Solar drying process to obtain high standard "deglet-nour" date fruit

The present work aims to improve the quality of Algerian Deglet-Nour dates using an indirect solar drying technique preceded by hot water pretreatment. The final product quality was evaluated by three simultaneous testing parameters: microbiological degradation, sugar composition and color change. Convective solar drying experiments were firstly performed with a variable mode at an average temperature ranging between 39-55 degrees C. Four other experiments were conducted in constant mode under regulated temperatures (50 degrees C, 55 degrees C, 60 degrees C and 65 degrees C). The results of drying tests, led towards the choice of the treatment under controlled air temperature of 50 degrees C with air flow of 1.2m/s. Resulting drying time of 8 hours presents the advantage of to discard the night conservation problems by ensuring a continuous drying process. Owing to its low cost and green energy use, this study could offer a practical alternative to the conventional means currently used in industrial applications of postharvest heat treatments of dates. Practical applicationsDrying of naturally high humid dates and the rehydrated dry dates by direct exposure to the sun, is an old method for valorization the Deglet-Nour dates. Considerable losses occur during this drying process so the food quality can be seriously degraded. For an industrial application with improvement the quality of dried product, the natural sun drying should be replaced by the indirect solar drying means. This article aims to improve the quality of Deglet-Nour dates using an indirect solar drying technique preceded by adequate water steeping pretreatment. The results of the study will be useful in the sense of ensuring an added value by enhancing the product quality and avoid eventual problems induced by night storing of treated products. The obtained results also could offer a practical alternative to the conventional means currently used in industrial applications for post-harvest heat treatment of Deglet-Nour dates.