202 FOOD AND NUTRITIONAL ANALYSIS / Overview
FOOD AND NUTRITIONAL ANALYSIS
Contents
Overview
Sample Preparation
Additives
Antioxidants and Preservatives
Contaminants
Water and Minerals
Pesticide Residues
Mycotoxins
Soft Drinks
Coffee, Cocoa, and Tea
Alcoholic Beverages
Wine
Meat and Meat Products
Dairy Products
Vegetables and Legumes
Oils and Fats
Fruits and Fruit Products
Packaging Materials
for nitrogen estimation in 1885), together
Overview
with the concern over adulteration resulted in the
introduction of statutory legislation over the
composition of important food products in many
V Jain and K Gupta, Haryana Agricultural University,
countries. These forms of controls continued for
Hisar, India
B100 years until the 1970s, when rapid advances
& 2005, Elsevier Ltd. All Rights Reserved.
in food science and technology revolutionized the
manufacture of food. Media attentions have also
brought a public awareness of the links and causa-
tion between diet and health. As a result, today s so-
Introduction
phisticated consumers have become more concerned
The science of food and nutritional analysis has over the quality and compositions of their food pur-
chases, the contained ingredients, and the presence of
developed rapidly in recent years. Food scientists
analyze foods to obtain information about their additives and contaminants. Therefore, knowledge
composition, appearance, texture, flavor, shelf life, of the chemical and biochemical composition of
etc., and also to guarantee the quality of the product. foods is important to the health, well-being, and
safety of the consumers. Analytical characterization
Nevertheless, the term food and nutritional analysis
is often thought only to be concerned with the de- is also important for compliance with legal stand-
termination of food composition and its nutritive ards, quality assurance, and determination of nutri-
value/quality. tional value.
Various types of modern food analytical
The analysis of food began in the nineteenth
century utilizing microscopy. It was the first techniques have been developed, including elec-
analytical technique used by analysts such as trophoresis, chromatography, spectroscopy, rheol-
Accum and Hassall to identify food components ogical techniques, and sensory evaluation, to
and to detect adulteration. The development of meet the challenge of providing information on
improved analytical methods to determine the the diverse components of these complex food
composition of foods (such as Kjeldahl method materials.
FOOD AND NUTRITIONAL ANALYSIS / Overview 203
method selected must be specific, accurate, precise,
Information Sources
and sensitive for the substance to be analyzed. The
Standard Official Methods and Modern Information
sampling includes sample selection, preparation, and
Retrieval Systems
labeling. If it is not carried out properly/correctly it
Standard analytical methods approved by profes- leads to variability of results. Ideally, the sample
analyzed should have exactly the same properties as
sional associations/scientific agencies such as
the bulk of the sample (population) from which it
Association of Official Analytical Chemists, The
American Association of Cereal Chemists, and Amer- was taken. The major steps in sampling are identi-
fication of the population from which the sample is
ican Oil Chemist Society are used in food industry.
to be taken, location from which the sample should
(These methods are being improved and updated
be collected, and method of obtaining the gross
from time to time.) The computerized systems for
samples.
storing and retrieving scientific information are now
well developed (Table 1).
Techniques and Methods
Sampling
Spectroscopic Techniques
Food is a heterogeneous mixture of chemical sub-
stances; therefore, its analysis requires adequate A variety of spectroscopic techniques has been
methods of sampling and preserving. The analytical developed to analyze food materials (Table 2).
