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Item type:Publication, Access status: with files , Conversion of natural tissues and food waste into aerogels and their application in oleogelation(Royal Society of Chemistry (RSC), 2025-04-04); ; ; ; In this work, various natural tissues were for the first time directly converted into nanostructured aerogels by utilizing their intrinsic (meso-)porosity. In contrast to common aerogel production, no use of pure biopolymers, their extraction, dissolution, gelation or use of additives (e.g. crosslinkers, acids and bases) was necessary. The production process required washing of the wet starting material with water, a solvent exchange with ethanol and drying with supercritical CO2. The resulting materials exhibited low bulk densities (0.01–0.12 g cm−3), significant specific surface areas (108–446 m2 g−1) and mesopore volumes (0.3–2.6 cm3 g−1). Assessment of 20 different tissues including fruit pulp and peel, vegetable pulp, and mushrooms showed the generality of the approach. A broad spectrum of different microstructures was identified, whereas especially textural properties of samples derived from water rich pulp were highly similar to those found in classical biopolymer aerogels, for instance based on pectin or cellulose. Furthermore, the capability of the materials to structure liquid sunflower oil was shown: the produced oleogels exhibited exceptionally high oil uptake (max. 99%) and rheological properties similar to those of solid fats. Results suggest that supercritical drying of tissues (e.g. based on food waste) is a suitable approach for their upcycling into value added materials by a complete green and sustainable process. This research also contributes to sustainable development by transforming food waste into valuable aerogels and promoting science education through accessible, open-source STEM resources.Publicationtype: Journal Article70 30 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Transparent cellulose aerogels from concentrated salt solutions : synthesis and characterization(Wiley, 2024-08-29); ; ; In this work, nanostructured and transparent cellulose aerogels are synthesized via a purely salt induced approach from non‐modified microcrystalline cellulose type II. The production process requires in contrast to state of the art methods no pretreatment of cellulose or use of expensive cellulose‐solvents: it consists of hydrogel formation via cross‐linking of cellulose with calcium ions, a solvent exchange and a supercritical drying step. A systematic multiparameter study reveals that a high level of structural control is achievable: ratios of macro‐ to mesoporosity and the size of mesopores can be tailored by adjustment of the calcium ion content, while keeping a high overall porosity in the range of 92% – 96 %. The build‐up of homogeneous, fine pore structures results in a significant increase of the specific surface area as compared to conventional calcium‐free aerogels (684 vs. 300 m² g⁻¹). Remarkably, the Ca²⁺‐cross‐linking renders aerogels transparent, with Rayleigh scattering being the dominant scattering mechanism. Additional ion exchange to Ca²⁺ in the hydrogel‐state leads to further reduction of the pore size and to products with optimized optical properties, e.g., light transmission of 91% at an incidents light wavelength of 800 nm and a substrate thickness of 1.5 mm.Publicationtype: Journal Article108 77 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , 83 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Oleogels from mesoporous whey and potato protein based aerogel microparticles : influence of microstructural properties on oleogelation ability(Elsevier, 2023); ; ; ; Animal-based whey protein isolate (WPI) and plant-based potato protein isolate (PPI) aerogel microparticles (particle size ∼40–77 μm) were produced via top-down wet milling of alcogels followed by supercritical–CO2–drying and used as matrices for structuring of liquid sunflower oil. pH variation (pH 3.0, 7.0, 9.0) during heat-induced gelation was used to tune aerogel microstructural properties, resulting in high specific surface areas (347–480 m2/g) and mesopore volumes (2.3–5.6 m3/g) as well as different macro-to mesoporous ratios. Oleogels oil content (70–84 wt.