly in the
production of sauces and savoury ready meals. For example, Cheddar, Gruyere,
Parmesan, Pecorino and Monterey Jack are used to garnish products such as
lasagne dishes, baked potatoes, and grilled products requiring a cheese topping.
Mascarpone can be used to thicken sauces, while Gorgonzola is used to flavour
sauces.
Generally considered to be chilled foods, cheese falls into two categories
(IFST 1990). Mould ripened soft cheese and cream cheese are classed as
category 2 products, requiring storage at 0oCto+5oC, while hard cheese and
processed cheese are category 3 products and must be stored at temperatures
not exceeding 8oC. The UK Food Safety (Temperature Control Regulations)
1995 state the need for chilled foods to be kept at, or below 8oC. It should be
recognised that many hard cheeses will not mature properly at chill
temperatures and storage above 8oC may be needed. In such cases the
scientific assessment of food safety is recommended (SCA 1997) based on an
intelligent interpretation of appropriate microbiological safety factors, such as
those suggested by CCFRA (1996). Cheese is made from milk or milk derived
materials, by fermentation with LAB and, importantly, the use of a proteolytic
enzyme, usually chymosin, to form a curd from which whey is drained to yield
a solid product which may or may not be ripened. In some instances a
secondary microbial flora, such as moulds, may be used to promote the
ripening process. A large number of cheese varieties exist world-wide and Fox
(1993) suggests the number exceeds 1000. Difficulties are encountered in
classifying cheese varieties and Scott (1981) proposes systems of classification
based on composition, ripening characteristics and moisture contents. Broadly,
cheese can be defined as ‘ripened cheese’, ‘mould ripened cheese’ and
‘unripened or fresh cheese’ (Bylund 1995).
48 Chilled foods
Ripened cheese
Cheese of this type sold as retail chilled foods includes varieties such as
Parmesan, Cheddar, Cheshire, Lancashire, Double Gloucester, Red Leicester,
Dunlop, Emmental, Gruyere, Edam, and Queso Manchego. Ripened cheese may
be sold for domestic use as cut cheese or pre-packed in vacuum or modified
atmosphere packaging. For industrial use ripened cheese is usually provided as
block cheese, which is then cut, bowl chopped or milled according to
requirements. However, cheese grated and packed in pouches is also supplied to
the industrial and catering markets. Though ripened cheeses vary considerably
in appearance, flavour, texture, etc., each type shares common basic steps in
production, as follows:
1. Raw milk may or may not be pasteurised (Emmental is an unpasteurised
ripened cheese).
2. Starter (LAB) is added to the milk which is then ripened at the temperature
required to achieve the appropriate rate of starter activity.
3. Rennet (containing the proteolytic enzyme, chymosin) is added to form a
coagulum.
4. The curd is cut to release the whey.
5. The whey is removed.
6. The curd is textured.
7. The curd is salted (this may be either by dry salting prior to, or after
hooping, or by brining after removal from hoops).
8. The curd is contained in a hoop or mould to shape the cheese.
9. The cheese is stored and ripened.
An outline of Cheddar cheese production is given in Table 2.8. The quality of
ripened cheese is dependent on composition and in the case of long-hold
Cheddar cheese the factors of moisture in non-fat solids, fat in dry matter, pH
and salt in moisture are all critical to achieving the best quality (Muir 1996b).
During manufacture, cheese-makers will effect necessary process adjustments to
control these factors and maximise quality. Frazier and Westhoff (1988) state
that cheese may present mechanical or microbial defects. Microbial defects of
ripened cheese may occur during manufacture, e.g., spore-forming species of
Clostridium and Bacillus may produce gas holes and acid-proteolytic bacteria
may cause off flavours. During ripening lactate-fermenting Clostridium spp. and
heterofermentative lactics may give rise to ‘late-gas’ defects, and putrefaction
may be caused by putrefactive anaerobes such as Clostridium tyrobutyricum and
Clostridium sporogenes. Finished cheese can be spoiled by a variety of
organisms, including, Oospora caseovorans causing white mould growth in the
eyes of Swiss cheese, Penicillium spp. giving rise to a variety of mould
discolorations and Brevibacterium linens causing red/orange spots. During the
manufacture of ripened cheese care is taken to monitor the rate of acid
development. In cases where acid production is slow, the risk exists that
Staphylococcus aureus may develop to numbers sufficient to cause a toxin
Raw material selection: dairy ingredients 49
hazard. Consequently, cheese-makers often operate a ‘slow cheese’ procedure,
which ensures such cheese is identified and tested for toxin prior to release to the
market.
