Dairy powders: Impact of surface composition and heterogeneity on functional properties

This study investigates the surface characteristics of four industrial dairy powders - Skim Milk Powder (SMP), Whole Milk Powder (WMP), Instant Filled Milk Powder (IFMP), and Cheese Powder (CP) - across multiple length scales, aiming to understand how these characteristics influence their physical and functional properties. Using X-ray Photoelectron Spectroscopy on large area (multiple particles), it was observed that surface composition remains consistent across different particle sizes within each powder type. Notably, SMP exhibited a more hydrophilic surface compared to the other powders, particularly CP. At the particle scale (single particle – 10 μm × 10 μm), Atomic Force Microscopy (AFM) analysis revealed uniform surface structures. Among the samples, CP and SMP displayed smoother surfaces whereas WMP and IFMP exhibited more textured topographies. High-resolution (2 μm × 2 μm) AFM assessments highlighted distinct differences in surface structures among the powders. Nanomechanical measurements indicated that SMP had the highest Young's modulus suggesting a stiffer surface, while CP had the lowest, indicating a softer surface. Finally, these findings underscore the significance of surface characteristics at various scales in determining the functional performance of dairy powders, here flowability and wettability.