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In this study, the effect of coffee beans processing (decaffeination and roasting) on their antioxidant capacity and total phenolic content has been investigated. In a total of 64 regular as well as decaffeinated (un)roasted coffee samples, these characteristic parameters were determined spectrophotometrically using the DPPH free-radical method and the Folin-Ciocalteu assay. While the total phenolic content remained unchanged regardless of the processing method used, the antioxidant capacity of the samples varied depending on their treatment being affected mainly by the decaffeination procedure chosen.

This work is focused on monitoring changes in the concentrations of 5-hydroxymethylfurfural, ethanol, and carbohydrates during the mead production using various analytical techniques, namely micellar electrokinetic chromatography with spectrophotometric detection, gas chromatography coupled to flame-ionization detector, and hydrophilic interaction liquid chromatography with refractive-index detector, respectively. In this study, production of three mead samples made by different Czech beekeepers has been monitored. The individual mead fractions were regularly sampled for two months of fermentation and always analysed with the aid of the optimised analytical approach.

The five most common artificial sweeteners were analysed in various samples of food and beverages and other products using hydrophilic-interaction liquid chromatography coupled with mass spectrometry. The optimised method employed Hypersil Gold HILIC analytical column combined with a binary mobile phase of 50 mmol/L ammonium acetate in water (pH 5; A)/acetonitrile (B) operating at a gradient program of 90–65 % B for 10 min. The individual sweeteners were quantified by the calibration curve method and the data obtained compared with the data declared on the packaging.

The aim of this study was to monitor selected pesticides (Carbendazim, Acetamiprid, Thiacloprid, Epoxiconazole, Metconazole, Prochloraz, Deltamethrin, and T-fluvalinate) in honey and mead samples by reversed-phase liquid chromatography with spectrophotometric detection after QuEChERS extraction. The final separation was performed on YMC triart C18 column with mobile phase consisting of water and acetonitrile. The identification of selected pesticides in samples of honey and mead was performed on the basis of retention times conformity with the standards and quantification using the calibration curve method., Cílem této studie bylo sledovat vybrané pesticidy (Carbendazim, Acetamiprid, Thiacloprid, Epoxiconazol, Metconazol, Prochloraz, Deltamethrin a T-fluvalinát) ve vzorcích medu a medoviny kapalinovou chromatografií v systémech s obrácenými fázemi se spektrofotometrickou detekcí po extrakci QuEChERS. Konečná separace byla provedena na koloně YMC triart C18 s mobilní fází sestávající z vody a acetonitrilu. Identifikace vybraných pesticidů ve vzorcích medu a medoviny byla provedena na základě shody retenčních časů se standardy a kvantifikace byla provedena metodou kalibrační křivky.

The storage resistance of 21 selected phenolic compounds present in ten samples of commercially available green tea was monitored using the HPLC/MS/MS over a 16 weeks period using multivariate statistical analysis to compare the different types of packaging. The HPLC/MS/MS method with the computer-aided analysis enabled the fast evaluation of the long-time storage resistance of valuable compounds present in green tea, yielding useful information to customers about their degradation, which affected the sensory properties of the green tea, such as taste and colour. An explanatory data analysis provided an initial visualization of the multivariate data matrix while a factor analysis, hierarchical cluster analysis and discriminant analysis enabled the classification of the green tea samples into clusters according to the storage resistance of the compounds of interest. A significant reduction in the content of all monitored compounds was indicated after 3 weeks of storage, which was also found to be dependent on the type of packaging used. The samples in a plastic box were more stable during long-time storage in comparison to the samples in a paper box., 21 vybraných fenolových sloučenin přítomných v deseti vzorcích komerčně dostupného zeleného čaje bylo monitorováno pomocí HPLC / MS / MS po dobu 16 týdnů. Stabilita těchto látek během skladování byla zhodnocena pomocí vícerozměrné statistické analýzy. Metoda HPLC / MS / MS s vícerozměrnými statistickými metodami (PCA, FA, DA) umožnila rychlé vyhodnocení dlouhodobé odolnosti cenných sloučenin přítomných v zeleném čaji při dlouhodobém skladování a přinesla zákazníkům užitečné informace o jejich degradaci, která ovlivnila senzorické vlastnosti zeleného čaje jako je chuť a barva. Významné snížení obsahu všech sledovaných sloučenin bylo indikováno po 3 týdnech skladování, u kterého bylo také zjištěno, že závisí na typu použitého obalu. Vzorky v plastové krabičce byly během dlouhodobého skladování stabilnější ve srovnání se vzorky v papírové krabičce.

