Electrical characterization of milk samples by electrical impedance spectroscopy (EIS)

This work presents a study of electrical impedance spectroscopy (EIS) as an alternative to characterize milk, aiming to develop an analysis methodology with advantages over other methods, such as portability and low cost. The behavior of the electrical impedance module, the real part and the imaginary part (reactance), and the derived quantities such as admittance, phase and diffusion coefficient (D) were also analyzed and will be discussed. Comparisons of the measured spectra with theoretical models of equivalent circuits were carried out in order to understand the electrical behavior of the samples. Understanding this electrical phenomenon will help in the development of future analysis methodologies. The results indicated that milk is a solution with predominantly resistive behavior with an estimated resistance value of 500 Ohms, with low storage load due to low viscosity. The best-fitting equivalent circuit was a mixed RC model consisting of a series resistor coupled with a resistor in parallel with a capacitor.--

Mathematical models for correlating electrical parameters and milk adulterants

This work presents mathematical models obtained from electrical measurements to control of milk quality and detection of adulterations, especially by ethanol, sodium chloride and sodium bicarbonate. These substances may cause changes in the electrical properties of raw milk. Electrical measurements are non-destructive and fast techniques. The proposed models correlate the addition of the mentioned substances with measurements of conductance and phase angle at a fixed frequency of 100 Hz. Linear models were proposed from the data and the independence, normality, lack of adjustment and homoscedasticity were verified. The detection limits obtained based on conductance were 0.01 %, 0.03 g/L and 2.1 g/L for samples adulterated with ethanol, sodium chloride and sodium bicarbonate, respectively. The limits for measurements based on the phase angle were 0.4%, 1.3 g/L and 16.4 g/L, respectively. The results demonstrated that the proposed models may be a powerful tool to improve milk analysis methodologies.Este trabalho apresenta modelos matemáticos obtidos a partir de medidas elétricas para controle da qualidade do leite e detecção de adulterações, principalmente por etanol, cloreto de sódio e bicarbonato de sódio. Essas substâncias podem causar alterações nas propriedades elétricas do leite cru. As medições elétricas são técnicas não destrutivas e rápidas. Os modelos propostos correlacionam a adição das substâncias mencionadas com medições de condutância e ângulo de fase a uma frequência fixa de 100 Hz. Modelos lineares foram propostos a partir dos dados e verificou-se independência, normalidade, falta de ajuste e homocedasticidade. Os limites de detecção obtidos com base na condutância foram de 0,01%, 0,03 g / L e 2,1 g / L para amostras adulteradas com etanol, cloreto de sódio e bicarbonato de sódio, respectivamente. Os limites para medições baseadas no ângulo de fase foram de 0,4%, 1,3 g / L e 16,4 g / L, respectivamente. Os resultados demonstraram que os modelos propostos podem ser uma ferramenta poderosa para aprimorar as metodologias de análise do leite

Study of Quality Factor (Q) and Phase Angle (θ) obtained per electrical impedance to characterization and detection adulteration in honey.

The quality control of honey is very important for the food industry and for the final consumer. Honey has constantly been the target of adulteration, usually with the aim of illegally increasing profit. However, the analytical methods used in the fraud investigation sometimes are very complex and beyond time-consuming. Electrical measurements appear as a good alternative to the traditional methods of analysis due to its practicality and low costs. In order to show the applicability of some electrical parameters derived from the impedance technique for honey quality control analysis, in the present study, samples were purposefully adulterated with syrup to simulate adulteration conditions. Then, they were submitted to electrical impedance analysis with frequency scanned from 10 Hz to 2 MHz. The impedance module (Z), the phase angle  and the quality factor (Q) data were collected and studied. The results showed that there is a linear correlation between the frequencies relative to the peaks of the Q for samples and adulterant concentration with coefficient of determination of ~0.992. The proposal to use the Q as a property to be used in methodologies of analysis is the main contribution from this study, since it is traditionally little mentioned in the literature

Electrical characterization of milk samples by Electrical Impedance Spectroscopy (EIS)

This work presents a study of electrical impedance spectroscopy (EIS) as an alternative to characterize milk, aiming to develop an analysis methodology. The behavior of the electrical impedance module, the real part and the imaginary part (reactance), and the derived quantities such as admittance, phase and diffusion coefficient (D) were also analyzed and will be discussed. Comparisons of the measured spectra with theoretical models of equivalent circuits were carried out in order to understand the electrical behavior of the samples. Understanding this electrical phenomenon will help in the development of future analysis methodologies and applications. The results indicated that milk is a solution with predominantly resistive behavior with resistance of approximately 500 Ohms, capacitance of about of 0.5 MicroFarad (μF) and admittance of the order of MiliSiemens (mS), presenting small storaged charge due to low viscosity. The best-fitting equivalent circuit was a mixed RC model consisting of a series resistor coupled with a resistor in parallel with a capacitor