Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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components have been associated with migraine, such

as food colorings (erytrosin), food flavorings, licorice

extract, pesticides, boron, aspartame, vitamins (A, D,

niacin), minerals (calcium, manganese), herbal tea,

and seafood. However the prevalence is low, and

further research is needed to ascertain their role in

migraine.

Vasoactive Amines

0027 A variety of amines have been implicated in the

development of headache, most commonly the

vasoactive monoamines tyramine, tryptamine, nor-

epinephrine (noradrenaline), epinephrine (adrena-

line), dopamine, beta-phenylethylamine, serotonin,

and synephrine.

0028 Ingested monoamines are normally inactivated by

MAO, found in high amounts in the gut and which

prevent monoamines from the diet to enter the gen-

eral circulation in significant amounts. However, if

large amounts of monoamines are present in foods or

if the enzymes are inhibited by genetically deficient

metabolism or by MAO inhibitor drugs, the metabol-

ism is prevented. A MAO defect would act in precipi-

tating migraine through the mechanism of increased

absorption of vasoactive substances. Headaches have

also been described in patients under treatment with

MAO inhibitor drugs.

0029 The monoamines that are not metabolized are free

to act directly on blood vessels. They are also known

to cause release of endogenous active substances, cre-

ating the potential for migraine and also for hyper-

tensive crisis.

0030 Tyramine Tyramine is a vasoactive amine that

promotes blood pressure elevation, resulting in pain.

Tyramine leads to cerebral vasoconstriction and sub-

sequent rebound vasodilatation that causes a mi-

graine attack in susceptible persons. Episodes can be

accompanied by nausea and visual abnormalities.

Symptoms are evident 1–12 h after ingestion of food

containing tyramine. A dose of 10 mg tyramine

has been associated with migraine onset; however,

levels of 6 mg can cause migraine in patients under

treatment with MAO inhibitors. Alcohol has been

observed to facilitate tyramine absorption.

0031Tyramine is found in a number of foodstuffs, most

notably aged and fermented foods and beverages.

Cheeses (especially Camembert, Cheddar, Parmesan,

and Emmental), overripe bananas, avocado, canned

figs, peanuts, pickled herring, dried and fermented

meat products and alcoholic beverages (wine, beer)

are known to contain tyramine.

0032Phenylethylamine Similarly to tyramine, pheny-

lethylamine causes headaches after 12 h of ingestion

of 3 mg by susceptible individuals. Chocolate, a com-

monly cited trigger of headache, is specially rich in

phenylethylamine. An ordinary chocolate bar may

have at least 3 mg phenylethylamine per 56 g. Dark

chocolate has been found to be more potent than milk

chocolate in causing migraine.

0033Serotonin Chemically, serotonin is 5-hydroxytrypt-

amine. It is a neurotransmitter that acts as a powerful

constrictor of arteries, reducing blood supply to the

brain, causing migraine. Because serotonin released

from platelets has been suggested to initiate migraine,

a decreased platelet serotonin content attained by a

reduced intake of serotonin and the serotonin precur-

sor tryptophan might be beneficial. Serotonin-rich

foods include bananas, tomatoes, and walnuts. A

protein-tryptophan-reduced diet decreased headache

frequency and skin symptoms in patients with mi-

graine-like headache. Therefore, the intake of foods

with a high tryptophan-to-protein ratio should be

restricted.

tbl0005 Table 5 Causes of diet-precipitated headache or migraine and foods involved

Substances Foods

Food components

Vasoactive amines

Tyramine Aged cheeses (cheddar, Swiss, Gouda,

Roquefort, Stilton, parmesan), sausages, pickled herring, red wine, beer

Phenylethylamine Chocolate, cocoa

Serotonin Banana, tomato, walnuts, tryptophan-rich protein

Ethanol Wine, beer

Caffeine Coffee, tea, cola, and candy withdrawal

Copper Chocolate, cocoa, nuts, shellfish, distillates produced

in copper stills, wheat germ

Additives

Nitrites Aged, canned, and cured meat such as hot dog, bacon, ham, salami, cheese (read labels)

Monosodium glutamate Chinese food, soy sauce, instant soup, bouillon cubes, meat tenderizer, seasonings,

ready-to-eat dishes, snacks (read labels)

3944 MIGRAINE AND DIET

0034 Other amines Dopamine is found in the pod of

Italian broad green (fava) bean and bananas. Synefr-

ine and octopamine are found in citrus fruits, includ-

ing oranges, lemons, and grapefruit. Port, Chianti,

and red wines, and some other alcoholic drinks con-

tain histamine, which is also a vasoactive amine.

Ethanol

0035 Alcoholic beverages may provoke migraine. Ethanol,

which has both central and direct vasodilator proper-

ties, is a well-known potential trigger for migraine.

The vasodilatation is assumed to be the result of

depression or alteration of the central vasomotor

centers, since the direct action of alcohol on blood

vessels is insignificant. Ethanol can inhibit MAO,

thus preventing amine metabolism and enhancing its

activity. Ethanol can induce migraine in some persons

regardless of the amount consumed. It generally

occurs 7 h after drinking, usually starting in the

following morning. Clinically, excessive dietary salt

intake also appears to potentiate alcoholic migraine.

0036 Some believe that congeners present in the majority

of the alcoholic beverages are even more potent con-

tributors to migraine than ethanol itself. Three

troublesome chemicals associated with wine are

histamine, tyramine, and phenylethylamine. Further-

more, compounds in the flavonoid fraction of wine

have been observed to cause release of active sub-

stances.

