Comparative study of the extraction of phenolic compounds from Sargassum muticum using alkaline or enzymatic hydrolysis as pre-treatment followed by pressurized liquid extraction

Abstract

The brown seaweed Sargassum muticum has been recognized as a potential source of phenolic compounds, mainly phlorotannins, which had shown high antioxidant potential in vitro. Several researches have suggested that phlorotannins are likely to be integral structural components of brown-algal cell walls. Possible linkages between the cell wall (alginic acid) and phlorotannins through ester bonds and hemiacetal bonds, both of which are covalent bonds, would mean that strong extraction conditions are required for their isolation. The present study compared the extraction yields of phenolic compounds from Sargassum muticum as well as their antioxidant activity using alkaline and enzyme-assisted hydrolysis followed by a pressurized liquid extraction (PLE). Alkaline and enzymatic pre-treatment was employed in order to degrade cell wall polysaccharides to oligosaccharides prior to the extraction of phenolic compounds from the residual biomass. Alkaline degradation was performed using NaOH 1.0 M at 2.5 h and enzyme assisted extraction was completed using Alcalase (protease) and Viscozyme (carbohydrase) at their optimum hydrolysis conditions at 2 and 4 h. The residual biomass was separated from hydrolyzed polysaccharides and submitted to extraction process by pressurized liquid extraction. Results in terms of amount of total phenols and antioxidant activity were also compared to those attainable without previous hydrolysis.

The obtained results showed that the extraction yield of phenolic compounds using viscozyme or alcalase were similar, independently of the treatment duration. On the other hand, antioxidant activity was higher using alcalase than viscozyme. In the residual biomass, the phenolic compounds extracted were higher when the pre-treatment was done with Viscozyme (11.464 mg GAE/ g algae) than Alcalase (7.92 mg GAE/ g algae) and Alkalyne degradation (7.66 mg GAE/ g algae). Regarding the antioxidant activity, a similar trend was observed. Nevertheless, it was found that the extraction without previous hydrolysis presented the highest extraction yield, TFC and antioxidant activity among all extractions, suggesting that the PLE procedure without any pre-treatment is capable of extracting most phenolic compounds present in the algae.