Study On The Microwave Vacuum Drying Quality Characteristics And Mechanism Of Ablane

Abalone is also known as Haliotidae, which is rich in nutrient with delicious taste. Dehydrated abalone is the one of the main abalone products. It is necessary to develop a new processing technology for dehydrated abalone, because traditional drying methods are lack of energy conservation, technology innovation and quality assurance. Microwave vacuum drying is a new technology integrating microwave drying and vacuum drying, which has characteristics of fast drying rate, environmental protection and operability. The microwave vacuum drying (MVD) technology was applied to abalone drying in this study. The effects of pretreatment, microwave power, vacuum and load on abalone dried by Microwave vacuum technology were studied systematically. The MVD characteristic and drying dynamics model of abalone was established. There was optimized MVD process parameter of abalone. Finally, MVD was compared with the sun drying, hot-air drying and vacuum freeze-drying. The main results were concluded as follows.1. The effects of pre-drying treatments on the drying process for abalone were studied, taking drying characteristic, color, rehydration and texture as the evaluation indexes. The results showed that:when the salt concentration was7.5%, the quality of dehydrated abalone was the best and microwave vacuum drying rate significantly accelerated. Considering the drying efficiency and products quality, a good pretreatment of abalone is immersion in7.5%salt solution and boiling for2min.2. MVD characteristics of abalone were studied by the effects of microwave power, vacuum degree and load on the dehydration rate. It showed that the MVD process of abalone was divided into three stages:speed-up, constant-speed and speed-down. There were obvious effects of microwave power, vacuum degree and load on abalone drying rate. The increasing microwave power and vacuum or the reducing load could speed up the rate of water loss, shorten the drying time, but it did not always follow this rule. Application analysis software MATLAB was used to analyze the regression rule of microwave vacuum drying characteristics of abalone. The drying procedure of abalone could accurately be described by the Page model and satisfied the Page equation: lnMR=-rtN, of which lnr=-2.8562-0.3875X1-0.0095X2-0.0115X3+0.0001X4, N=1.4738-0.0527X10.0009X2-0.0006X3-0.0098X4, R2=0.9765.3. The processing parameters of microwave power, the vacuum and load were optimized. The relatively optimizing processing parameters for microwave vacuum drying of abalone were determined:the microwave power was2kW, the vacuum was-80kPa, the loading was150g.4. The quality of abalone dried by sun drying (SD), freeze drying (FD), hot-air drying (HAD), and microwave-vacuum drying (MVD) were investigated. The quality parameters were compared according to the rehydration, color, texture, content of amino acid and sensory characteristics. The cohesiveness and chewiness of the products dehydrated by MVD were much better than other methods. The color of these products was most acceptable by the consumers. The amino acids content of MVD abalone was more even distributed than the others processing method. It showed porous structure of MVD abalone by electron microscopy. Consequently, the optimal drying method for the abalones was determined to be MVD.5. Under the optimum process conditions of microwave vacuum drying, the influences of MVD on abalone structure characteristics, microstructure and the content of flavor substances were referred. The results showed that hardness, stickiness and chewiness increased with the increasing processing time; SEM showed that tissue fibers of the abalone became slender and stretched state from expanded state, then muscle fibers deformed, and fiber gaps got widen at the end of drying process; the contents of esters, carboxylic acids, pyridines, aromatic of dried abalone increased making it rich in aroma.6. The rehydration process of the dried abalone is an indispensable key step for abalone cooking and further processing. Effects of microwave power, vacuum degree and salt solution concentration were investigated. The rehydration procedure of abalone could accurately be described by the model as: ln(-lnMRf)=-1.5376-0.0934X1-0.0077X2-0.0491X3+0.0135X4+0.5547X5+0.0186X,X5+0.0015X2X5+0.0071X3X5-0.0039X4X5-0.0410X52, R2=0.9021.And the predicted values were nearly consistent with the experimental values.