Experimental Study On Drying Characteristics And Its Effects On The Quality Of Jujube Treated In Microwave Drying Followed By Hot-Air Drying

The jujube was Rhamnaceae Ziziphus jujube’s ripe fruit,rich nutritions and high water content,short harvest period.After harvesting,if jujubes was’t be dried immediately,mildew and rot exacerbate might happened,that could cause the.great economic losses which was one of the bottlenecks limit in the development of jujube industry.Therefore,researching the jujube drying technology was great significance to improve the quality of jujube.The drying characteristics and mathematical model of jujube dried by microwave combined hot air drying methods were studied,and the effects of different drying methods on the sensory property,physical and chemical characteristics,degree of browning were investigated in this paper to confirm the feasibility of microwave followed by hot air drying method.Based on the research of topoic and further analysis of data,the conclusions can be summarized as followed:1.The segmented hot-air drying tests showed that after a brief speed up the drying stage entered the constant drying stage,the drying rates slowed down in the later time;the internal temperature was higher than the surface temperature.The intermittent microwave drying showed that,at the beginning,drying rate rapidly increased,before entering the contant drying stage.From the four kinds of the segmented hot-air drying,No.11 was the best one.From the four kinds of intermittent microwave drying,the unit operations drying of 12 mins was the better one.2.The drying times of the combined methods were shortened more than 11%compared with segmented hot-air drying method;the combined drying methods especially the intermittent numbers of microwave 7 was superiority,no matter from drying rates,or the surface and internal temperature.We contrast energy consumption and the product quality of jujube dried by the four combined drying methods,the drying method of intermittent numbers of microwave 7 was the best.The drying curve conformed to the model of the Page,it could predict the moisture content variation during the process of microwave followed by hot air drying methods(p<0.0001).3.A Box-Behnken experimental design and response surface methodology involving 3 variables(materials input,intermittent numbers of microwave,hot-air drying times of high temperature)at 3 levels were employed to optimize the Vitamin C、flavonoids content and A420 of dried Chinese jujube.It had proved that the model was reasonable and reliable,it could be used in the production of forecasts.The optimal values of these parameters were as follows:materials input 305g,dried under 119W for 12 min,pause for 4min,intermittent numbers of microwave 7,hot-air drying times of at 55℃ 9h,hot-air drying times of 50℃12h.Under these conditions,Vitamin C content,flavonoids content and A420 were 36.22 mg/100g,35.53 mg/100g,0.3079.It took only 80%of segmented hot-air drying times.Conclusion:Microwave drying followed by hot-air drying method was valuable to be used in practical production of jujube drying.4.The jujube dried by combined drying methods was bright,full shape,shrinkage slight,comprehensive evaluation of the appearance quality better.The jujube’s color parameters L*,b*,a*was significant different among several drying methods.The structure of jujube dried by vacuum drying method most same the fresh sample;the jujube dried by combined drying method had good porous structure.The Vitamin C contents of jujube dried by combined and vacuum drying methods was higher than segmented hot-air and intermittent microwave drying methods.The flavonoids contents of jujube dried by different four drying methods were almost identical,so were the total sugar contents of jujube dried by segmented hot-air and intermittent microwave drying methods,the total phenol contents of jujube dried by segmented hot-air and vacuum drying methods had the same situation.A420 of jujube dried by combined and vacuum drying methods was lower.