Valorization of rehydrated Deglet-Nour dates by an experimental investigation of solar drying processing method

• A laboratory scale direct solar dryer was constructed and investigated.
• The solar drying of hard date palm fruits, Deglet-Nour variety, was studied.
• Three improvements in the dryer operating modes were proposed and compared.
• Combination drying mode has been selected as the most adequate process.
• Selected mode ensures a high quality of product and allows short duration of treatment.

In objective to valorize hard Deglet-Nour dates, a new postharvest processing method was proposed and investigated using a laboratory scale direct solar dryer. Date samples were soaked in distilled water then dried by solar drying mean. In order to improve the quality and consumer acceptance of this date variety, three proposed drying enhancements: drying under shade (DUS), drying with photovoltaic powered ventilation (DSV) and combination drying mode (DCM) were tested and compared with the basis case of natural ventilation drying (DNV). The obtained experimental results classified the drying with solar ventilation drying mode (DSV) and combination drying mode (DCM) in favorable operating conditions needed for the studied case. Measured air drying temperatures ranged between 41.8 and 56.0 °C and 39.3 and 51.2 °C respectively for the two above techniques. The drying duration to obtain the standard moisture content (0.35 kg/kg DM) was respectively 5.25 and 8 h. Regarding quality criteria and processing time, the combination drying mode was selected as the most adequate process.