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

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L46/27. (See Sensory Evaluation: Sensory Character-

istics of Human Foods; Practical Considerations.)

0089 The butter must first be stored or ‘tempered’ at



C for 24 h prior to examination. A sample (plug)

of bulk or tub butter is taken using a borer. For other

retail portions, the brick or roll is cut half way down,

and the lower half is broken apart.

0090 The qualities measured are:

0091 Flavor and aroma. These are judged by the smell

and taste. A portion of the butter should be tasted

but not swallowed. (See Sensory Evaluation:

Aroma; Taste.)

0092 Consistency. A very good butter should have a

close body and waxy texture and should be well

spreadable. The appearance of the butter will pro-

vide the experienced butter grader with much in-

formation. A portion of the plug is broken off to

enable the texture to be examined, and a section is

cut to observe the cut surface. Scoring reflects

the desirability of the compact ‘plastic’ nature of

butter produced by modern technology. The more

open and grainier consistency of traditional butter

may be viewed as a defect or alternatively con-

sidered in the ‘specialties’ category. (See Sensory

Evaluation: Texture.)

0093 Appearance and finish. Evenness of color and

absence of free moisture, giving a ‘clean, dry’

butter, are the requirements for good-quality

butter. Traditionally made butter had a very open

texture, and free moisture was a frequent fault.

With the advent of the vacuum section in continu-

ous buttermakers, this particular characteristic or

fault is now rarely seen. (See Sensory Evaluation:

Appearance.)

Each of these attributes is given a score, dependent

on the perceived relative importance of the character-

istic. Scoring for acceptance for intervention storage

is shown in Table 1. The United States Department of

Agriculture (USDA) defines detailed criteria for

butter grading based on flavor, body, color, and salt

characteristics (USDA Standards for Butter, 58.2621–

27, 1989).

Defects

0094 Defects that arise in the finished product can nor-

mally be attributed to problems arising from two

main areas: (1) the quality of the original milk or

cream and its handling; (2) manufacturing defects;

or a combination of both.

0095Taints and poor microbiological quality will give

rise to off-flavors. A reduced shelf-life and physical

defects can be caused by poor hygiene, temperature

abuse, the use of inappropriate pumps, and over-

agitation.

0096Utilizing cream received from other sources can

give rise to numerous problems unless the receiving

plant can be absolutely sure of the conditions under

which it was produced and handled.

0097Operating faults, such as an imbalance between the

speed of the first section of the buttermaker and too

slow a cream flow, will cause the grains to be too

large. Consequently, the buttermilk will not drain

away cleanly, and the result will be a streaky, weak-

bodied butter with free moisture.

0098Underchurning, with too high a cream flow and

too slow a churn speed, results in small grains and

incomplete separation of the fat and aqueous phases.

This gives a butter with a very high moisture content

and a pale color.

0099Overworking due to, for example, too much

product in the working section, excessive con-

veyor speed, or apertures being too restricted, will

give a weak-bodied, lifeless, and sticky butter,

difficult to handle and likely to lose points at

grading.

0100An open-textured butter with uneven salt and

moisture distribution may be caused by too slow an

auger speed, inadequate vacuum or too little product

in the working section, or insufficient restriction at

the adjustable apertures.

0101A mottled butter with excess moisture or excess

salt can be the result of an inaccurate salt:water

ratio in the slurry, or an improperly mixed slurry.

0102Packed butters held under chilled conditions have

a finite life. Defects can develop from exposure to

light, and taints are easily absorbed if butter is

stored near strong flavors or smells. Foil-wrapped or

sealed retail packs stored under the recommended

chilled conditions should retain their premium

quality for 2 months, whereas parchment-wrapped

butters will develop surface faults after some 4–6

weeks.

See also: Butter: Properties and Analysis; Colloids and

Emulsions; Cream: Types of Cream; Lactic Acid

Bacteria; Milk: Processing of Liquid Milk; Plant Design:

Basic Principles; Designing for Hygienic Operation;

Process Control and Automation; Sensory Evaluation:

Sensory Characteristics of Human Foods; Texture;

Aroma; Taste; Starter Cultures; Whey and Whey

Powders: Production and Uses

tbl0001 Table 1 Scoring for acceptance for intervention storage

Maximum Required

Appearance 5 4

Consistency 5 4

Flavor 5 4

BUTTER/The Product and its Manufacture 725

Further Reading

Murphy MF (1990) In: Robinson RK (ed.) Dairy Micro-

biology, 2nd edn, vol. II. London: Elsevier.

Rajah KK and Burgess KJ (eds) (1991) Milk Fat, Produc-

tion, Technology and Utilization. Huntingdon, UK:

Society of Dairy Technology.

Romney AJD (ed.) (1990) CIP: Cleaning in Place, 2nd edn.

Huntingdon, UK: Society of Dairy Technology.

Rothwell J (ed.) (1988) Cream Processing Manual, 2nd edn.

Huntingdon, UK: Society of Dairy Technology.

Wilbey RA (1991) In: Russell JB and Pritchard L (eds)

Analysis of Oilseeds Fats and Fatty Foods. London:

Elsevier.

Wilbey RA (1994) In: Robinson RK (ed.) Advances in Milk

Processing. Modern Dairy Technology, 2nd edn. vol. 1.

London: Chapman & Hall.

