ANALYSIS OF FOOD PRODUCTS
<![if !supportLists]>1.<![endif]>Introduction
Foodanalysis is the discipline dealing with the development, application and studyof analytical procedures for characterizing the properties of foods and theirconstituents. These analytical proceduresare used to provide information about a wide variety of differentcharacteristics of foods, including their composition, structure,physicochemical properties and sensory attributes. This information is critical to our rational understanding of thefactors that determine the properties of foods, as well as to our ability toeconomically produce foods that are consistently safe, nutritious and desirableand for consumers to make informed choices about their diet. The objective of this course is to reviewthe basic principles of the analytical procedures commonly used to analyzefoods and to discuss their application to specific food components, e.g. lipids,proteins, water, carbohydrates and minerals. The following questions will beaddressed in this introductory section: Who analyzes foods? Why do they analyzefoods? What types of properties are measured? How does one choose anappropriate analytical technique for a particular food?
1.1. Reasons for AnalyzingFoods
Foods areanalyzed by scientists working in all of the major sectors of the food industryincluding food manufacturers, ingredient suppliers, analytical servicelaboratories, government laboratories, and University research laboratories.The various purposes that foods are analyzed are briefly discussed in thissection.
1.1.1. Government Regulations and Recommendations
Governmentregulations and recommendations are designed to maintain the general quality ofthe food supply, to ensure the food industry provides consumers with foods thatare wholesome and safe, to inform consumers about the nutritional compositionof foods so that they can make knowledgeable choices about their diet, toenable fair competition amongst food companies, and to eliminate economicfraud. There are a number of Government Departments Responsible for regulatingthe composition and quality of foods, including the Food and DrugAdministration (FDA), the United States Department of Agriculture (USDA), theNational Marine Fisheries Service (NMFS) and the Environmental ProtectionAgency (EPA). Each of these governmentagencies is responsible for regulating particular sectors of the food industry andpublishes documents that contain detailed information about the regulations andrecommendations pertaining to the foods produced within those sectors. These documents can be purchased from thegovernment or obtained on-line from the appropriate website.
Standards
Governmentagencies have specified a number of voluntary and mandatory standardsconcerning the composition, quality, inspection, and labeling of specific foodproducts.
Mandatory Standards:
<![if !supportLists]>·<![endif]>Standards of Identity. These regulations specifythe type and amounts of ingredients that certain foods must contain if they areto be called by a particular name on the food label. For some foods there is amaximum or minimum concentration of a certain component that they must contain,e.g., “peanut butter” must be less than 55% fat, “ice-cream” must begreater than 10% milk fat, “cheddar cheese” must be greater than 50% milk fatand less than 39% moisture.
<![if !supportLists]>·<![endif]>Standards of Quality. Standards of quality havebeen defined for certain foods (e.g., canned fruits and vegetables) toset minimum requirements on the color, tenderness, mass and freedom fromdefects.
<![if !supportLists]>·<![endif]>Standards of Fill-of-Container. These standardsstate how full a container must be to avoid consumer deception, as well asspecifying how the degree of fill is measured.
Voluntary Standards:
<![if !supportLists]>·<![endif]>Standards of Grade. A number of foods, includingmeat, dairy products and eggs, are graded according to their quality, e.g.from standard to excellent. For example meats can be graded as “prime”, “choice”,“select”, “standard” etc according to their origin, tenderness, juiciness,flavor and appearance. There are clear definitions associated with these descriptorsthat products must conform to before they can be given the appropriatelabel. Specification of the grade of afood product on the label is voluntary, but many food manufacturers opt to dothis because superior grade products can be sold for a higher price. Thegovernment has laboratories that food producers send their products too to betested to receive the appropriate certification. This service is requested and paidfor by the food producer.
