Determination of optimum conditions for spray-drying of peach juice-skim milk blend using response surface method

The objective of present study was to determine the optimum conditions for spray drying of peach juice-skim milk blend. The experiments were designed according to a 3-level-3-factor Box-Behnken design (BBD) using response surface methodology (RSM). The effects of fruit juice to skim milk powder as drying aid (40:60-60:40 %), inlet air temperature (110- 130 ◦C) and compressed air flow rate (300- 700 L/h) on drying yield, physical properties (water activity, moisture content, bulk density, solubility, hygroscopicity and wet ability time) and antioxidant activity of the resultant powder were investigated. The results indicated that increasing the inlet air temperature significantly caused an increase in drying yield, bulk density, solubility, hygroscopicity and wet ability time and a decrease in water activity and moisture content of peach powder ( ). Ratio of fruit juice to skim milk powder had the same effects on drying yield and the examined physical properties as inlet air temperature; however, its effects on moisture content and hygroscopicity were not statistically significant ( ). The compressed air flow rate showed no significant effects on drying yield and physical properties ( ) but it significantly deceased the antioxidant activity of the peach powder ( ). Similarly, the inlet air temperature resulted in decreased antioxidant activity; however, ratio of fruit juice to skim milk powder affected the bioactivity of the powder significantly positively. RSM described that upon optimum drying conditions of 60:40 % ratio of fruit juice to skim milk powder, 126 ◦C inlet air temperature and 404 L/h compressed air flow rate, it is possible to produce peach powder with drying yield of 65.8%, water activity of 0.27, moisture content of 3.38%, bulk density of 6.54 g/cm3, solubility of 85.65%, hygroscopicity of 0.035 g water/g powder, wet ability time of 7.2 s and antioxidant activity of 35.31%.