Table 1 Organizations that issue standard food analysis methods and modern information retrieval systems
Name of organizations/acronym Area of analysis
Name of organizations
American Association of Cereal Chemists (AACC) Cereals
American Oil Chemists Society (AOCS) Oil seeds
Analytical Methods Committee of the Royal Society of Chemistry, UK (AMC) Various
Association Francaise de Normalization (French Standard Organization) (AFNOR) General
Association Internationale de I Industrie des Bouillons et Potages (International Association of the Stock Soups
and Soup Industry) (AIIBP)
Association of Official Analytical Chemists, USA (AOAC) Food, agriculture
Association of Public Analysts, UK (APA) Various
British Standards Institution (BSI) General
Corn Industries Research Foundation Inc. (CIRF) Starch products
Deutsche Gesellschaft fur Fettwissenschaft (DGF) Oils and fats
European Economic Community(EEC) Various
Food and Agriculture Organization, UN (FAO) Agriculture
Federation of Oils, Seeds and Fats Association (FOSFA) Oils and fats
International Association of Seed Crushers (IASC) Vegetables oils and fats
International Association for Cereal Chemistry (ICC) Cereals
International Commission on Microbiological Specification for Food (ICMSF) Food (general)
International Commission for Uniform Methods of Sugar Analysis (ICUMSA) Sugar
International Dairy Federation (IDF) Dairy products
International Office of Cocoa, Chocolate and Sugar Confectionery (IOCCC) Cocoa, confectionery
International Organization of the Flavour Industry (IOFI) Flavor
International Organization for Standardization (ISO) General
International Union of Pure and Applied Chemistry (IUPAC) General
Institute of Brewing, UK (IOB) Beer
Nordisk Metodik-kommittee for Livsmedal (NMKL) Food
Nederlands Normalisatie-Instituut (NNI) General
Office Internationale de la Vigne et du Vin (OIV) Wine
Modern information retrieval systems
Database
AGRICOLA, BIOSIS PREVIEWS, CAB abstracts, CRIS, Food science and technology abstracts,
Science citation index
Website
http/agrifor.ac.uk, www.altavista.com, www.biacore.com, www.bmn.com, www.rediff.com,
www.cabi.com, www.google.com, www.yahoo.com, http://www.worldmedicus.com
204 FOOD AND NUTRITIONAL ANALYSIS / Overview
Table 2 Spectroscopic methods for food analysis
Type of spectroscopy Information obtained Nature of material required
Atomic absorption and emission Analysis of elements Solution
Atomic fluorimetry Analysis of elements Solution
Circular dichroism Conformation of proteins Solution of optically active molecules
Dielectric Moisture content Native
Electron spin resonance Physical state Native material
Nuclear magnetic resonance Physical state and chemical analysis Native material or solid or liquid extract
Near-IR and mid-IR Physical state and chemical structure Native material depending on type of IR
Mass spectroscopy Analysis of elements and structure determination Usually solid extracts
Raman Physical state Molecules
X-ray Structure composition Native material
UV visible absorption Chemical quantitative analysis Native
Table 3 Techniques for biological evaluation of food
Analysis using live system Analysis using biochemical techniques
Whole animal as Microbiological analysis Tissue and cell culture Immunochemical Enzymatic techniques
analytical tool analysis techniques
Assay on body Turbidimetric Cell culture Agglutination Substrate assay
Body weight changes Gravimetric method Organ or tissue culture Immunodiffusion methods
Digestibility assays Serial dilution assays Radioimmunoassay Endpoint methods
Analysis of food protein Acidimetric and Enzyme immunoassay Kinetic methods
and energy (PER, metabolic product
Immobilized enzymes
NPR), and net energy assay
assay
assay Diffusion plate assay
Tubular enzyme
reactions
Changes in nutrient
Enzyme electrodes
content of body
Rapid analysis strips
Energy balance
Bv, NPU
Immunoenzymatic
methods
Enzyme-linked
immunosorbent
assay
Enzyme multiplied
immunoassay
technique
Rheological Techniques
specific system of applied forces. These techniques
provide a measure of baking quality of flours, thick-
ening properties of biopolymers, texture, hardness,
Rheology is the study of flow of matter and defor-
flakiness, consistency in food, tenderness of meat,
mation and these techniques are based on their stress
and texture of fruits and vegetables. Rheological
and strain relationship and show behavior inter-
techniques have now become essential tools in food
mediate between that of solids and liquids. The
science and technology.
rheological measurements of foodstuffs can be based
on either empirical or fundamental methods. In the
Biological Techniques
empirical test, the properties of a material are related
to a simple system such as Newtonian fluids or Biological techniques encompass two method-
Hookian solids. The Warner Bratzler technique is an ological approaches: live systems and biochemical
empirical test for evaluating the texture of food ma- techniques. Live systems employ (1) whole animal,
terials. Empirical tests are easy to perform as any (2) microorganisms, and (3) cell and tissue culture
convenient geometry of the sample can be used. The methods as tools in food analysis. Biochemical tech-
relationship measures the way in which rheological niques include uses of enzymes and immunochemical
properties (viscosity, elastic modulus) vary under a techniques (Table 3).
FOOD AND NUTRITIONAL ANALYSIS / Overview 205
Live systems as analytical tools Different life sys- growth stimulation, and then by turbidimetry meas-
tems have been utilized in assessing composition and urement, gravimetry measurement, diffusion plate
nutritional quality of foods. assay, and metabolic product assay.