0037 In addition to the usual alcoholic beverages (wine,

beer), many cough preparations, tonics, mouth-

washes, liquid vitamins, and nonprescription drugs

contain high concentrations of ethanol.

Copper

0038 Foods that are high in copper have been responsible

for the precipitation of migraine. Copper is involved

in metabolic and enzymatic activities such as hemo-

globin synthesis, bone and elastic tissue development,

and normal function of the central nervous system.

Copper is known to be necessary for the metabolism

of vasoactive amines such as serotonin, tyramine,

and catecholamines. Abnormal copper metabolism

following ingestion of copper-containing foods

would lead to decreased inactivation of amines and

therefore the onset of migraine.

0039 There are substances that can facilitate copper ab-

sorption causing migraine, among them citrate, glu-

tamate, and histamine. Glutamate from MSG acts to

transport significant amounts of copper to tissues,

facilitating copper absorption. Histamine is known

to bind and transport copper to tissues.

0040 Foods containing high levels of copper include liver,

cocoa, chocolate, nuts, shellfish, mushrooms, wheat

germ, and certain cereals. Whiskies and distilled

beverages that are produced in copper stills can also

be a source of copper.

Caffeine

0041Caffeine is an ingredient of coffee, cola, tea, choc-

olate, and many over-the-counter and prescription

analgesic compounds. It is a vasoconstrictor; however

it does not cause headache as a primary manifest-

ation. But rebound vasodilatation may occur, causing

a migraine-like withdrawal headache when excessive

caffeine consumption is suddenly interrupted. For

example, a person who consumes large quantities of

caffeine-containing beverages during the week may

experience a headache on weekends if caffeine con-

sumption is decreased. The headache is relieved by

taking another dose.

0042Theobromine, a methylxanthine found in cocoa

that is similar in chemical structure to caffeine, may

act as the headache trigger.

Food Additives

0043Nitrates An aching headache often accompanied by

facial flushing occurs in sensitive persons exposed to

nitrites added to cured meats. As little as 5–10 mg

sodium nitrite may provoke headache in a migraine-

prone person. Headaches are noted to occur 35 min

after sodium nitrite ingestion, and last approximately

1–2h.

0044Up to 0.02% of nitrate and nitrite compounds are

employed in meat products to create a pink color, to

impact a cured flavor, and to prevent botulism. These

foods include bologna, salami, sausage, pepperoni,

bacon, frankfurters, corned beef, beef jerky, lunch

meats, canned ham, and sausages. In some countries,

nitrate can also be added to cheese to prevent late

blowing. Migraine sufferers are advised to eliminate

cured meats from their diets.

0045Monosodium glutamate MSG is another chemical

that migraine patients are often advised to restrict.

The amount of MSG added to food has increased

enormously since its first introduction. It is a com-

monly used food additive that enhances the taste of

meat in particular and is used in appreciable quantities

in the preparation of food in Chinese restaurants.

MSG is now found in varying amounts in many food

products, among them bacon bits, baking mixtures,

bouillon cubes, bread stuffing, breaded foods, canned

meats, cheese dips, corn chips, dry roasted peanuts,

frozen dinners and pizza, gelatins, oriental foods,

potato chips, pot pies, salad dressings, salt substitutes,

seasonings, soups, soy sauce, and meat tenderizers.

0046As little as 3–10 mg of this compound may provoke

headache in a migraine-prone person. The Chinese

restaurant syndrome is well documented and includes

MIGRAINE AND DIET 3945

symptoms of tightening of the muscles of the face and

throat, constriction of muscles of the back and neck,

paresthesia of the mucous membranes of the mouth

and palate, nausea, giddiness and dizziness, flushing

and sweating of the face, severe pain in jaws, and a

band-like headache. The syndrome occurs within

20–30min after eating foods with a significant

amount of MSG.

Treating Migraine Headache

004 7 When having severe headaches, it is important to see

a doctor for evaluation and diagnosis. Several thera-

peutic methods, both nonpharmacologic and phar-

macologic, may prove useful. The approach to

pharmacologic treatment is either abortive (acute)

or prophylactic (preventive). The ergotamines remain

the agents of choice for abortive therapy of migraine.

For greatest benefit, these preparations must be taken

either during the aura or as soon as possible after the

headache starts. If a patient experiences more than

two migraines a month or abortive agents are inef-

fective or contraindicated, prophylaxis should be

considered. A variety of agents have been shown to

be useful, but proptanolol is the safest and most

effective. Patients on preventive medication still

require acute treatment for breakthrough attacks.

0048 Nonpharmacologic techniques are oriented pri-

marily to reducing the frequency as well as the sever-

ity of migraine attacks. The first step in prevention is

the elimination of triggering factors, which should be

reviewed thoroughly with each patient. A detailed

diary of when you have a headache (date, time, sever-

ity, possible triggering factors, time and amount of

exposure, treatment used, the outcome) may help

determine what may influence your headaches and

could give you an idea of what triggers you may

want to eliminate or avoid. It is important that time

be taken to identify those sensitivities and eliminate

only those foods related to the patient’s migraine.

Many times patients are given lists admonishing

them to avoid all foods that have ever been implicated

in migraine causation. This can create apprehension

about eating, and the resultant avoidance of a variety

of foods can lead to malnutrition and cachexia in the

conscientious patient. An overconcern with diet can

also be a psychological stressor that may further ag-

gravate the headache problem. A diary can also help

you see how well your medication and lifestyle

changes are working.

