Enzymatic fractionation of brewer’s spent grain and bioconversion of lignin-rich fractions in a colon model in vitro
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School of Chemical Technology |
Doctoral thesis (article-based)
| Defence date: 2016-04-15
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Authors
Date
2016
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Degree programme
Language
en
Pages
86 + app. 48
Series
Aalto University publication series DOCTORAL DISSERTATIONS, 45/2016, VTT Science, 124
Abstract
The objectives of this thesis were to produce lignin-rich fractions from brewer's spent grain (BSG) and to study the interactions of the lignin in these fractions with colon microbiota in vitro. Different milling pre-treatments were studied to enhance enzymatic hydrolysis of BSG carbohydrates. Ball-milling, which was the most efficient treatment, increased carbohydrate solubilisation from 23 to 45 %. Thus, milling notably improved enzymatic solubility of cell wall polysaccharides but was not effective enough to enable their total hydrolysis. Two lignin-rich fractions (24 and 40 % lignin content) were obtained by enzymatic fractionation of BSG using carbohydrases and proteases. In addition, a separate alkaline extraction provided BSG-derived material with low ferulic acid content. BSG and the fractions were used to study if lignin is degraded and metabolised by colon microbiota in a metabolic model and if lignin suppresses microbial conversions in the colon. A number of mono- and dimeric phenolic metabolites were formed upon digestion of BSG and the fractions by the microbiota. It appeared that many of them were structurally lignin-related indicating their release from lignin and conversion by colon microbiota. However, the extent of lignin degradation was estimated to be low. No notable suppression of microbial conversions was detected based on the formation of linear short chain fatty acids. In addition, experiments with pure strains of lactobacilli and bifidobacteria showed no inhibition of growth by a lignin-rich fraction. Association of lignin with carbohydrates or proteinaceous material may have reduced the possible antimicrobial effects of lignin. The results of the present study provide new information on the significance of lignin as part of dietary fibre indicating its partial metabolism by colon microbiota.Tämän väitöskirjatyön tavoitteena oli valmistaa ligniinipitoisia jakeita panimomäskistä sekä tutkia näiden jakeiden avulla ligniinin ja suolistomikrobien vuorovaikutuksia. Erilaisten jauhatusten vaikutusta mäskin hiilihydraattien entsymaattiseen hydrolyysiin tutkittiin, ja kuulamyllytys osoittautui tehokkaimmaksi parantaen hiilihydraattien hydrolysoituvuutta 23 %:sta 45 %:iin. Jauhatus ei kuitenkaan ollut riittävän tehokas esikäsittely hiilihydraattien kokonaishydrolyysin kannalta. Kaksi ligniinipitoista jaetta (24 ja 40 % ligniiniä) valmistettiin hiilihydraatteja ja proteiineja pilkkovien entsyymien avulla. Lisäksi emäskäsittelyllä tuotettiin jae, josta ferulahapot oli lähes kokonaan poistettu. Mäskin ja sen jakeiden avulla tutkittiin paksusuolen olosuhteita simuloivassa metaboliamallissa, pilkkovatko suolistomikrobit ligniiniä ja estääkö ligniini mikrobien aineenvaihdunnan toimintoja. Metaboliamallissa muodostui pieniä, fenolisia aineenvaihduntatuotteita, joista useat olivat rakenteensa perusteella todennäköisesti ligniiniperäisiä. Ligniinin pilkkoutuminen vaikutti kuitenkin vähäiseltä. Lyhyiden, suoraketjuisten rasvahappojen muodostumisen perusteella ligniini ei haitannut mikrobien hiilihydraattifermentaatiota. Ligniini ei myöskään estänyt laktobasillien tai bifidobakteerien kasvua. Ligniinin sidonnaisuus hiilihydraatteihin tai proteiiniperäiseen materiaaliin saattoi suojata mikrobeja ligniinin mahdollisilta antimikrobisilta ominaisuuksilta. Tutkimuksen tulokset antavat uutta tietoa ligniinin hajoamisesta suolistossa sekä sen merkityksestä osana ravintokuitua.Description
Supervising professor
Linder, Markus, Prof., Aalto University, Department of Biotechnology and Chemical Technology, FinlandThesis advisor
Poutanen, Kaisa, Prof., VTT Technical Research Centre of FinlandBuchert, Johanna, Prof., Natural Resources Institute Finland, Finland
Keywords
brewer's spent grain, enzymatic fractionation, lignin, colon microbiota, colon metabolic model, panimomäski, entsymaattinen fraktiointi, ligniini, suolistomikrobisto, metabolinen paksusuolimalli
Other note
Parts
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[Publication 1]: Niemi P., Faulds C.B., Sibakov J., Holopainen U., Poutanen K., Buchert J. (2012) Effect of a milling pre-treatment on the enzymatic hydrolysis of carbohydrates in brewer's spent grain. Bioresour. Technol. 116, 155-160.
DOI: 10.1016/j.biortech.2012.04.043 View at publisher
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[Publication 2]: Niemi P., Martins D., Buchert J., Faulds C.B. (2013) Pre-hydrolysis with carbohydrases facilitates the release of protein from brewer's spent grain. Bioresour. Technol. 136, 529-534.
DOI: 10.1016/j.biortech.2013.03.076 View at publisher
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[Publication 3]: Niemi P., Tamminen T., Smeds A., Viljanen K., Ohra-aho T., Holopainen-Mantila U., Faulds C.B., Poutanen K., Buchert J. (2012) Characterization of lipids and lignans in brewer’s spent grain. J. Agric. Food Chem. 60, 9910–9917.
DOI: 10.1021/jf302684x View at publisher
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[Publication 4]: Niemi P., Aura A.-M., Maukonen J., Smeds A., Mattila I., Niemelä K., Tamminen T., Faulds C.B., Buchert J., Poutanen K. (2013) Interactions of a lignin-rich fraction from brewer’s spent grain with gut microbiota in vitro. J. Agric. Food Chem. 61, 6754‒6762.
DOI: 10.1021/jf401738x View at publisher
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[Publication 5]: Aura A.-M., Niemi P., Mattila I., Niemelä K., Smeds A., Tamminen T., Faulds C.B., Buchert J., Poutanen K. (2013) Release of small phenolic compounds from brewer’s spent grain and its lignin fractions by human intestinal microbiota in vitro. J. Agric. Food Chem. 61, 9744‒9753.
DOI: 10.1021/jf4024195 View at publisher