Thermo-acid pretreatment and enzymatic hydrolysis of a mixture of cocoa pod shell and brewer’s spent grain

Abstract

The use of agro-industrial residues (AIR) has stood out due to its constitution (cellulose, hemicellulose, starch, etc.) – which, when hydrolyzed, releases fermentable sugars – and, due to the fact that Brazil has a strong agro-industrial sector, this country has a great availability and variety of RAI. Thus, with a view to proposing the use of RAIs available in southern Bahia to obtain bioethanol, an equivalent mixture (w/w) of cocoa husk (CC) and brewer’s spent grain (BSG) was investigated. The best process conditions, which resulted in 224.37 µmol/g of reducing sugars (glucose) per weight of total solids, were defined with the aid of the Experimental Design statistical tool for the pretreatment [ratio of total solids of 5.3% (w/v), 0.5% (v/v) HCl and autoclaving time of 15 min] and for the hydrolysis [pH = 4.0, total enzymatic charge by weight of total solids of 40 U/g (commercial amylases), 70 °C and 30 min]. The hydrolyzed medium obtained was then fermented for 18 h, resulting in 4.6% (v/v) of etanol, and the results obtained so far indicate that the mixture of CC and BM, instead of the individual use of these residues, can be destined to different bioprocesses. It was also observed that increasing the proportion of CC in the mixture decreases the hydrolyzed mass, due to its different chemical composition, which proves the need to evaluate different pre-treatment techniques for different proportions of RAI and thus optimize the obtainment of sugars fermentable.