Determination of some quality parameters of milk powders produced by spraying with different spraying angles

In this study, the physicochemical and functional properties of milk powder samples produced at different spray angles (15°, 30°, 45° and 60°) by spray drying were investigated. For this purpose, each sample was analyzed in terms of moisture, water activity, protein, fat, ash, pH, titratable acidity, HMF (hydroxymethylfurfural), scorched particle content, color parameters (L*, a*, b*), DSC (thermal properties), particle size distribution, bulk density, Carr index, Hausner ratio, wettability, dispersibility, solubility, foaming capacity, flow stability, and cake strength. The results showed that moisture and water activity values of all samples remained within safe storage limits (≤5% moisture, low aw), indicating efficient drying and microbiological stability. No statistically significant differences were observed between the spray angles for protein, fat, ash or pH values, confirming that the drying conditions did not cause structural deterioration in the milk components. Although slight increases in HMF and scorched particles were detected due to thermal exposure, all results remained below industrial quality limits and did not pose a risk for product safety. Evaluation of the functional properties demonstrated that spray angle was a determining factor, particularly affecting particle morphology and rehydration behavior. Samples produced at wider angles (45° and 60°) exhibited larger and more porous particles with lower compactness, resulting in shorter wetting time, improved dispersibility and solubility, and better flow characteristics. Conversely, samples produced at narrower angles (15° and 30°) formed smaller and more compact particles, which increased bulk density while negatively affecting solubility and flowability due to greater particle–particle adhesion. Particle size distribution results confirmed that D[4,3], D[3,2] and d(0.9) values increased proportionally with wider spray angles, indicating a direct relationship between atomization geometry and particle structure. DSC analysis revealed that glass transition temperature (Tg), denaturation temperature (Td), and denaturation enthalpy (ΔH) values remained within acceptable ranges, showing that the thermal stability of milk proteins was preserved. In conclusion, the findings demonstrated that spray angle is a critical process parameter directly influencing the physical, structural, and functional characteristics of milk powder. The study emphasizes that, in addition to temperature and feed rate, atomization angle must also be considered during spray drying optimization, as it plays a decisive role in rehydration performance, flow behavior, and storage stability.