See also: Carbohydrates: Sugars – Chromatographic
Methods. Ethanol. Food and Nutritional Analysis: Alco-
holic Beverages. Infrared Spectroscopy: Near-Infrared.
pH. Quality Assurance: Primary Standards; Spectroscopic
Standards. Spectrophotometry: Organic Compounds.

Further Reading

Barrus NW and Evans JA (1991) A Handbook for Must

and Wine Analysis. University of Texas System.

Boulton RB, Singleton VL, Bisson LF, and Kunkee RE

(1996)

Principles

and

Practices

of

Winemaking.

Dordrecht: Kluwer Academic.

Gump BH and Pruett DJ (eds.) (1993) Beer and Wine

Production:

Analysis,

Characterization

and

Tech-

nological Advances (ACS Symposium Series). American
Chemical Society.

Peynaud E and Spencer AFG (1984) Knowing and Making

Wine. New York: Interscience.

Ribereau-Gayon P (ed.) (2000) The Handbook of Enology.

New York: Wiley.

Margalit Y (1990) Winery Technology and Operations

Handbook. Wine Appreciation Guild.

OIV (1999) Compendium of International Methods

of

Analysis

of

Wines

and

Musts.

Paris:

OIV

Publications.

Ough CS and Amerine MA (1988) Methods for Analysis of

Musts and Wines. New York: Wiley.

Watkins TR (ed.) (1997) Wine Nutritional and Therapeutic

Benefits (ACS Symposium Series). American Chemical
Society.

Zoecklein BW, Fugelsang KC, Gump BH, and Nury FS

(1995) Wine Analysis and Production. Dordrecht:
Kluwer Academic.

Meat and Meat Products

M O’Keeffe

, The National Food Centre (Teagasc),

Dublin, Republic of Ireland

& 2005, Elsevier Ltd. All Rights Reserved.

Introduction

The analysis of meat and meat products is a signi-
ficant activity in the general area of food analysis
since they represent an important and relatively ex-
pensive component of the diet. Characterization of
meat through chemical analysis is of importance to
meat buyers in the food processing industry and is
the subject of a large amount of regulatory control in
most countries. Analysis of meat products is of im-
portance for the food processing industry in product
development, quality control/assurance, and for nu-
tritional labeling. In addition, meat products are
covered by a range of regulatory requirements to
which adherence can be checked by chemical ana-
lyses. This article describes the analyses used for
meat and meat products, covering both major and
minor constituents, and addresses the range of meth-
ods available for particular analytes.

Major Analytes

Fresh or unprocessed meat is characterized normally
by microbial tests, by measurement of physical at-
tributes such as tenderness and color, and by ‘prox-
imate’ analysis; that is, the proportions of the major
constituents of moisture, protein, fat, and ash

(inorganic material) in the meat. In the case of car-
cass meat, other measurements such as pH and color
are commonly made to give an indication of quality.
Meat is often tested for its freshness through rancid-
ity tests such as peroxide value and thiobarbituric
acid (TBA) number, which give a measure of ox-
idative rancidity in the fat, and the free fatty acid
value, which gives a measure of hydrolytic rancidity.
Spoilage of meat can be measured through assay of
the total volatile basic nitrogen (TVBN), which is
related to protein breakdown.

In the case of comminuted meat (e.g., burgers), the

purpose of analysis is to characterize the main con-
stituents (moisture, protein, fat, ash) and also to
determine to what extent it differs from the intact
meat. For example, typical analyses applied to com-
minuted meat samples might include meat species
identification and determination of collagen and car-
bohydrate content. As the meat products move fur-
ther away from the original entire meat, a range of
analyses is used to characterize the food, particularly
assays for nonmeat proteins, for additives such as
salts, and for preservatives. In the case of cured meat
and cured meat products, the important analyses are
for salt, nitrite and nitrate, and other additives such
as sugars and phosphorus (polyphosphates).

Meat products, under regulations, are defined ac-

cording to ‘meat content’ and this may be calculated
from compositional data. The percentage ‘fat-free
meat’ is calculated from the total nitrogen content
(corrected for any nonmeat nitrogen) using nitrogen
factors specific for meat of each species. ‘Meat con-
tent’ is calculated as the ‘fat-free meat’ plus the fat.

302

FOOD AND NUTRITIONAL ANALYSIS

/ Meat and Meat Products

Related analyses in the meat and meat products

area are the analysis of curing brines and of special
meat fractions such as mechanically recovered meat
(MRM). Completing the list of analyses on meat and
meat products are the mineral and vitamin assays
used to characterize the nutritional status of these
foods.

Sampling and Preparation

Meat and other edible tissues of animals are difficult
samples to analyze because of the nonuniformity and
inherent instability of the sample. Because of the high
water content (

X70%) of raw meat, meat samples

are particularly prone to change either in storage or
during preparation for analysis. This is more of a
problem for raw meat than for meat products, which
are often ‘stabilized’ by some of the constituents
added to the meat or by the processing procedures
(cooking, curing) used.

In the case of raw carcass meat, another problem is

that of obtaining a representative sample. Because
the muscles of the animal (the primal cuts) are
irregular in shape and in fat content, samples for
analysis must be clearly defined in terms of anatom-
ical position. In the case of boxed beef, which is used
in meat processing, it is important to have a sample
representative of the total content, particularly in
terms of lean and fat.

Samples of meat are taken either from defined lo-

cations, as multiple subsamples over the entire ma-
terial, which are combined to form the analytical
sample, or as a single sample after comminuting and
mixing to ensure homogeneity. Preferably raw meat
samples should be analyzed immediately but, if this is
not possible, refrigerated or frozen storage is re-
quired to prevent (reduce) alteration to the sample.

Having defined the batch that is to be sampled, the

sampling must be such as to ensure that the batch
will be characterized adequately from the analyses.
The number of samples to be taken from a batch
depends on criteria such as the number of discrete
units in the batch, the importance of the analyte, and
the confidence required from the results. Since these
are subjective or variable criteria, the number of
samples is determined initially and then particular
procedures of sampling are followed.

