Effect of dry‐ and moist‐heat treatment processes on the structure, solubility, and in vitro digestion of macadamia protein isolate

This study aimed to enhance the solubility and digestibility of macadamia protein isolate (MPI) for potential utilization in the food industry. The impact of dry- and moist-heat treatments at various temperatures (80, 90, and 100°C) and durations (15 and 30 min) on macadamia protein's microstructure, solubility, molecular weight, secondary and tertiary structure, thermal stability, and digestibility were investigated and evaluated. The heating degree was found to cause roughening of the MPI surface. The solubility of MPI after dry-heat treatment for 15 min at 100°C reached 290.96 ± 2.80% relative to that of untreated protein. Following heat treatment, the bands of protein macromolecules disappeared, while MPI was stretched by vibrations of free and hydrogen-bonded hydroxyl groups. Additionally, an increase in thermal stability was observed. After heat treatment, hydrophobic groups inside the protein are exposed. Heat treatment significantly improved the in vitro digestibility of MPI, reaching twice that of untreated protein. The results also demonstrated that dry- and moist-heat treatments have distinct impacts on MPI, while heating temperature and duration affect the degree of modification. With a decreased ordered structure and increased random coil content, the dry-heat treatment significantly enhanced the in vitro digestibility of MPI. The digestibility of MPI after dry-heat treatment for 30 min at 90°C increased by 77.82 ± 2.80% compared to untreated protein. Consequently, compared to moist-heat treatment, dry-heat treatment was more effective in modifying macadamia protein. Dry-heat treatment of 30 min at 90°C was determined as the optimal condition. PRACTICAL APPLICATION: Heat treatment enhances MPI characteristics, potentially advancing macadamia-derived food production, including plant-based beverages and protein supplements.