Applications in Food Analysis

It should be pointed out at the outset of this section that, where previous oxidative treatment of the sample is not involved, it is possible to speciate with the polarographic/voltammetric techniques. Thus it is possible, for example, to determine separately Cr(III) and Cr(VI), Sn(II) and Sn(IV), Ti(III) and Ti(IV), Fe(II) and Fe(III), etc. This can be most important where one oxidative state of a substance is more toxic or more nutritionally valuable than an other. 

One of the more important areas of application lies in the determination of metalhc substances in liquid and solid foods, or the biological materials from which they originate. Because of the organic basis of these substances they very often contain compounds which can inhibit the responses of metalhc 

For example vitamin C in jams, fruit and vegetable juices can be determined directly. In fact, a large number of the vitamins can be determined polarographically in pharmaceutical preparations without elaborate 

Other metals such as the lanthanides and the platinum series can also be determined. Nearly all of the vitamins. A large number of organic substances, including substances active in pharmaceutical preparations. In many instances, the determination of organic substances is carried out using the glassy carbon electrodes at applied potentials in the positive zone relative to the Ag/AgCl reference electrode. 

Several examples of analytical work based on voltammetric polarographic techniques follow. Additional techniques are provided in references [67-80], together with suggested texts. All of these cover section 8.4 material. 

---

M. Cai eii and A. Mangia, Multidimensional detection methods for sepai ations and their application in food analysis . Trends Anal. Chem. 15 538-550 (1996). 

Solid-phase sorbents are also used in a technique known as matrix solid-phase dispersion (MSPD). MSPD is a patented process first reported in 1989 for conducting the simultaneous disruption and extraction of solid and semi-solid samples. The technique is rapid and requires low volumes (ca. 10 mL) of solvents. One problem that has hindered further progress in pesticide residues analysis is the high ratio of sorbent to sample, typically 0.5-2 g of sorbent per 0.5 g of sample. This limits the sample size and creates problems with representative sub-sampling. It permits complete fractionation of the sample matrix components and also the ability to elute selectively a single compound or class of compounds from the same sample. Excellent reviews of the practical and theoretical aspects of MSPD " and applications in food analysis were presented by Barker.Torres et reported the use of MSPD for the... 

Capillary electrophoresis (CE) is a modem analytical technique that allows the rapid and efficient separation of sample components based on differences in their electrophoretic mobilities as they migrate or move through narrow bore capillary tubes (Frazier et al., 2000a). While widely accepted in the pharmaceutical industry, the uptake of CE by food analysts has been slow due to the lack of literature dedicated to its application in food analysis and the absence of well-validated analytical procedures applicable to a broad range of food products. 

Nowadays, a large number of applications are available therefore, in this chapter, a selection of more important and interesting ones will be presented. Particular attention will be paid to the official, reference or rontine methods, as well as to selected experimental approaches. The number of applications in food analysis is increasing at a rapid pace and it seems rather difficult to be exhaustive in this held. 

Detection of amino acids is typically by UV absorption after postcolumn reaction with nin-hydrin. Precolumn derivatization with ninhydrin is not possible, because the amino acids do not actually form an adduct with the ninhydrin. Rather, the reaction of all primary amino acids results in the formation of a chromophoric compound named Ruhemann s purple. This chro-mophore has an absorption maximum at 570 nm. The secondary amino acid, proline, is not able to react in the same fashion and results in an intermediate reaction product with an absorption maximum at 440 nm. See Fig. 5. Detection limits afforded by postcolumn reaction with ninhydrin are typically in the range of over 100 picomoles injected. Lower detection limits can be realized with postcolumn reaction with fluorescamine (115) or o-phthalaldehyde (OPA) (116). Detection limits down to 5 picomoles are possible. However, the detection limits afforded by ninhydrin are sufficient for the overwhelming majority of applications in food analysis. 

Motivation for protein determination Applications in food analysis Method of HPLC Refs. 

Applications in Food Analysis. In Fluorescence Analysis in Foods, L. Munck (ed.), Longman Scientific and Technical, New York, (1989), pp59-109. 

Simo, C., Elvira, C., Gonzalez, N., San Roman, J., Barbas, C. and Cifuentes, A. (2004) Capillary electrophoresis-mass spectrometry of basic proteins using a new physically adsorbed polymer coating. Some applications in food analysis, Electrophoresis, 25, 2056-2064. 

Comparison with a univariate approach. Also applicable in food analysis applications. 

