## 4 Discussion
In parallel, the substantial pigment content found in the residual pulp underscores the feasibility of circular economy strategies for valorising algal byproducts through integrated biorefinery approaches [101]. Overall, the results advocate for a broader utilization of both primary and residual biomass fractions in pigment extraction and functional food development. To assess the antioxidant capacity of macroalgal extracts, Total Phenolic Content (TPC) and Ferric Reducing Antioxidant Power (FRAP) are two commonly employed methods that provide complementary insights. The TPC assay quantifies the total concentration of phenolic compounds in a sample and offer a direct indication of the extract's potential health benefits. Studies have reported a wide range of TPC values in brown algae, depending on species, season, and extraction method [102; 103]. The FRAP assay evaluates the ability of antioxidants in the sample to reduce Fe\({}^{3+}\) to Fe\({}^{2+}\) under acidic conditions, thus measuring the electron-donating capacity of the extract [41]. This method is particularly useful for screening the antioxidant potential of complex matrices like seaweed extracts. Given the growing demand for natural antioxidants in the food, cosmetic, and pharmaceutical industries, the evaluation of macroalgal extracts using TPC and FRAP remains a vital step in bioactive compound screening. Furthermore, integrating these assays within biorefinery models enhances the sustainable exploitation of algal biomass, allowing for the valorisation of both primary and secondary metabolites. The Total Phenolic Content (TPC) among the three seaweed species and the residual pulp showed statistically significant differences, ranging from 2.47 \(\pm\) 0.33 mg GAE\(\cdot\)g\({}^{-1}\) in _L. ochroleuca_ to 4.94 \(\pm\) 0.31 mg GAE\(\cdot\)g\({}^{-1}\) in _S. polyschides_ (Figure 4). These results highlight the species-specific variability in phenolic compound accumulation, which is known to be influenced by genetic, environmental, and seasonal factors, such as light availability, temperature, and nutrient levels [104; 105]. _S. polyschides_ displayed the highest TPC, suggesting a stronger antioxidant potential and increased relevance for bioactive applications, particularly in the food, pharmaceutical, and cosmceeutical industries. Regarding _S. polyschides_, previously published results obtained with methanolic extracts [20] showed a higher phenolic content (66.89 \(\pm\) 0.002 mg GAE\(\cdot\)g\({}^{-1}\) extract) than ours. On the other hand, the aqueous extracts of _L. ochroleuca_ and _S. polyschides_ from the study by [PERSON] et al. [44] had lower values than those obtained in the present study. The relatively low TPC in _L. ochroleuca_ may reflect its lower biosynthetic capacity for phenolic production or reduced accumulation due to physiological or ecological differences. _L. ochroleuca_ showed a higher total polyphenol content than that obtained in the present study [75], as well as the TPC obtained by [PERSON] et al. [106] for _M. pyrifera_, which was also harvested in winter. _M. pyrifera_ and its residual pulp exhibited intermediate TPC values, with the pulp (4.86 \(\pm\) 0.12 mg GAE\(\cdot\)g\({}^{-1}\)) containing slightly more phenolics than the raw seaweed biomass (3.36 \(\pm\) 0.13 mg GAE\(\cdot\)g\({}^{-1}\)). This may be attributed to processing effects, where cell disruption and thermal exposure enhance the release of bound polyphenols from the algal matrix. It should also be stressed that the study from [PERSON] et al. [106] used algae species harvested in distinct locations at different times of the year, and a residue from a previous extraction. In the subsequent hydroethanolic extraction of the residue, the temperature, polar organic solvent (ethanol) and water caused further damage to the cell membrane, and the antioxidant compounds were more easily extracted. All these factors, together with the sequential extraction, are likely to have influenced the antioxidant activity of the extracts.