Abstract

The aim of this study was to evaluate the effect of air outlet temperature (75 and 85 °C) and milk type on proximate composition, water activity, particle size distribution, color, and rehydration ability of spray-dried skim dromedary and cow’s milk powders. While the water activity of powders was close to 0.4 when spray-dried at 75 °C air outlet temperature, it ranged from 0.2 to 0.3 for a production at 85 °C air outlet temperature. Skim dromedary milk powder had a lower water activity than skim cow’s milk powder after spray-drying at 85 °C air outlet temperature. Spray-drying yields were greater at the higher air outlet temperature (85 °C) for both skim milk powders. The particle size distributions of spray-dried skim milk powders were centered around 14–20 µm. The particles of skim dromedary milk powders were smaller than those of skim cow’s milk powders as skim dromedary milk was less viscous, leading to smaller sprayed droplets. No significant influence of spray-drying conditions on particle size distribution was observed for dromedary milk powders. Regardless of the spray-drying conditions and the milk type, the produced powders were very bright and had a low color saturation. Scanning electron microscopy images showed that spray-dried powders appeared as agglomerates of small particles with angular shapes rather than individual particles. All investigated spray-dried powders were considered non-wettable, hardly dispersible, and fairly soluble. Skim dromedary milk powder produced at 85 °C air outlet temperature showed a significantly higher solubility index than the same formulation spray-dried at 75 °C outlet air temperature. The opposite was obtained for skim cow’s milk powder. These results demonstrated that the outlet drying air temperature significantly influenced water activity, spray-drying yield and solubility of spray-dried dairy powders.

摘要

本研究的目的是评估空气出口温度（75 和 85 °C）和牛奶类型对喷雾干燥脱脂单峰骆驼和牛奶粉末的近似成分、水分活度、粒度分布、颜色和再水合能力的影响. 当在 75 °C 的出风口温度下喷雾干燥时，粉末的水分活度接近 0.4，而在 85 °C 的出风口温度下生产时，其水分活度在 0.2 到 0.3 之间。脱脂单峰骆驼奶粉在85°C的出风温度下喷雾干燥后的水分活度低于脱脂牛奶。在较高的空气出口温度 (85 °C) 下，两种脱脂奶粉的喷雾干燥产量更高。喷雾干燥脱脂奶粉的粒径分布集中在 14–20 µm 左右。脱脂单峰骆驼奶粉的颗粒比脱脂牛奶粉的颗粒小，因为脱脂单峰骆驼奶的粘性较低，导致喷雾液滴更小。对于单峰骆驼奶粉，没有观察到喷雾干燥条件对粒度分布的显着影响。无论喷雾干燥条件和牛奶类型如何，所生产的粉末都非常明亮且色彩饱和度低。扫描电子显微镜图像显示，喷雾干燥的粉末呈现为具有棱角形状的小颗粒聚集体，而不是单个颗粒。所有研究的喷雾干燥粉末都被认为是不可润湿的、难以分散的和相当可溶的。在 85 °C 出风温度下生产的脱脂单峰骆驼奶粉显示出比在 75 °C 出风温度下喷雾干燥的相同配方显着更高的溶解度指数。脱脂牛奶的情况正好相反。这些结果表明，出口干燥空气温度显着影响喷雾干燥乳粉的水分活度、喷雾干燥产量和溶解度。