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Nutritional Labeling
In 1990, theUS government passed the Nutritional Labeling and Education Act (NLEA), which revisedthe regulations pertaining to the nutritional labeling of foods, and made itmandatory for almost all food products to have standardized nutritional labels.One of the major reasons for introducing these regulations was so thatconsumers could make informed choices about their diet. Nutritional labelsstate the total calorific value of the food, as well as total fat, saturatedfat, cholesterol, sodium, carbohydrate, dietary fiber, sugars, protein,vitamins, calcium and iron. The label may also contain information aboutnutrient content claims (such as “low fat”, “low sodium” “high fiber” “fat free”etc), although government regulations stipulate the minimum or maximum amountsof specific food components that a food must contain if it is to be given oneof these nutrient content descriptors. Thelabel may also contain certain FDA approved health claims based on linksbetween specific food components and certain diseases (e.g., calcium andosteoporosis, sodium and high blood pressure, soluble fiber and heart disease,and cholesterol and heart disease). The information provided on the label canbe used by consumers to plan a nutritious and balanced diet, to avoid overconsumption of food components linked with health problems, and to encourage greaterconsumption of foods that are beneficial to health.
Authenticity
The price ofcertain foods is dictated by the quality of the ingredients that they contain. Forexample, a packet of premium coffee may claim that the coffee beans are fromColumbia, or the label of an expensive wine may claim that it was produced in acertain region, using a certain type of grapes in a particular year. How do weverify these claims? There are many instances in the past where manufacturershave made false claims about the authenticity of their products in order to geta higher price. It is therefore important to have analytical techniques thatcan be used to test the authenticity of certain food components, to ensure thatconsumers are not the victims of economic fraud and that competition among foodmanufacturers is fair.
Food Inspection and Grading
Thegovernment has a Food Inspection and Grading Service that routinelyanalyses the properties of food products to ensure that they meet theappropriate laws and regulations. Hence, both government agencies and foodmanufacturers need analytical techniques to provide the appropriate informationabout food properties. The most important criteria for this type of test are oftenthe accuracy of the measurements and the use of an official method. Thegovernment has recently carried out a survey of many of the official analyticaltechniques developed to analyze foods, and has specified which techniques mustbe used to analyze certain food components for labeling purposes. Techniqueshave been chosen which provide accurate and reliable results, but which arerelatively simple and inexpensive to perform.
1.1.2. Food Safety
One of themost important reasons for analyzing foods from both the consumers and themanufacturers standpoint is to ensure that they are safe. It would beeconomically disastrous, as well as being rather unpleasant to consumers, if afood manufacturer sold a product that was harmful or toxic. A food may beconsidered to be unsafe because it contains harmful microorganisms (e.g., Listeria,Salmonella), toxic chemicals (e.g., pesticides, herbicides) orextraneous matter (e.g., glass, wood, metal, insect matter). It is therefore important that foodmanufacturers do everything they can to ensure that these harmful substancesare not present, or that they are effectively eliminated before the food isconsumed. This can be achieved by following “good manufacturing practice” regulationsspecified by the government for specific food products and by having analyticaltechniques that are capable of detecting harmful substances. In many situationsit is important to use analytical techniques that have a high sensitivity, i.e.,that can reliably detect low levels of harmful material. Food manufacturers andgovernment laboratories routinely analyze food products to ensure that they donot contain harmful substances and that the food production facility isoperating correctly.
1.1.3. Quality control
The foodindustry is highly competitive and food manufacturers are continually trying toincrease their market-share and profits. To do this they must ensure that theirproducts are of higher quality, less expensive, and more desirablethan their competitors, whilst ensuring that they are safe and nutritious.To meet these rigorous standards food manufacturers need analyticaltechniques to analyze food materials before, during and after the manufacturingprocess to ensure that the final product meets the desired standards. In a foodfactory one starts with a number of different raw materials, processes them ina certain manner (e.g. heat, cool, mix, dry), packages them forconsumption and then stores them. The food is then transported to a warehouseor retailer where it is sold for consumption.
