A sustainable ultrasonic and microwave-assisted sequential extraction strategy of metabolites from Porphyridium sp.

Microalgal biomass is an increasingly attractive resource for sustainable biofuel production and the extraction of high-value co-products due to its fast growth and high lipid content. However, conventional extraction methods often rely on large volumes of solvents, contributing to environmental degradation. This study proposes innovative approaches to minimize solvent use and waste while enhancing lipid extraction and sequential recovery of valuable metabolites using advanced ultrasonic and microwave pretreatment techniques. The current study aimed to enhance lipid extraction efficiency from Porphyridium purpureum by effectively disrupting its rigid cell walls and reducing the need for excessive solvent volumes. FUSE, operated at 30 % power for 20 min with a methanol:chloroform mixture (1:2 v/v), proved the most efficient, achieving a lipid yield of 31.4 ± 0.41 %, while reducing extraction time and solvent consumption. Protein and carbohydrate contents were quantified at 32.14 ± 0.35 % and 35.2 ± 0.22 %, respectively. Post lipid extraction, sequential recovery of proteins, carbohydrates, and bioactives were carried out with residual biomass, two sequences: protein-lipid-carbohydrate and lipid-protein-carbohydrate. These sequences resulted in maximum co-product recovery of 69 % lipid and 57 % carbohydrate, and 65 % protein and 52 % carbohydrate, respectively. These sequential extraction processes maximized resource utilization, minimized waste, and demonstrated a zero-waste approach aligned with Sustainable Development Goal 7 and circular economy principles. The findings highlight the potential of microalgal biorefineries to reduce the environmental impact of biofuel and biochemical production by adopting green, solvent-minimizing extraction technologies that enhance resource efficiency and sustainability.