Dept. of Molecular Biosciences and Bioengineering, Univ. of Hawaii, Honolulu, Hawaii 96822, U.S.A.
J Food Sci. 2014 Feb;79(2):E195-201. doi: 10.1111/1750-3841.12335. Epub 2014 Jan 21.
The dielectric (DE) properties, specifically the DE constant (ε') and loss factor (ε''), were measured for vacuum-dried and freeze-dried potato samples at a microwave frequency of 2.45 GHz over a range of different moisture contents (MCs) using a DE probe and also a 2-probe electrochemical impedance spectroscopy (EIS). Third-order polynomial models (ε' = f₁(MC); and ε'' = f₂(MC)) at room temperature were developed for regression analysis. Additionally, at various temperatures (T), biphasic 3rd-order polynomial models (ε' = f₁(MC, T); and ε'' = f₂(MC, T)) were obtained to determine ε' and ε'' as a function of MC and T using measured data. The vacuum-dried potato sample showed a good fitness of ε' and ε'' (R² = 0.95 and 0.96, respectively) to the regression model with the range of MCs from 18% to 80% (w/w), while the freeze-dried potato sample showed a good fitness of ε' and ε'' to the 1st-phase regression model with MC < 50% w/w (R² = 0.95 and 0.96, respectively) and the 2nd-phase regression model with MC > 50% w/w (R² = 0.94 to 0.96). EIS measurements were also used to obtain correlation impedances for ε' and ε'' determined by the DE probe method. The resulted regression analysis meets the demands for simple, rapid, and accurate assessment for transient values of ε' and ε'' of food products during dehydration/drying processes. The EIS method was verified to be a successful alternative to direct measurements of ε' and ε''.
介电（DE）特性，特别是 DE 常数（ε'）和损耗因子（ε''），使用 DE 探头和 2 探针电化学阻抗谱（EIS）在微波频率为 2.45GHz 下，在不同水分含量（MC）范围内测量真空干燥和冷冻干燥的马铃薯样品。在室温下，为回归分析开发了三阶多项式模型（ε'=f₁(MC)；ε''=f₂(MC)）。此外，在不同温度（T）下，获得了双相三阶多项式模型（ε'=f₁(MC, T)；ε''=f₂(MC, T)），以使用测量数据确定ε'和ε''作为 MC 和 T 的函数。真空干燥的马铃薯样品的 ε'和 ε''（R²分别为 0.95 和 0.96）与 MC 范围为 18%至 80%（w/w）的回归模型拟合良好，而冷冻干燥的马铃薯样品的 ε'和 ε''与 MC <50%w/w（R²分别为 0.95 和 0.96）的第一相回归模型和 MC >50%w/w（R²为 0.94 至 0.96）的第二相回归模型拟合良好。EIS 测量也用于获得通过 DE 探头方法确定的 ε'和 ε''的相关阻抗。所得回归分析满足在脱水/干燥过程中对食品瞬态值 ε'和 ε''进行简单，快速和准确评估的要求。EIS 方法被证明是直接测量 ε'和 ε''的成功替代方法。
