Stable isotope dilution assays (SIDAs) for the determination of the most important mycotoxins of the black mold Alternaria, namely, alternariol and alternariol monomethyl ether, have been developed. For this purpose, deuterated alternariol and alternariol methyl ether were synthesized by palladium catalyzed protium-deuterium exchange from the unlabeled toxins. Reaction conditions were chosen in such a manner that the formation of the [(2)H(4)]-isotopologues was favored. The synthesized products were characterized by LC-MS, NMR, and UV-spectroscopy. On the basis of the use of [(2)H(4)]-alternariol and [(2)H(4)]-alternariol methyl ether as internal standards, SIDAs were developed and applied to the determination of alternariol and alternariol methyl ether in beverages using LC-MS/MS. Method validation revealed a high sensitivity, i.e., low limits of detection (alternariol, 0.03 microg/kg; alternariol methyl ether, 0.01 microg/kg) and limits of quantitation (alternariol, 0.09 microg/kg; alternariol methyl ether, 0.03 microg/kg), respectively. Recovery from spiked apple juice was 100.5 +/- 3.4% for alternariol (range 0.1-1 microg/kg) and 107.3 +/- 1.6% for alternariol methyl ether (range 0.05-0.5 microg/kg). Interassay precision (expressed as coefficient of variation, CEV) for alternariol was 4.0% (7.82 +/- 0.31 microg/kg; vegetable juice, naturally contaminated) and 4.6% (1.04 +/- 0.05 microg/kg; grape juice, naturally contaminated). For alternariol methyl ether, a CEV of 2.3% (0.79 +/- 0.02 microg/kg; vegetable juice, naturally contaminated) was obtained. Analysis of fruit juices showed low contamination with alternariol and alternariol methyl ether in general, but higher values of both toxins were found in wine and vegetable juices. The values for alternariol were higher than those for alternariol methyl ether in nearly any case. However, the developed SIDA has proven to be optimally suited for further studies on alternariol and alternariol methyl ether content in food samples to obtain further insight into possible health hazards for the consumer.
A stable isotope dilution assay (SIDA) for the Alternaria mycotoxin tenuazonic acid was developed. Therefore, [(13)C(6),(15)N]-tenuazonic acid was synthesized from [(13)C(6),(15)N]-isoleucine by Dieckmann intramolecular cyclization after acetoacetylation with diketene. The synthesized [(13)C(6),(15)N]-tenuazonic acid was used as the internal standard for determination of tenuazonic acid in tomato products by liquid chromatography tandem mass spectrometry after derivatization with 2,4-dinitrophenylhydrazine. Method validation revealed a limit of detection of 0.1 μg/kg and a limit of quantitation of 0.3 μg/kg. Recovery was close to 100% in the range of 3-300 μg/kg. Determination of tenuazonic acid in two samples of different tomato ketchups (naturally contaminated) was achieved with a coefficient of variation of 2.3% and 4.7%. Different tomato products (n = 16) were analyzed for their content of tenuazonic acid using the developed SIDA. Values were between 15 and 195 μg/kg (tomato ketchup, n = 9), 363 and 909 μg/kg (tomato paste, n = 2), and 8 and 247 μg/kg (pureed tomatoes and comparable products, n = 5).
As a basis for sodium reduction, interactions between sodium and wheat bread ingredients and their impact on salt perception in bread crumb were examined. The theoretical sodium binding capacities of wheat proteins revealed that a maximum amount of 0.24% NaCl (based on flour) could be bound in bread crumb by ionic interactions between sodium ions and acidic amino acid side chains. However, the sodium binding capacities of wheat proteins, determined by a magnetic beads assay and a sodium-selective electrode, were only about 0.002% NaCl. They were negligible concerning the sensory perception of saltiness, as 0.075 and 0.3% NaCl were the lowest noticeable differences using bread containing 0 and 1% NaCl as a reference, respectively. Extracting bread crumb in a mastication simulator with ultrapure water, buffer solutions, and artificial and human saliva revealed that interactions between sodium and wheat bread ingredients were sufficiently weak to enable complete sodium extraction during simulated mastication.
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