| Method for drying all in,freeze drying (FD) is the best method for maintaing the material’s quality among all drying methods. For fruits and vegetables, the color, flavor, shape and taste of FD fruits and vegetables are very good. However, high energy consumption during FD process is a major problem that limits the wide application of this method on common fruits and vegetables. FD was replaced by two-stage tandem combined drying technologies, FD and vaccum microwave dyring (VMD), in order to decrease the energy consumption and maintain the quality well.High energy consumption and high cost limit the scale of freeze dried (FD) food. Tandem combined FD as pretreatment and microwave vacuum drying (MVD) can drastically reduce the energy consumption of FD. However, there exists significant difference in quality between combined dried products and traditional FD products. In order to resolve this problem, Dioscoreaceae served as test materials to study the pore character and drying mechanism of semi-moist fruits and vegetables during MVD. This program aims to make clear the shrinkage mechanism of fruits and vegetables as well as the strategy of microwave loading during MVD by investigating the low pressure discharge mechanism for semi-moist fruits and vegetables as well as the moving law of moisture in micro pore during MVD. It is also expected to find out the mechanism for moisture conversion of semi-moist fruits and vegetables during MVD by studying the effect of various factors during prefrozen and FD on the formation of pores.In this paper, the study found that the pretreatment of iron yam freeze-dried quality assurance is very important, without pretreatment of the iron yam color and appearance of the yam and drying effect is good after all did not protect color. And joint freeze drying process conditions is:the heating plate sublimation temperature20℃, parse temperature50℃,0.032MPa, vacuum freeze-dried time4.5h to freeze the best point of water. Vacuum microwave drying best microwave power is0.25W/g, vacuum degree is0.095MPa, the drying time is100min dry best product quality. Microwave drying stage using0to20min power of0.15W/g,20to50min power of0.35W/g,50-90min power of0.25W/g yam from different segmented dry power of the highest Vc content, drying time shortest lowest energy consumption, product no collapse or shrinkage phenomenon. The entire process of combined drying temperature should not be more than40℃, otherwise all affect the appearance and internal structure of product. Soluble polysaccharide because itself is stable, under the condition of all kinds of combined drying technology of polysaccharide content and no significant changes.By comparing the FD and VMD, FD-VMD and AD the four kinds of drying methods on the physical properties of iron yam, ultrastructure and sensory evaluation. In microwave vacuum drying process, through regular sampling after using micro CT scan technology to look inside the material distribution in water, observe the condition of moisture migration during the process of microwave vacuum drying, thus revealed in the process of microwave vacuum drying moisture migration features; Scanning electron microscope for the material in different aspects, studying the characteristics of the channel shrinkage and drying process of clearance study confirmed the iron yam in the microwave field in the microwave drying uniformity. By optical microscope, freeze-drying can be a very good maintain cell structure of the iron yam, freeze-dried iron yam structure in different time and fresh state, very close to the cells of honeycomb structure is well preserved, starch granules and fresh state... |
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