OPTIMIZATION OF SPRAY DRYING CONDITION FOR LONGAN DRINK POWDER USING RESPONSE SURFACE METHODOLOGY

A pilot scale spray dryer with cocurrent operation and a two-fluid nozzle atomizer was used for drying of longan juice. A three-factor Box Behnken design was adopted to investigate the effect of processing variables including ratio of maltodextrin added (0.4-0.6 g g^-1of total soluble solid), drying air temperature (165-185°C), and air velocity (1.45-1.80 m³ min^-1) on product yield, moisture content, density, and solubility. Significant regression models in the form of second order polynomial describing the product characteristics with respect to the independent variables were established, with the coefficient of determination greater than 0.8. Results showed that product yield increased with increase in ratio of maltodextrin added and in drying air temperature, whereas decreased with increase in air velocity. The most important factor affecting solubility was drying air temperature. The optimum condition at ratio of maltodextrin added 0.6 g per g, drying air temperature 185°C, and air velocity at 1.45 m³min^-1 provided high product yield and solubility.