302 FOOD AND NUTRITIONAL ANALYSIS / Meat and Meat Products
See also: Carbohydrates: Sugars  Chromatographic
Peynaud E and Spencer AFG (1984) Knowing and Making
Methods. Ethanol. Food and Nutritional Analysis: Alco- Wine. New York: Interscience.
holic Beverages. Infrared Spectroscopy: Near-Infrared.
Ribereau-Gayon P (ed.) (2000) The Handbook of Enology.
pH. Quality Assurance: Primary Standards; Spectroscopic
New York: Wiley.
Standards. Spectrophotometry: Organic Compounds.
Margalit Y (1990) Winery Technology and Operations
Handbook. Wine Appreciation Guild.
OIV (1999) Compendium of International Methods
Further Reading
of Analysis of Wines and Musts. Paris: OIV
Barrus NW and Evans JA (1991) A Handbook for Must Publications.
and Wine Analysis. University of Texas System. Ough CS and Amerine MA (1988) Methods for Analysis of
Boulton RB, Singleton VL, Bisson LF, and Kunkee RE Musts and Wines. New York: Wiley.
(1996) Principles and Practices of Winemaking. Watkins TR (ed.) (1997) Wine Nutritional and Therapeutic
Dordrecht: Kluwer Academic. Benefits (ACS Symposium Series). American Chemical
Gump BH and Pruett DJ (eds.) (1993) Beer and Wine Society.
Production: Analysis, Characterization and Tech- Zoecklein BW, Fugelsang KC, Gump BH, and Nury FS
nological Advances (ACS Symposium Series). American (1995) Wine Analysis and Production. Dordrecht:
Chemical Society. Kluwer Academic.
Meat and Meat Products
M O Keeffe, The National Food Centre (Teagasc),
(inorganic material) in the meat. In the case of car-
Dublin, Republic of Ireland
cass meat, other measurements such as pH and color
are commonly made to give an indication of quality.
& 2005, Elsevier Ltd. All Rights Reserved.
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
Introduction
value, which gives a measure of hydrolytic rancidity.
The analysis of meat and meat products is a signi-
Spoilage of meat can be measured through assay of
ficant activity in the general area of food analysis
the total volatile basic nitrogen (TVBN), which is
since they represent an important and relatively ex-
related to protein breakdown.
pensive component of the diet. Characterization of
In the case of comminuted meat (e.g., burgers), the
meat through chemical analysis is of importance to
purpose of analysis is to characterize the main con-
meat buyers in the food processing industry and is
stituents (moisture, protein, fat, ash) and also to
the subject of a large amount of regulatory control in
determine to what extent it differs from the intact
most countries. Analysis of meat products is of im-
meat. For example, typical analyses applied to com-
portance for the food processing industry in product
minuted meat samples might include meat species
development, quality control/assurance, and for nu-
identification and determination of collagen and car-
tritional labeling. In addition, meat products are
bohydrate content. As the meat products move fur-
covered by a range of regulatory requirements to
ther away from the original entire meat, a range of
which adherence can be checked by chemical ana-
analyses is used to characterize the food, particularly
lyses. This article describes the analyses used for
assays for nonmeat proteins, for additives such as
meat and meat products, covering both major and
salts, and for preservatives. In the case of cured meat
minor constituents, and addresses the range of meth-
and cured meat products, the important analyses are
ods available for particular analytes.
for salt, nitrite and nitrate, and other additives such
as sugars and phosphorus (polyphosphates).
Meat products, under regulations, are defined ac-
Major Analytes
cording to  meat content and this may be calculated
Fresh or unprocessed meat is characterized normally from compositional data. The percentage  fat-free
by microbial tests, by measurement of physical at- meat is calculated from the total nitrogen content
tributes such as tenderness and color, and by  prox- (corrected for any nonmeat nitrogen) using nitrogen
imate analysis; that is, the proportions of the major factors specific for meat of each species.  Meat con-
constituents of moisture, protein, fat, and ash tent is calculated as the  fat-free meat plus the fat.
FOOD AND NUTRITIONAL ANALYSIS / Meat and Meat Products 303
Related analyses in the meat and meat products are treated as a sample, and carcasses or meat cuts
area are the analysis of curing brines and of special exceeding 2 kg in weight, from which secondary
meat fractions such as mechanically recovered meat samples of 0.5 1 kg may be taken. The above stand-
(MRM). Completing the list of analyses on meat and ard deals with issues such as the inertness of the
meat products are the mineral and vitamin assays containers and the integrity of closures and the ne-
used to characterize the nutritional status of these cessity to store and transport samples at 0 21C (for
foods. 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.
Sampling and Preparation
Before analysis, meat samples must be ground in a
Meat and other edible tissues of animals are difficult suitable mincer or bowl-cutter to produce a homo-
samples to analyze because of the nonuniformity and geneous sample. Connective tissue is a particularly
difficult component of the meat sample to homo-
inherent instability of the sample. Because of the high
water content (X70%) of raw meat, meat samples genize and this is of importance in collagen analysis.
are particularly prone to change either in storage or Suitable comminution of meat samples is specified as
during preparation for analysis. This is more of a a mincer (meat chopper) plate size of 4 mm or less.
problem for raw meat than for meat products, which Equipment used for sample preparation must be
dry and clean and may be cooled or chilled. Speedy
are often  stabilized by some of the constituents
added to the meat or by the processing procedures sample preparation is required to reduce heating and
(cooking, curing) used. consequent evaporation of water, which would affect
In the case of raw carcass meat, another problem is the determination of moisture content. Blades must
that of obtaining a representative sample. Because be sharp to achieve consistent and fast comminution.
