Research On Influence Of Microwave Vacuum Drying On Drying Characteristics And Quality Of Lemon Slice

Containing rich vitamin A,vitamin P,vitamin C,flavonoid,citric acid,malic acid,limonene and trace elements such as Ca,Fe,Zn,P,Mg,lemon is a kind of high Ka low Na healthy food.In recent years,nutrition and health care value of lemon is recognized by more and more people,becoming a fruit popular in the mass.However,current lemon slice on market is mostly made by baking or naturally drying in the sun,the product not only shrinks and turns brown,but also its bioactive components and thermo sensitive nutrition losses greatly.Combining advantages of microwave and vacuum,microwave vacuum drying technology features rapid drying speed,high efficiency,low drying ambient temperature.So,with lemon as raw material,using microwave vacuum drying technology,this paper researches microwave vacuum drying characteristics of lemon slice and rule different microwave vacuum drying parameters influencing quality of lemon slice to optimize microwave vacuum drying process and determine optimum drying process parameter of lemon slice.In optimum process condition compare quality of microwave vacuum dried lemon slices with those produced in other drying method to determine feasibility of applying microwave vacuum drying technology to lemon slice,providing theoretical and technical support for lemon slice microwave vacuum drying technology.Main research content and conclusion of this paper is as follows:1.The influences of microwave power,vacuum degree and thickness of lemon slice on drying process were researched,the drying characteristics were investigated,and the microwave-vacuum drying characteristic curve and drying rate curve of lemon slices were obtained.The results show that the microwave power has the greatest influence on the microwave-vacuum drying process of lemon slices,the influence of the thickness of the lemon slice is moderate and minimized by the degree of vacuum.The dynamic model for microwave-vacuum drying of lemon slices was consistent with Page model,which can predict the microwave-vacuum drying process of lemon slices very well.2.The effects of different microwave power,vacuum degree and thickness of lemon slice on the main quality(vitamin C content,titratable acid content,rehydration rate,moisture absorption,color difference)of lemon slices in microwave-vacuum drying of lemon slices was researched.The results showed that with the increase of microwave power,the content of vitamin C gradually decreased,the titratable acid content decreased gradually,and the rehydration rate increased firstly and then decreased,and the moisture absorption decreased firstly and then increased,and the color difference increased gradually;With the increase of vacuum degree,vitamin C content gradually increased,titratable acid content decreased firstly and then increased,rehydration rate increased firstly and then decreased,moisture absorption increased gradually,and the color difference decreased gradually;With the increase of the thickness of the lemon slices,the content of vitamin C gradually increased,the titratable acid content decreased firstly and then increased,the rehydration rate firstly increased and then decreased,and the moisture absorption decreased firstly and then increased,and the color difference increased firstly and then decreased.3.Taking microwave power,vacuum degree and thickness of lemon slice as the influence factors,with vitamin C content,titratable acid content,rehydration rate,moisture absorption,color difference as the response value,the microwave-vacuum drying process and the parameters of optimum microwave-vacuum drying process of the lemon slices were optimized by using the design tests of Box – Behnken in three – factors and three – levels.The results showed that the optimum technological parameters of microwave drying were as follows: microwave power is 1kw,vacuum degree is 73.96 k Pa,the thickness of lemon slice is 4mm.Under the optimum conditions(microwave power was 1KW,vacuum degree was 74.0k Pa,the thickness of lemon slice was 4mm),the content of vitamin C is 204.68mg/100 g,the titratable acid content is 20.91%,the rehydration rate is 4.19,moisture absorption is 1.0112,color difference is 8.93.4.The quality of the dried lemon slices(vitamin C content,titratable acid content,rehydration rate,moisture absorption,color difference value,sensory quality,aroma components)obtained by four different drying techniques of hot air drying,microwave drying,heat pump drying and microwave vacuum drying was investigated.The results showed that the microwave-vacuum drying in the vitamin C content,titratable acid content,rehydration rate and color difference indicators is better than the other drying methods,which is slightly higher in terms of moisture absorption,but the overall difference is not large,which proves that microwave-vacuum drying technology has good feasibility in lemon slice dry system.