Physical, chemical, and technological properties of protein isolate obtained from hazelnut press cake as affected by drying technique

This study aimed to valorize hazelnut press cake, a hazelnut oil industry waste, by producing hazelnut protein isolates using alkaline extraction and isoelectric precipitation. The impact of refractance window drying at varying temperatures on the physical, chemical, and technological properties of protein isolates was comparatively evaluated in comparison to spray drying. Dry matter content, water activity, protein content, color, particle size, bulk density, tapped density, flow properties, solubility, water and oil holding capacity, surface hydrophobicity, emulsification, and foaming properties of protein isolates were analyzed. Results showed that the drying method and temperature significantly influenced the properties of the protein isolates. Spray drying produced protein isolates with better color, higher solubility, surface hydrophobicity, and foaming properties than refractance window drying. However, refractance window drying resulted in better flow and emulsification properties of protein isolates. The temperature of refractance window drying was found to be effective on protein content, color, particle size, bulk and tapped densities and emulsification properties of protein isolates. These findings suggest that both drying methods offer unique advantages for producing protein isolates from hazelnut press cake with tailored functionalities.