the muscles of the animal (the primal cuts) are Samples (preferably well chilled or slightly frozen)
irregular in shape and in fat content, samples for may be prepared by passing through a meat chopper
analysis must be clearly defined in terms of anatom- or mincer multiple (3 ) times, often using plates of
decreasing size where the sample is very large. Often,
ical position. In the case of boxed beef, which is used
in meat processing, it is important to have a sample quite small samples are received for analysis and a
representative of the total content, particularly in bottom-driven bowl cutter may be more appropriate.
terms of lean and fat. In the case of meat products that are a composite
Samples of meat are taken either from defined lo- (such as meat-filled pies), the analysis may require
cations, as multiple subsamples over the entire ma- separation of the sample into its constituent parts,
terial, which are combined to form the analytical weighing of each part, and analysis as separate sam-
sample, or as a single sample after comminuting and ples.
mixing to ensure homogeneity. Preferably raw meat
samples should be analyzed immediately but, if this is
not possible, refrigerated or frozen storage is re- Standard Methods
quired to prevent (reduce) alteration to the sample.
Moisture
Having defined the batch that is to be sampled, the
sampling must be such as to ensure that the batch Moisture is determined by measuring the loss in
will be characterized adequately from the analyses. weight of the sample on heating. A standard method
The number of samples to be taken from a batch (ISO 1442: 1997) used consists of drying a sample of
depends on criteria such as the number of discrete 5 8 g, mixed with predried sand, to constant weight
units in the batch, the importance of the analyte, and with 2 h periods in an oven at 103721C. Methods
the confidence required from the results. Since these approved by the Association of Official Analytical
are subjective or variable criteria, the number of Chemists (AOAC) for moisture include air-drying of
samples is determined initially and then particular a 2 g sample in a convection oven at 100 1021C for
procedures of sampling are followed. 16 18 h, at 1251C to constant weight, or under
The sampling of meat and meat products is vacuum at 95 1001C. An alternative procedure for
covered by an International Standard (ISO 3100-1: moisture determination is microwave drying;
1991). This standard gives general instructions and integrated systems exist consisting of an electronic
specifies procedures to be followed for taking pri- balance and control microprocessor that can give re-
mary samples and is intended primarily for commer- sults after a drying period of 3 5 min.
cial, rather than regulatory purposes. It distinguishes In all cases, moisture determination is based on
between units not exceeding 2 kg in weight, which recording the mass that evaporates from the sample
304 FOOD AND NUTRITIONAL ANALYSIS / Meat and Meat Products
under strictly defined circumstances of temperature temperature, rendering of the resultant digest (con-
and time. It is possible in some samples (1) that com- taining ammonium sulfate) alkaline with concentrat-
ponents other than water may be lost by evaporation ed sodium hydroxide, distillation of the liberated
or (2) that incomplete removal of water may occur ammonia into an excess of acid, and back-titration
due to formation of a  skin on the surface of the with acid to determine the ammonia content. This
sample. Moisture determination, therefore, requires ISO procedure (ISO 937: 1978) has been developed
close attention to the exact conditions used and from a macrosystem in special flasks to a microsys-
maintenance of constant conditions for each analysis. tem in tubes and in a variety of forms of automated
and semiautomated systems  many of which are
AOAC-approved methods.
Protein
An AOAC variation, still based on determination
The total nitrogen content of the sample is deter- of ammonia, is an automated system of digestion
mined after either reduction of all nitrogen to am- with determination using the colorimetric reaction of
monia or liberation of all nitrogen as nitrogen gas. ammonia with hypochlorite and phenol to produce
The  crude protein content of the sample is derived an indophenol absorbing at 630 nm.
from the ammonia/nitrogen content by use of ap- The Dumas method, based on determination of
propriate conversion factors. In the case of meat and gaseous nitrogen in the sample, has been approved
meat products, the factor 6.25 is used to convert by the AOAC for crude protein in an automated
ammonia/nitrogen to crude protein, on the basis that form for a variety of foodstuffs. The modern versions
16% of protein is nitrogen. of this system have fully automated sample intro-
Kjeldahl nitrogen is the classical assay for duction, combustion (9501C), removal of non-nit-
crude protein in meat, consisting essentially of a cat- rogenous gases, and reduction of nitrogenous gases
alyst-aided (sulfate salts and copper or mercury) to nitrogen, and determination of nitrogen content
digestion with concentrated sulfuric acid at elevated by a thermal conductivity cell (Figure 1). The Dumas
LECO nitrogen determinator  flow diagram
Mixing ballast
volume
Sample
gases
O2 carrier (H2O, O2, CO2
gas NO2, NO, N2)
Sample
Furnace
(950°C)
Surplus exhaust
Sample flow
HeN2
Aliquot Exhaust
solenoid
N2
O2 CO2 H2O cell
Exhaust
Reference flow
Thermal
conductivity
cell
He carrier
gas
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.)