The whole animal techniques are used in the nu-
tritional and toxicological evaluation of foods by
Cell and tissue culture methodology This method
providing a combined assessment of digestibility,
uses cell, tissue, or organs for analytical purposes.
metabolism of food, and nutritional evaluation of
These have been used in food toxicology and safety.
quality of foods. These approaches are aimed at
Toxic chemicals like pesticides, food additives, and
determining the changes in the nutrient content in
chemicals produced during processing and cooking
animal body in response to feeding a diet or meal
of foods are tested for their toxicity, mutagenicity,
containing that nutrient. The animal used in con-
and oncogenic properties using tissue culture
ducting food analysis assays include albino rats and
techniques.
mice, and guinea pigs, chicken, ducks, hamsters,
gerbils, dogs, and monkeys.
Biochemical techniques These techniques include
The changes in nutrient content and energy value
immunochemical and enzymatic techniques.
of foods required for animal body involves the meas-
Immunochemical techniques are based on specific
urements on animal body itself. These assays are
interactions of antibodies with antigens. Since macro-
based on body weight changes for analysis of food
molecules are present in microorganisms, food, and
protein and energy and include protein efficiency ra-
agricultural products and are good antigens, the an-
tio (PER), net protein ratio (NPR), and multilevel
tibodies against these molecules can be obtained in
assays. The second approach to estimate change in
response to the immunization with antigens, the sub-
the nutrient content of the body involves measure-
stances foreign to animals. The antibodies produced
ments of intake and output of nutrients from the
in response to a particular antigen are capable of
body and assay includes nitrogen or energy balance,
recognizing and binding due to the complementary
net protein utilization (NPU), biological value (BV),
binding site on the antibody with that of antigen.
and net energy.
The methods employed in food analysis include
The animal assay for evaluating toxic constituents
hemagglutination, precipitation, immunodiffusion,
(natural or added) of food uses lethality as an index
immunofluorecence, immunoeletrophoresis, radio-
and determines the dose of that toxic chemical to
immunoassays, and enzyme immunoassays. Enzyma-
kill/affect 50% of the test animal, referred to as
tic analysis means analysis with the aid of enzymes
LD50 dose. The response criteria can be toxicity,
using specific enzymatic reactions. The enzymatic
carcinogenicity, mutagenicity, reproduction, and
techniques are highly useful because of specificity and
metabolism.
sensitivity for measuring the concentration of com-
pounds. This reduces the time of analysis and avoids
Microbiological food assay Microbiological food
lengthy separations of the components. The immobi-
assays involve the use of microorganisms as a substi-
lized enzyme systems with electrochemical detection
tute for a higher animal. Since some of the nutritional
methods are used for analytical determinations
requirements of microorganisms and experimental
of food components that would be laborious or
animals are similar, it is possible to use micro-
otherwise impossible. These techniques require small
biological food assays to determine the substances
amounts of sample and do not require components to
that are essential constituents of living cells. These are
be extracted from their matrix. Enzymatic methods
based on the principle that in the presence of limiting
are used in the determination of structure of poly-
amount of specific nutrients, the amount of growth
meric macromolecules, quality indices of foods, and
is a function of concentration of this nutrient. These
nutritional and physical induced changes in human
are used for determination of amino acids, vitamins,
beings.
nucleic acids, heavy metals, growth factors, and the
nutritional value of proteins and antibodies. The mi-
Sensory Evaluation
croorganisms used for the assay are bacteria, fungi,
algae, yeast, and protozoa. The test organism selected Sensory evaluation is a scientific discipline used to
is based on nonpathogenicity, sensitivity, and specifi- evoke, measure, analyze, and interpret reaction to
city to the nutrient to be assayed, its rapid and repro- those characteristics of food material as they are
ducible growth, and ease in making growth perceived by the senses of sight, smell, taste, touch,
measurements. It can be assayed after adding the food and hearing (sound). The sensory attributes of qual-
sample extract to a liquid medium or gel medium, ity of food are measured to determine consumer
inoculated with the microbial culture followed by acceptance/preference in order to manufacture an
206 FOOD AND NUTRITIONAL ANALYSIS / Overview
acceptable and affective product at maximum pro- standard stimulus. The frequency method records
duction economy. The sensory attributes include ap- each comparison stimulus against a standard stimu-
pearance (color, size, shape, and consistency of liquid lus many times, thereby creating a difference
and semisolid products), kinesthetic (texture, con- response.
sistency, and viscosity), and flavor (taste and odor).
