Residual fractions from arthrospira platensis protein extraction as feedstock for ethanol production

Abstract

Microalgae are promising raw materials for biorefinery systems as they are rich in nutrients (proteins, carbohydrates, lipids, vitamins, pigments). Although there are different studies on the production of ethanol from microalgae with different types of pre-treatments for the utilisation of whole biomass, researches of ethanol production from residues of protein extraction from defatted biomass of Arthrospira platensis biomass has not been found in the literature. In this context, the objective of this study was to use the residues of the protein extraction process to produce ethanol (byproduct) in a biorefinery concept. Enzymatic hydrolysis (pH 5.5; 50 °C) were carried out with different concentrations (0.5, 1.0, 1.5% (v/v)) of the enzymes α-amylase and amyloglucosidase (AMG), added simultaneously. For the fermentation stage conducted with Saccharomyces cerevisiae, four different media were tested (H – pure hydrolysate; C1 – control 1, reduced sugars in the same proportion of medium H; C2 – control 2, simulating the production of sugarcane ethanol; HS – hydrolysate supplemented with nutrients in order to obtain the same composition as C2). The medium H presented better results than the others, it produced 8.06 g/L of ethanol over 12 h, with a 100% theoretical yield of ethanol. These results indicate that the nutrients present in the hydrolysate of the residual fractions were sufficient to promote yeast growth and ethanol production. Moreover, the results from this work show the feasibility to obtain protein concentrate and ethanol from Arthrospira platensis, in an integrated process. HIGHTLIGHTS It was possible to perform an integrated process to extract proteins and produce bioethanol from S. platensis. Nutrients on hydrolysate from residual fractions was sufficient to promote yeast growth and bioethanol production. Bioethanol production from hydrolysed residual fractions was 100% efficient.