Stress-induced enhancement of microalgal biochemical composition for sustainable biorefineries

Microalgae as third-generation biomass feedstock have contributed significantly to the field of bioenergy and bio-based products, supporting the circular economy. The biochemical composition of microalgal biomass, including carbohydrate, lipid and protein content, has been harnessed for various biofuels (bioethanol, biohydrogen, biogas, biodiesel) and biorefinery (vitamins, pigments, functional foods, bioactive proteins) products. Biochemical compositional enhancement through various simple modifications in cultivation strategies, such as nutrient (nitrate or phosphate) stress, salt stress, osmotic stress, modification in light intensities, etc., improves the efficiency of microalgal biomass as feedstock. This study is a comprehensive review of such strategies and mechanisms involved in enhanced carbohydrate, protein and lipid accumulation in microalgal biomass. The potential of microalgal biorefinery has been discussed with a focus on the production of natural pigments (chlorophyll, carotenoids, xanthophylls, etc.), vitamins and bioactive proteins as food supplements. This review suggests the implementation of biochemical enhancement strategies in application-based biorefinery studies.