Uso de coquetéis lignocelulolíticos produzidos por consórcio fúngico na sacarificação de bagaço de cana-de-açúcar e produção de etanol

Abstract

The present study evaluated the production of lignocellulolytic cocktails by solid-state fermentation (SSF), using sugarcane bagasse and wheat bran as substrates and the fungal strains Aspergillus niger SCBM1 (Ni), Aspergillus fumigatus SCBM6 (Fu), Ganoderma lucidum 601 (Ga), Trametes versicolor 561 (Tr) and Pleurotus ostreatus PLO6 (Pl) in monocultures and/or in consortia. The crude extracts produced were evaluated in the hydrolysis of sugarcane bagasse pretreated by autohydrolysis (AH) and by autohydrolysis followed by alkaline pretreatment (NaOH) (AH-Soda). The enzymatic cocktails that presented the best yields in terms of fermentable sugars were selected and evaluated in new hydrolyses experiments with high loads of solids and with addition of the surfactant Triton X-100. At last, alcoholic fermentations of the hydrolysates containing the highest glucose concentrations were carried out. In the SSF performed with isolated strains, the fermentation that used A. niger SCBM1 as inoculum (Ni – F1 extract) was the most outstanding in the production of enzymes, with maximum activities for endoglicanae (82.70 U/g), exoglicanae (80.48 U/g), β-xylosidase (145.01 U/g) and manganese peroxidase (3.38 U/g). For the SSF performed in co-culture of fungal strains, the extracts produced by consortia between Ni+Fu+Pl (F9), Ni+Tr+Pl (F6) and Ni+Ga+Pl (F10) presented the highest productions of cellulases and hemicellulases, mainly β-glucosidase (104.70, 171.09 and 106.10 U/g), β-xylosidase (89.72, 139.99 and 121.02 U/g) and xylanase (2582.38, 2267.96 and 1697.74 U/g), respectively. The crude cocktail produced from the consortium between Basidiomycetes (Tr+Ga+Pl) was the most efficient for laccase production (25.27 U/g). After the hydrolyses, the highest glucose concentrations were obtained in the hydrolysates of sugarcane bagasse pretreated by AH and AH-Soda using Ni extract (F1) with 10.78 and 10,32 g/L, Fu+Ga+Pl extract (F11) with 9.76 g/L (AH) and 10.60 g/L (AH-Soda) and Ni+Ga+Pl extract (F10) with 11.92 g/L in AH-Soda hydrolysate. For xylose, the highest release was obtained after F8 hydrolysis that used Ni+Fu+Tr extract in sugarcane bagasse pretreatment by AH (5.08 g/L). After alcoholic fermentation, 60.80 % (in relation to the theoretical maximum) of conversion was achieved in F1 (Ni hydrolysate), with a production of 3,20 g/L of ethanol and 58,15 % in F6 (3,08 g/L) of ethanol. In hydrolysis performed with high load of solids, the results obtained showed that the concentrations of total reducing sugars (TRS) increased from 15.54 to 44.84 g/L in Ni hydrolysate (F1), when the percentage of bagasse pretreatment by AH increased from 10 to 35 % . In the Ni+Tr+Pl (F6) hydrolysate, TRS concentration increased from 11.38 to 31.77 g/L under the same conditions. The addition of surfactant did not significantly influenced concentration of TRS in Ni hydrolysate (45.16 g/L). In the F6 hydrolysis, the TRS concentration increased from 30.94 to 48.16 g/L, suggesting that for this extract, the use of surfactant favored the enzymatic action. The fermentation of F6 hydrolysate produced 1.66 g/L of ethanol, with 88.03 % of conversion in relation to the theoretical maximum. The obtained results are promising and encourage additional studies using enzymatic extracts produced by fungal consortium in new hydrolysis conditions in order to enhance the production of fermentable sugars and second generation ethanol (2G ethanol).