A Critical Review on the Effect of Lignin Redeposition on Biomass in Controlling the Process of Enzymatic Hydrolysis

The key factor in lignocellulosic biorefinery is to extract maximum sugars from biomass as feedstock for the process of fermentation. The major barrier in extracting the sugars is the presence of lignin of biomass that primarily restricts the accessibility of cellulose to enzymes. Therefore, it is important to locate the presence and morphology of lignin to assess the reaction severity. In most of the severe pretreatment conditions, lignin is observed to condense and form spherical droplets on the surface of treated biomass. Such formation of pseudo-lignin differs in the action of cellulose hydrolysis from that of the initial or residual lignin content of biomass. In view of that, the present review is focused on the impact of various pretreatment techniques on the morphological changes in lignin and its subsequent redeposition or redistribution effect towards enzymatic hydrolysis process. Initially, the effect of different pretreatment methods is assessed which primarily resulted into the occurrence of lignin redeposition on the surface and interior of biomass. Thereafter, an in-depth insight is provided to understand the underlying mechanism of such formations of pseudo-lignin under severe reaction conditions. Finally, the study is concluded discussing the future recommendation to circumvent the interference of pseudo-lignin on enzymatic reactions. Hence, the present review article will not only help the readers to gain the knowledge on the formations and problems of pseudo-lignin obtained from biomass but also details the latest advancements that are involved to overcome the inhibitory effect of pseudo-lignin during the enzymatic hydrolysis of biomass.