One of themost important concerns of the food manufacturer is to produce a final productthat consistently has the same overall properties, i.e. appearance,texture, flavor and shelf life. When we purchase a particular food product weexpect its properties to be the same (or very similar) to previous times, andnot to vary from purchase-to-purchase. Ideally, a food manufacture wants totake the raw ingredients, process them in a certain way and produce a productwith specific desirable properties. Unfortunately, the properties of the rawingredients and the processing conditions vary from time to time which causesthe properties of the final product to vary, often in an unpredictable way. Howcan food manufacturers control these variations? Firstly, they can understand the role that different foodingredients and processing operations play in determining the final propertiesof foods, so that they can rationally control the manufacturing process toproduce a final product with consistent properties. This type of information can be established through research anddevelopment work (see later). Secondly,they can monitor the properties of foods during production to ensure that theyare meeting the specified requirements, and if a problem is detected during theproduction process, appropriate actions can be taken to maintain final productquality.
Characterizationof raw materials. Manufacturersmeasure the properties of incoming raw materials to ensure that they meetcertain minimum standards of quality that have previously been defined by themanufacturer. If these standards are not met the manufacturer rejects thematerial. Even when a batch of raw materials has been accepted, variations in itsproperties might lead to changes in the properties of the final product. Byanalyzing the raw materials it is often possible to predict their subsequentbehavior during processing so that the processing conditions can be altered toproduce a final product with the desired properties. For example, the color ofpotato chips depends on the concentration of reducing sugars in the potatoesthat they are manufactured from: the higher the concentration, the browner thepotato chip. Thus it is necessary to have an analytical technique to measurethe concentration of reducing sugars in the potatoes so that the fryingconditions can be altered to produce the optimum colored potato chip.
Monitoringof food properties during processing. Itis advantageous for food manufacturers to be able to measure the properties offoods during processing. Thus, if any problem develops, then it can be quicklydetected, and the process adjusted to compensate for it. This helps to improvethe overall quality of a food and to reduce the amount of material and timewasted. 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 theprocessing conditions to eliminate this problem. Traditionally, samples areremoved from the process and tested in a quality assurance laboratory. Thisprocedure is often fairly time-consuming and means that some of the product isusually wasted before a particular problem becomes apparent. For this reason,there is an increasing tendency in the food industry to use analyticaltechniques which are capable of rapidly measuring the properties of foodson-line, without having to remove a sample from the process. These techniquesallow problems to be determined much more quickly and therefore lead toimproved product quality and less waste. The ideal criteria for an on-linetechnique is that it be capable of rapid and precise measurements, it isnon-intrusive, it is nondestructive and that it can be automated.
Characterizationof final product. Once the producthas been made it is important to analyze its properties to ensure that it meetsthe appropriate legal and labeling requirements, that it is safe, and that itis of high quality. It is also important to ensure that it retains itsdesirable properties up to the time when it is consumed.
A systemknown as Hazard Analysis and Critical Control Point (HACCP) has beendeveloped, whose aim is to systematically identify the ingredients or processesthat may cause problems (hazard analysis), assign locations (critical controlpoints) within the manufacturing process where the properties of the food mustbe measured to ensure that safety and quality are maintained, and to specifythe appropriate action to take if a problem is identified. The type ofanalytical technique required to carry out the analysis is often specified. Inaddition, the manufacturer must keep detailed documentation of the performanceand results of these tests. HACCP wasinitially developed for safety testing of foods, but it or similar systems are alsonow being used to test food quality.
1.1.4. Research and Development
In recentyears, there have been significant changes in the preferences of consumers forfoods that are healthier, higher quality, lower cost and more exotic. Individualfood manufacturers must respond rapidly to these changes in order to remaincompetitive within the food industry. To meet these demands food manufacturersoften employ a number of scientists whose primary objective is to carry outresearch that will lead to the development of new products, the improvement ofexisting products and the reduction of manufacturing costs.
