Enhancement of quercetin water solubility with steviol glucosides and the studies of biological properties

Abstract

Background: Quercetin, a flavonol contained in various vegetables and fruits, has various biological activities including anticancer, antiviral, anti-diabetic, and anti-oxidative. However, it has low oral bioavailability due to insolubility in water. Thus, the bioavailability of quercetin administered to human beings in a capsule form, was reported to be less than 1%, with only a small percentage of ingested quercetin getting absorbed in the blood. This leads to certain difficulties in creating highly effective medicinesMethods: Quercetin-rubusoside and quercetin-rebaudioside were prepared. The antioxidant activities of quercetin and Q-rubusoside were evaluated by DPPH radical scavenging method. Inhibition activities of quercetin and Quercetin-rubusoside were determined by measuring the remaining activity of 3CLpro with 200 μM inhibitor. The inhibition activity of quercetin, rubusoside and quercetin-rubusoside were determined by measuring the activity of human maltase which remains at 100 μM rubusoside or quercetin-rubusoside. The mushroom tyrosinase inhibition was assayed with the reaction mixture contained 3.3 mM L-DOPA in 50 mM potassium phosphate buffer (pH 6.8), and 10 U mushroom tyrosinase/ml with or without quercetin or quercetin-rubusoside. Results: With 10% rubusoside treatment, quercetin showed solubility of 7.7 mg/ml in water, and its solubility increased as the concentration of rubusoside increased; the quercetin solubility in water increased to 0.83 mg/mlas rubusoside concentration increased to 1 mg/ml. Quercetin solubilized in rubusoside solution showed DPPH radical-scavenging activity and mushroom tyrosinase inhibition activity, similar to that of quercetin solubilized in dimethyl-sulfoxide. Quercetin-rubusoside also showed 1.2 and 1.9 folds higher inhibition activity against 3CLpro of SARS and human intestinal maltase, respectively, than those of quercetin in DMSO.Conclusions: Quercetin can be solubilized in water with rebaudioside or rubusoside treatment. As Ru concentration increases, the solubility of quercetin in water increases. The solubilization of quercetin in Ru solution did not reduce its biological functions such as the DPPH radical-scavenging and mushroom tyrosinase activity; also, quercetin-rubusoside increased the inhibition activity against the 3CLpro of SARS and human intestinal maltase, when compared with the activity of quercetin in DMSO. Thus, rubusoside and rebaudioside are promising compounds which enhance the solubility of poorly water soluble compounds.Keywords: rubusoside, rebaudioside, flavonol, quercetin, human maltase, 3CLpro

Characterization of quinoa (Chenopodium quinoa) fermented by Rhizopus oligosporus and its bioactive properties

“…Antioxidant activities of quinoa or fermented quinoa were evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging method (Nguyen et al 2015 ). Quinoa extracted powder were diluted in 70% ethanol and centrifuged at 13,572× g for 10 min.…”

Activity of Anthracenediones and Flavoring Phenols in Hydromethanolic Extracts of Rubia tinctorum against Grapevine Phytopathogenic Fungi

“…Nonetheless, taking into consideration that the antifungal activity of both COS and stevioside alone was substantially lower than that of the R. tinctorum extract, and given that the use of most free anthraquinones in pharmaceutical industries is limited by their poor water solubility and low bioavailability [ 64 ], the observed strong synergistic behavior with COS and stevioside should probably be referred to a solubility and bioavailability enhancement through the formation of inclusion compounds or conjugate complexes (discussed, in the case of chitosan, in the recent review paper by Detsi et al [ 65 ] and, for steviol glycosides, in the works by Nguyen et al [ 66 , 67 ]). Examples of antifungal activity enhancement via the formation of conjugate complexes against GTDs have been previously reported in [ 25 , 26 , 68 ], albeit with worse EC 50 and EC 90 values than those reported in this work.…”

Composition and biochemical properties of l‐carnitine fortified Makgeolli brewed by using fermented buckwheat

“…Makgeolli. Quercetin has higher antioxidant activity compared to rutin (SC 50 of quercetin = 37.4 μM, SC 50 of rutin ≥1,000 μM) (Kong, Mat-Junit, Aminudin, Ismail, & Abdul-Aziz, 2012;Nguyen et al, 2015). In addition, an increase of l-carnitine contained in fermented buckwheat Makgeolli could increase the antioxidant activity because l-carnitine is an antioxidant compound that can prevent oxidative stress and regulate cellular respiration by nitric oxide (Brown, 1999).…”