Mozzarella is an important cheese in the industrial preparation of chilled
foods such as pizza and pizza ingredients supplied to the retail market and food
service outlets. Mozzarella is a ‘pasta filata’ cheese, which means that it is
characterised by an elastic, stringy curd. Traditionally made from the milk of
water buffalo, mozzarella is commonly made from cows’ milk and both kinds of
product can be found in supermarket chill cabinets. The initial stages of
mozzarella production are similar to those of Cheddar manufacture, however at
the point of milling a divergence occurs. Milled mozzarella curd is not salted,
but passes to a cooker-stretcher where it is worked mechanically under water at
a temperature of 65–80oC to obtain its laminar, ‘chicken breast’ qualities. It is
extruded into moulds and cooled to around 40oC to retain its rectangular block
shape, then placed in brine at 8–10oC and 15–20% salt concentration for
sufficient time to achieve a level of 1.6% salt.
Table 2.8 Outline of Cheddar cheese manufacture
Day 1 Raw milk (a) Standardise milk to give a fat to casein ratio of 1:0.7
(b) Pasteurise at 71.9oC for 15 seconds
(c) Cool to 29.5oC and fill cheese vats
(d) Add cheese starter at 1.5–3% of the milk volume – usually a
mixed culture of LAB based on Lactococcus lactis subsp.
lactis and Lactococcus lactis subsp. cremoris
(e) Ripen for 45 to 60 minutes – sufficient time for the titrateable
acidity (TA) of the milk to rise from 0.15–0.17% to 0.20–
0.22%
(f) Add rennet and form coagulum over 45 to 60 minutes
(g) Cut curd
(h) Scald by raising temperature to 39oC over 45 minutes
(i) Hold curd at 39oC for 45 to 60 minutes, agitate to encourage
syneresis
(j) Drain whey from the curd when TA reaches 0.20–0.24%
(k) Cheddar curd for 90 minutes, until TA reaches 0.65–0.85%
(l) Mill curd
(m) Salt at 2.0–3.5% of curd weight
(n) Hoop
(o) Press for 16 hours (overnight)
Day 2 (a) Remove cheese from hoop – pH between 4.95–5.15
(b) Bind/pack cheese to exclude air – vacuum packing in heat-
sealed polyethylene bags is common
(c) Box vacuum packed cheese to retain shape
(d) Ripen at 10–12oC for 3 to 18 months
(e) Pre-pack or sell as block cheddar
Adapted from: Banks, J.M. 1998. 2nd edition. Cheese. In, R. Early (ed). The technology of dairy
products. Blackie Academic and Professional, London.
50 Chilled foods
Mould ripened cheese
These cheeses utilise both bacterial cheese starters and moulds (fungi) to achieve
the required product characteristics. Because of the use of moulds, which are
biochemically very active compared with cheese starter bacteria, mould ripened
cheeses mature more quickly than ripened cheeses and, generally, have a shorter
shelf-life. Mould ripened cheeses are typified by Stilton and Roquefort which
are ‘blue cheeses’ by virtue of the activity of Penicillium roqueforti. In contrast,
Camembert is a white mould cheese, ripened by Penicillium cambemberti and
Geotrichum candidum. The manufacture of mould ripened cheese is similar to
the production of ripened cheese though, often, much less starter is used and the
curd is either only lightly scalded or not at all. A key difference is, of course, the
addition of moulds which may be added to the milk or mixed into the drained
curd, the latter being the case in Stilton manufacture. The presence of the blue
mould within the curd structure of maturing Stilton means that at the appropriate
time, usually 8 to 12 weeks after the day of make, the cheese can be penetrated
with cheese wires to allow air into the structure to stimulate mould growth and
blueing. In the case of Roquefort, the blue mould is carried on bread crumbs
which are mixed into the curd (Simon 1956). Alternatively, mould spores may
be dispersed in water and sprayed onto the surface of cheese to produce a
product such as Brie. Though not correctly mould ripened cheese, some products
utilise bacteria and yeasts in surface ripening. Smear ripened and washed rind
cheeses such as Munster obtain their orange/red coat from Brevibacterium
linens, and St. Nectaire is surface ripened by both bacteria and yeasts.
