EPR analysis of free radical components and antioxidant activity of bee pollen before and after gamma-irradiation

Evaluation of gamma irradiation effects on antioxidant capacity of propolis

The irradiation effects on antioxidant potential and on content of phenolic compounds of propolis ethanoic extracts were studied. It was found out that gamma treatment of samples with 2 and 10 kGy had a weak decreasing effect on the total phenolic content (TPC), while no change was observed in the propolis irradiated with 5 kGy. The antiradical activity of extracts was assessed by the DPPH free radical scavenging activity evaluated by Electron Paramagnetic Resonance (EPR) spectroscopy. The EPR results were in agreement with TPC. Some main phenolic compounds of the studied non-irradiated and irradiated samples were identified and compared by ultra-high performance liquid chromatography (UHPLC).

Gamma-irradiation of common biological samples for stable carbon and nitrogen isotope and elemental analyses

RATIONALE

Around the world biosecurity measures are being strengthened to prevent the spread of pests and diseases across national and international borders. Quarantine protocols that involve sample sterilisation have potential effects on sample integrity. The consequences of sterilisation methods such as gamma (γ)-irradiation on the elemental and chemical properties of biological samples have not been widely examined.

METHODS

We tested the effect of γ-irradiation (50 kGy) on the stable carbon and nitrogen isotope compositions (δ¹³ C and δ¹⁵ N values) and elemental concentrations (C % and N %) of common biological samples (fish, plants and bulk soils). The analysis used a continuous flow system consisting of a Delta V Plus isotope ratio mass spectrometer connected with a Thermo Flash 1112 elemental analyser via a ConFlo IV interface. Results were compared using two one-sided tests (TOST) to test for statistical similarity between paired samples.

RESULTS

There was no change in the δ¹⁵ N values or N % of γ-irradiated samples, and only small changes to the δ¹³ C values of consumers (range: 0.01‰ to 0.04‰), producers (-0.02‰ to 0.04‰) and sediments (0‰ to 0.07‰). The magnitude of change in δ¹³ C values was greatest at low carbon concentrations but appeared negligible when measured against replicated sample analysis and the combined analytical uncertainty (i.e., 0.10‰). The C % values of irradiated samples were higher for consumers (0.23%) and lower for producers and sediments (0.04% and 0.05%, respectively) which may have implications for certain types of biological material.

CONCLUSIONS

Routine γ-irradiation has little effect on the stable carbon and nitrogen isotope compositions of common biological samples and marginal effects on carbon elemental concentrations. This is unlikely to warrant concerns since the observed difference is typically of a magnitude lower than other sources of potential uncertainty.

Optimisation of Bee Pollen Extraction to Maximise Extractable Antioxidant Constituents

This paper presents the findings of a comprehensive review on common bee pollen processing methods which can impact extraction efficiency and lead to differences in measured total phenolic content (TPC) and radical scavenging activity based on 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) data. This hampers the comparative analysis of bee pollen from different floral sources and geographical locations. Based on the review, an in-depth investigation was carried out to identify the most efficient process to maximise the extraction of components for measurement of TPC, DPPH and FRAP antioxidant activity for two bee pollen samples from western Australia (Jarrah and Marri pollen). Optimisation by Design of Experiment with Multilevel Factorial Analysis (Categorical) modelling was performed. The independent variables included pollen pulverisation, the extraction solvent (70% aqueous ethanol, ethanol, methanol and water) and the extraction process (agitation, maceration, reflux and sonication). The data demonstrate that non-pulverised bee pollen extracted with 70% aqueous ethanol using the agitation extraction method constitute the optimal conditions to maximise the extraction of phenolics and antioxidant principles in these bee pollen samples.