Study On Osmotic Dehydration And Combined Drying Of Asparagus Lettuce

The drying disciplinarian and desiccation characteristic during osmotic dehydration and combined drying of asparagus lettuce have been studied, in order to investigate the osmotic dehydration disciplinarian of cauliform vegetables and to exploit the foreground of the osmotic dehydration applying to vegetables process.Influence of different factors such as pretreatment methods, temperature etc on osmotic dehydration of asparagus lettuce was studied by tracking down the rate of water loss and the rate of solid gain. The results showed that slice cutting can increase the water loss; blanching can badly embarrass osmotic dehydration; agitation can accelerate mass transfer; the solid gain was increased with the increase of temperature, but the water loss didn't have the same disciplinarian; high sucrose concentration improves water loss effectively and reduces solid gain. Influence of osmotic solution combination, temperature and ratio of sample to solution was studied by the orthogonal experiment, and the result suggests that the major influential factor of water loss is osmotic solution combination; the major influential factor of solid gain is temperature. The best processing technology of osmotic dehydration is that the concentration of solution is 60 percent sucrose/10 percent salt, at 30°C, with the sample/solution ratio of 1:10.After osmotic dehydration, the intermediate moisture asparagus lettuce was dried by hot air and microwave respectively. The desiccation characteristic, preserving of vitamin C, water activity, rehydration, color and luster were studied during the combined drying. The results showed that the products of osmotic dehydration combined hot air display better quality than that of single hot air, such as 7～10 times increased on Vc retain ratio, 10% depressed on water activity, 2～3 times increased on rehydration. About 1/2 operation time of the dry process can be shorten by osmotic dehydration combined microwave, meanwhile the water activity depresses, and the quality of products was improved compare with the drying method of osmotic dehydration combined hot air.