Properties and Analysis

A M Fearon, The Queen’s University of Belfast,

Belfast, UK

Introduction

0001 In the manufacture of traditional creamery butter,

cream is churned to bring about a phase inversion

and then worked to give a product having a continu-

ous fat phase and a disperse phase containing water

and globular fat. The properties of butter are deter-

mined both by its chemical composition and by the

physical treatments applied throughout its manufac-

ture. This article reviews the physical properties and

chemical composition of butter, what factors affect

these properties, and how they may be determined.

Physical Changes During Churning

0002 The first stage of the physical transformation of

cream into butter by churning occurs during the

aging or tempering of the cream prior to churning.

During this period, milk fat crystallizes and the fat

globule membrane is weakened. The churning pro-

cess is based on the incorporation of air into cream to

create a foam and is achieved by vigorous agitation.

Fat globule membranes, already weakened by cold

aging, are further damaged by the mechanical stresses

applied, and liquid fat escapes. This brings about

collapse of the foam and clumping of the fat globules

to produce butter granules which are then worked

together to form butter. Some globular fat is present

in the final product, but the amount will depend

on the prechurning tempering treatment and the

severity of the working conditions before and after

processing.

Butter Microstructure

0003The microstructure of traditional creamery butter

and the influence of processing factors thereon

have been studied using freeze-fracture techniques in

association with electron microscopy. These have

shown how cream tempering conditions can influence

the crystallization pattern of milk fat within the glob-

ules and hence their process stability and, ultimately,

product firmness. The cold–warm–cold cream

tempering procedure, which was developed to im-

prove the spreadability of winter butter, results in

globules with a thick surface shell of solid fat and

crystal aggregates of varying shape and size in the

liquid fat in the interior. This type of cream globule

can withstand mechanical stress during churning and

consequently gives a softer butter with a higher pro-

portion of globular fat than that obtained from a low-

temperature cream treatment. Electron microscopy

studies have also shown how intensive mechanical

working of butter during processing destroys fat

globules, resulting in a highly homogeneous structure

with a more crystalline interglobular phase and

consequently a firmer texture. A recent develop-

ment in butter manufacture has been the application

of scraped surface technology, developed by the

margarine industry, to produce a more spreadable

product.

Chemical Changes During Churning

0004Butter is basically a concentration of milk fat along

with some water and milk solids-not-fat (MSNF).

The composition of the fat in butter reflects that of

the original milk fat, although there is some loss of

phospholipids, sterols, and free fatty acids, particu-

larly volatile fatty acids, into the buttermilk during

separation and churning. Greater change occurs in

the physical state of milk fat during churning than

in the chemical nature of its constituents. However,

the combination of agitation of the milk during

milking with extended holding of the milk on the

farm and at the factory before pasteurization lead

also to an increase in concentration of free fatty

acids and consequently lipolyzed flavor in the

product. The increase in lipolysis is probably due to

increased accessibility of the fat to lipolytic enzymes

because of damage to or loss of the protective milk fat

globule membrane. Lipolyzed flavor may increase in

stored butter due to the preferential release of short-

chain fatty acids by enzymes with a high specificity

726 BUTTER/Properties and Analysis

for these acids (secreted by psychrotrophic bacteria).

In sweet cream butter (as opposed to lactic or ripened

butter), in particular unsalted butter, the primary

cause of flavor impairment is lipolytic rancidity.

Thus, good manufacturing practice, at both the

farm and the factory, is necessary to prevent a high

level of free fatty acids in the final product.

Chemical and Physical Properties of

Butter

Chemical Composition and Analysis

0005 The composition of butter is described in the food

regulations of most countries. Typically, butter con-

tains 80–84% milk fat, 15.3–15.9% water, about

1% milk solids other than fat (casein, lactose, and

minerals) and 0.03–1.8% salt. Milk fat is the only

fat permitted in butter, although in some countries

lower-melting milk fat fractions may be added during

manufacture to produce a softer product which

complies with the definition of ‘butter.’ A maximum

water content (16%) is usually stated as it is import-

ant for the good keeping properties of the product.

Butter may be salted or unsalted, but may not contain

any added antioxidants. In some countries, natural

coloring agents, such as annatto, turmeric, carotene,

or curcumin are permitted. Neutralizing salts and

lactic acid cultures are allowed for the manufacture

of ripened or lactic butters.

0006 Analytical methods for butter are included in the

inventory prepared by the International Dairy Feder-

ation (IDF), the Association of Official Analytical

Chemists (AOAC) and the International Standards

Organization (ISO) on methods of analysis for milk

and milk products. Apart from standard methods of

analysis of butter components (moisture, fat, solids-

not-fat, and salt), other analytical methods are cata-

loged, including methods to characterize milk fat, to

determine the presence of a foreign fat, and to detect

rancidity in butter.

0007 Not surprisingly, many of the analyses for butter

are concerned with the composition and properties of

its fat. Some classical chemical constants for milk fat

are summarized in Table 1.

0008 Milk fat contains a comparatively high proportion

of water-soluble volatile fatty acids, in particular

butyric acid. The presence of these is the basis of

both traditional (Reichert–Meissl, Kirschner) and

modern (chromatography) tests to detect the presence

of adulterating fat. Iodine value (a measure of unsat-

uration) is a useful identifier of summer or winter

butter but it has commercial value too. Butter-makers

in mainland Europe and Ireland apply the appropri-

ate cream-tempering treatment, the Alnarp process,

to produce harder or softer butter on the basis of

cream iodine value.

