Subject food analysis

Immunometric methods find increasingly wide applications owing to their superiority and continuous improvements. One of the major advantages of immunometric methods is that they provide consumers with early information (prior to food consumption) on possible health hazards (allergenic characteristics) of specific food products. The sensitivity of immunoassays is largely dependent on the type of a compound subject to analysis (up to lOpg/mL of the analyte). 

The chemical score is determined as follows. The contents of the indispensable amino adds of egg albumin (ovalbumin), which is used as a reference protein, and the food protein in question arc determined. Egg albumin is considered to be ideal and nutritionally complete The test requires several steps. The protein must be purified, hydrolyzed to the constituent amino acids, and then subjected to analysis using an amino acid analyzer. The values for each of the indispensable amino acids for ovalbumin and the test protein are then listed as shown in Table 8.14. The contents of the various amino acids in the two proteins are then compared. The amino acid in the test protein that is present in the low cst level, on a percentage basis, can be found by examining the table. This amino acid is called the limiting amino acid of the protein. The value of the percentage is the chemical score. Table S.14 indicates that the quantity of lysine in oat protein is 51% that in egg protein. Hence, the chemical score of oat protein is 51,... 

Similar demands for speciation of trace elements exist for food analysis. Substantial differences in the biological availability are known for several essential elements and depend on the form in which they are present in the diet. The chemical bases for these differences are known for cobalt, iron, and chromium but not for zinc, copper, and selenium. The importance of speciation in food analysis is best demonstrated by the example of iron. That element, when part of heme compounds, is well absorbed, and there is little influence on the absorption by other factors in the diet. Nonheme iron, on the other hand, is not readily absorbed and, in addition, is subject to many influences from dietary ingredients those influences are poorly understood and probably not completely known (14). 

Liquid membrane electrodes are subject to interferences from ions other than that of prime selectivity. For example, the Ca-ISE is also responsive to Mg2+ and Ba2+, the selectivity coefficients being approximately 0.01 for each ion. This indicates that the electrode is only 100 times more sensitive to Ca than to these ions, and this is normally much more important with respect to Mg than to Ba where food analysis is concerned. There are techniques which can be used to minimise the interference of Mg2+. 

With a prescriptive approach to quality assessment, duplicate samples, blanks, standards, and spike recoveries are measured following a specific protocol. The result for each analysis is then compared with a single predetermined limit. If this limit is exceeded, an appropriate corrective action is taken. Prescriptive approaches to quality assurance are common for programs and laboratories subject to federal regulation. For example, the Food and Drug Administration (FDA) specifies quality assurance practices that must be followed by laboratories analyzing products regulated by the FDA. 

Discriminant Sensory Analysis. Discriminant sensory analysis, ie, difference testing, is used to determine if a difference can be detected in the flavor of two or more samples by a panel of subjects. These differences may be quantitative, ie, a magnitude can be assigned to the differences but the nature of the difference is not revealed. These procedures yield much less information about the flavor of a food than descriptive analyses, yet are extremely useful eg, a manufacturer might want to substitute one component of a food product with another safer or less expensive one without changing the flavor in any way. Several formulations can be attempted until one is found with flavor characteristics that caimot be discriminated from the original or standard sample. 

The development of precise and reproducible methods of sensory analysis is prerequisite to the determination of what causes flavor, or the study of flavor chemistry. Knowing what chemical compounds are responsible for flavor allows the development of analytical techniques using chemistry rather than human subjects to characterize flavor (38,39). Routine analysis in most food production for the quaUty control of flavor is rare (40). Once standards for each flavor quaUty have been synthesized or isolated, they can also be used to train people to do more rigorous descriptive analyses. 

The Federal Food, Dmg and Cosmetic (FDAC) Act defines dmgs as "...articles intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease in man..." and "articles (other than food) intended to affect the stmcture of any function of the body of man." In the United States and elsewhere, the introduction of a new dmg is subject to a sequence of weU-defined stages of development and approval (4). Each stage involves either scientific testing or submission and preparation of data and analysis review (Fig. 2). 

In 1996, Mondello et al. (48) published a review article on the applications of HPLC-HRGC developed for food and water analysis over the period from 1986 to 1995. These authors cited 98 references, grouped by following a chronological order and by the subject of the application, as follows ... 

Though the literature is replete with methods of measuring the moisture content, truly accurate as well as practical methods are virtually nonexistent in the food field. The situation is well illustrated in what is probably the best compendium on this subject, the Official and Tentative Methods of Analysis of the Association of Official Agricultural Chemists (2). It becomes apparent from an examination of this volume that the stress is laid not so much on accuracy as on reproducibility and practicability of a method. Though these last two factors are for the most part the only ones of importance in the control of processing procedures and in standardization of products of commerce, the factor of accuracy is, nevertheless, of extreme importance to the research worker who endeavors to establish broad quantitative generalizations for the conditions that govern the stability of foods. 

In most studies, phytoestrogen intake has been estimated by direct methods that evaluate food intake either by recall (food-frequency questionnaires -FFQs) or by record (food diary), and subsequently by composition databases based on information of this kind. Food-frequency questionnaires are widely administered to subjects involved in epidemiological studies. Their validity and reproducibility is considered sufficient when statistically correlated to data obtained from dietary records (a properly-completed and comprehensive food diary) and from analysis of blood and urine samples (Kirk et ah, 1999 Huang et al, 2000 Yamamoto et al, 2001 Verkasalo et al, 2001). FFQs can be repeated several times a year and may be administered to large populations. Such an approach provides an easy and low-cost method of assessing the... 

The determination and analysis of sensory properties plays an important role in the development of new consumer products. Particularly in the food industry sensory analysis has become an indispensable tool in research, development, marketing and quality control. The discipline of sensory analysis covers a wide spectrum of subjects physiology of sensory perception, psychology of human behaviour, flavour chemistry, physics of emulsion break-up and flavour release, testing methodology, consumer research, statistical data analysis. Not all of these aspects are of direct interest for the chemometrician. In this chapter we will cover a few topics in the analysis of sensory data. General introductory books are e.g. Refs. [1-3]. 

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. 

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