Extraction and characterization of bioactive compounds from brown seaweed (Undaria pinnatifida) sporophyll using two sequential green extraction techniques

This work aims to prepare the functional extracts from Undaria pinnatifida sporophyll using a consecutive green extraction methodology known as supercritical carbon dioxide (SC-CO2) along with subcritical water extraction (SWE). For the SC-CO2 extraction, a variable pressure from 20 to 30 MPa was applied at a constant temperature of 50 °C and compared with hexane extraction. The amount of fucoxanthin and beta-carotene was quantified from the extracted oils along with fatty acids. The yield of the fucoxanthin ranged from 12.38 ± 0.10 mg/g to 20.22 ± 0.14 mg/g and beta-carotene was 0.57 ± 0.01 mg/g to 0.99 mg/g of extracted oil. Arachidonic and eicosapentaenoic acid (EPA) considered as health-beneficial PUFAs were highly abundant in the U. pinnatifida sporophyll oils. A variable temperature range from 120 °C to 220 °C was used for SWE of de-oiled biomass. For comparison, hot water extraction, and ethanol extraction were used as controls. Physicochemical compositional parameters (total sugar, reducing sugar, protein, phenolic content, and flavonoid content), antioxidant activities, and antihypertensive and antibacterial activities of the hydrolysates were evaluated. The maximum content of total sugar, reducing sugar, total protein, phenolics, and flavonoids were 165.03 ± 0.40 mg glucose/g, 53.15 ± 0.50 mg glucose/g, 113.62 ± 0.66 mg BSA/g, 38.04 ± 0.18 mg PE/g, and 10.34 ± 0.24 mg PE/g, respectively, at SWE temperatures of 140 °C, 180 °C, 180 °C, and 200 °C. Antihypertensive activity exhibited its highest value at 180 °C. The antioxidant activity of ABTS+, DPPH, and antimicrobial activity was highest at 200 °C. Bioactive compounds and the functional properties of the extracts using SC-CO2 and SWE from U. pinnatifida sporophyll were revealed for the first time in the study. The authors believe the findings of this research will bring new insight to the scientists for the industrial application of U. pinnatifida sporophyll.