0009Although more than 450 fatty acids have been

identified in milk fat, only about 12 of these

(Table 2) play a significant role in determining its

physical, chemical, and nutritional properties. For

detailed information on the composition of milk fat

it is necessary to use chromatographic techniques.

The fatty acid profile of milk fat is obtained by first

preparing the more volatile fatty acid methyl esters

and then separating these by gas–liquid chromatog-

raphy (GLC) using a capillary column and a flame

ionization detector. A triacylglycerol fingerprint of

the fat may also be obtained using capillary column

GLC, with resolution on the basis of carbon number

and degree of unsaturation. Rapidly developing high-

performance liquid chromatography (HPLC) tech-

niques have found application for the resolution

tbl0001Table 1 Chemical constants for milk fat

Chemical constant Value

Saponification value (SV) 220–240

SV ¼ mg KOH needed to saponify 1 g fat

Iodine value (IV) 26–42

IV ¼ g iodine reacted with 100 g fat

Reichert – Meissl number (RMN) 20–35

RMN ¼ cm

of 0.1 mol l

1

alkali needed to neutralize

the water-soluble volatile fatty acids distilled from

5 g saponified fat

Polenske number (PN) 1.0–3.3

PN ¼ cm

of 0.1 mol l

1

alkali needed to neutralize the

water-insoluble volatile fatty acids distilled from 5 g

saponified fat

Kirschner number (KN) 18–30

KN ¼ cm

of 0.1 mol l

1

alkali needed to neutralize the

water-soluble volatile fatty acids distilled from 5 g

saponified fat and which form soluble silver salts

Data from Walstra P, Jenness R (1984) Dairy Chemistry and Physics,

pp. 377–457. Chichester: Wiley.

tbl0002Table 2 Major fatty acids found in milk fat triacylglycerols

Fattyacid g per100 g fatty acid Class

4:0 3.3

4.9 Saturated short-chain

6:0 1.6

8:0 1.3 7.4 Saturated medium-chain

10:0 3.0

)

12:0 3.1

14:0 9.5 50.4 Saturated long-chain

16:0 26.3

)

18:0 14.6

16:1 2.3

32.1 Monounsaturated

18:1 29.8

18:2 2.4

3.2 Polyunsaturated

18:3 0.8

Data from Gurr MI (1989) In: Cambie RC (ed.) Fats for the Future, pp. 41–61.

Chichester: Ellis Horwood.

BUTTER/Properties and Analysis 727

of milk triacylglycerols whilst a combination of tech-

niques, e.g., silver ion chromatography and reversed-

phase HPLC, and new methods combining gas

chromatography–mass spectrometry (GC-MS) can

provide more detailed information on the molecular

structure of milk fat.

0010 Factors influencing chemical composition The fatty

acids in milk fat originate from two main sources:

those acids synthesized de novo in the mammary

gland, C

–C

and a proportion of C

acids,

and those arising directly from the diet and taken

up by the mammary gland from the circulating

blood, i.e., the remainder of C

and the longer-

chain C

acids. The principal factors which influence

the relative contributions of fatty acids from these

two sources are stage of lactation (shorter-chain

acids) and composition of diet (longer-chain acids).

Summer grazing of fresh pasture leads to a softer milk

fat with a decrease in C

16:0

and an increase in C

18:0

and C

18:1

acids, whilst the reverse occurs during

winter feeding of concentrates and silage.

0011 Supplementation of the cows’ diet with fats or oils

to increase energy input, especially in early lactation,

can also affect fatty acid composition. Generally, such

a diet will tend to increase the yields of fatty acids

18:0

and C

18:1

while decreasing the levels of the

shorter- and medium-chain acids, C

–C

. If the sup-

plemented fat is presented in a protected form, it

can pass through the rumen without being subjected

to ruminal hydrolysis or biohydrogenation and

the composition of the resulting milk fat will reflect

that of the supplement. Protected fats also allow

rumen metabolic activity to proceed unimpaired

by the adverse effect of large amounts of fat. The

technology to produce protected fats has developed

considerably since the early 1970s and is currently

in use in Australia to produce butter with higher

proportions of C

18:1

18:2

and C

18:3

fatty acids

and lower proportions of the saturated C

and

fatty acids. This butter has greatly improved

spreadability whilst changes in the proportions of

saturated-to-unsaturated fatty acids and the presence

of n-3 fatty acids enhance the contribution of milk fat

to human nutrition. Previous problems of rapid oxi-

dation of milk fat arising from the high content of

polyunsaturated fatty acids have been avoided by

including additional vitamin E in the cows’ diet.

This additional natural antioxidant is transferred

into the milk.

0012 An alternative approach to feeding protected fats

has been based on exploiting the C

18:0

to C

18:1

con-

version which occurs during milk fat biosynthesis by

the action of desaturase enzymes in the cows’ intes-

tine and mammary gland. The cows’ diet must supply

a high proportion of C

fatty acids (e.g., from oil-

seed cereals) in order to optimize the desaturating

activity of the bovine tissue. The resulting milk fat

has an increased level of C

18:1

(oleic) acid and a

reduced level of C

16:0

(palmitic) acid. Monounsatu-

rated acids are less susceptible to oxidative reactions

than polyunsaturated acids and the increased content

of oleic acid in butter greatly enhances its spread-

ability at low temperatures.

