Monday, April 29, 2013
Exhibit Hall
We will present the phenomenon and mechanism of significant enhancement in enzymatic saccharification of lignocelluloses at elevated pH of 5.5 – 6.0 (measured pH). This phenomenon contradicts a well-established concept of “optimal pH 4.8 – 5.0” for enzymatic hydrolysis that is exclusively practiced in numerous laboratories throughout the world. To provide mechanistic understanding and validate the observed phenomenon, four enzymatic hydrolysis lignin residues were isolated from lodgepole pine pretreated by either dilute acid or Sulfite Pretreatment to Overcome Recalcitrance of Lignocelluloses (SPORL). The adsorption isotherms of a commercial cellulase (CTec2) to these lignin residues at 50oC were measured at a pH range of 4.5 – 6.0. The zeta potentials of these lignin samples were also measured. The study discovered that elevated pH significantly increased lignin surface charge (negative), causing lignin to become more hydrophilic, coordinately reducing its affinity to cellulase and consequently the nonspecific binding of cellulase. The reduction in nonspecific cellulase binding to lignin is also attributed to enhanced electrostatic interactions at elevated pH through the increased negative charges of most cellulase enzymes with low pI of less than 5.0. The gains in enzymatic saccharification efficiencies at elevated pH for the four different pretreated lignocelluloses were found to be linearly proportional to the amount of reduction in nonspecific cellulase binding to lignin measured at the corresponding elevated pH. Because an elevated pH of 5.5 - 6.0 is favoable for fermentation, and can be easily implemented commercially without very limited cots, this study has both scientific importance and practical significance.