Dehydration of strawberries with different drying techniques and the effect of ultrasound pretreatment on some quality criteria

In this thesis, the drying time and quality characteristics of strawberry slices were investigated by drying strawberry fruits under different drying conditions after ultrasonic (US) pretreatment. After separating the control group from the fruits to be dried with hot air at 70°C, US pretreatment was applied at 40kHz frequency for 10, 20, 30 minutes in an ultrasonic water bath with a raw material:water ratio of 1:4 and dried at 70°C at an air speed of 1.2 m/s. In the fruits to be dried in microwave (MW), the control group was separated and US pre-treatment was applied at 40 kHz frequency for 30 min with a raw material:water ratio of 1:4 and dried in microwave at 180W power. During drying, weight measurements and samples were taken at certain intervals. Water soluble dry matter (°Brix) and pH analyses were performed on fresh strawberry samples and after US pretreatment. In addition, total dry matter, titratable acidity, ash, ascorbic acid, rehydration capacity, Hunter L, a, b, total colour change, browning index, hue angle, chroma parameters were analysed before and after drying. The effect of US was clearly determined in strawberry slices dried at 70°C and with MW. The cavitation of ultrasound in strawberry slices caused the rapid release of moisture in the product and the drying time of the samples dried at 70°C was shortened by 14.3% in the sample dried at 10 minutes US, 28.6% in the sample dried at 20 minutes US and 42.8% in the sample dried at 30 minutes US. In the sample dried in the microwave, it caused 12.5% shortening in the sample with 30 min US application. The prolongation of the application time of the US pretreatment is very effective in shortening the drying time. Dried strawberry samples were sensory evaluated by a group of 14 panellists. In the analyses, all strawberry samples received high scores in terms of general appreciation. The most appreciated strawberry samples were the strawberry samples dried with hot air at 70°C using 30 US. The variation of the separable moisture content (MR) values obtained by drying the strawberry samples dried at 70°C and with MW and ultrasound assisted drying was statistically investigated using 8 different thin layer drying models and MATLAB 2012b programme. As a result of the evaluation of the data obtained with thin layer models, it was concluded that the model that best describes the change of the moisture content value of the strawberry according to the time with the fewest parameters among the models applied is the Newton model.