不同乳基婴幼儿配方乳粉的理化性质和表面组成

Physicochemical Properties and Surface Composition of Infant Formula Powders Made from Different Milks

为探究不同乳基对婴幼儿配方乳粉稳定性的影响,本研究对以牛乳和羊乳为基料制备的婴幼儿配方乳粉的水分质量分数和水分活度(water activity,aw)、玻璃化转变温度(glass transition temperature,T_(g))、乳糖结晶度、溶解度、色度、蛋白组成、总脂肪酸和表面游离脂肪酸组成等理化性质进行分析,用X射线光电子能谱(X-ray photoelectron spectroscopy,XPS)仪对乳粉表面成分进行测定,并通过扫描电子显微镜(scanning electron microscopy,SEM)观察乳粉表面形貌。结果表明:羊乳婴幼儿配方乳粉具有较好的理化性质,与牛乳婴儿配方乳粉相比具有较低的水分质量分数、a_(w)、色度和T_(g),而结晶度和溶解度接近,通过气相色谱-质谱(gas chromatography-mass spectrometry,GC-MS)对脂肪酸含量进行测定发现,牛乳和羊乳婴幼儿配方乳粉均表现出总脂肪酸中不饱和脂肪酸含量较高,表面游离脂肪酸中饱和脂肪酸含量较高的特点;十二烷基硫酸钠聚丙烯酰胺凝胶电泳(sodium dodecyl sulfate-polyacrylamide gel electropheresis,SDS-PAGE)分析结果表明,羊乳配方乳粉中β-酪蛋白含量较高,酪蛋白含量的差异影响了乳粉粉末表面成分的组成;因此XPS测定结果表现为羊乳婴幼儿配方乳粉表面成分中的脂肪相对含量较低,蛋白质相对含量较高,这一结果解释了在SEM中观察到牛乳婴幼儿配方乳粉的粉末颗粒更团聚、更致密的现象。综上,由于酪蛋白组成的不同,婴幼儿配方粉的理化性质和表面组成发生改变,从而影响了婴幼配方乳粉的稳定性。

This study was conducted in order to explore the influence of different milks on the stability of infant formula milk powder.The physicochemical properties of infant formula milk powders made from goat milk and cow milk such as moisture content,water activity(a_(w)),glass transition temperature(T_(g)),lactose crystallinity,solubility,color,protein composition,total fatty acid and the composition of surface free fatty acids were analyzed.The surface components were determined by X-ray photoelectron spectroscopy(XPS),and the surface morphology was observed by scanning electron microscopy(SEM).The results showed that goat milk infant formula powder had good physicochemical properties.Compared with cow milk infant formula powder,goat milk infant formula powder had lower moisture content,aw,chroma and T_(g),but similar crystallinity and solubility.Fatty acid composition analysis by gas chromatography-mass spectrometry(GC-MS)showed that in both infant formula powders,unsaturated fatty acids accounted for a higher percentage of the total fatty acids,while saturated fatty acids accounted for a higher percentage of the surface free fatty acids.The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE)showed that the content ofβ-casein in goat milk infant formula powder was higher,and the difference in casein content affected the surface components of milk powder.Consistently,the XPS results showed that goat milk infant formula had a relatively low fat content and a relatively high protein content in the surface composition,which could explain the more agglomerated and denser particles of cow milk infant formula powder observed by SEM.The above results indicated that the physicochemical properties and surface composition of infant formula powders made from different milks are different due to the difference in casein composition,affecting the stability of infant formula powder.