Powdered infant formula is usually manufactured by ingredients mixing, homogenization, pasteurization, evaporation and spray drying. Effects of unit operations on the microstructure, thermal properties and other characteristics of preterm infant formula, fat (F), serum (S), and pellet (P) fractions on centrifugation were investigated using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Differential Scanning Calorimetry (DSC), and Fourier Transform Infrared (FTIR) spectroscopy. After homogenization, particles which may be casein and denatured whey proteins were observed on the surface of F fraction in microstructure images. DSC results showed that the onset temperature of the second endothermic peak of F fraction shifted to higher temperature, and an endothermic transition appeared at 173.3 °C in P fraction. The -CH2 group corresponding to F fraction showed less intensity in FTIR spectrum after homogenization. Microstructure images for S and P fractions showed larger aggregates due to the pasteurization processing. Apparent exothermic transition in DSC curve occurred at 101.6 °C indicated whey protein aggregation. Spray drying resulted in some open areas in F fraction and lager aggregates in S fraction revealed by microstructure pictures. A new exothermic transition appeared at 93.6 °C in DSC curve of S fraction. Changes in amide I and amide II regions in FTIR spectra of samples resulted from pasteurization and spray drying indicated the changes in secondary structure of casein and whey proteins. All results indicated that homogenization, pasteurization, and spray drying exhibited pronounced impacts on the microstructure, thermal properties and structural characteristics of samples. PRACTICAL APPLICATION Preterm infant formula is an important dairy food for preborn infants. Our results indicate that unit operations especially homogenization, pasteurization, and spray drying during the processing have the most impacts on the microstructure, thermal properties and other characteristics of infant formula. This work provides further understanding of component interactions during the processing of infant formula and theoretical basis for the production of dairy food.

中文翻译：

---

加工对早产儿奶粉结构和热学性能的影响

粉状婴儿配方奶粉通常通过配料混合、均质化、巴氏杀菌、蒸发和喷雾干燥来制造。使用扫描电子显微镜 (SEM)、透射电子显微镜 ( TEM)、差示扫描量热法 (DSC) 和傅里叶变换红外 (FTIR) 光谱。均质化后，在微观结构图像中观察到 F 级分表面可能是酪蛋白和变性乳清蛋白的颗粒。DSC结果表明，F馏分的第二个吸热峰的起始温度向更高温度移动，P馏分在173.3 ℃出现吸热转变。对应于F级分的-CH2基团在均质化后的FTIR光谱中显示出较低的强度。由于巴氏杀菌处理，S 和 P 级分的显微结构图像显示较大的聚集体。DSC 曲线中的表观放热转变发生在 101.6 °C 表明乳清蛋白聚集。微观结构图片显示，喷雾干燥导致 F 部分中的一些开放区域和 S 部分中的较大聚集体。S馏分的DSC曲线在93.6°C出现了一个新的放热转变。巴氏杀菌和喷雾干燥导致样品FTIR光谱中酰胺I和酰胺II区域的变化表明酪蛋白和乳清蛋白的二级结构发生了变化。所有结果表明均质化、巴氏杀菌和喷雾干燥对微观结构有显着影响，样品的热性能和结构特征。实际应用 早产儿配方奶粉是一种重要的乳制品，适用于早产儿。我们的研究结果表明，加工过程中的单元操作，尤其是均质化、巴氏杀菌和喷雾干燥对婴儿配方奶粉的微观结构、热性能和其他特性影响最大。这项工作为进一步了解婴儿配方奶粉加工过程中的成分相互作用提供了理论基础。婴儿配方奶粉的热特性和其他特性。这项工作为进一步了解婴儿配方奶粉加工过程中的成分相互作用提供了理论基础。婴儿配方奶粉的热特性和其他特性。这项工作为进一步了解婴儿配方奶粉加工过程中的成分相互作用提供了理论基础。