Seasonal Variations in Bioactive Compounds and Antioxidant Activity in the Leaves of Sasa quelpaertensis

Sasa quelpaertensis Nakai (SQ; Jeju-Joritdae) is an endemic species in Korea distributed on Jeju Island. This plant, which is typically used as a type of herbal tea, has anti-inflammatory, anti-cancer, antioxidant, and anti-melanogenic effects. We investigated variations in the chemical compositions of the phenolic compounds and antioxidant activity of SQ leaves based on the harvest time and assessed its radical scavenging abilities using 2,2’-azino-bis-(3-ethylbenzothiazolin-6-sulfonic acid) diammonium salt (ABTS+) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays, while also assessing its ability to inhibit cellular reactive oxygen species (ROS). The levels of bioactive compounds and the antioxidant activity of Sasa quelpaertensis Nakai leaf water extract (SQW) differed by season. SQW collected in the spring, in which the total phenolic and flavonoid contents were highest, also contained the highest levels of vanillic acid and isoorientin (6-C-glycosylflavone) among the different extracts collected. This extract exhibited the second highest radical scavenging activity and the highest cellular ROS inhibitory ability in PC12 neuronal cells. Thus, spring is the most appropriate season for the collection of SQ leaves from the wild and for the harvesting of SQ leaves in the field for industrial use. SQ leaves harvested in the spring, with high levels of neuroprotective bioactive compounds, including vanillic acid and isoorientin, may be a promising material for the prevention of neurodegenerative diseases.