%) and firmness (0.55–1.25 N) were related to pH during gelation, yielding firmest oleogels for aerogel templates produced at pH 9. All oleogel samples showed high physical stability, as shown by oil holding capacity (OHC) up to 95%. Minimization of macropore volume, high mesopore fractions, and high specific surface areas were found to increase OHC. Results suggest that for WPI and PPI, different aerogels microstructures induced by different gelation pH rather than protein nature, to be the driving factor affecting aerogel oleogelation ability and demonstrate the versatility of the aerogel particle-template approach in terms of protein source, thus highlighting the importance of aerogel microstructure design to fine-tune oleogel properties.Publicationtype: Journal Article118 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Workshop GRK 2462 "Processes in Natural and Technical Particle-Fluid-Systems" (PintPFS) : 26th & 27th of September 2022, Hamburg, Germany : conference proceedings(2022-09-26); ; ; ; In the framework of Research Training Group GRK 2462 “Processes in Natural and Technical Particle-Fluid-Systems” (PintPFS), funded by the German Research Foundation (DFG), researchers from the fields of civil engineering, mechanical engineering, process engineering, and materials sciences investigate natural and technical Particle-Fluid-Systems (PFS) in an interdisciplinary approach. As PFS are ubiquitous in everyday life and relevant for many processes in industry, pharmacy, and food production, they represent a fascinating field of research with potential for promising and useful discoveries in many aspects.Publicationtype: Conference Proceedings407 2182 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Hydro- and aerogels from ethanolic potato and whey protein solutions: Influence of temperature and ethanol concentration on viscoelastic properties, protein interactions, and microstructureDenaturation, aggregation, and gelation of protein solutions can be induced through increased temperatures and the presence of organic solvents. Depending on the molecular features of the involved proteins, the denaturation conditions lead to very different gel properties. However, it is poorly understood how organic solvents in combination with heat treatments can be used to modify the textural properties of protein gels. In this study, the combined effects of heat and ethanol (EtOH) treatment on hydrogel formation by whey (WPI) and potato protein isolates (PPI) were investigated. The different protein hydrogels were subjected to a complete solvent exchange with EtOH and dried with supercritical CO2 to obtain aerogels with a high inner surface area. Increasing EtOH concentration during thermally induced hydrogel formation reduced the temperature of unfolding up to a point where denaturation occurred at room temperature. WPI and PPI formed very different gels in the presence of EtOH. WPI gels with an EtOH content below 10% (w/w) were elastic and mainly linked through disulfide bonds. Higher EtOH content led to weak gels, mainly linked through electrostatic and hydrogen bonds. For PPI gels, increasing EtOH content did not influence the protein interactions within the gels, and textural properties were very similar. The textural properties of the resulting aerogels were dependent on the type of protein interactions created in the hydrogels. This work provides insights into the way food proteins form gel networks and how these interactions can be manipulated to produce gels with tailor-made properties.Publicationtype: Journal Article120 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Conversion of whey protein aerogel particles into oleogels : effect of oil type on structural features(Multidisciplinary Digital Publishing Institute (MDPI), 2021-11-23); ; ; ; Protein aerogel particles prepared by supercritical-CO₂-drying (SCD) of ground whey protein (WP) hydrogels (20% w/w, pH 5.7) were converted into oleogels by dispersion in selected edible oils (castor, cod liver, corn, flaxseed, MCT, peanut and sunflower oil). The obtained oleogels were analysed for oil content, microstructure, rheological properties, and ATR-FTIR spectra. Except for castor oil, solid-like, plastic materials with comparable composition (80% oil, 20% WP) and rheological properties (G′~3.5 × 10 5 Pa, G″~0.20 × 10 5 Pa, critical stress~800 Pa, tanδ~0.060) were obtained. Optical and confocal microscopy showed that the generated structure was associated with the capillary-driven absorption of oil into the porous aerogel particles interconnected via particle-particle interactions. In this structure, the oil was stably entrapped. Results evidenced the reduced role of edible oil characteristics with the exception of castor oil, whose high polarity probably favoured particle–oil interactions hindering particle networking. This work demonstrates that WP aerogels could be regarded as versatile oleogel templates allowing the structuring of many edible oils into solid-like materials.Publicationtype: Journal ArticleScopus© Citations 18 169 291 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Hydrophobic Modification of Biopolymer Aerogels by Cold Plasma Coating(Multidisciplinary Digital Publishing Institute (MDPI), 2021-09-04); ; ; ; The aim of this work was to evaluate the potential of cold plasma