Biochemical characterisation of sugar beet pulp and its biotechnological product Curran®

Abstract

For the production of biotechnological materials, sustainable resources are required that do not compete with the food supply. Such a material is the cheap and plentiful sugar beet pulp (SBP), a cell-wall-rich by-product from the sugar industry. The long-term goal of this study is to improve effective waste management of SBP and its application as a carbohydrate-rich material.

I have characterised SBP and its derived biotechnological product, Curran®, by investigating the chemical composition, the constituent polysaccharides’ molecular mass and the product’s potential to interact with water. Curran® has valuable rheological properties and thus numerous potential industrial uses, for example as an additive in paints. Viscosity of Curran® is considered the most significant parameter to distinguish between high- and low-value products (high viscosity is usually regarded as being of higher value). Therefore, a wide range of different viscosity experimental Currans® (eC) were selected for this project.

I hypothesised that the composition, as well as polysaccharides’ molecular mass, have a significant influence on viscosity. Results from this project showed that eC are a changed cell wall polymer network, comprising essentially all the cellulose, much of the hemicellulose but only low levels of pectins.

I further tested whether the molecular mass of hemicellulosic and pectic polysaccharides in eC affects viscosity of the product. All hemicelluloses and pectins in eC showed decreased molecular mass compared with the polysaccharides in SBP. In addition, high-viscosity eC contained the smallest pectic polysaccharides. This led to the conclusion that viscosity increases with decreasing molecular mass of the non-cellulosic polysaccharides. I finally investigated the accessibility of hydroxyl (–OH) groups in the polysaccharide network of eC products and other carbohydrate samples. The –OH group availability is an important factor for the interaction of eC with other industrial ingredients.

Hence, the availability of –OH groups was hypothesised to correlate with viscosity of the eC products. This work established an easy, but sensitive, method for the relative quantification of available –OH groups in different carbohydrate materials such as paper, xyloglucan, SBP and eC products. The method is based on the quantification of 3H remaining bound to carbohydrate samples after removal of 3H2O by desiccation.

The percentage of 3H retained and hence availability of –OH groups in eC products increased with increasing viscosity. Greater availability of –OH groups might increase the interaction of eC particles with each other and water molecules which leads to enhanced viscosity. Furthermore, the addition of these eC or Curran® products to paints may benefit the paint’s properties (such as cracking resistance in hot or cold conditions).

The findings of this thesis contribute to an improved understanding of Curran’s® rheological properties and may lead to an optimised production of Curran®. In future, this might inform strategies of adding Curran® to a wide range of products and thereby increase the use of “waste” for biobased materials.