authenticity of certain food components, to ensure that consumers are not the victims
of economic fraud and that competition among food manufacturers is fair.
Food Inspection and Grading
The government has a Food Inspection and Grading Service that routinely
analyses the properties of food products to ensure that they meet the appropriate laws
and regulations. Hence, both government agencies and food manufacturers need
analytical techniques to provide the appropriate information about food properties. The
most important criteria for this type of test are often the accuracy of the measurements
and the use of an official method. The government has recently carried out a survey of
many of the official analytical techniques developed to analyze foods, and has
specified which techniques must be used to analyze certain food components for
labeling purposes. Techniques have been chosen which provide accurate and reliable
results, but which are relatively simple and inexpensive to perform.
1.1.2. Food Safety
One of the most important reasons for analyzing foods from both the
consumers and the manufacturers standpoint is to ensure that they are safe. It would be
economically disastrous, as well as being rather unpleasant to consumers, if a food
manufacturer sold a product that was harmful or toxic. A food may be considered to be
unsafe because it contains harmful microorganisms (e.g., Listeria, Salmonella), toxic
chemicals (e.g., pesticides, herbicides) or extraneous matter (e.g., glass, wood, metal,
insect matter). It is therefore important that food manufacturers do everything they can
to ensure that these harmful substances are not present, or that they are effectively
eliminated before the food is consumed. This can be achieved by following “good
manufacturing practice” regulations specified by the government for specific food
products and by having analytical techniques that are capable of detecting harmful
substances. In many situations it is important to use analytical techniques that have a
high sensitivity, i.e., that can reliably detect low levels of harmful material. Food
manufacturers and government laboratories routinely analyze food products to ensure
that they do not contain harmful substances and that the food production facility is
operating correctly.
1.1.3. Quality control
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The food industry is highly competitive and food manufacturers are
continually trying to increase their market-share and profits. To do this they must
ensure that their products are of higher quality, less expensive, and more desirable than
their competitors, whilst ensuring that they are safe and nutritious. To meet these
rigorous standards food manufacturers need analytical techniques to analyze food
materials before, during and after the manufacturing process to ensure that the final
product meets the desired standards. In a food factory one starts with a number of
different raw materials, processes them in a certain manner (e.g. heat, cool, mix, dry),
packages them for consumption and then stores them. The food is then transported to a
warehouse or retailer where it is sold for consumption.
One of the most important concerns of the food manufacturer is to produce a
final product that consistently has the same overall properties, i.e. appearance, texture,
flavor and shelf life. When we purchase a particular food product we expect its
properties to be the same (or very similar) to previous times, and not to vary from
purchase-to-purchase. Ideally, a food manufacture wants to take the raw ingredients,
process them in a certain way and produce a product with specific desirable properties.
Unfortunately, the properties of the raw ingredients and the processing conditions vary
from time to time which causes the properties of the final product to vary, often in an
unpredictable way. How can food manufacturers control these variations? Firstly, they
can understand the role that different food ingredients and processing operations play
in determining the final properties of foods, so that they can rationally control the
manufacturing process to produce a final product with consistent properties. This type
of information can be established through research and development work (see later).
Secondly, they can monitor the properties of foods during production to ensure that
they are meeting the specified requirements, and if a problem is detected during the
production process, appropriate actions can be taken to maintain final product quality.
Characterization of raw materials. Manufacturers measure the properties of
incoming raw materials to ensure that they meet certain minimum standards of quality
that have previously been defined by the manufacturer. If these standards are not met
the manufacturer rejects the material. Even when a batch of raw materials has been
accepted, variations in its properties might lead to changes in the properties of the final
product. By analyzing the raw materials it is often possible to predict their subsequent
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behavior during processing so that the processing conditions can be altered to produce
a final product with the desired properties. For example, the color of potato chips
depends on the concentration of reducing sugars in the potatoes that they are
manufactured from: the higher the concentration, the browner the potato chip. Thus it
is necessary to have an analytical technique to measure the concentration of reducing
sugars in the potatoes so that the frying conditions can be altered to produce the
optimum colored potato chip.
Monitoring of food properties during processing. It is advantageous for
food manufacturers to be able to measure the properties of foods during processing.
Thus, if any problem develops, then it can be quickly detected, and the process
adjusted to compensate for it. This helps to improve the overall quality of a food and to
reduce the amount of material and time wasted. For example, if a manufacturer were
producing a salad dressing product, and the oil content became too high or too low
they would want to adjust the processing conditions to eliminate this problem.
