Structural features and enzymatic digestibility of Napier grass fibre treated with aqueous ammonia

Abstract

We characterised the structural changes of Napier grass after treatment with aqueous ammonia (27%, w/w) at a solid:liquid ratio of 1:12 for 14 days at ambient temperature and evaluated its enzymatic digestibility. This treatment protected carbohydrates in the fibre and greatly reduced lignin content (58.7% lignin removal), resulting in the deconstruction of the fibrous matrix. Although the relative cellulose content increased, the degree of crystallinity of the treated fibre increased only marginally from 42.9 to 50.0%, which can be attributed to the partial disruption of the cellulose crystal structure. Aqueous ammonia treatment markedly promoted the enzymatic cellulose digestibility, increasing from 18 to 53% with an enzyme loading of 30FPU/g biomass. Supplementation of cellulase with xylanase (30FPU cellulase+100XU xylanase/g biomass) improved the final extent of hydrolysis and greatly enhanced the final glucose yield, approaching to 80% glucan conversion.