Thomas Marie E C, Scher Joël, Desobry-Banon Sylvie, Desobry Stéphane
ENSAIA. Lab. Physico-chimie et Génie Alimentaires, Vandoeuvre-Lès-Nancy cedex, France.
Crit Rev Food Sci Nutr. 2004;44(5):297-322. doi: 10.1080/10408690490464041.
Milk powders are now considered as food ingredients, mainly because of the functional properties of milk proteins. During the storage of milk powders, many physicochemical damages, mainly dependent on lactose glass transition occur. They have important consequences on physical (flowability) and functional properties (solubility, emulsifying, and foaming properties) of milk powders. First, lactose crystallization modifies the microstructure and chemical composition of the surface of powder particles. Thus, milk powders flowability is decreased. Since the structure of milk proteins is destabilized, its solubility is damaged. Moreover, particle collapse and caking occur and mainly decrease the physical properties of milk powders (density and flowability). The mechanical stresses involved may also enhance proteins unfolding, which is detrimental to solubility. Finally, molecular mobility is favored upon ageing, and both chemical (Maillard reaction) and enzymatic reactions occur. Maillard reaction and oxidation enhance protein interactions and aggregations, which mainly lessen milk powders solubility. Maillard reaction also decreases emulsifying and foaming properties. Storage temperature and relative humidity have been considered as the predominant factors involved, but time, milk components, and their physical state also have been implied.
奶粉现在被视为食品原料，主要是因为乳蛋白的功能特性。在奶粉储存期间，会发生许多物理化学损伤，主要取决于乳糖的玻璃化转变。它们对奶粉的物理（流动性）和功能特性（溶解性、乳化性和起泡性）有重要影响。首先，乳糖结晶会改变粉末颗粒表面的微观结构和化学成分。因此，奶粉的流动性会降低。由于乳蛋白的结构不稳定，其溶解性会受到损害。此外，颗粒会发生塌陷和结块，主要降低奶粉的物理性质（密度和流动性）。所涉及的机械应力也可能增强蛋白质的展开，这对溶解性不利。最后，老化会促进分子运动，会发生化学（美拉德反应）和酶促反应。美拉德反应和氧化会增强蛋白质的相互作用和聚集，这主要会降低奶粉的溶解性。美拉德反应还会降低乳化性和起泡性。储存温度和相对湿度被认为是主要影响因素，但时间、牛奶成分及其物理状态也有影响。
