Response surface optimisation of spray dryer operational parameters for low‐phenylalanine skim milk powder

Summary The aim of this study was to optimise the spray‐drying process for low‐phenylalanine (low‐Phe) milk. Influence of inlet air temperature (100, 150 and 200 °C), feed flow rate (5, 10 and 15 mL min−1) and air flow rate (400, 600 and 800 L h−1) on the solubility, yield, water activity and moisture content (MC) of the milk powder were assessed using response surface methodology. The following optimum process parameters were determined: inlet air temperature of 160 °C, feed flow rate of 8 mL min−1and air flow rate of 400 L h−1. The predicted values for the solubility, yield, water activity and MC were 98.77%, 88.08%, 0.263% and 5.48%, respectively. With the optimum parameters, the experimental values for the solubility, yield, water activity and MC were 97.56 ± 0.03%, 87.00 ± 0.10%, 0.26 ± 0.01% and 5.53 ± 0.08%, respectively. The similarity of the experimental results to the predicted values verified the models.