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The aim of this study was to establish an overview of the HMF (5-hydroxymethylfurfural) content of different vinegar samples. A reverse-phase HPLC method with diode-array detection without extensive sample cleanup was used. The recoveries of HMF in spiked vinegar were found to be in the range of 95−101%. The detection limit was in the range of 80 μg/L. The sample preparation consisted simply of dilution and filtration of the vinegar samples. The HMF content was analyzed in various kinds of vinegar (n = 120) and balsamic vinegar (n = 35). Depending on their HMF content the vinegars could be divided into four groups:  samples with no, low, medium, and high HMF concentrations. Few vinegar samples investigated contained no HMF. Most of the other samples contained HMF in a low range up to 10 mg/L, whereas sherry vinegar and some apple vinegars had concentrations up to 35 mg/L. Only the balsamic vinegars showed a very high concentration of 300 mg/L to 3.3 g/L of HMF. The highest concentrations were found in traditionally produced balsamic vinegar samples. Depending on their age, up to 5.5 g/kg could be determined. Keywords: 5-Hydroxymethylfurfural (HMF); vinegar; balsamic vinegar; HPLC

The solution structure of Escherichiu coli tRNA$' (anticodon GGU) and the residues of this tRNA in contact with the a2 dimeric threonyl-tRNA synthetase were studied by chemical and enzymatic footprinting experiments. Alkylation of phosphodiester bonds by ethylnitrosourea and of N-7 positions in guanosines and N-3 positions in cytidines by dimethyl sulphate as well as carbethoxylation of N-7 positions in adenosines by diethyl pyrocarbonate were conducted on different conformers of tRNA:hr. The enzymatic structural probes were nuclease S1 and the cobra venom ribonuclease. Results will be compared to those of three other tRNAs, tRNAAspp, tRNAPhe and tRNATrp, already mapped with these probes.The reactivity of phosphates towards ethylnitrosourea of the unfolded tRNA was compared to that of the native molecule. The alkylation pattern of tRNATh' shows some similarities to that of yeast tRNAPhe and mammalian tRNATrp, especially in the D-arm (positions 19 and 24) and with tRNATrp, at position 50, the junction between the variable region and the T-stem. In the T-loop, tRNAThr, similarly to the three other tRNAs, shows protections against alkylation at phosphates 59 and 60. However, tRNA:h' is unique as far as very strong protections are also found for phosphates 55 to 58 in the T-loop. Compared with yeast tRNAAspp, the main differences in reactivity concern phosphates 19, 24 and 50.Mapping of bases with dimethyl sulphate and diethyl pyrocarbonate reveal conformational similarities with yeast tRNAPhe. A striking conformational feature of tRNATh' is found in the 3'-side of its anticodon stem, where G40, surrounded by two G residues, is alkylated under native conditions, in contrast to other G residues in stem regions of tRNAs which are unreactive when sandwiched between two purines. This data is indicative of a perturbed helical conformation in the anticodon stem at the level of the 30-40 base pairs.Footprinting experiments, with chemical and enzymatic probes, on the tRNA complexed with its cognate threonyl-tRNA synthetase indicate significant protections in the anticodon stem and loop region, in the extraloop, and in the amino acid accepting region. The involvement of the anticodon of tRNA:h' in the recognition process with threonyl-tRNA synthetase was demonstrated by nuclease S1 mapping and by the protection of G34 and G35 against alkylation by dimethyl sulphate. These data are discussed in the light of the tRNA/synthetase recognition problem and of the structural and functional properties of the tRNA-like structure present in the operator region of the thrS mRNA.The understanding of the specific recognition and aminoacylation of tRNAs by their cognate aminoacyl-tRNA synthetases requires a precise structural knowledge of a number of different tRNA/synthetase systems. With such information it is expected one will find the conformational differences and similarities existing between such different systems and reveal structural rules responsible for the recognition process. From the tRNA point of view, many experimental (see...

New methodologies based on supercritical fluid extraction (SFE) have been developed for the determination of fat-soluble vitamins in processed foods. The results obtained so far indicate that SFE is well suited to extraction of fat-soluble vitamins from food products, although validation work is required to establish accuracy and precision. The vitamins investigated were A, E and beta-carotene, and the processed foods were UHT milk, milk powder, minced meat, liver paste, infant formula, canned baby food and margarine. Extraction equipment employed analyte collection on either a solid-phase trap or in a solvent. After extraction, the samples were saponified and the vitamins determined using reversed-phase liquid chromatography with ultraviolet or fluorescence detection. Sample throughput was at least 12 samples day(-1), i.e. at least twice the number achievable with a conventional extraction methodology. The detection limits for the vitamins in different processed foods were well below 0.1 microg g(-1). Recoveries (in comparison with vitamin levels obtained using conventional solvent extraction) were close to 100% for experienced personal with access to modern automatic equipment. To reach this level, it was necessary to protect the vitamins with an antioxidant during the different steps of the analysis procedure, to add methanol or ethanol to the extraction cell to facilitate the analyte extraction from the food matrix, and when using a solid-phase trap, to employ a fractionated extraction-elution procedure to prevent breakthrough losses. The developed methods were tested in a validation exercise between five laboratories, which had taken part in the method development, and in an intercomparison between 10 laboratories including laboratories with less experience of vitamin determination. The within-laboratory RSD was generally < or = 11%. The average of the between-laboratory relative standard deviation (RSD) was about 23% in the validation, and increased to about 40% in the intercomparison. Ruggedness tests performed at different steps of the project showed that different types and models of equipment did not give large differences in recoveries. Thus, the increasing RSD can largely be ascribed to differences in experience in vitamin analysis of the participants.