Structural characterisation and sorption capability of whey protein aerogels obtained by freeze-drying or supercritical drying

Whey protein isolate (WPI) hydrogels were converted into aerogels by freeze-drying (FD) or supercritical drying (SCD). SCD resulted in denser aerogels, with a network of closely-associated WPI microgel aggregates, and pore size <1 mu m in diameter. In the FD aerogels, individual aggregates were fused and formed a self-supporting protein matrix with larger pores (2-5 mu m in diameter). Both aerogels showed a glass transition at 161 +/- 4 degrees C and maintained their original porosity at room temperature at an equilibrium relative humidity <80%. The kinetics of both water and oil uptake were slower in the SCD aerogel than in the FD aerogel. While water absorption caused aerogel swelling and destructuring, the oil-loaded aerogels retained their integrity and adsorbed up to 75% (w/w) oil. The oil-loaded aerogels showed differences in firmness and oil holding capacity (OHC) depending on the drying procedure applied: SCD samples presented a higher firmness (similar to 30 N) and OHC (similar to 96%) than the FD samples (similar to 19 N, OHC similar to 45%). This study demonstrates that the drying technique selected can substantially alter the functional attributes of whey protein aerogels.

Automated summary

This study demonstrated that the drying technique used (freeze-drying or supercritical drying) significantly affects the structure and functional properties of whey protein aerogels. Supercritical drying resulted in denser aerogels with smaller pores and slower water and oil uptake kinetics, while freeze-dried aerogels had larger pores and faster uptake rates.