Comprehensive Waste-Free Utilization of <i>Caulerpa lentillifera</i> : Extraction, Protein Content, Bioactive Profiling, Antioxidant Activity, and Dye Adsorption Capacity

Caulerpa lentillifera (CL), a fast-growing marine macroalgae with a rich profile of nutrients and bioactive compounds, presents significant potential for circular and sustainable resource utilization. However, its commercial scalability remains limited due to a lack of integrative studies beyond nutritional profiling. This study presents a comprehensive framework for the waste-free valorization of CL by examining the upstream, midstream, and downstream processes. Extraction was performed by evaluating the solvent polarity, sample state, drying techniques, and homogenization. Antioxidant properties were assessed through total phenolic content, total flavonoid content, and free-radical scavenging assays. At higher extract concentrations, an apparent decline in H2O2 scavenging activity was observed, which was identified as an analytical artifact caused by spectral interference from newly formed, strongly absorbing species, rather than a true loss of antioxidant capacity. Bioactive profiling was conducted via GC-MS, FTIR, and UV–visible spectrophotometry to characterize the phytochemical diversity across drying methods. Protein analysis was performed using an adapted formol titration following Kjeldahl digestion. This modification replaces the specialized distillation step with a simpler titration while still requiring the standard hazardous digestion. The approach provides a practical and accessible alternative for protein determination in resource-limited laboratories. As a downstream application, the use of fresh and residual biomass for methylene blue dye removal was investigated, with adsorption capacity, thermodynamic, and kinetic modeling providing insights into the mechanism and scalability. The integrative approach underscores the feasibility of CL as a zero-waste, multipurpose marine resource for sustainable high-value commodity.