Effect of variables on the production of red-fleshed pitaya powder using response surface methodology

Abstract

Using response surface methodology, a central composite design technique was used to investigate the effect of spray drying conditions on red-fleshed pitaya powder properties. The process was carried out on Buchi mini spray dryer SD-04 using maltodextrin 12DE as encapsulating agent. The number of experiment conducted was sixteen runs with the variables of nozzle size, nozzle pressure, feed temperature and drying air flow rate were keeping constant throughout the study. Independent variables were within the following ranges: inlet air temperature (156- 224°C), feed flow rate (16.6-33.4 ml/min) and maltodextrin concentration (31.6- 48.4%). The product powder was analyzed for moisture content and bulk density. Results showed that the data were adequately fitted to second order polynomial model with coefficient of determination, Fr are 0.8984 and 0.8428 for moisture content and bulk density respectively at 99% confidence level. Both linear inlet air temperature and feed flow rate had significant effect on powder moisture content. On the other hand, powder bulk density was significantly affected by both linear maltodextrin concentration and inlet air temperature. The best spray drying conditions within the experimental ranges for minimum powder moisture content would be inlet air temperature, feed flow rate and maltodextrin concentration of 224°C, 22.9 ml/min and 40% respectively, yields 3.88% moisture content. For the maximum powder bulk density, the best value for inlet air temperature, feed flow rate and maltodextrin concentration were 156°C, 16.6 ml/min and 48.4% respectively, yields 0.45 g/ml bulk density.