Characteristics of freeze-infrared combined drying of jujube slices

Abstract

Objective： Optimized the drying process of jujube slices and improved the product quality. Methods： Taking jujube slices as the research object, the correlation between conversion moisture content, infrared temperature and slice thickness and drying time and drying rate was studied, and the change rule of effective moisture diffusion coefficient of jujube slices in FD-IRD with conversion moisture content, infrared temperature and slice thickness was calculated, and the drying activation energy of jujube slices in FD-IRD was calculated according to the test data. Results： The lower the conversion moisture content is, the shorter the infrared drying time was. But the lower the conversion moisture content would greatly increase the freeze drying time. Proper increase of infrared drying temperature was beneficial to increase the effective diffusion coefficient of water. The thinner the slice is, the higher the drying rate was. Reducing the slice thickness can improve the effective water diffusion coefficient and shorten the drying time. The front and rear two stages were both speeds reducing drying processes. The effective moisture diffusion coefficients of freeze-drying and infrared drying under different drying conditions by solving Fick's second law were 3.39×10-9~9.47×10-9 and 3.34×10-9~2.01×10-8 m2/s, respectively; The drying activation energy of the infrared drying stage was 59.03 kJ/mol calculated by Anius formula. Conclusion： The conversion moisture content is 30%, and the infrared temperature is 60 ℃. Under the condition of slice thickness of 6 mm, the freeze infrared combined drying technology has short drying time and high efficiency.

Keywords

• jujube slices
• dry
• freeze-infrared drying
• drying characteristics
• drying kinetics