Process Optimization of Spray-Dried Aquafaba and Comparison with Freeze-Drying: Techno-Functional Performance and Structural Attributes

This study aimed to optimize the spray-drying (SD) process for aquafaba and compare the physical and techno-functional properties of the resulting powder with those of its freeze-dried (FD) counterpart. A Box–Behnken design was employed to evaluate the effects of inlet air temperature (150–190 °C), air speed (3.5–4.3 m/s), and feed flow rate (0.3–0.5 L/h) on 14 quality responses. The optimized SD conditions were determined to be an inlet air temperature of 189 °C, an air speed of 4.2 m/s, and a feed flow rate of 0.3 L/h. Validation experiments demonstrated that the developed models had high predictive capacity, with only a small discrepancy (0.56–5.88%) between the predicted and experimental values. Comparative analysis showed that the optimized SD powder had significantly lower moisture content (2.47%) and water activity (0.18) than the FD powder (3.51% and 0.34, respectively), indicating superior storage stability. In addition, the SD powder exhibited greater whiteness (82.37), higher water solubility (88.44%), and substantially greater foaming capacity (266.67%) than the FD sample (243.33%). Although the FD powder demonstrated better wettability and water absorption capacity because of its porous structure, FTIR spectroscopy and protein secondary structure analysis confirmed that SD preserved the functional integrity of aquafaba. Specifically, SD induced a transition from disordered random-coil structures to more ordered β-sheet and β-turn configurations, thereby improving foaming performance. Overall, these findings indicate that optimized spray-drying is a highly efficient and industrially scalable alternative to freeze-drying for producing functional aquafaba powder for use as a plant-based egg substitute.