In the present paper the results regarding the influence of UV-irradiation with 254 nm wavelength on the molecular weight of chitosan are presented. The concentration of chitosan solution was 0.5%(w/w) in 0.1 M acetic acid. The degree of deacetylation, determined by potentiometric titration in an acidic solution by alkaline, was 81%. Viscosity-average molecular weight of chitosan was determined using an Ubbelohde capillary viscometer. Mark–Houwink equation for the calculation of molecular weight was applied. The results showed that the viscosityaverage molecular weight of chitosan was decreasing with increasing time of exposure to UV-irradiation. Spectroscopic analysis of UV-Vis and FTIR confirmed the photodegradation processes of chitosan. The increasing absorbance in UV-Vis spectra indicated the formation of new chromophoric groups after UV-irradiation of chitosan. Microscopic studies showed changes on the surface of the irradiated films of chitosan and decrease of the surface roughness.
The biodegradable blends of chitosan and starch with different component ratios were prepared by casting method. Obtained thin films were UV-irradiated (λ = 254 nm) and changes in chemical structure were monitored using FTIR and UV-Vis spectroscopies. It was found that the chitosanstarch blends were more susceptible to UV irradiation comparing to pure starch specimen. FTIR spectra of blends suggest partial interactions between chitosan and starch macrochains.
The free radical scavenging activity of ethanolic extracts of propolis (EEP) at the concentrations of 3%, 7%, and 10% was examined. The impact of storage temperature and exposure to ultraviolet (UV) light on the interactions of extracts of propolis with the model DPPH free radicals was also determined. The quenching of an X-band electron paramagnetic resonance spectra of DPPH free radicals by the extracts stored at room temperature, heated at the temperature of 50 oC and exposed to UV-irradiation, were compared. The examined propolis ethanolic extracts revealed an antioxidative character. The storage of the samples at a higher temperature (50 oC) caused a decrease of the scavenging activity equaling to 7% and 10% EEP. UV-irradiation of the 3% EEP increased the quenching of DPPH free radical lines. The reverse effect was observed for the 7% and 10% propolis extracts. The 3% ethanolic extract of propolis is more stable for storage at 50ºC, and less than other analyzed EEP susceptible for UV-irradiation. Alterations of the antioxidative properties of the analyzed EEP and changes in the kinetics of their interactions with free radicals, indicate that 3%, 7%, and 10% propolis extracts should not be exposed to the temperature of 50 oC and UV-irradiation.
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.