Kinetic analysis and phenolic influence during multi-step enzymatic hydrolysis of hydrothermal pretreated sago pith (Metroxylon sagu) for liquid sugar production

Abstract

Sago pith, a potential substrate for liquid sugar production, presents challenges due to its complex lignocellulosic structure and the presence of phenolic compounds. This study aimed to elucidate the structural changes in sago pith during pretreatment, investigate enzyme kinetics, and assess the influence of phenolic compounds in multi-step enzymatic hydrolysis. Phenolic compounds were extracted from sago pith, and pretreated sago pith flour (PSPF) was obtained. Enzymatic hydrolysis employed α-amylase, xylanase, mannanase, and cellulase, with kinetics and phenolic effects analyzed. FTIR and optical microscopy revealed changes in PSPF, including alterations in lignin distribution, cellulose, and hemicellulose concentrations, starch granule disruption, and partial phenolic compound removal. The process primarily solubilized amorphous cellulose, starch, and soluble lignin into the liquid fraction. Following this, multi-step enzymatic hydrolysis using α-amylase, xylanase, and amyloglucosidase significantly enhanced sugar yields by maximizing enzyme–substrate interaction and enabling enzyme synergy, achieving a conversion degree of 95–98% after 216–240 h. This approach also demonstrated potential for extracting phenolic by-products from PSPF through enzyme-assisted methods. Furthermore, phenolic accumulation in PSPF influenced enzyme activity: at lower phenolic concentrations, the compounds acted as activators for α-amylase and xylanase, while at higher concentrations, they inhibited enzymatic activity. This study presents a novel approach by using the entire sago pith, including starch and lignocellulose fractions, and examining the dual role of sago pith phenolic compounds in enzymatic hydrolysis, which has not been explored in previous research.