Foodstuffs sample analysis

Because of the low infectious dose of STEC, laboratory diagnosis of STEC in foodstuffs is becoming of great importance. It s essential to dispose of rapid and reliable methods to detect STEC presence in a suspected sample and to eventually get back to the source of contamination. STEC detection methods are mainly applied in hospital for stool samples analysis from patients suffering from HC or HUS and in food industry. The latter is very demanding in methods to guarantee the safety of their products. This paper will review the principal methods for STEC detection and will discuss their advantages and their drawbacks. 

The low cross-section of the reaction of I(n,p) I with fast neutrons (cf Table 2.3) and a low abundance of neutrons with energies higher than 9MeV, which are needed for this reaction, in the neutron spectrum of a nuclear reactor result in a detection limit which is not sufficient for iodine determination in most types of foodstuffs, even if an RNAA procedure is applied. However, this reaction, which is completely independent in relation to the reaction of I(n, ) I with thermal and epithermal neutrons may be useful for cross-checking results in analysis of foodstuff samples with higher iodine contents, using the so-called self-verification principle in NAA (Byrne and Kucera, 1997). Detection limits of various NAA modes, which were achieved in the authors laboratory are compared in Table 2.4. 

The method described by Barnes and co-workers [7] focused on MBT and BT because tests confirmed that both MBTS and CBS were unstable and broke down rapidly during food analysis to give MBT and BT as the main products. Two extraction procedures were used one for milks, yoghurts and infant formulae the other for all other foodstuffs. Sample extracts were then analysed by LC-APCI-MS using... 

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. 

Lesueur, C., R Knittl, M. Gartner et al. 2008. Analysis of 140 pesticides from conventional farming foodstuff samples after extraction with the modified QuEChERS method. Food Control. 19 906-914. 

The elements listed in the table of Figure 15.2 are of importance as environmental contaminants, and their analysis in soils, water, seawater, foodstuffs and for forensic purposes is performed routinely. For these reasons, methods have been sought to analyze samples of these elements quickly and easily without significant prepreparation. One way to unlock these elements from their compounds or salts, in which form they are usually found, is to reduce them to their volatile hydrides through the use of acid and sodium tetrahydroborate (sodium borohydride), as shown in Equation 15.1 for sodium arsenite. 

Microscopy (qv) plays a key role in examining trace evidence owing to the small size of the evidence and a desire to use nondestmctive testing (qv) techniques whenever possible. Polarizing light microscopy (43,44) is a method of choice for crystalline materials. Microscopy and microchemical analysis techniques (45,46) work well on small samples, are relatively nondestmctive, and are fast. Evidence such as sod, minerals, synthetic fibers, explosive debris, foodstuff, cosmetics (qv), and the like, lend themselves to this technique as do comparison microscopy, refractive index, and density comparisons with known specimens. Other microscopic procedures involving infrared, visible, and ultraviolet spectroscopy (qv) also are used to examine many types of trace evidence. 

Mycotoxins, toxic metaboUtes of some fungi, can be assayed by immunochemical techniques to determine concentration in animal feed and foodstuffs. Some of the analytes assayed in kits and the detection limits are Hsted in Table 4 (45). These assays are especially advantageous for routine analysis of large samples of foodstuffs (45,46). 

The sample preparation is generally typical of the LC analysis of many foodstuffs although the specific substances of interest will differ widely. 

Such yes/no decisions are of great importance in foodstuffs control and environmental analysis. They also play an important role in pharmacy in the form of content uniformity tests. Without suitable screening methods for rapid detection of positive samples it would scarcely be possible to carry out economic doping controls and toxicological investigations or to recognize medicament abuse. 

Council Directive 85/591/EEC of 20 December 1985 Concerning the Introduction of Community Methods of Sampling and Analysis for the Monitoring of Foodstuffs Intended for Human Consumption, Off. J. Eur Commun., L372, 50 (1985). Also available on the Word Wide Web http //www./europa.eu.int/eur-lex/en/lifydat/1985/en 385L0591.html. 

EC (European Commission) (1998), Commission directive No 98/53/EC of 16 July 1998 laying down the sampling methods and the methods of analysis for the official control of the levels for certain contaminants in foodstuffs , Official J. Europ. Communities, L201, 93-101. 

There are two main types of routine analysis carried out, i.e. those required for screening purposes, where one is testing a large number of individual unrelated samples, e.g. work-place drugs screening, and those for surveillance activities, e.g. monitoring foodstuffs for the level of toxic metals. 

Dry-ashing Ignition of organic matter in a furnace. Resulting ash dissolved in acid for further analysis Metals in organic solid samples (e.g. metals in foodstuffs)... 

