Extraction and bioactivity assessment of bio‐oil from <i>Kappaphycus alvarezii</i> biomass using the Bligh, Dyer and Soxhlet method

Abstract The lipid composition and algal oil content in red macroalgae play a crucial role in sustainable biofuel and bioactive compound production. In the present study, various extraction methods including biomass pretreatment through ultrasonication and conventional lipid extraction techniques such as Bligh &amp; Dyer and Soxhlet were employed for lipid extraction from Kappaphycus alvarezii . Among these methods, pretreatment of ultrasonication combined with solvent extraction (PT + SE) resulted in highest extraction yield of 21.5% ± 0.38%, surpassing the yield achieved by the Bligh‐Dyer method (PT + BD) and the control method, which yielded 19.42% ± 0.1% and 10.7% ± 0.15%, respectively. PT + SE oil possesses lower values in molecular weight, viscosity, and density when compared to PT + BD oil. The trans‐esterified samples of PT + BD (T1) and PT + SE (T2) respectively demonstrated greater efficiency in converting methyl esters, with T2 achieving a conversion rate of 92% ± 0.21%, while T1 achieved 84.15% ± 0.15%. It was observed that T2 had a high scavenging rate of 86.42% ± 0.22% indicating its significant ability to neutralize free radicals. In contrast, T1 exhibited a slightly lower scavenging rate of 69.56% ± 0.1%, when compared to T2. T2 sample demonstrated remarkable proteinase inhibition of 79.16% ± 0.18, comparable to salicylic acid, indicating the presence of potent anti‐inflammatory salicylic acid analogues in the algal oil. Both lipid‐extracted oil (T1and T2) showcased significant antioxidant and anti‐inflammatory activities, with T2 oil demonstrating superior inhibition of free radicals and proteinase enzymes.