Rice bran extract: an inexpensive nitrogen source for the production of 2G ethanol from sugarcane bagasse hydrolysate

Abstract

Selection of the raw material and its efficient utilization are the critical factors in economization of second generation (2G) ethanol production. Fermentation of the released sugars into ethanol by a suitable ethanol producing microorganism using cheap media ingredients is the cornerstone of the overall process. This study evaluated the potential of rice bran extract (RBE) as a cheap nitrogen source for the production of 2G ethanol by Scheffersomyces (Pichia) stipitis NRRL Y-7124 using sugarcane bagasse (SB) hemicellulosic hydrolysate. Dilute acid hydrolysis of SB showed 12.45 g/l of xylose and 0.67 g/l of glucose along with inhibitors. It was concentrated by vacuum evaporation and submitted to sequential detoxification (neutralization by calcium hydroxide and charcoal adsorption). The detoxified hydrolysate revealed the removal of furfural (81 %) and 5-hydroxymethylfurfural (61 %) leading to the final concentration of glucose (1.69 g/l) and xylose (33.03 g/l). S. stipitis was grown in three different fermentation media composed of detoxified hydrolysate as carbon source supplemented with varying nitrogen sources i.e. medium #1 (RBE + ammonium sulfate + calcium chloride), medium #2 (yeast extract + peptone) and medium #3 (yeast extract + peptone + malt extract). Medium #1 showed maximum ethanol production (8.6 g/l, yield 0.22 g/g) followed by medium #2 (8.1 g/l, yield 0.19 g/g) and medium #3 (7.4 g/l, yield 0.18 g/g).

Hemicellulosic ethanol production by immobilized cells ofScheffersomyces stipitis: Effect of cell concentration and stirring

“…The SB was mixed with H 2 SO 4 (98% purity) at a ratio of 100 mg H 2 SO 4 / g of dry bagasse for 20 min at 121 C, using 10% substrate concentration. 11,12 After hydrolysis, the reaction mixture was cooled, recovered and was stored at 4 C. The hydrolysate was concentrated under a reduced pressure by a concentrator of 32L capacity at 70 C in order to obtain a xylose concentration of 30 g/L. This concentrated hydrolysate was subsequently detoxified following the method of Alves et al 13 to remove inhibitors generated during dilute acid hydrolysis.…”

Immobilization of Scheffersomyces stipitis cells with calcium alginate beads: A sustainable method for hemicellulosic ethanol production from sugarcane bagasse hydrolysate

“…Pichia stipitis) is promising candidate for ethanol production from dilute acid (C 5 sugars) and enzymatic hydrolysates (C 6 sugars) from lignocellulosics [12,13,15,16]. Application of immobilized cells is a promising method to increase the cell mass concentration in the fermenter which in-turn increase the productivity and minimize the processing cost [17].…”

“…The hydrolysis was performed in a reactor of 100L capacity. The SB was mixed with H 2 SO 4 (98% purity) in a ratio of 100 mg H 2 SO 4 / g of dry bagasse for 20 min at 121 °C, using 10% substrate concentration [11,12].…”

“…Dilute acid hydrolysis usually performed at temperature (120-180 ºC) and residence times (15-60 min) [9]. However, dilute acid hydrolysis of SB employing the conditions (121 ºC, 20 min, 100 mg H 2 SO 4 / g of dry bagasse) have shown appreciable sugar levels with fewer cell wall derived inhibitors [11,12]. It is necessary to eliminate these inhibitors from hemicellulosic hydrolysates prior to microbial fermentation in order to obtain optimum ethanol yields [13].…”

“…It is necessary to eliminate these inhibitors from hemicellulosic hydrolysates prior to microbial fermentation in order to obtain optimum ethanol yields [13]. Sequential calcium oxide based neutralization followed by activated charcoal adsorption has shown efficient removal of inhibitors from acid hydrolysates [12]. D-xylose is the principal sugar in hemicellulosic hydrolysates and the fermentation of D-xylose still has many challenges [14].…”