A First Approach to the Optical and Antioxidant Properties of Propolis Collected at Different Sites of Algarve Region

摘要

Propolis is a natural honeybee product known to be beneficial to human health. It has a very complex chemical composition, highly dependent on the respective collection site, although phenolic compounds stands for the major fraction responsible for propolis biological activities. Up to now, all assays for determining composition and biological properties have been done after extraction of the raw material with appropriate solvents. Studies concerning the properties of Portuguese propolis are scarce. In the present work, propolis collected at three different sites in the Portuguese province of Algarve, differing in both the soil and vegetation, were compared in respect to their optical and anti-oxidant properties. Two main goals were attempt: 1) to check the antioxidant activity of the methanol extracts of propolis and 2) to test the applicability of the Visible/Near infrared spectroscopy (Vis/NIRS) on the propolis raw material and to determine the best conditions to obtain the respective reflectance spectra, in order to establish in the long-term a rapid and non-invasive technique for propolis screening collected in the Algarve area. The amount of total phenols in propolis ranged from 1,710 to 4,195 mg/ml. The highest phenols levels were predominantly found in Maqui samples. The hierarchy of ability for scavenging DPPH radicals was maqui area > mountain area > transition area. Additionally, Maqui samples were shown to be the best antioxidants, since they were able to promote more easily the reduction of Fe(III) to Fe(II). The Vis/NIR diffuse reflectance spectra obtained differed according to the collecting sites, although all of them exhibited a peak around 875nm. Mountain North samples had the highest R values at all wavelengths, followed by the Mountain South. Minimal values were shown by the Transition Zone samples, particularly from 650 upwards. Maqui samples R spectra presented intermediate values.