Physical Properties

0013Physical constants Values for physical constants of

milk fat are presented in Table 3. The refractive index

for milk fat at 40



C was once a valuable indication of

its purity, but nowadays many fats used in the mar-

garine industry will give a similar figure. The specific

gravity of milk fat may be measured at different tem-

peratures, although the difference in specific gravity

between milk fat and other fats is greatest at around



0014Milk fat melts and solidifies over a temperature

range so, rather than having a melting or solidifica-

tion point, it has a melting and solidification interval

(Table 3). Ideally, these ranges should coincide, but

the dependence of the solidification interval on the

rate of cooling and the influence of previous thermal

history on the melting interval, as well as the dissol-

ution rather than melting of fat crystals during

heating, means that they rarely do so. Further infor-

mation on the melting behavior of milk fat may be

obtained using differential scanning calorimetry. This

analysis is based on the thermal transitions that occur

in a substance during heating and cooling.

0015The solid fat content in milk fat over a range of

temperatures may be measured by nuclear magnetic

resonance (NMR). This technique operates on the

principle that protons placed in a strong magnetic

field can, under certain circumstances, absorb energy

from electromagnetic waves. This absorption, termed

NMR, depends on the physical state of the protons

and allows determination of the solid fat content

(% SFC). The method was previously applied to

butter only for research purposes but is now a regular

quality control test for the dairy spreads, the physical

tbl0003Table 3 Physical constants of milk fat

Physicalconstant Value

Refractive index (40



C) 1.4524–1.4561

Specific gravity (37.8



C) 0.910–0.913

Melting interval 28–33



Solidification interval 24–19



Data from Kirk RS and Sawyer R (eds) (1991) Pearson’s ChemicalAnalysis of

Foods, 9th edn, pp. 574–608. Essex: Longman.

728 BUTTER/Properties and Analysis

properties of which at refrigerator temperatures are

an important selling point.

0016 Rheology Butter may be described as a plastic fat

and depicted for rheological purposes by the Bingham

model which describes ideal plastic behavior. In rheo-

logical terms, a plastic material flows when a stress

greater than a limiting value (yield value) acts on it.

However, aspects of butter behavior, such as work

softening and thixotropic hardening, can only be

explained by viscoelastic theories. Various instru-

mental techniques to measure butter firmness were

evaluated by the IDF, which recommended the cone

penetrometer as easy, quick, and cheap to use and

with acceptable reproducibility. The IDF method

relates penetration depth (p) to apparent yield stress

(AYS) by the equation AYS ¼ gW/pp

tan

(

a), where

W is the cone mass, g the acceleration due to gravity

and a the cone angle. For more detailed information

on the textual characteristics of butter, a two-bite

compression test using the Instron Universal Testing

Equipment can be carried out. This provides a texture

profile from which such properties as fracturability,

hardness, cohesiveness, and springiness can be meas-

ured. German butter manufacturers favor the sectility

test which measures the force at a set rate needed to

cut through a portion of tempered butter with a wire

of certain diameter and length.

0017 Factors that influence butter consistency A number

of factors, not all within the control of the manufac-

turer, influence butter consistency. The proportion of

solid fat in butter is highly correlated with product

firmness and is strongly influenced by the cows’ diet.

Feeding is responsible for the difference in firmness

between summer and winter butters and can be dir-

ectly related to the change in fatty acid composition

of the milk fat, which is due largely to the changeover

from summer grazing to winter silage and concen-

trates.

0018 The number and size of fat crystals also affect

consistency and are usually determined by crystalliza-

tion temperature and rate during aging of the cream.

Slow or stepwise cooling promotes the formation of

fewer, larger crystals and a lower SFC which favor a

softer fat. Cream aging is not required when butter is

produced by scraped surface technology. The manu-

facturing process creates very many small (b

) crystals

in a firm, homogeneous product. Firmness is greatly

reduced by mechanical working and, as fat crystal-

lization is completed during production, postmanu-

facture hardening, common in traditional creamery

butter due to crystal growth, is avoided.

0019 Plastic fats like butter have a three-dimensional

crystal network held together by reversible weak van

der Waals attractive bonds and irreversible stronger

bonds formed where crystals have grown together

postmanufacture. During mechanical working of

butter, such as the microfixing of bulk butter prior

to retail packaging, the hardness of butter is reduced

(work softening); and although the butter becomes

harder again over several weeks it will not reach its

original value. Work softening may be explained by

the breaking of the bonds in the crystal network,

while the reformation of reversible bonds into a new

network structure is responsible for the gradual

increase in hardness. This property of work softening

has been exploited by butter manufacturers to pro-

duce an easier-spreading butter. Recovery of hardness

during storage is slower at low temperatures but is

accelerated by temperature fluctuations, hence such a

product requires careful control during marketing.

0020Nutritional properties of butter Butter, along with

other fat-containing dairy products, contributes just

under 25% of dietary lipid in the UK and concern has

been focused on the relationship of dietary lipid to

coronary heart disease (CHD) and atherosclerosis.