Discrimination Tests
The evaluation is done to determine quality criteria
by which raw materials and finished products may be
Food analysis is based on difference testing, the fun-
graded and classified. The sensory techniques help
damental approach to sensory analysis of food. A
food scientists to determine the conformity of a food
simple difference test permits one of the two re-
with established government or trade standards and
sponses  Yes, there is a difference or  No, there is a
food grades and product development while main-
no difference . In directional difference testing, a
taining desirable sensory characteristics. The tech-
judge is asked which sample is more in a predefined
nique of sensory evaluation uses humans as data
characteristic. The predesignated standard must be
generators; hence, it is influenced by cultural, psy-
similarly understood and used by all the judges. A
chological, religious, social, and climatic factors,
large number of difference tests, single stimulus,
physical and educational status of an individual,
paired comparison, paired difference, triangle, dual
availability, and nutritional knowledge. Highly
standard, multiple standard, and multiple pairs, are
trained groups of experts are employed for evaluat-
used to detect the sensory differences (such as sweet-
ion to minimize the effects of such factors. For
ness, softness, color, etc.) between the two or more
complete sensory evaluation of food, two types of
samples.
tests  analytical sensory tests and affective tests
(like dislike) are performed (Table 4).
Quantitative Test (Intensity)
The analytical sensory tests are confined to sen-
This approach of sensory evaluation is based on de-
sitivity, discriminatory, quantitative (intensity), and
scription of scaling, i.e., ranking category (or inter-
descriptive or qualitative analysis of the sensory at-
nal) and magnitude estimation (or ratio). Ranking is
tributes of food.
used for grouping of the products based on their
A sensitivity test is a measure of sensitivity to a
quality or order of preference. The scoring on
human stimulus and is expressed as threshold, which
category scale involves the use of a limited number
is a fixed value at a given moment of time. The
of categories, designated in terms of numbers, letters,
threshold may be absolute or differential, which is
or points on a line. The magnitude estimation is a
measured using various psychological methods. The
type of ratio scaling that measure the relationship
threshold is determined by approaching and receding
between physical and sensory criteria. Any number is
from standard stimulus by short steps and the thresh-
assigned to the first stimulus. A proportional number
old is that step where the judge s response shifts from
is assigned to reflect its strength in comparison to the
one category to another. In the method of average
first.
error (or the method of adjustment), the judge ad-
justs the concentration of the comparison with the
Descriptive Analysis
In descriptive analysis small groups of highly trained
judges with considerable experience with the com-
modity under study develop adjectives to character-
Table 4 Human response of sensory systems corresponding to
selected physical properties of foods
ize the qualitative properties of the product
(attributes like appearance, aroma, texture, taste,
Physical property Sensory system Human sensation
etc., are analyzed). The data of sensory analysis ex-
(stimulus)
periments are subjected to statistical analysis to get
Density Kinesthetic, haptic Heavy, light
reliable results. Instrumental methods are also used
Moisture content Haptic, thermal Dry, wet, soggy
to correlate physicochemical measurements with sen-
pH Gustation, pain Harsh, sharp, sour
Radiant energy Visual Appearance, color sory judgments (Table 5).
Shear Kinesthetic, haptic Hard
Surface abrasion Haptic, pain Rough, prickly
Effective testing/acceptance testing By acceptance
Solubility Gustation Taste
testing we mean measuring liking or preference for a
Temperature Thermal system Cold, hot
Texture Olfaction Odor product. Preference is that expression of appeal of
Vapor pressure Kinesthetic, haptic Thin, thick
one product versus another that can be measured
Vibration/pitch Auditory Sound, e.g., crisp,
directly by comparing two or more products with
crunchy, sizzle
each other. The nine-point hedonic scale method
FOOD AND NUTRITIONAL ANALYSIS / Overview 207
Table 5 Analytical methds and consumer measurements of sensory attributes
Analytical tests
Stimulus concentration
Sensitivity Quantitative Qualitative
Threshold Discrimination Scaling Duration Descriptive analysis
Methods of limits Paired comparison Ordering or ranking Time intensity Texture profile
Methods of adjustments Paired difference Category (internal) Flavor profile
or average error
Frequency method Duo trio Magnitude estimation Dilution profile
(ratio)
Dual standard Quantitative descriptive
analysis
Multiple standard Other methods
Triangle
Consumer tests
Effective
Acceptance Preference Hedonic test
Accept/reject what is Select one over the Degree of like and
available other dislike
occupies a niche for the sensory evaluation of prod-
Food Components
uct acceptance/preference. The measure of liking
Knowledge regarding the major constituents of food
preference is a sensory evaluation model for me-
(e.g., carbohydrates, amino acids, proteins, lipids,
asuring product acceptance and it represents the final
dietary fiber, and nutritional and antinutritional
phase of test resources with discrimination and de-
components) is necessary so as to guage the extent
scriptive analysis test. The sensory acceptance test is
of any structural change that occurs during process-
a cost-effective resource that has a major role in the
ing and storage of foods, which may affect the qual-
development of successful products.
ity and safety of the food product.