Traditionally, samples are removed from the process and tested in a quality assurance
laboratory. This procedure is often fairly time-consuming and means that some of the
product is usually wasted before a particular problem becomes apparent. For this
reason, there is an increasing tendency in the food industry to use analytical techniques
which are capable of rapidly measuring the properties of foods on-line, without having
to remove a sample from the process. These techniques allow problems to be
determined much more quickly and therefore lead to improved product quality and less
waste. The ideal criteria for an on-line technique is that it be capable of rapid and
precise measurements, it is non-intrusive, it is nondestructive and that it can be
automated.
Characterization of final product. Once the product has been made it is
important to analyze its properties to ensure that it meets the appropriate legal and
labeling requirements, that it is safe, and that it is of high quality. It is also important to
ensure that it retains its desirable properties up to the time when it is consumed.
A system known as Hazard Analysis and Critical Control Point (HACCP)
has been developed, whose aim is to systematically identify the ingredients or
processes that may cause problems (hazard analysis), assign locations (critical control
points) within the manufacturing process where the properties of the food must be
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measured to ensure that safety and quality are maintained, and to specify the
appropriate action to take if a problem is identified. The type of analytical technique
required to carry out the analysis is often specified. In addition, the manufacturer must
keep detailed documentation of the performance and results of these tests. HACCP
was initially developed for safety testing of foods, but it or similar systems are also
now being used to test food quality.
1.1.4. Research and Development
In recent years, there have been significant changes in the preferences of
consumers for foods that are healthier, higher quality, lower cost and more exotic.
Individual food manufacturers must respond rapidly to these changes in order to
remain competitive within the food industry. To meet these demands food
manufacturers often employ a number of scientists whose primary objective is to carry
out research that will lead to the development of new products, the improvement of
existing products and the reduction of manufacturing costs.
Many scientists working in universities, government research laboratories and
large food companies carry out basic research. Experiments are designed to provide
information that leads to a better understanding of the role that different ingredients
and processing operations play in determining the overall properties of foods. Research
is mainly directed towards investigating the structure and interaction of food
ingredients, and how they are effected by changes in environment, such as
temperature, pressure and mechanical agitation. Basic research tends to be carried out
on simple model systems with well-defined compositions and properties, rather than
real foods with complex compositions and structures, so that the researchers can focus
on particular aspects of the system. Scientists working for food companies or
ingredient suppliers usually carry out product development. Food Scientists working in
this area use their knowledge of food ingredients and processing operations to improve
the properties of existing products or to develop new products. In practice, there is a
great deal of overlap between basic research and product development, with the basic
researchers providing information that can be used by the product developers to
rationally optimize food composition and properties. In both fundamental research and
product development analytical techniques are needed to characterize the overall
properties of foods (e.g., color, texture, flavor, shelf-life etc.), to ascertain the role that
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each ingredient plays in determining the overall properties of foods, and to determine
how the properties of foods are affected by various processing conditions (e.g.,
storage, heating, mixing, freezing).
1.2 Properties Analyzed
Food analysts are interested in obtaining information about a variety of
different characteristics of foods, including their composition, structure,
physicochemical properties and sensory attributes.
1.2.1 Composition
The composition of a food largely determines its safety, nutrition,
physicochemical properties, quality attributes and sensory characteristics. Most foods
are compositionally complex materials made up of a wide variety of different chemical
constituents. Their composition can be specified in a number of different ways
depending on the property that is of interest to the analyst and the type of analytical
procedure used: specific atoms (e.g., Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur,
Sodium, etc.); specific molecules (e.g., water, sucrose, tristearin,
β−lactoglobulin), types of molecules (e.g., fats, proteins, carbohydrates, fiber,
minerals), or specific substances (e.g., peas, flour, milk, peanuts, butter). Government
regulations state that the concentration of certain food components must be stipulated
on the nutritional label of most food products, and are usually reported as specific
molecules (e.g., vitamin A) or types of molecules (e.g., proteins).
