Ochratoxin C

The main disadvantages of an immunoaffinity cleanup for OA could in some cases be the lack of specificity for ochratoxin A (since a cross-reaction with ochratoxin C can occur (60)), the potential contamination with release of ochratoxin A from the support of the IA (61), and the high cost of each column, although some authors considered the possibility of regenerating the column for further analyses (30). 

These compounds were found to be important mycotoxin constituents of Aspergillus species shortly after the discovery of the aflatoxins (see Chap. 2.). The ochratoxins are isocoumarin derivatives coupled with p-phenylalanine. The major representatives of this class of pentaketides are shown in Fig. 6.2. Ochratoxin B (324) is the dechloro analog of ochratoxin A (323), which is the most important member of this group with respect to its toxicity. The corresponding methyl and ethyl esters of ochratoxin A (323) and B (324) were found also in Aspergillus species and the ethyl ester of ochratoxin A (323) has been named ochratoxin C (325). Ochratoxin a (326) is a free carboxylic acid that represents the dihydroi-socoumarin nucleus of ochratoxin A (323). 

From a toxicological point of view, the most important representative of this group of mycotoxins is ochratoxin A, 3R)-N-[(5-chloro-3,4-dihydro-8-hydroxy-3-methyl-1-0X0-lH-2-benzo-pyran-7-yl)carbonyl]-L-phenylalanine (12-92), the molecule of which phenylalanine JV-substituted with a derivative of 3R)-3,4-dihydro-3-methylisocoumarine that contains at C-5 a chlorine atom to which are attributed the toxic effects of ochratoxin A. The incorporation of the chlorine atom into the skeleton of ochratoxin A is done by the action of chloroperoxidase the chlorine donor is inorganic chloride. Ochratoxin B (12-92) differs from ochratoxin A only in the absence of the chlorine atom, while ochratoxin C (12-92) is an ethyl ester of ochratoxin A. Ochratoxins a, p and y resulting from from parent compounds by the loss of phenylalanine caused by peptide bond hydrolysis, are virtually non-toxic, in addition to ochratoxin B, and are not routinely monitored. 

Studer-Rohr, I, Dietrich, D. R., Schlatter, J., Schlatter. C., The occurrence of ochratoxin A in coffee, Food Chem. Toxicol., 33(5), 341, 1995. (CA123 8219g)... 

This NRL sensor was used for fhe rapid detection of Campylobacter jejuni and small toxins, including several mycotoxins [ochratoxin A, fumonisin B, aflafoxin Bi, and deoxynivalenol (DON)] from food pro-ducfs (Ngundi et ah, 2005, 2006 Sapsford et ah, 2006). They used a sandwich immunoassay formaf fo detect C. jejuni in milk and yogurt and a competitive immunoassay format to detect the mycotoxins. 

Bogs, C., Battilani, P., and Geisen, R. (2006). Development of a molecular detection and differentiation system for ochratoxin A producing Penicillium species and its application to analyse the occurrence of Penicillium nordicum in cured meat. Int. J. Food Microbiol. 107, 39 7. 

Brera, C., Soriano, J. M., Debegnach, F., and Miraglia, M. (2005). Exposure assessment to ochratoxin A from the consumption of Italian and Hungarian wines. Microchem. J. 79, 109-113. 

Serra, R., Mendoca, C., and Venancio, A. (2006). Fungi and ochratoxin A detected in healthy grapes and wine production. Lett. Appl. Microbiol. 42, 42 7. 

Three methods are usually adopted for confirmation of ochratoxin A (a) methylation (methods A and B), (b) ammonia derivative formation, and (c) LC-MS confirmation. 

Method A 50 /jl (ca 250 ng) of the stock solution or of the purified extract is transferred into a reaction tube. One ml of boron trifluoride is added to the methanol, the cap is closed, and the tube is kept on a block heater (80°C) for 10 min. Two ml of water and 2 ml of -hexane are added. After thorough mixing, the layers are left to separate. Using disposable glass Pasteur pipettes, the upper layer is transferred to a clean, small vial. The extraction is repeated another two times with 2-ml portions of n-hexane. The hexane extracts are taken to dryness with a nitrogen stream, and the residue is dissolved in 1 -2 ml of injection solvent. Ochratoxin A is confirmed by the presence of an OA-methyl ester peak at delayed retention time and the disappearance of the OA peak (62). 

C Micco, MA Ambruzzi, M Miraglia, C Brera, L Benelli, S Corneli. Evaluation of ochratoxin A in human milk. Food Add Contam 12 351-354, 1995. 

Sibanda L, De Saeger S, Bama-Vetro I, Van Peteghem C (2002) Development of a Solid-Phase Cleanup and Portable Rapid Flow-Through Enzyme Immunoassay for the Detection of Ochratoxin A in Roasted Coffee. J Agric Food Chem 50 6964... 

Sergent T, Garsou S, Schaut A, De Saeger S, Pussemier L, Van Peteghem C, Larondelle Y, Schneider YJ. 2005. Differential modulation of ochratoxin A absorption across Caco-2 cells by dietary polyphenols, used at realistic intestinal concentrations. 

Work Item C determination of ochratoxin A in cereals and cereal products -HPLC method with immunoaffinity clean-up. 

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