Drying of pretreated apricot by combined solar and radio frequency system

In this study, the drying of pre-treated apricots was investigated in a new combined drying system (a pilot-scale combined solar assisted air and hot air-assisted radio frequency drying system). Sulfuring and/or immersion in a phenolic extract were applied as pretreatments. In sulfuring process elemental sulfur with different concentrations (0.5, 1.0, 1.5, 2.0, 2.5 kg of elemental sulfur/ton of apricot) was used. In phenolic extract treatment different concentration of phenolic extract (0.25, 0.75, 1.25, 1.75, 2.25 % extract) obtained from pistachio hull was used. The drying conditions, solar-assisted air-drying temperature, solar-assisted air-drying time, air flow rate, the distance of RF electrodes, and RF drying time were 63.5 °C, 895 min, 5.5-6 m/s, 77 mm, and 385 min, respectively. The quality of apricots dried by developed system have been compared with the apricots dried with traditional drying method in terms of moisture content, browning index, color, texture, phenolic content, antioxidant activity and residual sulfur content. According to the results, the best quality dried apricots were obtained after sulfuring (2 kg of elemental sulfur/ton of apricot). The color (Lab), moisture, hardness, residual sulfur content, browning measurement are characteristics of this final product were 45.2±1.9, 17.8±1.4, 36.2±2.7, 20.54±0.97, 1355.87±64.73, 1598±30.8, 0.22±0.02 respectively. Financial support for this study is provided by TUBITAK Project No: 118O026. Key words: Dried Apricot, Sulfuring Process, Air Assisted Solar Srying, RF Drying