Hidrólise da biomassa da macroalga marinha vermelha Gracilaria birdiae para obtenção de produtos de interesse industrial

Abstract

The high content of hydrolyzable carbohydrates in the composition of macroalgae is the basis for obtaining several products of industrial importance. However, studies are needed to establish the ideal conditions for hydrolysis and fermentation of carbohydrates in these organisms. The objective of this study was to evaluate the effects of the parameters sulfuric acid concentration (SAC), algae biomass concentration (GbBC), and reaction time (RT) on the hydrolysis of the red macroalgae Gracilaria birdiae, aiming at the establishment of optimal conditions for the obtaining solutions rich in monosaccharides, organic acids, and furanic compounds. The biomass of Gracilaria birdiae rich in carbohydrates (73.01 ± 1.03, %) was hydrolyzed from an experimental design using the statistical tool Rotational Central Compound Design (RCCD) combined with the Response Surface Methodology (RSM). The results showed that each independent variable had a distinct and significant influence on the reaction. Sugar production was more affected by the concentration of algae biomass, while sulfuric acid concentrations had more effects on 5-hydroxymethylfurfural and organic acids. The most suitable conditions for obtaining glucose (28.56 ± 0.72 g.L-1) and galactose (108.03 ± 1.32 g.L-1) were at 121 ° C, with 1.3 mol.L-1 sulfuric acid 1,841.59 g.L-1 of algae biomass and time of 20 min. For cellobiose (25.39 ± 0.43 gL-1), the conditions were 0.6 mol.L-1 sulfuric acid, 680 g.L-1 of biomass and 10 min for 5-HMF (19.82 ± 0, 43 g.L-1), were 0.6 mol.L-1 sulfuric acid, 680 g.L-1 of biomass and 30 min and for levulinic (38.88 ± 0.58 gL-1) and formic acids (26.75 ± 0.54 g.L-1) and sulfuric acid 2.0 mol.L-1, 680 g.L-1 of biomass and 30 min. Glucose and galactose in the hydrolysates of the optimal range of hydrolysis were fermented by a yeast strain Saccharomyces cerevisiae acclimated to galactose (ScGal). GbH3 (GbBC: 230 g.L-1; SAC: 0.8 M and RT 10 min) showed the best ethanol yield and productivity whose conversion factors (g.g-1) were YP/S gli 0.843 ± 0,001, YP/S gal 0.664 ± 0.010, YEtOH 1.427 generating the maximum concentration of 7.82 ± 0.06 g.L-1 of ethanol. Therefore, the results obtained in this study showed that the hydrolysates of Gracilaria birdiae obtained under optimized conditions, constitute good sources of commercially important molecules that can be purified, as well as solutions rich in fermentable carbohydrates, which can be used to produce a variety of compounds with biotechnological value, including ethanol.