FOOD AND NUTRITIONAL ANALYSIS / Meat and Meat Products 305
Table 1 Performance of Kjeldahl and Dumas methods for de-  total fat (ISO 1443: 1973), which involves an hy-
termination of protein in meat products (12 different laboratories,
drolysis with hydrochloric acid prior to the solvent
30 different samples)
fat extraction. For some meat product samples, sim-
Performance measurement Kjeldahl Dumas ple extraction of fat with solvent may be incomplete;
method method
digestion with hydrochloric acid liberates the fat by
hydrolyzing proteins and carbohydrates. In both cas-
Repeatability (Sr) 0.11 0.40 0.12 0.41
es, the sample is oven-dried at 103721C prior to
Reproducibility (SR) 0.29 0.49 0.18 0.46
Protein, overall mean (n ź 360) 15.59% 15.75%
extraction with solvent. The fat content is deter-
mined by weighing the residue after evaporation of
From King-Brink M and Sebranek JG (1993) Combustion method
the solvent.
for determining crude protein in meat and meat products. JAOAC
International 76: 787 793. The primary AOAC method is a Soxhlet method,
similar to the ISO  free fat method. An automated
form of the Soxhlet petroleum spirit (petroleum
method is attractive because it is a fully automated ether) method is approved by the AOAC, using
system, avoids use of corrosive and contaminant equipment such as the SoxtecTM apparatus. In this
chemicals, and is a rapid method. However, the small procedure, multiple samples, mixed with sand, are
sample size (o1 g) used in the Dumas method places predried at 1251C (1 h) prior to a rapid solvent ex-
critical requirements for homogeneity of sample that traction step. There are two other AOAC-approved
may not be as easily attained with meat samples as methods that are widely used for fat determination in
with other sample types. The Dumas method com- meat and meat products. One method uses the Foss-
pares well with the Kjeldahl method both in terms of letTM apparatus comprising a shaker or reactor that
the performance criteria of repeatability and repro- extracts the fat from the sample by very vigorous
ducibility and protein content determined, as shown shaking in a metal container with perchloroethylene
from the results of an AOAC collaborative study for 2 3 min. The specific gravity of the extract is
among 12 different laboratories and using 30 differ- measured in a magnetic float cell controlled by a po-
ent meat and meat product samples (Table 1). tentiometer. The fat content can be determined from
However, the Dumas method gives slightly higher the difference in specific gravity between pure perch-
protein values overall compared with the Kjeldahl loroethylene and the extract. The second method is
method, which may be due to atmospheric nitrogen based on microwave-predrying of the sample, ex-
and/or additional nitrogen detected from basic ami- traction of fat from the dried sample with dichloro-
no acids. In samples with relatively low protein con- methane in a custom-built extractor, and microwave-
centration (o30%), the difference between the two drying of the residue prior to weighing the extracted
methods may not be of practical significance. fat.
There may be a requirement to characterize the Both the Foss-let and the microwave systems are
proteins in a meat product in terms of their amino relatively rapid, a complete procedure taking not
acid content. This may be determined by hydrolysis more than 10 15 min. Both these methods are very
1
with concentrated hydrochloric acid (6 mol l ) and attractive for situations where rapid analyses are re-
separation and identification of the individual amino quired, such as online for product control. However,
acids either (1) by ion exchange chromatography and where large batches of samples are to be analyzed
colorimetric measurement using ninhydrin, or (2) by and where results are not required within 24 h, the
high-performance liquid chromatography of fluores- Soxhlet solvent extraction, or the more rapid So-
cent derivatives of the amino acids. xtecTM system, may be preferable. These latter tech-
niques do not require constant attention, as is the
case for the rapid methods. Good comparison be-
Fat
tween results obtained by Soxhlet extraction and the
Standard methods for the determination of fat in Foss-let technique has been reported. In the case of
meat and meat products are based on extraction of the microwave-based system, adjustment factors
the fat from the sample using a lipophilic solvent and have been defined for different classes of meat prod-
ucts to overcome a negative bias in the method.
determination of the extracted fat by weighing or by
measurement of specific gravity (relative density) Supercritical fluid extraction (SFE) has been ap-
changes in the extractant solvent. There are two ISO plied also for determination of fat in meat and meat
methods for fat in meat and meat products, one for products. Supercritical carbon dioxide, produced
 free fat (ISO 1444: 1996), which consists of repeat- using elevated pressure (7.4 MPa) and temperature
ed extraction of the sample with n-hexane or petro- (311C), extracts the fat from samples that have been
leum spirit in a Soxhlet apparatus, and the other for mixed with moisture-absorbing agents, such as
306 FOOD AND NUTRITIONAL ANALYSIS / Meat and Meat Products
diatomaceous earth. The advantage of this technique For laboratory measurements, an ISO method for
is that there is no waste solvent disposal problem and pH (ISO 2917: 1999) specifies either homogenization
a number of samples may be extracted simultane- of the sample in potassium chloride solution and in-
ously. A number of studies have shown good agre- sertion of the electrode(s) into the extract, or intro-
ement between the SFE and the Soxhlet methods. duction of the electrode into prepared holes in the
X-ray absorption technology (e.g., Anyl-RayTM) is nonhomogenized sample. Other methods specify
used in the meat industry to determine indirectly the preparation of a slurry of the ground sample with
fat content of meat. The meat sample (B7kg) is an equal weight of water, or preparation of a
transilluminated with X-rays and the absorption of homogenate in the ratio of one part meat to five
1
energy is related to the mineral content of the sample. parts sodium iodoacetate (5 mmol l )/potassium
1
Fat content is calculated from the relationship be- chloride (150 mmol l ).
tween fat, protein, water, and mineral content of meat.
