Influence of Inlet Drying Air Temperature and Milk Flow Rate on the Physical, Optical and Thermal Properties of Spray-dried Camel Milk Powders

Abstract

The influence of milk flow rate and inlet drying air temperature on the physical, optical and thermal properties of laboratory spray-dried camel milk powders is investigated. The physical, thermal and optical properties of laboratory spray-dried camel milk powders at three inlet drying air temperatures (110, 120 and 130 °C) and two milk flow rates (166 and 248 cm3/h) were evaluated. These properties are fundamental to understanding the quality, stability, final application and portability of the milk powders. Following this, the results were compared to commercial milk powder (CMM). Specifically, we evaluated the influence of the inlet drying air temperatures and feed rates on the reconstitution properties, particle properties, bulk, colour and thermal properties. Using response surface methodology (RSM), the findings indicated that the inlet drying air temperatures significantly influenced moisture content, and the L* a* b* colour properties (p < 0.0001) of the powders. However, the bulk and reconstitution properties were significantly influenced by the milk flow rate (p < 0.0001). The thermograms of all the milk powders had three endothermic peaks and two shifts. The onset of the glass transition increased in temperature with decreasing moisture content of the powders varying from 37.49 to 44.21 °C. Scanning electron microscopy (SEM) images of the laboratory spray dried powders were hollow and collapsed compared with the commercial samples which were spherical and rough with small cracks, dents and pores. The results demonstrated that both the inlet drying air temperature and the milk flow rate influenced the thermal, optical and physical properties of laboratory spray-dried powders.