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Innovative processing of brown seaweed for value-added products

Författare

Summary, in English

The increasing depletion of fossil fuels, rising greenhouse gas emissions, and a growing global population have increased the need for sustainable food and energy sources. Traditional industrial biotechnology, which relies on plant-based feedstocks, competes with food production for arable land. In contrast, marine macroalgae do not require cultivatable land, irrigation by fresh water or fertilizers, and are a promising alternative due to fast growth, productivity, and high carbohydrate content. This study focuses on the potential of brown macroalgae as a sustainable source for production of value-added chemicals, food products, and ingredients.
In this research, various pre-treatment methods, including acid, heat, and enzymatic treatment, were performed to solubilize carbohydrates from brown seaweed for subsequent biorefinery utilization. The extracts from acid and heat treatment of Laminaria digitata showed its potential to be used as feed for cultivating thermophilic bacteria, such as Rhodothermus marinus and Bacillus methanolicus, respectively, which are able to produce bioactive compounds and can be used as microbial cell factories, demonstrating the suitability of the extracts for replacing terrestrial carbohydrates for bacterial cultivation.
Biofuel production through fermentation using various microbes, revealed that Thermoanaerobacterium AK17 could utilize not only glucose but also mannitol and glucans released by enzymatic treatment of the brown seaweed L. digitata in ethanol production. Additionally, Clostridial strains studied in this thesis showed different nutrient requirements, but, however, they were able to utilize glucan and mannitol available in the L. digitata hydrolysates for the production of acetone/isopropanol, butanol, and ethanol (A/IBE).
A lactic acid bacteria consortium was shown to be able to ferment mannitol from A. esculenta. This could be a way to increase the shelf life of the seaweed, an alternative to current storage techniques.
Laminarin is a glucan composed of β-1,3(6) linked glucose unit and is a storage carbohydrate in brown seaweed. Enzymes capable of degrading and modifying laminarin and laminari-oligosaccharides were explored for potential valorization of this glucan. In this study, two novel GH17 enzymes were identified in the marine bacterium Muricauda lutaonensis; one is an endo-acting laminarinase, capable of degrading laminarin into short-chain oligosaccharides with a degree of polymerization (DP) 2-4, with potential prebiotic properties. The other is β-1,3-glucanosyltransglycosylase which utilizes β-1,3 linked oligosaccharides with DP above 5 as a donor to introduce β-1,6 linked branches or kinks into β-1,3-glucans, which have potential bioactive properties.
These findings collectively offer invaluable insights into the potential of brown macroalgae as a renewable, sustainable source for biofuels and value-added biomolecules.

Avdelning/ar

Publiceringsår

2023-11-21

Språk

Engelska

Dokumenttyp

Doktorsavhandling

Förlag

Division of Biotechnology, Lund University

Ämne

  • Microbiology

Status

Published

Handledare

ISBN/ISSN/Övrigt

  • ISBN: 978-91-8096-010-6
  • ISBN: 978-91-8096-011-3

Försvarsdatum

15 december 2023

Försvarstid

09:00

Försvarsplats

Lecture Hall KC:A, Kemicentrum, Naturvetarvägen 14, Faculty of Engineering LTH, Lund University, Lund

Opponent

  • Øystein Arlov (Senior Research.)