Biorefinery in a pulp mill: use of wood-based hemicelluloses for the production of oligomers for food and health applications

PhD project

Hemicelluloses, along with cellulose and lignins, represent one of the main constituents of wood The goal of our research is the rational approach to the production of bioactive carbon resources from a yet unexploited and abundant industrial waste: hemicelluloses. For this purpose, we will first extract hemicellulose from softwood using autohydrolysis process. The degree of oligomerisation as well as the functional groups of hemicellulose preparation will be characterised. In the next step this preparation will undergo refinement with chosen glycolytic enzymes in order to obtain small oligomers. Resulting hemicellulose fractions will be analysed for their prebiotic properties, using cell growth analysis of human gut symbionts known to be involved in human health and well-being.

 

Our project addresses the challenge of producing high-added-value molecules for human health- prebiotics - from non-food vegetal biomass, using green fractionation technologies. This fully complies with the so-called biorefinery concept aiming at preparing new molecules from vegetal biomass. This will be achieved thanks to the development of new techniques and through collaboration between the “Biorefinery: chemistry and eco-processes” team of LGP2, that is specialized in developing environmentally friendly wood fractionation processes, and also in wood components characterization, and the TheREx/TIMC-IMAG laboratory dedicated to the development of new innovative biological therapies.

Main results

The overall objectives of this project were first to extract and to characterize hemicelluloses oligosaccharides candidate products. Then their prebiotic effects were assessed both in vitro on pure selected strains and in vivo on mice model.

 

The first step was to work on oligosaccharides production and purification in order to optimize the extraction of hemicelluloses from wood by autohydrolysis. The extracted products were then fractionated and characterised in terms of osidic composition, impurities (organic acids, sugar degradation products, lignin), and oligomers’ structure.

 

The second phase demonstrated the good in vitro fermentability of hemicelluloses oligomers by beneficial bacteria (Bifidobacterium adolescentis, Akkermansia muciniphila and Lactobacillus salivarius) compared to a pathogen (Escherichia coli LF82). The parameters of interest were the bacterial growth, short chain fatty acid (SCFA) production, or depletion of carbohydrates in the broth. Although bacterial response was different among the different hemicellulose oligomers fractions, the ethanol:water precipitate (PPeth) fraction was the best candidate for further experimentation since it strongly induced a growth of B. adolescentis while being more convenient to produce (on a laboratory scale). The bacterium selectivity for a specific fraction seemed to be linked in priority to the degree of polymerization rather than acetylation degree, even if the acetylation seems to slow down the fermentation.

 

The third and final stage involved in vivo experimentation in a mouse model. 57BL/6J mice were used to gain knowledge on the effect of softwood hemicellulose oligosaccharides on gut homeostasis. While 8 mice were fed with standard diet (a control group), the other 8 mice received PPeth fraction dissolved in the water. A metagenomic analysis of the 16S ribosomal RNA in caecal samples revealed that the caecal microbiota depends strongly on diet: the hemicellulose-fed mice showed a significant increase in Bacteroidetes and diminished growth of Firmicutes and Proteobacteria. Hemicelluloses did not only modulate bacterial population, it also increased production of SCFA, an important source of energy. The ratio tryptophan/kynurenine increased as well as serotonin and its precursor. Finally, no inflammation was detected.

 

All these results imply that oligosaccharides extracted from softwood hemicellulose can potentially be very interesting as prebiotics

CONTACTS

Christine Chirat (Project PI)
Bertrand Toussaint (co-PI)
Vivien Deloule (PhD student)

 

PARTNERS

Laboratoire de génie
des procédés papetiers

Centre hospitalier universitaire de Grenoble

 

FUNDING

Tec21

PUBLICATIONS

 

Deloule et al. 2020. Prebiotic role of softwool hemicellulose in healthy mice model. Journal of Functionnal Foods, 64, 103688. https://doi.org/10.1016/j.jff.2019.103

Deloule et al. 2017. Production of hemicellulose oligomers from softwood chips using autohydrolysis followed by an enzymatic post-hydrolysis. Holzforschung, 71(7-8), 575-581. https://doi.org/10.1515/hf-2016-0181

 

PATENT

Chirat et al. Prebiotic composition comprising galactoglucomannans. France, Patent WO2019180396 (A1), 26 Sept. 2019.

 

VALORISATION


Technology maturation (SATT Linksium): Hemicellprebio (2018)

Startup incubation (SATT Linksium): WHN - Wood for Health and Nutrition (2019)