88E-30 |
Improving the effectiveness of osmotic dehydration by microwave pretreatment |
W. C. WANG, Department of Food Science and Technology, DaYeh University, 112 Shan-Jiau Rd., Da-Tsuen, Changhua, 515, Taiwan and W. J. Su. Osmotic dehydration is very time-consuming. By using microwave pretreatment, physical properties of raw materials may be changed, which could be a way to increase the process effectiveness. Our objectives were to develop the potential effectiveness of microwave pretreatment, investigate the effect on physical properties, and compare the product quality. Papaya, guava and sweet potato strips (3x3x0.5cm3) were heated by microwave before osmotic dehydration. Two power-time combinations with same energy input were experimented (480W-10min and 800W-6min for papaya, 480W-15min and 800W-9min for guava and sweet potato), whereas traditional boiling water dipping was conducted as control. Samples were first used in a 3-step consecutive soaking process, with sugar concentration increase by 10Brix per 3hr, and then the osmotic dehydration process was modified according to the sugar uptake enhancement. After osmotic dehydration, final products were produced by 5hr, 80oC hot air drying. Hardness, color and sorption isotherm were determined. The microwave pretreatment strongly increased sugar uptake of papaya from 23 to 29Brix during the first 3hr soaking, while 4 and 1Brix increment were found for guava and sweet potato, respectively. The difference could be due to different structures. Most low-wattage-long-time treatments provided better thermal effects. By adjusting procedures, papaya preheated by microwave could reach the same final sugar uptake (53Brix) within 5.8hr, compared to 9hr for traditional samples. Process time reduction for guava was 2.3hr, while the effectiveness on sweet potato was limited. Data showed that no significant difference on water activity and hardness. Final products from microwave pretreatment were found brighter than traditional ones; less oxidation/browning could be the reason. The osmotic dehydration rate could be increased up to 5 to 34% by microwave pretreatment. Quality of final products was found no significant difference, which indicates that microwave pretreatment could save processing time without sacrificing product quality.
Session 88E, Fruit & Vegetable Products: Processing
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