Enzymatic degradation of glucan in the water insoluble fraction of pretreated grasses is influenced by ratio glucan: xylan: lignin

A major aspect of biomass valorisation is the decomposition of plant cell wall into its most abundant polymeric structures. These structures (cellulose, hemicellulose and lignin) are the source for production of fuels and chemicals. Nonetheless, the structural complexity of  plant cell wall added to the lack of knowledge about plant cell wall decomposition dynamics make such processes still a challenge. Decomposition of plant cell wall is requiring certain pretreatment followed by enzymes incubation. 

Studies performed so far mainly focuses on the effect of a specific type of pretreatment under certain conditions for enzyme hydrolysis of cellulose to glucose. There are no studies using a systematic approach to understand the effect of removal of hemicellulose and lignin on cellulose hydrolysis. The evaluation of the effect of acid and alkali catalysis at elevated temperatures for different grass type lignocellulosic biomass has been performed. Carbohydrate and lignin mass balances were calculated of selected residues and hydrolysates after catalysis, to understand which part of hemicellulose and lignin is solubilized. Next, enzymatic saccharification of glucan was correlated to the ratio of hemicellulose/lignin/glucan in the different water insoluble residues. Alkali pretreatment resulted into extensive lignin removal, but it also provoked xylan degradation or losses. Acid pretreatment resulted into higher solubilization of xylan while lignin remained. Xylan solubilisation, increased glucan hydrolysis of residual glucan by enzymes but, at too extensive removal of xylan, the glucan hydrolysis became less efficient. Lignin removal increased cellulose saccharification by the enzymes used. Addition of a xylanase-enriched enzyme cocktail almost completely hydrolysed glucan.