Effect of air temperature and velocity on moisture diffusivity in relation to physical and sensory quality of dried pumpkin seeds

Fluidized Bed Drying of Pumpkin (Cucurbita sp.) Seeds

“…Drying rate curves have not been previously reported for pumpkin or squash seeds but drying was reported to occur in the falling-rate period [16,18]. Uddin et al [16] noted that pumpkin seeds have a high surface area to volume ratio and lose moisture from both surfaces during the fluidized bed drying process compared with loss of moisture primarily from the top surface during tray drying. Drying rates are therefore expected to be higher during fluidized bed drying.…”

“…Redness (+a* values) and yellowing (+b* values) of seeds decreased as temperature was increased from 50 to 80 °C. Uddin et al [16] reported the discoloration of whole, salted pumpkin seeds at drying temperatures above 70 °C and at higher air velocity settings (3–4 m/s), attributing this to nonenzymatic browning under harsher drying conditions. There was a decrease ( p ≤ 0.05) in fat content of the seed powders as drying temperature increased from 50 to 70 °C.…”

“…While drying of seeds for the preparation of powder has been carried out using sun drying, the most common drying method is oven (tray) drying (60 °C, 4–24 h) [2,4,8,11,13,14]. The pioneering research works on the drying characteristics of pumpkin seeds have focused primarily on the drying of salted (25% ( w/w ) NaCl, 1 h) seeds with a view to optimizing the drying process to produce a snack [13,15,16]. Drying curves for salted seeds of the hull-less variety ( Cucurbita styriaca ) dried at 40–60 °C (0.8 m/s) in a laboratory scale hot air dryer, as well as in the open sun and in a solar tunnel dryer have been presented [13].…”

“…The Moisture Ratio ( MR ) data was modelled using six thin layer models and the effective diffusivity values ( D eff ) were found to be similar to those presented by the previous author for de-hulled seeds, possibly due to the higher temperatures and air velocities used. A comparison of tray and fluidized-bed drying of whole, salted seeds was continued at temperatures of 70–90 °C and air velocities of 2.0–4.0 m/s [16]. Drying conditions of 70 °C, 2 m/s was recommended for salted seeds.…”

“…High heat and moisture transfer are achieved due to thorough mixing of the material resulting in uniform temperature distribution and increased surface area for drying. While there is potential for use of this type of drying for pumpkin seeds, too rapid drying can, however, result in seed discoloration and undesirable changes in seed texture, as reported for salted pumpkin seeds [16].…”