The sampling of meat and meat products is

covered by an International Standard (ISO 3100-1:
1991). This standard gives general instructions and
specifies procedures to be followed for taking pri-
mary samples and is intended primarily for commer-
cial, rather than regulatory purposes. It distinguishes
between units not exceeding 2 kg in weight, which

are treated as a sample, and carcasses or meat cuts
exceeding 2 kg in weight, from which secondary
samples of 0.5–1 kg may be taken. The above stand-
ard deals with issues such as the inertness of the
containers and the integrity of closures and the ne-
cessity to store and transport samples at 0–2

1C (for

analyses to be completed within 24 h) or frozen
(where longer storage is required). The standard also
describes the use of seals and the information to be
attached to the sample container label.

Before analysis, meat samples must be ground in a

suitable mincer or bowl-cutter to produce a homo-
geneous sample. Connective tissue is a particularly
difficult component of the meat sample to homo-
genize and this is of importance in collagen analysis.
Suitable comminution of meat samples is specified as
a mincer (meat chopper) plate size of 4 mm or less.

Equipment used for sample preparation must be

dry and clean and may be cooled or chilled. Speedy
sample preparation is required to reduce heating and
consequent evaporation of water, which would affect
the determination of moisture content. Blades must
be sharp to achieve consistent and fast comminution.
Samples (preferably well chilled or slightly frozen)
may be prepared by passing through a meat chopper
or mincer multiple (3

) times, often using plates of

decreasing size where the sample is very large. Often,
quite small samples are received for analysis and a
bottom-driven bowl cutter may be more appropriate.

In the case of meat products that are a composite

(such as meat-filled pies), the analysis may require
separation of the sample into its constituent parts,
weighing of each part, and analysis as separate sam-
ples.

Standard Methods

Moisture

Moisture is determined by measuring the loss in
weight of the sample on heating. A standard method
(ISO 1442: 1997) used consists of drying a sample of
5–8 g, mixed with predried sand, to constant weight
with 2 h periods in an oven at 103

721C. Methods

approved by the Association of Official Analytical
Chemists (AOAC) for moisture include air-drying of
a 2 g sample in a convection oven at 100–102

1C for

16–18 h, at 125

1C to constant weight, or under

vacuum at 95–100

1C. An alternative procedure for

moisture

determination

is

microwave

drying;

integrated systems exist consisting of an electronic
balance and control microprocessor that can give re-
sults after a drying period of 3–5 min.

In all cases, moisture determination is based on

recording the mass that evaporates from the sample

FOOD AND NUTRITIONAL ANALYSIS

/ Meat and Meat Products

303

under strictly defined circumstances of temperature
and time. It is possible in some samples (1) that com-
ponents other than water may be lost by evaporation
or (2) that incomplete removal of water may occur
due to formation of a ‘skin’ on the surface of the
sample. Moisture determination, therefore, requires
close attention to the exact conditions used and
maintenance of constant conditions for each analysis.

Protein

The total nitrogen content of the sample is deter-
mined after either reduction of all nitrogen to am-
monia or liberation of all nitrogen as nitrogen gas.
The ‘crude protein’ content of the sample is derived
from the ammonia/nitrogen content by use of ap-
propriate conversion factors. In the case of meat and
meat products, the factor 6.25 is used to convert
ammonia/nitrogen to crude protein, on the basis that
16% of protein is nitrogen.

Kjeldahl nitrogen is the classical assay for

crude protein in meat, consisting essentially of a cat-
alyst-aided (sulfate salts and copper or mercury)
digestion with concentrated sulfuric acid at elevated

temperature, rendering of the resultant digest (con-
taining ammonium sulfate) alkaline with concentrat-
ed sodium hydroxide, distillation of the liberated
ammonia into an excess of acid, and back-titration
with acid to determine the ammonia content. This
ISO procedure (ISO 937: 1978) has been developed
from a macrosystem in special flasks to a microsys-
tem in tubes and in a variety of forms of automated
and semiautomated systems – many of which are
AOAC-approved methods.

An AOAC variation, still based on determination

of ammonia, is an automated system of digestion
with determination using the colorimetric reaction of
ammonia with hypochlorite and phenol to produce
an indophenol absorbing at 630 nm.

The Dumas method, based on determination of

gaseous nitrogen in the sample, has been approved
by the AOAC for crude protein in an automated
form for a variety of foodstuffs. The modern versions
of this system have fully automated sample intro-
duction, combustion (950

1C), removal of non-nit-

rogenous gases, and reduction of nitrogenous gases
to nitrogen, and determination of nitrogen content
by a thermal conductivity cell (Figure 1). The Dumas

LECO nitrogen determinator – flow diagram

Mixing ballast

volume

Sample

Furnace

(950

°

C)

O

2

carrier

gas

Aliquot
solenoid

Sample flow

HeN

2

O

2

CO

2

H

2

O

Reference flow

N

2

cell

Surplus exhaust

Exhaust

Exhaust

Thermal
conductivity
cell

He carrier
gas

Sample
gases
(H

2

O, O

2

, CO

2

NO

2

, NO, N

2

)

Figure 1

Crude protein determination by the Dumas method for total nitrogen with the ‘LECO’ apparatus. (Reproduced from

O’Keeffe M (1992) Chemical analysis of animal feed and human food. In: Smyth MR (ed.) Chemical Analysis in Complex Matrices, pp.
241–287. Chichester: Ellis Horwood.)

304

FOOD AND NUTRITIONAL ANALYSIS

/ Meat and Meat Products

method is attractive because it is a fully automated
system, avoids use of corrosive and contaminant
chemicals, and is a rapid method. However, the small
sample size (

o1 g) used in the Dumas method places

critical requirements for homogeneity of sample that
may not be as easily attained with meat samples as
with other sample types. The Dumas method com-
pares well with the Kjeldahl method both in terms of
the performance criteria of repeatability and repro-
ducibility and protein content determined, as shown
from the results of an AOAC collaborative study
among 12 different laboratories and using 30 differ-
ent meat and meat product samples (Table 1).
However, the Dumas method gives slightly higher
protein values overall compared with the Kjeldahl
method, which may be due to atmospheric nitrogen
and/or additional nitrogen detected from basic ami-
no acids. In samples with relatively low protein con-
centration (

o30%), the difference between the two

methods may not be of practical significance.