The scale was developed to access the degree of
acceptability of food items, beverages, cosmetics,
Major Components
paper products, etc., by measuring the degree/
magnitude of like/dislike.
Moisture Water content/moisture content is the
most ubiquitous substance in nature, the largest
Nutritional Evaluation of Food Processing
single constituents of all living things and affects
Although processed foods are not considered to be as quality, value, and freshness of food and is of major
nourishing as fresh and unprocessed foods, there is an concern in food, paper, and plastic industries. Mois-
increasing demand for processed foods, which are ture determination is a widely used fundamental an-
available throughout the year. Food processing alytical operation, which satisfies the technological,
involves a wide variety of industrial processes with a analytical, commercial, and regulatory necessities in
correspondingly large variety of products. The opti- the processing, testing, and storage of food products
mum quality maintenance of the product attributes and is an index of economic value, stability, and
are compared in relation to the origin as  fresh like nutritional quality of food products.
characteristics of preserved fresh products and  just Removal of water for processing/storage purposes
cooked like attributes of preserved cooked products. either by conventional dehydration or freezing and
New techniques such as modified atmosphere pack- drying alters the native functional properties of
ing, edible and biodegradable packing materials, high- foods. Simple, rapid, and accurate methods for mois-
pressure short-duration treatment, biopreservation, ture determination in raw, processed, and stored
high-voltage inputs, and a combination of different food products are used to know the nutritive value of
mild treatments help in preserving the quality at- food products. A homogenous food sample should
tributes of the processed food. be prepared using a number of electrical/mechanical
208 FOOD AND NUTRITIONAL ANALYSIS / Overview
devices like blenders, graters, grinders, homogeni- carbohydrate determination in foods are summa-
zers, and mincers for the determination of moisture rized in Table 7.
by any of the analytical methods given in Table 6, Neutral monosaccharides, uronic acids, hexosa-
which are classified as direct and indirect procedures. mines, and sialic (neurominic acids) are identified
The weight of sample is taken before and after and determined by specific colorimetric reactions.
it is dried, and the moisture content is calculated. The principle behind the techniques rests on the con-
Instruments used for moisture determination are densation of the degraded products of the neutral
simple to use and provide rapid and reliable measure- monosaccharides (hexose, pentose and methyl pen-
ments and are suitable for routine quality control tose) by sulfuric acid with anthrone, cysteine hydro-
applications. chloride, orcinol, and phenol reagents. Uronic acids
may be determined by colorimetric and manometric
Carbohydrates Carbohydrates are a major source procedures. While sialic acids are determined after
of energy for humans and are present in all foods chemical/enzymatic hydrolysis, gravimetric and Van-
(grains, vegetables, fruits, and milk), and vary Soest detergent based methods are used to determine
in form from simple monosaccharides (fructose,
cellulose, hemicellulose, and fiber.
glucose, galactose, sorbitol) to oligosaccharides
(maltose, sucrose, lactose, raffinose, stachyose, ver-
Amino acids and proteins A large variety of pro-
bascose), and more complex polysaccharides (starch,
teins, either from animal origin (eggs, fish, meat, and
cellulose, etc.).
milk) or plant origin (cereal, pulses, fruits, and
The complete analysis of foodstuffs may require
vegetables) is available from food sources. There is a
the determination of simple sugars and reducing
practical need to determine amino acids, proteins,
sugars (fructose, glucose, galactose, sorbitol, mal-
and protein quality, and to monitor and regulate
tose, lactose), oligosaccharides (sucrose, raffinose,
protein quality in food production, processing,
stachyose, verbascose), polysaccharides (starch,
storage, and marketing, which emphasizes the im-
cellulose, etc.), and fibers, which vary in amount/
portance of protein quality. The comprehensive nu-
form and all of which may play an important
tritional evaluation of protein quality of food and
role in the quality of the product. Methods of
food products begins with the determination of
nitrogen content, essential amino acid concentra-
tions, amino acids, protein types, and assessment of
Table 6 Classification of analytical methods for moisture
determination
Direct methods Indirect methods
Direct methods usually yield Indirect methods are rapid,
Table 7 Major methods of carbohydrate analysis
accurate and absolute value nondestructive and easily
