Variations in structure and saccharification efficiency of biomass of different sorghum varieties subjected to aqueous ammonia and glycerol pretreatments

Abstract

Sorghum biomass is a potential feedstock for lignocellulosic bioethanol production. The selection of suitable sorghum variety is essential to obtain high ethanol yield. In this paper we screened sorghum varieties belonging to sweet sorghum, post rainy sorghum, and hybrid sorghum. These varieties were screened based on their agronomic traits, amenability to pretreatment methods, and enzymatic digestibility. The sorghum biomass was pretreated using glycerol (60 %) at 190 ̊C for 60 min and aqueous ammonia (15 %) at 120 ̊C for 60 min. The digestibility of the pretreated biomass was determined using commercial cellulase (Cellic CTec2) at 10U/g loading, and the structural changes in the pretreated biomass were analyzed by spectroscopy and scanning electron microscopy. Sweet sorghum varieties showed significant variations in phenotypic traits such as fresh stalk yield, dry fodder yield, and juice yield. The cellulose digestibility among the sorghum varieties after the pretreatment also differed significantly. The cellulose digestibility levels of glycerol range from 64 % to 89 % and ammonia pretreated sorghum from 63 % to 81 %. The total sugar yields varied from 227 mg/g to 356 mg/g and 209 mg/g to 313 mg/g for sorghum pretreated with ammonia and glycerol, respectively. Although the delignification of sorghum varieties was higher (31%–65%) after ammonia pretreatment than glycerol pretreatment, the cellulose digestibility was higher for the glycerol pretreated biomass. These results indicated that effect of delignification on cellulose digestibility is trivial. This study explores factors affecting pretreatment and cellulose digestibility of sorghum varieties for maximum sugar yield in the cellulosic ethanol process.