Conversion of natural tissues and food waste into aerogels and their application in oleogelation†

Abstract

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.