Traditional methods Recent methods
and are manual and time automated
consuming
Physical and electrical
Physical methods Physicochemical methods
Drying method methods
Determine the quantity of a Provide more rapid analysis
Chemical desiccation AC and DC conductivity
particular sugar present in with a greater precision and
Freeze-drying Dielectric capacitance
food specificity
Oven drying Microwave absorption
Hydrometry
Chromatography and
Vacuum drying
Polarimetry
electrophoresis
Spectroscopic methods
Refractometry
Paper chromatography
Distillation method IR absorption
Thin-layer chromatography
Azotropic distillation Near-IR reflectance Chemical methods
Gas chromatography
Nuclear magnetic resonance Classical methods
Chemical methods
Liquid chromatography
Neutron and g-ray scattering Ferricyanide method
Generation of acetylene
Ion-exchange chromatography
Iodometry method
Heat on mixing with H2SO4 Refractometry
Sonic and ultrasonic
Karl Fischer titration
Colorimetric methods Biochemical methods
Based on chemical reagents Enzymatic methods: used for
Extraction method
used starch and cell wall
Gravimetric method
Anthrone carbohydrates
Thermogravimetric analysis
Clegg-anthrone
Flow injection analysis
Copper reduction
Absolute methods
Automated method
Dinitrosalicylate
Dew point method
Phenol/sulfuric acid
Gas chromatography
Nelson-Somogyi
Manometric method
Neocuproine
Psychrometry
Picric
Volumetric
FOOD AND NUTRITIONAL ANALYSIS / Overview 209
nutritional value including digestibility (in vitro and Table 8 Methods of protein determination
in vivo assays), and biological evaluation (PER,
Name of method Principle used
NPU, BV, growth parameters, etc.) by taking albino
Chemical methods
rats, guinea pigs, and human beings as experimental
Biuret method Based on binding of copper(II) to a
models. Enzymatic and microbiological tests may al-
peptide bond in protein molecules
so evaluate nutritional quality of foods. Amino acids
at alkaline pH values (measured
can be determined by colorimetric and enzymatic
between 540 and 650 nm)
Lowry method Based on reduction of Folin
methods after hydrolysis of proteins in a specific
Ciocalteau reagent by oxidation
medium used to diminish destruction of essential
of tyrosine, tryptophan on
amino acids after separation by different techniques
polypeptide side chain (measured
(column chromatography, thin-layer chromatogra-
at 750 nm)
phy (TLC), gas chromatography (GC), high-perfor- Dye binding Based on the measurements of
excess dye remaining in solution
mance liquid chromatography, etc.). The availability
after removal of the precipitated
of all the essential amino acids in food proteins
protein dye complex
can be measured with the enzymatic ultrafilteration
Physical methods
digest.
UV spectrophotometry Based on absorption maximum at
The determination of protein in food/food prod-
280 nm, due to presence of a side
ucts depends on a measurement of a specific element
chain of aromatic amino acids
or chemical group in the proteins, which may be
(Tyr and Try)
carried out either directly by using chemical or phys- Fluorimetry Based on emission of fluorescence
excited at 275 or 345 nm
ical properties. Based on nitrogen content, protein
IR reflectance Based on characteristics
content can be estimated by Kjeldahl s method
absorbance spectra at different
(AOAC). Ammonical nitrogen produced after de-
wavelengths
struction of organic matter of foods is multiplied by a
Refractometry Based on change in refractive index
coefficient of 6.25 for animal, vegetable, and pulse by the displacement of proteins
Turbidimetry Based on change in intensity of light
proteins and by 5.7 for cereals to obtain protein
due to protein diffusion
contents. Ammonia content can also be determined
Immunological method Based on interaction between an
by using an ammonia-specific electrode, based on the
antigen and its corresponding
difference in potential between a reference electrode
antibody
and a measurement electrode, and with the help of
Nessler s reagent. Protein content in food/food prod-
ucts may be determined by various chemical and
physical methods as given in Table 8.
which are already listed as determination of amino
Specific protein components in food/food products
acid composition and essential amino acids, and
can be determined by chromatography (ion-exchange
enzymatic tests, microbiological methods, and bio-
chromatography, PC, TLC, GC, LC, etc.), elect-
logical measures.
rophoresis, and immunology or their combination. It
is also necessary to use high-resolution techniques
such as reversed phase LC, ion-exchange LC, size- Lipids The analysis of lipids in food has three dis-
exclusion LC, slab electrophoresis, and capillary tinctive objectives: to determine (1) total lipid con-
electrophoresis (CE). tent, (2) the composition, and (3) the quality of
All protein determination methods described are lipids.
not absolute and demand some form of calibration.
