Formation of hydrophobic zein aerogels via supercritical carbon dioxide drying

Zein is a promising sustainable plant-based material; however, its use for aerogel fabrication and the effects of pH and ethanol concentration on zein gelation and aerogel properties remain poorly understood. Therefore, this study evaluated the influence of these parameters on gel formation and the resulting zein aerogels prepared by supercritical carbon dioxide (SC-CO₂) drying. Zein (40%, w/v) gels were prepared under different pH conditions (4, 6, and 8) and ethanol concentrations (50%, 65%, and 80% w/w) and characterized in terms of morphology, textural characteristics, functional groups, crystallinity, chemical interactions, mechanical properties, and surface hydrophobicity. The aerogels showed surface areas of 14.7 to 37.3 m²/g, with the highest values obtained at pH 4 and 80% ethanol (37.3 m²/g). The aerogels showed mesoporous structures with pore sizes of 16.8-30.1 nm and pore volumes of 0.08-0.19 cm³/g, while pH 6 and low ethanol concentrations resulted in reduced surface areas. FTIR analyses indicated that the protein secondary structure remained relatively unaffected by processing conditions, with α-helix and β-aggregate conformations prevailing. Hardness increased with increasing pH and ethanol concentration, and all aerogels exhibited high hydrophobicity with water contact angles ranging between 103 and 129°. These findings highlight the potential of zein, a renewable protein derived from corn byproducts, as a sustainable material for producing hydrophobic bioaerogels.