0049Most experts in headache suggest that foods that

have vasoactive properties should be avoided

(Table 6). It is also important to eat a healthy diet,

at regularly scheduled times, not skipping a meal. In

addition, patients should be consistent in their sleep-

ing patterns. There should be a regular bedtime and

patients should wake up at the same time each morn-

ing. Stress and anxiety management strategies, such

as regular exercise, relaxation techniques, biofeed-

back, or cognitive-behavioral therapy may also have

a role in treatment.

Seealso: Alcohol:PropertiesandDetermination;

Amines; Caffeine; Copper:Propertiesand

Determination;Physiology; Nitrates and Nitrites;

Premenstrual Syndrome: Nutritional Aspects; Taste

Enhancers

Further Reading

Diamond S, Prager J and Freitag FG (1986) Diet and head-

ache. Is there a link? Headache 79(4): 279–285.

Goadsby PJ, Lipton RB and Ferrari MD (2002) Drug ther-

apy: migraine – current understanding and treatment.

New England Journal of Medicine 346(4): 257–270.

Harrison DR (1986) Copper as a factor in the dietary

precipitation of migraine. Headache 26: 248–250.

Hasselmark L, Malmgren R and Hannerz J (1987) Effects

of a carbohydrate-rich diet, low in protein-tryptophan,

in classic and common migraine. Cephalalgia 7: 87–92.

Journal of the American Medical Association Patient page.

Available at www.ama-assn.org/consumer.htm.

National Headache Foundation Available at www.heada-

ches.org.

National Institute of Neurological Disorders and Stroke

Headache. Available at www.ninds.nih.gov.

tbl0006 Table 6 Dietary suggestions for migraine patients

No alcoholic beverage, particularly red wines

No aged or strong cheese, particularly cheddar cheese

Avoid chicken livers, pickled herring, pods of broad beans

Use monosodium glutamate (MSG) sparingly. Avoid foods containing MSG

Avoid cured meats such as hot dogs, bacon, ham, and salami, if these can be demonstrated to evoke migraine.

Avoid foods containing nitrate and nitrite

Eat three well-balanced meals per day. Avoid skipping meals, prolonged fasting, or excessive ingestion of carbohydrates at any

single sitting

Avoid chocolate

All of these foods have been demonstrated to contain vasoactive materials of varying types and all have, in specific circumstances, evoked migraine in

predisposed patients.

3946 MIGRAINE AND DIET

Peatfield RC (1995) Relationship between food, wine,

and beer-precipitated migrainous headaches. Headache

35(6): 355–357.

Peatfield RC, Glover V, Littlewood JT, Sandler M and

Clifford Rose F (1984) The prevalence of diet-induced

migraine. Cephalalgia 4(3): 179–183.

Perkin JE and Hartje J (1983) Diet and migraine: a review

of the literature. Perspective in Practice 83(4): 459–

463.

Raskin NH and Knittle SC (1976) Ice-cream headache and

orthostatic symptoms in patients with migraine. Head-

ache 16(5): 22–25.

MILK

Contents

Liquid Milk for the Consumer

Processing of Liquid Milk

Physical and Chemical Properties

Analysis

Dietary Importance

Liquid Milk for the Consumer

J Manners, University of Melbourne, Parkville,

Victoria, Australia

H Craven, Food Science Australia, Werribee, Victoria,

Australia

Introduction

0001 Historically, milk from cows and other mammals has

been an important source of nutrients, especially pro-

tein for humans. Traditionally, villages and individual

families tended one or two animals such as cows,

goats, or buffalo, which provided milk for immediate

consumption and then meat when the animal was

slaughtered. Over time, the number of animals in a

milking herd has increased from the one-animal

situation to herds of tens and hundreds of animals.

With this increase in size of herds, there have been

developments in how the animals are milked and how

the milk is handled from milking to receival at the

milk factory.

Composition of Milk

0002 Milk is a complex biological fluid consisting of fats,

proteins, minerals, vitamins, enzymes, and sugar. The

composition of milk varies according to the breed of

the animal, the genetic background of the animal, the

stage of lactation, the nutritional quality of the

animal’s feed, the frequency of milking, the incidence

of disease such as mastitis, and general environmental

conditions.

0003Animals from different species and breeds produce

milk of varying fat, protein, and lactose content and

volume. For example, Friesian or Holstein animals

are more likely to produce larger quantities of milk

with a lower percentage of fat compared to milk

produced by a Jersey animal. Buffaloes produce

milk with a higher fat and protein content than

cows, while goats’ milk has a lower lactose content

compared to cows’ milk. Within breed types, animals

are largely selected for breeding on the basis of their

performance as producers of milk measured in terms

of fat, protein, and volume.

0004The greatest changes in composition occur during

early lactation. Colostrum, the first milk after

calving, has a high concentration of fat and protein,

especially immunoglobulins, and a low concentration

of lactose. Over the first weeks of lactation, the fat

and protein levels decrease while the lactose levels

increase. Table 1 compares the composition of colos-

trum with that of milk produced 10 days later. The

volume of milk produced by the cow increases during

the early stages of lactation and after peaking slowly

declines towards the latter stages of lactation. This

decline usually coincides with the development of

pregnancy in the animal.

