Optimization Of Hot Air Microwave Coupled Drying Process And Study On Drying Dynamics Model For Red Jujube

Drying is an important processing method for red dates to reduce raw material loss,retain flavor and nutrients.Currently,a single drying method has problems such as high drying energy consumption,easy oxidation and browning of heat sensitive nutrients,and hardening and crusting in the later stages of drying.Joint drying can overcome the limitations brought by single drying,not only improving the quality of jujube drying,but also increasing the drying rate.This article takes red dates as the research object and uses hot air microwave coupled drying technology to dry them.The effects of different pre-treatment methods on the quality of red dates are compared,and the best pre-treatment method is selected.On the basis of single factor experiments,the response surface method is used to optimize the optimal process parameters,study the drying kinetics changes under different drying conditions,and select the best drying kinetics model.The main research content and conclusions are as follows:（1）Exploring the effects of different pre-treatment methods（blanching,freeze-thaw,alkaline ethyl oleate impregnation,ultrasonic treatment）on the nutritional quality,color,microstructure,volatile substances,and taste of hot air microwave coupled drying of red dates.The results showed that compared with blanching,freeze-thaw,and alkaline ethyl oleate impregnation pretreatment,ultrasonic pretreatment can effectively improve the quality of dried red dates and facilitate the formation of loose porous structures.The color difference value is 5.78,the vitamin C（Vc）content is 74.37 mg/100 g,the total phenol content is317.09 mg/100 g,the browning degree is 0.25,the rehydration ratio is 2.04,and the types of volatile substances are increased,Ultrasonic treatment is an excellent pre-treatment method for red dates.（2）On the basis of single factor experiments,with hot air temperature,microwave power,and load capacity as influencing factors,and Vc content,color difference,and rehydration ratio as evaluation indicators,response surface methodology was used to optimize the drying process parameters of red dates.The optimal parameters were coupled with drying under the same conditions for quality comparison with single drying.Regression models were established using response surface methodology for various factors related to Vc content,color difference,and rehydration ratio,with R2 values of 0.9936,0.9911,and 0.9771,respectively;The order of influence of various factors on color difference,Vc content,and rehydration ratio is hot air temperature>microwave power>payload;The optimal process parameters obtained from the response surface are hot air temperature of 49℃,microwave power of 94 W,and load capacity of 190 g;Under optimal parameters,the quality of jujube under coupled drying is higher than that under single hot air and microwave drying..（3）Explore the drying curves,effective water diffusion coefficients,and drying activation energy of jujube under different hot air temperatures（40℃,45℃,50℃,55℃,60℃）,microwave power（60 W,80 W,100W,120 W,140 W）,and load capacity（100 g,150 g,200 g,250 g,300 g）,and screen the optimal drying kinetics model.The research results indicate that the entire drying process of red dates belongs to a rate reducing drying process,with a water diffusion coefficient ranging from 4.12261×10^-9to 1.18917×10^-8m²·s^-1,which is is positively correlated with hot air temperature and microwave power,and negatively correlated with payload.The drying activation energy of red jujube was calculated to be 37.18 k J/mol using the Arrhenius formula.Fit the hot air microwave coupled drying process of red dates with five commonly used thin layer drying models,evaluate the five drying models through the determination coefficient（R²）,root mean square error（RMSE）,and chi square（X²）values,and select the optimal drying model under different drying parameters.Comparing the fitting degree of various models,the Wang and Singh models can better reflect and predict the moisture changes during the hot air microwave coupled drying process of red dates.