Comparative analysis of different drying methods in the production of solid oat milk beverages: Insights into physicochemical properties and quality attributes

Abstract

This study evaluates the effects of freeze-drying, hot-air drying, and spray drying on the physicochemical properties and quality attributes of solid oat milk derived from oat core flour (OCF). Different enzymatic treatments were applied to enhance starch and protein degradation before drying. Results showed that freeze-drying retained the highest water-holding capacity (WHC) due to its porous structure, while hot-air drying induced Maillard reactions, reducing lightness and whiteness. Spray-dried samples presented acceptable hydration and color properties, which showed comparable level to the market product. Besides, Spray-dried samples exhibited higher zeta-potential (−30 mV), indicating improved colloidal stability. Enzymatic treatments significantly reduced centrifugal sedimentation rate (SR) and apparent viscosity, particularly in spray-dried samples, which formed stable starch-protein/lipid complexes. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) revealed structural modifications in starch and protein, with spray drying promoting electrostatic interactions. Thermal analysis showed spray-dried samples had higher denaturation temperatures and enthalpy (ΔH = 1.77 J/g), reflecting enhanced thermal stability. Confocal laser scanning microscopy (CLSM) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) confirmed uniform protein distribution and reduced aggregation in spray-dried products. Intermolecular force analysis suggested that the uniform protein distribution might be supported by the dominant ionic bonds. Correlation analysis linked protein tertiary structure to thermal stability and zeta-potential, highlighting the role of protein conformational changes in functional properties. Overall, spray drying combined with dual-enzyme treatment demonstrated optimal performance in producing solid oat milk with desirable sensory, structural, and functional properties, making it a promising method for industrial solid oat milk production.