Engineering of Dietary Fibres

QC 20260518

Abstract

The food industry is one of the largest in Sweden and through it, large side streams are being generated. One such is bran, derived from cereal grains, composed of extractable dietary fibres capable of becoming novel materials such as laccase-driven crosslinked hydrogels. This thesis will explore the valorisation of these fibres through enzymatic modifications, as novel delivery vessel and potential prebiotic properties in order to integrate significant food losses into a circular economy with added health benefits towards the populace.

Feruloylated arabinoxylans previously extracted from wheat (WAX) and rye (RAX)were treated with selective arabinofuranosidases to successfully remove arabinose substitutions not containing ferulic acid moieties, exposing the xylan backbone. This lead largely to a reduced degree of crosslinking in WAX and RAX hydrogels. Rheological and morphological features were affected by the removal with an increase in viscoelastic properties in RAX hydrogels and lead to a more ordered network structure while WAX hydrogels saw the opposite effect regarding both features.

Residual β-glucans in WAX and RAX extracts were investigated. Their molecular weight differed from commercially available β-glucans derived from cereal endosperm, but ratios of cellotriosyl and cellotetraosyl remained similar to previously reported β-glucans. Removal of β-glucans from WAX and RAX extracts using a lichenase prior to laccase-crosslinking resulted in lowered viscoelastic properties for WAX hydrogels and an increase for RAX hydrogels. The removal likely exposes the arabinoxylan backbone similarly to arabinose removal. Freeze-drying at lower temperatures prior to regeneration of hydrogels lead to decreased pore size in hydrogels but increased porosity in RAX hydrogels and decreased in WAX hydrogels,which in turn lead to a decrease in viscoelastic properties in WAX hydrogels but increased in RAX hydrogels. Difference in chemical and physical interactions between the arabinoxylan network between WAX and RAX is believed to be behind their different behaviours. WAX and RAX hydrogels successfully encapsulated and retained target biomolecules of varying sizes and properties as a proof of concept. Pore size and porosity did not severely affect retention of smaller molecules such asglucose and tryptophan but for larger proteins. Addition of a gut bacteria xylanase triggered release of encapsulated molecules.

The common gut bacteria Bacteroides ovatus was successfully grown on WAX, RAX and CAX (corn arabinoxylans) extracts and hydrogels, producing health beneficial short chain fatty acids as secondary metabolites, highlighting the potential prebiotic properties of the extracts and hydrogels. Structural and biochemical differences between carbon sources affected growth, metabolite production and expression levels for enzymes related to arabinoxylan degradation. This thesis has demonstrated that dietary fibres can be effectively valorised by tuning them for multifunctional hydrogels contributing to a circular economy and improved public health.

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