Food Analysis

Food scientists and technologists determine the chemical composition and physical characteristics of foods routinely as part of their quality management, product development, or research activities. Consumer, government, and food industry concern for food quality and safety has increased the importance of analyses that determine composition and critical product characteristics. To successfully base decisions on results of any analysis, one must correctly conduct all three major steps in the analysis: (1) select and prepare samples, (2) perform the assay, and (3) calculate and interpret the results. The choice of analysis method is usually based on the objective of the analysis, characteristics of the method itself, and the food matrix involved.Validation of the method is important, as is the use of standard reference materials to ensure quality results. Rapid methods used for quality assessment in a production facility may be less accurate but much faster than official methods used for nutrition labeling. Endorsed methods for the chemical analyses of foods have been compiled and published by various scientific organizations. Such official methods allow for comparison of results between different laboratories and for evaluation of new or more rapid procedures. This chapter provides introductory information on the topics summarized above that lays the foundation before covering various specific methods of food analysis in other chapters.

Various kinds of standards set for certain food products by federal agencies make it possible to get essentially the same food product whenever and wherever purchased in the USA. Knowledge of government regulations relevant to the chemical analysis of foods is extremely important to persons working in the food industry. Federal laws and regulations reinforce the efforts of the food industry to provide wholesome foods, to inform consumers about the nutritional composition of foods, and to eliminate economic frauds. In some cases, they dictate what ingredients a food must contain, what must be tested, and the procedures used to analyze foods for safety factors and quality attributes. This chapter describes the US federal regulations (except nutrition labeling, which is covered in Chap. 3) as they relate to food composition and analysis. The chapter also includes information about specifications for foods purchased by government agencies, along with food standards and safety practices established by international organizations.

A major reason for analyzing the chemical components of foods in the USA is nutrition labeling regulations. Nutrition label information is not only legally required in many countries, but also is of increasing importance to consumers as they focus more on health and wellness. This chapter focuses is on nutrition labeling regulations in the USA, as specified by the Food and Drug Administration (FDA), with a brief summary of regulations for the Food Safety and Inspection Service (FSIS) of the United States Department of Agriculture (USDA). The FDA and FSIS of the USDA have coordinated their regulations on nutrition labeling. Nutrition labeling regulations define the format for the nutrition information, and give the rules and methods to report specific information. Specifications include sample collection procedures, the method of analysis to be used, and the nutrient levels required to ensure compliance with nutrition labeling regulations. Specific nutrient content claims and health claims are allowed on the nutrition label. The nutrition labeling regulations covered in this chapter are only those closely linked to food analysis. Readers are referred to appropriate sections of the Code of Regulations for all details of FDA and USDA regulations.

The study of food analysis involves a considerable amount of time learning principles, methods, and instrument operations and perfecting various techniques. These areas are extremely important, but much of our effort would be for naught if there were no ways to evaluate the data obtained from the various analytical assays. Having a good understanding of the data and how to interpret the data are critical to good decision making, whether in the food industry or in a research laboratory. This chapter focuses on statistical methods to evaluate the data obtained from analytical techniques. The chapter primarily covers how to evaluate replicate analyses of the same sample for accuracy and precision, but attention also is given to the determination of best line fits for standard curve data. A section of the chapter describes sensitivity and limit of detection as related to various analytical methods and regulatory agency policies. Additional information includes the proper use of significant figures, rules for rounding off numbers, and use of various test to reject grossly aberrant individual values.

