Author:

Keywords:

Dihydrostevioside, fluorescence detection, Fenton reaction, glucose, sucrose, OH-radical

Abstract:

Steviol glycosides (SVGlys) are well known as natural, non-caloric sweeteners. Not only their use as a sugar substitute is interesting, but also positive pharmaceutical effects to the human health were observed after intake of larger doses. These positive effects can be ascribed to the scavenging activity of SVGlys on reactive oxygen radicals. Two aspects were examined with regard to the scavenging capabilities of SVGlys. The first relates to the fact that SVGlys are composed of sugars, while the other related to the steviol (SV) scaffold containing a double bond. In this project scavenging activities of rebaudioside A (RebA), stevioside (Stev) and leaf extract were compared to those of glucose (Glc) and sucrose (Suc). Also experiments concerning a possible correlation between scavenging activity and sugars or their number of OH-groups were done. To check if the double bond of the steviol scaffold is responsible for the scavenging activity, experiments with the hydrogenated compound dihydro-stevioside (DH-Stev) were done. The scavenging activity was measured by means of a competitive reaction of OH-radicals from the Fenton reaction between terephtalic acid and the SVGly. The scavenging capability was expressed as the inhibitory concentration in mM (mmol/L) which reduces 50% of the radicals (IC50). Some optimization concerning temperature, reaction time, and volume of the reaction mixture were performed. Different scavenging capabilities were observed at 37°C and 70°C. At temperature of 70°C and an incubation time of 16 hours, reproducibility was ensured. SVGlys showed higher scavenging activities than sugars. The IC50 values of RebA, Stev and DH-Stev were similar. A good quadratic correlation between scavenging activity and the number of OH-groups was found. The scavenging activity of SVGlys is apparently not caused to a major extent by the double bond in the steviol moiety, as the IC50 concentration for DH-Ste does not differ much from that of Ste. To further prove the correlation between scavenging activity and the number of OH-groups of sugars further experiments are suggested.