Unripened cheese
This category includes cottage cheese, quarg (fromage frais), cream cheese and
full fat soft cheese. All are found in the retail chilled foods market and are used
in the industrial production of chilled foods. Traditionally, cottage cheese is
made without the use of rennet. An acid coagulum is made from whole or
skimmed milk by fermentation with LAB, e.g., Streptococcus lactis,
Streptococcus cremoris and Leuconostoc citrovorum at a temperature of 20–
22oC for up to 16 hours. A short incubation time of 6 hours is possible when
rennet is used. The coagulum is cut and scalded at 49–55oC, the curd is washed
with water at 49oC and then drained of diluted whey to yield cottage cheese with
a granular, shotty texture. The production of quarg is similar to the quick set
method of cottage cheese manufacture. Skimmed milk is used to produce a
coagulum which is not scalded, as whey is removed by centrifugal separation in
a quarg separator to yield a product of typically 17.5% total solids. The use of
cheese starters gives a characteristic flavour which contrasts with that of yogurt.
Cream may be blended with quarg to produce high fat products, though
traditionally quarg is a low fat cheese. Fromage frais is a marketing appellation
intended to make quarg more attractive to consumers. Cream cheese and full fat
soft cheese are made by fermenting standardised milk with cheese starters and
adding rennet to form a weak coagulum. Centrifugal separation is used to reduce
the moisture content of the curd in each case, yielding a product of typically
Raw material selection: dairy ingredients 51
51% total solids and 46% fat in the case of cream cheese, and 39% total solids
and 30% fat in the case of full fat soft cheese.
Processed cheese
Often made from ripened cheese which has not achieved the required standard at
grading, processed cheese is produced by cooking cheese in steam-jacketed
vessels at 80–110oC. Different cheeses are combined according to flavour
requirements, though enzyme modified cheese is also used. Phosphates and
citrates function as emulsifier and stabiliser systems and regulate the pH of
products. Processed cheese with a pH of 5.2–5.6 is hard to firm and forms block
cheese which may be sliced or grated for use as a topping or garnish in savoury
meals and pizzas. A pH of 5.6–5.9 gives a spreading cheese of the type used in
sandwiches.
2.7 Chilled desserts
Many chilled desserts utilise milk-based ingredients to provide flavour, texture
and colour. Gelled desserts and mousses often use pasteurised milk, though milk
concentrate is an option. Milk proteins contribute to viscosity, help to emulsify
fat and contribute colour. Cream is a common ingredient and whipping cream
assists in the development of an aerated structure as well as providing a rich
flavour. In products containing chocolate, the addition of milk solids is
important to the development of a milk chocolate colour. Cre`me brule′e
(originally Cambridge burnt cream) can be based on cre`me fra??che and skimmed
milk, which provide a golden yellow colour in the form of Maillard browning, as
well as texture, viscosity and a richness of flavour. Milk is a base ingredient of
custard desserts. It provides the water to hydrate the modified maize starch used
to thicken the product and provide viscosity, and contributes to flavour and
mouthfeel, especially when full cream milk is used.
As with most products in the chilled desserts sector, variations on product
types are possible, for instance milk may be substituted with low fat yogurt to
make a ‘reduced calorie’ custard style product. Milk is also one of the two main
ingredients in chilled rice puddings. It provides the moisture needed to swell rice
grains, acts as a heat transfer medium during cooking and imparts flavour and
colour to the product. Cheesecakes, as their name implies, incorporate cheese,
though the type of cheese used varies according to the type of cheesecake made.
Baked cheesecake can be based on cottage cheese or cream cheese, or a blend of
the two. The cheese is used along with other ingredients such as sugar, starches
and gums to thicken and stabilise (in traditional products egg yolk, cornflour and
milk would be used) to produce a filling for a pastry case, which, when cooked,
gels to form the smooth textured, cheesy-rich tasting centre of the product. Fresh
cheesecakes are based on quarg, fromage frais and cream cheese, and blends of
these cheeses, often filled into or onto a biscuit base. A thickening and stabilising
system is required to control the viscosity of the cheese mix and various
52 Chilled foods
hydrocolloids such as starches and alginates are used. Many chilled desserts are
topped with whipped cream and an obvious example is trifle, which is usually
based on layered jelly and sponge cake beneath a whipped cream topping.