There may be a requirement to characterize the

proteins in a meat product in terms of their amino
acid content. This may be determined by hydrolysis
with concentrated hydrochloric acid (6 mol l

 1

) and

separation and identification of the individual amino
acids either (1) by ion exchange chromatography and
colorimetric measurement using ninhydrin, or (2) by
high-performance liquid chromatography of fluores-
cent derivatives of the amino acids.

Fat

Standard methods for the determination of fat in
meat and meat products are based on extraction of
the fat from the sample using a lipophilic solvent and
determination of the extracted fat by weighing or by
measurement of specific gravity (relative density)
changes in the extractant solvent. There are two ISO
methods for fat in meat and meat products, one for
‘free fat’ (ISO 1444: 1996), which consists of repeat-
ed extraction of the sample with n-hexane or petro-
leum spirit in a Soxhlet apparatus, and the other for

‘total fat’ (ISO 1443: 1973), which involves an hy-
drolysis with hydrochloric acid prior to the solvent
fat extraction. For some meat product samples, sim-
ple extraction of fat with solvent may be incomplete;
digestion with hydrochloric acid liberates the fat by
hydrolyzing proteins and carbohydrates. In both cas-
es, the sample is oven-dried at 103

721C prior to

extraction with solvent. The fat content is deter-
mined by weighing the residue after evaporation of
the solvent.

The primary AOAC method is a Soxhlet method,

similar to the ISO ‘free fat’ method. An automated
form of the Soxhlet petroleum spirit (petroleum
ether) method is approved by the AOAC, using
equipment such as the Soxtec

TM

apparatus. In this

procedure, multiple samples, mixed with sand, are
predried at 125

1C (1 h) prior to a rapid solvent ex-

traction step. There are two other AOAC-approved
methods that are widely used for fat determination in
meat and meat products. One method uses the Foss-
let

TM

apparatus comprising a shaker or reactor that

extracts the fat from the sample by very vigorous
shaking in a metal container with perchloroethylene
for 2–3 min. The specific gravity of the extract is
measured in a magnetic float cell controlled by a po-
tentiometer. The fat content can be determined from
the difference in specific gravity between pure perch-
loroethylene and the extract. The second method is
based on microwave-predrying of the sample, ex-
traction of fat from the dried sample with dichloro-
methane in a custom-built extractor, and microwave-
drying of the residue prior to weighing the extracted
fat.

Both the Foss-let and the microwave systems are

relatively rapid, a complete procedure taking not
more than 10–15 min. Both these methods are very
attractive for situations where rapid analyses are re-
quired, such as online for product control. However,
where large batches of samples are to be analyzed
and where results are not required within 24 h, the
Soxhlet solvent extraction, or the more rapid So-
xtec

TM

system, may be preferable. These latter tech-

niques do not require constant attention, as is the
case for the rapid methods. Good comparison be-
tween results obtained by Soxhlet extraction and the
Foss-let technique has been reported. In the case of
the microwave-based system, adjustment factors
have been defined for different classes of meat prod-
ucts to overcome a negative bias in the method.

Supercritical fluid extraction (SFE) has been ap-

plied also for determination of fat in meat and meat
products. Supercritical carbon dioxide, produced
using elevated pressure (7.4 MPa) and temperature
(31

1C), extracts the fat from samples that have been

mixed with moisture-absorbing agents, such as

Table 1

Performance of Kjeldahl and Dumas methods for de-

termination of protein in meat products (12 different laboratories,
30 different samples)

Performance measurement

Kjeldahl

method

Dumas

method

Repeatability (S

r

)

0.11–0.40

0.12–0.41

Reproducibility (S

R

)

0.29–0.49

0.18–0.46

Protein, overall mean (n

¼ 360)

15.59%

15.75%

From King-Brink M and Sebranek JG (1993) Combustion method
for determining crude protein in meat and meat products. JAOAC
International 76: 787–793.

FOOD AND NUTRITIONAL ANALYSIS

/ Meat and Meat Products

305

diatomaceous earth. The advantage of this technique
is that there is no waste solvent disposal problem and
a number of samples may be extracted simultane-
ously. A number of studies have shown good agre-
ement between the SFE and the Soxhlet methods.

X-ray absorption technology (e.g., Anyl-Ray

TM

) is

used in the meat industry to determine indirectly the
fat content of meat. The meat sample (

B7 kg) is

transilluminated with X-rays and the absorption of
energy is related to the mineral content of the sample.
Fat content is calculated from the relationship be-
tween fat, protein, water, and mineral content of meat.

Where the fat in a meat or meat product sample is

to be characterized in terms of the fatty acid profile,
extraction of the fat with chloroform/methanol is
required. This solvent mixture, while it may not give
complete fat extraction, is used to ensure no chemical
change to the lipids and the extraction of phospho-
lipids. Fatty acid analysis of the extracted fat is un-
dertaken by formation of volatile methyl esters of the
fatty acids (ISO 5509: 2000) and determination by
gas chromatography (ISO 5508: 1990).

Ash

Ash is the residue remaining after incineration of the
sample in a furnace at temperatures in excess of
500

1C. The AOAC method specifies drying of the

sample and charring before ignition at 525

1C. The

ISO method (ISO 936: 1998) specifies incineration of
the sample at 550

7251C, in a muffle furnace, fol-

lowing drying and carbonization of the sample either
(1) separately in an oven and on a hot-plate or (2) in
the furnace by gradually raising the temperature. In
all cases, the ash is determined by weighing of the
residue and care must be taken in handling the silica
dishes to avoid losses.

