**5. Conclusions**

This study evaluated sulfated polysaccharide from marine brown alga *P. boryana* ethanol precipitation (PBP) as a source of natural antioxidants. Preliminary chemical characterization revealed its composition and the contribution of sulfate content, fucose, and galactose towards the bioactive properties. Results sugges<sup>t</sup> the ability of PBP to protect ROS mediated cell damage and to inhibit oxidative stress in zebrafish. The increased antioxidant pathway protein expression of Nrf2 and its resulting CAT, SOD protein levels accompanied the e ffect of PBP. Hence, PBP is a potential source of antioxidants that could be successfully utilized in healthy functional and cosmeceutical sectors.

**Author Contributions:** Conceived and designed the experiments: Y.-J.J.; Performed the experiments: L.W., T.U.J.; Analyzed data: L.W., T.U.J.; Contributed reagents/materials/analysis tools: K.K.A.S., S.I.K., J.-S.L.; Wrote the paper: T.U.J. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was financially supported by a gran<sup>t</sup> from the "Marine Biotechnology program—20170488", funded by the Ministry of Oceans and Fisheries, Korea.

**Acknowledgments:** This research was financially supported by a gran<sup>t</sup> from the "Marine Biotechnology program—20170488", funded by the Ministry of Oceans and Fisheries, Korea.

**Conflicts of Interest:** The authors declare to possess no competing interests.