2.8 Ready meals
Many ready meals contain milk based ingredients. In pasta-based meals such as
lasagne dishes milk and cream are used in the production of sauces where the
whitening properties of milkfat globules and milk proteins can be of benefit. The
casein also functions as an emulsifier, helping to incorporate added fat or butter.
Various cheeses such as Parmesan, Cheddar, and Gruyere may be used as
lasagne toppings, to give a golden brown finish. Dough-based products such as
pizzas and tortilla-style products use cheese to provide an attractive finish and to
enhance aroma. In such instances it is important that the cheese provides the
correct melt characteristics. Mozzarella is the genuine pizza cheese, but blends
of Mozzarella and Cheddar are sometimes used, and processed cheese may also
find its way into some products.
Cheese is an important ingredient in the manufacture of some quiches, where
it provides colour, texture and flavour. It is also used to enhance the consumer
appeal of products such as potato gratin, by providing surface finish and, in this
instance, Gruyere can often be found listed in the ingredients declaration
alongside cream and butter. Many meat dishes contain dairy products, e.g.,
Lamb Provenc?al may contain Cheddar cheese as a garnish and cream and creme
fra??che to thicken the sauce and provide flavour. Yogurt and butteroil are used in
the preparation of sauces for ethnic dishes and pseudo-ethnic foods such as
Chicken Tikka Masalla, and, for instance, the sauce of Chicken Pasanda may
contain cream to provide richness, whitening and gloss. Savoury pouring sauces
such as pasta sauces utilise cream and butter for flavour and gloss, as well as
skimmed milk solids for whitening and emulsification purposes. The same is so
of soups. Fresh soups such as cream of tomato contain cream and butter for
flavour and gloss and sodium caseinate to increase viscosity, while asparagus
soup may contain reconstituted skimmed milk powder and double cream for
similar reasons.
2.9 Maximising quality in processing
2.9.1 Effect of heat on milk proteins
The heat stability of milk is influenced mainly by the heat stability of whey
proteins. At temperatures above 65oC for more than a few seconds the
denaturation of whey proteins proceeds quickly and at 90oC for five minutes it is
complete. In contrast, casein is not, strictly, heat denaturable. The order of heat
stability of whey proteins seems to depend on the method of assessment (Fox
and McSweeney 1998), but generally, C11-lactalbumin is considered to be more
Raw material selection: dairy ingredients 53
heat stable than C12-lactoglobulin, followed by blood serum albumin and then the
immunoglobulins. With the heat denaturation of whey proteins, C12-lactoglobulin
complexes irreversibly with C20-casein via disulphide bridges. This phenomenon
interferes with the action of chymosin in cheese making, but it can increase the
apparent heat stability of products such a skimmed milk powder. The effect of
heat on whey proteins, causing them to gel, can be of benefit to food
manufacturers as gelled whey proteins can be used to modify the textural
properties of foods and bind water. Though various factors affect the gelling
properties of whey proteins and particularly whey protein concentration, pH, salt
concentration and the presence of fat (Mulvihill and Kinsella 1987).
Concentrated whey protein products with protein levels exceeding 90% are
made for use as food ingredients and can find application in chilled products
such as soups and sauces.
2.9.2 Mechanical damage to milk and cream
The quality and function of liquid milk and cream may be impaired by
mechanical action causing the destabilisation of the emulsion. The degree of
destabilisation is dependent on a number of factors, including the shear rate, the
fat content, the milkfat globule size and the ratio of solid to liquid fat.
Mechanical destabilisation, e.g., as a consequence of over pumping or poor
transport line design, can lead to an increase in free fat in raw milk, which is
then susceptible to hydrolysis by lipoprotein lipases (Harding 1995).
2.9.3 Microbially induced proteolysis and lipolysis
Raw milk stored under refrigerated conditions is subject to microbial proteolysis
and lipolysis due to Pseudomonas spp. and proteolysis due to psychrotrophic
sporeformers of the genus Bacillus: mainly B. cereus, B. circulans and B.
mycoides. While pasteurisation will destroy vegetative organisms, Bacillus spp.
can survive and give rise to proteolysis in chilled liquid products. Additionally,
though pasteurisation may denature indigenous lipases, bacterial lipases are
considerably more heat resistant and can survive, giving rise to hydrolytic
rancidity and the development of rancid flavours caused mainly by free butyric
and caproic acids. The quality of dairy products is dependent on the quality of
raw milk and processors must safeguard against the growth of bacteria that
promote proteolysis and lipolysis. Post-pasteurisation contamination must also
be prevented, as the reintroduction of these contaminant organisms (amongst
others) can lead to the development of off-flavours and the loss of functionality
in products.
