Effect of extrusion conditions and hydrolysis with fiber-degrading enzymes on the production of C5 and C6 sugars from brewers’ spent grain for bioethanol production

Abstract

Please cite this article as: Heredia-Olea E., Pérez-Carrillo E., Serna-Saldívar S.O. Effect of extrusion conditions and hydrolysis with fiber degrading enzymes in the production of C5 and C6 sugars from brewers' spent grain for bioethanol production. Effect of extrusion conditions and hydrolysis with fiber-degrading enzymes on the production of C5 and C6 sugars from brewers' spent grain for bioethanol production The bioconversion of brewers' spent grain into bioethanol was investigated in the present study using thermoplastic extrusion and the use of fiber degrading enzymes. The extrusion conditions i.e. tempering moisture, screws speed, and temperature of last zone of the barrel were taken into account in order to optimize the yield of C5 and C6 sugars during the subsequent enzymatic hydrolysis step of the fibers. The most important variable that affected the sugar yield was the extrusion temperature, followed by the screws speed. The best extrusion conditions were 20% tempering moisture, 200 rpm and 50 °C. No enzymatic and yeast inhibitors were detected in any of the enzymatically-treated fiber hydrolyzates. The fermentation resulted in 5.43 mL bioethanol per 100g of extruded brewers' spent grain (dry weight basis). The only sugar consumed was glucose. The free amino nitrogen amount quantified in the hydrolyzates was as low as >20 mg L -1 , negatively affecting sugars consumption during the fermentation and consequently the ethanol yield.

Intensifying ethanol production from brewer’s spent grain waste: Use of whole slurry at high solid loadings

“…Alkali, acid or hydrothermal pretreatments are usually performed to deconstruct the lignocellulosic matrix and enable access to sugars in the cellulosic fraction [9][10][11][12][13][14]. Applying such strategies, it has been possible to achieve ethanol concentrations ranging from 4.3 to 22.0 g L −1 , with yields between 23% and 81% [9][10][11][12][13][14][15][16][17]. Such values are considered insufficient when envisaging bioethanol production.…”

An Overview of Extrusion as a Pretreatment Method of Lignocellulosic Biomass

“…While Karunanithy and Muthukumarappan [117] found the best result by decreasing the screw speed from 150 to 50 rpm, Heredia et al [118] obtained their bests results by increasing the screw speed from 100 up to 200 rpm. However, it is important to notice that Heredia et al [118] ran the extrusion under 20% moisture at 50 • C, while Karunanithy and Muthukumarappan [117] worked at 15% moisture content and 150 • C. It is also possible to vary the screw speed between high and low settings during the extrusion process. In that case, a way to overcome the rise of the SME is to lower the torque at high screw speeds [64,78].…”

“…It must be related to other extrusion parameters. For example, Karunanithy and Muthukumarappan [117] extruded switchgrass, while Heredia et al [118] extruded Brewers' spent grain. Both studies recorded opposite behavior about screw speed over the glucose recovery yield.…”

The Potential of Brewer’s Spent Grain in the Circular Bioeconomy: State of the Art and Future Perspectives

“…Widely used pretreatment techniques comprise acid hydrolysis, alkaline wet oxidation and steam explosion, which involve high temperatures and pressures and often lead to the formation of compounds that negatively affect the further fermentation of sugars into ethanol. In contrast, enzymatic hydrolysis, which is carried out under mild conditions, does not generate hazardous by-products (Heredia-Olea et al, 2015). For example, application of two laccase preparations from Pleurotus ostreatus on milled BSG resulted in up to 94% of phenols reduction.…”