Optimizing Light Intensity for the Co-Production of Fucoxanthin and Polyunsaturated Fatty Acids in Isochrysis galbana

This study assessed the effects of different intensities of broad-spectrum white LED light (PAR range: 415–748 nm) on growth, fucoxanthin accumulation, and fatty acid composition of Isochrysis galbana. This study classified light intensity into three categories based on the white LED light source: high (HL, 150 μmol·m−2·s−1), medium (ML, 80 μmol·m−2·s−1), and low (LL, 30 μmol·m−2·s−1). The results showed that biomass concentration was optimized under high light intensity (HL, 150 μmol·m−2·s−1), whereas low light (LL, 30 μmol·m−2·s−1) yielded the highest fucoxanthin concentration (71.15 mg/L on day 12) and the only positive volumetric fucoxanthin productivity (3.14 mg/L/d) among the three treatments tested. The results further showed that low light (LL, 30 μmol·m−2·s−1) produced maximum cell density (10.08 × 106 cells/mL) and the most polyunsaturated fatty acids (PUFAs), particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which constituted 1.93% and 22.47% of total fatty acids, respectively. This study demonstrates that low-intensity (LL, 30 μmol·m−2·s−1) white LED light supports the maximum co-production of valuable metabolites in I. galbana, establishing a scientific basis for scaling up I. galbana cultivation for nutraceutical and aquafeed applications.