There are two main types of proficiency testing scheme. First, there are those set up to assess the competence of a group of laboratories to undertake a very specific analysis, e.g. lead in blood or the number of asbestos fibres in air collected on membrane filters. Secondly, there are those schemes used to evaluate the performance of laboratories across a certain sector for a particular type of analysis. Because of the wide range of possible analyte/matrix combinations it is not practicable to assess the performance of laboratories when analysing all the possible sample types. Instead, a representative cross-section of analyses is chosen (e.g. determination of different pesticide residues in a range of foodstuffs or the determination of trace levels of metals in water samples). 

The technique is used predominantly for the isolation of a single chemical species prior to a determination and to a lesser extent as a method of concentrating trace quantities. The most widespread application is in the determination of metals as minor and trace constituents in a variety of inorganic and organic materials, e g. the selective extraction and spectrometric determination of metals as coloured complexes in the analysis of metallurgical and geological samples as well as for petroleum products, foodstuffs, plant and animal tissue and body fluids. 

Atomic absorption spectrometry is one of the most widely used techniques for the determination of metals at trace levels in solution. Its popularity as compared with that of flame emission is due to its relative freedom from interferences by inter-element effects and its relative insensitivity to variations in flame temperature. Only for the routine determination of alkali and alkaline earth metals, is flame photometry usually preferred. Over sixty elements can be determined in almost any matrix by atomic absorption. Examples include heavy metals in body fluids, polluted waters, foodstuffs, soft drinks and beer, the analysis of metallurgical and geochemical samples and the determination of many metals in soils, crude oils, petroleum products and plastics. Detection limits generally lie in the range 100-0.1 ppb (Table 8.4) but these can be improved by chemical pre-concentration procedures involving solvent extraction or ion exchange. 

The Council and the Commission must adopt positive fists of additives, authorised to the exclusion of all others, fists of foods in which the additives may be used with conditions of use, and rules on carrier solvents. The Standing Committee on Foodstuffs must approve adoption of purity criteria for listed additives and, if necessary, methods of analysis to verily these purity criteria, sampling procedures and methods of analysis for food additives in food. The directive includes provisions that a member state may temporarily suspend or restrict application of an authorisation if it has detailed grounds for considering that the use of the additive in food, although permitted, endangers health. The... 

Member States shall ensure that the validation of methods of analysis used within the context of official control of foodstuffs by the laboratories referred to in Article 7 of Directive 89/397/EEC comply whenever possible with the provisions of paragraphs 1 and 2 of the Annex to Council Directive 85/591/EEC of 23 December 1985 concerning the introduction of Community methods of sampling and analysis for the monitoring of foodstuffs intended for human consumption.7... 

Because of the status of the CAC described above, the work that it has carried out in the area of laboratory quality assurance must be carefully considered. One of the CAC Committees, the Codex Committee on Methods of Analysis and Sampling (CCMAS), has developed criteria for assessing the competence of testing laboratories involved in the official import and export control of foods. These were recommended by the Committee at its 21st Session in March 19979 and adopted by the Codex Alimentarius Commission at its 22nd Session in June 1997 10 they mirror the EU recommendations for laboratory quality standards and methods of analysis. The guidelines provide a framework for the implementation of quality assurance measures to ensure the competence of testing laboratories involved in the import and export control of foods. They are intended to assist countries in then-fair trade in foodstuffs and to protect consumers. 

The electropherogams demonstrate the baseline separation of dyes even in the presence of complicated accompanying matrices such as mint syrup. The LOD and LOQ values were between 1.0 - 1.7 and 3.2 - 5.5 jUg/ml, respectively, and the RSD of migration time and peak areas ranged 1.3 - 1.8 per cent and 2.0 - 3.1 per cent. The migration times of the dyes were Tartrazine, 9.97 min Sunset yellow FCF 6.73 min Amaranth, 8.41 min New coccine, 7.49 min Allura red AC, 5.43 min Patent blue V calcium salt, 4.23 min. The amounts of synthetic dyes found in commercial samples are compiled in Table 3.38. It has been stated that the analysis time is rapid and the method makes possible the separation and determination of these dyes at ppm levels in various foodstuffs [186],... 

Sample collection and preparation for the analysis of 1,2-dibromoethane in foods includes the purge-and-trap method, headspace gas analysis, liquid-liquid extraction, and steam distillation (Alleman et al. 1986 Anderson et al. 1985 Bielorai and Alumot 1965, 1966 Cairns et al. 1984 Clower et al. 1985 Pranoto-Soetardhi et al. 1986 Scudamore 1985). GC equipped with either ECD or HECD is the technique used for measuring 1,2-dibromoethane in foodstuffs at ppt levels (Clower et al. 1985 Entz and Hollifield 1982 Heikes and Hopper 1986 Page et al. 1987 Van Rillaer and Beernaert 1985). 

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