Polyphenols, antioxidant and antimicrobial activities of leaf and bark extracts of Solidago canadensis L.

Abstract

The leaf and bark of Solidago canadensis L. (SCL) contain a wide range of bioactive compounds that may be responsible for their biological activities. However, little information is available about their specific active compounds, as well as their contributions to the antioxidant and antimicrobial properties. This study investigated the total phenolics, tannins and flavonoid contents and antioxidant and antimicrobial activities of high pressure (HPE) or ultrasound (UE) assisted ethanolic extracts from leaf and bark of SCL at three ripening stages (vegetative growth (VG), full bloom (FB) and maturity after flowering (MF)). The antioxidant activities and contents of total phenolic (TPC), tannins (TTC) and flavonoids (TFC) varied with ripeness stage, tissue type and extraction method. Overall, the UE leaf extracts at the FB stage exhibited the highest TPC (3.8mg GAE/g DM), 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging capacity (0.547mg AAE/g DM) and oxygen radical absorbing capacity (ORAC) value (57.86mmol TE/g DM). The HPE extracts of MF samples had the greatest TFC (2.45mg RE/g DM) and reducing power (3.38). The greatest TTC (4.17g/100g DM) was observed in the ethanolic extracts at the MF stage. All leaf extracts exhibited antimicrobial activity against Listeria monocytogenes and Staphylococcus aureus, but only the HPE extracts of the VG samples showed activity against Salmonella spp. The UE leaf extracts at the MF stage demonstrated the maximum inhibitory potency against Escherichia coli, L. monocytogenes and S. aureus. These results highlighted the potential of using S. canadensis extracts as natural antimicrobial and antioxidant substances for food applications.