Food quality is monitored at various processing stages, but 100% inspection is rarely possible, or even desirable. To ensure a representative sample of the population is obtained for analysis, sampling and sample reduction methods must be developed and implemented. Sampling is a vital process, since it is often the most variable step in the entire analytical procedure. The selection of the sampling procedure is determined by the purpose of the inspection, the nature of the population and product, and the test method. This chapter covers various aspects of sampling to be considered: homogenous vs. heterogeneous samples; discrete vs. continuous populations; sampling for attributes vs. variables; consumer risk vs. vendor risk of sampling; manual vs. continuous sampling; probability vs. nonprobability sampling; numerous choices of sampling plans; and precision analysis vs. power analysis to estimate sample size. Challenges continue after the sample is collected, including proper sample storage and identification, often followed by sample size reduction to an amount suitable for sample preparation. That sample preparation often involves grinding to a particle size appropriate for analysis then storage prior to analysis, both of which must be done in ways to prevent sample degradation. The principles described in this chapter are intended to provide a basis for understanding, developing, and evaluating sampling plans and sample handling procedures for specific food analysis applications.

Spectroscopy deals with the production, measurement, and interpretation of spectra arising from the interaction of electromagnetic radiation with matter. There are many different spectroscopic methods available for solving a wide range of analytical problems. The methods differ with respect to the species to be analyzed (e.g., molecular or atomic spectroscopy), the type of radiation-matter interaction to be monitored (e.g., absorption, emission, or diffraction), and the region of the electromagnetic spectrum used in the analysis. Spectroscopic methods are very informative and widely used for both quantitative and qualitative analyses. Spectroscopic methods based on the absorption or emission of radiation in the ultraviolet (UV), visible (Vis), infrared (IR), and radio (nuclear magnetic resonance, NMR) frequency ranges are most commonly encountered in traditional food analysis laboratories. Each of these methods is distinct in that it monitors different types of molecular or atomic transitions. This chapter explains the basis of these transitions to provide the necessary background for separate chapters on each type of spectroscopy.

Spectroscopy in the ultraviolet-visible (UV-Vis) range, the subject of this chapter, is one of the most commonly encountered laboratory techniques in food analysis. The analytical signal in such assays is based on either the emission or absorption of radiation in the UV-Vis range. This signal may be inherent in the analyte or a result of a chemical reaction involving the analyte. This chapter covers the following spectroscopy concepts: UV (200–359 nm) vs. Vis (350–700 nm) portions of the electromagnetic spectrum, absorbance vs. fluorescence, qualitative vs. quantitative analysis, components of a spectrophotometer, and the use of Beer’s law and a calibration curve to estimate the analyte concentration of a test solution. Quantitative absorption spectroscopy, the most common of the subdivisions within UV-Vis spectroscopy, is the basis of many techniques described in other chapters.

Infrared (IR) spectroscopy is currently widely used in the food industry for both qualitative and quantitative analysis of ingredients and finished foods. Mid-IR, near-IR, and Raman spectroscopy requires much less time to perform quantitative analysis than do many conventional wet chemical or chromatographic techniques. This chapter describes the techniques of mid- and near-IR and Raman spectroscopy, including the principles by which molecules absorb IR radiation, the components and configuration of commercial IR spectrometers, sampling methods for IR spectroscopy, and qualitative and quantitative applications of these techniques to food analysis. Infrared (IR) spectroscopy refers to measurement of the absorption of different frequencies of IR radiation by foods or other solids, liquids, or gases. IR spectroscopy measures the absorption of radiation in the near-IR (λ = 0.8–2.5 μm) or mid (λ = 2.5–15 μm) regions by molecules in food or other substances. By using multivariate statistical techniques, infrared instruments can be calibrated to measure the amounts of various constituents in a food sample based on the amount of IR radiation absorbed at specific wavelengths.

The major challenge in mineral analysis is to accurately measure these elements in a food matrix that contains much higher concentrations of other components (i.e., carbohydrates, proteins, and fats) as well as other mineral elements that may interfere. In comparison with traditional wet chemistry methods for mineral analysis, atomic absorption spectroscopy (AAS), atomic emission spectroscopy (AES), and inductively coupled plasma-mass spectrometry (ICP-MS) methods are capable of measuring trace concentrations of elements in complex matrices rapidly and with excellent precision. While AAS quantifies the absorption of electromagnetic radiation by well-separated neutral atoms, AES measures emission of radiation from atoms in excited states. Developed more recently, ICP has been mated with MS to form ICP-MS instruments that are capable of measuring mineral elements with extremely low detection limits. This chapter covers the preparation of samples for analysis by these methods; the difference in the principles and instrumentation between AAS, AES, and ICP-MS; and the comparative advantages and disadvantages of the methods.

Nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical technique with a wide variety of applications, from structural elucidation of complex molecules, to 3D-imaging of fresh tissue, to simple ingredient assays for quality assurance. NMR differs from most other forms of spectroscopy because the nucleus is the subject of analysis and the excitation step uses radio-frequency electromagnetic energy. Whereas other spectroscopy techniques may be used to determine the nature of the functional groups present in a sample, only NMR spectroscopy can provide the data necessary to determine the complete structure of a molecule. The NMR instrument consists of a cryomagnet with the transmitter and receiver antennae in the central bore, an electronics console with the transmitter and receiver hardware, and a data/work station that controls all the functions of the instrument. In addition to NMR spectrometers, with both solids and liquids applications, there are other related instruments, such as magnetic resonance imaging (MRI), that are based on the same principles, but yield different information. This chapter covers the basic principles and applications of NMR spectroscopy, as well as a brief description of relaxometry, MRI, and the use of NMR as part of a rapid moisture and fat analysis system.

Mass spectrometry (MS) is a powerful analytical technique that can solve most complex problems faced by the food analytical chemist, both in a qualitative and quantitative manner. Since the qualitative and quantitative aspects of MSs are so powerful, they are routinely coupled with gas chromatography (GC) or high-performance liquid chromatography (HPLC), and find growing use with static sample introduction techniques. The power of the MS technique is due to its ability to place a charge on a molecule, thereby converting it to an ion in a process called ionization. The generated ions are then separated according to their mass-to-charge ratio (m/z) by subjecting them to a combination of radio-frequency (RF) and electrostatic fields in a mass analyzer and finally detected by highly sensitive detectors. The resulting signals from the detectors are digitized and processed by software to display the information as a mass spectrum, which reveals its molecular mass and its structural composition, leading to identification. An additional stage of ion fragmentation may be included before detection to elicit structural information in a technique known as tandem MS. This chapter covers the principles of MS and the instrumentation for ionization and mass analysis, details of various techniques (GC-MS, HPLC-MS, tandem MS, and high resolution MS), and food applications of MS.

Chromatography has many applications for analysis of various foods components. It differs from other methods of separation in that a wide variety of materials, equipment, and techniques can be used. This chapter focuses on the principles of chromatography, as background information for the detailed principles and application of high-performance liquid chromatography (HPLC) and gas chromatography (GC) covered in Chap. 13 and 14, respectively. This chapter gives the basics of chromatography as a separation method based on the partitioning of a solute between a mobile phase and a stationary phase. Based on the physicochemical characteristics of the analyte and the availability of instrumentation, a chromatographic system is chosen to separate, identify and quantify the analyte. Chromatographic modes include adsorption, partition, hydrophobic interaction, ion exchange, affinity, and size exclusion chromatography. Factors to be considered when developing a separation include mobile phase variables, as well as column efficiency, selectivity, and capacity. Following detection, a chromatogram provides both qualitative and quantitative information via retention time and peak area data.

High-performance liquid chromatography (HPLC) is a chromatographic technique of great versatility and analytical power that can be applied to any compound with solubility in a liquid that can be used as the mobile phase. HPLC is widely used in food analysis to quantitate small molecules and ions and to separate and purify macromolecules. This chapter describes the details and various options for each of the HPLC system components: pump, injector, column, detector, and data system. A broad variety of column packing materials have contributed greatly to the widespread use of HPLC. The chapter includes details and example applications for separations achieved with normal-phase, reversed phase, hydrophobic interaction, ion-exchange, size-exclusion, and affinity chromatography.

