Multiscale imaging approaches for simultaneously mapping distribution of multiple components in infant formula powders

Abstract

To improve simultaneous characterization of structural and compositional features of infant formula powder the objectives of this study were to: 1) advance micro and macroscale fluorescence imaging methods to characterize the distribution of sugars, proteins and lipids in infant formula powder and 2) understand the impact of processing conditions and storage on the microstructure of infant formula powder. For micro and macroscale fluorescence imaging of infant formula, the samples were pre-stained with a trace amount of fluorescently labeled milk proteins, a fluorescent analogue of a simple sugar and a lipid specific chemical stain prior to spray drying. The labeled samples of infant formula powder from evaporator, collection chamber and cyclone units of a spray dryer were collected and analyzed using particle size measurements, scanning electron microscopy, confocal laser microscopy and widefield fluorescence macroscopy. In addition, the powder samples were also analyzed after storage for 6 months. The results of this study demonstrate that pre-staining of the infant formula powder eliminates the potential artifacts introduced by post-staining labeling of the infant formula powders using solvents. The results demonstrate that significant (p < 0.05) spatial co-localization of the fluorescence signal corresponding to the distribution of lipids, sugars and proteins in freshly prepared food powders analyzed using both micro and macroscale imaging. The results also illustrate the presence of void regions in food powders possibly due to entrapment of air during spray drying. The results also indicate separation of fluorescent sugar substrate and Nile Blue labeled lipids upon extended storage of food powders under ambient conditions. Overall, this study provides a novel labeling and imaging approaches to simultaneously image distribution of lipids, sugars and protein in a model food powder. The results also illustrate relatively high uniformity in distribution of macronutrients in a spray-dried powder.