The influence of different pretreatments strategies on the release of phenolics and their consequential inhibitory effect on the enzymatic hydrolysis of sugarcane bagasse

The complete utilization of plant cell wall components requires an efficient pretreatment that allows good carbohydrate and lignin recoveries, while significantly increasing the accessibility of the cellulose. However, sugarcane bagasse has proven to be a recalcitrant feedstock with effective cellulose hydrolysis influenced by pretreatment and substrate factors. Our previous work on sugarcane bagasse showed that the residual lignin in association with cellulose after pretreated appeared to be the major barrier limiting the efficient enzymatic hydrolysis of the cellulosic component when  low enzyme loadings were used. As well as the highly documented inhibitory effect of the residual lignin via unproductive binding of the deconstruction enzymes and lignin’s association within the substrate matrix limiting cellulose accessibility, it has also been suggested that the soluble phenolics that are released during the course of hydrolysis could contribute to the slowdown in the hydrolysis rate/inhibition of the enzymes. To try to better understand the possible contribution of released phenolics to the overall gradual slowdown of the enzymatic hydrolysis rate and inhibition, soluble phenolics derived from the  sugarcane bagasse pretreated by five different pretreatments (including acid and alkaline, with and without sulphonation) were investigated. It was apparent that the different pretreatment methods affected the pattern of phenolics solubilisation as well as the hydrolytic performance of commercial cellulase mixtures used at various protein loadings on a range of pretreated sugarcane bagasse substrates. The possible mechanisms behind this inhibition and possible ways to minimise inhibition when low enzyme loadings and high substrate concentrations are used will be discussed.