Processing of oat dietary fibre for improved functionality as a food ingredient

Juhani Sibakov

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    A dry fractionation process was developed based on defatted oats. Lipid removal by supercritical carbon dioxide extraction enabled concentration of the main components of oats: starch, protein, lipids and cell walls into specific fractions. A defatted oat bran concentrate (OBC) with 34% beta-glucan was obtained after two grinding and air classification steps. Ultra-fine grinding was needed to further dissociate the macronutrients of oat bran particles. Electrostatic separation was used to separate particles rich in beta-glucan and starch from those rich in arabinoxylan. The beta-glucan from defatted OBC was enriched from 34 to 48% after two steps of electrostatic separation. The 48% beta-glucan fraction was further enriched by a combination of jet-milling and air classification, yielding a fraction with up to 56% beta-glucan. OBC was further processed by partial depolymerisation of beta-glucan with acid- or enzyme-catalysed hydrolysis at relatively low water content using a twin-screw extruder as a bioreactor. The hydrolysed oat brans were extracted with hot water and centrifuged to obtain a water-soluble phase and an insoluble residue. The time-dependent gelling of the water-soluble phase was monitored for 14 weeks at 5 °C. Acid hydrolysis depolymerised the beta-glucan molecules from their original average molecular weight (Mw) of 780 to 34kDa (polydispersity 4.0–6.7), and enzymatic hydrolysis down to 49 kDa (polydispersity 19.0–24.2). At 1.4–2.0% beta-glucan concentration, solutions of beta-glucan molecules with Mw>50 kDa agglomerated rapidly, whereas solutions of smaller molecules (34–49 kDa) remained as stable dispersions for longer. Gelling was strongly concentration-dependent; at 1.4 to 1.6% beta-glucan concentration gelling occurred after 7 to 12 weeks of storage, whereas at 1.8 to 1.9% concentration gelling occurred already after 2 weeks. OBC was used in extruded products in five different forms (untreated, ultra-fine ground, enzymatically hydrolysed and hot-water extracted solubles and insoluble residue). Addition of untreated OBC decreased the expansion (172%) and resulted in harder texture (258 N) compared to extrudates based on 100% endosperm flour (EF) (199% and 148 N, respectively). When OBC was separated into water-insoluble (WIS-OBC) and water-soluble (WS-OBC) fractions, significant differences were observed in the resulting extrudates. Ten percent addition of WIS-OBC fraction significantly decreased the expansion (163%) and increased the hardness (313 N) of EF-based extrudates, whereas 10 or 20% addition of WS-OBC enhanced the expansion (218–226%) and resulted in less hard textures (131–146 N). The improved texture was most probably due to the high amount of soluble fibres and low protein content.
    Translated title of the contributionKauran ravintokuidun prosessointi elintarvikekäytön parantamiseksi
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Laakso, Simo, Supervising Professor
    • Poutanen, Kaisa, Thesis Advisor, External person
    Publisher
    Print ISBNs978-951-38-8165-8
    Electronic ISBNs978-951-38-8166-5
    Publication statusPublished - 2014
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • oats
    • oat bran
    • dietary fibre
    • beta-glucan
    • arabinoxylan
    • defatting
    • supercritical carbon dioxide extraction
    • dry fractionation
    • grinding
    • air classification
    • electrostatic separation
    • jet-milling
    • acid hydrolysis
    • enzymatic hydrolysis
    • low water content
    • extrusion
    • oat-based extrudates
    • mechanical properties
    • extrudate structure

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