Study of Four Onion Varieties Drying Kinetics in an Oven and a Solar Greenhouse

Onion production (Allium cepa L.) in Senegal reached 390 000 tons in 2016. Due to post-harvest losses, annual demand (150 000 and 250 000 tons) is being met through imports. This work consists in proposing a drying process at a lower cost to overcome this dependence and preserve the quality of the product. The optimization of local onion varieties drying in an oven and in solar greenhouse, as well as the physicochemical characterization of the products were carried out. The moisture of fresh onion bulb varies between 85.56 ± 0.60 and 89.13 ± 0.69 (%). To obtain a moisture £ 8.89 ± 0.16 (%) ensuring stability, the optimal drying conditions in the oven are 60° C / 6H (Galmi Violet) and 7H (Safari, Gandiol F1 and Orient F1). Under these conditions, the content of polyphenols in g equivalent of gallic acid / 100 g db increases (0.111 ± 0.0040 to 0.312 ± 0.0041 before drying, 0.546 g ± 0.0117 to 0.837 ± 0.0091 after drying). Optimum solar drying in a greenhouse is obtained between temperatures of 35 to 65° C / 8H-9H. From a perspective of sustainable development, the perspective is the modeling of drying kinetics in a solar greenhouse.