Enhancement of the lipid and β-carotene contents of the brown seaweed Halidrys siliquosa (Sargassaceae) using low light LEDs.

Aquaculture is a rapidly developing sector worldwide aiming to sustainably exploit and valorise natural bioresources. Seaweeds contain a range of valuable bioactive metabolites making them amenable to optimised exploitation via multi-compound biorefinery pipelines developed as a result of recent circular bioeconomy initiatives. The content of seaweeds in sought-after metabolites can be modulated by altering the conditions they are exposed to, such as light intensity and quality. Here, the brown seaweed Halidrys siliquosa (Sargassaceae) found in Irish coastal waters, which is not as abundant as other Fucales with high exploitation potential, was the focus of a lab-based cultivation experimentation. Fronds of H. siliquosa collected from a tidal pool in northwest Ireland were exposed for 10 days to different regimes of low light illumination using white, red, blue and green LEDs. Their biomass was then analysed in terms of lipid, protein and carbohydrate contents together with their antioxidant potential and carotenoid pigments. Results showed that a 5-day exposure to green light increased the β-carotene content of the biomass by 26.5% (up to 2.3 mg g-1 DW). Furthermore, after 10 days, the lipid content of H. siliquosa was increased to 119 mg L g-1 DW (+ 20%). In terms of antioxidant activity, increases (+ 14%) were observed both under white light and green light exposure. Optimised illumination regimes using LEDs can constitute effective post-harvest treatments to enrich seaweeds, such as H. siliquosa, and maximise their output of valuable metabolites.