在营养配方的生产过程中,高蛋白奶粉的溶解性差可能是一个问题,以及最终用户。改善粉末溶解度的一种可能方式是通过在喷雾干燥期间使用高压气体注入在颗粒结构中产生空泡和孔。这项研究的目的是确定颗粒形态的变化是否会影响物理性质,比如水合,水吸附,结构强度,玻璃化转变温度,和α-弛豫温度。四种牛奶浓缩蛋白粉(MPC,80%,w/w,蛋白质)产生,即,常规(R)和附聚(A),不注入氮气,常规(RN)和附聚(AN),注入氮气。电子显微镜证实,氮气注入增加了粉末颗粒的球形度,并在规则和团聚系统中产生了带有孔的断裂结构。环境扫描电子显微镜(ESEM)表明,与非氮注入粉末(R和A)相比,氮注入增强了RN和AN的水分吸收和溶解度。特别是,在超过100%相对湿度(RH)的最终膨胀时,R,A,AN,和RN粉末的粒径分别增加了25、20、40和97%。氮气(NI)的注入不影响比热玻璃化转变温度(Tg),这是可以预期的,因为粉末成分没有变化,然而,粉末的团聚确实影响Tg。有趣的是,NI产生的多孔粉末颗粒确实改变了α-弛豫温度(在44%RH下R和AN粉末之间的差异高达〜16°C)和结构强度(在44%RH下R和AN粉末之间的差异高达〜11°C)。这项研究的结果提供了对氮气注入MPC粉末的形态和物理机械性能变化的深入了解。
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.