A common practice is to determine ash content on

samples that have been oven-dried for moisture de-
termination. While ash may be used for determina-
tion of metals, salts, etc., attention must be given to
the possibility of losses due to volatility of these
components of the sample at the very high ashing
temperatures used.

pH

The pH of meat is an important measure of quality, a
higher than normal pH (

4pH 6.2 at 24 h after

slaughter) or a lower than normal pH (

opH 5.9 at

45 min after slaughter) indicating conditions known
as DFD (dark, firm, dry) and PSE (pale, soft, ex-
udative) meat, respectively. The determination of
such meat is important as the uses to which it can be
put are limited. Such pH measurements are made on
the carcass with a spear probe.

For laboratory measurements, an ISO method for

pH (ISO 2917: 1999) specifies either homogenization
of the sample in potassium chloride solution and in-
sertion of the electrode(s) into the extract, or intro-
duction of the electrode into prepared holes in the
nonhomogenized sample. Other methods specify
preparation of a slurry of the ground sample with
an equal weight of water, or preparation of a
homogenate in the ratio of one part meat to five
parts sodium iodoacetate (5 mmol l

 1

)/potassium

chloride (150 mmol l

 1

).

Collagen

Determination of the collagen content of meat prod-
ucts is important in controlling the eating quality
(toughness) and for ensuring that too high an amount
of low-grade meat, with a high level of connective
tissue, is not in a product. Collagen content is deter-
mined from an analysis for the amino acid

L

-hydro-

xyproline, which occurs at much higher levels in
collagen than in other muscle proteins.

The ISO method for

L

-hydroxyproline (ISO 3496:

1994) involves hydrolysis of the sample with sulfuric
acid, at 105

1C for 16 h. After filtration and dilution

of the hydrolysate, the

L

-hydroxyproline content is

determined by oxidation with chloramine-T and re-
action with p-dimethylaminobenzaldehyde to form a
colored complex that is measured spectrophotomet-
rically at 558 nm. This method requires close atten-
tion to detail, particularly the color reaction which
must be carried out under exact temperature and
time conditions (60

70.51C for 20 min). The repeat-

ability of the determination is assured by preparation
of a calibration graph with each batch of samples.
Using a specific microwave oven for digestion can
reduce the time for this procedure to 30 min, so that
the total time for analysis can take less than 3 h.

The collagen content is determined by multiplica-

tion of the

L

-hydroxyproline result by a factor of 8

(corresponding to the hydroxyproline content of col-
lagen being equal to 12.5%, where the nitrogen-to-
protein factor is 6.25).

Additives

In the production of meat products, additives such as
salts, sugars, and preservatives are used. Analyses for
these substances are important in that maximum
levels allowed in foods are specified in various na-
tional regulations such as the US Food and Drugs
Administration and the European Commission DG
SANCO.

The standard methods for sodium chloride in meat

products are titrimetric methods in which the salt is
extracted from the sample, reacted with excess silver

306

FOOD AND NUTRITIONAL ANALYSIS

/ Meat and Meat Products

nitrate to form a silver chloride precipitate, and the
residual silver nitrate titrated with thiocyanate. The
ISO method (ISO 1841-1: 1996) specifies an extrac-
tion with hot water and precipitation of proteins
with Carrez reagents (potassium hexacyanofer-
rate(II) and zinc acetate solutions), followed by acid-
ification of the filtered extract with nitric acid before
addition of excess silver nitrate. The silver chloride
precipitate is coagulated with nitrobenzene and
the residual silver nitrate titrated with potassium
thiocyanate. In the AOAC method, the sample is
treated with excess silver nitrate before extraction by
boiling with dilute nitric acid and titration of residual
silver nitrate is with ammonium thiocyanate. This
method is appropriate for samples with a sodium
chloride content

X1%.

Another ISO method (ISO 1841-2: 1996), based

on potentiometric titration with a silver nitrate so-
lution using a silver electrode, is appropriate for
samples with a sodium chloride content

X0.25%.

The sample is dispersed in water and an aliquot is
acidified by addition of nitric acid, prior to titration.

Alternative methods for salt determination include

use of a chloride ion-selective electrode and a semi-
quantitative indicating strip method based on the
reaction of chloride ion with silver chromate to pro-
duce silver chloride.

The salts associated with cured meats, nitrates and

nitrites, are assayed by aqueous extraction and colo-
rimetric determination. The ISO methods involve
extraction in hot water containing borax solution
and deproteination of a portion of the extract with
Carrez reagents. Nitrite (ISO 2918: 1975) is deter-
mined directly by formation of an azo dye with
sulfanilamide and N-(1-naphthyl)ethylenediamine
dihydrochloride which is measured at 538 nm. Ni-
trate (including nitrite) (ISO 3091: 1975) is deter-
mined by cadmium reduction to nitrite and azo dye
formation. Reduction of nitrate to nitrite may be
carried out on a special column (as in the ISO meth-
od) or using ‘spongy’ cadmium. Care must be taken
to prevent interference from ascorbic acid if it is
present in the sample at relatively high levels
(

420 mg ml

 1

).

Other methods for nitrates and nitrites include the

AOAC procedure in which m-xylenol is nitrated and
the nitro-xylenol is distilled into sodium hydroxide
solution to form a colored sodium salt that is deter-
mined with ultraviolet spectrophotometry at 450 nm.
Gas chromatography with electron capture detection
and high-performance liquid chromatography have
been used for determination of nitrate and nitrite
derivatives.