1.2.2 Structure
The structural organization of the components within a food also plays a large
role in determining the physicochemical properties, quality attributes and sensory
characteristics of many foods. Hence, two foods that have the same composition can
have very different quality attributes if their constituents are organized differently. For
example, a carton of ice cream taken from a refrigerator has a pleasant appearance and
good taste, but if it is allowed to melt and then is placed back in the refrigerator its
appearance and texture change dramatically and it would not be acceptable to a
consumer. Thus, there has been an adverse influence on its quality, even though its
chemical composition is unchanged, because of an alteration in the structural
organization of the constituents caused by the melting of ice and fat crystals. Another
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familiar example is the change in egg white from a transparent viscous liquid to an
optically opaque gel when it is heated in boiling water for a few minutes. Again there
is no change in the chemical composition of the food, but its physiochemical properties
have changed dramatically because of an alteration in the structural organization of the
constituents caused by protein unfolding and gelation.
The structure of a food can be examined at a number of different levels:
• Molecular structure (∼ 1 – 100 nm). Ultimately, the overall
physicochemical properties of a food depend on the type of molecules present, their
three-dimensional structure and their interactions with each other. It is therefore
important for food scientists to have analytical techniques to examine the structure and
interactions of individual food molecules.
• Microscopic structure (∼ 10 nm – 100 µm). The microscopic structure
of a food can be observed by microscopy (but not by the unaided eye) and consists of
regions in a material where the molecules associate to form discrete phases, e.g.,
emulsion droplets, fat crystals, protein aggregates and small air cells.
• Macroscopic structure (∼ > 100 µm). This is the structure that can be
observed by the unaided human eye, e.g., sugar granules, large air cells, raisons,
chocolate chips.
The forgoing discussion has highlighted a number of different levels of
structure that are important in foods. All of these different levels of structure contribute
to the overall properties of foods, such as texture, appearance, stability and taste. In
order to design new foods, or to improve the properties of existing foods, it is
extremely useful to understand the relationship between the structural properties of
foods and their bulk properties. Analytical techniques are therefore needed to
characterize these different levels of structure. A number of the most important of
these techniques are considered in this course.
1.2.3. Physicochemical Properties
The physiochemical properties of foods (rheological, optical, stability,
“flavor”) ultimately determine their perceived quality, sensory attributes and behavior
during production, storage and consumption.
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• The optical properties of foods are determined by the way that they
interact with electromagnetic radiation in the visible region of the spectrum, e.g.,
absorption, scattering, transmission and reflection of light. For example, full fat milk
has a “whiter” appearance than skim milk because a greater fraction of the light
incident upon the surface of full fat milk is scattered due to the presence of the fat
droplets.
• The rheological properties of foods are determined by the way that the
shape of the food changes, or the way that the food flows, in response to some applied
force. For example, margarine should be spreadable when it comes out of a
refrigerator, but it must not be so soft that it collapses under its own weight when it is
left on a table.
• The stability of a food is a measure of its ability to resist changes in its
properties over time. These changes may be chemical, physical or biological in origin.
Chemical stability refers to the change in the type of molecules present in a food with
time due to chemical or biochemical reactions, e.g., fat rancidity or non-enzymatic
browning. Physical stability refers to the change in the spatial distribution of the
molecules present in a food with time due to movement of molecules from one
location to another, e.g., droplet creaming in milk. Biological stability refers to the
change in the number of microorganisms present in a food with time, e.g., bacterial or
fungal growth.
• The flavor of a food is determined by the way that certain molecules in
the food interact with receptors in the mouth (taste) and nose (smell) of human beings.
The perceived flavor of a food product depends on the type and concentration of flavor
constituents within it, the nature of the food matrix, as well as how quickly the flavor
molecules can move from the food to the sensors in the mouth and nose. Analytically,
the flavor of a food is often characterized by measuring the concentration, type and
release of flavor molecules within a food or in the headspace above the food.
Foods must therefore be carefully designed so that they have the required
physicochemical properties over the range of environmental conditions that they will
experience during processing, storage and consumption, e.g., variations in temperature
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or mechanical stress. Consequently, analytical techniques are needed to test foods to
ensure that they have the appropriate physicochemical properties.
1.2.4. Sensory Attributes
Ultimately, the quality and desirability of a food product is determined by its
interaction with the sensory organs of human beings, e.g., vision, taste, smell, feel and
hearing. For this reason the sensory properties of new or improved foods are usually
tested by human beings to ensure that they have acceptable and desirable properties
before they are launched onto the market. Even so, individuals' perceptions of sensory
attributes are often fairly subjective, being influenced by such factors as current trends,
nutritional education, climate, age, health, and social, cultural and religious patterns.