Two inversely related cholesterol-containing blood

lipid fractions, low-density lipoprotein (LDL) and

high-density lipoprotein (HDL), have an important

influence on these diseases. High concentrations of

plasma LDL generally indicate an increased risk of

CHD with dietary saturated fats tending to increase

LDL concentrations and polyunsaturated fats tending

to reduce them. Milk fat, although containing about

30% oleic acid (C

18:1

), is defined as a saturated fat,

probably because of the low levels of polyunsaturated

fatty acids present. Butter itself has been shown to

cause elevated LDL levels and this has been linked not

only to its content of saturated fatty acids but also

to their esterified configuration. However, there is

now evidence that cis monounsaturated fatty acids,

far from occupying a neutral position in the diet

and CHD, actually lower LDL concentrations whilst

maintaining beneficial HDL levels. Consequently, the

new ‘monobutters’ containing elevated levels of

monounsaturated fatty acids (mostly oleic acid) will

be attractive to consumers not only for improved

spreadability but also for health reasons.

0021Interest has been shown recently in a branched-

chain unsaturated fatty acid which is normally

found in relatively small quantities in milk fat, conju-

gated linoleic acid (CLA). CLA, or its major isomer

found in milk, cis-9, trans-11-octadecadienoic acid,

has shown significant anticarcinogenic activity, anti-

atherogenic activity and other beneficial biological

activity in studies with human cells and animals.

CLA can arise directly in milk fat from biohydrogena-

tion of dietary linoleic (18:2) acid in the cows’ rumen.

BUTTER/Properties and Analysis 729

Its major route into milk fat however, is via the desat-

uration of trans vaccenic acid, trans-11 18:1, (TVA),

which is formed during the biohydrogenation of both

linoleic and linolenic (18:3) acid. On reaching the

cows’ mammary gland, TVA is desaturated to CLA

by the D

9

stearoyl Co-A desaturase enzyme. There

are a number of research programs directed at in-

creasing this and other functional fatty acids in milk

fat by modifying the cows’ diet.

0022 Government recommendations for a healthy diet

have included a reduction in total fat intake, particu-

larly saturated fat. However, the balance of nutrients,

fat types, and ratio of n-6:n-3 fatty acids must also be

considered. Milk fat is an important source of fat-

soluble vitamins, especially vitamin A, and provides

small but useful amounts of vitamin D to diets

of children, pregnant and lactating women, whose

requirements are particularly high.

0023 Dietary lipids, of the correct balance, are essential

for our health but, in general, food will be eaten only

if it is palatable. Milk fat contributes not only a

pleasant flavor and aroma, but also an attractive

texture and mouth feel.

0024 Additives and contaminants Certain additives such

as salt, natural coloring agents, lactic cultures, and

neutralizing salts may be permitted in butter but these

vary from country to country. However, butter may

also contain very low concentrations of other com-

ponents, called contaminants. Although contamin-

ants are primarily synthetic chemicals, they also

include microbial toxins, endogenous plant toxicants,

heavy metals, and radionuclides. A comprehensive

review of milk contaminants in Europe has been

published by the IDF.

0025 Chemicals such as the organocholorine-type pesti-

cides and polychlorinated biphenyls have been scru-

tinized as they are lipophilic and tend to accumulate

in the fat. However, levels of these chemicals detected

in butter are below limits set in most countries and

there is legislation in place governing their use.

Organophosphates and carbamates are also widely

used as pesticides but, as they are not lipophilic and

are readily broken down by the cow, they give less

cause for concern.

0026 The risk of contamination of milk by such sub-

stances as detergents, disinfectants, and plasticizers

(from packing materials and pipelines) may be min-

imized by good production practice both on the farm

and at the factory. Antibiotics in milk can have a

detrimental effect on the manufacture of cultured

products and their use on farms is governed by legis-

lation. Strict control of feed manufacture should

avoid mold growth and the possibility of mycotoxin

production and contamination of the milk.

0027There is little heavy metal contamination of butter

through the feed, the cow acting as an effective filter.

However, some contamination with copper and iron

from dairy equipment can occur during and after

milking; these metals act as prooxidants and the

manufacturing treatments which are applied to butter

make its component fat phase particularly suscep-

tible.

0028There is little cause for concern over radionuclide

levels in milk. Nevertheless, following the Chernobyl

reactor incident in May 1986 and the associated

increase in radioactive fallout over Europe, especially

Scandinavia, monitoring of agricultural produce still-

takes place. The isotopes concerned were iodine-131,

cesium-134, and cesium-137. Although iodine-

131 has a short half-life of 8 days, iodine accumulates

in the thyroid gland and high concentrations can be

reached. Milk was found to contain all three radio-

active isotopes of concern but butter had very low

levels, with the isotopes being distributed in the serum

rather than the fat phase.

Dairy Spreads

0029Traditional table spread products such as butter must

compete with the plethora of blended dairy spreads

on the market. These blends have improved spread-

ability over butter, are more competitively priced, and

appeal to the health lobby owing to their increased

levels of unsaturated fatty acids and, in some

instances, lower fat contents.

0030The simplest type of dairy spread may be obtained

by blending cream or butter with a liquid vegetable

oil such as soya bean oil. The mixture of cream and

vegetable oil may be churned in a batch or continuous

butter-maker, but if oil is added to butter itself, high

shear rates are required to insure good mixing.

