# Green Macrolgae Biomass Upcycling as a Sustainable Resource for Value-Added Applications
###### Abstract  
As the global demand for eco-friendly food ingredients grows, marine macroalgae emerge as a valuable resource for multiple applications using a circular bioeconomy approach. In this study, green macroalgae _Uliva flexuosa_, naturally accumulated in aquaculture ponds as a residual biomass (by-product) of shrimp and oyster farming, were investigated regarding their bioactivity, chemical composition, and antioxidant properties. The use of aquaculture by-products as raw materials not only reduces waste accumulation but also makes better use of natural resources and adds value to underutilized biomass, contributing to sustainable production systems. For this, a comprehensive approach including the evaluation of its composition and environmentally friendly extraction of bioactive compounds was conducted and discussed. Green macroalgae exhibited high fiber (37.63% dry weight, DW) and mineral (30.45% DW) contents. Among the identified compounds, palmitic acid and linoleic acid (\(\omega\)-6) were identified in the highest concentrations. Pigment analysis revealed a high concentration of chlorophylls (73.95 mg/g) and carotenoids (17.75 mg/g). To evaluate the bioactivity of _Uliva flexuosa_, ultrasound-assisted solid-liquid extraction was performed using water, ethanol, and methanol. Methanolic extracts showed the highest flavonoid content (59.33 mg QE/100 g), while aqueous extracts had the highest total phenolic content (41.50 mg GAE/100 g). Ethanolic and methanolic extracts had the most potent DPPH scavenging activity, whereas aqueous and ethanolic extracts performed best at the ABTS assay. Overall, we show the upcycling of _Uliva flexuosa_, an underexplored aquaculture by-product, as a sustainable and sensible strategy for multiple value-added applications. reputose; seaweed; marine by-products; phytochemicals; natural resources +
Footnote †: journal: Applied sciences  
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Footnote 1: [[https://doi.org/10.3390/app15147927](https://doi.org/10.3390/app15147927)]([https://doi.org/10.3390/app15147927](https://doi.org/10.3390/app15147927))to bioremediation activities [1; 2], and in some cases, cultivation may not be required, as they can naturally occur as secondary biomass streams. Additionally, the extraction process is less impactful [2]. Life cycle assessment (LCA) studies have shown that macroalgae cultivation emits fewer greenhouse gases, consumes less freshwater, and results in lower eutrophication potential compared to conventional agricultural crops [3; 4; 5; 6]. Marine macroalgae are a promising reservoir of bioactive metabolites [7; 8]. Their nutrient-dense composition, including dietary fibers, minerals, essential fatty acids, and compounds with antioxidant properties [9; 10; 11; 12], makes them valuable candidates for the development of functional foods and supplements [13; 14; 15]. Examples of algal-based products include seaweed-enriched pasta and fortified vegetable creams. Additionally, hydrocolloids extracted from algae are widely used in the food industry as thickening and stabilizing agents. Macroalgae have also been incorporated into infant formulas and specialized clinical diets due to their nutritional and functional properties [16; 17; 18]. However, their biochemical composition is highly diverse and dynamic, influenced by species diversity, seasonality, temperature, and geographic location. These factors significantly affect their nutritional and functional properties, particularly the concentration of minerals, pigments, and polysaccharides [19]. Recent studies have highlighted the potential applications of unique marine algae bioactive compounds [1; 20]. Among these, chlorophylls and carotenoids from green algae have drawn attention due to their antioxidant capacity, anti-inflammatory, and health-relevant properties, making them valuable resources for food applications and natural pigment markets [21; 22; 23; 24].