Optimization of ultrasonic rehydration conditions of dried tomatoes

The aim of the study is to compare the ultrasonic rehydration process which was applied at the optimum points that were determined by optimization of the ultrasonic rehydration conditions with the traditional rehydration methods of dried tomatoes; and additionally to investigate its effects on some quality properties which are important for dried products. Rehydration conditions were optimizated using the Response Surface Method (RSM). In the optimization of dried tomatoes, rehydration capacity, color a* (redness) value and tissue value (dependent variable) were selected in response. Ultrasonic (37 kHz) rehydration was performed at three different temperatures (20, 60, 80ºC), time (2, 31, 60 min) and water ratio (1/50, 1/75, 1/100 g/water g). As a result of optimization, two optimum points and three rehydration conditions based on literature data were determined. The optimum points and the conditions selected from the literature were rehydrated by ultrasonic and conventional methods and the results were compared. It was determined that ultrasound application significantly increased the rehydration capacity of the samples. In addition, when the color values of the samples were examined, it was found that the samples giving the brightest (L*=24.66) and the most red (a*=13.67) color values were obtained by the production at optimum points. As a result, it was determined that ultrasound application positively affected the tissue, pH and water activity values of the samples, but caused lycopene value losses. It was observed that the application of ultrasonic at the optimum points decreased the total dry matter value. These results are seen as proof that ultrasound can be used for rehydration capacity. In addition, it was determined that the rehydration capacity and redness (a*) values of the dried tomatoes rehydrated by ultrasound were higher, while the textural values were softer.