Optimizacija i validacija ICP-OES metode i ciklične voltametrije za određivanje elementnog sastava i antioksidativne aktivnosti odabranih sorti jagodastog voća
Within this doctoral dissertation, the optimization and validation of the ICP-OES method was performed in order to determine the elemental composition of strawberries, blackberries, raspberries and blueberries. The accuracy of the ICP-OES method ranges from 94.61% to 103.6%. The accuracy of the method ranges from 2.48% to 7.60%. The most abundant macroelement in analyzed samples was K, followed by Ca, P, Mg and Na. The analyzed samples are characterized by a very low sodium content. The most abundant microelement was Mn, followed by Fe, Cu, Zn and Si. The content of Al, Cd and Pb in all analyzed fruit samples was below the prescribed limits and did not pose a risk to human health. The content of total polyphenolic compounds, flavonoids and total anthocyanins in acid methanolic, methanolic, 96% ethanolic, 60% ethanolic, aqueous and acetone extracts was determined by UV/Vis spectrophotometry. The highest content of total polyphenolic compounds, flavonoids and total anthocyanins was detected in acidified methanol extracts. The antioxidant activity of all mentioned extracts was examined by spectrophotometric assays (ABTS, DPPH, FRAP and RP). Blueberry samples exibited the highest antioxidant activity, followed by blackberries, raspberries and strawberries. Optimization of working conditions (scanning speed and pH value of the sample solutions) in cyclic voltammetry was performed in order to determine the antioxidant activity of the samples by electrochemical method. There were 4 peaks observed on cyclic voltammograms. The first anodic peak at potential between 0.310 V and 0.350 V in cyclic voltammograms is due to the oxidation of flavonols (quercetin and its glycosides) and caffeic acid. The second, third and fourth anodic peaks at potentials between 0.426 V and 0.444 V, 0.524 V and 0.540 V, and 0.638 V and 0.756 V, respectively, can be attributed to anthocyanins and hydroxycinnamic acids (ferulic and coumaric acid). A high degree of positive correlation was observed between electrochemical and spectrophotometric in vitro methods for antioxidant activity determination. Identification and quantification of individual polyphenolic compounds (caffeic, ferulic, coumaric and ellagic acids; rutin, kaempferol, quercetin and their glycosides;glycosides of cyanidin, pelargonidine, delfinidine, peonidine, petunidine and malvidin) was performed by HPLC method. The kinetics of thermal degradation of total anthocyanins in berry jams with higher and lower sugar content was investigated. Activation energies (Ea) of thermal degradation reactions of total anthocyanins at high temperatures (90-105 °C) were calculated. The stability of individual anthocyanins in fruit jams was monitored by HPLC. In order to differentiate the tested samples on the basis of the content of elements and individual polyphenolic compounds, as well as on the basis of antioxidant activity, correlation analysis, principal component analysis (PCA) and cluster analysis (CA) were applied.
Biobibliografija: str. 307-312,Bibliografija: str. 291-309. Datum odbrane: 13.09.2022. Analytical Chemistry
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