Effect of spray drying conditions on the techno-functional and rheological properties of hazelnut protein isolate

In this thesis, hazelnut protein isolate obtained from defatted hazelnut meal was converted into powder form using different drying methods, and the effects of these processes on the techno-functional and rheological properties of the isolates were evaluated. Hazelnut protein isolate was produced by alkaline extraction followed by isoelectric precipitation and subsequently dried by freeze drying (FD) and spray drying at different inlet air temperatures (SD 140, SD 160, SD 180, and SD 200). The pH-dependent solubility of the protein isolates exhibited a minimum around pH 4 (approximately 30–35%) and increased markedly under alkaline conditions (pH 10–12), reaching values between 70% and 82%. Water-holding capacity ranged from 4.11 to 4.32 g/g, while oil-holding capacity varied between 1.92 and 2.89 g/g. Foam capacity and foam stability were measured in the ranges of 19.0–23.2% and 11.9–19.4%, respectively, and the emulsion stability index (ESI) ranged from 23.2 to 40.8. Higher spray-drying temperatures resulted in improved emulsion stability and increased viscosity, particularly in the SD 180 and SD 200 samples. Protein digestibility remained high and similar for all samples, ranging from 77.7% to 78.9%. Color analysis showed higher L* values in spray-dried samples compared to freeze-dried samples (approximately 50 to 62–66), along with increased total color difference (ΔE). FTIR analysis revealed drying-induced modifications at the level of protein secondary structure. Overall, the results indicate that drying method and processing intensity are key factors influencing the functional and rheological performance of hazelnut protein isolates.