Mathematical modeling of the enzymatic saccharification process of lignocellulosic biowaste

Abstract

Lignocellulose is a biowaste produced in large quantities by industries; approximately 181.5 billion tons are produced annually in the world. This makes this type of residue a qualifiable candidate resource of energy, which nowadays, is underutilized. It is estimated that the food processing industry produces around 1.3 billion tons per year. In Mexico, the craft beer industry produces 3.8 thousand tons per year of brewers' spent grain. Being Mexico's fastest-growing industry, it can be considered a suitable source of biowaste. Brewers spent grain is considered a lignocellulosic material, which possesses a complicated structure containing lignin, hemicellulose, and cellulose. Due to its complexity, diversity, and recalcitrance to degradation, specific pretreatments to degrade it have been developed, such as biological, chemical, physical, and physicochemical. Notwithstanding, in nature, fungi are well-known microorganisms capable of degrading it through a tremendous battery of enzymes that are secreted in an ordered and systematic fashion. Nonetheless, the full understanding of this process, and the order in which each enzyme acts on lignocellulose, is far to be elucidated. Therefore, the present thesis aims to develop fungi bio-inspired mechanistic mathematical model capable of describing the enzymatic degradation process of lignocellulose biomass (brewers spent grain) and evaluate it through different experiments. Sequential addition of enzymes to biowaste, as well as experiments involving the addition of a pool without key enzymes that were further added at a specific time, were evaluated. Overall, results revealed that the lignin is not the most resilient and dense layer of lignocellulose as it has been believed. On the contrary, it seems lignin forms pore-like structures and diffuses through all different layers of this substrate. When hemicellulases (xylanases and pectinases) were not present in the enzyme pool, the reaction was not favored, indicating the importance of this polymer in lignin structure. These results gave an idea of how fungi work in nature and how the polymer layers are organized in lignin. However, to fully confirm these findings, more tests need to be performed to generate a robust and proven mechanistic mathematical model, enabling us to lay the foundations of a potential industrial-scale process.