Of particular interest in cooked cured meat prod-

ucts

is

the

determination

of

nitrosamines,

carcinogenic products resulting from the reaction of
secondary amines with the nitrites used for curing.
The AOAC official method is based on distillation
under vacuum of the nitrosamines from the sample in
mineral oil into a trap. The trapped nitrosamines are
collected in methylene chloride, concentrated by
evaporation, and determined by gas chromatogra-
phic analysis using a thermal energy analyzer. Re-
cently, a method was approved by the AOAC for the
following three volatile N-nitrosamines in minced
meat:

N-nitrosodimethylamine,

N-nitrosopyrroli-

dine, and N-nitrosomorpholine. In this method, the
sample is mixed with anhydrous sodium sulfate and
Celite, packed into a glass chromatographic column,
and eluted with pentane–dichloromethane. The elu-
ate passes through a second column containing acid
Celite, on which the nitrosamines are trapped. The
nitrosamines are eluted from this second column
with dichloromethane, the eluate is concentrated,
and the nitrosamines determined by gas chro-
matographic analysis using a thermal energy ana-
lyzer.

Phosphate and polyphosphates are determined as

total phosphorus in the ISO method (ISO 2294:
1974). The sample is digested with nitric and sulfuric
acids and the orthophosphate is precipitated as
quinoline 12-molybdophosphate. The precipitate is
collected on a glass filter, dried, and weighed and
expressed as phosphorus pentoxide. A similar pro-
cedure described by the AOAC is ashing of the sam-
ple at 550

1C, boiling of the ash in dilute nitric acid

and filtration before precipitation of quinoline 12-
molybdophosphate.

An alternative approach to these gravimetric meth-

ods is determination procedure based on the forma-
tion of colored complexes. Orthophosphate in acidic
solution reacts with molybdic acid and vanadic acid
to form yellow–orange vanadomolybdophosphoric
acid which has maximum absorption at 330 nm.
Another approach is a two-stage reaction in which
yellow phosphomolybdate is produced from the ad-
dition of ammonium molybdate to the orthophos-
phate in acidic solution, and the phosphomolybdate
is then reduced by ascorbic acid to a molybdenum
blue, which is measured at 890 nm. This last method
is the basis for an AOAC-approved spectrophoto-
metric method.

In some countries, sulfur dioxide is used as a pre-

servative in meat products. Sulfur dioxide occurs in
many forms in food but quantitative tests for the
material in meat products are normally for total (free
plus bound) sulfur dioxide. The AOAC method ap-
plied to meat products consists of liberation of sulfur
dioxide from the sample by heating with hydrochlo-
ric acid, distillation into hydrogen peroxide solution,

FOOD AND NUTRITIONAL ANALYSIS

/ Meat and Meat Products

307

which then reacts with the sulfur dioxide to form
sulfuric acid, and titration with sodium hydroxide
using methyl red indicator. Gravimetric determina-
tion is also possible by addition of barium chloride to
the titrated liquid resulting in a precipitate of barium
sulfate, which can be isolated by filtration, dried, and
weighed. Special apparatus for the AOAC proce-
dures (the modified Monier–Williams method and
the optimized Monier–Williams method) have been
developed.

An alternative to the hydrogen peroxide/sulfuric

acid titration with alkali is distillation of sulfur di-
oxide from the acidified sample into excess iodine
solution. A proportion of the iodine, equivalent to
the amount of sulfur dioxide, is reduced to iodide,
and the residual iodine is titrated with sodium
thiosulfate using starch as indicator. This more rap-
id method is suitable for meat products where other
volatile sulfur compounds do not interfere, and it has
been developed for use with automated distillation
systems.

Another AOAC approved method for sulfites in

meat is the qualitative test based on decolorization of
malachite green solution when mixed with a sample
containing sulfites. This may be used to screen sam-
ples prior to quantitative determination as described
above.

Two other methods have been approved by AOAC

for determination of sulfites in food. One is a quan-
titative assay based on malachite green decolorizat-
ion using flow injection analysis. Sulfite is released
from a sample slurry with alkali, then the test stream
is acidified to produce sulfur dioxide gas which dif-
fuses across a Teflon membrane into a flowing stream
of malachite green, and the extent of decolorization
is measured at 615 nm. The other method is based on
ion exclusion chromatography with sulfur dioxide
being released by alkali extraction, and the diluted
filtrate is injected onto an anion exclusion column
linked to an electrochemical detector.

The presence of added starch in meat products is

determined by a titrimetric method for reducing
sugars. The ISO (ISO 5554: 1978) and AOAC de-
scribe methods for starch which involve extraction
with water, clarification with Carrez reagents, and
acid hydrolysis of the isolated starch. Determination
of the resultant reducing sugars is by reaction with
Fehling’s solution (containing copper sulfate), oxida-
tion of potassium iodide with the excess copper(II),
and titration of the liberated iodine with thiosulfate,
according to the Luff–Schoorl method.

Starch, and individual sugars, may be determined

in meat products using enzymatic kit methods.
Starch is extracted from the sample and hydrolyzed
by the enzyme amyloglucosidase to

D

-glucose. The

quantity of

D

-glucose is determined by a two-stage

reaction involving hexokinase and dehydrogenase
enzymes. The specific glucose-6-phosphate dehy-
drogenase utilizes the coenzyme nicotinamide ade-
nine dinucleotide phosphate (NADP). The reaction
of the enzyme with the sugar involves reduction of
NADP to NADPH, which is measured spectromet-
rically at 340 nm:

Starch

þ ðn  1ÞH

2

O



!

Amyloglucosidase

n

D

-glucose

D

-Glucose þ ATP 

!

Hexokinase

ADP

þ glucose-6-phosphate

Glucose-6-phosphate

þ NADP

þ



!

G6P dehydrogenase

Gluconate-6-phosphate

þ NADPH þ H

þ

Metals

Analyses for metals in meat and meat products are
carried out by atomic spectrometry, generally after
dry-ashing and solubilization of the ash in acid.
Sodium and potassium, being present at relatively
high levels in meats, are determined by atomic emis-
sion spectrometry, while other metals, such as cad-
mium, copper, iron, lead, and zinc, are determined by
atomic absorption spectrometry. An alternative
method applicable to most metals is inductively cou-
pled plasma atomic emission spectrometry.

The AOAC method for arsenic involves ashing at

600

1C, dissolving the ash in dilute hydrochloric acid

with the addition of metallic zinc, and the arsenic is
distilled as arsine (AsH

3

) into an iodine solution.

