The relation between the supramolecular structure of cellulose and its hydrolysability
Doktorsavhandling, 2015

The liberation of fermentable sugars from cellulosic biomass during enzymatic hydrolysis is often incomplete. One of the factors limiting the efficiency of enzymatic hydrolysis is the structural properties of cellulose. The aim of the work presented in this thesis was to increase our understanding of the relation between enzymatic hydrolysis and the structural properties of cellulosic substrates. The enzymatic hydrolysis of a number of cellulosic substrates derived from softwood preparations used in the pulp and paper industry, as well as model substrates, were studied. The differences in cellulosic substrates before and after enzymatic hydrolysis are described on the nanometre scale in terms of their supramolecular structure, i.e. the lateral dimensions of fibrils and fibril aggregates, the accessible surface area, the crystallinity and porosity, using solid-state nuclear magnetic resonance spectroscopy. The substrates were imaged and structural changes in the cellulosic substrates were characterized in real time on the micrometre scale in terms of their molecular density, ordering and autofluorescence, employing nonlinear optical microscopy. A strong correlation was found between the average pore size and the specific surface area of the starting material and the enzymatic conversion yield. The overall degree of crystallinity and the lateral dimensions of the fibrils increased in some samples as a result of hydrolysis. Avicel had a higher carbon–hydrogen bond density and a different pattern of ordered structures than the never-dried pulp fibres, possibly reflecting the collapse of the macromolecular structures during drying and rewetting. Monitoring of the substrates during enzymatic hydrolysis revealed substrate-characteristic hydrolysis pattern. The response of the most widely studied filamentous fungus for cellulase production, Trichoderma reesei, to cellulosic substrates with different supramolecular structures was studied. Substantial differences were found in the profile of the enzymes produced, despite the fact that there were only minor differences in the chemical composition of the cellulose-rich substrates. Culture filtrates from five filamentous fungi cultivations were evaluated regarding their ability to improve saccharification of the industrial cellulase cocktail Celluclast 1.5L. It was demonstrated that supplementing commercial cocktails with enzymes from carefully selected fungi can result in significantly more efficient saccharification of biomass.

Cellulose I

SHG

Cellulases

CARS

Imaging

Trichoderma reesei

MPEF

CP/MAS 13C-NMR

Secretomics

KB-salen, Kemihuset, Kemigården 4
Opponent: Bernd Nidetzky

Författare

Ausra Peciulyte

Chalmers, Biologi och bioteknik, Industriell bioteknik

Impact of the supramolecular structure of cellulose on the efficiency of enzymatic hydrolysis

Biotechnology for Biofuels,; Vol. 8(2015)

Artikel i vetenskaplig tidskrift

As a result of the increasing burden on the environment and the scarcity of natural resources, we need to find new ways of supplying a growing population with products for daily life. In a bio-based economy we want to produce bioplastics, biochemicals and biofuels from plant biomass. Cellulose is a renewable resource, and can provide the starting point for many products that can satisfy the increasing demand for sustainable and biocompatible products. Cellulose serves as a strengthening component in plants, and its structure is therefore resilient and complex. We need to use certain enzymes, known collectively as cellulases, which are produced by other microorganisms, such as bacteria and filamentous fungi, to degrade cellulose into glucose, which can serve as an energy source. In the laboratory, these microorganisms are grown under harsh conditions, where the production of enzymes takes place in closed tanks containing nutrients, which are stirred while air is supplied. The aim is to produce large amounts of enzymes within a few days, so that they can be added to cellulose to break down the cellulose into glucose as quickly as possible. During the course of this work, I studied the structure of cellulose during enzymatic hydrolysis with the aim of expanding our knowledge on the reason why cellulose is so difficult to break down and, in the longer perspective, to improve enzymatic hydrolysis.

Drivkrafter

Hållbar utveckling

Ämneskategorier

Industriell bioteknik

Styrkeområden

Livsvetenskaper och teknik

ISBN

978-91-7597-301-2

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 3982

KB-salen, Kemihuset, Kemigården 4

Opponent: Bernd Nidetzky