Gas chromatography (GC) has been used for the determination of a wide range of food components, but it is ideally suited to the analysis of thermally stable volatile substances. The outstanding resolving properties of GC and the wide variety of detectors contribute to the sensitivity or selectivity in analysis. This chapter discusses details of GC sample preparation, hardware, columns, and chromatographic theory as it is uniquely applied to GC. Sample preparation generally involves the isolation of solutes from foods, which may be accomplished by headspace analysis, distillation, preparative chromatography, or extraction. Some analytes can then be directly analyzed, while others must be derivatized prior to analysis to increase volatility or temperature stability. The GC consists of a gas supply and regulators (pressure and flow control), injection port, column and column oven, detector, electronics, and a data recording and processing system. The analyst must be knowledgeable about the characteristics of each of these GC components and understand basic chromatographic theory to balance the properties of resolution, capacity, speed, and sensitivity. New GC developments and applications will likely be related to multidimensional GC.

Moisture assays can be one of the most important analyses performed on a food product and yet one of the most difficult from which to obtain accurate and precise data, for reasons described in this chapter. The first sections of this chapter describe both direct and indirect methods for moisture content analysis: instrumentation, principles, procedures, applications, cautions, advantages, and disadvantages. The choice of moisture analysis method is often determined by the expected moisture content, nature of other food constituents (e.g., highly volatile, heat sensitive), equipment available, speed necessary, accuracy and precision required, and intended purpose (e.g., regulatory or in-plant quality control). Latter parts of this chapter describe water activity measurement, since it parallels the measurement of total moisture as an important stability and quality factor. Determining both the water content and the water activity of a food provides a complete moisture analysis. Also included in the chapter is a major section on moisture sorption isotherms. With an understanding of the techniques described in this chapter, one can apply appropriate moisture analyses to a wide variety of food products.

Ashing is an important first step in proximate or specific mineral analysis. Ash refers to the inorganic (mineral) residue remaining after the combustion or complete acid-facilitated oxidation of organic matter in food. This chapter covers the instrumentation, principles, procedures, advantages, and disadvantages various ashing procedures. The two major types of ashing analysis, dry ashing and wet ashing, can be accomplished by conventional means or by the use of microwave systems. The procedure of choice depends upon the use of the ash following its determination, and limitations based on cost, time, and sample numbers. Conventional dry ashing is based upon sample incineration at high temperatures (500-600°C) in a muffle furnace. Wet ashing (acid-facilitated oxidation) is often used as a preparation for specific elemental analysis by atomic absorption, inductively coupled plasma, and/or mass spectrometry. Microwave ashing (dry or wet) is faster than conventional methods and requires little additional equipment or space, but sample throughput may be a limiting factor.

Determination of food lipid content is important because of regulatory requirements, nutritive value, and functional properties. This chapter includes the typical required sample preparation steps of predrying the sample, particle size reduction, and acid hydrolysis. The majority of the chapter covers the instrumentation, principles, procedures, advantages, disadvantages and applications of various fat determination methods. The total lipid content of foods is commonly determined by organic solvent extraction methods, based on the solubility characteristics of lipids. Common extraction methods are continuous (e.g., Goldfish), semicontinuous (e.g., Soxhlet), or discontinuous (e.g., Mojonnier). Solvent extraction followed by gas chromatography analysis is required for nutrition labeling. Nonsolvent wet extraction methods, such as the Babcock or Gerber, are commonly used for certain types of food products. Instrumental methods, such as nuclear magnetic resonance (NMR), infrared, accelerated solvent extraction (ASE), supercritical fluid extraction (SFE), and x-ray absorption, are also available as rapid methods that may be useful for quality control.

