Frações residuais do processo de extração de proteínas da biomassa de Spirulina platensis como matéria-prima para produção de bioetanol

Abstract

Spirulina platensis is a promising microalgae for biorefinery systems due to its rich composition in biocomposites such as proteins and carbohydrates. However, despite all the advantages of obtaining biofuels from microalgae, its economic viability still needs to be improved. In this context, the aim was to evaluate the production of bioethanol from residual fractions of the process of obtaining protein concentrate from S. platensis. The enzymatic hydrolysis of the biomass residual fractions obtained after the extraction of lipids and proteins was carried out; from the obtained hydrolyzate, the bioethanol production was evaluated. The biomass was initially defatted in Soxhlet extractor; sequentially, the extraction of proteins in alkaline medium assisted by ultrasonic method was conducted (LUPATINI et al., 2017). The residual fractions (solid residue of the extraction and liquid residue of the protein precipitation) were combined in the ratio of 100 g×L-1 and autoclaved for the starch liquefaction. The enzymatic hydrolysis was carried out with 0.5; 1.0 and 1.5% of α-amylase and amyloglucosidase (AMG) added simultaneously (50 oC, pH 5.5, 24 hours). The pH and temperature of the hydrolysis were determined by the enzymatic activities evaluation of the enzymes in starch. The hydrolysis was followed by the removal of aliquots every 2 h of reaction for the analysis of reducing sugars (RS) (Somogyi-Nelson method). In the study of bioethanol production from the hydrolyzate, Saccharomyces cerevisiae was inoculated at 30 oC under stationary conditions, in four different culture media: hydrolyzate (H) obtained under the best hydrolysis conditions, control medium (C1) with the same sugar concentration as H, control medium (C2) with sugar concentration simulating the production of bioethanol from sugar cane, and a medium containing the hydrolyzate supplemented (HS) to reach the same sugar concentration of the C2 medium. The kinetics of the cultures were monitored by aliquot removal at regular intervals for determining the concentration of biomass, RS and bioethanol. Enzymatic hydrolysis with 1.0% of the enzymes reached an efficiency of 77,51% in 12 h of reaction. In the alcoholic fermentation, the results for the biomass concentration were higher in the control media (C1 and C2), while for the H and HS media the highest values for bioethanol production were observed, reaching 8.06 g×L-1 of bioethanol in 12 h of fermentation, with 100% efficiency and productivity of 0.533 g×L-1×h-1 for medium H. These results indicate that the residual fractions of the lipid and protein extraction process of S. platensis biomass have potential as a raw material for the production of bioethanol in a biorefinery system.