Comparison of an indirect hybrid solar cabinet dryer and a solar tunnel dryer on drying kinetics and quality of tree tomato powder
Creators: name: Maitha, Isaac
name: Okoth, Michael Wandayi
name: Njue, Lucy
name: Mbuge, Duncan
Publisher: name: Zenodo
Year: 2025
Subjects: Drying kinetics
Mathematical modelling
Modified Page model
Innovative Greenhouse solar dryer
Solar tunnel dryer

description: According to world Bank, 2018 the post-harvest losses of fruits was 45% in East Africa and projects more that will triple by 2030 if no radical actions or interventions taken.Drying is one of the methods of fruits preservation and the process requires thermal energy of temperature to remove water content from the fruits and convert them into value added products like fruit powder which are less bulk, easy to package, transport, store and use as ingredients. Different types of energy sources have a direct impact on our global and environmental development with some rural places suffering from lack of resources or access to grid power which could also be inadequate or too costly if available. Solar energy plays an important role for drying food products compared to other sources since ancient times.To address the challenges an Innovative greenhouse dryer (IG) was technologically advanced and tested as an alternative and potential low-cost fruit drying system in Kenya to traditionally preserve fruits using modern technology. This study aimed at evaluating technological innovation that can be adapted by smallholder producers and SMEs in the tree tomato value chain in order to reduce post-harvest losses, as well as diversify the fruit into sustainable high-quality, functional value added, and shelf stable powder product or food ingredient. Two solar dryers, a solar tunnel dryer and an innovative greenhouse hybrid solar drier, were used to evaluate the drying kinetics, safety and quality characteristics of tree tomato powder. As drying time increased, the moisture content of the samples from both driers generally decreased. The Tree tomato pulp which had highest average initial moisture content of 91.03% (w.b.) attained an average final moisture content of 8.46% (w.b.) after drying for 9 hours in the solar tunnel drier while for the innovative hybrid greenhouse solar drier the samples which had an average initial moisture content of 89.92% attained a final moisture content of 8.33% after drying for 13 hours. The Moisture ratio decreased from 1.00 to 0.09 in both driers. Ten thin-layer drying models were fitted to the experimental data and parameters then analyzed to predict the moisture ratio of tree tomato pulp during the drying process using both driers. For the solar drier, only four models (Page, Modified Page, Midilli-Kuck, and Approximate Diffusion) exhibited a close correlation with experimental data and therefore used to assess the drying behavior of the samples. From the statistical analysis, the modified page model was best suited to simulate the drying of the product. For the innovative hybrid greenhouse solar drier upon analysis, only four models (Page, Modified Page, Midilli-Kuck, and Wang-Singh) exhibited a strong correlation with the experimental data and consequently used to assess the drying behavior of the tree tomato pulp. The Modified Page model emerged as the most appropriate for simulating the drying process, demonstrating a superior fit to the experimental data. Comparing the drying kinetics, solar tunnel dryer, was characterized by a higher drying constant (k=0.1459) and a moderate n value (4.022), exhibiting a more consistent drying rate across the drying process which suggests a more controlled and even moisture removal, particularly effective for maintaining uniform drying through early to later stages. Conversely, the innovative greenhouse dryer, with a lower k (0.1156) and a high n value (8.128), displayed rapid initial drying followed by a more gradual decrease in moisture removal over time. The Water Solubility % (WS %) at 80 oC was 99.02 as compared to 98.81from the solar tunnel dryer which was a better technological property. The functional properties which included the Total Phenols, Flavonoids, Antioxidant activity and Vitamins A and C where all higher in the innovative greenhouse dryer than in the solar tunnel dryer. From the overall physical, technological and functional point of view, the innovative greenhouse dryer was the best in quality performance of tree tomato powder production to overcome the problems associated with post-processing handling, packaging, and storage.