Determination of microbiological contamination, antibacterial and antioxidant activities of natural plant hazelnut (Corylus avellana L.) pollen

Abstract

The aim of our study is to determine microbial contamination, antibacterial and antioxidant activities of 14 pollen samples of Corylus avellana collected from different locations in Slovakia. Microbiological analysis was carried out in two steps: microbiological assays and studies of antibacterial activity of pollen extracts. The antimicrobial properties of pollen extracts were carried out with the disc-diffusion method. Methanol (70%), ethanol (70%) and distilled water were used for pollen extracts. Five strains of bacteria such as gram-negative (Salmonella enterica subsp. enterica CCM 3807, Escherichia coli CCM 2024, and Yersinia enterocolitica CCM 5671) and gram-positive (Staphylococcus aureus CCM 2461 and Bacillus thuringiensis CCM 19T) were tested. Antioxidant activity of pollen extracts was determined by the DPPH method. Bacterial analysis includes the determination of the total bacterial count ranged from 4.08 to 4.61 log CFU g−1, mesophilic aerobic bacteria ranged from 3.40 to 4.89 log CFU g−1, mesophilic anaerobic bacteria ranged from 3.20 to 4.52 log CFU g−1, coliform bacteria ranged from 3.30 to 4.55 log CFU g−1, yeasts and filamentous fungi ranged from 3.00 to 3.56 log CFU g−1. Microscopic filamentous fungi Aspergillus spp., Alternaria spp., Penicillium spp., Cladosporium spp., Rhizopus spp., and Paecylomyces spp. were isolated from hazelnut pollen. Yersinia enterocolitica was the most sensitive strain among ethanolic and methanolic pollen hazelnut extracts. Staphylococcus aureus was the most sensitive strain against aqueous hazelnut pollen extracts. We determined the following sensitivity against ethanol pollen extracts respectively: Yersinia enterocolitica > Salmonella enterica > Staphylococcus aureus > Bacillus thuringiensis > Escherichia coli. Methanol pollen extracts had shown following sensitivity: Yersinia enterocolitica > Salmonella enterica > Escherichia coli > Staphylococcus aureus > Bacillus thuringiensis. Aqueous extracts had shown the following sensitivity: Staphylococcus aureus > Salmonella enterica > Escherichia coli > Bacillus thuringiensis > Yersinia enterocolitica. Hazelnut pollen extracts have over 82% antioxidant capacity in samples from non-urban zones. An elevated level of antioxidant potential in the pollen is determined by its biological properties conditioned by biologically active substances. DPPH method allowed characterizing pollen as a source of antioxidants.