polymerization as a simple, fast and versatile technique for deposition of protective hydrophobic and oleophobic polymer layers on hydrophilic biopolymer aerogels. Polymerization of different fluorinated monomers (octafluorocyclobutane C<sub>4</sub>F<sub>8</sub> and perfluoro-acrylates PFAC-6 and PFAC-8) on aerogel monoliths derived from alginate, cellulose, whey protein isolate (WPI) and potato protein isolate (PPI) resulted in fast and significant surface hydrophobization after short process times of 5 min and led to superhydrophobic surfaces with static water contact angles up to 154° after application of poly-C<sub>4</sub>F<sub>8</sub> coatings. Simultaneous introduction of hydro- and oleophobicity was possible by deposition of perfluoro-acrylates. While the porous structure of aerogels stayed intact during the process, polymerization inside the aerogels pores led to the generation of new porous moieties and resulted therefore in significant increase in the specific surface area. The magnitude of the effect depended on the individual process settings and on the overall porosity of the substrates. A maximization of specific surface area increase (+179 m<sup>2</sup>/g) was obtained by applying a pulsed wave mode in the C<sub>4</sub>F<sub>8</sub>-coating of alginate aerogels.Publicationtype: Journal ArticleScopus© Citations 13 285 333 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Microstructures of potato protein hydrogels and aerogels produced by thermal crosslinking and supercritical dryingAerogels are highly porous structures created from hydrogels by solvent exchange and supercritical CO2 drying. They can be produced from proteins and used for encapsulation of active ingredients. In this work, the structural relationship between various protein based hydrogels and aerogels was investigated. We compare egg white protein (EWP) and patatin rich potato protein isolates (PPI) in terms of gel and aerogel production thereof. Thereby, aerogels were produced for the first time from patatin-rich potato protein isolates. Both protein sources can form strong hydrogels, but they differ in their molecular properties, especially regarding the presence of reactive groups available for covalent crosslinking. Therefore, we studied the rheological profiles of hydrogels of both protein groups and applied the ratio of elastic modulus at gel formation temperature (G'hot) and after cooling to ambient temperature (G'cool) as criterion for comparing gel formation capacities produced from structurally different proteins. The ratio G'cool/G'hot was also identified as an indicator of the relation of non-covalent bonds to covalent and/or hydrophobic interactions and for characterizing aerogel structural properties. PPI hydrogels were found to be dominated by hydrophobic interactions, while covalent disulfide bonds determine EWP hydrogel stabilization. Nevertheless, PPI and EWP hydrogel and aerogels showed similar stabilities. More than the protein source, the pH during hydrogel formation was found to decisively influence the protein interaction potential and gel/aerogel characteristics. Irrespective of the protein source low pH led to brittle aerogels with high specific surface areas and low G'cool/G'hot ratios. At a pH close to the isoelectric point (IEP) brittle gels with low specific surface areas and high G'cool/G'hot ratios were measured. At alkaline pH gels were most stable, the specific surface area and G'cool/G'hot ratios were intermediate. Overall, the results help to control the structural properties of gels and aerogels towards potential applications in food systems.Publicationtype: Journal Article248 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Cellulose aerogel particles: control of particle and textural properties in jet cutting process(Springer, 2021-01); ; ; ; Reported approach aims for the synthesis of spherical cellulose beads with high production rates (0.7–4.1 kg/h of hydrogel) via the so-called jet cutting method. To form particles, jets of aqueous cellulose/sodium hydroxide solutions were cut into pieces and collected in a gelation bath (30 wt% aqueous H2SO4, 20 °C). After solvent exchange with ethanol and subsequent supercritical drying, cellulose aerogel particles were obtained. The particles showed high specific surface areas (ca. 400 m2/g) and low bulk (untapped) densities (0.06–0.10 g/cm3). Variation of cellulose content (4–7 wt%) and jet cutting process parameters (cutting frequency, nozzle diameter, jet velocity) turned to be useful parameters for controlling the particles size and shape. Highly spherical particles with sphericity SPH ≥ 0.92 were obtained in a broad range of achievable particle sizes (0.4–1.0 mm), with an optimum of SPH at 6 wt% cellulose content.Publicationtype: Journal ArticleScopus© Citations 16 270 386