Many scientistsworking in universities, government research laboratories and large foodcompanies carry out basic research. Experiments are designed to provideinformation that leads to a better understanding of the role that different ingredientsand processing operations play in determining the overall properties of foods.Research is mainly directed towards investigating the structure and interactionof food ingredients, and how they are effected by changes in environment, suchas temperature, pressure and mechanical agitation. Basic research tends to becarried out on simple model systems with well-defined compositions andproperties, rather than real foods with complex compositions and structures, sothat the researchers can focus on particular aspects of the system. Scientists working for food companies oringredient suppliers usually carry out product development. FoodScientists working in this area use their knowledge of food ingredients andprocessing operations to improve the properties of existing products or to developnew products. In practice, there is a great deal of overlap between basicresearch and product development, with the basic researchers providinginformation that can be used by the product developers to rationally optimize foodcomposition and properties. In bothfundamental research and product development analytical techniques are neededto characterize the overall properties of foods (e.g., color, texture,flavor, shelf-life etc.), to ascertain the role that each ingredientplays in determining the overall properties of foods, and to determine how theproperties of foods are affected by various processing conditions (e.g., storage,heating, mixing, freezing).
1.2 Properties Analyzed
Foodanalysts are interested in obtaining information about a variety of differentcharacteristics of foods, including their composition, structure,physicochemical properties and sensory attributes.
1.2.1 Composition
Thecomposition of a food largely determines its safety, nutrition, physicochemicalproperties, quality attributes and sensory characteristics. Most foods are compositionally complexmaterials made up of a wide variety of different chemical constituents. Theircomposition can be specified in a number of different ways depending on theproperty that is of interest to the analyst and the type of analyticalprocedure used: specific atoms (e.g., Carbon, Hydrogen, Oxygen,Nitrogen, Sulfur, Sodium, etc.); specific molecules (e.g., water,sucrose, tristearin, b-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 foodcomponents must be stipulated on the nutritional label of most food products,and are usually reported as specific molecules (e.g., vitamin A) ortypes of molecules (e.g., proteins).
1.2.2 Structure
Thestructural organization of the components within a food also plays a large rolein determining the physicochemical properties, quality attributes and sensorycharacteristics of many foods. Hence,two foods that have the same composition can have very different qualityattributes if their constituents are organized differently. For example, acarton of ice cream taken from a refrigerator has a pleasant appearance andgood taste, but if it is allowed to melt and then is placed back in therefrigerator its appearance and texture change dramatically and it would not beacceptable to a consumer. Thus, there has been an adverse influence on itsquality, even though its chemical composition is unchanged, because of analteration in the structural organization of the constituents caused by themelting of ice and fat crystals. Another familiar example is the change in eggwhite from a transparent viscous liquid to an optically opaque gel when it isheated in boiling water for a few minutes. Again there is no change in thechemical composition of the food, but its physiochemical properties havechanged dramatically because of an alteration in the structural organization ofthe constituents caused by protein unfolding and gelation.
The structure of a foodcan be examined at a number of different levels:
<![if !supportLists]>·<![endif]>Molecular structure (~ 1 – 100 nm). Ultimately,the overall physicochemical properties of a food depend on the type ofmolecules present, their three-dimensional structure and their interactionswith each other. It is therefore important for food scientists to haveanalytical techniques to examine the structure and interactions of individual foodmolecules.
<![if !supportLists]>·<![endif]>Microscopic structure (~ 10 nm – 100 mm). The microscopic structure of afood can be observed by microscopy (but not by the unaided eye) and consists ofregions in a material where the molecules associate to form discrete phases, e.g.,emulsion droplets, fat crystals, protein aggregates and small air cells.
<![if !supportLists]>·<![endif]>Macroscopic structure (~ > 100 mm). This is the structure that can beobserved by the unaided human eye, e.g., sugar granules, large aircells, raisons, chocolate chips.
