PULSED-ELECTRIC-FIELDS PRETREATMENT TO HIBISCUS (Hibiscus sabdariffa L.) CALYCES TO ENHANCE DRYING KINETICS AND PRODUCT STABILIZATION

Hibiscus sabdariffa L. is an unconventional food plant (PANC) with high nutritional and functional value, mainly due to the high contents of phenolic compounds as anthocyanins. However, these bioactive compounds are highly susceptible to degradation during product stabilization by drying. Thus, the application of Pulsed Electric Field (PEF) in Hibiscus sabdariffa L. calyces as a pretreatment to enhance drying was investigate under different electrical strengths (1.5, 3.0, and 4.5 kV/cm; 50 pulses,10 us;10 Hz). After PEF application, samples were placed in perforated trays and subjected to convective drying at 50 ^oC over 24 h. Exponential and Page model were fitted to experimental data to describe drying mechanisms. Exponential model (R²>0.95) showed drying rates increasing from 0.0056 min-1 (control) up to 0.0162 min-1 (p<0.05) with increasing PEF electrical strength. Additionally, Page model (R²>0.99) indicated the presence of sub-diffusion mechanism (n<1) in the control sample while a more Fickian diffusion (n=1) in PEF-treated ones – resulting in curves with different behavior. This evidence showed that electroporation reduced internal resistance to water removal. Estimated time required to reach ca.12% of moisture content, recommended to stabilize plant products, decreased from 540 min (control) to 253 min, 135 min and 134 min when applying PEF under electrical strength of 1.5, 3.0 and 4.5 kV/cm, respectively. The reduction of up to 75.2% in the drying time avoid long exposure time of hibiscus calyces to hot air flow. Thus, PEF not only promoted more efficient drying process but also suggests lower exposure time by the calyces to phenolic compounds degradation.