Using sweet sorghum bagasse for production of amylases required for its grain hydrolysis via a biorefinery platform

Abstract

Sweet sorghum plant, a widely grown energy crop, was utilized through a biorefinery process, by which its grains were hydrolyzed by the crude amylases produced from its bagasse. The hemicellulosic part of the bagasse was hydrolyzed with 0.5–1.0% sulfuric acid at 140–180 °C for 30–60 min and applied for amylase production using halotolerant bacterium Nesterenkonia sp. strain F. In the hydrolysate obtained at 140 °C for 60 min using 1% acid, Nesterenkonia showed 73.3 U/mL amylase activity by the consumption of 16.2 g/L xylose and 8.3 g/L other sugars. Supplementation of the hydrolysates with sorghum grain resulted in 38–67% higher amylase production. Furthermore, addition of biocompatible surfactants of Tween 20 and Tween 80 (0.1 g/L) increased the activity to 93 and 97 U/mL, respectively. The resulting crude enzyme was used in the process of ethanol production from both tannin-containing and tannin-free sorghum grains (6%), leading to 17.7 and 17.0 g/L bioethanol production, respectively. Through the cultivation of Nesterenkonia on the hemicellulosic hydrolysates, 5–10 g/L volatile fatty acids (VFA), 0.36–0.69 g/L acetone-butanol-ethanol (ABE), and 468–721 mg/L single cell protein (SCP) were also produced. The obtained SCP contained most of the essential amino acids and relatively high amounts of phenylalanine (8%), threonine (7%), methionine (6%), and lysine (6%). © 2018 Elsevier B.V.