Czech Journal of Food Sciences, 2003 (vol. 21), issue 1
13C CP/MAS NMR spectra of pectins: a peak-fitting analysis in the C-6 region
A. Synytsya, J. Opíková, J. Brus
Czech J. Food Sci., 2003, 21(1):1-12 | DOI: 10.17221/3471-CJFS 
13C CP/MAS NMR spectra of pectin samples were measured and interpreted. The influence of methylesterification and O-acetylation on chemical shifts of pectin carbons was studied using model pectate, pectinates, and their acetylated derivatives. The spectra were analysed also by peak fitting in C-6 region to obtain the values of methylation (DM), amidation (DAm) and acetylation (DAc), degrees. The results were in a good agreement with both convenient methods (photometry, elemental analysis) and the NMR method based on the relative areas of OCH3 (DM) and CH3 (DAc) resonances.
Determination of vinyl chloride monomer in food contact materials by solid phase microextraction coupled with gas chromatography/mass spectrometry
I. Jordáková, J. Dobiáš, M. Voldich, J. Poustka
Czech J. Food Sci., 2003, 21(1):13-17 | DOI: 10.17221/3472-CJFS
The present study concerns the optimisation of the headspace solid phase microextraction (HS/SPME) combined with gas chromatography/mass spectrometry (GC/MS) for the vinyl chloride monomer determination. Samples of PVC materials were analysed using the Carboxen/Polydimethylsiloxane (CX/PDMS) 75 µm fibre. For this fibre, the achieved limit of detection was 0.05 µg/kg, and that of quantification 0.17 µg/kg, respectively, with RSD 5%. The levels of VCM found ranged from 0.29 to 0.44 mg/kg, in the case of foil, the VCM content determined was 3.65 mg/kg which means that the maximal limit allowed was exceeded.
Changes on Storage of Peanut Oils Containing High Levels of Tocopherols and β-Carotene
Jan Pokorný, Lucie Parkányiová, Zuzana Réblová, Ludmila Trojáková, Hidetoschi Sakurai, Tatsuo Uematsu, Mitsuyoshi Miyahara, Tomohiro Yano
Czech J. Food Sci., 2003, 21(1):19-27 | DOI: 10.17221/3473-CJFS
We compared changes of tocopherols and b-carotene in a traditional peanut oil (cultivar Virginia, 30.5% linoleic acid) with a modified high-oleic peanut oil (cultivar SunOleic, 2.7% linoleic acid), developed in Florida, USA. The initial contents of tocopherols and trace lipid oxidation products, including hydroperoxides, were of the same order in both oils. The stability against oxidation was tested under the conditions of the Schaal Oven Test at 40 and 60°C, in emulsion, using AOM, Rancimat, and the apparatus Oxipres at 100°C. Tocopherols were determined using HPLC with an electrochemical detection (without previous saponification). The high-oleic...
Wheat flour dough alveograph characteristics predicted by NIRSystems 6500
M. Hrušková, P. Šmejda
Czech J. Food Sci., 2003, 21(1):28-33 | DOI: 10.17221/3474-CJFS
Rheological quality of wheat dough prepared from 130 variety, stream, and commercial wheat flour samples (wheat harvest 1999, 2000 and 2001) was assessed with alveograph. Spectra of all samples were measured on spectrograph NIRSystems 6500. Calibration equations with cross and independent validation for all rheological characteristics were computed by NIR Software ISI Present WINISI II using MPLS and PLS methods. The quality of the prediction was evaluated by the coefficient of correlation between the measured and the predicted values from cross and independent validation. A statistically significant dependence between the predicted and the measured...
Properties of thin metallic films for microwave susceptors
J. Česnek, J. Dobiáš, J. Houšová, J. Sedláček
Czech J. Food Sci., 2003, 21(1):34-40 | DOI: 10.17221/3475-CJFS
Thin Al films of varying thickness, i.e. 3 to 30 nm, were deposited onto polyethylene-terephthalate film by evaporation in the vacuum of 3 × 10-3 Pa. The dependence of DC (direct current) surface resistance on thickness was measured using a four-point method. The surface resistance exhibits the size effect in accordance with the Fuchs-Sondheimer theory. The microwave absorption properties of the prepared films of various metallization thickness were measured in a microwave field at the microwave power of 1.8 mW. The maximum microwave absorption at 2.45 GHz was found to occur in a layer of optical density of about 0.22.