Ammonium molybdate is added to the solution and,
through a series of reactions assisted by heating,
molybdenum blue is formed which is determined
spectrophotometrically at 840 nm.

The determination of calcium in meat products,

especially in mechanically recovered (or separated)
meat (MRM/MSM), is an important estimation of
the amount of bone material included in the meat.
The AOAC method describes an acid digestion of the
sample and reaction of an aliquot of the filtered
digest with excess ethylenediaminetetraacetic acid
(EDTA) under alkaline conditions to form a chelated
complex with calcium ion. The excess EDTA is then
titrated with calcium carbonate using hydroxynaph-
thol blue as indicator.

Kit Methods for Additives and Metals

A variety of qualitative or semiquantitative kit
methods based on indicating test strips (e.g., Mercko-
quant

s

), color comparators (e.g., Aquaquant

s

,

Microquant

s

), and photometric determinations

(e.g., Spectroquant

s

) are available. These kit methods

308

FOOD AND NUTRITIONAL ANALYSIS

/ Meat and Meat Products

may be used for onsite measurements or for screen-
ing assays. Typical analytes measured are nitrite/
nitrate, sulfite, phosphate, and metals.

Analyses for Adulteration

Meat Species Identification

The determination of the animal species contributing
to the meat(s) in a meat product is important for
marketing purposes. It may be necessary, in some
cases, to ensure the absence of meat of a particular
species, such as pork. A number of methods for meat
species identification are used which are based on
immunological antigen–antibody reactions, on pro-
tein isolation techniques, such as electrophoresis, or
on DNA analysis.

The AOAC methods are based on agar gel

immunodiffusion tests for beef and for poultry meat
in meat products. These tests use stabilized reagent
paper disks containing beef (or poultry) antibody and
beef (or poultry) antigen. The samples are applied to
the agar plate by absorbing fluids on to paper disks,
which are then placed on the plate. Diffusion of an-
tigen and antibody components occurs during incu-
bation for 18–24 h and the immunoprecipitin lines
are examined for presence of beef (or poultry) in the
samples (Figure 2). These tests are limited in that
they are suitable only where the adulterant is present
at

X10%.

Agar gel immunodiffusion methods have been

produced as commercial kits and a further develop-
ment is dipstick assays for meat species identifi-
cation. The immunoreagents are immobilized on a
dipstick and a color change, occurring in less than
1 h, identifies the presence of a particular meat spe-
cies, with a detection limit of

B1% lean meat.

Enzyme-linked immunosorbent assays (ELISAs) in

kit form are most widely used giving relatively rapid
and inexpensive methods for multispecies identifica-
tion. A typical format for such an ELISA is to coat
different strips of the normal 12

8-well plate with

antisera formed against serum albumin of the various
species of interest. An extract of the meat product is
added to the antibody-coated wells, incubated to en-
sure antibody binding of the serum albumin, and,
after washing, a second antibody coupled with en-
zyme is introduced. The ‘sandwich’ is visualized by
addition of a substrate to the enzyme. ELISAs have
been developed, also, for meat species identification
in cooked meat products. These ELISAs are quite
specific and sensitive (

B1% of each species can be

detected) but are qualitative, or at best, semiquanti-
tative.

Methods for meat species identification based

on DNA analysis benefit from the heat stability of
the DNA molecule and its high specificity. Originally,
DNA methods consisted of immobilization of par-
tially purified and denatured DNA, extracted from
the meat product sample, on a nylon membrane,
followed by hybridization of a species-specific
segment of labeled (colorimetric, fluorescent, or
chemiluminescent) DNA with any complementary
sequences of DNA present on the membrane. More
recently, a DNA amplification method – the polym-
erase chain reaction – has been used, but this is a
relatively expensive and technically demanding tech-
nique.

Nonmeat Proteins

Assays to detect the presence of nonmeat proteins,
such as soya protein, are based on similar antigen–
antibody methodologies as are used for meat species
identification. An AOAC method for soya protein in
raw and heat-processed meat products uses an indi-
rect ELISA technique. The soya protein is extracted
from the sample as acetone powder and renatured by
dilution with buffer. The soya protein reacts with an
excess of antibody and the unbound antibody is im-
mobilized in wells that have been coated with an-
tigen. A second antibody conjugated to enzyme
labels the immobilized antibody and substrate is
added to give a color reaction, the extent of which is
inversely related to the amount of soya protein ex-
tracted from the sample (Figure 3). This procedure is
very lengthy and test kits utilizing a direct ELISA give
more rapid results. Qualitative microscopic methods
are also used to detect the presence of soya in meat
products.

Skim milk powder or milk proteins may be used in

meat products. The presence of milk powder is

(a)

(b)

A

A

B

B

S

S

S

S

Figure 2

Agar immunodiffusion technique. (a) Illustrates the

reference line formed between beef reference antigen B and an-
tibeef antibody A and two negative samples S. (b) Illustrates a
positive beef sample on the left, shown by complete fusion of its
immunoprecipitin line with the reference line. The presence of the
nonspecific line shows that the sample on the right is negative for
beef. (Reprinted with permission from Official Methods of Ana-
lysis (2000) 17th edn., AOAC International, Gaithersburg, MD,
Sec. 39.1.36, AOAC International.)

FOOD AND NUTRITIONAL ANALYSIS

/ Meat and Meat Products

309

determined by a quantitative assay for the distinctive
milk sugar, lactose. The AOAC method describes the
determination of lactose as a reducing sugar using
Benedict solution. Prior to the determination of lac-
tose, all other reducing sugars in the sample are
fermented with Baker’s yeast. Lactose may be deter-
mined directly in a procedure that involves hot-water

extraction of the sugar, freeze-drying to remove the
water, formation of a silyl derivative of the lactose
followed by determination using gas–liquid chro-
matography with flame ionization detection. Alter-
native methods for direct determination of the milk
proteins in meat products are based on enzyme
immunoassays or electrophoresis.

