Combination of freeze concentration and spray drying for the production of feijoa (Acca sellowiana b.) pulp powder

Feijoa (Acca sellowiana B.) is a fruit harvested in South America that is characterized by its nutritional value, high pectin content and high trading potential. In this study, freeze concentration was combined with spray drying to produce feijoa powder. Freeze concentration technology is proposed as a step prior to spray drying to increase the solid concentration and to avoid the feijoa gelation process. The drying parameters were optimized by studying the inlet air temperature (180, 195 and 210 °C), maltodextrin concentration (7, 16 and 25%) and atomizer system (two-fluid nozzle or rotary disk) on a pilot scale spray dryer. The process yield, moisture content, water activity, hygroscopicity, solubility, and colour preservation were determined. The freeze concentration technique allowed the solid content to increase without causing gelation and with low differences in colour. Statistical analysis showed that the maltodextrin concentration significantly affected all the response variables after spray drying. In addition, the temperature affected the solute yield and particle size. The optimum spray drying conditions to obtain feijoa pulp powder were 22.64% maltodextrin concentration, 180 °C inlet air temperature and nozzle as the atomizer system. At these optimum conditions, feijoa pulp powder with a 26.6% process yield, 6.5% (wb) moisture content, 20.7% hygroscopicity, 0.16 water activity, 92.8% solubility and ΔE of 27.71 were obtained. The combination of freeze concentration and spray drying allowed the production of fruit pulp powders from sensitive or gelled fruit pulps.