multiPS: Innovative multienzymatic prebiotic synthesis

Galactooligosaccharides (GOS) are formed in a side reaction of lactose hydrolysis by the enzyme β-galactosidase, in which the galactose residue remaining at the active center is not transferred to water, but to another sugar molecule (so-called transgalactosylation). The extent of this transgalactosylation depends primarily on the organism of origin of the β-galactosidase and the initial lactose concentration. GOS are considered prebiotics and can be labeled as dietary fiber from 3 monomers (EU Regulation No. 1169/2011). Due to their structural similarity to human breast milk oligosaccharides, GOS promote the growth of positive intestinal flora (bifidobacteria and lactobacilli) in infants and adults alike. They also inhibit pathogenic germs (cancer protection), promote calcium absorption and improve stool consistency. Due to their high pH and temperature stability, GOS can be added to a variety of foods (e.g. fruit juices, baked goods, ...).

Whey can serve as a possible source of lactose for GOS synthesis. It is a by-product of cheese production, whereby only approx. 1 kg of product (hard cheese) is obtained from 10 liters of raw material (milk), but at the same time approx. 9 liters of whey are produced. In Germany, the whey volume in 2023 was approx. 14 million tons (Milchindustrie-Verband e.V., Annual Report 2023/2024). In addition to lactose, whey also contains lactose salts and whey proteins. The exact composition depends on the product (hard cheese, soft cheese, cream cheese, ...) and the specific process control in the dairy.

It is known that these other whey ingredients can lead to a change in the behavior (activity, stability, transgalactosylation activity) of β-galactosidase and thus to changes in GOS yields compared to synthetic buffers. Therefore, the synthesis conditions may have to be adapted if a substrate change from the optimal buffer to real systems (whey, whey permeate) takes place.

The project aims to realize value creation and sustainable use of dairy by-products by converting the lactose they contain into prebiotic galactooligosaccharides (GOS). For this purpose, a multi-enzyme system consisting of four different enzymes is used for the first time in order to achieve an intensification of the synthesis process and thus increase the yield (especially of longer-chain GOS) on the one hand and to remove unconverted substrate (lactose) and thus produce high-purity GOS products on the other. Several valuable products are thus obtained from the low-priced lactose, which are used in the food industry (GOS as prebiotics) or pharmaceutical industry (lactobionic acid).