Where the fat in a meat or meat product sample is Collagen
to be characterized in terms of the fatty acid profile,
Determination of the collagen content of meat prod-
extraction of the fat with chloroform/methanol is
ucts is important in controlling the eating quality
required. This solvent mixture, while it may not give
(toughness) and for ensuring that too high an amount
complete fat extraction, is used to ensure no chemical
of low-grade meat, with a high level of connective
change to the lipids and the extraction of phospho-
tissue, is not in a product. Collagen content is deter-
lipids. Fatty acid analysis of the extracted fat is un-
mined from an analysis for the amino acid L-hydro-
dertaken by formation of volatile methyl esters of the
xyproline, which occurs at much higher levels in
fatty acids (ISO 5509: 2000) and determination by
collagen than in other muscle proteins.
gas chromatography (ISO 5508: 1990).
The ISO method for L-hydroxyproline (ISO 3496:
1994) involves hydrolysis of the sample with sulfuric
Ash
acid, at 1051C for 16 h. After filtration and dilution
Ash is the residue remaining after incineration of the of the hydrolysate, the L-hydroxyproline content is
sample in a furnace at temperatures in excess of determined by oxidation with chloramine-T and re-
5001C. The AOAC method specifies drying of the action with p-dimethylaminobenzaldehyde to form a
sample and charring before ignition at 5251C. The colored complex that is measured spectrophotomet-
ISO method (ISO 936: 1998) specifies incineration of rically at 558 nm. This method requires close atten-
the sample at 5507251C, in a muffle furnace, fol- tion to detail, particularly the color reaction which
lowing drying and carbonization of the sample either must be carried out under exact temperature and
(1) separately in an oven and on a hot-plate or (2) in time conditions (6070.51C for 20 min). The repeat-
the furnace by gradually raising the temperature. In ability of the determination is assured by preparation
all cases, the ash is determined by weighing of the of a calibration graph with each batch of samples.
residue and care must be taken in handling the silica Using a specific microwave oven for digestion can
dishes to avoid losses. reduce the time for this procedure to 30 min, so that
A common practice is to determine ash content on the total time for analysis can take less than 3 h.
samples that have been oven-dried for moisture de- The collagen content is determined by multiplica-
termination. While ash may be used for determina- tion of the L-hydroxyproline result by a factor of 8
tion of metals, salts, etc., attention must be given to (corresponding to the hydroxyproline content of col-
the possibility of losses due to volatility of these lagen being equal to 12.5%, where the nitrogen-to-
components of the sample at the very high ashing protein factor is 6.25).
temperatures used.
Additives
pH
In the production of meat products, additives such as
The pH of meat is an important measure of quality, a salts, sugars, and preservatives are used. Analyses for
higher than normal pH (4pH 6.2 at 24 h after these substances are important in that maximum
slaughter) or a lower than normal pH (opH 5.9 at levels allowed in foods are specified in various na-
45 min after slaughter) indicating conditions known tional regulations such as the US Food and Drugs
as DFD (dark, firm, dry) and PSE (pale, soft, ex- Administration and the European Commission DG
udative) meat, respectively. The determination of SANCO.
such meat is important as the uses to which it can be The standard methods for sodium chloride in meat
put are limited. Such pH measurements are made on products are titrimetric methods in which the salt is
the carcass with a spear probe. extracted from the sample, reacted with excess silver
FOOD AND NUTRITIONAL ANALYSIS / Meat and Meat Products 307
nitrate to form a silver chloride precipitate, and the carcinogenic products resulting from the reaction of
residual silver nitrate titrated with thiocyanate. The secondary amines with the nitrites used for curing.
ISO method (ISO 1841-1: 1996) specifies an extrac- The AOAC official method is based on distillation
tion with hot water and precipitation of proteins under vacuum of the nitrosamines from the sample in
with Carrez reagents (potassium hexacyanofer- mineral oil into a trap. The trapped nitrosamines are
rate(II) and zinc acetate solutions), followed by acid- collected in methylene chloride, concentrated by
ification of the filtered extract with nitric acid before evaporation, and determined by gas chromatogra-
addition of excess silver nitrate. The silver chloride phic analysis using a thermal energy analyzer. Re-
precipitate is coagulated with nitrobenzene and cently, a method was approved by the AOAC for the
the residual silver nitrate titrated with potassium following three volatile N-nitrosamines in minced
thiocyanate. In the AOAC method, the sample is meat: N-nitrosodimethylamine, N-nitrosopyrroli-
treated with excess silver nitrate before extraction by dine, and N-nitrosomorpholine. In this method, the
boiling with dilute nitric acid and titration of residual sample is mixed with anhydrous sodium sulfate and
silver nitrate is with ammonium thiocyanate. This Celite, packed into a glass chromatographic column,
method is appropriate for samples with a sodium and eluted with pentane dichloromethane. The elu-
chloride content X1%. ate passes through a second column containing acid
Another ISO method (ISO 1841-2: 1996), based Celite, on which the nitrosamines are trapped. The
on potentiometric titration with a silver nitrate so- nitrosamines are eluted from this second column
lution using a silver electrode, is appropriate for with dichloromethane, the eluate is concentrated,
samples with a sodium chloride content X0.25%. and the nitrosamines determined by gas chro-
The sample is dispersed in water and an aliquot is matographic analysis using a thermal energy ana-
acidified by addition of nitric acid, prior to titration. lyzer.
