Microalgal proteins for a circular bioeconomy: Nutritional, material, and chemical valorization

Microalgae have attracted increasing attention as a renewable biomass source due to their rapid growth, high protein content, and potential for carbon capture and wastewater treatment. However, current research and industrial utilization primarily focus on lipids and carbohydrates for biofuel and bioproduct generation, while protein-rich residues are often discarded as waste. The valorization of microalgal proteins remains in its infancy, with limited studies addressing their full potential. The valorization of microalgal proteins remains in its infancy, with limited studies addressing their full potential. Recent studies have demonstrated that microalgal proteins can be effectively extracted using mechanical (e.g., ultrasonication, high-pressure homogenization) and non-mechanical (e.g., enzymatic hydrolysis, freeze-thaw) methods, achieving extraction efficiencies of up to 66.8%. These proteins have been applied in the development of nutraceuticals, animal feed, and biofertilizers. Furthermore, thermochemical processes such as hydrothermal liquefaction and pyrolysis, along with catalytic pathways (e.g., Ga/HZSM-5 catalysis, metal-free activation), enable the conversion of proteins into nitrogen-containing chemicals-such as fatty amides, nitriles, and N-heterocycles-with applications in agrochemicals, pharmaceuticals, and polymers. N-doped carbon materials derived from microalgae exhibit specific capacitances up to 468F/g and enhanced performance in energy, catalysis and environmental technologies. Despite these advances, challenges persist in separation efficiency, product selectivity, and heavy metal contamination in natural algae. Future directions include utilizing water bloom microalgae, developing integrated systems for reaction and separation, and promoting circular bioeconomy strategies. Harnessing the full potential of microalgal proteins offers a pathway toward zero-waste biorefineries while making contributions to sustainable materials development and environmental protection.