Analiza katehina, procijanidina, makro i mikroelemenata u crnoj, mlečnoj, i beloj čokoladi i kakaou u prahu i njihov antioksidativni potencijal

The aim of this doctoral dissertation was то determinе the chemical composition, as well as то investigatе of the antioxidative activity of white, milk, dark chocolate and cocoa powder samples. The total polyphenols, flavonoids, as well as total and monomer anthocyanins, were determined using UV/Vis spectrophotometry. Spectrophotometric methods (ABTS, DPPH, FRAP, and PFRAP) and electrochemistry method – cyclic voltammetry (CV) were used to test antioxidant activity. Тhere were three anode peaks оn cyclic voltammograms. The first and the third anodic current peaks can be ascribed to the oxidation of catechin-type flavonoids, while the second peak can be ascribed to the oxidation of phenolic acids. Procyanidins did not show any visible waves. The highest antioxidant activity was present in dark chocolate and cocoa powder samples, followed by milk and white chocolate samples. This is in agreement with the total content of polyphenols and flavonoids in the tested samples. The identification and quantification of polyphenolic compounds (protocatechuic acid, (+)-catechin, (-)-epicatechin, procyanidins B1, B2, B3 and B4, cyanidin-3-O-galactoside and cyanidin-3-O-arabinoside) and alkaloid theobromine were carried out using HPLC chromatography. The influence of storage temperature (4 °С – 35 °С) and thermal processing (95 °С – 125 °С) on the stability of catechin-type flavonoids, total flavonoids, and anthocyanins in dark chocolate and cocoa powder samples was also studied. During storage and heating, the cocoa powder and dark chocolate flavonoids and anthocyanins degraded more quickly with an increase in temperature. To determine macro and microelements, the ICP-OES methods were optimized and validated. Among macroelements, K is most abudant in the samples of cocoa powder, followed by samples of dark, milk and white chocolate. This suggests that the content of K is directly related to the contribution of cocoa parts. After K, the content of P, Ca, Na, Mg is highest in white chocolate, followed by the milk chocolate, dark chocolate, and cocoa powder samples. Among the microelements, the most abundant are Fe, Si, and Zn. The content of potentially toxic metals, Pb and Cd, is below the maximum permissible levels (MPL) prescribed by national and world regulations. The differentiation of the tested samples based on the content of metals and polyphenol compounds, as well as based on their antioxidative activity, was done using principal component analysis (PCA) and cluster analysis (CA)