Experimental Research On Drying Characteristics And Quality Of Jujube Slices Under Different Drying Methods

In order to develop jujube products and solve the problem of jujube fruit hoarding,the semi-dried Jun jujube and the fresh Jun jujube were used as experimental material.After being sliced,the jujube slices with different thickness were respectively dried in the solar dryer(solar wall collector,glass greenhouse drying device and PC greenhouse drying device),freeze-drying machine,microwave oven and vacuum drying oven.After the experiment,the sensory evaluation,nutrients and microstructure were analyzed.The best experimental conditions will be selected to provide the oretical basis for industrial dried jujube slices.First of all,the four kinds of drying experiments were carried out with different thickness of the Jun jujube.In the scope of the experiment,the results showed that in the solar drying device,the glass greenhouse drying device had the best heat collection effect,the daily average temperature in the drying chamber was highest,when the radiation intensity was low,the solar wall collector had the best insulation effect,the drying effect of jujube slices on different layers is similar.The 4 mm thickness of jujube slices has the shortest drying time in the glass greenhouse drying device and the solar wall collector.After drying,dry base wet content of semi-dried jujube slices were 1%(glass greenhouse drying type)and 1.5%(solar wall collector),and dry base wet content of fresh jujube slices were 1%(glass greenhouse drying type)and 1.5%(solar wall collector).In vacuum freeze-drying,when the vacuum degree was 35 Pa,the temperature of heating plate was40 ?,the thickness of jujube slices were 4mm and 6 mm,the mass drying rate of the jujube slices was the highest.In microwave drying,70 W power should be selected and the drying time of semi dried jujube slices was about 17 min,and the drying time of fresh jujube slices was 51 min.In vacuum drying,the order of the factors affecting the drying time of the jujube slices were thickness,temperature and vacuum degree,and the best experimental condition was vacuum degree at 0.05 MPa,temperature at 65 ?and using 4 mm thickness of jujube slices.Then the Jun jujube slices of different thickness were subjected to quality research.The results of sensory evaluation show that:In solar drying experiment,the jujube slices with the thickness of 4 mm and 6 mm in the solar wall collector had the highest sensory score.Invacuum freeze-drying,the thickness was the highest impact on sensory evaluation,jujube slices with temperature of heating plate at 40 ?,vacuum degree at 35 Pa and thickness of 6mm had a highest sensory score.In microwave drying,microwave power 70 W power and 6mm thickness jujube slices had the highest sensory evaluation.In vacuum drying,the best sensory evaluation conditions was vacuum degree at 0.05 MPa,the temperature at 65?and using 4 mm thickness of jujube slices.Compare of the semi-dried jujube slices and fresh jujube slices in quality,the jujube slices obtained by fresh jujube slices are better than semi-dried jujube slices in color and appearance,however its aroma and taste are not as good as the semi-dried jujube slices.On nutrient composition,jujube slices obtained by fresh jujube had higher VC content than that obtained by semi-dried jujube slices,but jujube slices made from fresh jujube had lower total sugar content than that made from semi-dried jujube slices.The results of nutritional components test showed that the VC content and total sugar content of jujube slices obtained by vacuum freeze drying were the highest among the four drying methods,followed by solar drying and vacuum drying,the jujube slices obtained by microwave drying were the lowest.The sensory evaluation and drying characteristics of the semi dry jujube slices and fresh jujube slices were analyzed.The best experimental conditions for solar drying were the solar wall collector type device,and the thickness of jujube slices was 4 mm.The optimum conditions for vacuum freeze-drying at 35 Pa,temperature at 40 ? and 6 mm in thickness of jujube slices.The optimum drying conditions for microwave drying are power of 70 W and 6 mm thickness of jujube slices,and the optimum drying conditions for vacuum drying at 0.05 MPa,temperature at 65 ?and using 4 mm thickness of jujube slices.