2.9.4 Oxidative rancidity of milkfat
The development of oxidative rancidity in liquid milk and milk products
containing milkfat is dependent on the presence of oxygen. The primary
54 Chilled foods
substrate for oxidation is the polyunsaturated fatty acids, linoleic and
arachidonic, and those contained in the phospholipides and glycerides (Jenness
and Patton 1959). Oxygen attacks the methylene groups adjacent to the carbon
chain double bonds, giving rise to the formation of hydroperoxides. These
compounds are unstable and oxidation proceeds by a free-radical mechanism.
Sunlight and particularly light from fluorescent tubes can cause the auto-
oxidation of milkfat, as can the presence of iron and copper salts. In milk
products with low water activities the reaction rate of oxidation is highest at a
w
0.6, falling to a
w
0.4 and then rising again as a
w
reduces (Fellows 1997), which
is of significance to low-moisture, low-water-activity products.
2.9.5 Maillard reaction
The Maillard reaction is a non-enzymic browning reaction. It is the result of the
interaction between a carbonyl group and an amino group to form a glycosamine
and ultimately, melanoidins. The Maillard reaction occurs when milk is heated
sufficiently to induce a reaction between lactose and the amino acid, lysine. It
results in the development of a brown discoloration, often described as a cooked
colour, and associated strong flavours.
2.10 Food safety issues
Though dairy products have a very good food safety record, the main public
health concerns associated with milk and milk products relate to food-borne
disease organisms and food-poisoning organisms. Mycobacterium tuberculosis
and Coxiella burnetti are the most heat-resistant vegetative microbes found in
milk and both are food-borne disease organisms. Jay (1996) gives the D 65.6oC
as 0.20–0.30 minutes for the former and 0.50–0.60 minutes for the latter. This
compares with a D value at the same temperature of 1.6–2.0 seconds for Listeria
monocytogenes, a food-poisoning organism associated with soft cheese. The UK
Dairy Products (Hygiene) Regulations 1995 state microbiological standards for
raw cows’ milk for processing, requiring a plate count at 30oCofC20100,000
colony-forming units (cfu) per ml, and a somatic cell count of C20400,000. The
standards for some dairy products are also given and Jay (1996) reports milk
product standards in the USA. The vegetative food-poisoning organisms of main
concern in raw cows’ milk are Salmonella spp., Listeria monocytogenes,
Staphylococcus aureus, Campylobacter spp. and pathogenic E. coli.The
emergent pathogen E. coli O157 is of growing concern due to its association
with cattle (Buchanan and Doyle 1997). This is not, however, to say that raw
milk is automatically contaminated with these organisms. A survey of raw milk
carried out in England and Wales in 1995/96 found that of 1674 samples, 2%
were positive for Listeria monocytogenes, 6.7% were positive for Staphylo-
coccus aureus (one of the main causative organisms of mastitis) and 62% were
positive for Escherichia coli, an indicator of faecal contamination (Anon. 1999).
Raw material selection: dairy ingredients 55
Other possible hazards associated with raw milk include chemical contamina-
tion, such as antibiotics and other veterinary drugs residues, cleaning chemicals,
environmental contaminants and mycotoxins arising from animal feeds, and
physical contaminants such as wood, glass and metal.
