Kinjal K. Kubavat, Sanman Samova, Hetal Doctor, Gaurang M. Sindhav and Ramtej J. Verma
1. Hollman, P.C.; de Vries, J.H.; van Leeuwen, S.D.; Mengelers, M.J.; Katan, M. B. Absorption of dietary quercetin glycosides and quercetin in healthy ileostomy volunteers. Am. J. Clin. Nutr . 1995 , 62 , 1276-1282.
2. Bronner, C.; Landry, Y. Kinetics of the inhibitory effect of flavonoids on histamine secretion from mast cells. Agents Actions 1985 , 16 , 147– 151.
3. Reutrakul, V.; Ninguek, N.; Pohmakotr, M.; Yoosook, C.; Napaswad, C.; Kasisit, J.; Santisuk, T.; Tuchinda P. Anti HIV-1 flavonoid glycosides from
Martina Danihelová, Miroslav Veverka and Ernest Šturdík
Novel quercetin derivatives were prepared to change its physicochemical properties and effects on activity of proteolytic enzymes. For them preparation, the selective protection procedures some of the quercetin hydroxyl groups and acylation of the others with acylchlorides were used. The ability of these compounds to inhibit the activity of serine proteases e.g. trypsin, thrombin, urokinase and elastase was studied. In micromolar range, tested derivatives were the most potent inhibitors of thrombin. There was estimated better inhibition of thrombin for prenylated, acetylated, feruloyl and caffeoyl quercetin esters. Slight inhibitory effect of all quercetin derivatives on elastase was found. Among tested derivatives only diquercetin displayed better inhibiton. Trypsin and urokinase were inhibited by quercetin at comparable level. Slight improvement in inhibitory effect of trypsin and urokinase was seen for chloronaphtoquinone quercetin that revealed enhanced inhibiton of thrombin, too. However, no influence on elastase activity was determined for this compound. Obtained results indicate that certain modifications of quercetin structure could improve its biological properties.
Silvia Mošovská, Patrícia Petáková, Michal Kaliňák and Anna Mikulajová
The evaluation of antioxidant potential of food has received much attention in recent years. Antioxidant compounds can scavenge free radicals and thereby can protect the human body from free radicals. This study was focused on the isolation of curcuminoids from the dried turmeric rhizome, and studying their antioxidant activity. The presence of curcuminoids was identified in turmeric sample by Nuclear Magnetic Resonance (NMR) analysis. Since neutral curcumin is known to be poorly soluble, the synthesis of curcumin-cyclodextrin and curcumin-phospholipid complexes was also performed. The antioxidant activity of isolated curcuminoids was assessed by two methods (ABTS and FRAP assay) and their scavenging activities were compared with those of prepared complexes. The ability to reduce ABTS radical cation decreased as follows: quercetin > trolox > curcuminoids > curcumin-cyclodextrin complex > curcumin-phospholipid complex. The reducing potential of tested samples in descending order was quercetin > trolox > curcumin-cyclodextrin complex > curcuminoids > curcumin-phospholipid complex.
Anna Mikulajová, Dominika Šedivá, Eva Hybenová and Silvia Mošovská
Common buckwheat (Fagopyrum esculentum) and tartary buckwheat (Fagopyrum tataricum) cultivars originating in different world countries were investigated and compared for their quantitative and qualitative abundance of phenolics and flavonoids. Moreover, the antioxidant properties were tested using two different methods. The total phenolic and total flavonoid content ranged from 0.897 to 4.226 mg GAE g−1 dw and from 0.238 to 4.626 mg rutin g−1 dw, respectively. Flavonoids — rutin, quercetin, and hydroxybenzoic acids — gallic, protocatechuic, vanillic and syringic were identified and quantified. Rutin was the most abundant flavonoid and protocatechuic acid was the most abundant phenolic acid in evaluated cultivars. All cultivars showed significant antiradical properties, but their chelating activity was weak. The German cultivar of tartary buckwheat Lifago had significantly higher phenolic content and better antioxidant properties than other cultivars. The content of rutin was 24 times higher and free radicals scavenging activity about 70 % higher than the average value of other cultivars.
Martin Michalík, Ján Rimarčík, Vladimír Lukeš and Erik Klein
Very recently, a report on the antioxidant activity of flavonoids has appeared, where authors concluded that Hydrogen Atom Transfer mechanism represents the thermodynamically preferred mechanism in polar media (https://doi.org/10.1016/j.foodres.2018.11.018). Unfortunately, serious errors in the theoretical part of the paper led to incorrect conclusions. For six flavonols (galangin, kaempferol, quercetin, morin, myricetin, and fisetin), reaction enthalpies related to three mechanisms of the primary antioxidant action were computed. Based on the obtained results, the role of intramolecular hydrogen bonds (IHB) in the thermodynamics of the antioxidant effect is presented. Calculations and the role of solvation enthalpies of proton and electron in the determination of thermodynamically preferred mechanism is also briefly explained and discussed. The obtained results are in accordance with published works considering the Sequential Proton-Loss Electron-Transfer thermodynamically preferred reaction pathway.
Mariana Sandu, Lucian Mihail Bîrsă and Lucian Gabriel Bahrin
developmental regulators. Curr. Opin. Plant Biol. 2005, 8, 317-323.
6. Liu, C. W.; Murray, J. D. The Role of Flavonoids in Nodulation Host- Range Specificity: An Update. Plants. 2016, 5, 33.
7. Luo, M.; Wan, S.; Sun, X.; Ma, T.; Huang, W. Interactions between auxin and quercetin during grape berry development. Sci. Hortic- Amsterdam. 2016, 205, 45-51.
8. Yin, R.; Han, K.; Heller, W.; Albert, A.; Dobrev, P. I.; Zazimalova, E.; Schaffner, A. R. Kaempferol 3-O-rhamnoside-7-O-rhamnoside is an endogenous flavonol inhibitor of polar