Spray-air contact and operating conditions in tall and short-form co-current spray dryers affect relevant physico-chemical properties of microencapsulated chia oil (Salvia hispanica L.)

Abstract

A design of experiments for chia oil microencapsulation was performed in two co-current dryers: a tall-form (TF-SD) and a short-from spray dryer (SF-SD). The effects of air inlet temperature and volumetric feed rate were analyzed. The responses were the outlet air properties, physico-chemical characteristics of powders, the estimated droplet evaporation time and the additional exposure time of dry particles in the chamber. The droplet evaporation time was calculated by considering evaporation in still-air and drying only during the constant rate period. The calculated values were 69.67–105.98 ms and 1.45–2.74 s for TF-SD and SF-SD, respectively. The contact of product with hot air caused by back-mixing and the extended residence time in the chamber may explain the poor oxidative stability of powders from SF-SD. The peroxide index values were 1.72–4.51 and 16.10–96.65 meq. O2/kg oil for TF-SD and SF-SD, respectively. The oxidative stability indexes were 5.14–6.52 and 0.26–0.80 h for TF-SD and SF-SD, respectively. A global optimization was performed for TF-SD since it yielded products with the best chemical quality. The process condition that simultaneously optimized the responses was 160 °C × 2.8 mL/min. Finally, additional characterization of the optimal powders ensured the stability of the core: fatty acid profile before and after in-vitro digestion, thermogravimetric analysis, differential scanning calorimetry, moisture sorption behavior and surface morphology.