Comparison of sodium hydroxide and sodium bicarbonate pretreatment methods for characteristic and enzymatic hydrolysis of sago palm bark

Abstract

ABSTRACTThe present work utilized a by-product of the starch industry in Malaysia, Sago bark waste (SB), for pretreatment and enzymatic hydrolysis. SB was subjected to two types of alkaline pretreatment to assess their effect on SB characteristic, inhibitor formation, and enzymatic hydrolysis sugar yield. Dilute sodium hydroxide (DSH) and dilute sodium bicarbonate (DSB) were used for SB pretreatment. The pretreatment was carried out in a conventional heating environment (120ºC) for 10 min before the enzymatic hydrolysis step. The results showed that the treated SB by DSB resulted in higher removal of lignin (28%) compared to DSH (25%). The TGA, XRD, and SEM analysis results revealed that both types of pretreatment have slight differences. The crystallinity index (CI) for DSH and DSB was 43.2% and 41.2%, respectively. Meanwhile, HPLC results illustrated that the only inhibitor present in the pretreatment liquor is acetic acid at 0.25 mg/ml for DBS pretreatment and 0.063 mg/ml for DSH pretreatment. 229 ± 12 mg/g of total reducing sugar was found using DSH pretreatment, which is slightly higher than that one was obtained by DSB pretreatment (219 ± 16 mg/g) after enzymatic hydrolysis step. A similar observation was found on glucose and xylose yield. These results make us interfere that the diluted level of sodium bicarbonate can lead to approximately similar results of sodium hydroxide, which offer a cheap route of the pretreatment process.