In Silico-Supported Methods for Sustainable and Targeted Isolation of Natural Compounds from Side-Streams of Food Production

The aim of this thesis was to develop resource-saving, sustainable and toxicologically harmless processes for the extraction of bioactive natural substances from side-streams of food production that are intended for use in dietary supplements, cosmetics or pharmaceuticals. The “Conductor-like Screening Model for Real Solvents” (COSMO-RS), based on thermodynamic calculations, is a suitable in silico model to minimize the necessary preliminary tests. Natural Deep Eutectic Solvents (NADES) are generally formed by mixing hydrogen bond acceptors (HBA) and hydrogen bond donors (HBD) and represent a promising alternative to conventional extraction with solvents, which are often toxicologically questionable, highly flammable, and environmentally harmful.

First this study analyzed the phytochemical composition of peanut hulls (Arachis hypogaea). As a result, the main compounds of an ethanolic peanut hull extract were first identified using high-performance liquid chromatography coupled with electrospray mass spectrometry (HPLC-ESI-MS). The targeted in silico-selection (COSMO-RS) of a suitable biphasic solvent system was then carried out to separate the main components of the extract using countercurrent chromatography (CCC). The chromatographic separation of the extract was performed by high-performance countercurrent chromatography (HPCCC) using the biphasic solvent system consisting of n-hexane/ethyl acetate/methanol/water, whereby three flavonoids could be isolated. The successful in silico-selection of a biphasic solvent system for the isolation of flavonoids from an ethanolic peanut hull extract using HPCCC was described for the first time. The identity and purity of three isolated flavonoids were analyzed using HPLC-ESI-MS/MS and nuclear magnetic resonance spectroscopy (1D/2D-NMR).

Furthermore, in this thesis, the biphasic solvent system consisting of n-hexane/ethyl acetate/methanol/water (HEMWat) was selected as a suitable system for the separation of stilbenoids from an ethanolic grapevine extract using an in silico-supported selection method (COSMO-RS). Subsequently, two stilbenoids were isolated by HPCCC using the offline heart-cut technique. The identity and purity of the isolated stilbenoids were analyzed using HPLC-ESI-MS/MS and 1D/2D-NMR. In addition, a targeted extraction approach using NADES systems was applied to obtain a stilbenoid-containing extract from grapevine canes. For this purpose, an in silico-supported pre-selection (COSMO-RS) of customized NADES systems for the extraction of stilbenoids was made, which was described for the first time in this thesis. Several extraction methods were evaluated, and the ultrasonic-assisted extraction method was found to be the most promising due to its shorter extraction time. By using this method, an extraction yield comparable to that of conventional methods using ethanolic extractants was achieved.

This method of prior in silico-selection of NADES systems and ultrasonic-assisted extraction was also used in this work to extract oligomeric stilbenoids from grapevine roots. For the most suitable NADES system, the extraction parameters water content, molar ratio HBA/HBD, the biomass/NADES ratio and the extraction time were optimized, resulting in a higher extraction yield of stilbenoids with the optimal parameters compared to the extraction with conventional methods using ethanolic extractants. The first analytical studies on the storage stability of stilbenoids in NADES systems showed that stilbenoids can be stored in the NADES system composed of choline chloride and 1,2-propanediol. However, they become unstable when stored in a NADES system prepared from fructose and lactic acid. For the preparation of a NADES-free extract, the NADES components could be removed using adsorbent materials (Amberlite® XAD-16N resin).

The results of this thesis showed that both an in silico-supported selection of the biphasic solvent system for the isolation of bioactive natural compounds from crude extracts using HPCCC and the selection of customized NADES systems for the extraction of natural compounds could be carried out successfully. In addition, the potential of a NADES-based, solvent-free as well as environmentally friendly extraction of oligomeric stilbenoids, which represent an interesting alternative to conventional extraction agents, was demonstrated for the first time.