Hydrophilic or hydrophobic coating of whey protein aerogels obtained by supercritical-CO2-drying: Effect on physical properties, moisture adsorption and interaction with water and oil in food systems

Aerogel monoliths, prepared by water-to-ethanol substitution and supercritical-CO2-drying of whey protein hydrogels, were dip-coated with hydrophilic (alginate, AL; agar, AG) or hydrophobic (ethylcellulose, EC) polymers. AL coating induced aerogel collapse, due to solvent absorption. AG and EC rapidly set onto aerogel surface, forming layers of 65 and 100 μm thickness, respectively. While AG-coating induced 20% volume shrinkage, 25% apparent density increase and 75% firmness increase, EC-coating maintained the original aerogel structure. Upon exposure to 100% equilibrium relative humidity, aerogels showed moisture uptake in the order AG-coated>uncoated>EC-coated. When immersed in water or oil, the AG-coated aerogel showed an uptake respectively 40 and 60% lower than the uncoated control. The oil barrier capacity of AG-coated aerogel was also demonstrated in a lipid food system (stearin-oil mixture). Although not reducing oil uptake, EC-coating reduced water uptake by 30% and its water barrier properties were demonstrated upon immersion in an aqueous food system (water-flour batter). Industrial relevance: The obtained results indicate tailored coating as a feasible strategy to enhance aerogel functionality in food. This would open further possibilities, including the use of aerogels as smart food ingredients able to modulate aroma and bioactive delivery both in the food product and during digestion. These findings are thus important in supporting the industrial development of aerogel-based ingredients with customized functionalities.