Increasing the level of oil to improve spreadability at

low temperatures results in oiling-off and loss of body

at higher temperatures. This can be avoided by mim-

icking margarine manufacturers and including a pro-

portion of saturated (hydrogenated) fat to maintain

body and aid emulsion stability. Typically, such a

product would contain a vegetable oil such as soya

bean oil, a partially hydrogenated oil and cream, and

may be manufactured in a continuous butter-maker

or, more commonly, by using scraped-surface tech-

nology. The fat content of these two types of dairy

spreads is usually in the region of 70–80%.

0031The third type of dairy spread available is the low-

fat product. In low-fat spreads the aqueous phase

makes up about 52–75% of the product compared

with a maximum of 16% in butter. The fat phase is

composed of vegetable oils, hydrogenated vegetable

oils and possibly milk fat, with sodium caseinate or a

730 BUTTER/Properties and Analysis

buttermilk protein concentrate added for both flavor

and water-binding/emulsification purposes. The early

low-fat products contained milk fat as the principal

fat but both financial and consistency considerations

have led to the development of products having no or

very low levels of milk fat and depending on the milk

protein for flavor. One particular problem arises with

these products due to the use of milk protein. As the

fat content is reduced, the water-in-oil emulsion

becomes less stable and milk protein, when added to

such products with fat levels around 40%, tends to

promote a phase inversion to an oil-in-water emul-

sion. This problem may be overcome by increasing

the milk protein level (and increasing the cost), modi-

fying their properties by heat treatment and by

carefully selecting the emulsifier and stabilizer levels

needed to maintain a stable emulsion. This type of

product, which most closely resembles margarine,

is manufactured using margarine technology in a

scraped-surface cooler to bring about crystallization,

mainly in the b

form. During manufacture, it is crit-

ical for the keeping properties of the product that

good moisture distribution with large numbers of

discrete moisture droplets and an absence of channel-

ing is achieved. All three types of dairy spreads, as

with the new spreadable butters, require packaging in

tubs, as the traditional foil laminate or parchment

wrapping provides inadequate support. Because of

increased levels of unsaturated fats and an increased

aqueous phase (which results in a larger size of

moisture droplet), these products should be stored

at a low temperature to preserve chemical and

microbiological quality.

See also: Butter: The Product and its Manufacture;

Contamination of Food; Dairy Products – Nutritional

Contribution; Fatty Acids: Dietary Importance; Milk:

Physical and Chemical Properties

Further Reading

Baer RJ (1996) Production and utilization of dairy cows’

milk and products with increased unsaturated fatty

acids. In: Phillips CJC (ed.) Progress in Dairy Science,

pp. 247–262. Oxon: CAB International.

Christie WW (1997) Advances in Lipid Methodology –

Four. Dundee: Oily Press.

De Man JM (1999) Principles of Food Chemistry,

pp. 311–353. Gaitersburg, Maryland: Aspen.

Gurr MI (1989) Dairy fats: nutritional nasties or

dietary delights? In: Cambie RC (ed.) Fats for

the Future, pp. 41–61. Chichester: Ellis Horwood.

IDF (1981) Evaluation of the Firmness of Butter. Inter-

national Dairy Federation Bulletin Document no. 135.

Brussels: International Dairy Federation.

IDF (1991) Residues and Contaminants. Special Issue 9101.

Brussels: International Dairy Federation.

IDF (1996) Inventory of IDF/ISO/AOAC Adopted

Methods of Analysis and Sampling of Milk and Milk

Products, 5th edn. International Dairy Federation Bul-

letin no. 312. Brussels: International Dairy Federation.

Juriaanse AC and Heertje I (1988) Microstructure of short-

enings, margarine and butter – a review. Food Micro-

structure 7: 181–188.

Keogh MK, Quigley T, Connolly JF and Phelan JA (1988)

Anhydrous milk fat. 4. Low fat spreads. Irish Journal of

Food Science and Technology 12: 53–75.

Kirk RS and Sawyer R (eds) (1991) Pearson’s Chemical

Analysis of Foods, 9th edn, pp. 574–608. Essex: Long-

man.

Pariza MW (1997) Conjugated linoleic acid, a newly recog-

nised nutrient. Chemistry and Industry No. 12. June:

464–466. West Sussex: Society of Chemical Industry,

John Wiley & Sons Ltd.

Walstra P and Jenness R (1984) Dairy Chemistry and Phys-

ics, pp. 377–457. Chichester: Wiley.

Wilbey RA (1994) Production of butter and dairy based

spreads. In: Robinson RK (ed.) Advances in Milk Pro-

cessing. Modern Dairy Technology, vol. 1, 2nd edn, pp.

107–158. London: Chapman & Hall.

BUTTER/Properties and Analysis 731

Cabbage See Vegetables of Temperate Climates: Commercial and Dietary Importance; Cabbage and

Related Vegetables; Leaf Vegetables; Oriental Brassicas; Carrot, Parsnip, and Beetroot; Swede, Turnip, and

Radish; Miscellaneous Root Crops; Stem and Other Vegetables

CADMIUM

Contents

Properties and Determination

Toxicology

Properties and Determination

G Zurera Cosano and M A Amaro Lo

pez, University

of Co

rdoba, Co

rdoba, Spain

Background

0001 Cadmium is a natural element in the earth’s crust

(atomic number ¼48, atomic weight ¼112.411, elec-

tronic configuration (K

)4d

, and oxidation

states 2). Cadmium metal is generally described as

bluish or silver white in color, and as being relatively

soft, ductile, and malleable, but this form is not

common in the environment. It is usually found as a

mineral combined with other elements such as oxygen

(cadmium oxide), chlorine (cadmium chlorine), or

sulfur (cadmium sulfate, cadmium sulfite). These

compounds are all stable solids that do not evaporate,

although cadmium oxide is often found as part of

small particles present in air.

