Sargassum angustifolium brown macroalga as a high potential substrate for alginate and ethanol production with minimal nutrient requirement

Abstract

The brown macroalga, Sargassum angustifolium harvested from the Persian Gulf in the summer and winter was exploited within a biorefinery approach for valuable bioproducts and ethanol production. This alga mainly contained alginate (20.9–22.4%), glucan (36.2–43.1%), lignin-like materials (i.e., polyphenols; 11.8–25.8%), and ash (43.8–35.5%). The biomass protein content was highly depended on the harvesting season, where the biomass harvested in summer and winter comprised 11.9% and 19.7% protein, respectively. The alginate was first extracted in the form of sodium alginate. Then, the residual biomass obtained during alginate extraction was used for bioethanol production through the separate hydrolysis and fermentation. The results demonstrated that 44.5 (28.0) to 53.3 (32.5) kg of ethanol and 2.4 × 102 (2.2 × 102) kg of sodium alginate could be obtained from each tone of summer (winter) algal biomass. During the extraction of alginate, a nutrient-rich extract, “macroalgal extract”, was produced. This extract was successful substitute for yeast extract, which was necessary for the ethanolic fermentation. The results revealed the great potential of S. angustifolium for implementation as a source of sodium alginate, a nutrient-rich extract, and bioethanol.