The potential of supercritical drying as a “green” method for the production of food-grade bioaerogels: A comprehensive critical review

Bioaerogels or biopolymer-based aerogels are emerging as eco-friendly and sustainable alternatives to inorganic aerogels. Aerogels are porous, lightweight and interconnected structures, having several prospective applications in food systems. Polysaccharides, proteins, or their combinations are exploited for the fabrication of aerogels. Supercritical drying is a viable “green” alternative for the production of bioaerogels. The aerogels are typically produced by the sol-gel route to form a hydrogel, followed by solvent exchange and supercritical drying. The significant physical properties of the bioaerogels in food systems include porosity, surface area, bulk density, thermal conductivity, rheology, water absorption, and oil absorption properties. All these properties impact the bioactive impregnation properties of the aerogels. The major process parameters influencing the final aerogel properties during drying include pressure, temperature, CO2 flowrate, and depressurization rate. Apart from the applications in food packaging, aerogels can be converted into oleogels which can be great alternatives to conventional fats. Although CO2 is non-toxic, environment-friendly, and abundant, the copious use of solvents and alcohols during solvent exchange can question the potential of scCO2 as a green technique. Process intensification by recycling spent CO2 and reuse of the solvent, low energy consumption, and drying times justify supercritical drying as a “green” technique.