Alternative methods for salt determination include Phosphate and polyphosphates are determined as
use of a chloride ion-selective electrode and a semi- total phosphorus in the ISO method (ISO 2294:
quantitative indicating strip method based on the 1974). The sample is digested with nitric and sulfuric
reaction of chloride ion with silver chromate to pro- acids and the orthophosphate is precipitated as
duce silver chloride. quinoline 12-molybdophosphate. The precipitate is
The salts associated with cured meats, nitrates and collected on a glass filter, dried, and weighed and
nitrites, are assayed by aqueous extraction and colo- expressed as phosphorus pentoxide. A similar pro-
rimetric determination. The ISO methods involve cedure described by the AOAC is ashing of the sam-
extraction in hot water containing borax solution ple at 5501C, boiling of the ash in dilute nitric acid
and deproteination of a portion of the extract with and filtration before precipitation of quinoline 12-
Carrez reagents. Nitrite (ISO 2918: 1975) is deter- molybdophosphate.
mined directly by formation of an azo dye with An alternative approach to these gravimetric meth-
sulfanilamide and N-(1-naphthyl)ethylenediamine ods is determination procedure based on the forma-
dihydrochloride which is measured at 538 nm. Ni- tion of colored complexes. Orthophosphate in acidic
trate (including nitrite) (ISO 3091: 1975) is deter- solution reacts with molybdic acid and vanadic acid
mined by cadmium reduction to nitrite and azo dye to form yellow orange vanadomolybdophosphoric
formation. Reduction of nitrate to nitrite may be acid which has maximum absorption at 330 nm.
carried out on a special column (as in the ISO meth- Another approach is a two-stage reaction in which
od) or using  spongy cadmium. Care must be taken yellow phosphomolybdate is produced from the ad-
to prevent interference from ascorbic acid if it is dition of ammonium molybdate to the orthophos-
present in the sample at relatively high levels phate in acidic solution, and the phosphomolybdate
1
(420 mgml ). is then reduced by ascorbic acid to a molybdenum
Other methods for nitrates and nitrites include the blue, which is measured at 890 nm. This last method
AOAC procedure in which m-xylenol is nitrated and is the basis for an AOAC-approved spectrophoto-
the nitro-xylenol is distilled into sodium hydroxide metric method.
solution to form a colored sodium salt that is deter- In some countries, sulfur dioxide is used as a pre-
mined with ultraviolet spectrophotometry at 450 nm. servative in meat products. Sulfur dioxide occurs in
Gas chromatography with electron capture detection many forms in food but quantitative tests for the
and high-performance liquid chromatography have material in meat products are normally for total (free
been used for determination of nitrate and nitrite plus bound) sulfur dioxide. The AOAC method ap-
derivatives. plied to meat products consists of liberation of sulfur
Of particular interest in cooked cured meat prod- dioxide from the sample by heating with hydrochlo-
ucts is the determination of nitrosamines, ric acid, distillation into hydrogen peroxide solution,
308 FOOD AND NUTRITIONAL ANALYSIS / Meat and Meat Products
which then reacts with the sulfur dioxide to form quantity of D-glucose is determined by a two-stage
sulfuric acid, and titration with sodium hydroxide reaction involving hexokinase and dehydrogenase
using methyl red indicator. Gravimetric determina- enzymes. The specific glucose-6-phosphate dehy-
tion is also possible by addition of barium chloride to drogenase utilizes the coenzyme nicotinamide ade-
the titrated liquid resulting in a precipitate of barium nine dinucleotide phosphate (NADP). The reaction
sulfate, which can be isolated by filtration, dried, and of the enzyme with the sugar involves reduction of
weighed. Special apparatus for the AOAC proce- NADP to NADPH, which is measured spectromet-
dures (the modified Monier Williams method and rically at 340 nm:
the optimized Monier Williams method) have been
Amyloglucosidase
developed.
Starch þðn 1ÞH2O ! nD-glucose
An alternative to the hydrogen peroxide/sulfuric
Hexokinase
acid titration with alkali is distillation of sulfur di- D-Glucose þ ATP ! ADP þ glucose-6-phosphate
oxide from the acidified sample into excess iodine
G6P dehydrogenase
Glucose-6-phosphate þ NADPþ !
solution. A proportion of the iodine, equivalent to
the amount of sulfur dioxide, is reduced to iodide,
Gluconate-6-phosphate þ NADPH þ Hþ
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
Metals
volatile sulfur compounds do not interfere, and it has
Analyses for metals in meat and meat products are
been developed for use with automated distillation
carried out by atomic spectrometry, generally after
systems.
dry-ashing and solubilization of the ash in acid.
Another AOAC approved method for sulfites in
Sodium and potassium, being present at relatively
meat is the qualitative test based on decolorization of
high levels in meats, are determined by atomic emis-
malachite green solution when mixed with a sample
sion spectrometry, while other metals, such as cad-
containing sulfites. This may be used to screen sam-
mium, copper, iron, lead, and zinc, are determined by
ples prior to quantitative determination as described
atomic absorption spectrometry. An alternative
above.
method applicable to most metals is inductively cou-
Two other methods have been approved by AOAC
pled plasma atomic emission spectrometry.
for determination of sulfites in food. One is a quan-
The AOAC method for arsenic involves ashing at
titative assay based on malachite green decolorizat-
6001C, dissolving the ash in dilute hydrochloric acid
ion using flow injection analysis. Sulfite is released
with the addition of metallic zinc, and the arsenic is
from a sample slurry with alkali, then the test stream
distilled as arsine (AsH3) into an iodine solution.
is acidified to produce sulfur dioxide gas which dif-
Ammonium molybdate is added to the solution and,
fuses across a Teflon membrane into a flowing stream
through a series of reactions assisted by heating,
of malachite green, and the extent of decolorization
molybdenum blue is formed which is determined
is measured at 615 nm. The other method is based on
spectrophotometrically at 840 nm.
ion exclusion chromatography with sulfur dioxide
The determination of calcium in meat products,
being released by alkali extraction, and the diluted
especially in mechanically recovered (or separated)
filtrate is injected onto an anion exclusion column
meat (MRM/MSM), is an important estimation of
linked to an electrochemical detector.
the amount of bone material included in the meat.
