Green extraction approach for green microalga Tetraselmis tetrahele: Enhanced phenolic yield and bioactivity via Ultrasound-Assisted extraction

Microalgae are gaining attention as promising natural sources of bioactives due to their rich nutrient content. This study investigates the effects of ultrasound-assisted extraction (UAE) parameters (i.e., solvent composition, temperature, solid-to-solvent ratio, and time) on the extraction of phenolic compounds from Tetraselmis tetrahele. The UAE parameters were determined at a solid-to-solvent ratio of 1:75, a temperature of 25 °C, and an extraction time of 15 min with 75% ethanol as the solvent. Phenolic profile, total phenolic content, total flavonoid content, radical scavenging activity of DPPH and ABTS, photosynthesis pigment (chlorophyll a, b, and total carotenoid), anti-collagenase activity, and metabolic profile of Tetraselmis tetrahele extract obtained using UAE were determined. Tetraselmis tetrahele extracts obtained using the selected UAE method demonstrated significantly higher (p < 0.05) levels in gallic acid (1.81%), 4-hydroxybenzoic acid (7.0%), total phenolic content (84.0%), total flavonoid content (56.2%), ABTS (101.3%), chlorophyll a (119.4%), chlorophyll b (174.3%), total carotenoids (173.2%) and anti-collagenase activity (15.9%) compared to the maceration method. These findings provide UAE as a green and scalable method for maximizing the phenolic yield and support the application of Tetraselmis tetrahele in the development of high-value products across pharmaceutical, cosmetic, and functional food industries.