A study on drying of stanley plums with different drying systems

In this thesis, drying characteristics of Stanley variety of plum was investigated using different drying methods. Sample cores weren't removed and subjected to any mechanical process before drying. Samples were tested in two groups. These are; (1) Pretreated samples with 1% NaOH solution at room temperature, (2) Non-pretreated samples. Samples were dried with hot air, microwave-assisted hot air and infrared-assisted hot air. Plums were dehydrated at air temperature of 60, 70 and 80°C, microwave and infrared power of 300, 400 and 500 W and constant velocity of drying air of 2 m/s. Drying process was continued until moisture content of samples was reduced to 20% (w.b.). Rehydration capacity was measured for every hour of first 8 hours and at the end of 24 hours. Bulk density and volumetric shrinkage of dried samples were determined using toluene method. According to the results of this research; • Drying time of pretreated and non-pretreated samples was 3074 and 3218 min, respectively, when infrared-assisted hot air used (at 60°C drying air temperature and 300 W infrared power). Drying times were 4780 and 5280 min for pretreated and non-pretreated samples respectively, when only hot air used for drying (drying temperature of 60°C). • When the rehydration capacities of samples were examined; rehydration capacity of dried samples was increased for all air assisted applications when the drying air temperature was 60°C. The rehydration capacities of samples were decreased when the air temperature, microwave and infrared power increased. • Higher lightness (L*) value of the dried samples were obtained using all microwave-assisted hot air applications. The nearest Chroma (C) value to fresh sample was obtained when pretreated samples dried at drying air temperature of 60°C. The nearest hue angle was determined using only hot air for drying. The lowest value of browning index for dried samples was obtained when microwave or infrared assisted hot air used. iii • Bulk density of all dried samples were higher than fresh samples. Bulk density and shrinkage values were close to each other at the all drying conditions. • According to results of microwave or infrared assisted hot air applications, specific energy consumption of samples was quitely higher when the only hot air at the temperature of 60 and 70°C used. When drying air temperature of 80°C was applied, minimum specific energy value was obtained.