Rabbit Cd,Zn-metallothionein (Cd,ZnMT), synthetically prepared Cd-metallothionein (CdMT), and apometallothionein (apoMT) have been studied at a mercury electrode and at two types of carbon electrode. At the mercury electrode, different metallothioneins can only be distinguished in cases where their contact with the mercury electrode surface is short. With prolonged time, a mercury compound is formed and its peaks prevail over all the original MT peaks. This conclusion is supported by comparison with apoMT voltammetry at mercury and carbon electrodes. At glassy carbon or carbon composite electrodes, apoMT can be distinguished and determined in the presence of MTs. For both MTs studied, the formation of metal-free S groups can be observed with prolonged electrolysis at negative potentials; this process is reversible and after several CV cycles, the original structure is reestablished.

No abstract

The hoppy aroma in beer is characterized by an overall pleasant profile. The impacts of five Czech hop cultivars, Rubin, Saaz, Vital, Harmonie, and Kazbek, were tested on the hop aroma of the resulting beers, compared with a control beer sample, which was hopped with a commercial hop extract during wort boiling. GC-MS analysis was used for the identification and quantification of aroma-active compounds in the hops and beer. Dry hopping was successful in terms of improving the hoppy aroma in beer. Odorants such as β-myrcene, linalool, geraniol, β-citronellol, humulene epoxide I, and 2-methylbutyl-2-methylpropanoate were found at higher concentrations than the control in all dry-hopped beers. To quantify the success of dry hopping, the transfer rates of hop odorants were calculated. Those of linalool, geraniol and humulene epoxide I were adequate, whereas the transfer rates of polar compounds, e.g., β-myrcene, were relatively low, mostly due to their polarity. Changes in hop oil constituents were clearly notable, with the generation of β-citronellol, the release of other terpene alcohols from their glycosides or oxidation of α-humulene. Yeast metabolism also played an important role in these changes.

Conductometric assessment of electrolyte leakage from spring barley plant organs subjected to higher cadmium concentrations 10-2 – 10-4 mol l-1 revealed serious tissue damage. Therefore plants were grown under controlled environment conditions in a phytotron in Knop´s nutrient solution in two variants – the control variant without cadmium and experimental variant treated during the growth of plants with CdCl2 solution of 10-5 mol l-1. Barley plants were then separated into roots, residual caryopses, leaf bases, and leaves. Lyophilized samples were analyzed for the uptake and redistribution of cadmium, calcium, copper, iron, zinc, and manganese in plant organs by spectrometric methods. Cadmium caused significant decrease of calcium and manganese levels in all analyzed plant parts indicating that cadmium was a distinctive antagonist to intake of these metals. Cadmium treatment also lowered amounts of zinc and iron in roots. An opposite trend was characteristic for Cu, where Cd stress caused significant Cu increase and retention in roots and significant decrease in leaves. The combined usage of the electroanalytical technique - conductometry and spectrometric methods (ICP-OES, AAS) proved to be a useful tool for monitoring of tissue damage and intake and transfer of cadmium and macro- and microelements into barley organs.

Cd, Cu and Zn complexes of two synthetically prepared peptides, (g-Glu-Cys) 2 -Gly and (g-Glu-Cys) 3 -Gly, were studied as models of plant metallothioneins by several voltammetric methods. Reduction peak of the complex in which the stechiometric ratio of molar concentrations of Cd(II) and peptide corresponds to coordination of one Cd(II) by four sulfur atoms (E p = ¹814 mV to ¹910 mV, DPV) is suitable for speciation. CSV after adsorption of Cu(I) complex on HMDE is also convenient, and two peaks (E p = ¹817 mV to ¹850 mV and E p = ¹940 mV to ¹953 mV) are attributed to plant MT with Cu(I). Cd and Cu complexes can be distinguished by different dependences for adsorptive accumulation of complexes on HMDE. In both cases the presence of zinc ions interferes with voltammetric speciation. Results of voltammetric studies were applied to the analysis of algal extracts, prepared from alga Chlorella, which was grown in cadmium enriched medium. Successful voltammetric identification of plant metallothionein in this type of material has been performed, in agreement with results from AAS and UV spectroscopy.