0005Clinical or subclinical mastitis in the udder results

in changed composition of the milk with decreased

levels of lactose and potassium and increased levels of

sodium, chloride, and serum proteins. In addition, a

large number of somatic cells and bacteria are pre-

sent. The higher number of somatic cells results in an

increased concentration of the enzyme plasmin in the

milk. Plasmin is a protease which is normally found in

the blood stream. The industry commonly uses the

MILK/Liquid Milk for the Consumer 3947

levels of somatic cells in milk as a screening test for

the incidence of mastitis. A count of under 200 000

somatic cells per milliliter in bulk herd milk generally

indicates an absence of mastitis, while levels above

400 000 per milliliter indicate a high incidence of

mastitis in the herd.

0006 The impact of feed consumed by the cow on the

composition of milk is complex. Overall, animals on

nutritionally superior feed will produce more milk

with a higher level of fat and protein than animals

on feed of lower nutritional quality. The quantity and

type of fat and the composition of the nonlipid

compounds in the feedstuffs affect the fat content

and composition.

0007 In cold climates, animals are generally housed

indoors and the feed is bought to them. The volume

of production and composition of milk from cows

housed indoors is likely to be different to that pro-

duced by animals in temperate or tropical climates

which are fed by range-grazing. The difference in

composition and volume may also be related to the

nutritional quality of the feed.

Milking

0008 Historically, milk has been extracted from the udder

by manual stimulation and expression of milk from

the teats. The milk is collected in a small storage

vessel such as a bucket or can. Manual milking is

commonly carried out where the numbers of cows

are small and there is plenty of available labor. As

herds have grown in size, mechanical means of

extracting milk have been introduced. These are gen-

erally called milking machines. The milk is extracted

from the teat and udder by a pulsating vacuum in

rubber liners called teat cups which fit around the

teat. In most situations the milk is carried from the

cow through pipelines to the milk storage vessel.

These vessels may range from a bucket for milk

from an individual cow to vats or silos of large

capacity. The silos may be used for the storage of

the milk from the several milkings.

0009Herds are generally milked twice a day during most

of the lactation period: the frequency is reduced to

once a day as the milk yield declines. Research work

has demonstrated that more frequent milking, such as

three times a day, can increase the total volume of

milk, but this is not a common practice amongst dairy

farmers.

Control of Microbial Contamination

0010Milk from the udder of a healthy cow contains very

few microorganisms. However, addition of micro-

organisms during the milking process and growth of

contaminating microorganisms will reduce the time

required for milk to spoil. To minimize the addition of

microbes to the milk, the farmer needs to prevent

contamination of milk through the process of milking

and transport to storage vessels.

0011The exterior of the teat and udder must be

carefully washed to remove residues of manure

and dirt, which contain large numbers of microorgan-

isms. It has been demonstrated that the optimal treat-

ment to minimize addition of bacteria to milk is

to dry the udder carefully with a clean cloth after

washing. In some situations such as large herds, stra-

tegic washing of udders is carried out. This involves a

judgment about the level of visual contamination on

the udder.

0012Another important source of microbial contamin-

ation is the hygienic condition of the rubbers and

pipelines of the milking equipment. The materials

used for the transport and storage of raw milk must

be easy to clean and sanitize. Stainless steel and

plastic are easy to clean and are more resistant to

mechanical damage than rubber, wood, and other

materials. Fat and protein deposits in the pipelines

and storage vessels will prevent sanitizer solutions

acting on bacteria. In addition, cracked rubberware

is difficult to clean and sanitize effectively.

0013Other sources of contamination are water supplies

used for washing udders and equipment, exposure

of the milk to the air, dirty cloths used for cleaning

udders, and the presence of mastitis in the udder.

The total microbial count of milk can increase

dramatically when an udder is infected with mastitis.

0014Care must be taken when milking to minimize the

possible transfer of mastitis infection from one

animal to another. Precautions used by farmers in-

clude dipping the rubber teat cups in a chemical sani-

tizer solution such as iodophor, dipping the teats after

milking with a disinfectant such as iodophor, use of

good-quality running water to wash udders, and

single-use towels to dry udders after washing. The

incidence of mastitis infection can be increased by

the use of malfunctioning milking machines. Many

tbl0001 Table 1 Typical composition of milk at the start of lactation and

10 days later

Component Start of lactation

concentration

(gper100 ml)

10 days after commencement

oflactation: concentration

(gper100 ml)

Fat 6.5 3.8

Protein

Casein 5.0 2.6

Globulins 11.1 0.7

Lactose 2.9 4.9

Ash 1.2 0.8

Total solids 26.7 12.6

3948 MILK/Liquid Milk for the Consumer

mastitis control programs include regular mainten-

ance checks of rubberware and mechanical parts.

0015 After milking, the major concern is to minimize the

growth of microorganisms during the storage and

transport of milk from the farm to the factory. The

temperature of the milk from the cow is about 37



or body temperature. To minimize the growth of

microorganisms, it is necessary to reduce the tem-

perature to less than 5



C in a short period. In many

situations, the temperature is lowered on the farm

using a water cooling system based on plate or tubu-

lar heat exchange before the milk enters the milk

storage vats.

Storage

0016 Many storage vats or silos are now equipped with

refrigeration units which are able to reduce the tem-

perature to less than 5



C. In some areas, the milk

may be stored in cans in a large refrigerator for 1–2

days before dispatch to the factory. In areas where

refrigeration is not common, the milk is collected once

or twice per day from the farm or may be taken by the

farmer to a milk collection depot. The milk is gener-

ally cooled at the milk collection depot before dis-

patch to the factory. The microbiological quality of

milk received at the factory is dependent upon the

initial contamination of the milk during the milking

process and subsequent transport to storage vessels,

the temperature of the milk during storage, and the

length of time of storage. Table 2 shows the number

of microorganisms in milk of varying quality stored at

different temperatures.

