Food carbohydrates & Lignin

Carbohydrates determine to a large extent quality attributes of the final food product while polysaccharides (e.g. pectic substances, hemicelluloses, cellulose) as present in fresh fruits and vegetables (e.g. ripeness, texture) determines their typical characteristics as well as their processing characteristics in the manufacture of foods (juices, nectars, purees, preserves). 

Polysaccharides also influence the extractability of important constituents of plant raw materials like sugar, oil, proteins, etc. Dietary fibers and prebiotic oligosaccharides, including mammalian milk oligosaccharides, play an important role in human and animal health, and their behaviour in the gastrointestinal tract strongly depend on the chemical structure of these fibers.

Aim

We aim to establish relationships between the chemical fine structure of the carbohydrate and the corresponding functional property of this carbohydrate (isolated or as present in the original product).

Typical materials studied are: cereals like wheat, corn; fruits and vegetables like apple, tomato, carrots, potatoes, soybeans; food ingredient like pectin, galactomannans, xanthan, as well as human milk and fermentation digests.

Techniques

In general, various classes of oligo- and polysaccharides as present in fruits, vegetables, cereals or food products derived here from and of agrotechnological by-products are extracted and characterised by e.g.sugar (linkage) composition, substituents, molecular weight. Unknown carbohydrate structures are separated by (preparative) chromatography and characterised using mass spectrometry and NMR. 

Enzymatic fingerprinting methods using pure and well characterised enzymes are being used and further developed to enable ‘sequencing’ of complex carbohydrate structures using state-of-the-art LC-MS platforms. The fate of individual prebiotic and dietary fiber structure during the digestion and fermentation in in vitro models as well in human and animals are monitored using the same analytical techniques.

The theme ‘Lignocellulose biochemistry’ studies the changes in carbohydrates and of lignin during plant biomass conversion processes. Understanding of fungal and enzymatic-driven routes to degrade the plant carbohydrates and lignin is a major topic within this theme. These processes are not only limited to the more well-known biorefinery’s existing to produce food, fuels, and value-added chemicals from biomass, but also relating projects e.g. biomass composting for mushroom growth, or feed digestibility (animal nutrition) are part of this theme.

We study mainly conversion of grasses, of which the plant cell walls are majorly composed of cellulose, hemicellulosic arabino-glucurono-xylan and of lignin. These three polymers contribute to the plant cell wall architecture, which influences physical characteristics like toughness (and degradability), and water binding capacity. A better understanding of the chemical fine-structure of the cell wall architecture’s network will provide a better understanding of how to influence changes in biomass architecture and it’s enzymatic (biological) degradation.

Aim

• Monitor changes in lignin and plant carbohydrate levels and composition during pretreatment, fungal growth, enzymatic processes, and during animal digestion
• Understand mode-of-action of (fungal) hydrolytic and oxidative carbohydrate and lignin degrading enzymes and their effect on the chemical fine structure of natural substrates.

Techniques

For the lignin analysis, we have set-up a new method via pyrolysis-GC-MS, making use of a mildly extracted 13C-lignin isolate from wheat straw as internal standard. This method allows us to specifically quantify residual lignin content in situ, while simultaneously providing structural insights. Further lignin characterisation via NMR (HSQC) has been set up. 

Carbohydrate analysis is applied in situ or/and after extraction polysaccharides. Examples of analysis are carbohydrate content and composition, the sugar linkage composition, the type and amount of substituents on the carbohydrates present. Various chromatographic and mass spectrometric techniques are available.