Impact of Instant Controlled Pressure Drop Treatment on Dehydration and Rehydration Kinetics of Green Moroccan Pepper (Capsicum Annuum)

AbstractA comparative study of various drying techniques were carried out on Green Moroccan Peppers GMPs, Traditional Hot Air Drying, Swell Drying SD, and freeze drying, in order to compare the dried product's behavior during drying and rehydration. Moreover, starting accessibility, and water effective diffusivity during drying and rehydration were studied. The water holding capacity of dried GMPs were investigated as well. The impacts of Instant Controlled Pressure Drop process (DIC) on dehydration and rehydration kinetics and functional properties (water holding capacity) were compared to Freeze Drying (FD) and Traditional Hot Air Drying processes (THD). DIC treatment was carried out on pre-dried peppers (classical hot air drying at 50°C, 265Pa initial partial pressure of vapor in the air flux, 1.2 m s-1) to reach a moisture content of 20% dry basis varying the saturated steam pressure (ranged from 0.1 to 0.6MPa) and heating time (ranged from 9 to 35 s) and keeping the initial water content constant at 20% db. Drying and rehydration kinetics of DIC-textured and untreated peppers were well interpreted by a specific model coupling a starting superficial interaction with Fickian diffusion. Response parameters (dependent variables) were the dehydration and rehydration starting accessibility Ws (g H2O/g dry matter), effective diffusivity Deff (m2 s-1) and drying time td0,05% (min). Response Surface Methodology RSM was employed. Compared to THD, DIC treatment dramatically increased the starting accessibility and the effective water diffusivity during hot air drying; it allowed the drying time needed to get a final water content of 0.05% db, to decrease by 1.7 times. Regarding the rehydration ability, the time needed to reach 300% db, were reduced 3.7 times under optimum DIC conditions. Fickian diffusion model could not explain FD rehydration, which appeared as a pure water/surface interaction. Water Holding Capacity of DIC dried products was higher than FD and THD