Red onions are commonly grown crops in the Philippines. The country’s favorable climate and soil conditions make it an ideal environment for cultivating these onion varieties. The high moisture content of onion makes it susceptible to fungus growth, particularly Aspergillus niger, which causes spoilage and agricultural losses. To extend the shelf-life of onions, drying is a technique that reduces water activity and moisture content (MC). Drying onions until the MC is 5% inhibits the growth of microorganisms and ultimately increases their longevity. This research attempts to predict the optimum temperature and shortest drying time to achieve 5% MC in red onions. Three mathematical models, the Laplace Transform Model, Page Model, and Non-linear Decomposition Model, were examined to describe the drying behavior of thinly sliced red onions at 50, 60, and 70°C using a tray dryer. The Page model gave the best fit for red onions with the least total error and highest coefficient of determination. The optimum temperature was observed to be 70°C, which was efficient in producing quality onions without any fungal growth at the shortest drying time of 67.27 minutes. A tray dryer was designed to dry 100 kg of red onions for a small-scale setting using 40 trays with dimensions 1.4 × 0.8 × 1.7 m and a heating requirement of 13.77 kW with solar heat as the primary source of energy and a recirculating mechanism of air as innovations.

Aspergillus niger, drying kinetics, mathematical model, moisture content, onions, tray dryer.

The Page Model best fits the drying behavior of red onion with the least total error, the highest coefficient of determination, and good visual inspection. The optimum drying temperature was 70°C with the shortest drying time of 67.27 mins. to attain 5% moisture content in red onion. Quality dried red onion was produced without the growth of Aspergillus niger. A tray dryer was designed to dry 100 kg of red onions for a small-scale setting with dimensions 1.4 × 0.8 × 1.7 m using 40 trays and a heating requirement of 13.77 kW. Solar panels and a recirculating mechanism of air were innovations

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L.D. Pestaño, M.K. Gaspar, A.F. Quizon and R.L. Sandoval (2024). Numerical Simulation of the Drying Kinetics of Red Onions (Allium cepa) to Prevent the Growth of Aspergillus niger and the Design of a Tray Dryer for Small-Scale Setting. International Journal on Emerging Technologies, 15(1): 22–29.