The Kjeldahl s method remains the only official 1. Total lipid content. There are physical and
method currently available for calibration purposes chemical procedures for oil/fat estimation. In phys-
and maintains its position as the most frequently ical procedures, lipids are not isolated and samples
used technique for the determination of organic nit- are used directly, and lipids are estimated by nuclear
rogen in food products. CE and immunochemical magnetic resonance (NMR) spectroscopy. In chem-
(enzyme-linked immunosorbent assay) techniques ical procedures, lipids are extracted by refluxing the
are most suitable for rapid separation and quantifi- sample in suitable solvents (like petroleum ether)
cation of individual food proteins and are promising by using standard methods (AOAC or AOCS).
for widespread use in food protein analysis due to Different classes of lipids such as neutral lipids
their high sensitivity, specificity, and simplicity of (by nonpolar solvents such as petroleum ether,
operation. There are numerous methods for the eval- hexane), phospho- or glycolipids (by polar solvents
uation of the nutritional quality of food proteins, such as methanol) can be extracted and used for
210 FOOD AND NUTRITIONAL ANALYSIS / Overview
quantitative determination. TLC, column chro- spectrometry, polarography, X-ray spectrometry,
matography, HPLC are specific techniques used for mass spectrometry, and activation analysis are im-
separation of various classes of lipid. portant physical methods used for the determination
of minerals, and are suitable for determination of
2. Composition of oil/fat. To study the composi-
alkaline metals, provide accurate and reproducible
tion of oil/fat it is essential to test the purity of an oil/
results, and offers simultaneous determination of
fat for adulteration, accidentally or voluntarily. The
numerous elements.
specific fatty acid in fat can be determined by GC by
preparing methyl esters with sodium methoxide.
Other food components It is also important to
Mass spectrometry coupled to GC (GC MS) is the
analyze the toxic constituents/antinutritional factors,
most powerful tool for identification of fatty acids
which are present naturally in foods, produce a del-
separated by GC. Free fatty acids in oil (index of
eterious effect when ingested by humans or animals.
rancidity) can be determined by titration against
The toxic constituents/antinutritional factors, which
standard alkali. Infrared (IR) spectroscopy, Raman
are present naturally in foods are flatous producing
spectroscopy, and ultraviolet (UV) spectroscopy
factors, protease inhibitors, hemagglutinins (lectin),
(200 400 nm) are used to detect isomers (trans and
and saponins present in legumes, and glucosinolates
cis) of unsaturated fatty acids and conjugated double
(in oil seed crops), cyanogens (in bitter almond, lima
bonds. It is important to study saponification value
beans), gossypol (in cotton), and lathyrogen (seeds of
(depict fatty acid chain length), iodine value (give the
Lathyrus species). A large number of standard
degree of unsaturation), and hydroxyl value (free
(AOAC) analytical techniques are adopted to deter-
fatty acids present in fats).
mine the food components such as bitter compounds
like anthocyanins, carotenoids (pigments), flavono-
Ash and Mineral Components
ids, phenols, terpenoids, vitamins, aroma com-
The determination of ash/minerals in food contrib-
pounds, alcohols, organic acids, antioxidants and
utes to assessment of a food s nutritional value and
preservatives etc.
refers to elements and verifying if the food contains
some minerals in quantities dangerous to the health
See also: Amino Acids. Carbohydrates: Overview.
of the consumer, whether their presence is natural or Food and Nutritional Analysis: Sample Preparation;
Packaging Materials. Liquid Chromatography: Over-
adulteration of certain food stuffs/processed or
view. Thin-Layer Chromatography: Overview.
stored food products.
Ash content is a measure of total minerals and is a
reliable index of nutritional value for many foods
(tea, flour, edible gelatin, etc.) and feed (for poultry
Further Reading
and cattle) and is recognized as a useful tool in de-
AACC (1983) Approved Methods of Analysis, 8th edn. St.
termining the nature and distribution of mineral
Paul, MN: American Association of Cereal Chemists.
constituents of food. Ash is the inorganic material
AOAC (1995) Official Methods of Analysis, 16th edn. As-
left after complete oxidation of organic material at
sociation of Official Analytical Chemists, Arlington,
high temperatures (500 6001C).
Virgini, USA.
Ash is prepared by two direct procedures (dry and
AOCS (1990) Official Methods of Recommended Practic-
wet ashing) and an indirect technique (conduct-
es. Chicago, IL: American Oil Chemists Society.
ometeric method that can determine the total
Fennema OR (1996) Food Chemistry. New York: Dekker.
electrolyte content of foods), governed by the
Gruenwedel DW and Whitakar JR (eds.) (1984) Food
following purpose: the particular constituents to be
Analysis: Principles and Techniques, vols 1 4. New
determined and the method of analysis to be used. York: Dekker.
James CS (1994) Analytical Chemistry of Foods. London:
Dry ashing is the standard method to determine ash
Blackie Academic and Professional.
content of a sample (AOAC). For wet ashing the
Kulp K and Ponte JG Jr (2000) Handbook of Cereal Sci-
sample is digested in a mixture of HNO3 and
ence and Technology, 2nd edn. New York: Dekker.
