Patrícia dos Santos Costa

The influence of presaccharification, fermentation temperature and yeast strain on ethanol production from sugarcane bagasse.

Ethanol can be produced from cellulosic biomass in a process known as simultaneous saccharification and fermentation (SSF). The presence of yeast together with the cellulolytic enzyme complex reduces the accumulation of sugars within the reactor, increasing the ethanol yield and saccharification rate. This paper reports the isolation of Saccharomyces cerevisiae LBM-1, a strain capable of growth at 42 °C. In addition, S. cerevisiae LBM-1 and Kluyveromyces marxianus UFV-3 were able to ferment sugar cane bagasse in SSF processes at 37 and 42 °C. Higher ethanol yields were observed when fermentation was initiated after presaccharification at 50°C than at 37 or 42° C. Furthermore, the volumetric productivity of fermentation increased with presaccharification time, from 0.43 g/L/h at 0 h to 1.79 g/L/h after 72 h of presaccharification. The results suggest that the use of thermotolerant yeasts and a presaccharification stage are key to increasing yields in this process.

Enhancing of sugar cane bagasse hydrolysis by Annulohypoxylon stygium glycohydrolases.

The aim of this study was to develop a bioprocess for the production of β-glucosidase and pectinase from the fungus Annulohypoxylon stygium DR47. Media optimization and bioreactor cultivation using citrus bagasse and soybean bran were explored and revealed a maximum production of 6.26 U/mL of pectinase at pH 4.0 and 10.13 U/mL of β-glucosidase at pH 5.0. In addition, the enzymes extracts were able to replace partially Celluclast 1.5L in sugar cane bagasse hydrolysis. Proteomic analysis from A. stygium cultures revealed accessory enzymes, mainly belong to the families GH3 and GH54, that would support enhancement of commercial cocktail saccharification yields. This is the first report describing bioreactor optimization for enzyme production from A. stygium with a view for more efficient degradation of sugar cane bagasse.

Xylanase production by endophytic Aspergillus niger using pentose-rich hydrothermal liquor from sugarcane bagasse

Fungal xylanases have been widely studied and various production methods have been proposed using submerged and solid-state fermentation. This class of enzyme is used to supplement cellulolytic enzyme cocktails in order to enhance the enzymatic hydrolysis of plant cell walls. The present work investigates the production of xylanase and other accessory enzymes by a recently isolated endophytic Aspergillus niger DR02 strain, using the pentose-rich liquor from hydrothermal pretreatment of sugarcane bagasse as carbon source. Batch and fed-batch submerged cultivation approaches were developed in order to minimize the toxicity of the liquor and increase enzyme production. Maximum xylanase activities obtained were 458.1 U/mL for constant fed-batch, 428.1 U/mL for exponential fed-batch, and 264.37 U/mL for pulsed fed-batch modes. The results indicated that carbon-limited fed-batch cultivation can reduce fungal catabolite repression, as well as overcome possible negative effects of toxic compounds present in the pentose-rich liquor. Enzymatic panel and mass spectrometric analyses of the fed-batch A. niger secretome showed high levels of xylanolytic enzymes (GH10, GH11, and GH62 Cazy families), together with cellobiohydrolase (G6 and GH7), β-glucosidase, β-xylosidase (GH3), and feruloyl esterase (CE1) accessory enzyme activities. The yields of glucose and xylose from enzymatic hydrolysis of hydrothermally pretreated sugarcane bagasse increased by 43.7 and 65.3%, respectively, when a commercial cellulase preparation was supplemented with the A. niger DR02 constant fed-batch enzyme complex.