The effects of input variables on the output variables were investigated. The input variables for spray drying of whole milk powder (NS) were inlet air temperature and feed flow rate. The inputs variables for spray drying of orange juice powder (S) were inlet air temperature and maltodextrin concentration. Thus, drying air parameters and the characteristics of liquid feed were observed in both processes.
Table 1 presents the spray drying parameters and moisture content at different inlet air temperatures. This operating parameter showed similar effects for both spray dried products. Hot dry air has constant humidity and very low relative humidity. When hot air is contacted with liquid droplet, the heat required to vaporize the moisture comes from the sensible heat. It caused the reduction of inlet air temperature to outlet air temperature. As increase in the inlet air temperature resulted in significant increase in the outlet air temperature. As the outlet air temperature increased, the outlet air humidity also increased but relative humidity reduced [4]. Moreover, high inlet air temperature led to greater efficiency of heat and mass transfers. It provided greater driving force for moisture evaporation, and produced powder with low moisture content. Similar findings were observed by [9]; [10]; [11]; [12]; and [13]. Therefore, adjusting inlet air temperature could regulate outlet air temperature and it could be an indirect measurement of moisture content.