Protein content analysis of foods and ingredients is important for a variety of reasons. This chapter covers the instrumentation, principles, procedures, advantages, disadvantages, and applications of various protein analysis methods that are based on the unique characteristics of proteins and amino acids. The Kjeldahl and Dumas methods measure nitrogen. Infrared spectroscopy is based on absorption of a wavelength of infrared radiation specific for the peptide bond. Copper-peptide bond interactions contribute to the analysis by the biuret, Lowry, and bicinchoninic acid (BCA) methods. Specific amino acids are involved in the Lowry, BCA, dye-binding, and UV 280 nm methods. The BCA method also utilizes the reducing power of proteins in an alkaline solution. These and other protein analysis methods differ in their speed and sensitivity. Because of the complex nature of various food systems, problems may be encountered to different degrees in protein analysis by available methods. Certain methods are required as official methods for nutrition labeling, rapid methods may be suitable for quality control purposes, and other very sensitive methods are required for work with a minute amount of protein.

This chapter covers the principles, procedures, and applications of carbohydrates analysis commonly used for nutrition labeling, quality assurance, or research for food ingredients and/or products. While chromatographic methods have largely replaced many older methods, some older methods continue to be commonly used for research and quality assurance [e.g., colorimetric methods for total carbohydrate (phenol-sulfuric acid method), various reducing sugar methods (e.g., Somogyi-Nelson method), and physical measurements (based on specific gravity or refractive index)]. Chromatographic methods (high-performance liquid chromatography and gas chromatography) separate mixtures into their component sugars, identify each component by retention time, and provide a measurement of the quantity of each component. Enzymic methods are specific and sensitive, but seldom, except in the case of starch, is determination of only a single component desired. In the absence of a universal procedure for analysis of most polysaccharides, their analysis generally involves isolation followed by identification based on hydrolysis to constituent monosaccharides and their determination. An exception is starch, which can be measured specifically by digestion to glucose using specific enzymes (amylases), followed by measurement of the glucose released. Insoluble dietary fiber, soluble dietary fiber, and total dietary fiber are each composed primarily of non-starch polysaccharides. Methods for the determination of total dietary fiber and its components rely on removal of the digestible starch using amylases and removal of digestible protein with a protease, leaving a non-digestible residue.

This chapter describes the principles and procedures for three types of methods applied to vitamin analysis: bioassays, microbiological and chemical assays. The chemical assays are emphasized, especially high-performance liquid chromatography (HPLC) because many vitamins are commonly measured by HPLC as official or unofficial methods. The various methods described are, in general, applicable to the analysis of more than one vitamin and several food matrices. However, the analytical procedures must be properly tailored to the analyte in question and the biological matrix to be analyzed. Covered in the chapter are the critical aspects of sample preparation and extraction of a vitamin from the food matrix prior to analysis.

The mineral content of water and foodstuffs is important because of their nutritional value, toxicological potential, interactive effects with processing and texture of some foods, and flavor (in the case of salt).This chapter describes the principles, procedures, and applications of traditional methods for analysis of minerals involving titrimetric and colorimetric procedures, ion selective electrodes, and benchtop analyzer to measure salt content.The traditional methods described have maintained widespread usage in the food industry despite the development of more modern instrumentation such as ion chromatography (Chap. 13), atomic absorption spectroscopy, and inductively coupled plasma-atomic emission spectroscopy (Chap. 9).Traditional methods generally require chemicals and equipment that are routinely available in an analytical laboratory, and are within the experience of most laboratory technicians.Additionally, traditional methods often form the basis for rapid analysis kits (e.g., AquaChek® for calcium, and Quantab® for salt determination) and for automated benchtop analyzers for salt content.The principles of these test kits and automated analyzers are explained in the chapter.

Titratable acidity and pH are two interrelated concepts in food analysis that deal with acidity. Each of these quantities is analytically determined in separate ways and each provides its own particular insights on food quality. For example, while pH is important to assess the ability of a microorganism to grow in a specific food, titratable acidity is a better predictor than pH of how organic acids in the food impact flavor. Unlike strong acids that are fully dissociated, food acids are only partially ionized. Some properties of foods are affected only by this ionized fraction of acid molecules while other properties are affected by the total acid content. This chapter focuses on the principles and procedures involved in measuring pH and titratable acidity. pH, which is the negative log (base 10) of the hydrogen ion concentration, is measured with a pH meter and the millivolt is converted to pH using the Nernst equation. Titratable acidity, which measures the total acid concentration in a food, is determined by titration of intrinsic acids with a standard base. The concept of Brix/acid ratio is covered in this chapter, since the perception of a tart flavor caused by organic acids is strongly influenced by the presence of sugars.