The Hazard Analysis Critical Control Point (HACCP) system is now
recognised as the best method of food safety control. Its use is encouraged by the
World Health Organization and the International Commission on Microbiolo-
gical Specifications for Foods. Within the EU all food businesses are required to
implement the first five of the seven principles of HACCP (EEC 1993). In the
UK the European directive is manifested in food safety regulations (HMSO
1995). It is not intended to describe the use of HACCP here. Early (1997)
addresses its use in the dairy industry, while Leaper (1997) and Mortimore and
Wallace (1998) give a detailed description of its general application. Miller et al
(1997) consider HACCP in relation to quantitative risk assessment in the control
of Listeria monocytogenes. In milk processing the control of hazards concerns
(a) the prevention of contamination by hazards and (b) either the elimination of
hazards in milk products or their reduction to acceptable levels. Effective herd
management and good milking practice serve to reduce the contamination of
raw milk by potential hazards to human health arising on the farm. Standards for
the production, storage and transport of raw milk, such as those laid down in the
UK’s National Dairy Farm Assurance Scheme should be observed. Organisa-
tions charged with the responsibility of milk collection must guard against the
contamination of raw milk by transit vehicles and good hygienic practice must
be observed in the management and maintenance of milk tankers. Ideally the
temperature of raw milk should not exceed 4oC at the point of collection, though
milk above this limit may be processed in the UK according to requirements
stated in the regulations (Anon. 1995b). The chilling of milk immediately after
milking prevents the growth of mesophilic pathogens and spoilage organisms.
Psychrotrophic organisms will still grow at low temperature, however, and the
storage life of raw milk must be limited prior to processing in order to avoid
quality defects arising from proteolysis and lipolysis caused by biochemically
active species such as Pseudomonas spp. At the factory raw milk is stored in
thermally insulated silos to await processing. Commonly the milk passes
through coarse filters on entry to silos, which serve to remove physical
contaminants which may be potentially hazardous in nature.
In the manufacture of most dairy products pasteurisation is the key critical
control point for the elimination or reduction of microbial pathogens. The food-
borne disease organisms, Mycobacterium tuberculosis and Coxiella burnetti, and
the vegetative food poisoning organisms, Salmonella spp., Listeria mono-
cytogenes, Staphylococcus aureus, Campylobacter spp. and pathogenic E. coli
spp. are all destroyed by pasteurisation at 71.7oC for 15 seconds. Spore-forming
bacteria such as Clostridium and Bacillus spp. will, of course, survive. Because
no further heat treatment occurs after milk pasteurisation in the production of
many chilled dairy products extreme care must be taken to prevent post-
pasteurisation contamination by pathogenic microbes and spoilage organisms.
56 Chilled foods
Within dairy factories high standards of hygiene and housekeeping are
maintained to prevent the possibility of contamination from plant, equipment
and the manufacturing environment. Barrier hygiene is commonly practised to
preserve the integrity of hygiene standards and especially to prevent the
transmission of microbial contaminants from raw milk to pasteurised milk areas.
While some dairy products used as ingredients in chilled foods manufacture will
receive heat treatments in chilled foods processing, the standards and systems
used to make the ingredients are no less stringent than those used in the
manufacture of chilled dairy products. Indeed, in the manufacture of products
such as milk powders extreme care is taken to prevent the post-pasteurisation
contamination of product, as considered by Mettler (1989; 1992; 1994).
2.11 Future trends
The traditional milk-based ingredients used in chilled products manufacture and
traditional chilled dairy products will not change in the future. Developments are
most likely to involve the innovation and diversification of non-traditional
consumer products such as milk-based desserts, and formulated chilled foods
(desserts, soups, sauces and ready meals) which utilise the functionality of milk
based ingredients. Advances in processing technologies will lead to new kinds of
milk based ingredients tailored for use in specific applications, as will
improvements in the empirical understanding of the behaviour of milk
components in food systems. Notions of competitive advantage and market
share drive companies operating in the chilled dairy products and dairy
ingredient sectors. The quest for sustainable economic growth, the ‘Holy Grail’
of all companies operating in Western economies, will stimulate the creation of
‘technological partnerships’ in food product innovation. By fusing the
intellectual processes of customers and suppliers new possibilities and, hence,
new opportunities will be created. By precisely matching customers’ require-
ments and technical capabilities with the abilities of suppliers, milk-based
ingredients will be finely tuned to function in specific chilled foods systems and
to create attributes which set products apart from those of competitors. To a
certain extent this is already happening, as ingredients suppliers already select
raw materials from specific sources for processing in specific ways, for use in
specific products. Whey powder derived from different sources, e.g., Emmental,
Cheddar or acid casein whey, can offer different functional behaviour when
blended with stabilisers and thickeners, for use in chilled dessert applications.
The demineralisation of whey by different techniques, or varying mineral
balances resulting from finely controlled demineralisation, can yield ‘selected
functional performance’. Skimmed milk from different countries offers different
performance standards, as does butter which varies widely in flavour and
melting characteristics according to breed of cow and country of origin.
