Produção de etanol de segunda geração pelo uso de complexo enzimático de cepas selecionadas do ecossistema do cerrado

Abstract

Ethanol s sustainable growth, energy supply structure and fuel efficiency have resulted in more worldwide increases for ethanol use than for any other renewable fuel alternative to gasoline. Thus, the study of second generation ethanol (2GE) is one of the most important steps for the valorisation of byproducts that are generated from agrofood industry activities and for promoting better use of surplus sugarcane bagasse in ethanol production. The microorganisms that are able to produce cellulase complex enzyme can be found in various environments including the Brazilian Savanna (Cerrado) ecosystem, which comprises about 5% of the biodiversity in the world. The cerrado has significant potential for producing commercial enzymes by solid state fermentation (SSF) of various agro- industrial wastes and byproducts. In this doctoral thesis, 71 select strains of fungi from the Brazilian Savanna in Minas Gerais State (Triângulo Mineiro-MG) were processed using SSF from sugarcane bagasse and rice bran to produce crude enzyme complex (CEC). The CEC and Saccharomyces cerevisiae were used to produce ethanol from sugarcane bagasse. Six strategies to increase ethanol yield from sugarcane bagasse were evaluated and simultaneous saccharification and fermentation were optimised using a neural network. The following strategies were evaluated: a) CEC was extracted after SSF by employing different extractive mediums (cheese whey, Tween 80 and hydrolysed cheese whey); b) successive fermentations; c) fed-batch fermentation; d) co-fermentations using Saccharomyces cerevisiae followed by Pichia stipitis and reversing the order of fermentation; e) separated hydrolysis and fermentation and f) use of concentrated CEC. The CECs produced by Mucor racemosus Fresenius and Aspergillus niger showed propensities for producing ethanol. In this study, the combined use of CEC and these fungi resulted in 30.1 g/l of ethanol after 72 h of fermentation using mixed biomass of cheese-whey and sugarcane bagasse and CEC from Mucor racemosus Fresenius; 29.0 and 32.0 g/l from CEC produced by Mucor racemosus Fresenius and Aspergillus niger, respectively, after 120 h of sucessive fermentations; 20.6 g/l of ethanol using CEC produced by Aspergillus niger and concentrated by rotoevaporation. The neural network study showed that a maximum ethanol concentration of 12.6 g/l was achieved under the optimal conditions of 47 h, 88.4% of CEC, 36.6 °C, 34.6 g/l of inoculum and 250 g/L of sugarcane bagasse. Results indicate that ethanol concentrations correspond with studies, reported in the literature, of commercial enzymes produced under optimised conditions, which suggests the importance of screening new strains and using CEC in 2GE production.