The presence of added starch in meat products is
The AOAC method describes an acid digestion of the
determined by a titrimetric method for reducing
sample and reaction of an aliquot of the filtered
sugars. The ISO (ISO 5554: 1978) and AOAC de-
digest with excess ethylenediaminetetraacetic acid
scribe methods for starch which involve extraction
(EDTA) under alkaline conditions to form a chelated
with water, clarification with Carrez reagents, and
complex with calcium ion. The excess EDTA is then
acid hydrolysis of the isolated starch. Determination
titrated with calcium carbonate using hydroxynaph-
of the resultant reducing sugars is by reaction with
thol blue as indicator.
Fehling s solution (containing copper sulfate), oxida-
tion of potassium iodide with the excess copper(II),
Kit Methods for Additives and Metals
and titration of the liberated iodine with thiosulfate,
according to the Luff Schoorl method. A variety of qualitative or semiquantitative kit
Starch, and individual sugars, may be determined methods based on indicating test strips (e.g., Mercko-
in meat products using enzymatic kit methods. quants), color comparators (e.g., Aquaquants,
Starch is extracted from the sample and hydrolyzed
Microquants), and photometric determinations
by the enzyme amyloglucosidase to D-glucose. The (e.g., Spectroquants) are available. These kit methods
FOOD AND NUTRITIONAL ANALYSIS / Meat and Meat Products 309
may be used for onsite measurements or for screen- Enzyme-linked immunosorbent assays (ELISAs) in
ing assays. Typical analytes measured are nitrite/ kit form are most widely used giving relatively rapid
nitrate, sulfite, phosphate, and metals. 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
Analyses for Adulteration
antisera formed against serum albumin of the various
species of interest. An extract of the meat product is
Meat Species Identification
added to the antibody-coated wells, incubated to en-
The determination of the animal species contributing
sure antibody binding of the serum albumin, and,
to the meat(s) in a meat product is important for
after washing, a second antibody coupled with en-
marketing purposes. It may be necessary, in some
zyme is introduced. The  sandwich is visualized by
cases, to ensure the absence of meat of a particular
addition of a substrate to the enzyme. ELISAs have
species, such as pork. A number of methods for meat
been developed, also, for meat species identification
species identification are used which are based on
in cooked meat products. These ELISAs are quite
immunological antigen antibody reactions, on pro-
specific and sensitive (B1% of each species can be
tein isolation techniques, such as electrophoresis, or
detected) but are qualitative, or at best, semiquanti-
on DNA analysis.
tative.
The AOAC methods are based on agar gel
Methods for meat species identification based
immunodiffusion tests for beef and for poultry meat
on DNA analysis benefit from the heat stability of
in meat products. These tests use stabilized reagent
the DNA molecule and its high specificity. Originally,
paper disks containing beef (or poultry) antibody and
DNA methods consisted of immobilization of par-
beef (or poultry) antigen. The samples are applied to
tially purified and denatured DNA, extracted from
the agar plate by absorbing fluids on to paper disks,
the meat product sample, on a nylon membrane,
which are then placed on the plate. Diffusion of an-
followed by hybridization of a species-specific
tigen and antibody components occurs during incu-
segment of labeled (colorimetric, fluorescent, or
bation for 18 24 h and the immunoprecipitin lines
chemiluminescent) DNA with any complementary
are examined for presence of beef (or poultry) in the
sequences of DNA present on the membrane. More
samples (Figure 2). These tests are limited in that
recently, a DNA amplification method  the polym-
they are suitable only where the adulterant is present
erase chain reaction  has been used, but this is a
at X10%.
relatively expensive and technically demanding tech-
Agar gel immunodiffusion methods have been
nique.
produced as commercial kits and a further develop-
ment is dipstick assays for meat species identifi-
Nonmeat Proteins
cation. The immunoreagents are immobilized on a
dipstick and a color change, occurring in less than
Assays to detect the presence of nonmeat proteins,
1 h, identifies the presence of a particular meat spe-
such as soya protein, are based on similar antigen
cies, with a detection limit of B1% lean meat.
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
B B
dilution with buffer. The soya protein reacts with an
excess of antibody and the unbound antibody is im-
S S S S
mobilized in wells that have been coated with an-
A A
tigen. A second antibody conjugated to enzyme
labels the immobilized antibody and substrate is
(a) (b) added to give a color reaction, the extent of which is
inversely related to the amount of soya protein ex-
Figure 2 Agar immunodiffusion technique. (a) Illustrates the
tracted from the sample (Figure 3). This procedure is
reference line formed between beef reference antigen B and an-
tibeef antibody A and two negative samples S. (b) Illustrates a very lengthy and test kits utilizing a direct ELISA give
positive beef sample on the left, shown by complete fusion of its
more rapid results. Qualitative microscopic methods
immunoprecipitin line with the reference line. The presence of the
are also used to detect the presence of soya in meat
nonspecific line shows that the sample on the right is negative for
products.