0017 Milk stored at low temperatures for extended

periods is more likely to have large numbers of psy-

chrotrophic bacteria present. Some of these bacteria

may produce heat-stable enzymes (lipases and/or pro-

teases) which will survive pasteurization and could

therefore cause flavor defects in the finished product.

Research work has demonstrated that enzymatic ac-

tivity is unlikely if the numbers of microorganisms are

less than 1 million per milliliter. Conversely, if milk is

not cooled until hours after milking, the number of

microorganisms may increase to in excess of 1 million

per milliliter. Cooling of the milk after microbial

numbers have increased significantly will increase

the shelf-life only marginally.

0018It has been suggested that an alternative means for

extending the shelf-life in regions without adequate

refrigeration is to use the antibacterial activity of the

lactoperoxidase enzyme system. Small quantities of

hydrogen peroxide are added to milk to activate the

lactoperoxidase system. The technique has been

trialled successfully in Kenya, Sri Lanka, and Mexico.

0019Key factors in the successful use of the system to

reduce the frequency of pick-up to once per day in-

clude relatively low numbers of microbes and reduc-

tion of the storage conditions for milk to less than



C. Other techniques that have been demonstrated

to extend the shelf-life of raw milk are thermization

and addition of carbon dioxide.

0020One means of extending the shelf-life of milk on

the farm is to separate the cream from the skim milk.

The skim milk may be used to feed animals such as

pigs while the cream is transported to the factory once

or twice per week.

0021In countries that experience severe winters, steps

must be taken to minimize the likelihood of the

milk freezing. Freezing and thawing of milk in

uncontrolled conditions may result in disruption of

the fat globules and coagulation of protein, which

will cause problems with subsequent processing and

manufacture.

Transport of Milk from Farm to Milk

Collection Depot

0022Milk sold by the farmer for manufacturing and

processing is transported from the farm to the milk

collection and receival depot in a number of ways. In

countries with many small herds, the farmer or house-

holder carries the milk to a milk collection center.

Here the milk is graded for organoleptic quality,

weighed, and then cooled before transport to the

larger milk manufacturing factory. The number of

milk collection centers will depend upon the density

of the herds and the relative ease of transport from the

farm. The milk collection center may be cooperatively

owned by the farmers or owned by the milk factory.

In some countries, the milk is purchased by a middle-

man from the farmers and transported to the factory.

0023In areas where farms produce large volumes of

milk and the means of transport is more advanced,

the factory may collect the milk from the farm on

a twice-daily, daily, or alternate days basis. The

frequency of collection will depend upon the storage

conditions for the milk on the farm, the volume of

tbl0002 Table 2 Influence of storing milk for 24 h at different

temperatures on the bacterial content of three milk samples

with varying numbers of bacteria

Time of

storage (h)

Storage

temperature

(



Standard plate count at 30



(CFUml

1

)

Sample A Sample B Sample C

0 1500 45 000 260 000

24 5 1600 46 000 660 000

24 10 10 500 126 000 8 900 000

24 15 220 000 860 000 32 000 000

24 20 580 000 1 570 000 128 000 000

MILK/Liquid Milk for the Consumer 3949

milk, and the distance from the factory. If the milk is

not cooled on the farm it should be cooled immedi-

ately on arrival at the factory before storage. A road

tanker of varying size may be used to pick the milk up

or a tray truck able to carry cans or churns. Insulated

tankers will be used for the transport of refrigerated

milk. On arrival at the farm the driver usually meas-

ures the volume of milk and assesses whether the milk

is organoleptically acceptable for pick-up. Samples of

milk may also be taken for testing at the factory for

composition and quality parameters.

Testing for Payment and Quality

0024 A range of tests are carried out on raw milk supplies.

A farmer may be paid for milk according to the

volume of milk supplied, the quantity of fat, and

other components such as protein and whether the

milk is contaminated by added water, excessive

numbers of bacteria, residues of antibiotic and other

chemicals, somatic cells, and extraneous matter

such as dirt. The payment systems vary around the

world. In many countries, regulatory bodies or

factories may establish minimum quality levels or

standards for milk. The analytical techniques used

to test for quality parameters will depend upon the

quality standard, the number of suppliers, the accur-

acy required for results, and available technology.

The use of automated instruments for measurement

of milk composition, somatic cells, and bacterial

numbers enables faster feedback of results to the

farmer.

Payment

0025 Historically, volume and fat content have been used

for payment purposes. Where milk is used for con-

sumption in a liquid form, the farmer is normally paid

on volume basis provided the milk contains a

minimum content of fat and solids-nonfat (SNF) and

meets other defined quality standards. In some coun-

tries, where milk is used for manufacture of product,

it is purchased on a fat content basis while other

countries have introduced compositional payment

based upon fat and protein content. Simple tests to

determine the fat content of milk have been available

for many years but development of instrumentation

such as infrared equipment to determine SNF and

protein has enabled companies to test for fat, protein,

or SNF and volume on a daily basis. The frequency of

testing milk for payment purposes depends upon the

local situation.