The importance of fat characterization is evident in many aspects of the food industry, including ingredient technology, product development, quality assurance, product shelf life, and regulatory aspects. Also, lipids are closely associated with health, requiring analysis for specific lipids of interest. The methods described in this chapter are used to characterize bulk oils and fats and the lipids in foodstuffs. Methods described for bulk oils and fats are used to determine characteristics such as melting point; smoke, flash, and fire points; color; degree of unsaturation; average fatty acid chain length; and amount of polar components. The peroxide value, thiobarbituric acid (TBA), and hexanal tests can be used to measure the present status of a lipid with regard to oxidation, while the oil stability index (OSI) can be used to predict the susceptibility of a lipid to oxidation and the effectiveness of antioxidants. Lipid fractions, including fatty acids, triacylglycerols, phospholipids, and cholesterol, are commonly analyzed by chromatographic techniques such as gas chromatography (GC) and thin layer chromatography (TLC).

This chapter covers the principles, procedures, and applications of a variety of techniques used to separate and characterize proteins. Separation techniques rely on the differences in the solubility, size, charge, adsorption characteristics of protein molecules. Commonly used protein separation techniques include the following: ion-exchange chromatography, affinity chromatography, dialysis, ultrafiltration, size-exclusion chromatography, electrophoresis [sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing, and capillary electrophoresis]. Proteins can be characterized by their amino acid content, nutritional value, and functional properties. Chromatographic techniques are used to determine the amino acid composition of a protein. The nutritional quality of a protein is determined by its amino acid composition and protein digestibility, measured for nutrition labeling purposes by expensive and time consuming assays, protein digestibility-corrected amino acid score (PDCAAS) or protein efficiency ratio (PER). Other more rapid methods and calculations can be done to assess nutritional value for other purposes. Common tests of protein functionality for a particular food application include solubility, emulsification, foaming, and gelation.

Phenolic compounds and other antioxidants are of great interest since they have the potential to stabilize food products against lipid deterioration. Also, because many diseases such as diabetes and certain forms of cancer are linked to oxidative stress, phenolic compounds from food products and other plant sources are of interest for disease prevention. Thus, there is a demand to measure phenolic compounds in food products and to evaluate the antioxidant capacity of individual food constituents, extracts, and ingredients. Assays described in this chapter are of four types: (total) phenolics, hydrogen atom transfer-based antioxidant capacity assays, single-electron transfer-based antioxidant capacity assays, and accelerated lipid oxidation assays. Methods to determine the total phenolic contents of food products such as the Folin-Ciocalteu assay are unspecific and do not, depending on the overall composition of the food product, necessarily reflect the phenolic contents. Therefore, wherever possible, it is advised to study individual phenolic compounds by using various chromatography approaches. The chapter includes cautions regarding the types of antioxidant capacity assays used to screen compounds for delaying lipid oxidation and potential health benefits.

Due to the specificity and sensitivity of enzymes, they are valuable analytical devices for quantitating compounds that are enzyme substrates, activators, or inhibitors. This chapter reviews the principles of enzymology then provides examples of how enzymatic analyses are used in food systems. In enzyme-catalyzed reactions, the enzyme and substrate are mixed under specific conditions (pH, temperature, ionic strength, substrate concentration, and enzyme concentrations). Changes in these conditions can affect the reaction rate of the enzyme and thereby the outcome of the assay. The enzymatic reaction is followed by measuring either the amount of product generated or the disappearance of the substrate. Applications for enzyme analyses will increase as a greater number of enzymes are purified and become commercially available. The measurement of enzyme activity is useful in assessing food quality and as an indication of the adequacy of heat processes such as pasteurization and blanching. Immobilized enzyme sensors will likely increase in importance for in-line process control in the food industry.