The forgoingdiscussion has highlighted a number of different levels of structure that areimportant in foods. All of these different levels of structure contribute tothe overall properties of foods, such as texture, appearance, stability andtaste. In order to design new foods, or to improve the properties of existingfoods, it is extremely useful to understand the relationship between thestructural properties of foods and their bulk properties. Analytical techniquesare therefore needed to characterize these different levels of structure. Anumber of the most important of these techniques are considered in this course.
1.2.3. Physicochemical Properties
Thephysiochemical properties of foods (rheological, optical, stability, “flavor”)ultimately determine their perceived quality, sensory attributes and behaviorduring production, storage and consumption.
<![if !supportLists]>·<![endif]>The optical properties of foods are determinedby the way that they interact with electromagnetic radiation in the visibleregion of the spectrum, e.g., absorption, scattering, transmission andreflection of light. For example, full fat milk has a “whiter” appearance thanskim milk because a greater fraction of the light incident upon the surface offull fat milk is scattered due to the presence of the fat droplets.
<![if !supportLists]>·<![endif]>The rheological properties of foods aredetermined by the way that the shape of the food changes, or the way that the foodflows, in response to some applied force. For example, margarine should bespreadable when it comes out of a refrigerator, but it must not be so soft thatit collapses under its own weight when it is left on a table.
<![if !supportLists]>·<![endif]>The stability of a food is a measure of itsability to resist changes in its properties over time. These changes may bechemical, physical or biological in origin. Chemical stability refers tothe change in the type of molecules present in a food with time due to chemicalor biochemical reactions, e.g., fat rancidity or non-enzymatic browning.Physical stability refers to the change in the spatial distribution ofthe molecules present in a food with time due to movement of molecules from onelocation to another, e.g., droplet creaming in milk. Biologicalstability refers to the change in the number of microorganisms present in afood with time, e.g., bacterial or fungal growth.
<![if !supportLists]>·<![endif]>The flavor of a food is determined by the waythat certain molecules in the food interact with receptors in the mouth (taste)and nose (smell) of human beings. Theperceived flavor of a food product depends on the type and concentration offlavor constituents within it, the nature of the food matrix, as well as howquickly the flavor molecules can move from the food to the sensors in the mouthand nose. Analytically, the flavor of afood is often characterized by measuring the concentration, type and release offlavor molecules within a food or in the headspace above the food.
Foods musttherefore be carefully designed so that they have the required physicochemicalproperties over the range of environmental conditions that they will experienceduring processing, storage and consumption, e.g., variations intemperature or mechanical stress. Consequently, analytical techniques areneeded to test foods to ensure that they have the appropriate physicochemicalproperties.
1.2.4. Sensory Attributes
Ultimately,the quality and desirability of a food product is determined by its interactionwith the sensory organs of human beings, e.g., vision, taste, smell,feel and hearing. For this reason thesensory properties of new or improved foods are usually tested by human beingsto ensure that they have acceptable and desirable properties before they arelaunched onto the market. Even so, individuals' perceptions of sensoryattributes are often fairly subjective, being influenced by such factors ascurrent trends, nutritional education, climate, age, health, and social,cultural and religious patterns. To minimize the effects of such factors anumber of procedures have been developed to obtain statistically relevantinformation. For example, foods are often tested on statistically large groupsof untrained consumers to determine their reaction to a new or improved productbefore full-scale marketing or further development. Alternatively, selectedindividuals may be trained so that they can reliably detect small differencesin specific qualities of particular food products, e.g., the mint flavorof a chewing gum.
Althoughsensory analysis is often the ultimate test for the acceptance or rejection ofa particular food product, there are a number of disadvantages: it is timeconsuming and expensive to carry out, tests are not objective, it cannot beused on materials that contain poisons or toxins, and it cannot be used toprovide information about the safety, composition or nutritional value of afood. For these reasons objective analytical tests, which can be performed in alaboratory using standardized equipment and procedures, are often preferred fortesting food product properties that are related to specific sensoryattributes. For this reason, many attempts have been made to correlate sensoryattributes (such as chewiness, tenderness, or stickiness) to quantities thatcan be measured using objective analytical techniques, with varying degrees ofsuccess.