Assessment of Spoilage

A number of methods are used to determine spoilage
of meat. These methods are directed at measuring
changes in protein and fat that indicate deterioration
due to spoilage. Protein breakdown is determined
through measurement of TVBN. The meat sample is
extracted with trichloroacetic acid, the extract made
alkaline with sodium hydroxide, the volatile bases
distilled into standard acid, and the TVBN deter-
mined by back-titration with standard alkali.

Deterioration of fat causes rancidity of which there

are two types – hydrolytic rancidity, caused by a
combination of microorganisms and moisture, and
oxidative rancidity, caused by oxygen interacting
with unsaturated fatty acids. Hydrolytic rancidity is
measured as the quantity of free fatty acids (FFA) in
the fat; the fat is extracted from the meat into chlo-
roform, a portion of the extract is mixed with neutral
alcohol, and the FFA titrated directly with alkali
(using phenolphthalein as indicator). A number of
methods are available to measure oxidative rancidity
including peroxide value (PV), TBA value, and ani-
sidine value (AnV). The PV is determined on a chlo-
roform extract by measuring the oxidation of
potassium iodide to iodine through titration with
thiosulfate. TBA and AnV are determined as colori-
metric reactions between aldehydes and 2-thiobar-
bituric acid and between carbonyl compounds and
p-anisidine, respectively.

The suitability of meat is established by ensuring

that the values for TVBN, FFA, PV, TBA, and AnV
are below specified levels which have been estab-
lished as correlating with off-flavors in the meat.

Limitations of Current Analytical
Procedures

Analysis of meat using standard methods is relatively
slow and does not give results that can be used
to influence the manufacturing process. Major
developments in meat analysis technology have oc-
curred in both offline and online systems that give
rapid analysis capability.

Systems based on microwave energy have been

developed for determination of moisture, fat, and

Antigen: soy protein
Antibody raised in a rabbit

Samples and standards are
incubated with excess antibody
seperately

1.

3. Mixture is incubated in wells;
excess antibody is immobilized
in wells, remainder is washed
out

Excess antibody is labeled by
incubating with antibody
conjugated to enzyme ,
remainder is washed out

4.

Substrate is added and
incubated to assay
enzyme activity

5.

6. Color intensity of product

is measured at 405 nm

Unknown antigen levels are estimated by comparing
with appropriate standards (see calibration curve)

7.

Sensitized wells are prepared
by passive adsorption
of antigen remainder is
washed out

2.

Samples solublized in buffered urea, then diluted

Antiglobulin – enzyme conjugate, raised in goat
and chemically coupled to phosphatase

Figure 3

Schematic diagram of soya protein determination by

the ELISA procedure. (Reprinted with permission from Official
Methods of Analysis (2000) 17th edn., AOAC International, Gait-
hersburg, MD, Sec. 39.1.3;

& AOAC International.)

310

FOOD AND NUTRITIONAL ANALYSIS

/ Meat and Meat Products

protein in meat. Automated systems are available
that determine moisture and fat content gravimetri-
cally and calculate protein using a factor, giving re-
sults within 5–10 min. Microwave energy may be
used, also, to give rapid Kjeldahl digestion (10 min)
for direct determination of crude protein.

A very promising technology for both offline and

online applications is near-infrared (NIR) spectros-
copy. NIR radiation energy causes bending or
stretching of bonds such as –C–H, –O–H, and –N–
H to produce absorbance spectra (Figure 4). The ab-
sorption of energy at wavelengths in the NIR region
(750–2500 nm) can be used to analyze for constitu-
ents of meat and meat products. A requirement for
use of NIR analysis is the development of calibra-
tions for the analytes of interest, involving chemical
analysis of many (

X100) samples representative of

the ranges of analytes and variations in the product.
Successful applications of NIR technology in meat
analysis have been done for moisture, protein, and
fat. Salt has been determined by NIR in meat prod-
ucts based on a displacement of the water absorb-
ance peak at 1806 nm. The particular advantage of
NIR analysis is that all analytes may be determined
simultaneously. Limitations in the use of NIR ana-
lysis are the time and expense required for the
development of robust calibrations and the high
product specificity of calibrations, which may limit
the capability of the technology to give accurate re-
sults when there are changes in product composition.

A particular attraction of NIR analysis is the pos-

sibility of using it online to monitor meat constituents
continuously. Fiber optic probe technology has been
successfully adapted to deliver the incident energy
and record the reflected energy from the sample. A

higher energy wavelength range of 750–1100 nm is
often used to achieve sufficient penetration of energy
into intact meat surfaces for nondestructive analysis
online. Apart from quantitative compositional anal-
ysis, NIR has been applied to qualitative analysis, to
predict tenderness of beef carcasses, meat quality of
pork carcasses, and to confirm the animal species of
comminuted meat (Figure 5).

A variety of technologies are being applied to on-

line analysis of carcasses and meat cuts, total body
electrical conductivity (TOBEC), video image anal-
ysis (VIA), and ultrasound scanning. TOBEC meas-
ures the interference produced in an electromagnetic
field by the carcass/meat cut and this is related to
moisture content and, indirectly, to lean meat con-
tent. TOBEC has been used for online measurement
of the lean meat content of boxed boneless beef for
over a decade and is being used also for the grading
of pork carcasses and hams. VIA has been used for
determining the fat/lean content of boxed beef and
has been applied also to grading beef, pork, lamb,
and turkey carcasses. VIA is being developed to pre-
dict the eating quality of beef. Ultrasound scanning
has also been applied to automate pig carcass gra-
ding. For example, the AUTOFOM

TM

equipment

may be more accurate at predicting the lean content
of carcasses than are conventional grading probes
used on the slaughterline, and the equipment gives
information also on the leanness of individual cuts.

