The Effect of High Protein Powder Structure on Hydration, Glass Transition, Water Sorption, and Thermomechanical Properties

Valentyn A Maidannyk; David J McSweeney; Sharon Montgomery; Valeria L Cenini; Barry M G O'Hagan; Lucille Gallagher; Song Miao; Noel A McCarthy

doi:10.3390/foods11030292

The Effect of High Protein Powder Structure on Hydration, Glass Transition, Water Sorption, and Thermomechanical Properties

Foods. 2022 Jan 21;11(3):292. doi: 10.3390/foods11030292.

Authors

Valentyn A Maidannyk¹, David J McSweeney^{1

2}, Sharon Montgomery¹, Valeria L Cenini³, Barry M G O'Hagan³, Lucille Gallagher³, Song Miao¹, Noel A McCarthy¹

Affiliations

¹ Food Chemistry and Technology Department, Teagasc Food Research Centre, Moorepark, Fermoy, P61 C996 Co. Cork, Ireland.
² School of Food and Nutritional Sciences, University College Cork, T12 K8AF Co. Cork, Ireland.
³ School of Biomedical Sciences, University of Ulster, Coleraine BT52 1SA, UK.

Abstract

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 (T_g), which could be expected as there was no change to the powder composition, however, the agglomeration of powders did effect T_g. 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.

Keywords: dynamic mechanical analysis (DMA); environmental scanning electron microscope (ESEM); gas injection; glass transition; milk protein concentrate (MPC); structural strength; α-relaxation.