An integrated approach based on sequential fractionation and specific enzymatic saccharification of green algae Ulva sp. biomass.

Marine green algae of the genus Ulva are abundant worldwide. In the case of eutrophication, they can be stranded in large quantities, thereby causing ecological and economic problems. Compared to other macroalgae, this biomass remains underexploited on an industrial scale. Thus, the aim of this study was to develop an integrated downstream process applicable to the biomass of the green algae Ulva sp., allowing a major sequential recovery of high-added-value fractions corresponding to pigments, ulvan, alkali-soluble hemicelluloses, and cellulose. Indeed, the proposed concept using cascade extractions enable to produce 0.64 ± 0.16 % of pigments rich in chlorophylls and caroténoids, 28 ± 0.8 % of ulvan, 5 ± 0.3 % of alkali-soluble hemicelluloses and 10 ± 0.4 % of cellulose based on initial dry weight. Characterization of the extracted polysaccharides and verification of their purity were confirmed using FTIR and monosaccharide composition analyses. To better evaluate the biodegradability and the success of the extraction procedure, enzymatic saccharification was applied at the end of the cascade using the cellulose fraction as the substrate. In parallel, saccharification of the total algal biomass was also carried out under the same conditions. Results showed a significant improvement in conversion yields from 74.6 ± 0.85 % to 84 ± 0.7 % showing that Ulva's cellulose fraction can be a promising candidate for biofuels production. This study presents a sustainable biorefinery approach that allows almost complete fractionation and bioconversion of green macroalgae, and integrates the concept of a circular bio-economy.