Effect of food thickener on the structural and rheological properties of fermented milk and soy beverage powders and rehydrated beverages

The growing demand for convenient and shelf-stable products has stimulated interest in the production of powdered foods; however, the drying process and ingredient formulation can significantly affect techno-functional properties, requiring a better understanding of how these conditions influence the rehydration of powdered products. This study evaluated the impact of spray drying (SD) and freeze drying (FD), as well as the incorporation of modified corn starch before and after fermentation, on the physical, structural, and rheological properties of fermented dairy and soy beverages. The particle size distribution results showed that the FD samples exhibited larger D 4,3 diameters than the SD powders, and zeta potential values indicated that thickener addition decreased charge repulsion, likely through protein-polysaccharide interactions. FTIR analysis revealed minimal spectral changes due to starch incorporation, although soy beverages showed drying-related differences in the Amide II region. Rheological analysis confirmed pseudoplastic behavior in all formulations, with modified starch increasing overall consistency and viscosity, particularly in dairy beverages and FD powders. Fluorescence microscopy showed no major structural changes caused by starch, although the SD process disrupted milk agglomerates. In conclusion, the drying technique and food thickener exerted a significant influence on viscosity and overall rehydration. At the same time, the application before and after fermentation showed little difference, offering valuable insights for formulating powdered fermented beverages.