Research On Far Infrared Radiation Combined With Hot Air Drying Of Jujube Slices

With the development of national economy,jujube slices are more and more favored by the market because of its crisp and refreshing,flavor and so on.The traditional fried jujube slices tasted better,but the oil content of the product is too high that it cannot meet the people's pursuit of health.Therefore,it is of great significance to develop energy-saving and time-saving drying technology for exploring new processing methods of jujube slices.In this paper,the drying kinetics of far infrared radiation combined with hot air drying for fresh jujube is studied by using a self-made device,as well as the effects of infrared temperature,hot air temperature,irradiation distance and thickness of jujube slices on Vc content,total sugar content,total phenol content and color of jujube slices.Then the experiment is carried out to optimize the parameters of the far infrared radiation combined with hot air drying process based on the response surface and the optimum process parameters are obtained.On this basis,far infrared radiation combined with hot air drying is compared with single hot air drying and single far infrared drying to provide technical support and theoretical basis for later industrial production.The main contents and research results of this paper are as follows:(1)In the process of far infrared radiation drying,the quality of jujube slices are affected by infrared temperature,irradiation distance and thickness.Single-factor experiments show that the infrared temperature was 130?150?,the infrared distance was 6?10 cm and the thickness of jujube was 2?6 mm.The optimum technological parameters of far infrared radiation drying were obtained by orthogonal design.The results are as follows:the infrared temperature was 150? the infrared distance was 8 cm and the thickness was 4 mm.Under these conditions,the content of Vc was 85.00 mg/100g,the content of total sugar was 80.22%and content of total phenol in dried jujube slices was 23.80 mg/g.(2)Eight models were used to simulate the far infrared radiation combined with hot air drying of jujube slices,and the fitting degree of the models was compared.The model fitting optimization index showed that Page,Modified page and Approximation of diffusion can simulate the process of far infrared hot air drying and predict the moisture change during drying.(3)The far infrared radiation combined with hot air drying of jujube slices was optimized by Box-Behnken design.The results showed that the temperature of hot air was 72?,the infrared temperature was 150?,the infrared distance was 6 cm and the thickness of jujube was 5 mm.(4)According to the analysis of drying characteristics of jujube slices by different drying techniques,the drying time of far infrared radiation combined with hot air drying was the shortest and that of hot air drying was the longest.As far as the drying rate is concerned,the far infrared radiation combined with hot air drying solved the problem that the drying rate was reduced due to the surface hardening at the later stage of the drying process.At the same time,the advantage of water diffusing from inside to outside during the drying process was retained and the drying time was reduced while the drying efficiency was improved.(5)The contents of Vc in dried jujube slices treated with hot air,far infrared radiation and a combination of far infrared radiation and hot air ware 63.52,85.00 and 82.37 mg/100g.The content of Vc treated with hot air was significantly lower than that in the other two drying methods(p<0.05).The contents of total sugar in dried jujube slices treated with hot air,far infrared radiation and a combination of far infrared radiation and hot air were 62.82%,80.12%and 80.22%.The content of total sugar in jujube slices treated with hot air was significantly lower than that of the other two drying methods(p<0.05).The contents of total phenol in dried jujube slices treated with hot air,far infrared radiation and a combination of far infrared radiation and hot air were 16.72,23.80 and 35.34 mg/g.The content of total phenol treated with far infrared radiation combined with hot air was significantly higher than that in the other two drying methods(p<0.05).The color difference(?E)of jujube slices treated with hot air,far infrared radiation and a combination of hot air and far infrared radiation were 8.26,7.32 and 6.20.The color was the best under the far infrared radiation combined with hot air drying.In a conclusion,the quality of jujube slices is the worst after the hot air drying and the quality of jujube slices is the best after the far infrared radiation combined with hot air drying.