Quality

0026 Over the years, the quality parameters used to deter-

mine whether milk is fit for sale by a farmer have

increased from simple sensory evaluations using sight

and taste to complex analyses for the presence of

chemical residues.

0027In developed dairy industries, where herds are large

and the milk is used primarily for manufacturing

purposes, the tests used to determine the quality of

milk – apart from compositional analysis – include

total bacterial numbers, presence of antibiotic resi-

dues, presence of added water, numbers of thermo-

duric bacteria, coliforms and other bacterial groups,

presence of extraneous matter or sediment, number of

somatic cells, residues of iodide, pesticides, and other

chemicals. Table 3 summarizes typical standards for

the different quality parameters.

0028In other countries, milk quality tests, such as alco-

hol stability, methylene blue reduction, or resazurin,

are used to determine the extent of microbial contam-

ination while specific gravity determination may

detect adulteration by water and other substances.

Generally, failure to comply with quality standards

results in a penalty such as rejection of the milk for a

specified period or a payment discounted from the

normal payment level.

Potential Public Health Risks

0029The consumption of unpasteurized milk by humans

poses potential risks from the following factors:

transmission of disease from the animal, transmission

of disease from a human milker or handler of milk

before consumption, or growth of undesirable

organisms in the milk. Pathogenic bacteria which

may be excreted in the milk by diseased animals

include Mycobacterium tuberculosis, Brucella abor-

tus, Staphylococcus aureus, Streptococcus agalacti-

ciae, Escherichia coli, Listeria monoctyogenes,

Leptospira spp. and Coxiella burnettii. In many coun-

tries, stringent veterinary surveillance of herds has

significantly reduced the risk of tuberculosis and bru-

cellosis transmitted to humans by milk. With the

exception of C. burnettii, which requires a higher

heat treatment than normal pasteurization condi-

tions, all other organisms are killed by effective pas-

teurization. A number of cases of food-poisoning

tbl0003Table 3 Typical standards for different quality parameters of

raw milk

Plate count 50 000^300 000 colonies ml

1

Freezing point 0.548 to 0.520



Antibiotic residues 0.0025–0.1 mgml

1a

Methylene blue reduction > 5 h

Somatic cells 200 000–400 000 ml

1

Thermoduric bacteria 1000–30 000 ml

1

Penicillin G-equivalent.

3950 MILK/Liquid Milk for the Consumer

outbreaks caused by Campylobacter strains and Lis-

teria monoctyogenes have been traced to the con-

sumption of raw or improperly pasteurized milk.

0030 Human handlers of milk may cause problems if

they are clinically or subclinically infected with

Salmonella spp., particularly Salmonella typhi,or

Streptococcus pyogenes, and contaminate the milk

during the milking, storage, and transport process.

Heat treatment of the milk equivalent to pasteuriza-

tion will eliminate milk as a likely vehicle for food

poisoning by these organisms. Many health author-

ities recommend the scalding of raw milk by bringing

milk to the boil before consumption in the home. This

form of heat treatment kills microbes with the poten-

tial of causing disease and also increases the shelf-life

by killing many bacteria which will spoil the milk.

0031 Care needs to taken with the quality of feedstuffs,

including grains, to prevent the possibility of contam-

ination of the milk by aflatoxins.

Direct Sales from the Farm to the Public

0032 The practice of direct sales of nonheat-treated milk

from the farm to the public will depend upon the

country. In some countries direct sales are prohibited

while in other countries the practice may be permitted

if the farmer has the herd regularly checked by a

veterinarian for absence of specific diseases and

carries out strict hygienic practices during milking,

storage, and packaging. Some farmers may heat-treat

the milk using a batch or high-temperature, short-time

(HTST) pasteurization system, while other farmers

sell raw or unpasteurized milk. The degree of surveil-

lance by health authorities of farms that sell raw or

heat-treated milk for human consumption varies from

regular to no inspections or surveillance.

See also: Aflatoxins; Buffalo: Milk; Campylobacter:

Properties and Occurrence; Escherichia coli:

Occurrence; Listeria: Properties and Occurrence; Milk:

Processing of Liquid Milk; Physical and Chemical

Properties; Analysis; Dietary Importance; Mycobacteria;

Pasteurization: Principles; Sheep: Milk; Spoilage:

Bacterial Spoilage; Staphylococcus: Properties and

Occurrence

Further Reading

Banks W and Dalgleish DG (1990) Dairy Microbiology. In:

Robinson, RK (ed.) The Microbiology of Milk, 2nd edn.

pp. 1–36. London: Elsevier.

Bramley AJ and McKinnon CH (1990) The Microbiology

of Raw Milk. In: Robinson RK (ed.) The Microbiology

of Milk, 2nd edn, pp. 163–208. London: Elsevier.

Fox PF and McSweeny PLH (1998) Dairy Chemistry and

Biochemistry. London: Blackie Academic and Profes-

sional.

Harding F (ed.) (1995) Milk Quality. London: Blackie

Academic and Professional.

IDF (1990) Milk Collection in Warm Developing Coun-

tries. Brussels: International Dairy Federation.

IDF (1994) The Significance of Pathogenic Microorganisms

in Raw Milk. Brussels: International Dairy Federation.

IDF (1995) Milk Payment System for ex Farm Milk, Anti-

biotic Testing, Mastitis Control. Bulletin 305. Brussels:

International Dairy Federation.

IDF (1996) Bacteriological Quality of Raw Milk. Brussels:

International Dairy Federation.

IDF (1997) Residues and Contaminants in Milk and Milk

Products. Brussels: International Dairy Federation.

