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Study of beer photodegradation by optical methods
Tayari, Tomáš ; Gabriel, Petr (advisor) ; Lustig, František (referee)
If beer is exposed to light radiation, it very quickly creates an undesirable unpleasant so- called lightstruck flavor. According to current ideas, 3-methyl-2-butene-1-thiol (MBT) is responsible for the lightstruck flavour in beer. The formation of MBT is associated with non- enzymatic reactions in which isohumulones and sulfuric components of amino acids and their derivatives emerge. Riboflavin (vitamin B2), which absorbs light and reacts with isohumulones in the excited state, acts as a photocatalyst. Light degrades riboflavin into its photoproducts. The aim of this work was to verify the possibilities of optical detection of beer photodegradation. An apparatus for detecting spectrally differentiated fluorescence intensity with a replaceable excitation LED source was constructed. The apparatus allows the excitation emission matrix of fluorescence (EEM) to be measured with selected excitation wavelengths. The fluorescence signal is scanned by a spectrophotometer with 90 ř offset to the excitation beam and corrected by its intensity which was detected in a straight line. The light source and detectors are connected to the measuring chamber via optical fibers. The fluorescence spectra of riboflavin, its photoproduct lumichrome and samples of fresh and defined light-damaged beer were measured on the...
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The Comparison of Methods for the Determination of Riboflavin in Medical Preparations.
Houšť, Jiří ; Nesměrák, Karel (advisor) ; Rychlovský, Petr (referee)
Cílem této bakalářské práce bylo porovnat vybrané analytické metody sloužící ke stanovení riboflavinu v určených léčivých přípravcích. Mezi metody, u kterých probíhalo jejich zhodnocení z hlediska pravdivosti, preciznosti a časové náročnosti, byla zařazena spektrofotometrie v UV/VIS oblasti, spektrofluorimetrie a voltametrie. Jednotlivá stanovení probíhala na pěti různých přípravcích, které se nacházely ve čtyřech lékových formách: tablety, potahované tablety, lyofilizáty pro přípravu infuzního roztoku a sirup. Nejpravdivější výsledky poskytlo spektrofotometrické stanovení v UV/VIS oblasti, pravým opakem bylo stanovení voltametrické. Nejpreciznější metodou byla spektrofluorimetrie. Časově nejnáročnější se ukázala voltametrie, nejméně času naopak zabralo spektrofotometrické stanovení v UV/VIS oblasti. Klíčová slova: riboflavin, UV/VIS spektrofotometrie, fluorimetrie, voltametrie
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Hyaluronane interactions with hydrophobic solutes
Slezáková, Dagmar ; Knotková,, Kateřina (referee) ; Pekař, Miloslav (advisor)
The diploma thesis is based on the study of hydrophobic interactions of the native hyaluronan with selected solutes. On the basis of a literature search were chosen fluorescent probes and fluorescing biologically active substances, which are useful for investigation of colloids as 6-(p-toluidino)-2-naphthalenesulfonic acid (polarity probe), lipophilic vitamin (±)-alpha-tocopherol, pyrene (polarity probe) and finally hydrophilic vitamin riboflavin. In the experimental part of this thesis was studied the influence of solvents with different polarities, or more precisely dielectric constant, on the emission spectra, as well. There were investigated interactions of native hyaluronan with TNS and then interactions, which were influenced by the ionic strength. Such influenced interactions were not observed, that was probably due to the strong solvation´s wrapping of the hyaluronan. Interactions were observed after the process of lyophilisation followed-up by the rehydratation of the samples. For the next study of interactions the riboflavin was chosen and was investigated the REES effect in the native hyaluronan in different concentrations of its different molecular weights. In this case were not observed any shifts in the emission maximum with the excitation wavelenght shift and that is why the interactions of hyaluronan with riboflavin were not demonstrated in the field of chosen concentrations. By using another probe alpha-tocopherol was investigated the associative behaviour of hyaluronan and moreover was observed anisotropy of alpha-tocopherol in different concentrations of different molecular weights of native hyaluronan. The anisotropy reached high values in contrast to the reference solute that was the mixture of glycerol and ethanol. The anisotropy depended more on the molecular weight than on the concentration of hyaluronan. Interactions of hyaluronan were also studied by using the polarity probe pyrene in different concentrations of different molecular weights of the hyaluronan. The pyrene 1:3 ratio did not show the concentration dependence within the chosen concentrations except for the molecular weight 253.9 kg mol–1. Both probes alpha-tocopherol and pyrene were performed by the process of lyophilisation followed-up by the rehydratation, which improved interactions of these probes with hyaluronan.
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