Abstract Shrinkage of potato and carrot (cylinders and slabs) was determined during convective drying at air temperature of 25, 55 or 65 °C with air speed of 1.6 or 0.5 m/s. Initial moisture content of slab samples at different positions within the carrot root and potato tuber was determined gravimetrically and by the vacuum method at 60°C. Structure of potato slabs at exterior and center of tuber was analysed by Scanning Electron Microscope (SEM). Glass transition temperature (Tg) was approximately 50 °C for dry potato (0.021 kg/kg dm), and 40 °C for dry carrot (0.005 kg/kg dm) indicating that potato and carrot would be in rubbery state throughout drying at 65 °C. Glass transition of the samples could be observed at the end of the drying process with air temperature of 25 °C. The initial moisture content of carrot at exterior and center of root were identical. However, the center potato layers had initial moisture content higher than the exterior potato layers. SEM images showed that the cells of the exterior potato samples had smaller volume with higher starch content than the center sample, thus indicating a correlation between structure characteristics and initial solids content. For all drying conditions used in this study, shrinkage of carrot samples (cylinders and slabs) had a linear relationship with moisture content during drying. For potato, however, a change in the slope of the shrinkage curve as a function of moisture content during drying was observed for cylinder samples. For potato slabs, only those having initial moisture contents lower than 5.5 ± 0.5 kg water/kg dm showed a similar change in slope, otherwise slabs presented a straight line for the whole water content range. The air temperature and air speed had no effect on the shrinkage behaviour of both carrot and potato samples under the operation conditions used in this study. No significant impact of glass transition on shrinkage of carrot and potato samples has been found, and if any this impact would be considered minor. Differences in starch content, in structure of the cellular material and its relationship with mechanical properties of material may explain the different shrinkage behaviour observed in this work.

中文翻译：

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空气干燥过程中细胞食物的收缩

摘要 在空气温度为 25、55 或 65 °C 和风速为 1.6 或 0.5 m/s 的条件下对流干燥期间，确定了马铃薯和胡萝卜（圆柱体和板坯）的收缩率。胡萝卜根和马铃薯块茎内不同位置的板坯样品的初始含水量通过重量法和真空法在 60°C 下测定。用扫描电子显微镜（SEM）分析了马铃薯块茎外部和中心的结构。干马铃薯 (0.021 kg/kg dm) 的玻璃化转变温度 (Tg) 约为 50 °C，干胡萝卜 (0.005 kg/kg dm) 的玻璃化转变温度 (Tg) 约为 40 °C，表明马铃薯和胡萝卜在 65 ℃。在空气温度为 25 °C 的干燥过程结束时，可以观察到样品的玻璃化转变。胡萝卜在外部和根中心的初始水分含量相同。然而，中心马铃薯层的初始水分含量高于外部马铃薯层。SEM 图像显示，外部马铃薯样品的细胞体积较小，淀粉含量高于中心样品，因此表明结构特征与初始固含量之间存在相关性。对于本研究中使用的所有干燥条件，胡萝卜样品（圆柱体和板坯）的收缩率与干燥过程中的水分含量呈线性关系。然而，对于马铃薯，在圆筒样品中观察到作为干燥过程中水分含量的函数的收缩曲线斜率的变化。对于马铃薯板，只有那些初始含水量低于 5.5 ± 0.5 kg 水/kg dm 的板才显示出类似的斜率变化，否则，板坯在整个含水量范围内呈现一条直线。在本研究中使用的操作条件下，空气温度和空气速度对胡萝卜和马铃薯样品的收缩行为没有影响。没有发现玻璃化转变对胡萝卜和马铃薯样品的收缩有显着影响，如果有任何影响，这种影响将被认为是次要的。淀粉含量、细胞材料结构的差异及其与材料机械性能的关系可以解释在这项工作中观察到的不同收缩行为。没有发现玻璃化转变对胡萝卜和马铃薯样品的收缩有显着影响，如果有任何影响，这种影响将被认为是次要的。淀粉含量、细胞材料结构的差异及其与材料机械性能的关系可以解释在这项工作中观察到的不同收缩行为。没有发现玻璃化转变对胡萝卜和马铃薯样品的收缩有显着影响，如果有任何影响，这种影响将被认为是次要的。淀粉含量、细胞材料结构的差异及其与材料机械性能的关系可以解释在这项工作中观察到的不同收缩行为。