Supramolecular characteristics, morphology and functional properties of commercial fat-filled powders from cow milk, goat milk and soy

Abstract

The quality of a powder is determined by its functional attributes such as wettability, bulk density, flowability and dissolution, which in fat-filled powders, is associated with supramolecular structure. Processing conditions can change powder structure, and during spray drying, specific components may migrate preferentially toward the powder surface changing powder functional attributes. Such structure-function-processing causative relationships are not always clear. This study investigated the association between supramolecular characteristics and powder functional properties. We compared the structure, morphology and functional attributes of commercial nutritional powders prepared from goat and cow milk and soy. We used correlative microscopy of the same samples using confocal laser scanning microscopy (CLSM), Nile Red/Fast Green stains, and scanning electron microscopy (SEM) and compared against functional attribute data (including wettability, insolubility and density) to look for relationships. CLSM showed a clear difference in the fat supramolecular structure between the different powder types. Although all samples had a similar total fat content, soy-based powders revealed a distinct fat distribution with a higher amount of surface free fat. In contrast, bovine-based powders presented a surface with higher protein content, with fat mainly inside of the particle. The free fat analysis, using solvent extraction technique, validated the CLSM results. The amount of free fat was significantly different between powder types with soy-based showing the highest amount and bovine-based having the lowest amount. SEM revealed that bovine-based samples had smoother surfaces, while goat-based samples showed large amounts of small particles on the surface of larger powder particles. The functional properties of the different powder types were also distinct. Soy-based powders presented highest insolubility and water activity and lower bulk and tapped density, while, goat-based powders had the longest wetting time and highest tapped density. The results show a complex interplay between powder structure and functional properties