Research On Drying Characteristics And Mathematical Models Of Papaya Slices In Different Drying Methods

Papaya is a kind of fruits with high nutritional value.After harvested,the fruits are still breathing intensity and easily perishable.Therefore,it is difficult to reserve them.However,these problems can be solved efficiently by drying the fruits.At present,there are some studies on the drying of papaya.Although some studies have been done on the drying characteristics of papaya,the optimization of process parameters such as quality,drying rate and unit energy consumption of dried papaya is not yet reported,and the drying process of internal water migration,heat transfer and mass transfer law is not proven.Based on this,the papaya was studied in this article.First of all,in order to optimize the vacuum freeze drying of papaya,the method of comprehensive drying index was used to value the quality of dying products.Secondly,in order to prove the theoretical and practical advantages of combined microwave-convective hot air drying of papaya slices,several test index values,such as color change,rehydration ratio,unit energy consumption and drying rate during drying process were investigated,and the technological parameters of hot air temperatures,microwave power densities and hot air velocities were optimized;The drying kinetics model and effective moisture diffusivity model of papaya slices during combined microwave-convective hot air drying were established.Thirdly,the characteristics of microwave vacuum drying of papaya were studied to achieve the optimal conditions;at the same time,by fitting the test data,the comprehensive weighted score and the experimental factors(microwave power density,cavity absolute pressure,material thickness)were used to established the mathematic model.Finally,according to the evaluation of 4 different indicators(color,rehydration ratio,drying rate,unit energy consumption),choosing the best drying method of papaya slice among the vacuum freeze drying,combined microwave-convective hot air drying and microwave vacuum drying.The conclusions are as follows:Vacuum freeze drying:the sublimation temperature and the material thickness had a significant effect on the test results,while the pre-freezing temperature had no significant effect on the test results.The optimum conditions are as follows:the material thickness is 3 mm,the sublimation temperature is 35?,and the pre-freezing temperature is-40?.Hot air?microwave and combined drying:hot air temperature levels are 50,60,70?,microwave power density levels are 3.3,5.5,7.7 W/g.The hot air drying,microwave drying and hot air microwave drying process of papaya slices are composed of accelerating and decelerating stages.During the process of combined drying,the influence sequence of various factors on the comprehensive effect of drying was microwave power density,air temperature,air velocity.And the optimum drying conditions is:hot air temperature is 60 degrees centigrade,the microwave power density of 5.5 W/g,the hot air speed is 0.5 m/s.So compared with single drying,the combined drying can obtain comprehensive high quality products,fast drying rate and unit energy consumption.Combined microwave-convective hot air dehydration:the Page model can be used to predict the relationship between the moisture content and drying time of papaya slices in combined microwave-convective hot air dehydration,and the effective water diffusion coefficient Deff is between 2.533×10-9?6.0792×10-9 m2/s.Microwave vacuum drying:the optimum conditions is microwave power density of 10 W/g,the cavity absolute pressure of 3.3 KPa,the material thickness of 7 mm,the microwave power density affect the drying effect significantly and the cavity absolute pressure and material thickness on drying comprehensive effect is not significant,the primary and secondary order is:microwave power density,cavity material thickness,absolute pressure.Comparison results of evaluation indexes of vacuum freeze drying,hot air microwave coupled drying and microwave vacuum drying:Dry products were 8.85,13.36,11.73 total color difference.If the color of dying product worked as the evaluation index,the vacuum freeze drying is the best way to dry papaya.The drying rehydration ratio are 5.68,4.15,5.25 respectively,so if the rehydration ratio as evaluation index,the vacuum freeze drying is the best method to dry papaya.The drying rate of different drying ways followed by 1.62,26.34,9.47(g/100g)/min,so if the drying rate as the evaluation index,the combined microwave-convective hot air dehydration is the best drying way.The drying unit energy consumption is 371 684.02,12 388.16,275 214.60 KJ/kg respectively,so if in terms of unit energy consumption,the combined microwave-convective hot air dehydration is the best drying way.Therefore,in order to achieve high drying product quality of fruits and vegetables,the enterprise can choose the method of vacuum freeze drying.Whereas if considering the comprehensive index,the enterprise can use combined microwave-convective hot air dehydration.