Quality evaluation of dried tomato fruit and optimization of drying conditions using a modified solar dryer...

In the current study, a modified solar dryer (SD) integrated automatic solar collector tracker (ASCT) was used for drying tomato fruit (TF) at three slice thicknesses of 4, 6, and 8 mm on both drying systems at three air speeds of 1, 1.5, and 2 m/s until reaching the equilibrium moisture content. Where the comparison study was conducted between the ASCT, and another SD integrated with a fixed solar collector (FSC). The obtained results of the current study showed that the maximum solar intensity and ambient air temperature during the test period were 900 W/m², and 43.6 °C, respectively. As well as the highest efficiency of the PV system was 16.69% at the same time. On the other hand, the height, greatest diameter and smallest diameter of the TF used in the current study ranged between (4.6 and 5.2 cm), (3.5 and 4.2 cm), and (3.4 and 4.1 cm), respectively. As well as both the athematic and geometric diameters ranging between 3.87 and 4.47 cm and 2.26 and 2.38 cm, the sphericity values of tomatoes tend to have a round shape. In addition, the obtained results that there was no significant effect of the hot air velocities on the drying time, but the final moisture content (MC) decreased with increasing the hot air velocities. The lowest final MC was 6%, and it was recorded with a slice thickness of 4.0 mm that dried on SD integrated with ASCT. Additionally, color analysis showed that, the darkest tomato slices were dried on the SC integrated with FSC at a hot air velocity of 1.0 m/s. Meanwhile, the intensity of red and yellow colors significantly increased after drying with the SD integrated with ASDT. Furthermore, the chemical analysis of the dried tomato slices showed that the highest rehydration ratio of 4.43 kg water/kg dry matter was obtained for the dried tomato slices dried on SD integrated with ASCT at a hot air velocity of 1.5 m/s and a slice thickness of 8.0 mm. As well as the highest values of pH were monitored on the dried tomato slices on ASCT in comparison to the other tomato slices dried on FSC. Also, the highest ascorbic acid content recorded was 141 mg/100 g (d.b.) in tomato slices with an 8.0 mm thickness, dried using SD combined with FSC at an air velocity of 2 m/s. After drying, the total phenols content increased in all dried tomato samples but decreased with lower hot air velocities.