Measurement of synthetic solutions imitating alcoholic fermentation by dielectric spectroscopy

Abstract

Having the possibility to use a wide spectrum of elecromagnetic waves, dielectric spectroscopy is a technique commonly used for electrical characterization of dielectrics or that of materials with high energy storage capacity, just to name a few. Based on the electrical excitation of dipoles (polymer chains or molecules) or ions in relation to the characteristics of a weak external electric field, this method allows the measurement of the complex permittivity or impedance of polarizable materials, each component having a characteristic dipole moment.In recent years, the food industry has also benefited from the potential offered by this technique, whether for the evaluation of fruit quality or during the pasteurization of apple juice [1-3]. As the tests are fast and do not destroy the products, dielectric spectroscopy proved to be an experimental tool suitable for online measurements as well as long-term monitoring.The main objective of this study is to evaluate this technology’s potential to offer a new indicator of alcoholic fermentation during wine production. Synthetic solutions with only one component (fructose, glucose and alcohol) and several components imitating alcoholic fermentation were measured. Initially, two temperatures (18°C and 28°C) were used for simple solutions measurement and the results showed a significant impact of the temperature. At 18°C, simple solutions of fructose and alcohol at different concentrations were well distinguished but not at 28°C. Furthermore, the results were found to be dependent on the electrode measuring system (2 or 4 electrodes exhibit different results) but not on the type of electric excitation (sinusoidal excitation or a combination of two different excitation waves). While analyzing the data, strong correlations (>0,95) were found between the impedance values and the type of investigated solutions. This indicated the high potential of this technology as a new indicator for alcoholic fermentation control.   

References

1. Garcı́a, A., et al., Dielectric characteristics of grape juice and wine. Biosystems Engineering, 2004. 88(3): p. 343-349.
2. Fazayeli, A., et al., Dielectric spectroscopy as a potential technique for prediction of kiwifruit quality indices during storage. Information Processing in Agriculture, 2019.
3. Zhu, X., et al., Frequency- and temperature-dependent dielectric properties of fruit juices associated with pasteurization by dielectric heating. Journal of Food Engineering, 2012. 109(2): p. 258-266.