The antioxidant properties of different matrices can be determined using various methods. In this work, two spectrophotometric methods based on the scavenging activity of the radicals DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2’- azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) were used together with a spectrophotometric method based on the ferric reduction power of phenolic compounds. The results obtained using all three methods were compared and discussed for infusions prepared from different parts of stinging nettle (Urtica dioica L.). The relation with the time of harvest and location of grow were also examined. Finally, the antioxidant capacity of all the studied nettle infusions were correlated with the total phenolic content determined using Folin–Ciocalteu reagent.

Secondary reaction of amino acid L-proline with 4-acetamido-o-benzoquinone as a product of the enzymatic oxidation of acetaminophen mediated by mushroom tyrosinase isolated from Agaricus bisporus has been studied by amperometric detection in the batch injection analysis configuration and by ultraviolet-visible spectrophotometry. Actually, this scientific work is focused on finding out whether it would be possible to develop an indirect electrochemical method based on the amperometric biosensing suitable for monitoring of the L-proline in various honey samples. For optimum content of acetaminophen (100 :mol dm–3) and tyrosinase (3.33 :g cm–3), a satisfactory linear range from 0.1 to 0.5 mmol dm–3 L-proline was obtained for absorption maximum at 332 nm. However, it is necessary to mention that the indirect determination of L-proline by the amperometric tyrosinase biosensor still presents a challenge in the field of developing biological sensors for monitoring of this amino acid.

The aim of this study was to monitor the caffeine and glucose content in several energy drinks. The caffeine was determined by (direct) differential pulse voltammetry at a glassy carbon paste electrode in 0.5 mol L–1 sulfuric acid at a potential step of 5 mV, potential amplitude of 40 mV, and the scan rate of 50 mV s–1. The content of glucose was determined using amperometric glucose biosensor in 0.1 mol L–1 phosphate (pH 7.0) buffer solution at a constant voltage of +0.4 V and stirring speed of 400 min–1. The selected samples were analysed and the results obtained compared to those declared by manufactures. Except to three samples, namely "Monster", "Red Bull" (without sugar) and "Spark", the individual results were in good agreement with the declared amounts. Moreover, based on the analyses performed, it can be stated that the energy drinks "Big Shock!" and "Red Bull" are the best source of energy when considering the found total sugar via the glucose content.

In a daily basis, the pharmaceutic and cosmetic industry makes effort in advertising their products with a promise to avoid diseases or health problems. Among one of the most popular substances is nowadays, without doubts, hyaluronic acid (HA). Due to its natural origin allowing its biodegradability and non-toxicity, HA is widely used as a component of joint supplements or as a substance ensuring moisturizing properties. Here, interest is focused on the determination of hyaluronic acid in commonly available non-prescription products using different analytical techniques followed by comparison of the determined content with that declared by manufacturers.

Nowadays, the use of drug-delivery systems becomes more and more popular. The use of the supporting medium for drug substances may serve to delay and control the drug release. Biodegradable polymers, such as hyaluronic acid (HA), represent the most natural materials beneficially used for such systems. In this work, we focused on the preparation of hyaluronic acid nanoparticles using low-molecular weight HA (LMW-HA; 11 and 30 kDa) which is rarely used because the size of the obtained particles is usually higher than those of the high-molecular weight form. To verify the suitability of LMW-HA for the preparation of nano-scale particles, different cross-linking strategies were chosen. The hydrodynamic diameters of prepared nanoparticles and the structure compactness were then compared. Adipic acid dihydrazide was used as a conventional cross-linker which leads to monodisperse nanoparticles (186 nm, 255 nm resp.) and compact structure. The use of bis(3-aminopropyl)amine as a novel approach for covalent cross-linking of HA results in the particles with higher hydrodynamic diameters (592 nm, 317 nm resp.) and with less compact structure. Both strategies were then combined with a goal to reduce the hydrodynamic diameters to the nanoscale format and tighter structure. The results obtained has shown a slight improvement (208 nm, 286 nm resp.), but with negligible effect on the structure of particles.