La Fondation De Technologie Laitie

re du Quebec (1985)

Dairy Science and Technology. Quebec: Les Presses de

l’Universite

Laval.

Marth EH and Steele JL (eds) (1998) Applied Dairy Micro-

biology, pp. 1–64. New York: Marcel Dekker.

Varnam AH and Sutherland JP (1994) Milk and Milk Prod-

ucts Technology, Chemistry and Microbiology. London:

Chapman and Hall.

Walstra P, Geurts TJ, Noomen A et al. (1999) Dairy

Technology Principles of Milk Properties and Pro-

cesses, pp. 1–187. New York: Marcel Dekker.

Welch RAS, Burns SR, Davis SR et al. (eds) (1997) Milk

Composition, Production and Biotechnology. New

York: CAB International.

Wong NP (ed.) (1988) Fundamentals of Dairy Chemistry,

3rd edn. New York: Van Nostrand.

Processing of Liquid Milk

J Manners, University of Melbourne, Parkville,

Victoria, Australia

H Craven, Food Science Australia, Werribee, Victoria,

Australia

Background

0001Advances in technology and the demand by larger

communities of people for a regular supply of various

types of milk have led to the development and appli-

cation of a range of processes for liquid milk. These

include a defined heat treatment to minimize changes

to the product while eliminating pathogenic bacteria

and extending shelf-life, addition of supplements to

improve nutritional value or flavor, and modification

of composition to standardize consistency or improve

dietary content.

Types of Products

0002Traditionally, the principal product sold as liquid

milk was whole milk, heat-treated and packed in a

MILK/Processing of Liquid Milk 3951

returnable container such as glass bottles. In recent

years, changes in customer demands and techno-

logical advances have increased the range of liquid

milk products available. Major types of liquid milk

range from skim or nonfat milk, reduced- or low-fat

milk, high-fat milk to reduced-fat, high-protein

products. These may be sold as natural-flavored

milk or with added flavors such as chocolate, coffee,

and strawberry. The products may be heat-treated

using conventional pasteurization or ultrahigh tem-

perature (UHT) processing. Flavored milk products

usually contain added sugar, coloring and flavoring

agents and additives such as stabilizers. The range

of flavors added to milk depend on the cultural

background of the market. Chocolate-flavored

milk is a popular product in many countries. Milks

mixed with fruit juice or fruit pulp have been

marketed successfully in some countries, while the

consumption of drinking yogurt is growing. The

typical compositions for different milk products are

compared in Table 1.(See Fermented Milks: Types

of Fermented Milks; Heat Treatment: Ultra-high

Temperature (UHT) Treatments; Stabilizers: Types

and Function.)

0003 Milks may be sold with added vitamins, such as

vitamins A and D, to increase the dietary intake of

essential nutrients. In recent years, with increased

awareness of the risks of osteoporosis, calcium has

been added to some milk products. Low-lactose

milk made by the addition of the enzyme, lactase,

to milk before or after heat treatment is gaining

a market share in markets with a large number

of lactose-intolerant consumers. (See Calcium: Pro-

perties and Determination; Cholecalciferol: Physi-

ology; Dairy Products – Nutritional Contribution;

Food Intolerance: Lactose Intolerance; Milk Allergy;

Lactose; Osteoporosis; Retinol: Physiology.)

0004 Other new products incorporate Lactobacillus

acidophilus and Bifidobacterium spp. in liquid

milk to assist those with sensitive gastrointestinal

tracts. In Australia, sales of pasteurized ultrafiltered

low-fat milk have increased steadily since the

initial market launch. (See Acidophilus Milk;

Bifidobacteri in Foods; Lactic Acid Bacteria;

Membrane Techniques: Principles of Ultrafiltration;

Probiotics.)

0005In many countries, the new types of milk products

have steadily eroded the market share of whole milk

over time to the situation in Canada and The Nether-

lands, where reduced-fat milk accounts for more than

half of the total milk sales.

Collection and Storage of Raw Milk

0006As many milk-processing dairies are located near the

market in urban areas, the milk is transported in

large-capacity tankers to the processing dairy from

milk collection depots in the farming areas. The milk

is usually cooled at the depot before dispatch to the

processing dairy. Some processing dairies may receive

milk directly from farms.

0007On arrival at the milk-processing dairy, the milk is

inspected for quality attributes such as temperature,

flavor, smell, and presence of extraneous matter and

volume. Samples of milk may be taken to determine

fat and solids-nonfat content, numbers of bacteria,

freezing point and presence of antibiotic residues. The

actual tests performed on incoming supplies of milk

depend on a company’s quality program for inspec-

tion of raw materials and the requirements of regula-

tory authorities. (See Milk: Liquid Milk for the

Consumer.)

0008After the tanker load has been accepted for use,

the milk is pumped into a storage vessel designated

for raw milk. The milk may be filtered during the

pumping process to reduce the level of extraneous

matter. It may be necessary to cool the incoming

milk to 5



C to minimize the growth of contaminating

microorganisms. Plate heat exchangers are com-

monly used to cool the milk before storage. In many

countries, the temperature of milk during storage and

the allowed time for storage before pasteurization are

limited by regulatory requirements. However, storage

conditions of less than 5



C and 48 h maximum are

generally accepted as good manufacturing practice by

the industry across the world. Storage of milk above



C and extended times of storage encourage the

growth of psychrotrophic bacteria, which may cause

organoleptic defects.

