| The project aiming at the two major problems those have not been studied on jujube powder field:hygroscopic and sterilization, in this paper they were studied and analyzed. Firstly, jujube(Zizyphus jujube cv. Junzao) was used to be dried by short and medium-wave infrared drying, and then crush to superfine grinding jujube powder. Moisture sorption isotherm and glass transition temperature were determined by the gravimetric method and differential scanning calorimetry, respectively. The state diagram of jujube powder was developed using the fitted moisture sorption isotherm and glass transition temperature curve, the sorption samples were also observed by the X-ray diffraction and scanning electron microscopy (SEM). Based on the kinetic and thermodynamic analysis of the sorption process, the mechanism of moisture sorption was expounded. Seondly, jujube(Zizyphus jujube cv. Dongzao) was used to be dried by explosion puffing drying, and then crush to jujube powder. The bactericidal effect of short and medium-wave infrared radiation on the numbers of total bacteria, mold and yeast in winter jujube powder at various conditions were measured. The effect on water moisture and color were discussed. The Weibull model was used to analyze the bactericidal curves at different conditions.(1) In the research on the water sorption of jujube powder, the sorption behavior displayed "J" type isotherms, which may be due to the high sugar content of superfine grinding jujube powder. At a certain temperature, the equilibrium moisture content of superfine grinding dried jujube powder increased with the increasing of water activity. The glass transition temperature of jujube powder was decreased with the increasing of moisture content, and the glass transition temperature was decreased from 19.08 to -58.71 ℃ as moisture content (wet basis) of jujube powder was increased from 0.073 to 0.330 g/g. There was a significant linear relationship between Tgi and Aw (R2=0.99), and Tgi decreased with the increasing of Aw, the linear relationship between them was Tgi=-206.92 Aw+34.43. According to the state diagram at 25℃ of the superfine grinding jujube powder, when the moisture content (dry basis) was less than 0.0566 g/g,at the same time, the water activity was lower than 0.13, the storage condition was suitable for superfine grinding jujube powder.(2) The main sugar of short and medium-wave infrared drying superfine grinding jujube powder sugar is glucose, fructose and sucrose, and the contents were 16.45% and 13.56% and 56.53%, respectively, which type sugar sorption of moisture is fructose. The sugar crystallinity and surface roughness increased with the increasing of relative humidity.(3) Seven kinds of kinetics models were used to fit the moisture sorption isotherms at 25℃,35℃ and 45℃, the suitable model to describe the moisture sorption isotherm characteristics of superfine grinding jujube powder was BET model through the fitting statistical parameter analysis. The thermodynamic analysis shows that the isosteric heat of sorption and the differential entropy increased with the decreasing of moisture content, and they showed a linear positive correlation. According to the entropy enthalpy complementary theory, the moisture sorption process of superfine grinding jujube powder is controlled by entropy.(4)There is a significant influence of short and medium-wave infrared treatment on jujube powder sterilization result at different temperatures and time. The results showed that with the increase of temperature and time, the bactericidal effect were improved, while the water moisture was decreased, the color change increased. Weibull model was suitable for the kinetic analysis of bacterial inactivation, and the kinetic curve shape is more stable at 100～110℃. Considering the effect of sterilization, moisture, color and equipment operation cost, the suitable condition for sterilization is 120℃ for lmin. |
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