Analysis of Foods

Laboratory of Foodomics, Institute of Food Science Research (CIAL-CSIC), Madrid, Spain 

Liquid chromatography (LC) has become a useful tool in food analysis to ascertain food quality, to implement regulatory enforcement, or to comply with national and international food standards. LC is chosen for multiple applications because it can be applied to a wide range of different samples, allows separation of compounds ranging from ions to biopolymers, and employs mild separation conditions, such as low temperature, thus precluding the thermal decomposition of unstable compounds, such as vitamins or pol)q)henols. LC also provides good sensitivity, resolution, and selectivity. 

Foods are complex matrices, and frequently, the components of interest are present in small amounts compared to macronutrients, such as proteins, carbohydrates, or lipids these compounds, when present in large amounts, can interfere with the determination of minor components. There are several ways to overcome this problem in LC (a) to increase the specificity of the separation/detection method, (b) to improve the selectivity of the sample preparation step prior to LC, or (c) both. 

Among the sample preparation techniques prior to LC, solid-phase extraction (SPE) has been widely used to remove interferences from the food matrix and to concentrate the anal rtes of interest. SPE is based on the selective retention of compoimds on a sorbent housed in a disposable extraction minicolimm (or cartridge). To cover a wide range of polarities, several sorbents, of polar, nonpolar, ionic, and pol)rmeiic materials, can be used. 

TABLE 11.1 Compositional Analysis of Foods and the Preferred Analytical Technique  

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An important application of these results lies in the analysis of food flavorings using a combination of gas-phase chromatography and mass spectrometry (121, 122). Similarly, metabolic products of chlo-methiazole have been characterized (123). 

Several standard methods for the quantitative analysis of food samples are based on measuring the sample s mass following a selective solvent extraction. For example, the crude fat content in chocolate can be determined by extracting with ether for 16 h in a Soxhlet extractor. After the extraction is complete, the ether is allowed to evaporate, and the residue is weighed after drying at 100 °C. This analysis has also been accomplished indirectly by weighing a sample before and after extracting with supercritical GO2. 

Analytical Procedures. Standard methods for analysis of food-grade adipic acid are described ia the Food Chemicals Codex (see Refs, ia Table 8). Classical methods are used for assay (titration), trace metals (As, heavy metals as Pb), and total ash. Water is determined by Kad-Fisher titration of a methanol solution of the acid. Determination of color ia methanol solution (APHA, Hazen equivalent, max. 10), as well as iron and other metals, are also described elsewhere (175). Other analyses frequendy are required for resia-grade acid. For example, hydrolyzable nitrogen (NH, amides, nitriles, etc) is determined by distillation of ammonia from an alkaline solution. Reducible nitrogen (nitrates and nitroorganics) may then be determined by adding DeVarda s alloy and continuing the distillation. Hydrocarbon oil contaminants may be determined by ir analysis of halocarbon extracts of alkaline solutions of the acid. 

R. S. Kirk and R. Sawyer, Pearson s Composition and Analysis of Foods, Longmans Scientific and Technical Books, Essex, U.K., 1991, p. 537. Y. Pomeianz and C. E. Meloan, Food Analysis, Von Nostiand Reinhold, New York, 1987, p. 708. 

Biopolymers are employed in many immunological techniques, including the analysis of food, clinical samples, pesticides, and in other areas of analytical chemistry. Immunoassays (qv) are specific, sensitive, relatively easy to perform, and usually inexpensive. For repetitive analyses, immunoassays compare very favorably with many conventional methods in terms of both sensitivity and limits of detection. 

Compatibility physieal influenee with tool ehemieal methods of sample preparation and the stage of determination based on any prineiple of an analytieal signal generation, the opportunity of automation of a sample preparation stage, eontrol, modeling of eonditions of analytieal proeess opens prospeets for their use in the analysis of food-stuffs, environment objeets, geologieal samples, ete. 

Ultrasound Sample Prepai ation method was used for the analysis of food products. 

Often, planar chromatography is used as a preparative step for the isolation of single components or classes of components for further chromatographic separation or spectroscopic elucidation. Many planar chromatographic methods have been developed for the analysis of food products, bioactive compounds from plant materials, and essential oils. 

H Egan, R Sawyer and R S Kirk, Pearson s Chemical Analysis of Foods, 8th edn, Longman, Harlow, 1981, p 240... 

The diet of the 19 century residents of Upper Canada was determined from historical sources and was reproduced in order to carry out chemical analysis. Stable carbon isotope analysis of food and human bone demonstrates that the spacing between the food eaten and the bone collagen is around 5.6%o. The value may vary slightly from this estimate since the latter is based on a reconstructed diet and a large number of bone samples, which exhibit a small amount of variation. Nevertheless, this empirically derived result agrees well with estimates from field (Vogel 1978), and laboratory studies (reviewed in Ambrose 1993). 

A recent method, still in development, for determining total 4-nitrophenol in the urine of persons exposed to methyl parathion is based on solid phase microextraction (SPME) and GC/MS previously, the method has been used in the analysis of food and environmental samples (Guidotti et al. 1999). The method uses a solid phase microextraction fiber, is inserted into the urine sample that has been hydrolyzed with HCl at 50° C prior to mixing with distilled water and NaCl and then stirred (1,000 rpm). The fiber is left in the liquid for 30 minutes until a partitioning equilibrium is achieved, and then placed into the GC injector port to desorb. The method shows promise for use in determining exposures at low doses, as it is very sensitive. There is a need for additional development of this method, as the measurement of acetylcholinesterase, the enzyme inhibited by exposure to organophosphates such as methyl parathion, is not an effective indicator of low-dose exposures. 

