Regulation of light quality on lipid production, biodiesel quality, and nutritional quality of Phaeodactylum tricornutum

Light quality is important for microalgal biomass and bio-component accumulation. In this study, 8 kinds of combined monochromatic red (R) and blue light (B) were employed to grow Phaeodactylum tricornutum using white light (W) as a control. The results indicated that P. tricornutum had the highest specific growth rate under white light, reaching 0.151 (day(-1)), and the highest biomass (dry weight), reaching 302.77 mg L-1. The red light and 2R5B were the best for P. tricornutum producing carotenoids and protein, respectively. Carbohydrate was not significantly affected by light quality. The lipid content and lipid production under 5R2B were the highest, reaching 27.85% (per dry weight) and 75.56 mg/L (per culture), respectively. The best production of palmitic acid (C16:0), palmitoleic acid (C16:1 (n7)), and eicosapentaenoic acid (EPA, C20:5 (n3)) was observed at 4R3B, red light, and 1R6B respectively. The highest proportions per total fatty acids of C16:0, C16:1 (n7), and EPA were determined as 26.57%, 60.59%, and 13.87%, which were 15.71%, 11.37%, and 29.49% higher than those under white light, respectively. Compared with white light, cells that were grown under blue light, red light, and 1R6B revealed the improved lipid nutrition quality, reduced AI and TI values, increased HI (h/H) values, and increased n3:n6 ratios (under 1R6B only). Combined monochromatic light (except 1R6B) produced biodiesel with higher CN values, lower DU and IV values, and higher oxidation stability, but slightly reduced fluidity at low temperatures. The manipulated spectrum or light quality is a promising strategy to regulate the product property of P. tricornutum cultures.