beef. (Reprinted with permission from Official Methods of Ana-
Skim milk powder or milk proteins may be used in
lysis (2000) 17th edn., AOAC International, Gaithersburg, MD,
Sec. 39.1.36, AOAC International.) meat products. The presence of milk powder is
310 FOOD AND NUTRITIONAL ANALYSIS / Meat and Meat Products
Antigen: soy protein extraction of the sugar, freeze-drying to remove the
Antibody raised in a rabbit
water, formation of a silyl derivative of the lactose
Samples solublized in buffered urea, then diluted
followed by determination using gas liquid chro-
Antiglobulin enzyme conjugate, raised in goat
matography with flame ionization detection. Alter-
and chemically coupled to phosphatase
native methods for direct determination of the milk
Samples and standards are proteins in meat products are based on enzyme
1. 2. Sensitized wells are prepared
incubated with excess antibody
by passive adsorption
immunoassays or electrophoresis.
seperately
of antigen remainder is
washed out
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
3. Mixture is incubated in wells;
distilled into standard acid, and the TVBN deter-
excess antibody is immobilized
in wells, remainder is washed
mined by back-titration with standard alkali.
out
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
4. Excess antibody is labeled by
the fat; the fat is extracted from the meat into chlo-
incubating with antibody
conjugated to enzyme ,
roform, a portion of the extract is mixed with neutral
remainder is washed out
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
5. Substrate is added and
potassium iodide to iodine through titration with
incubated to assay
enzyme activity
thiosulfate. TBA and AnV are determined as colori-
metric reactions between aldehydes and 2-thiobar-
bituric acid and between carbonyl compounds and
6. Color intensity of product
p-anisidine, respectively.
is measured at 405 nm
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-
7.
Unknown antigen levels are estimated by comparing
lished as correlating with off-flavors in the meat.
with appropriate standards (see calibration curve)
Figure 3 Schematic diagram of soya protein determination by
the ELISA procedure. (Reprinted with permission from Official
Limitations of Current Analytical
Methods of Analysis (2000) 17th edn., AOAC International, Gait-
hersburg, MD, Sec. 39.1.3; & AOAC International.)
Procedures
Analysis of meat using standard methods is relatively
determined by a quantitative assay for the distinctive
slow and does not give results that can be used
milk sugar, lactose. The AOAC method describes the to influence the manufacturing process. Major
determination of lactose as a reducing sugar using developments in meat analysis technology have oc-
Benedict solution. Prior to the determination of lac- curred in both offline and online systems that give
tose, all other reducing sugars in the sample are rapid analysis capability.
fermented with Baker s yeast. Lactose may be deter- Systems based on microwave energy have been
mined directly in a procedure that involves hot-water developed for determination of moisture, fat, and
FOOD AND NUTRITIONAL ANALYSIS / Meat and Meat Products 311
3.0
3
C
Raw pork
2.5
2
C
8.0% Fat
CCC C C
38.4% Fat
C
C
C
2.0 P P
1
C CC C C C C P P
C
C
C
PP P
C C C
C PPP
PP P
P
C
P
C
1.5 0
C T P P
C P P
T P
P P
TT T
T
P PP P
T
T CT T
T
P
 1
CT T T
1.0
T
T T T
T T
T
T
TT
 2
0.5 T T
T
T
 3
0.0
800 1000 1200 1400 1600 1800 2000 2200 2400  2  1 0 1 2 3
Wave length (nm)
Discriminant axis 1
Figure 4 Spectra of homogenized raw pork at two levels of fat.
Figure 5 Discriminant scores plot for homogenized chicken
(From Norris KH (1984) Reflectance spectroscopy. In: Stewart
(C), turkey (T), and pork (P) meats. (From Downey G (2003) The
KK and Whitaker JR (eds.) Modern Methods of Food Analysis,
National Food Centre (Teagasc), personal communication.)
pp. 167 186. Westport, CT: AVI Publishing.)
protein in meat. Automated systems are available higher energy wavelength range of 750 1100 nm is
that determine moisture and fat content gravimetri- often used to achieve sufficient penetration of energy
cally and calculate protein using a factor, giving re- into intact meat surfaces for nondestructive analysis
sults within 5 10 min. Microwave energy may be online. Apart from quantitative compositional anal-
used, also, to give rapid Kjeldahl digestion (10 min) ysis, NIR has been applied to qualitative analysis, to
for direct determination of crude protein. predict tenderness of beef carcasses, meat quality of
A very promising technology for both offline and pork carcasses, and to confirm the animal species of
online applications is near-infrared (NIR) spectros- comminuted meat (Figure 5).
copy. NIR radiation energy causes bending or A variety of technologies are being applied to on-
stretching of bonds such as  C H,  O H, and  N line analysis of carcasses and meat cuts, total body
H to produce absorbance spectra (Figure 4). The ab- electrical conductivity (TOBEC), video image anal-
sorption of energy at wavelengths in the NIR region ysis (VIA), and ultrasound scanning. TOBEC meas-
(750 2500 nm) can be used to analyze for constitu- ures the interference produced in an electromagnetic
ents of meat and meat products. A requirement for field by the carcass/meat cut and this is related to
use of NIR analysis is the development of calibra- moisture content and, indirectly, to lean meat con-
tions for the analytes of interest, involving chemical tent. TOBEC has been used for online measurement
analysis of many (X100) samples representative of of the lean meat content of boxed boneless beef for
the ranges of analytes and variations in the product. over a decade and is being used also for the grading
Successful applications of NIR technology in meat of pork carcasses and hams. VIA has been used for
analysis have been done for moisture, protein, and determining the fat/lean content of boxed beef and
fat. Salt has been determined by NIR in meat prod- has been applied also to grading beef, pork, lamb,
ucts based on a displacement of the water absorb- and turkey carcasses. VIA is being developed to pre-
ance peak at 1806 nm. The particular advantage of dict the eating quality of beef. Ultrasound scanning
NIR analysis is that all analytes may be determined has also been applied to automate pig carcass gra-
simultaneously. Limitations in the use of NIR ana- ding. For example, the AUTOFOMTM equipment
lysis are the time and expense required for the may be more accurate at predicting the lean content
development of robust calibrations and the high of carcasses than are conventional grading probes
product specificity of calibrations, which may limit used on the slaughterline, and the equipment gives
the capability of the technology to give accurate re- information also on the leanness of individual cuts.
sults when there are changes in product composition.
