Supercritical Carbon Dioxide Drying for Creating Porous Red Lentil Proteins: Effects of pH and Solvent Exchange

Drying plays a crucial role in protein processing as it directly influences the structural stability and functional properties of proteins. With a growing demand for sustainable and plant-based protein sources, red lentil protein (RLP) has gained much attention as a promising alternative plant protein. This study explores the effect of different drying techniques, namely freeze-drying (FD), air drying (AD), and supercritical carbon dioxide drying (SCD) at different pH ranges (acidic pH 4.5 (SCD-A) and neutral pH 7 (SCD-N)) on structural and functional characteristics of RLP. SCD RLP (119 m²/g) exhibited a significantly higher surface area than the ones dried using AD (0.07 m²/g) and FD (0.30 m²/g) (p < 0.05), contributing to enhanced solubility and functionality. The SCD samples had superior foaming capacity (FC) (183%), creaming index (CI) (48%), and water absorption index (WAI) (3.21%) compared to the FD and AD samples. The FD samples had a lower solubility and non-homogeneous particle size compared to SCD and AD samples, resulting in reduced functional properties. The differential scanning calorimeter (DSC) and X-ray diffraction (XRD) analyses confirmed the thermal stability and amorphous nature of SCD RLP, respectively, while scanning electron microscopy (SEM) images revealed a well-developed porous microstructure. Furthermore, the Fourier transform infrared spectroscopy (FTIR) results confirmed that the neutralization process reduced protein hydrophobicity, thereby enhancing its solubility and colloidal stability. Overall, SCD proved to be a promising alternative for RLP drying, offering improved functionality, better structural integrity, and potential for sustainable, large-scale industrial applications. PRACTICAL APPLICATIONS: This research demonstrates the potential of SCD as a scalable and green technology for processing plant-based proteins. SCD aids in producing porous proteins with enhanced water/oil absorption and solubility, enabling them to function as carriers or delivery systems for nutrients and bioactive compounds. These properties make SCD proteins suitable for use as advanced ingredients in food and nutraceutical applications.