Producing and optimizing fig juice powder in a semi-industrial spray dryer with two fluid nozzles

The main problems of dried figs are the decrease of its quality due to activity of the harmful microorganism, the production aflatoxin B1 and pest by some insects, such as Plodia, so proper processing operations on this product are necessary. In this research, the ability to produce fig concentrate powder using spray dryer was investigated. The experiment was carried out in two steps. In the first stage, the effect of different levels of maltodextrin (three levels of 30, 40 and 50%) and silicon dioxide (two levels of 3 and 5%) on performance of dryer in powder production and optimal levels of additives was determined. In the second step, the effect of factors, temperature (two levels of 150 and 170 oC), inlet feed flow rate (two levels of 3 and 5 liters per hour) and nozzle pressure (two levels of 3 and 5 bar) in a completely randomized deign (CRD) on production performance and physical properties of fig concentrate powder were studied. The results showed that levels of 40% maltodextrin and 5% silicon dioxide had the highest effect on optimum powder production and lack of stickiness and lump (P≥0.50). In addition, it was found that the machine's performance increases with increasing inlet air temperature, increasing nozzle pressure and reducing feed flow rate. Decrease of flow rate of feed inlet and increase of the inlet air temperature and the nozzle pressure resulted in the production of a powder with lower moisture content and smaller diameter particle size (P≥0.50). It was also found that temperature, flow rate and nozzle pressure had a significant effect on powder solubility (P≥0.01). During 4 weeks of shelf life of selected powder sample (40% maltodextrin and 5% silicon dioxide, air temperature 170 °C, flow rate 3 liters per hour and pressure 5 bar) the values of color factors L*, a* and b* decreased 18, 9.1 and 9.41%, respectively.