Morphological characterization of powder milk and their relationship with rehydration properties

Microstructure and morphology of milk powder has an important influence on rehydration or instant properties such as wettability, dispensability and solubility; as water diffusion capability depends on the surface area and particles porosity. Recent advances in microscopy and image analysis have been useful for quantitative evaluation of morphology and structure of food materials. The aim of this work was to study the morphology and microstructure of five different milk agglomerates and their relationship with their rehydration properties. Light stereomicroscope (LS) and Environmental Scanning Electron microscope (ESEM) were used to obtain the images of milk powder agglomerates and image analysis was performed to evaluate their morphology and texture. Wettability, dispersibility and solubility were analyzed by traditional methods. Image analysis provide different morphological and textural parameters such as perimeter, area, major length, shape factor, compactness, fractal dimension of contour (FDc), fractal texture (FT) and entropy (En). Solubility (0.66mL to 2.16mL) and wettability (8.95s to 8019s) rose as particle size increased (110 to 435 firri). Shape factor (0.427 to 0.641) increased when compactness (24.39 to 42.34), FDc (1.129 to 1.141) and dispersibility (97.58 % to 99.54%) values decreased. The size of the milk agglomerates increased as FDc, FT (2.59 to 2.67) and En (4.86 to 5.59) showed larger values, which according to literature could be associated with larger tortuosity and roughness on the surface. These changes can be associated with a better rehydration capability. These results show relationships between the microstructure and morphology of milk powder agglomerates and their rehydration capability.