Poor solubility of high protein milk powders can be an issue during the production of nutritional formulations, as well as for end-users. One possible way to improve powder solubility is through the creation of vacuoles and pores in the particle structure using high pressure gas injection during spray drying. The aim of this study was to determine whether changes in particle morphology effect physical properties, such as hydration, water sorption, structural strength, glass transition temperature, and α-relaxation temperatures. Four milk protein concentrate powders (MPC, 80%, w/w, protein) were produced, i.e., regular (R) and agglomerated (A) without nitrogen injection and regular (RN) and agglomerated (AN) with nitrogen injection. Electron microscopy confirmed that nitrogen injection increased powder particles’ sphericity and created fractured structures with pores in both regular and agglomerated systems. Environmental scanning electron microscopy (ESEM) showed that nitrogen injection enhanced the moisture uptake and solubility properties of RN and AN as compared with non-nitrogen-injected powders (R and A). ). In particular, at the final swelling at over 100% relative humidity (RH), R, A, AN, and RN powders showed an increase in particle size of 25, 20, 40, and 97% respectively. The injection of nitrogen gas (NI) did not influence calorimetric glass transition temperature (Tg), which could be expected as there was no change to the powder composition, however, the agglomeration of powders did effect Tg. Interestingly, the creation of porous powder particles by NI did alter the α-relaxation temperatures (up to ~16 °C difference between R and AN powders at 44% RH) and the structural strength (up to ~11 °C difference between R and AN powders at 44% RH). The results of this study provide an in-depth understanding of the changes in the morphology and physical-mechanical properties of nitrogen gas-injected MPC powders.
Bibliographical noteFunding Information:
Funding: This work was supported by the Food Institutional Research Measure (FIRM) project “Developing the next generation of high protein spray dried dairy powders with enhanced hydration properties” (DAIRYDRY 15-F-679) funded by both the Irish Department of Agriculture, Food and Marine and the Department of Agriculture, Environment and Rural Affairs in Northern Ireland.
© 2022 by the authors. Licensee MDPI, Basel, Switzerland.
- gas injection
- milk protein concentrate (MPC)
- glass transition
- dynamic mechanical analysis (DMA)
- structural strength
- environmental scanning electron microscope (ESEM)
- Environmental scanning electron microscope (ESEM)
- Dynamic mechanical analysis (DMA)
- Gas injection
- Glass transition
- Structural strength
- Milk protein concentrate (MPC)