Ultrasound-assisted extraction enhances recovery of antioxidant-rich carbohydrate fraction from mixed microalgae...

The effects of ultrasonic processing parameters on the functional and physicochemical properties of microalgae carbohydrates remain poorly understood, despite evidence from plant-based extractions showing that sonication conditions strongly influence bioactive compound yield and antioxidant activity from carbohydrates. This study investigated the effects of ultrasonic-assisted extraction (UAE) parameters on the yield, composition, and antioxidant activity of carbohydrates extracted from defatted mixed microalgae biomass. A single-factor approach was employed to test different extraction times (10-30 min), amplitudes (20-100 %), and solid-to-solvent ratios (1:10-1:30 g/mL). All analyses were conducted in triplicate, and statistical significance was determined at p < 0.05. Results showed that processing time was the most influential factor in improving antioxidant activity. Under optimal UAE conditions (25 min, 100 % amplitude, 1:15 g/mL), the extract contained significantly higher uronic acid, sulphate, and fibre contents (p < 0.05) compared to hot water extraction. These changes corresponded to stronger antioxidant activity (∼35 % increase in DPPH radical scavenging). Correlation analysis further revealed that uronic acid had the strongest positive influence on antioxidant activity. In conclusion, UAE improved both the yield and antioxidant properties of microalgae carbohydrates compared with hot water extraction. With its high fibre content and bioactivity, the extract may have potential applications as a functional food ingredient.