Solar dryers have been used for decades in drying agricultural products, at varying degrees of success. The quest for improved performance of, and access to solar dryers has led to the development of several designs of solar dryers. This study evaluated the performance of the DehytrayTM, a relatively new solar dryer made up of food grade plastic, in comparison with sun drying using plantain, okra and pepper as test crops in five replicated trials. Freshly harvested crops were divided into two batches, weighing 1.3 kg each. The first batch was blanched with salty water (7 g/100 g) for 2 to 4 minutes while the other was unblanched. Fresh, sun-dried and solar dried samples were analyzed for their proximate composition and microbial load using standard methods. Drying efficiency was determined using standard equations while three thin layer drying models namely; Page, Midili-Kucuk and Logarithmic were applied to the experimental data compared according to their coefficient of determination (R2) and root mean square error (RMSE), which were predicted by non-linear regression analysis using Microsoft Excel solver, 2018. Mean temperatures ranged from 55–65 oC and 25.5–34.3 oC for DehytrayTM solar dryer and sun drying, respectively. Efficiency of the dryer ranged between 16.6–28.1% (blanched) and 16.3–33.7% (unblanched) for plantain, 18.2–29.8% (blanched) and 19.4–28.8% (unblanched) for okra and 11.7–17.8 % (unblanched) and 11.2–17.7% (blanched) for pepper. Efficiency of the sun drying ranged from 1.1–2.1% (blanched) and 1.4 to 2.3% (unblanched) for plantain, 1.3 to 3.1 % (blanched) and 1.6 to 3.7% (unblanched) for okra and 0.7 to 0.9 % (unblanched) and 0.7 to 1.1% (blanched) for pepper. There was a good retention of nutrients (crude protein, crude fibre, ash content, crude fat and CHO — carbohydrate) on the solar dried crop compared to that of the sun-dried crop. Mean airflow rate in the DehytrayTM was 0.021 m3/s compared to 0.49 m3/s in the sun drying. The portability and performance of the DehytrayTM makes it a viable option in the humid tropics.
Keywords: DehytrayTM, drying model, sun drying, solar drying, efficiency, postharvest operation.