Almost any organic molecule in food can be determined using immunoassays as long as the specific antibodies are available. The remarkable selectivity and sensitivity of these assays are the result of the strong binding affinity between antibodies and their antigens. In the food analysis area, immunoassays are widely used for chemical contaminants analysis, identification of bacteria and viruses, and detection of proteins in food and agricultural products (e.g., allergens and meat species content, seafood species identification, and detection of genetically modified plant tissues). This chapter on immunoassays compares and contrasts direct vs. indirect assays and competitive vs. non-competitive assays. It describes the principles and procedures for enzyme-linked immunosorbent assays (ELISA), lateral flow strips, and immunoblots (Western blot and dot blot). Methods covered are compared and contrasted, giving advantages, disadvantages, and applications. Also described is immunoaffinity purification and its applications.

Oxygen demand is a commonly used parameter to evaluate the potential effect of organic pollutants (e.g., from a food processing facility) on either a wastewater treatment process or a receiving water body. Because microorganisms utilize these organic materials, the dissolved oxygen is greatly depleted from the water, which can have a detrimental effect on fish and plant life. This chapter focuses on the two main methods used to measure the oxygen demand of water and wastewater: biochemical oxygen demand (BOD) and chemical oxygen demand (COD). Described in the chapter are the principles, procedures, applications, and limitations of each method. The BOD test measures the amount of oxygen required by microorganisms to oxidize the biodegradable organic matter present in water and wastewater. The COD method determines the quantity of oxygen consumed during the oxidation of organic matter in water and wastewater by potassium dichromate. The COD test can be used to monitor routinely the biodegradability of organic matter in water and wastewater if a relationship between COD and BOD has been established.

Food scientists often need to measure physical properties related to both behavior during food processing and the sensory texture of food products. Rheological properties are determined by applying and measuring forces and deformations as a function of time. To convert these measurements into fundamental physics-based rheological properties requires an understanding of the material and testing method. This chapter covers the fundamentals of rheology, various rheological fluid models, and rheometry of three types: (1) compressions, extension, and torsion analysis, (2) rotational viscometry, and (3) oscillatory rheometry. In the rheometry section, numerous rheometers commonly used in the food industry are described. Also, a section in the chapter on tribology describes how this subfield of rheology is related to the friction-related textural attributes of food.

Thermal analysis is a series of laboratory techniques that measure physical and chemical properties of materials as a function of temperature and time.Thermal analysis results provide insight into the structure and quality of both starting materials and finished products. The physical structure (amorphous, crystalline, semi-crystalline) of a material creates a set of physical properties, which in turn define end-use properties, such as texture and storage stability. Areas of application include quality assurance, product development, and research into new materials, formulations, and processing conditions.This chapter covers the principles, experimental conditions, common measurements, and applications of the two most frequently used thermal analysis techniques, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).Also covered is modulated temperature DSC (MDSC®).This chapter includes illustrated application of thermal analysis to a variety of food materials.

Food scientists who establish quality control specifications for their product are very aware of the importance of color and appearance. While subjective visual assessment and visual color standards are still used in the food industry, objective instrumental color measurements are extensively employed. This chapter provides a brief description of human physiology of vision and an overview of the different color-ordering and color-measuring systems. Included are the CIE tristimulus system and tristimulus colorimeters, with coverage of the Hunter Lab system, the CIEL*a*b* system, and the L*C*H* system. Also covered are sample preparation and presentation to get measurements that are repeatable and that correspond to visual appearance. The chapter is limited to presenting the basic underlying principles that allow for an understanding of how color of food products should be measured.

