Hemicellulose Research Group

WheatWe are focusing on characterization, modification, and utilization of polysaccharides, especially plant-derived hemicelluloses (xylans, mannans). The more efficient utilization of renewable polymers is one of the challenges for the sustainable development in the future. Hemicelluloses constituting 25-30% of plant materials are the second most abundant plant polysaccharides after cellulose. Hemicelluloses consist of several structurally different polysaccharides that exist in the plant cell walls closely associated with cellulose. In spite of their abundance, hemicelluloses are not yet as effectively utilized as starch and cellulose. Unlike starch, hemiselluloses are not digested by humans, which makes them an interesting raw material both for food (dietary fibre, prebiotics) and chemical industries.

We work with xylans from cereals and woods as well as with different mannans. In addition we collaborate with cereal technologists in the beta-glucan research and are studying on exopolysaccharides, such as different dextrans produced by lactic acid bacteria. One of our aims is to understand better the structure - function relationships of polysaccharides. We are also interested on production of specific oligosaccharides using selective enzymatic hydrolysis, and preparation of films and nanocomposites from renewable hemicellulosic polymers. Enzymes are actively utilized as selective tools in analytics and for targeted modifications of polysaccharide structures and functionalities. The research is done in close collaboration with wood, food, organic and polymer chemists, and food technologists. We work both in national and international collaborative projects funded by the Academy of Finland, Tekes, various foundations and EU.

The PhD education is carried out within two national graduate schools GGS and BIOREGS.

Presently our research focuses on the following topics of xylans, mannans and dextrans: Chemical characterization - Structure-function relationships - Enzymatic modifications and degradation - Production and structure elucidation of oligosaccharides - Chemical modification and functionalization – Bio-based materials: packaging films, polysaccharide aerogels, and emulsions.

Structural characterization and physicochemical properties

NMR spectraIn order to exploit polysaccharides better, their structure-function properties need to be understood. Chemical composition and molecular weight affect largely the physical properties of polymers. The development of reliable analysis methods for chemical structure and molecular mass analysis of polysaccharides is thus of high importance. For the analysis of molar mass, molecular conformation and solution properties of polysaccharides, we focus on two complementary techniques: the high performance size exclusion chromatography (HPSEC) and the asymmetric flow field flow fractionation (AFFFF), which both are equipped with multiple detectors. NMR and mass spectroscopy methods are used for detailed structural analysis. The main focus is on cereal arabinoxylans and bacterial dextrans, which both function for example as food hydrocolloids. Dextran research is conducted in close collaboration with VTT.

Enzymes as selective tools

Oxidized xyloglucanEnzymes have an inherited specificity and require low energy input and represent thus an environmentally sustainable alternative to conventional industrial conversions. We are focusing on both hydrolytic and oxidative carbohydrate-acting enzymes. Enzymes hydrolysing hemicelluloses and dextrans are used as analytical tools, for controlled structural modifications, and for total hydrolysis to monomeric sugars. We are also collaborating with the Swedish research group in the expression of fungal enzymes in plats, particularly in poplar. Of the oxidases, we are focusing on galactose oxidase, which is selectively oxidizing the C-6 hydroxyl to an aldehyde in the terminal galactose units. We have recently shown this modification to result in significant changes in the rheological properties of galactose-containing galactoxyloglucan and galactomannan. Furthermore, the reactive aldehyde can be further used for targeted chemical functionalization.  

Bio-based materials

Packaging films. Polysaccharides provide a sustainable alternative to synthetic plastics, which are currently widely used as food packaging materials. To protect the packed product from the outside environment, barrier properties as well as mechanical strength and flexibility are required. The presence of oxygen inside food packaging is associated with deterioration of the food, reducing the quality and taste of the product. Polysaccharides have shown to be rather good barriers against the permeation of oxygen. We study the potential of different xylans and mannans, especially that of spruce galactoglucomannans, in films and composite films with nanocelluloses. Hemicelluloses have shown promising properties for manufacturing of biodegradable films and coatings for food packaging. The research is carried out in collaboration with Finnish, Swedish, and French experts. 

Polysaccharide aerogels. Aerogels are porous and lightweight, but mechanically strong materials, some of which have excellent thermal insulation properties and/or sorption capacity. Aerogels are prepared from gels by replacing the liquid phase by air, maintaining the dimensions of the solid network. We utilize the ability of certain polysaccharides to form gels, by different mechanisms, in the preparation of bio-based aerogels. Potential future applications for such materials include food and packaging use.

Emulsions. Some hemisellulosic polysaccharides show emulsion stabilizing capacity. The sustainability, water-solubility, and low viscosity of these hemicelluloses in aqueous environment make them potential novel food hydrocolloids for various applications. Our research deals with the mechanisms of emulsion stabilization by hemicelluloses, especially spruce galactoglucomannans.

Analytical facilities

HPSEC analysisThe main analytical methods applied include high performance anion-exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD), gas chromatography (GC-FID, GC-MS), NMR-spectroscopy, mass spectrometry (AP-MALDI- and ESI-MS/MS), high performance size-exclusion chromatography (HPSEC) with RI, UV, differential viscometer and dual angle light scattering (RALS and LALS) detectors, and asymmetric flow field flow fractionation (AFFFF) with RI, UV, FL and light scattering (MALLS and DLS) detectors. AFFFF enables accurate analysis of sizes and shapes of different polymers and their aggregates as the separation is carried out in an open channel and can analyse molecules and particles from nanometers up to tens of micrometers. Presently we are also developing methods for feasible UHPLC-MS analysis of oligosaccharides, and we are working with the French collaborators to produce new specific antibodies for labelling of xylan side groups. One of our strengths is enzyme-assisted oligo- and polysaccharide analysis. We have also facilities needed for the characterization of mechanical, sorption, and barrier properties of films and other packaging, including a newly acquired, modern oxygen transmission rate (OTR) analyzer.

Principal investigators: professor Maija Tenkanen, docent Kirsi Mikkonen (bio-based materials)

For further information and publications click the name of the corresponding person.

Group members:  university lecturer, docent Päivi Tuomainen, university lecturer, docent Kirsti Parikka, docent Leena M. Pitkänen, Dr Mari Lehtonen, Dr. Jose Martin Ramos Diaz
PhD students: Abdul Ghafar, Paula Hirsilä, Qiao Shi,Minna Juvonen, Yan Xu

Group alumni: Dr. Susanna Heikkinen, Dr. Sun-Li Chong, Dr. Helena Pastell, Dr. Ndegwa Maina, docent Liisa Virkki, Dr. Sanna Koutaniemi