See also: Atomic Absorption Spectrometry: Principles
A particular attraction of NIR analysis is the pos-
and Instrumentation. Atomic Emission Spectrometry:
sibility of using it online to monitor meat constituents
Principles and Instrumentation. Carbohydrates: Starch.
continuously. Fiber optic probe technology has been
Clinical Analysis: Glucose. Extraction: Solvent Extrac-
successfully adapted to deliver the incident energy
tion Principles. Food and Nutritional Analysis: Dairy
and record the reflected energy from the sample. A Products; Oils and Fats. Gravimetry. Immunoassays,
log (I/R)
Discriminant axis 2
312 FOOD AND NUTRITIONAL ANALYSIS / Dairy Products
Applications: Food. Immunoassays, Techniques:
Kirk RS and Sawyer R (1991) Pearson s Composition and
Enzyme Immunoassays. Infrared Spectroscopy: Near- Analysis of foods, 9th edn. Harlow: Longman Scientific
Infrared. Lipids: Fatty Acids. Liquid Chromatography:
& Technical.
Food Applications. Microscopy Applications: Food.
Lawrie RA (1998) Lawrie s Meat Science, 6th edn.
Nitrogen. Nitrosamines. pH. Phosphorus. Proteins:
Cambridge: Woodhead Publishing Ltd.
Foods. Sampling: Theory; Practice. Sulfur. Water
Lumley ID (1996) Authenticity of meat and meat products.
Determination. X-Ray Absorption and Diffraction:
In: Ashurst PR and Dennis MJ (eds.) Food Authentica-
X-Ray Absorption.
tion, pp. 108 139. London: Blackie.
Pomeranz Y and Meloan CE (1994) Food Analysis: Theory
and Practice, 3rd edn. New York: Chapman Hall.
Further Reading
Savell JW (2000) Meat Science Laboratory Manual, 7th
Baltes W (1990) Rapid Methods for Analysis of Food and edn. Boston: American Press.
Food Raw Material. Hamburg: Behr s Verlag. Sebranek JG (1998) Rapid methods for compositional
Bauer F (1991) Microwave digestion of proteins for rapid analyses of meat and meat products. In: Tunick MH (ed.)
determination of hydroxyproline in meat products. In: New Techniques in the Analysis of Foods, pp. 161 169.
Baltes W, Eklund T, Fenwick R, et al. (eds.) Strategies for New York: Kluwer Academic Publishers.
Food Quality Control and Analytical Methods in Eu- Swatland HJ (1995) On-line Evaluation of Meat. Lancas-
rope, vol. II, pp. 552 556. Hamburg: Behr s Verlag. ter: Technomic Publishing Co.
Bauer F (1996) Chemical analysis to monitor the quality of Young OA, Frost DA, West J, and Braggins TJ (2001) An-
meat and meat products. In: Taylor SA, Raimundo A, alytical Methods. In: Hui YH, Nip W-K, Rogers RW, and
Severini M, and Smulders FJM (eds.) Meat Quality and Young OA (eds.) Meat Science and Applications, pp.
Meat Packaging, pp. 183 194. Utrecht: ECCEAMST. 104 126. New York: Dekker.
Dairy Products
R J Marshall, London Metropolitan University, London,
microorganisms. In addition, milk itself may be
UK
analyzed for freezing point and dirt. Methods can be
used for different products with a little adaptation in
& 2005, Elsevier Ltd. All Rights Reserved.
most cases.
Physical Analysis of Milk
Introduction
Freezing Point
Many of the components in milk and dairy products
can be analyzed by standard methods approved by Water may get into milk from milking machinery,
the International Dairy Federation (IDF). In Decem- accidentally or fraudulently. Dilution of milk changes
ber 2000, the IDF and the International Organizat- its freezing point. The WHO method uses a thermo-
ion for Standardization (ISO) agreed to publish statically controlled water bath cooled by electrical
standards jointly and these are printed, distributed, refrigeration and a thermistor probe. There are two
and sold exclusively by the ISO Secretariat. Many of types of instrument: the first determines a plateau in
the methods are also published by the Association of the freezing curve and the other, used for routine
Official Analytical Chemists (AOAC). The World screening, reads at a fixed time from the start of
Health Organization (WHO) has approved certain freezing.
methods. Some of the methods have been used for In the approved method, supercooled milk is in-
many years but, particularly in microbiology, there duced to freeze by mechanical vibration that causes
have been recent advances that have improved our the temperature to rise to a plateau corresponding to
ability to determine microorganisms more specifically. the freezing point. Standard solutions of sodium
An analysis of dairy products includes the prox- chloride are used for calibration. The method gives
imates: total solids, protein, fat, energy, ash, acidity, excellent agreement between different laboratories
and specific gravity, and the specifics: lactose, sodi- testing the same sample of milk (o0 0051C).
um, potassium, calcium, copper, chloride, phosphate, The addition of 1% water in milk raises the free-
citrate, lactose, preservatives and antibiotics, added zing point by about BT/100, where T is base free-
dyes, detergent residues, organic residues, and zing point of authenticated samples. Dietary, daily,