The effect of pretreatment on enzyme synergism between various lignocellulolytic enzymes on hardwoods - a comparative evaluation of Populus, Eucalyptus and Acacia spp. as potential feedstocks for sugar release

Currently, there is a growing interest in utilizing hardwoods as feedstocks for bioethanol production, due to their fast growth coppices, large biomass production, ability to adapt to different environments and the ease of their delignification during the pretreatment processes. In this study, three hardwoods were subjected to two pretreatments (Organosolv and Steam explosion) and compared with respect to how these pretreatments affect their compositional and structural characteristics. A rational design of synergistic lignocellulolytic enzyme cocktails to efficiently degrade the respective pretreated hardwoods was conducted. Intra-molecular synergism (between enzymes hydrolysing the same polysaccharide) cocktails were designed as follow: a cellulolytic core-set (Cel5A, Cel6A, Cel7A and Cel7B purified from Celluclast) for the optimal release of glucose, and a xylanolytic core-set (Trichoderma viride β-xylanase, Helix pomatia α-glucuronidase and Clostridium thermocellum α-arabinofuranosidase) for the optimal release of xylose was formulated using factorial design and response surface methodology. Using the optimal intra-molecular synergistic cocktails, an inter-molecular synergism (between enzymes hydrolysing various polysaccharides associated with each other) cocktail was established for optimal glucose and xylose release from the various pretreated hardwood substrates. The effect of auxiliary (non-GH family) enzymes (such as Orpinomyces sp. acetyl xylan esterase and Agaricus bisporus laccase) on the efficiency of the inter-molecular synergistic cocktail on sugar release was also evaluated. This study provided insights into the effects of various pretreatments on the chemical composition, morphology and enzymatic hydrolysis of the substrate and assessed whether the same lignocellulolytic cocktail can be used to efficiently hydrolyse different hardwood species.