1.3. Choosing an Analytical Technique
There areusually a number of different analytical techniques available to determine aparticular property of a food material. It is therefore necessary to select themost appropriate technique for the specific application. The analyticaltechnique selected depends on the property to be measured, the type of food tobe analyzed, and the reason for carrying out the analysis. Information aboutthe various analytical procedures available can be obtained from a number ofdifferent sources. An analytical procedure may already be routinely used in thelaboratory or company where you are working. Alternatively, it may be possibleto contact an expert who could recommend a certain technique, e.g., aUniversity Professor or a Consultant. Often it is necessary to consultscientific and technical publications. There are a number of different sourceswhere information about the techniques used to analyze foods can be obtained:
1.3.1 Books
Foodanalysis books may provide a general overview of the various analyticalprocedures used to analyze food properties or they may deal with specific food componentsor physicochemical characteristics.Consulting a general textbook on food analysis is usually the best placeto begin to obtain an overview of the types of analytical procedures availablefor analyzing foods and to critically determine their relative advantages anddisadvantages.
Food Analysis, 2ndEdition. S.S. Nielsen, Aspen Publishers
Food Analysis: Theory andPractice. Y. Pomeranz & C.E. Meloan, Chapman and Hall
Food Analysis: Principlesand Techniques. D.W. Gruenwedel and J.R. Whitaker, Marcel Dekker
Analytical Chemistry ofFoods. C.S. James, Blackie Academic and Professional
1.3.2. Tabulated OfficialMethods of Analysis
A number ofscientific organizations have been setup to establish certain techniques asofficial methods, e.g. Association of the Official Analytical Chemists(AOAC) and American Oil Chemists Society (AOCS). Normally, a particularlaboratory develops a new analytical procedure and proposes it as a newofficial method to one of the organizations. The method is then tested by anumber of independent laboratories using the same analytical procedure and typeof equipment stipulated in the original proposal. The results of these testsare collated and compared with expected values to ensure that the method givesreproducible and accurate results. After rigorous testing the procedure may beaccepted, modified or rejected as an official method. Organizations publishvolumes that contain the officially recognized test methods for a variety ofdifferent food components and foodstuffs. It is possible to consult one ofthese official publications and ascertain whether a suitable analyticalprocedure already exists or can be modified for your particular application.
1.3.3. Journals
Analyticalmethods developed by other scientists are often reported in scientificjournals, e.g., Journal of Food Science, Journal of Agriculture and FoodChemistry, Journal of the American Oil Chemists Society, Analytical Chemistry.Information about analytical methods in journals can often be obtained bysearching computer databases of scientific publications available at librariesor on the Internet (e.g., Web of Science, Medline).
1.3.4. Equipment and ReagentSuppliers
Manycompanies that manufacture equipment and reagents used to analyze foodsadvertise their products in scientific journals, trade journals, tradedirectories, and the Internet. These companies will send you literature thatdescribes the principles and specifications of the equipment or test proceduresthat they are selling, which can be used to determine the advantages andlimitations of each technique.
1.3.5. Internet
The Internetis an excellent source of information on the various analytical proceduresavailable for analyzing food properties.University lecturers, book suppliers, scientific organizations,scientific journals, computer databases, and equipment and reagent supplierspost information on the web about food analysis techniques. This information can be accessed usingappropriately selected keywords in an Internet search engine.
1.3.6. Developing a NewTechnique
In somecases there may be no suitable techniques available and so it is necessary todevelop a new one. This must be done with great care so as to ensure that thetechnique gives accurate and reliable measurements. Confidence in the accuracy of the technique can be obtained byanalyzing samples of known properties or by comparing the results of the newtechnique with those of well-established or official methods.