The future of food research and food production resides in controlling and manipulating food structures to give the desired functionality. This chapter provides an overview of some direct and indirect microstructure characterization tools that have been borrowed by food scientists from other science disciplines to help better understand food systems and correlate structure to food functionality.Modern microscopy and chemical imaging tools allow users to not only determine food morphology and ingredient distribution, but also to quantify dimension parameters, concentrations, fractions, and kinetic constants. Covered in the chapter are various microscopy techniques that can be used to help determine the morphology of food (i.e., light microscopy, electron microscopy, energy dispersive x-ray spectroscopy, atomic force microscopy).Also covered are various chemical imaging techniques (i.e., Fourier transform infrared, Raman, fluorescence, and confocal laser scanning microscopy) to help identify the distribution of ingredients with different chemical and physical characteristics.X-ray diffraction is covered as a physical structural tool to help understand molecular arrangement or crystallinity.X-ray computed tomography is covered as a way to quantitate in 3-D with non-destructive imaging.

Consumer concerns and government regulations focused on the safety of foods dictate the need for analysis of various food contaminants, residues, and chemical constituents of concern.These compounds include pesticide residues, mycotoxins, antibiotic residues, GMOs, allergens, food adulterants, packaging material hazardous chemicals, environmental contaminants, and certain other chemicals.This chapter covers the screening methods and quantitative methods that are commonly used for the detection and quantification of several food hazards, in addition to some recently developed methods for the detection of newly identified and emerging food hazards.Included are both rapid screening methods and more time consuming quantitative methods required to meet the needs of industry and government, in an effort to ensure a safe and reliable food supply.Sampling and sample preparation are covered because they can be a significant challenge due to the low levels of the chemicals and the complex food matrices.Methods referred to in this chapter include many techniques covered in other chapters (e.g., high-performance liquid chromatography, gas chromatography, mass spectrometry, immunoassays, enzyme inhibitor assays), and others not previously covered (DNA methods using polymerase chain reaction, certain colorimetric assays).This chapter on chemical contamination is intended to compliment that of Chap. 35 on Food Forensic Investigations.

Analysis for extraneous matter is an important element both in the selection of raw materials for food manufacturing and for monitoring the quality of processed foods. Defect action levels (DALs) of specific products are established for amounts of extraneous matter considered unavoidable and of no health hazard. However, the presence of extraneous material in a food product is unappealing, can pose a serious health hazard to the consumer, and represents lack of good manufacturing practices and sanitary conditions in production, storage, or distribution of food. This chapter provides an overview of basic official methods to isolate extraneous matter from foods, using a series of physical and chemical means to separate the extraneous material for identification and enumeration. Major concerns in the analysis of food products for extraneous matter by traditional methods are the subjectivity of methods and the availability of adequately trained analysts. The chapter also includes an overview of more sophisticated techniques to pinpoint the nature and source of contaminants (x-ray radiography, x-ray microtomography, electrical conductance, impact-acoustic emission, microscopy techniques, near-infrared spectroscopy, and enzyme-linked immunosorbent assays).

This chapter provides an introduction to the craft of food forensic investigation, which is described as a logical process for the investigation of root causes for a product that is perceived to be physically objectionable to a customer or consumer because it may have an off-odor/taint, have been contaminated by foreign material during processing or at some later time, or have been intentionally tampered with by an outside party. Products under these circumstances must be analyzed from a perspective different than simply understanding the quality or composition of a product. Food forensic tools and experienced personnel are critical to determine the root cause of both product failures and food tampering. When a product is reported with a problem, it is important to follow codified standard operation procedures to analyze the product to identify what the problem is, where and when it occurred in the supply chain, and how it occurred, so corrective action can be taken. Various specialized nondestructive and destructive techniques (e.g., microscopy, chemical spectroscopy/spectrometry, x-ray microtomography, x-ray diffraction, microchemistry) are critical to investigate such problems of foreign matter contamination. Sensitive instrumental techniques and simple sensory evaluation are critical to identify contaminants causing off-flavors/off-odors and taints. This chapter on food forensic investigations is intended to complement that of both Chap. 33 on chemical contamination and Chap. 34 on extraneous matter.