Controlling aerogel surface porosity to enhance functionality in foods

Aerogels based on biopolymers, such as proteins, are food-grade materials characterized by distinctive physical properties, which make them intriguing candidates for the development of new ingredients with unique functionalities. The aerogel typical aerated structure can be exploited to deliver health-protecting bioactives or reduce food calories by increasing air content. However, aerogel porosity is easily lost upon contact with liquid food ingredients (water and oil). This issue might be overcome by closing the pores at the aerogel surface. In this work, processing and formulation strategies were applied to increase the structural stability of whey protein aerogels obtained by traditional ethanol exchange and supercritical-CO2-drying. Aerogels characterized by different levels of surface collapse were obtained by subjecting alcolgels to a controlled ethanol evaporation procedure prior to supercritical-CO2-drying. Alternatively, aerogels were coated with hydrophilic (alginate, agar) or hydrophobic (ethylcellulose) polymers. Aerogel microstructure was studied by SEM. Water and oil absorption kinetics were then measured. Ethanol evaporation time, polymer concentration and gelation rate were identified as key parameters affecting aerogel surface structure, allowing to significantly decrease water and oil absorption kinetics in the aerogels. This study suggests that aerogel structure-driven functionalities could be maintained in complex food formulations by controlling aerogel surface porosity.