0009The milk in the storage vessels must be agitated

slowly to prevent the separation of fat. Mechanical

agitation or passage of compressed air through the

milk is commonly used by the dairy industry. Care

must be taken during agitation to minimize the possi-

bility of lipolysis caused by disruption of the milk fat

globules.

tbl0001 Table 1 Typical chemical composition (g per 100 g of product)

for different milk products

Product Fat Solids-nonfat Totalsolids

Whole milk 3.8–4.0 > 8.5 > 12.3

Skim milk 0.1 > 8.5 > 8.6

High-fat milk 5.0–6.9 > 8.5 > 13.5

Reduced-fat milk 1.0–2.0 > 8.5 > 9.5

Reduced-fat,

high-protein milk

1.0–2.0 11.3 12.3–13.3

Flavored milks may be made by adding sucrose, color, and flavors to the

typical formulations described.

3952 MILK/Processing of Liquid Milk

Preparation

0010 Before heat treatment and packaging, it may be

necessary to prepare the raw milk for processing.

Regulatory authorities in some countries permit the

milk depot to standardize the milk to desired fat and

solids level before dispatch to the processing dairies.

In other countries, this form of preparation is not

permitted. For skim milk, the fat is removed through

the separation process while low-fat, high-solids

products may require separation and the addition of

milk solids in the form of skim milk powder or skim

milk concentrate. In the preparation of flavored milk,

sugar, flavors, colors, and other additives are added to

the milk in the desired quantities. Often, these ingre-

dients are purchased in a dry, premixed form, and

blended with a small quantity of milk or water before

mixing with the raw milk. Sometimes, the syrup mix-

ture may be injected into the milk after pasteuriza-

tion.

Recombination

0011 Where the supply of raw milk fluctuates or is insuffi-

cient to meet the market needs, milk fat in the form of

butter oil and milk solids in the form of full cream or

skim milk powder may be used to prepare reconsti-

tuted or recombined milk. Recombination may also

be used where the available milk supply has a high

fat content. The butter, unsalted butter, and milk

powders must be selected carefully and stored to

ensure proper mixing of the materials and an absence

of undesirable flavors in the finished product. The

added water must be of a drinkable quality. In some

countries, vegetable fats may be used instead of milk

fat to prepare recombined milk. (See Recombined and

Filled Milks.)

Heat Treatment

0012 Milk is heat-treated to kill many of the microorgan-

isms present in raw milk. The heat treatment makes

the milk safe to drink and extends the potential

shelf-life. Several different forms of heat treatment

are used. These are pasteurization, UHT, and in-

container sterilization. Pasteurization is the most

commonly used form of heat treatment. The shelf-

life of the milk depends on the heat treatment used

in the process. (See Heat Transfer Methods; Heat

Treatment: Ultra-high Temperature (UHT) Treat-

ments; Pasteurization: Pasteurization of Liquid Prod-

ucts; Sterilization of Foods.)

Pasteurization

0013 This form of heat treatment evolved from Pasteur’s

discovery that heating wines to 50–60



C destroyed

many of the organisms responsible for spoilage. With

milk, a temperature–time combination sufficient to

kill the organism, Mycobacterium tuberculosis,

without adversely affecting the flavor, color, and

nutritional value is used. (See Mycobacteria.)

0014The two principal forms of pasteurization now

used by industry throughout the world are batch

pasteurization, where milk is held at a determined

temperature for a long time, and high-temperature,

short-time (HTST) pasteurization using a higher

temperature for a relatively short period. Typical tem-

perature–time combinations are 62–63



C for 30–

35 min for batch pasteurization and 72



C for 15 s

for HTST pasteurization. The temperature–time

combination may need to be increased for effective

pasteurization of products such as flavored milk with

higher levels of solids, or reduced for skim milk to

minimize damage to flavor and color. After heating,

the milk is cooled immediately to 5



C or lower.

0015The batch pasteurization process is carried out

using slow agitation of milk in a jacketed vat, which

can be heated and cooled. The cost of the equipment

is relatively low, but the labor and energy costs are

higher compared with the HTST system.

0016In the modern processing dairy with a large

throughput, the HTST pasteurization process is

favored, as the throughput can be as high as 50 000 l

1

, and energy costs are reduced by using the heated

milk to warm incoming milk in the regeneration

section of the pasteurizer. The heated milk is cooled

after pasteurization in the regeneration section.

0017The plate heat exchanger has historically been used

for HTST pasteurization (Figure 1). The plate design

offers a large surface area for heat transfer in a rela-

tively compact area. Once the milk reaches the de-

sired temperature of 72



C, it enters a holding tube

designed to ensure that all milk particles reside in the

tube for at least 15 s. A temperature probe is located

at the end of the holding tube. If the temperature falls

below the desired temperature, a flow diversion valve

is opened, which directs underprocessed milk back

into the balance tank. The pasteurizers need to be

checked regularly to ensure that there is no risk of

raw milk contaminating the pasteurized product.

0018Heat exchangers designed using a tubular system

have become increasingly popular in recent years.

The heat is transferred from heated outer tubes to

product in inner tubes. The tubular system is con-

sidered to be cheaper to maintain and can handle

products with a higher viscosity compared with a

plate heat exchanger.

0019In recent years, the design of pasteurizers and con-

trol systems used on pasteurizers has been improved

in response to public health problems thought to be

caused by inadequate pasteurization of milk.

MILK/Processing of Liquid Milk 3953