Table sugar, chemically known as sucrose, has received a bad reputation. Healthy lifestyle habits and the end of the European sugar quota lead to large amounts of unused sugar and plummeting prices. Sugar industry, agriculture and a variety of markets are looking for alternative uses of sucrose – or its derivatives.

One class of these derivatives are Cellodextrins, oligomers build up from glucose, one of the main two components of sucrose. Scientists from the Austrian Centre of Industrial Biotechnology (acib) and the Graz University of Technology found a way to produce Cellodextrins and control their oligomeric state for the first time.

Therefore, because of their prebiotic and health-promoting properties, Cellodextrins become of high importance for industrial products such as in human- and animal nutrition as well as bulking agents or cosmetics additives.

Uncontrolled reactions are troublesome. In chemistry this could even lead to explosions and release of toxic hazards. Fortunately, it is not that dangerous to produce cellodextrins in a controllable manner.

Still, these glucose polymers gave scientist a hard time. But now, for the first time, a new biotechnological finding within the EU-project CARBAFIN brings light into a process that was poorly understood so far: Scientists from the Austrian Centre of Industrial Biotechnology (acib) and Graz University of Technology discovered an efficient way to produce cellodextrins – and for the first time control their oligomeric state.

"In nature, these glucose oligomers consisting of three or more glucose monomers result from the breakdown of cellulose, part of every plant and the most important and common organic compound in the world.

However, they can also be build up from sugar sucrose as proposed in our research project", says acib-scientist Christiane Luley, pointing out why this discovery is crucial for several markets, but especially the sugar industry.

Luley: "The end of the European sugar quota of 2017, regulating production as well as in- and export, together with society's decreasing sugar consumption based on a healthier lifestyle led to plummeting prices." Since then, industry and agriculture are in desperate need of alternative uses for sugar.

CREATING VALUE FROM SUGAR

The CARBAFIN consortium aims to establish a new value chain for the utilization of surplus sugar beet biomass by converting the two components of sucrose, glucose and fructose, separately into value-added products at industrial scale.

One of these value chains will be cellodextrins, in other words oligosaccharides from glucose", says Luley.

In this particular field, the scientists are exploring relatively unknown territory, since the characterization and application of cellodextrins is still not fully understood.

Cellulosis, the breakdown of cellulose, either happens in the intestine of ruminants like cows by the help of symbiotic bacteria or during chemical hydrolysis in biofuel industry.

In both cases the reaction is uncontrolled and mixtures of cellooligosaccharides are obtained. Therefore, scientists can only predict the properties of the single oligomeric molecules.

Appropriate efficacy studies have not been carried out yet due to unavailability of material.

STRINGING TOGETHER THE CHAIN OF MONOMERS

“There are several reasons why cellodextrins are not broadly available“, says Luley, „with the most important one being the fact that it is extremely complex to produce cellodextrins with a specific chain length.“

What does that mean? These molecular chains are classified by their degree of polymerization (DP), indicating the number of linked glucose monomers they contain.

The common rule is, the longer the chain of glucose monomers (e.g. from 8 to 10), the less soluble it is, which makes it harder for the cell to use these chunks of oligosaccharides.

But solubility, and hence a control of the length of these cellodextrins, is a key factor for using these oligosaccharides for a variety of products: "We know that cellodextrins will be important for future applications in human and animal nutrition.

They are predicted to have prebiotic and health-promoting properties and also have potential as bulking agents or cosmetics additives."

CONTROL IS KEY

To control the DP, the scientists in CARBAFIN put the cart before the horse: "Other than the usual approach to break down cellulose by hydrolysis to get a mixture of different cellooligosaccharides, we used a bottom-up synthesis.

We build cellodextrin – starting with Glucose-1-phosphate coming from sucrose – adding one glucose molecule after the other with the help of Cellobiose Phosphorylase and Cellodextrin Phosphorylase to get a soluble, defined DP range from cellotriose (DP3) to cellohexaose (DP6) in consistent quantity and reproducible quality."

With this process, carried out in an aqueous solvent supported by phosphate removal, the acib- and TUG-scientists were able to shift the reaction equilibrium completely towards the product: "We conducted reaction engineering and found the perfect substrate- as well as enzyme ratios.

Now we have reached the proof of principle and are able to produce 40g of product per litre, which is near industrial scale (100g per litre)", reveals Luley proudly and ensures, that production of these cellodextrins in industrial scale will soon be possible for the first time.

SWEET PERSPECTIVES

This will be a major breakthrough and an opportunity for the global sugar market, finally being able to use several 100.000 tons of surplus sugar yearly.

Furthermore, the biocatalytic production process will enable the industry to introduce new business opportunities and completely new value chains in Europe. The industry partner in CARBAFIN, Pfeifer & Langen, will demonstrate the new production process in 100-L scale.

Soon the scientific findings could enable different industrial uses of sucrose for various markets. This would– in the fullest sense of the word – be sweet for sugar to take on new tasks.