Valorization Study of Treated Deglet-nour Dates by Solar Drying Using Three Different Solar Driers

Abstract

Deglet-nour variety is a specific date to the region of Maghreb countries and is a climacteric fruit with maturation spread out on the same palm. Dates fruits being harvested once a year; this situation makes the fruit post-harvest treatment necessary so as to minimize losses and avoid the eventual conservation and storage accidents particularly through rainy year or excessively hot climate. This paper presents an experimental investigation of Deglet-Nour treatment by hydration and solar drying process in order to recover and valorise this category. The first aim of this work is to study the effect of different temperature (20°C, 25°C 30°C, 35°C, 40°C, 45°C, 50°C and 55°C) of soaking in distilled water on the inversion reaction of sucrose and the second aim is to analyse the drying of hydrated Deglet-Nour dates by three different solar processes. Three drying kinetics have been established respectively in a direct natural convective solar drier, under indirect convective solar drier and in indirect natural solar drier. The experimental results show that the best case was obtained by soaking in water at T = 25°C to obtain hydrated dates with 0.5kg water/kg dry matter. Drying time to reach commercial water content (0.35kg water/kg dry matter) by the use of the three prototypes were respectively 22h, 11.5h and 2.5h. These tests also showed that the drying with indirect natural convective dryer provides a good product quality with acceptable duration, and it is satisfactory and competitive to a forced convective solar drying process. A good microbiological quality was observed on the final product obtained by each of the three different solar driers.