Effect of Swell-Drying on Mango (Mangifera indica) Drying Kinetics

Swell-Drying operation (SD) was applied on mangoes to evaluate its effect on drying kinetics: starting accessibility (delta W), apparent drying coefficient (D-app), and time to obtain a final moisture content of 20% d.b (t(f) = 20% d.b). Swell-drying consisted of (1) submitting fresh mangoes to a first pre-drying stage under Convective Air Drying (CAD) until a moisture content of 37% d.b; (2) applying Instant Controlled Pressure Drop (DIC) treatments on pre-dried mangoes by following a central composite rotatable design (steam pressure: 0.2-0.6 MPa and treatment time: 5 and 55 s); and (3) apply post-drying of mangoes under CAD. In both cases, CAD was performed at 60 degrees C and airflow of 1 m/s. Results showed that both the treatment time and the steam pressure impacted the D-app and the delta W. By comparing to the control, SD (0.54 MPa and 48 s) increased the D-app and delta W to 12.2 and 2.7 times, respectively. Moreover, SD triggers a significant reduction in post-drying time (t(f) = 20% d.b), being this of 2.4 h vs. 30.8 h. These results could be linked to the expansion of the internal pores of mangoes generated by the instant autovaporization of residual water triggered by DIC treatment.