0002 Most cadmium used is obtained as a byproduct from

the smelting of zinc, lead, or copper ores, probably

owing to its chemical similarity. Cadmium has a number

of important industrial applications, but it is used mostly

in metal plating (electroplating, alloys, and solders),

pigments, plastics (stabilizers for polyvinyl chloride),

batteries, photovoltaic cells, etc. Most uses of cadmium

are ‘dissip–ative,’ the products using it are widely dis-

tributed in the environmental and hard to recycle.

0003Cadmium is fairly widely distributed and is found

in shales and igneous rocks, coals, sandstone, lime-

stone, lake and oceanic sediments, and soil. Cadmium

has been listed as a pollutant of concern due to its

persistence in the environment, potential to bioaccu-

mulate, and toxicity to humans and the environment.

Though cadmium has come into widespread use only

fairly recently, it is quite likely that for many centuries

this highly toxic metal has caused incidents of food

poisoning. After mercury and lead, cadmium can

probably be considered next in importance as an

environmental pollutant.

Sources of Cadmium Exposure

0004Sources of exposure are many and include:

0005Breathing contaminated work-place air (battery

manufacturing, metal soldering or welding, smelting

and plating operations, lithography, and engraving).

0006Exposition of dust and fumes from the mining and

refining of metals and contaminated air from the

burning of fossil fuels (such as coal or oil) or the

incineration of municipal waste materials.

0007Eating foods containing cadmium; there are low

levels in all foods (highest in shellfish, liver, and

kidney), and drinking contaminated water.

.0008 Inhalation of cadmium in cigarette smoke (most

people who smoke have about twice as much

cadmium in their bodies as do nonsmokers).

0009 Application of phosphate fertilizers or sewage

sludge which increases cadmium levels in crops.

0010 The primary source of cadmium exposure is food,

since food materials tend to take up and retain

cadmium (for example, plants from the soil, fish

from water).

Occurrence in Foods

0011 In order to understand the biological effects of cad-

mium in foods, it is necessary to have some idea of the

distribution and occurrence of cadmium in air, water,

and soil. Cadmium enters the air from mining, indus-

try, and burning coal and household wastes and cad-

mium particles in air can travel long distances before

falling to the ground or water. It enters water and soil

from waste disposal and spills or leaks at hazardous

waste sites; it binds strongly to soil particles, and

some cadmium dissolves in water.

0012 Furthermore, it is essential to try to determine how

cadmium normally moves from one sector to another

and to explore the way in which human activities may

influence these processes. The importance of atmos-

pheric cadmium in relation to its potential effects on

humans lies not so much in its direct inhalation as in

its possible contribution to soil, water, and vegetation

through either dry or wet deposition and, ultimately,

to food. In this respect, the solubility, pH, and chem-

ical nature of the deposited fraction may be essential

factors for controlling concentrations in food.

Cadmium in Air

0013 Cadmium is universally present in the atmosphere in

amounts varying from 1 ng m

3

or less in rural or

uncontaminated areas to 10–50 ng m

3

in congested

urban areas. There is no definite relation of cadmium

levels to the size of cities; some small but highly

industrialized cities have levels which are greater

than those of some very large metropolitan areas.

The principal sources of cadmium in the atmosphere

are thought to have resulted from emissions from

smelters, reprocessing of various cadmium-contain-

ing metals, burning of plastics, or power generation

from coal.

0014 In areas around cadmium-emitting factories, cad-

mium concentrations in air are several hundred times

greater than those in noncontaminated areas. The

compounds of cadmium which exist in the atmos-

phere are not known with any certainty but it can

be assumed that they are nonvolatile and that they are

present in the particulate phase. Some of the probable

forms are the oxide, sulfide, sulfate, chlorides, and

other more complex ions or compounds.

Cadmium in Water

0015The cadmium content of water is extremely low. The

occurrence in drinking water has of course been of

special interest since this directly affects human

intake. Cadmium levels in water, in the absence of

contamination, are seldom above 1 mgl

1

. Contamin-

ation may occur as a result of the use of galvanized

pipes and cisterns. Cadmium-containing solders in

water heaters and other fittings can be another

cause. Pollution of water due to the use of cadmium-

rich sewage sludge for agricultural purposes has been

reported on a number of occasions. The mean con-

centration of cadmium in rainwater is 0.001 mgml

1

in clean areas and 0.0037 mgml

1

in contaminated

areas. The US Environmental Protection Agency esti-

mates that consumption of the reference dose (RfD)

of 0.0005 mg kg

1

day

1

for cadmium in drinking

water would likely not result in the occurrence of

chronic noncancer effects.

Cadmium in Soils

0016Agricultural soils receive inputs of cadmium from soil

supplements, such as phosphate fertilizers and sewage

sludge, and from atmospheric deposition. Although

the significance of sewage sludge as a source of cad-

mium contamination of soil is well established, Euro-

pean soil inventory studies indicate that, on a national

basis, phosphate fertilizer and atmospheric inputs are

the greatest sources of cadmium addition to soils.

