New Horizons of Science, Technology and Culture Vol. 6

In the Philippines, red and yellow onions are frequently cultivated. The country’s advantageous climate and soil traits create an optimal setting for growing these onion types. The elevated moisture levels in onions render them vulnerable to fungal growth, especially Aspergillus niger, leading to spoilage and economic losses in agriculture. Drying is a method used to prolong the shelf life of onions by decreasing moisture content and water activity. Dehydrating onions to a moisture content (MC) of 5% prevents the proliferation of microorganisms and ultimately extends their shelf life. This study aims to determine the ideal drying temperature and minimum duration for onions to reach 5% moisture content by assessing the least energy usage. Three mathematical models—Laplace Transform Model, Page Model, and Non-linear Decomposition Model—were analysed to characterise the drying behaviour of thinly cut red and yellow onions at temperatures of 50, 60, and 70°C, utilising a tray dryer with 20% relative humidity and an air velocity of 2 m/s. The Page model provided the optimal fit for red and yellow onions with the smallest overall error. The optimum drying temperature was observed at 70°C for both red and yellow onions, which was efficient in producing quality onions without any fungal growth at the shortest drying time of 25.6 and 24.74 minutes, respectively. The power requirement calculated at 70°C was 154.18 W for red onions and 148.07 W for yellow onions.  These results may serve as a basis for developing efficient drying protocols in red and yellow onion processing industries.