Mixotrophic cultivation of Chlorella vulgaris in Brassica carinata meal hydrolysate for enhanced lipid and lutein production

Microalgae are a renewable resource that has the potential to supply the bioeconomy with drop-in fuels and biomaterials. However, economic feasibility requires high biomass and metabolite productivities and low cultivation cost before algae technologies can be commercialized. In this context, agricultural residues can serve as inexpensive sustainable sources of fermentable carbohydrates that may help algae meet those requirements. The present study investigates this approach by cultivating Chlorella vulgaris in the biomass hydrolysate of the inedible cover crop Brassica carinata, which is the residue remaining after oil is extracted from the seeds for manufacturing sustainable aviation fuel. The biomass, termed carinata meal, was pretreated with phosphoric acid and then enzymatically hydrolyzed by cellulase enzyme, resulting in readily fermentable renewable sugars, primarily glucose. C. vulgaris cultivated in the hydrolysate showed higher lipid and lutein productivity compared to costlier commercial media. The optimal hydrolysate inclusion level of 50% (v/v) in BBM resulted in maximum lipid productivity of 75 mg L-1 day(-1) and lutein productivity of 4 mg L-1 day(-1), which were threefold and sixfold, respectively, higher than in expensive BBM. Time course studies revealed distinct biochemical alterations in the algae, shedding light on the effect of culture medium on lipid and lutein biosynthesis. Moreover, the fatty acid profile of mainly C16:0, C16:1, C18:0, and C18:1 looked promising for biodiesel manufacture. As a result, inexpensive CM hydrolysate may be a viable renewable alternative to high-cost synthetic media for algae cultivation as it enhances biomass and product yields.

Automated summary

The study found that using agricultural residues as cheap and sustainable sources of fermentable carbohydrates can increase biomass and product yields of microalgae. By cultivating Chlorella vulgaris in the hydrolysate of Brassica carinata residue, the algae showed higher lipid and lutein productivity compared to expensive commercial media. Time course studies revealed the effect of culture medium on lipid and lutein biosynthesis, and the fatty acid profile looked promising for biodiesel production. Inexpensive hydrolysate may be a viable alternative for algae cultivation.