Levels in soils vary widely from about 0.06 mg kg

1

in virgin soil to 10–20 mg kg

1

in the vicinity of some

smelters.

Cadmium in Plants

0017Some species of plants have an ability to concentrate

cadmium at levels that are sometimes much greater

than those in the immediate environment. The ratio

of cadmium concentration in plants to that in the

corresponding soil has been reported to be as high

as 10:1. The average cadmium content of terrestrial

plants is about 0.6 mg kg

1

, although there is obvi-

ously a very wide variation even in uncontaminated

areas. The range of values in species growing in clean

areas is of the order of 0.01–10 mg kg

1

or more, but

most plants contain below 1 mg kg

1

. However, some

root crops such as carrots and parsnip, and some leafy

crops such as spinach and lettuce, tend to contain

more cadmium than other plant foods. This is also

true of cereals and certain mushrooms, and this indi-

cates that plants tend to take up cadmium from the

soil, unlike lead. Variation in species is very great even

734 CADMIUM/Properties and Determination

in plants growing in the same area, and there is also

variation in different parts of the same plant. There

seems to be good evidence that plants generally show

increased tissue cadmium levels in response to an

increase in the environment from normal sources or

from soil, water, or air contamination.

0018 Plants primarily absorb cadmium from the soil

through their roots. This absorption is influenced

by, among other factors, particularly the pH of the

soil and the organic matter content. The cadmium

concentration in plants is inversely related to the

amount of organic matter in the soil. A large amount

of organic matter in the soil limits the availability

of cadmium to plants. Organic soils form the

strongest metal complexes and hence retain the

metal more firmly. An increased accumulation of

cadmium by plants fertilized with superphosphate

which contains cadmium as an impurity has been

reported. With aerial application, it has been shown

that the leaves of plants are an important entry point

for cadmium.

Contamination of Food During Processing

0019 The processing of vegetables prior to packaging can

modify the content of cadmium. Washing and blanch-

ing decrease cadmium to varying degrees. These

decreases are probably caused by cadmium being

leached during washing and blanching and by ther-

mal processing where cadmium is extracted into the

water of brine.

0020 Cadmium contamination occurs as a result of its

use in plate-manufacturing equipment. Cadmium is

readily soluble in weak acid solutions, so its use in

food-processing plants should be confined to parts

which do not come directly into contact with food.

Another source of cadmium contamination is the

utilization of ceramic and enameled utensils. Some

glazed pottery, especially of the craft and homemade

kind, is capable of releasing toxic amounts of cad-

mium and other metals into food.

0021 Enameled kitchenware can also be a source of cad-

mium contamination of food, especially those which

have bright colors, indicating the possible use of

cadmium pigments. Another domestic source of cad-

mium contamination is the decoration and printing

applied to glass tumblers and other containers. Fur-

thermore, the spices, condiments, coloring, and pre-

servatives which are added to foodstuffs may contain

cadmium and be a vehicle of contamination. (See

Food Poisoning: Classification.)

Cadmium Level in Foods

0022 As cadmium is ubiquitous in the environment, all

food is exposed to and contains cadmium. Except

where there has been pollution, cadmium is normally

found at a fairly low concentration in foodstuffs that

generally contain less than 50 ng g

1

0023The Codex Committee of Food Additives and Con-

taminants (Joint Food and Agriculture Organization

(FAO)/World Health Organization (WHO) Food

Standards Programme) indicates that the dietary

intake of cadmium fluctuates between 10 and 50 mg

person

1

day

1

for noncontaminated areas. The

major sources of cadmium dietary intake are cereals,

green leafy vegetables, potatoes, liver, and kidney

(80% of total cadmium intake). Most fish contains

little cadmium, with the average being less than

200 ng g

1

. Shellfish from unpolluted waters rarely

have an average cadmium concentration greater

than 1000 ng g

1

. A wide range of concentrations

has been reported by different workers (Table 1).

Analysis of Foods for Cadmium

0024For cadmium analysis, an important aspect is the

avoidance of airborne particulate contamination.

The low level of cadmium in foods and the ubiquitous

presence of significant levels of this element in some

reagents, containers, and air make it necessary for the

analyst to evaluate and eliminate all potential sources

of contamination at each stage of the analysis.

Sample Preparation

0025Prior to the destruction of the organic matter, the

sample should be subjected to drying and grinding

in order to remove water from the product without

reducing its dry-matter content. Normally, the mois-

ture is removed and the analytical result expressed on

a dry-weight basis. However, for nutritional purposes,

it is common practice to express the concentration on

a fresh-weight basis (i.e., wet-weight basis).

0026The drying procedure recommended by the Associ-

ation of Official Analytical Chemists (AOAC) is

vacuum oven drying at 100 mmHg pressure and at a

temperature of 70



C. The primary objective of grind-

ing a sample is to homogenize it and, at the same

time, reduce it to a suitable physical consistency so

that it can be easily measured or weighed. A number

of grinding procedures can be employed, but in any

case reducing the sample to a finer particle size is

desirable if the subsample chosen for analysis is to

be less than 1.0 g. With all grinding procedures, con-

tamination and segregation are potential sources of

error.

Organic Matter Destruction

0027The traditional methods to solubilize biological and

food samples are wet ashing with suitable oxidizing

agents and dry ashing. Wet ash digestions are charac-

terized by short ashing times (normally 3–4 h) and are

CADMIUM/Properties and Determination 735