Enhanced enzymatic digestibility of water lettuce by liquid hot water pretreatment

Liquid hot water (LHW) pretreatment conditions were optimized from various severities using response surface methodology to convert water lettuce (WL; Pistia stratiotes) to fermentable sugars to enhance the enzymatic digestibility of pretreated WL. The LHW pretreatment was performed using a 2% (w/v) WL loading over a temperature range of 152-208 degrees C and pretreatment times of 9-51 min. The optimal conditions for the LHW pretreatment were determined to be 190.7 degrees C for 51 min [a severity factor (log R0) of 4.38], which gave the highest total reducing sugar yield (17.26 g/L) and a high removal level of hemicellulose (68.32%) in the subsequent cellulase digestion. The physical structure of WL after pretreatment revealed changes to the WL structure that increased its susceptibility to attack by enzymes; an increased crystallinity, surface area, and total pore volume together with a lower hemicellulose and lignin content compared to the untreated WL.