热风干制温度对枣果微观组织结构的影响

为了研究热风干制温度对枣果微观组织结构的影响,该试验选用不同温度(35、40、45、50、55℃)热风干制枣果,利用石蜡切片、显微成像技术获得了热风干制过程中不同含水率条件下果肉细胞、空腔等结构参数的分布曲线,借助分布曲线的偏度、峰度(以鲜枣为参照)描述了微观结构参数在热风干制过程中的变化趋势,并建立了微观结构参数(果肉细胞、空腔横截面的面积比、周长比及当量直径比)与宏观干燥参数(水分比)的拟合方程。结果表明,利用微观结构参数分布曲线的偏度、峰度可较好地描述不同温度干制过程中细胞、空腔整体的变化趋势;干制过程中随着含水率的降低,果肉细胞、空腔结构参数的变化趋势均不具有一致性或连续性;不同温度相比之下,低温、高温干制过程对果肉细胞形态的改变均有较大影响,且高温(55℃)条件影响更大;不同温度热风干制过程中,由果肉细胞结构改变所引起的空腔塌缩和扩增同时存在,高温(55℃)条件对空腔的扩增、塌缩影响较大。果肉细胞,空腔结构参数比与水分比之间关系可用非线性模型描述(R2≥0.7283,Std≤25.1682%),模型可预测在不同温度热风干制过程中细胞、空腔随含水率的变化情况,研究结果可为热风干制新工艺的开发提供参考。

Effect of hot air drying temperature on microstructure of Chinese jujube

Chinese jujube is one of the most important dried fruits, and it is popular for its unique flavor, good taste and rich nutrition. Over the years, with the improvement of people’s living standards, more and more people require high-quality jujube products, however the existing processing technology can not satisfy the needs, so improving the processing technology becomes increasingly important. Currently, most researches have focused on the changes in the organizational structure of finally dried jujube, and fewer studies have focused on drying process.In order to study the effect of hot air drying temperature on microstructure of Chinese jujube, jujubes were dried under different temperature (35, 40, 45, 50 and 55℃). Paraffin section and microscopic imaging technology were used to obtain the distribution curve of the flesh cell and the cavity structure parameters during the hot air drying process. Distribution curve skewness and kurtosis (fresh jujube as the reference) were used to describe the changes of microstructure parameters during the hot air drying process, and the fitting equation of microstructure parameters (area ratio, perimeter ratio and equivalent diameter ratio of flesh cell to cavity cross-section) and macro drying parameter (moisture ratio) was established. The results indicated that the distribution curve skewness, kurtosis with various microstructural parameters could better describe the flesh cell and cavity changes trend during the drying process with different temperatures. Due to environmental stress response and differences in the distribution of moisture and heat, the shrinkage of pulp cells and the collapse or expansion of cavity were not with consistency or continuity during drying process of 5 temperatures. Comparing different temperatures, low temperature (35℃) and high temperature (55℃) drying process had great impact on flesh cells’ shape changes, and under high temperature (55℃) the shrinkage degree of pulp cells was more significant. During the hot air drying process, collapse and expansion of cavity both existed, which were more significant under high temperature, and cavity expansion was serious in early and post drying process. In actual production, we should not adopt prolonged high temperature or low temperature drying to avoid excessive shrinkage and cavity’s excessive expansion seriously, which affected the texture of flesh and the mouthfeel of jujubes. In drying process, jujube microstructure parameters did not decrease linearly with the decreasing of moisture content, but presented undulation changes. Therefore, the nonlinear model was used to describe the change of each microscopic parameter with different moisture content, and we found that the nonlinear model could better simulate the effect of cell perimeter ratio (R2>0.8379, standard deviation<2.9943%), however, the simulation effect of the cavity perimeter ratio was poor (R2>0.9229, standard deviation<25.1682%). So when the relationship between macro drying parameter and microstructure parameter during hot air drying process was establish, we could select the cell area ratio, cell perimeter ratio and cavity equivalent diameter ratio as microscopic parameters. Results can provide a reference for the development of new hot air drying technology.