HCLO4 (ratio 4:1).
Linden G (ed.) (1996) Analytical Techniques for Foods and
Gravimetry (for sulfur), titrimetric (chloride), fluo-
Agricultural Products. New York: VCH.
rimetry (Se, Al, F), colorimetric methods, or atomic
Multon JL (ed.) (1997) Analysis of Food Constituents.
spectroscopy are the traditional classical chemical
New York: Wiley-VCH.
methods for the determination of individual ele-
Nollet LML (ed.) (1996) Handbook of Food Analysis, vols
ments. Atomic spectroscopy techniques have a much
1 2. New York: Dekker.
higher sensitivity and specificity and provide a com- Nollet LML (ed.) (2000) Food Analysis by HPLC, 2nd
plete profile of elements in a food/feed. Emission edn. New York: Dekker.
FOOD AND NUTRITIONAL ANALYSIS / Sample Preparation 211
Oliveira FAR, Oliveira JC, Hendrickx ME, Korr D, and Sorensen (2000) Chromatography and Capillary
Gorris LGM (eds.) (1999) Processing Food: Quality Op- Electrophoresis in Food Analysis. New York:
timization and Process Assessment. New York: CRC Press. Springer.
Poumeranz Y and Meloan CE (1994) Food Analysis: Theory Wilson RH (ed.) (1994) Spectroscopic Techniques for Food
and Practice, 3rd edn. New York: Chapman and Hall. Analysis. New York: Wiley-VCH.
Sample Preparation
Kiyoshi Matsumoto, Kyushu University, Fukuoka,
corrected on the basis of dry matter (values of an-
Japan
hydrous material) or values of moisture contents are
Hiroyuki Ukeda, Kochi University, Nankoku, Japan
used in evaluating the analyzed value.
The general steps for sample preparation and sam-
& 2005, Elsevier Ltd. All Rights Reserved.
ple processing are (1) sampling and size reduction, (2)
comminution and homogenization, (3) pretreatments
of the sample, such as predrying or defatting, (4) pre-
Sample Preparation servation of the prepared sample, and (5) cleanup of
the analytical sample for instrumental analysis. This
In many respects, the sampling and preparation of a
article covers the practical considerations of sample
sample are critical steps in any technique of food
preparation necessary for food analysis.
analysis. The objective of sampling is to ensure that
the sample taken for analysis is representative of a
defined whole, and the method of sampling depends
Sampling and Size Reduction
on the size and nature of the defined whole.
Obtaining a sample for analysis that is represen- It is important to define clearly the population that is
tative of the whole is referred to as sampling, and to be sampled. Populations are generally finite, such
the total quantity from which a sample is obtained is as the size of a defined lot, except for evaluating a
called the population. An accurate and precise esti- process. The sampling methods selected depend on
mate of the quality of a population will only be ac- the purpose of the inspection, the nature of the
hieved by using an adequate sampling technique product, the nature of the test method, and the na-
because only a portion of the population is used for ture of the population being investigated. The basic
analysis. With a proper sampling technique, the es- principle for sampling is probability sampling. This
timated value will reflect the characteristics of the sampling plan provides a statistically sound basis for
population. obtaining representative samples while eliminating
Special care, however, is required in the sampling human bias and, therefore, is the most desirable. The
and sample preparation for food analysis because of most useful sampling method is random sampling in
the peculiarities of food. Foods are derived from which samples are simply taken at random from the
biological substances and contain various organic whole population. The random sampling process al-
compounds. Many of these components are influ- lows all parts of the population to have the same
enced by various external and internal influences chance of being sampled. The goal of providing the
such as temperature, light, moisture, microorgan- same chance can be achieved by means of random
isms, metabolism, and ripening. Therefore, rapid number tables or computer-generated random num-
preparation of food samples enough to prevent com- bers. Sample size is determined by lot size, the degree
position change is very important in food analysis. of accuracy required, and the expense of the test
Preparation at low temperatures during processing or method. However, a general standard for the number
storage in the frozen state is also effective for preven- to be sampled is proposed. For instance, to select the
ting the composition change of food samples. sample flour from sacks, the number of sacks to be
In food analysis, analyses are generally performed sampled is determined by the square root of the
on the edible portion of the defined food, discarding number of sacks in the lot.
the nonedible portion, unless the compositions with If the mass of the collected samples is too large for
respect to the total sample weight are required. Var- analysis, it is subjected to size reduction to obtain a
iations in moisture of food are relatively large, even smaller quantity for analysis. For granular or pow-
among the same kinds of food. Therefore, values dered material, such as cereals, pulses, nuts, and