Step-change flow rate liquid hot water pretreatment of sweet sorghum bagasse for enhancement of total sugars recovery

A step-change flow rate liquid hot water (SCFLHW) process was developed with the objective of improving the total sugars recovery including xylose and glucose from sweet sorghum bagasse (SSB). Total xylose yield increased from 60% for batch system (4.25% w/v, 18 min, 184 °C) to about 80% at an initial flow rate of 20 ml/min for 8 min, followed by a rate of 10 ml/min for 10 min. It was hypothesized that the flowing water could enhance the mass transfer and improves the sugars recovery. Although little lignin was removed, the 72 h enzymatic digestibility of treated sample was enhanced by the increase of flow rate. The lignin droplet redeposited on the surface of residual solids might play a crucial role in determining the enzymatic digestibility. The total recovery of sugars from SSB, after the pretreatment (first with the flow rate of 20 ml/min for 8 min, then 10 ml/min for 10 min) and 72 h enzymatic digestion, reached 83.7%, which is superior to the recovery using the SO2-steam pretreatment or ammonia fiber expansion.