Food Sampling & Analysis - VI

Criteria for Selection of an Appropriate Analytical Technique

Analysis is the process of breaking a complex topic or substance into smaller parts to gain a better understanding of it. The technique has been applied in the study of mathematics and logic since before Aristotle (384–322 B.C.), though chemical analysis as a formal concept is a relatively recent development. The field of chemistry uses analysis in at least three ways: to identify the components of a particular chemical compound (qualitative analysis), to identify the proportions of components in a mixture (quantitative analysis) and to break down chemical processes and examine chemical reactions between elements of matter. For an example of its use, analysis of the concentration of elements is important in managing a nuclear reactor, thus nuclear scientists will analyze neutron activation to develop discrete measurements within vast samples. A matrix can have a considerable effect on the way a chemical analysis is conducted and the quality of its results. Analysis can be done manually or with a device. Chemical analysis is an important element of national security among the major world powers with materials measurement and signature intelligence (MASINT) capabilities.

When it comes to food analysis, it narrowed down the field in to products that are man-made or natural is intended for human consumption or feeding animals. The food analysis is based on sampling and arraying its composition in accredited analytical methods to discuss various functions related to a given food. This can be chemical, physical or biological in nature, where the analytical technique must be selected based on the requirement of results of the analysis. Thus there are various different criteria available while selecting an appropriate 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 selected depends on the property to be measured, the type of food to be analyzed, and the reason for carrying out the analysis.

Some of the criteria that are important in selecting a technique are listed below:

Precision: A measure of the ability to reproduce an answer between determinations performed by the same scientist (or group of scientists) using the same equipment and experimental approach.

Reproducibility: A measure of the ability to reproduce an answer by scientists using the same experimental approach but in different laboratories using different equipment.

Accuracy: A measure of how close one can actually measure the true value of the parameter being measured, e.g., fat content, or sodium concentration.

Simplicity of operation: A measure of the ease with which relatively unskilled workers may carry out the analysis.

Cost: The total cost of the analysis, including the reagents, instrumentation and salary of personnel required to carry it out.

Speed: The time needed to complete the analysis of a single sample or the number of samples that can be analyzed in a given time.

Sensitivity: A measure of the lowest concentration of a component that can be detected by a given procedure.

Specificity: A measure of the ability to detect and quantify specific components within a food material, even in the presence of other similar components, e.g., fructose in the presence of sucrose or glucose.

Safety: Many reagents and procedures used in food analysis are potentially hazardous e.g. strong acids or bases, toxic chemicals or flammable materials.

Destructive or Nondestructive: In some analytical methods the sample is destroyed during the analysis, whereas in others it remains intact.

On-line or Off-line: Some analytical methods can be used to measure the properties of a food during processing, whereas others can only be used after the sample has been taken from the production line.

Official Approval: Various international bodies have given official approval to methods that have been comprehensively studied by independent analysts and shown to be acceptable to the various organizations involved, e.g., ISO, AOAC, AOCS.

Nature of Food Matrix: The composition, structure and physical properties of the matrix material surrounding the analyte often influences the type of method that can be used to carry out an analysis, e.g., whether the matrix is solid or liquid, transparent or opaque, polar or non-polar.

If there are a number of alternative methods available for measuring a certain property of a food, the choice of a particular method will depend on which of the above criteria is most important. For example, accuracy and use of an official method may be the most important criteria in a government laboratory which checks the validity of compositional or nutritional claims on food products, whereas speed and the ability to make nondestructive measurements may be more important for routine quality control in a factory where a large number of samples have to be analyzed rapidly.

Selection of Appropriate Analytical Method

When you decide the properties of the food to be analyzed and relevant criteria for the right analytical technique with your specific requirements, it is not difficult to find sources of information on appropriate official test methods. 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.      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. Some of the example books are; Food Analysis, 2nd 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, etc.

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 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.

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).

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.

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.

Development of a New Analytical 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 the technique can be obtained by analyzing samples of known properties or by comparing the results of the new technique with those of well-established or official methods.

One of the most important factors that must be considered when developing a new analytical technique is the way in which the analyte will be distinguished from the matrix.  Most foods contain a large number of different components, and therefore it is often necessary to distinguish the component being analyzed for ("the analyte") from the multitude of other components surrounding it ("the matrix"). Food components can be distinguished from each other according to differences in their molecular characteristics, physical properties and chemical reactions:

1. Molecular Characteristics: Size, shape, polarity, electrical charge, interactions with radiation.
2. Physical Properties: Density, rheology, optical properties, electrical properties, phase transitions (melting point, boiling point) specific for a particular component. It is necessary to identify the molecular and physicochemical properties of the analyte.
3. Chemical Reactions: Specific chemical reactions between the component of interest and an added reagent.

When developing an appropriate analytical technique that is sufficiently different from those of the components in the matrix. In some foods it is possible to directly determine the analyte within the food matrix, but more often it is necessary to carry out a number of preparatory steps to isolate the analyte prior to carrying out the analysis. For example, an analyte may be physically isolated from the matrix using one procedure and then analyzed using another procedure. In some situations there may be one or more components within a food that have very similar properties to the analyte. These "interferents" may make it difficult to develop an analytical technique that is specific for the analyte. It may be necessary to remove these interfering substances prior to carrying out the analysis for the analyte, or to use an analytical procedure that can distinguish between substances with similar properties. 

Reference:
http://people.umass.edu/~mcclemen/581Introduction.html
http://www.fao.org/docrep/006/y5022e/y5022e03.htm 
http://en.wikipedia.org/wiki/Analysis#Chemistry