Effects of successive microwave and enzymatic treatments on the release of p-hydroxycinnamic acids from two types of grass biomass

Biomass recalcitrance is one of the main bottlenecks in lignocellulosic biorefinery deployment. Physico-chemical pretreatments and enzymatic hydrolysis are two procedures that can be combined to overcome this recalcitrance. In this study microwave pretreatment has been selected for its relevant conditions that allow for biomass recalcitrance to be reduced, along with the maintenance of a low consumption of energy and reactants. A xylanolytic enzymatic cocktail, Rovabio® Advance, was investigated for its ability to hydrolyze maize stalks and Miscanthus leaves after pressurized, chemical-free microwave pretreatment. This combination was implemented to increase the breakage of ester bonds and thus facilitate the release of p-hydroxycinnamic acids. This study demonstrates how, in comparison with Miscanthus, both pretreatments are more effective in releasing p-hydroxycinnamic acids from maize stalks, due to their lower parietal content. The successive free-chemical process seems to be particularly promising on maize stalks, since it led to a ferulic acid release yield of 18.2%, compared to 5.5% for microwave pretreatment only or 7.6% when performing enzymatic hydrolysis without a microwave pretreatment step.