Tong Henry H Y, Wong Sammas Y S, Law Marcus W L, Chu Kevin K W, Chow Albert H L
School of Health Sciences, Macao Polytechnic Institute, Macao SAR, China.
Int J Pharm. 2008 Nov 3;363(1-2):99-105. doi: 10.1016/j.ijpharm.2008.07.016. Epub 2008 Jul 25.
Equilibrium moisture sorptions of two dried aqueous herbal extracts and their mixtures with dextrans of various molecular weights were investigated as a function of relative humidity at ambient temperature, and the data were analyzed by both the Guggenheim-Anderson-deBoer (GAB) and Brunauer-Emmett-Teller (BET) equations. Glass transition temperatures (T(g)) of the samples were measured by differential scanning calorimetry, and their dependence on the moisture contents of the extracts was analyzed by the linear, Fox and expanded Gordon-Taylor mathematical models. All dextran-extract mixtures exhibited single T(g) values, indicating that they existed as single homogeneous phases. The BET equation was found adequate for description of the moisture sorption isotherms for all samples. The dextrans appeared to reduce the hygroscopicity of the herbal extracts solely by a dilution effect. The observed increase in T(g) and accompanying decrease in tackiness of the herbal extracts in the presence of dextrans may be explained by the ability of dextrans to restrict the molecular mobility of simple sugars and to counteract the plasticizing effect of water in the extracts. The expanded Gordon-Taylor equation has proved useful in predicting the T(g) of hygroscopic amorphous herbal mixtures.
研究了两种干燥的水性草药提取物及其与不同分子量葡聚糖的混合物在环境温度下的平衡吸湿情况与相对湿度的关系，并通过 Guggenheim-Anderson-deBoer（GAB）和 Brunauer-Emmett-Teller（BET）方程对数据进行了分析。通过差示扫描量热法测量了样品的玻璃化转变温度（T(g)），并通过线性、Fox 和扩展 Gordon-Taylor 数学模型分析了其对提取物水分含量的依赖性。所有葡聚糖-提取物混合物均表现出单一的 T(g) 值，表明它们以单一均相存在。发现 BET 方程足以描述所有样品的吸湿等温线。葡聚糖似乎仅通过稀释作用降低了草药提取物的吸湿性。在存在葡聚糖的情况下，观察到的草药提取物 T(g) 的增加以及随之而来的粘性降低，可以通过葡聚糖限制单糖分子流动性并抵消提取物中水的增塑作用的能力来解释。扩展 Gordon-Taylor 方程已被证明可用于预测吸湿无定形草药混合物的 T(g)。