To a certain extent innovation in chilled dairy products and milk-based
ingredients for use in chilled foods will be restricted by the limits of raw
Raw material selection: dairy ingredients 57
material sources and processing technologies. Genetic engineering may,
however, create new and so far unimagined possibilities. The concept of
value-added has become a corner-stone of the consumer society, but free-market
competition acts constantly to erode the value which food manufacturers and
retailers are able to attach to their products. Consequently, new opportunities to
add value to food products are continually sought and genetic engineering may
hold the key to a new treasure chest in food product innovation. Kuzminski
(1999) states that increased earnings will come through enhanced value which
justifies higher prices and margins, and that biotechnology offers the potential to
create enhanced value. This idea is echoed by Shelton (1999), who reports
predictions that the food we will eat in the future will increasingly be based on
raw materials and ingredients tailored (engineered) to our individual tastes,
lifestyles and medical needs. Chilled foods manufacturers may be able to benefit
from genetic engineering technology in a number of ways. For example, the
insertion of genes from mammals not normally used in milk production, into
bovine genomes might give rise to milks with unusual functional properties
which can be exploited as novel ingredients in food manufacture. Also, bacteria
used for the production of fermented chilled dairy products may be genetically
engineered to yield new potentials, such as self-stabilising yogurts (no need to
add stabilisers and thickeners as they are produced ‘naturally’, in situ), or
bacterially vitaminized fermented milks and cheese, or products which contain
vaccines produced by starter bacteria fermentation. There may even be the
possibility of doing away with cows altogether. What is science fiction today
frequently becomes science fact tomorrow. So, what about genetically
engineering different strains of E. coli to produce the various components of
milk which can then be combined in preferred proportions to yield products
tailored for specific food applications? But if such a fiction becomes a fact, will
the products still be milk products?
2.12 References
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100.
ANON 1995b, Dairy Products (Hygiene) Regulations 1995, S.I. No. 1086.
HMSO, London.
ANON 1999, Raw cows’ drinking milk. Health and Hygiene, 20, 115–6.
BERK Z, 1986. Braverman’s introduction to the biochemistry of foods, Elsevier,
Amsterdam, p. 170.
BODYFELT F W, TOBIAS J and TROUT G M, 1988. Sensory evaluation of dairy
products, Van Nostrand/AVI, New York.
BRENNAN J G, BUTTERS J R, COWELL N D. and LILLEY A EV, 1990. 3rd edn. Food
engineering operations, Elsevier Applied Science, London, pp 187–8, 119–
21.
BUCHANAN R L and DOYLE M P, 1997 Foodborne disease significance of
58 Chilled foods
Escherichia coli O157:H7 and other enterohemorrhagic E. coli. Food
Technology, 51,69–76.
BYLUND G, 1995 Dairy processing handbook, Tetra Pak Processing Systems AB,
Lund, p. 288.
CCFRA, 1996 A code of practice for the manufacture of vacuum and modified
atmosphere packaged chilled foods, Guideline 11. Campden and Chorley-
wood Food Research Association, Chipping Campden, Gloucestershire, p. 18.
CLOAKE R R and ASHTON T R, 1982 Cream In: Technical guide for the packaging
of milk and milk products, 2nd edn. Bulletin of the International Dairy
Federation, Brussels, No. 143.
EARLY R, 1997 Putting HACCP into practice, International Journal of Dairy
Technology, 50 7–13.
EARLY R, 1998a 2nd edn. Liquid milk and cream. In: R. Early (ed) The
technology of dairy products. Blackie Academic and Professional, London,
pp. 1–49.
EARLY R, 1998b 2nd edn. Milk concentrates and milk powders. In: R. Early (ed)
The technology of dairy products, Blackie Academic and Professional,
London, pp. 228–300.
EEC, 1993 Council Directive 93/43/EEC (June 14, 1993) on the hygiene of
foodstuffs, Official Journal of the European Communities, July 19, 1993,
No. L 175/I.
FELLOWS P J, 1997 Food processing technology, Woodhead, Cambridge, p. 66.
FOX P F, 1993 2nd edn. Cheese: an overview. In: P. F. Fox. Cheese: chemistry,
physics and microbiology, Volume 1, General aspects, Chapman and Hall,
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