Water sorption isotherm, glass transition temperature (T_g), and caking properties of maca (Lepidium meyenii Walpers) powder were investigated. A broad endothermic shift reflecting continuously distributed glass transition was detected by differential scanning calorimetry, which prompted the evaluation of onset T_g and offset T_g. From the onset and offset T_g curves and water sorption isotherm, critical water activity (water activity at glass transition temperature of 25 °C) was determined to be 0.258 for the onset T_g and 0.480 for the offset T_g. The critical water activity values were validated by isothermal mechanical relaxation measurement. Caking properties of maca powder were compared with maltodextrin. The degree of caking and cake hardness for maltodextrin increased at a water activity just above critical water activity for onset T_g. Maca powder, on the other hand, showed a small degree of caking in the water activity range of 0.225 to 0.576, and the degree of caking drastically increased at a higher water activity. The hardness of maca cakes increased gradually at water activity values greater than 0.432. Since maca powder showed a continuously distributed glass transition, the molecular mobility required for caking was considered to have been provided incrementally by the increase in water activity above critical water activity for the onset T_g.

中文翻译：

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玛咖（Lepidium meyenii Walpers）粉末的连续分布玻璃化转变及其对结块性能的影响。

研究了玛咖（Lepidium meyenii Walpers）粉末的吸水等温线，玻璃化转变温度（T _g）和结块性能。通过差示扫描量热法检测到反映出连续分布的玻璃化转变的宽的吸热位移，这促使评估开始T _g和偏移T _g。根据起始和偏移T _g曲线以及吸水等温线，确定临界水活度（玻璃化转变温度为25°C时的水活度），起始T _g为0.258，偏移T _g为0.480。。临界水分活度值通过等温机械弛豫测量得到验证。将玛咖粉的结块特性与麦芽糊精进行了比较。麦芽糖糊精的结块程度和结块硬度在水分活度刚好高于开始T _g的临界水分活度时增加。另一方面，玛卡粉末在0.225至0.576的水活度范围内显示出较小的结块度，并且在较高的水活度下结块度急剧增加。水分活度值大于0.432时，玛卡饼的硬度逐渐增加。由于玛咖粉显示出连续分布的玻璃化转变，因此结块所需的分子迁移率被认为是通过在开始的T _g时高于临界水活度的水活度的增加而逐渐提供的。