See also: Atomic Absorption Spectrometry: Principles
and Instrumentation. Atomic Emission Spectrometry:
Principles and Instrumentation. Carbohydrates: Starch.
Clinical Analysis: Glucose. Extraction: Solvent Extrac-
tion Principles. Food and Nutritional Analysis: Dairy
Products; Oils and Fats. Gravimetry. Immunoassays,

–3

–2

–1

0

1

2

3

–2

–1

0

1

2

3

Discriminant axis 1

Discriminant axis 2

T

T

T

T

T

T

T

T

T

T

T

T

T TT

T

T

T

T

T

T

T

T

T

T

T

T T

C C

CCC

C

C

C

C

C

C

C C

C

C

C

C

C

CC

C C

C

C

C

C

C

C

C

C

P

P

P

P

P P

P

P

P P

PP

P

P

P

P

P

P

P

P

P

P P

P

P

P

P

Figure 5

Discriminant scores plot for homogenized chicken

(C), turkey (T), and pork (P) meats. (From Downey G (2003) The
National Food Centre (Teagasc), personal communication.)

log (I/R)

1.0

1.5

2.0

2.5

3.0

0.5

0.0

800

1000

1200

1400

1600

1800

2000

Wave length (nm)

2200

2400

Raw pork

8.0% Fat

38.4% Fat

Figure 4

Spectra of homogenized raw pork at two levels of fat.

(From Norris KH (1984) Reflectance spectroscopy. In: Stewart
KK and Whitaker JR (eds.) Modern Methods of Food Analysis,
pp. 167–186. Westport, CT: AVI Publishing.)

FOOD AND NUTRITIONAL ANALYSIS

/ Meat and Meat Products

311

Applications:

Food.

Immunoassays,

Techniques:

Enzyme Immunoassays. Infrared Spectroscopy: Near-
Infrared. Lipids: Fatty Acids. Liquid Chromatography:
Food Applications. Microscopy Applications: Food.
Nitrogen. Nitrosamines. pH. Phosphorus. Proteins:
Foods. Sampling: Theory; Practice. Sulfur. Water
Determination. X-Ray Absorption and Diffraction:
X-Ray Absorption.

Further Reading

Baltes W (1990) Rapid Methods for Analysis of Food and

Food Raw Material. Hamburg: Behr’s Verlag.

Bauer F (1991) Microwave digestion of proteins for rapid

determination of hydroxyproline in meat products. In:
Baltes W, Eklund T, Fenwick R, et al. (eds.) Strategies for
Food Quality Control and Analytical Methods in Eu-
rope, vol. II, pp. 552–556. Hamburg: Behr’s Verlag.

Bauer F (1996) Chemical analysis to monitor the quality of

meat and meat products. In: Taylor SA, Raimundo A,
Severini M, and Smulders FJM (eds.) Meat Quality and
Meat Packaging, pp. 183–194. Utrecht: ECCEAMST.

Kirk RS and Sawyer R (1991) Pearson’s Composition and

Analysis of foods, 9th edn. Harlow: Longman Scientific
& Technical.

Lawrie RA (1998) Lawrie’s Meat Science, 6th edn.

Cambridge: Woodhead Publishing Ltd.

Lumley ID (1996) Authenticity of meat and meat products.

In: Ashurst PR and Dennis MJ (eds.) Food Authentica-
tion, pp. 108–139. London: Blackie.

Pomeranz Y and Meloan CE (1994) Food Analysis: Theory

and Practice, 3rd edn. New York: Chapman Hall.

Savell JW (2000) Meat Science Laboratory Manual, 7th

edn. Boston: American Press.

Sebranek JG (1998) Rapid methods for compositional

analyses of meat and meat products. In: Tunick MH (ed.)
New Techniques in the Analysis of Foods, pp. 161–169.
New York: Kluwer Academic Publishers.

Swatland HJ (1995) On-line Evaluation of Meat. Lancas-

ter: Technomic Publishing Co.

Young OA, Frost DA, West J, and Braggins TJ (2001) An-

alytical Methods. In: Hui YH, Nip W-K, Rogers RW, and
Young OA (eds.) Meat Science and Applications, pp.
104–126. New York: Dekker.

Dairy Products

R J Marshall

, London Metropolitan University, London,

UK

& 2005, Elsevier Ltd. All Rights Reserved.

Introduction

Many of the components in milk and dairy products
can be analyzed by standard methods approved by
the International Dairy Federation (IDF). In Decem-
ber 2000, the IDF and the International Organizat-
ion for Standardization (ISO) agreed to publish
standards jointly and these are printed, distributed,
and sold exclusively by the ISO Secretariat. Many of
the methods are also published by the Association of
Official Analytical Chemists (AOAC). The World
Health Organization (WHO) has approved certain
methods. Some of the methods have been used for
many years but, particularly in microbiology, there
have been recent advances that have improved our
ability to determine microorganisms more specifically.

An analysis of dairy products includes the prox-

imates: total solids, protein, fat, energy, ash, acidity,
and specific gravity, and the specifics: lactose, sodi-
um, potassium, calcium, copper, chloride, phosphate,
citrate, lactose, preservatives and antibiotics, added
dyes, detergent residues, organic residues, and

microorganisms. In addition, milk itself may be
analyzed for freezing point and dirt. Methods can be
used for different products with a little adaptation in
most cases.

Physical Analysis of Milk

Freezing Point

Water may get into milk from milking machinery,
accidentally or fraudulently. Dilution of milk changes
its freezing point. The WHO method uses a thermo-
statically controlled water bath cooled by electrical
refrigeration and a thermistor probe. There are two
types of instrument: the first determines a plateau in
the freezing curve and the other, used for routine
screening, reads at a fixed time from the start of
freezing.

In the approved method, supercooled milk is in-

duced to freeze by mechanical vibration that causes
the temperature to rise to a plateau corresponding to
the freezing point. Standard solutions of sodium
chloride are used for calibration. The method gives
excellent agreement between different laboratories
testing the same sample of milk (

o0–0051C).

The addition of 1% water in milk raises the free-
zing point by about

BT/100, where T is base free-

zing point of authenticated samples. Dietary, daily,

312

FOOD AND NUTRITIONAL ANALYSIS

/ Dairy Products