One of themost important factors that must be considered when developing a new analyticaltechnique is the way in which “the analyte” will be distinguished from “thematrix”. Most foods contain a large number of differentcomponents, and therefore it is often necessary to distinguish the componentbeing analyzed for ("the analyte") from the multitude of othercomponents surrounding it ("the matrix"). Food components can bedistinguished from each other according to differences in their molecularcharacteristics, physical properties and chemical reactions:
<![if !supportLists]>·<![endif]>Molecular characteristics: Size, shape,polarity, electrical charge, interactions with radiation.
<![if !supportLists]>·<![endif]>Physical properties: Density, rheology, opticalproperties, electrical properties, phase transitions (melting point, boilingpoint).
<![if !supportLists]>·<![endif]>Chemical reactions: Specific chemical reactionsbetween the component of interest and an added reagent.
Whendeveloping an appropriate analytical technique that is specific for aparticular component it is necessary to identify the molecular andphysicochemical properties of the analyte that are sufficiently different fromthose of the components in the matrix. In some foods it is possible to directlydetermine the analyte within the food matrix, but more often it is necessary tocarry out a number of preparatory steps to isolate the analyte prior tocarrying out the analysis. For example, an analyte may be physically isolatedfrom 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 havevery similar properties to the analyte. These "interferents" may makeit difficult to develop an analytical technique that is specific for theanalyte. It may be necessary to remove these interfering substances prior tocarrying out the analysis for the analyte, or to use an analytical procedurethat can distinguish between substances with similar properties.
1.4. Selecting anAppropriate Technique
Some of thecriteria that are important in selecting a technique are listed below:
Precision: A measure of theability to reproduce an answer between determinations performed by the samescientist (or group of scientists) using the same equipment and experimentalapproach.
Reproducibility: Ameasure of the ability to reproduce an answer by scientists using the sameexperimental approach but in different laboratories using different equipment.
Accuracy: A measure ofhow close one can actually measure the true value of the parameter beingmeasured, e.g., fat content, or sodium concentration.
Simplicity of operation: Ameasure of the ease with which relatively unskilled workers may carry out theanalysis.
Cost: The total cost ofthe analysis, including the reagents, instrumentation and salary of personnelrequired to carry it out.
Speed: The time neededto complete the analysis of a single sample or the number of samples that canbe analyzed in a given time.
Sensitivity: A measureof the lowest concentration of a component that can be detected by a givenprocedure.
Specificity: A measureof the ability to detect and quantify specific components within a foodmaterial, even in the presence of other similar components, e.g., fructosein the presence of sucrose or glucose.
Safety: Many reagentsand procedures used in food analysis are potentially hazardous e.g. strongacids or bases, toxic chemicals or flammable materials.
Destructive/Nondestructive: Insome analytical methods the sample is destroyed during the analysis, whereas inothers it remains intact.
On-line/Off-line: Someanalytical methods can be used to measure the properties of a food duringprocessing, whereas others can only be used after the sample has been takenfrom the production line.
Official Approval: Variousinternational bodies have given official approval to methods that have beencomprehensively studied by independent analysts and shown to be acceptable tothe various organizations involved, e.g., ISO, AOAC, AOCS.
Nature of Food Matrix:The composition, structure and physical properties of the matrix materialsurrounding the analyte often influences the type of method that can be used tocarry out an analysis, e.g., whether the matrix is solid or liquid,transparent or opaque, polar or non-polar.
If there area number of alternative methods available for measuring a certain property of afood, the choice of a particular method will depend on which of the abovecriteria is most important. For example, accuracy and use of an officialmethod may be the most important criteria in a government laboratory whichchecks the validity of compositional or nutritional claims on food products,whereas speed and the ability to make nondestructive measurementsmay be more important for routine quality control in a factory where a largenumber of samples have to be analyzed rapidly.
