The Drying Characteristics And Quality Of Jujube Tablets Based On Different Drying Technology

The production of jujube is abundant in Xinjiang. But jujube rot and loss is very common and is a big problem due to lacking of suitable processing technology and not being timely processed. Besides the quality of jujube is very poor and the product variety is very few. When jujube is harvested, a larger part of the products belong to the defect product as their size, shape, maturity status, moisture content, appearance is far from the standard quality attributes. The commodity value of this defect product has not been fully developed. In order to solve the rapid processing problem for such defect jujube, two different infrared drying technologies were employed, namely short medium-wave infrared radiation combined with air impingement drying (SMIRAID) and medium far-infrared drying combined with vacuum freeze-drying (FDMFIR). The defect jujube was broken into mud and made into jujube tablets. Then effect of drying temperature, radiation distance, sample thickness, etc on drying kinetics and quality attributes such as sensory properties and vitamin c (VC) of jujube tablets were explored. SMIRAID drying jujube tablets aimed to explore the correlation between drying time and its quality attributes at different drying temperature (55,60,65,70, and 75℃), radiation distance (80,110, and 140 mm), and sample thickness (2,4 and 6 mm). FDMFIR drying jujube tablets aimed to study drying kinetics of jujube tablets during FDMFIR drying under the condition of freezing drying time (0.5,1.0,1.5,2.0,2.5 and 3.0 h), infrared temperature (62,65, and 68℃), sample thickness (2,4 and 6 mm, with the constant radiation distance of 110 mm. And the optimal parameters for during two kinds of drying processing for three goals of drying time, sensory quality and retention rate of VC was evaluated separately and selected based on the data standardization method.The research of SMIRAID drying characteristics of jujube tablets implies that, the drying temperature, radiation distance and sample thickness has remarkable effects in the drying duration of jujube tablets; The drying time of jujube tablets reduces with the increase in the drying temperature and it increases with increase of radiation distance and sample thickness of jujube tablets; It was observed that the SMIRAID drying processing occurred mainly in the falling rate period. Therefore, the moisture effective diffusivity (Deff) was determined by Fick’s second law. The Deff varied from 1.1540×10-10 to 2.4803×10-10m2/s with increasing drying temperature, and increased from 1.3553×10-10 to 3.2374×10-10 m2/s with decreasing radiation distance and sample thickness, separately. The drying activation energy was 26.92,15.10 and 11.27 kJ/mol at sample thickness of 2,4 and 6 mm calculated by Arrhenius equation, which means that the energy needed to start the drying process is small and drying can be performed easily using short medium-wave radiation combined with air impingement drying technology.The research of SMIRAID quality attributes of jujube tablets implies that, the drying temperature, radiation distance and sample thickness has remarkable effects sensory properties and retention rate of VC of jujube tablets; The optimal parameters of SMIRAID drying was obtained at the drying temperature of 65℃, sample thickness of 2 mm and radiation distance of 110 mm, and then largest comprehensive score of 0.8694 was obtained using data standardization of integrated assessment method taking account of the drying time, sensory quality and retention rate of VC. Through the determination coefficient (R2), root mean square error (RMSE), from the sum of squared residuals (χ2), and the error sum of squares (SSE) evaluation and analysis, Weibull distribution function is employed to simulate the SMIRAID drying behaviour of jujube tablets.The research of FDMFIR drying characteristics of jujube tablets implies that, the freeze-drying time, radiation temperature and sample thickness has remarkable effects has remarkable effects in the drying duration of jujube tablets; The drying time of jujube tablets reduces with the increase in the freeze-drying time and radiation temperature, and it increases with increase of sample thickness of jujube tablets.The research of FDMFIR quality attributes of jujube tablets implies that, the freeze-drying time, radiation temperature has not remarkable effects, but sample thickness has remarkable effects in sensory properties of jujube tablets; The freeze-drying time has remarkable effects in retention rate of VC of jujube tablets and increase with the increase in the freeze-drying time. But radiation temperature and sample thickness of jujube tablets has not remarkable effects in retention rate of VC of jujube tablets.The optimal parameters of FDMFIR drying was obtained with freeze-drying time 3 h, sequential drying temperature 65℃, sample thickness of 4 mm and radiation distance 110 mm, and then largest comprehensive score of 0.8517 was obtained.The two kinds of drying technology were compared and results illustrated that the drying time of jujube tablets by FDMFIR drying was about 106.7-126.7 min, which was extensively decreased compared to that dried under SMIRAID technologies even at the sample thickness drying time of jujube tablets at sample thickness of 2,4 and 6 mm used in FDMFIR drying was 76.30%,78.16% and 84.89% of that in SMIRAID jujube tablets, respectively.The current work provides theory and technical information for applying SMIRAID and FDMFIR to jujube tablets drying process.