Convective drying of naked seeded oil pumpkin seeds (Cucurbita pepo L.) in a medium scale batch dryer with different modes of air circulation

Abstract

The objective of this investigation was to improve the drying of naked seeded oil pump- ; kin seeds by applying higher drying air temperatures and alternate use of fresh air and circulation mode of the drying air flow. An additional goal was to investigate the influence of the drying temperature on seed germination characteristics. Drying in three phases in a flatbed batch dryer was applied. The temperatures of the drying air were in the range of 60 to 80°C for the first phase and the same or reduced, for the second and third phase. For the second and third phase fresh air and a circulating mode of drying air were applied alternatively. Drying at a constant temperature of 50°C and fresh air mode during the whole drying time, as usual applied in practice, was used as control. The specific drying energy, drying capacity and specific fuel consumption were calculated. The content of free fatty acids and the microbial count of the dried material have been measured, as well as the germination characteristics. Due to the higher drying air temperatures of above 60°C in the first phase, the specific drying energy was reduced by 13 to 21 %, compared to the control. Positive effects of alternating fresh air/circulation mode drying air flow were obtained. Higher drying air temperatures showed no negative influences on seed safety and quality. The seed germination rate was satisfactory for drying temperatures up to 60°C, which is in contrast to previous statements mentioning 40°C as the upper limit. In the future, additional tests should be performed using a drying air temperature of 70°C. The influence of alternating the drying air flow in the second and third phases should be tested in the future as well.