Zeitschrift fur Lebensmittel-Untersuchung und -Forschung最新文献

An improved procedure is described for the determination of retinol and alpha-tocopherol in milk and dairy products using high-pressure liquid chromatography (HPLC). Samples are saponified in sealed 10-ml serum vials in the absence of oxygen, cooled and neutralized by injecting glacial acetic acid into the system. Retinyl acetate and 5,7-dimethyltocol respectively are used as the internal standards. The solution is extracted with hexane and the organic phase is cleaned up on a sodium sulphate/aluminium oxide column. The solution is evaporated under vacuum and dissolved in ethanol for HPLC analysis. A short reversed-phase column packed with RP-18, using methanol as the eluent, allows fast separations of both the vitamins.

Aflatoxin B1-contaminated fruits were sorted out from 250 kg dried figs (five Turkish and three Greek batches) by bright-greenish-yellow fluorescence under UV light. The aflatoxins of the fluorescent figs were extracted by simple soaking in methanol. Aflatoxin B1 was determined by thin-layer chromatography. Parallel to this, an extraction for the determination of aflatoxin B1 was developed by a competitive ELISA and the two methods were compared with each other. In a highly contaminated batch of Turkish figs, statistically there was one fig among 350 which had a high aflatoxin content (greater than 100 ng/g fig) and one fig amongst 140 fruits with an aflatoxin B1 content of greater than 10 ng B1/g fig.

Heptafluorobutyryl isobutyl ester derivatives of amino acids were determined, using the thermionic nitrogen-phosphorus detector. The linearity of the detector (more than 5 decades), allows determinations above 0.3 pMol and 110 nMol, without the need for further dilution. Due to the specificity of the detector, no fractionation or other pretreatment of the samples prior to hydrolysis were necessary. The separation of the amino acid derivatives ranges from fair to excellent when comparing separations on packed columns with those on capillary columns. On the capillary analyser, however, only a few runs could be performed, since it was not available for a long enough period of time. The reproducibility of the determination was high in the monobasic amino acids, with a coefficient of variation (c.v.) of less than 3, but somewhat worse in arginine, histidine, cystine and minor components. Histidine needs an on-column acylation by the co-injection of the hydrolysate with acetic anhydride. The amino acids tryptophan, cysteic acid and methionine sulphone have not been investigated until now. A disadvantage of the procedure compared with other analytical methods is the rather complicated derivatisation, which until now, has not been easily automated. Finally, the practicability of the method is demonstrated by the results of eightfold determinations in 13 heat-treated (canned) food samples.

A continuous flow system was coupled to a high-pressure liquid chromatography (HPLC) system, resulting in an automated system for the determination of amprolium in egg yolk and (chicken) muscle tissue. The sample was diluted (yolk) or extracted (tissue) with water, and the solution obtained was dialysed against water as the recipient stream. Aliquots of the dialysed solutions were pumped onto a short pre-concentration column. By means of the mobile phase, the concentrate was back-flushed onto the analytical column and amprolium was separated from interfering substances, using a reversed phase ion-pair system. Amprolium was post-column oxidized to amprochrome, which was detected fluorometrically. Linear calibration curves for both yolk an muscle tissue were obtained in the 10-250 micrograms/kg range. The detection limit is approximately 3 micrograms/kg. This method was applied to eggs and muscle tissue, which were commercial obtained. Egg yolk was found to be frequently contaminated with low levels of amprolium (29.4% positive of 266 samples investigated; mean concentration of positive samples = 58 micrograms/kg), whereas only a few muscle samples contained detectable levels (4.9% positive of 81 samples investigated; mean concentration of positive samples = 5 micrograms/kg).

Lipid content and composition (classes), susceptibility to UV-catalysed oxidation and carotenoid content were determined in Antarctic krill (Euphausia superba Dana) stored for 72 h at 3 degrees C. Phospholipids making up 80% of krill lipids were observed to undergo the most drastic changes during storage. After 72 h of storage, their content dropped by about 20%; the largest drop was recorded in phosphatidylcholine, its content being reduced by almost half. The amount of free fatty acids increased to about 6% of lipids. No degradation was observed in triacylglycerols, diacylglycerols, and wax esters. Monoglycerides did not appear. The UV-catalysed lipid oxidation rate decreased with deteriorating freshness of krill, as evidenced by a slower oxidation reaction, much lower oxidation maximum attained by lipids from spoiled krill, slower carotenoid decomposition, slower coloration of lipids and a slower absorbance increase at 320 nm. As no significant differences were found between iodine numbers and the carotenoid content of the samples tested, differences in the oxidation rate can be explained by hyperoxide decomposition brought about by products of phosphatidylcholine break-down.

Residues of the contact fungicide Cymoxanil in grapes were determined by a multidimensional multicolumn high pressure liquid chromatography technique (MC-HPLC). The sample pretreatment is a simple water extraction. Further clean-up and trace enrichment of an aliquot of the aqueous acidic sample solution is performed on-line via an automatized microprocessor controlled MC-HPLC system. In the range of 0.05-2.0 mg/kg grapes good linearity is achieved. Recoveries of Cymoxanil added to untreated grapes range between 70% and 80% at 0.05 and 2.0 mg/kg values, respectively, with a reproductibility of s +/- 3% at 0.2 mg/kg (n = 5). The total time for analysis is approximately 30 min.