Enrichment of lipids from agar production wastes of Gracilaria lemaneiformis by ultrasonication: a green sustainable process

During the agar production of the red seaweed Gracilaria lemaneiformis, amounts of lipid constituents are destroyed and discarded as wastes, which can be utilized as sustainable alternative feedstocks for lipid production. Herein, a green ultrasound-assisted extraction (UAE) method using ethanol as an extraction solvent was carried out for the enrichment of lipids from the wastes. Meanwhile, the UAE-influenced conditions were optimized by response surface methodology (RSM), and the maximum yield (0.71 wt%) of lipids was obtained, which was higher than that of the conventional Soxhlet extraction (CSE) (0.44 wt%). The composition of fatty acids in lipids was analyzed by gas chromatography with flame ionization and mass spectroscopic detection (GC-FID/MS), respectively. The major fatty acid compositions were palmitic acid (59.20–63.25%), oleic acid (1.85–9.43%), and arachidonic acid (9.44–15.12%), while the free fatty acid (FFA) content of the UAE (94.67%) was higher than that of the CSE (73.12%). Moreover, the proportions of unsaturated fatty acids in the UAE were monounsaturated fatty acids (MUFAs) (10.94%) and polyunsaturated fatty acids (18.20%), both of which were much higher than those in CSE. In addition, the enrichment of lipids by UAE displayed superior antioxidant activities in the DPPH (IC50 = 18.65 mg/L), hydroxyl (IC50 = 13.68 mg/L), and superoxide (IC50 = 210.12 mg/L) radical scavenging assays. From the perspective of waste resource utilization and biorefinery, the green UAE technique could be potential for the enrichment of lipids from agar production wastes of G. lemaneiformis without compromising its quality, which may be useful in the algal development.