Kang Wenyu, Lu Jianfeng, Cheng Yudong, Jin Yinzhe
College of Food Science and Technology, Shanghai Ocean University, Lingang New City, Shanghai 201306, China.
College of Food Science and Technology, Shanghai Ocean University, Lingang New City, Shanghai 201306, China.
J Food Drug Anal. 2015 Sep;23(3):472-479. doi: 10.1016/j.jfda.2014.10.003. Epub 2015 Jan 5.
The concentration of alum additive in deep-fried dough sticks (DFDSs) was investigated using a coaxial probe method based on dielectric properties in the 0.3-10-GHz frequency range. The dielectric spectra of aqueous solutions with different concentrations of alum, sodium bicarbonate, and mixtures thereof were used. The correspondence between dielectric loss and alum concentration was thereby revealed. A steady, uniform correspondence was successfully established by introducing ω·ε″(ω), the sum of dielectric loss and conductor loss (i.e., total loss), according to the electrical conductivity of the alum-containing aqueous solutions. Specific, resonant-type dielectric dispersion arising from alum due to atomic polarization was identified around 1 GHz. This was used to discriminate the alum additive in the DFDS from other ingredients. A quantitative relationship between alum and sodium bicarbonate concentrations in the aqueous solutions and the differential dielectric loss Δε″(ω) at 0.425 GHz was also established with a regression coefficient over 0.99. With the intention of eliminating the effects of the chemical reactions with sodium bicarbonate and the physical processes involved in leavening and frying during preparation, the developed technique was successfully applied to detect the alum dosage in a commercial DFDS (0.9942 g/L). The detected value agreed well with that determined using graphite furnace atomic absorption spectrometry (0.9722 g/L). The relative error was 2.2%. The results show that the proposed dielectric differential dispersion and loss technique is a suitable and effective method for determining the alum content in DFDSs.
采用基于介电特性的同轴探头法，在0.3 - 10 GHz频率范围内研究了油条中明矾添加剂的浓度。使用了不同浓度明矾、碳酸氢钠及其混合物的水溶液的介电谱。由此揭示了介电损耗与明矾浓度之间的对应关系。根据含明矾水溶液的电导率，通过引入ω·ε″(ω)（介电损耗与导体损耗之和，即总损耗），成功建立了稳定、均匀的对应关系。在1 GHz左右识别出了由明矾因原子极化引起的特定共振型介电色散。这被用于区分油条中的明矾添加剂与其他成分。还建立了水溶液中明矾和碳酸氢钠浓度与0.425 GHz处的微分介电损耗Δε″(ω)之间的定量关系，回归系数超过0.99。为了消除制备过程中与碳酸氢钠的化学反应以及发酵和油炸所涉及的物理过程的影响，所开发的技术成功应用于检测市售油条中的明矾用量（0.9942 g/L）。检测值与使用石墨炉原子吸收光谱法测定的值（0.9722 g/L）吻合良好。相对误差为2.2%。结果表明，所提出的介电微分色散和损耗技术是测定油条中明矾含量的一种合适且有效的方法。