To minimize the effects of such factors a number of procedures have been developed
to obtain statistically relevant information. For example, foods are often tested on
statistically large groups of untrained consumers to determine their reaction to a new or
improved product before full-scale marketing or further development. Alternatively,
selected individuals may be trained so that they can reliably detect small differences in
specific qualities of particular food products, e.g., the mint flavor of a chewing gum.
Although sensory analysis is often the ultimate test for the acceptance or
rejection of a particular food product, there are a number of disadvantages: it is time
consuming and expensive to carry out, tests are not objective, it cannot be used on
materials that contain poisons or toxins, and it cannot be used to provide information
about the safety, composition or nutritional value of a food. For these reasons objective
analytical tests, which can be performed in a laboratory using standardized equipment
and procedures, are often preferred for testing food product properties that are related
to specific sensory attributes. For this reason, many attempts have been made to
correlate sensory attributes (such as chewiness, tenderness, or stickiness) to quantities
that can be measured using objective analytical techniques, with varying degrees of
success.
1.3. Choosing an Analytical Technique
There are usually a number of different analytical techniques available to
determine a particular property of a food material. It is therefore necessary to select the
most appropriate technique for the specific application. The analytical technique
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selected depends on the property to be measured, the type of food to be analyzed, and
the reason for carrying out the analysis. Information about the various analytical
procedures available can be obtained from a number of different sources. An analytical
procedure may already be routinely used in the laboratory or company where you are
working. Alternatively, it may be possible to contact an expert who could recommend
a certain technique, e.g., a University Professor or a Consultant. Often it is necessary to
consult scientific and technical publications. There are a number of different sources
where information about the techniques used to analyze foods can be obtained:
1.3.1 Books
Food analysis books may provide a general overview of the various analytical
procedures used to analyze food properties or they may deal with specific food
components or physicochemical characteristics. Consulting a general textbook on food
analysis is usually the best place to begin to obtain an overview of the types of
analytical procedures available for analyzing foods and to critically determine their
relative advantages and disadvantages.
Food Analysis, 2
nd
Edition. S.S. Nielsen, Aspen Publishers
Food Analysis: Theory and Practice. Y. Pomeranz & C.E. Meloan, Chapman
and Hall
Food Analysis: Principles and Techniques. D.W. Gruenwedel and J.R.
Whitaker, Marcel Dekker
Analytical Chemistry of Foods. C.S. James, Blackie Academic and
Professional
1.3.2. Tabulated Official Methods of Analysis
A number of scientific organizations have been setup to establish certain
techniques as official methods, e.g. Association of the Official Analytical Chemists
(AOAC) and American Oil Chemists Society (AOCS). Normally, a particular
laboratory develops a new analytical procedure and proposes it as a new official
method to one of the organizations. The method is then tested by a number of
independent laboratories using the same analytical procedure and type of equipment
stipulated in the original proposal. The results of these tests are collated and compared
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with expected values to ensure that the method gives reproducible and accurate results.
After rigorous testing the procedure may be accepted, modified or rejected as an
official method. Organizations publish volumes that contain the officially recognized
test methods for a variety of different food components and foodstuffs. It is possible to
consult one of these official publications and ascertain whether a suitable analytical
procedure already exists or can be modified for your particular application.
1.3.3. Journals
Analytical methods developed by other scientists are often reported in
scientific journals, e.g., Journal of Food Science, Journal of Agriculture and Food
Chemistry, Journal of the American Oil Chemists Society, Analytical Chemistry.
Information about analytical methods in journals can often be obtained by searching
computer databases of scientific publications available at libraries or on the Internet
(e.g., Web of Science, Medline).
1.3.4. Equipment and Reagent Suppliers
Many companies that manufacture equipment and reagents used to analyze
foods advertise their products in scientific journals, trade journals, trade directories,
and the Internet. These companies will send you literature that describes the principles
and specifications of the equipment or test procedures that they are selling, which can
be used to determine the advantages and limitations of each technique.
1.3.5. Internet
The Internet is an excellent source of information on the various analytical
procedures available for analyzing food properties. University lecturers, book
suppliers, scientific organizations, scientific journals, computer databases, and
equipment and reagent suppliers post information on the web about food analysis
techniques. This information can be accessed using appropriately selected keywords
in an Internet search engine.
1.3.6. Developing a New Technique
In some cases there may be no suitable techniques available and so it is
necessary to develop a new one. This must be done with great care so as to ensure that
the technique gives accurate and reliable measurements. Confidence in the accuracy of
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