## 4 Discussion
The residual pulp extract, therefore, showed interesting results, indicating that the primary extraction process of the biomass did not affect the whole biomass, leaving behind many of the bioactive compounds, which may be further explored. Brown algae are generally rich in phenolic compounds, which have antioxidant properties [107]. The results obtained from the FRAP assay showed a higher antioxidant capacity of the residual pulp than the other samples, and much higher than that of the _M. pyrifera_ biomass. Notably, _M. pyrifera_ and _L. ochroleuca_ showed markedly lower values, suggesting species-specific differences in antioxidant profiles (Figure 5). The elevated antioxidant potential of the residual pulp may be attributed to the accumulation or retention of bioactive compounds, such as phenolic acids (namely phloroglucinol) or reducing sugars, following upstream processing [25; 108]. These results support previous findings indicating that algal processing residues remain rich in valuable phytochemicals, thus reinforcing their potential for reuse within circular biorefinery models [101; 105]. Notably, this valorisation aligns with sustainable development goals by converting algal waste streams into functional ingredients for nutraceuticals or cosmetics [51]. The higher reducing power observed in _S. polyschides_ is consistent with earlier studies reporting significant levels of polyphenols and antioxidant activity in brown algae species [109; 110]. This is also in agreement with the TPC content of the species as analysed earlier. In contrast, the lower FRAP values of _L. ochroleuca_ and _M. pyrifera_ may reflect differences in biochemical composition, including lower concentrations of polyphenolic compounds, as previously described, or a higher proportion of non-reducing antioxidants such as carotenoids or vitamins, which are not effectively measured by the FRAP assay [111]. This reinforces the importance of using multiple assays to comprehensively evaluate antioxidant potential, as each method has different sensitivities to various antioxidant mechanisms. In summary, the high FRAP value of the residual pulp underscores its potential as a valuable byproduct rich in antioxidant compounds, which could be further explored for functional food, cosmetic, or other applications. This finding contributes to the growing body of literature advocating for the integration of waste streams into high value bioproduct development within macroalgal processing chains. The antioxidant profiles revealed by both the TPC and FRAP assays suggest a potential positive correlation between the total phenolic content and the ferric reducing capacity of the macroalgal samples and their byproducts. Notably, _S. polyschides_ exhibited the highest TPC among the seaweeds, closely followed by the residual pulp, which also demonstrated the highest FRAP value. This parallel trend supports the widely reported observation that phenolic compounds, particularly phlorotannin's in brown macroalgae, play a significant role in antioxidant activity due to their electron-donating capacity and metal-chelating properties [110; 111]. Furthermore, _L. ochroleuca_, which showed the lowest TPC, also exhibited the lowest FRAP value, reinforcing this possible correlation. Several studies have demonstrated strong correlations between TPC and FRAP values in various macroalgal species, indicating that polyphenols are key contributors to reducing power. Overall, our findings indicate that residual pulp from seaweed processing retains substantial content of proteins, lipids, carbohydrates, pigments and phenolics, representing a promising raw material for valorisation in biorefinery and circular economy strategies, particularly in the context of sustainable extraction of antioxidant-rich compounds from industrial byproducts [112; 113].