Buehler Martin G, Kindle Michael L, Carter Brady P
Decagon Devices, Inc., 2365 NE Hopkins Ct., Pullman, WA, 99163, U.S.A.
J Food Sci. 2015 Jun;80(6):E1243-52. doi: 10.1111/1750-3841.12887. Epub 2015 May 5.
Dielectric relaxation spectroscopy was used to characterize the glass transition time, tg , of polydextrose, where the glass transition temperature, Tg , and water activity, aw (relative humidity), were held constant during polydextrose relaxation. The tg was determined from a shift in the peak frequency of the imaginary capacitance spectrum with time. It was found that when the peak frequency reaches 30 mHz, polydextrose undergoes glass transition. Glass transition time, tg , is the time for polydextrose to undergo glass transition at a specific Tg and aw . Results lead to a modified state diagram, where Tg is depressed with increasing aw . This curve forms a boundary: (a) below the boundary, polydextrose does not undergo glass transition and (b) above the boundary, polydextrose rapidly undergoes glass transition. As the boundary curve is specified by a tg value, it can assist in the selection of storage conditions. An important point on the boundary curve is at aw = 0, where Tg0 = 115 °C. The methodology can also be used to calculate the stress-relaxation viscosity of polydextrose as a function of Tg and aw , which is important when characterizing the flow properties of polydextrose initially in powder form.
介电弛豫光谱法用于表征聚葡萄糖的玻璃化转变时间tg，其中在聚葡萄糖弛豫过程中玻璃化转变温度Tg和水分活度aw（相对湿度）保持恒定。tg是根据虚部电容谱的峰值频率随时间的变化来确定的。研究发现，当峰值频率达到30 mHz时，聚葡萄糖发生玻璃化转变。玻璃化转变时间tg是聚葡萄糖在特定的Tg和aw下发生玻璃化转变的时间。结果得到了一个修正的状态图，其中Tg随aw的增加而降低。这条曲线形成了一个边界：(a) 在边界以下，聚葡萄糖不发生玻璃化转变；(b) 在边界以上，聚葡萄糖迅速发生玻璃化转变。由于边界曲线由tg值指定，它有助于选择储存条件。边界曲线上的一个重要点是在aw = 0处，此时Tg0 = 115°C。该方法还可用于计算聚葡萄糖作为Tg和aw函数的应力松弛粘度，这在表征初始为粉末形式的聚葡萄糖的流动特性时很重要。
