Drying of osmotically predried kiwifruit by fluidized bed drier assisted by infrared wave

Kiwi is a fruit, which is often-heard in recent years and its production has increased in our country. Because of its aromatic substances and high vitamin C content, it is of high significance. In this study, after pre-drying, osmotic dehydration and then drying in a tray dryer, kiwifruits were dried up to 80.31±1.26% of total dry matter content by two different methods;(i) drying by the fluidized bed dryer with hot air, (ii) drying by the fluidized bed dryer with a combination hot air + infrared waves. By examining some quality characteristics of dried kiwifruit samples, the effects of the infrared wave use in fluid bed dryer have been investigated. Kiwifruits were sliced to 4.97±0.36 mm of thickness and then they were cut to 39.87±0.44 mm diameter by using an annular block. Pre-drying by the osmotic method in a sucrose solution of 60 ºBrix was performed until the samples reached dry matter content of 33.65±2.48% in a shaker incubator. Semi-dried samples were dried up to 61.30±2.11% of total dry matter content in a tray dryer. Then the samples were dried to 80.31±1.26% of total dry matter content by using two different methods. Drying time in fluidized bed dryer with combination of hot air + infrared waves as compared to only drying with hot air was found to shorten drying time rate by 42.69%, 44.21% and 29.73% at air-drying temperature of 50, 60, and 70 °C, respectively. It was observed that hot air+infrared combination significantly shortened the drying period. Effects of final drying methods on quality characteristics of kiwifruit were investigated by analyzing total dry matter, vitamin C, invert and total sugar, colour, water activity, rehydration capacity, bulk density, particle density, and shrinkage of final products. Final drying process conditions did not affect (p>0.05) bulk density, particle density, shrinkage degree, and rehydration capacity of the dry product, but they affected (p<0.05) water activity, sugar and vitamin C content, and color values. Water activity value dropped to an acceptable level of microbiological safety (<0.70 for all dried samples). A significant (p<0.05) decrease was observed in bulk density of the final product while there was not significant (p>0.05) change in particle density as compared to the raw material. Osmotic process decreased the vitamin C content of kiwifruit by 51.6%. Moreover, final drying process further increased vitamin C loss to values change from 69.4 to 83%. Significant changes were observed in L, a, and b values of kiwi fruit (p<0.05) due to final drying method. In conclusion short drying time, high vitamin C content, less of shrinkage, high L value, low of a and ΔE value samples has been recognized as the best product. The best final product was obtained by final drying method performed at 70 C using hot air+infrared combination. However, it dried was not different (p>0.05) from the product dried at 60 C with hot air + infrared combination. Keywords: Fluidized bed, infrared, osmotic dehydration, kiwifruit, drying