Production of dried vegetables and fruits by solar and heat pump dryer
1999
Kulaya Junarun (Rajabhat Institute Pibulsongkram, Phitsanulok (Thailand))
Heat Pump Dryer could control temperature, relative humidity and air velocity by computer for drying Fruits and Vegetables. Fruits and Vegetables used to study are Cabbage, Chinese Lettuce, White Beetroot leaf, Leek, Coriander, Ocium, Basilicum Mint and Ginger. Nam-Waa Banana, Hom-Thong Banana, Pineapple and mango. They were dried by Heat Pump Dryer (HPD), Hot Air Oven (HAO) and Sun drying (SD). Results showed that HP dried Cabbage, Chinese Lettuce, White Beetroot leaf and Coriander had satisfied color, smell, taste and texture. After rehydration by boiling 1-3 min, they absorbed over 80 percent water with quality equivalent to boiled fresh vegatables. The HAO and SD vegetables were faded and shrunk. Dried Ocium, Basilicum Mint and Ginger from 3 drying processes gave similar qualities which were greenish brown (except Ginger was light yellow). The optimum temperature for HPD was 52 (+-2 C) while blanced vegetables was 60 C, 40 percent RH and 2-3 m/sec air velocity. Dried Cabbage, Chinese Lettuce, White Beetroot leaf, Leek and Slice Ginger Contain 9.2, 4, 4, 4 and 3.9 percent moisture content respectively. For banana, results showed that SD gave golden yellow color, better taste and softerer texture banana than from HPD. Although the optimum drying period was 5 days in SDO, it is less time consuming and energy cost than HPD. HPD pineapple and mango had better quality than those from SDO. Chemicals used in the drying process could preserve color and texture of dried products. The products could be stored in refrigerator for up to 1 year with sightly change. The chemical compositions of dried products are Calcium, Phosphorous, Vitamin C, Crude Fiber. Fat and Tannin had non significant difference from each method.
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