Hemicellulose Research Group

Wheat We 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 - Preparation of biodegradable films.

Structural characterization and physicochemical properties

NMR spectra In 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.

Films and composites

Films from xylan Various packages are produced to protect and preserve food. Many foods must be protected from the ingress of oxygen, which reduces the quality and the taste of the product. Polysaccharides have shown to be rather good materials for barriers for oxygen. We are studying the potential of different xylans and mannas, especially that of spruce galactoglucomannans, in films and composite films with different nanocelluloses. Hemicelluloses have shown promising properties for manufacturing of biodegradable films and coatings for food packing. The research is carried out in collaboration with Finnish, Swedish and French experts.

Enzymes as selective tools

Oxidized xyloglucan Enzymes 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.

Analytical facilities

HPSEC analysis The 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 permeability properties of films

COST FP0901

Principal investigator: professor Maija Tenkanen

Group members: university lecturer, docent Päivi Tuomainen, university lecturer, docent Liisa Virkki, Dr. Sanna Koutaniemi, Dr. Kirsi Mikkonen, Dr. Kirsti Parikka. PhD students: Sun-Li Chong, Susanna Heikkinen, Qiao Shi, Minna Juvonen

Group alumni: Dr. Helena Pastell, Dr. Ndegwa Maina, Dr. Leena M. Pitkänen