Bhananker SM, O Donnell JT, Salem JR, Bishop 25 MJ The risk of anaphylactic reactions to rocuro-nium in the United States is comparable to that of vecuronium an analysis of food and drug administration reporting of adverse events. Anesth Analg 26 2005 101 819. 

Entz RC, Hollifield HC. 1982. Headspace gas chromatographic analysis of foods for volatile halocarbons. 

In the preceding section, we presented principles of spectroscopy over the entire electromagnetic spectrum. The most important spectroscopic methods are those in the visible spectral region where food colorants can be perceived by the human eye. Human perception and the physical analysis of food colorants operate differently. The human perception with which we shall deal in Section 1.5 is difficult to normalize. However, the intention to standardize human color perception based on the abilities of most individuals led to a variety of protocols that regulate in detail how, with physical methods, human color perception can be simulated. In any case, a sophisticated instrumental set up is required. We present certain details related to optical spectroscopy here. For practical purposes, one must discriminate between measurements in the absorbance mode and those in the reflection mode. The latter mode is more important for direct measurement of colorants in food samples. To characterize pure or extracted food colorants the absorption mode should be used. 

British Standard Institution, Methods for the Sensory Analysis of Foods, BS 5929-10 1999/ISOl 1037 1999, London, 1999. 

Multon, J., Ed., Analysis of Food Constituents, John WUey Sons, New York, 1996. CIE, Technical Report Improvement in Industrial Colour-Difference Evaluation, Pnblication 142-2001, Commission Internationale de I Eclairage, Vienna, 2001. Watson, D.H., Food Chemical Safety, vols. 1 and 2, CRC Press, Boca Raton, FL, 2002. King, S., Gates, M., and Scalettar, L., Eds., Current Protocols in Food Analytical Chemistry, John Wiley Sons, New York, 2001. 

Otles, S., Ed., Methods of Analysis of Food Components and Additives, CRC Press, Boca Raton, FL, 2005. 

Nollet, L.M.L., Food Analysis by HPLC, 2nd ed., Marcel Dekker, New York, 2000. Gennaro, M.C., Abrigo, C., and CipoUa, G., HPLC analysis of food colors and its relevance in forensic chemistry, J. Chromatogr. A, 674, 281, 1994. Gratzfeld-Huesgen, A. and Schuster, R., HPLCfor Food Analysis A Primer, Hewlett-Packard Company, Palo Alto, CA, 1996. 

Lloyd, A.G., Extraction and chemistry of cochineal. Food Chem., 5, 91,1980. Yamada, S. et al.. Analysis of natural colouring matters in food (IV). Methylation of cochineal colour with diazomethane for analysis of food products, J. Agric. Food Chem., 41, 1071, 1993. 

Huang, H.Y. et al.. Analysis of food colorants by capillary electrophoresis with large-volume sample stacking, J. Chromatogr. A, 995, 29, 2003. 

Maraz, A. et al.. Microbial analysis of food, in Safety in Agri-food Chains, Luning, P.A., DeVlieghere, R, and Verhe, R., Eds., Wageningen Academic Publishers, Wageningen, 2006, 471. 

Tennant, D.R., Risk analysis of food additives, in Food Chemical Safety, Volume 2 Additives, Watson, D.H., Ed., Woodhead Publishing, Cambridge, U.K., 2002, 61. 

T. Naes and E. Risvik (Editors), Multivariate Analysis of Data in Sensory Science. Data Handling in Science and Technology Series, Elsevier, Amsterdam, 1996 J.R. Piggott (Editor), Sensory Analysis of Foods. Elsevier, London, 1984. 

Wolf WR, Iyengar GC and Tanner JT (1990) Muted diet reference materials for nutrient analysis of foods preparation of SRM-1545 Total diet. Fresenius J Anal Chem 338 473-475. 

Examples of recent applications of food RMs for quality control in the analysis of foods and food products... 

Several articles and books have been published dealing with this subject. In this article, some of the techniques which are relevant to methods for the analysis of foods for pesticide residues will be discussed. 

Several methods have been discussed for the determination of method limitations when evaluating procedures for the determination of pesticides in food. A brief comparison of the methods discussed for the determination of the detection and quantification limits of methods used for the analysis of food products can be found in Table 2. 

Dallas, G. and Abbott, S. D., New approaches to the analysis of low-molecular-weight polymers, in Liquid Chromatographic Analysis of Food and Beverages, Vol. 2, Charalambous, G., Ed., Academic Press, New York, 1979, 509. 

Sharman, M. and Gilbert, J., Automated aflatoxin analysis of foods and animal feeds using immunoaffinity column clean-up and high-performance liquid chromatographic determination, /. Chromatogr., 543, 220, 1991. 

Herraiz, T., Sample preparation and reversed phase-high performance liquid chromatography analysis of food-derived peptides, Analytica Chimica Acta, 352, 119, 1997. 

Apart from styrene oligomers [514], it appears that OPLC analysis of polymer additives has not been reported. However, the technique has been used for analysis of food antioxidants (BHA, BHT, NDGA and propyl, octyl, and dodecyl gallate) on silica with five different solvent mixtures and densitometric detection [479],... 

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