The quality assessment of food and fodder products requires analysis of protein, carbohydrates and fat. The enzyme electrode-based analyzers originally developed for clinical chemistry have found only limited application in food analysis because they are only suitable for the determination of one parameter, mostly glucose or a disaccharide. The increasing concern for food quality require new types of biosensors allowing residual and hygiene control and on-line measurement of age and freshness (Tschannen, 1988). 

Relative to most other techniques discussed in this book, NMR has found a limited number of niche applications in food analysis. For example, the determination of oils is seeds (or fat in chocolate ), based upon low resolution, solid phase NMR is well used in quality control laboratories. Actually, most apphcations that found their way in food analysis are methods based upon the differences in relaxation times of various molecules e.g. free water molecules versus bound water molecules). Consequently, for the purpose of this particular chapter, we shall discuss only two specific applications of NMR to food analysis. These examples were chosen solely to demonstrate the broad range of applications that NMR can cover and the reader is advised that the mere fact that they were selected here should not be interpreted as a judgement of their value over other related references. 

Guilbault GG, Luong JHT (1995) Piezoelectroc immunosensors and their applications in food analysis. In Guilbault GG, Wagner G (eds) Food biosensor analysis. Dekker, New York... 

M. D. Luque de Castro, Flow Injection Analysis Its Possibilities and Applications in Food Analysis [in Spanish]. An. Bromatol., 37 (1986) 197. 

Liquid phase microextraction applications in food analysis. Journal of Chromatography A1218, 7415-7437... 

Some of the more important applications in food analysis include nitrates and nitrites in baby food products, excess of which can lead to induce methemoglobinemia (blue baby syndrome), and the monitoring of sulfite, which is added to many foodstuffs as a preservative and to bleach food starches, and is only recently being linked to serious health effects. Also, residual bromate can be monitored in bakery products from the continuing use of bromate salts as dough conditioners. 

Techniques based on micromachining technology are being increasingly exploited in the construction of commercially available sensor arrays, which find interesting applications in food analysis. The individual potentiometric sensors composing an array may be based on principles similar to those of classical potentiometric sensors. For practical... 

Table 1 Overview of microscopical techniques and applications in food analysis ...

Due to its high sensitivity and selectivity, liquid chromatography-mass spectrometry (LC-MS) is a powerful technique. It is used for various applications, often involving the detection and identification of chemicals in a complex mixture. Ultra Performance Liquid Chromatography Mass Spectrometry Evaluation and Applications in Food Analysis presents a unique collection of up-to-date UPLC-MS/MS methods for the separation and quantitative determination of components, contaminants, vitamins, and aroma and flavor compounds in a wide variety of foods and food products. 

The preparation of derivatives for TLC has been reviewed by Gasparic (1961) and Edwards (1980). Derivatization has been used in the TLC of amino acids where certain amino acids are easily converted into the so-called DANS forms (Jimethyl amino naphthalene suUbnyl) (Pataki and Niederweiser, 1967). These authors have studied a variety of amino acid derivatives on silica gel. The use of both pre- and post-chromatographic derivatization in TLC applications in food analysis has been discussed (Shalaby, 1996). For a recent update on the use of derivatization in TLC, see Cserhati and Forgacs (1996). 

This book contains several different NIR applications in food analysis, and many of them use multivariate data handling. Our aim in this chapter is to discuss the aspects of latent variable decomposition in principal component analysis and partial least squares regression and to illustrate their use by an application in the NIR region. 

It is believed that aluminum plays important roles in the pathology of Parkinson s disease, Alzheimer s disease, and diseases related to dialysis [75-77]. Therefore, a simple, well working direct potentiometric method could gain large-scale application in food analysis. For these, a selective electrode is needed. Being a three-valence ion, relatively less sensitivity is expected for a direct potentiometric aluminum measuring method. Unfortunately, a relatively small number of successful attempts have been reported about the fabrication of appropriate ion-selective aluminum electrodes. 

However, the sensitivity of NMR spectroscopy is the main limitation in its application in food analysis, when compared to MS techniques. The presence of toxins or pesticides in a foodstuff cannot be investigated by NMR spectroscopy, even if the increasing developments of NMR hardware are greatly improving its sensitivity. In spite of this, NMR spectroscopy turns out to be one of the most suitable techniques for food quality control and assurance, mainly because of its reproducibility and of its ability to analyse a foodstuff sample without or with minimal chemical treatment. 

---