Electrical impedance spectroscopy as the basis for an alternative methodology for detecting honey adulteration

Abstract

Quality control for the identification of honey adulterations is a very important topic in food safety, especially because honey are constantly target of adulterations. A common fraud in honey samples is the addition of syrup composed of water and sugar, with the illicit intention of increasing its volume. The traditional analytical methods for quality control, such as chromatography or spectrophotometric methods, are sometimes not effective on an industrial scale because demand a long time for experimentation and qualified professionals. Recently, our research group has proposed Electrical Impedance Spectroscopy as a fast and promising technique for quality control in honey. Thus, the objective of this work was to study changes in electrical impedance spectra in pure honey upon addition of sucrose syrup. The honey sample, certified by the Federal Inspection Service from MAPA were purposely adulterated with additional syrup (20%w/w sucrose solution) up to weight percentages of 0, 2.5, 5.0, 10.0, 15.0, 20.0 and 25.0%. Measurements were carried out using a HIOKI electrical impedance analyzer, in the frequency range of 10 Hz to 5 MHz. with an electrode of a parallel plate of platinum, which has been adapted to the instrument for measurements in liquids. Additionally, rheology measurements were carried out to support the discussions. The results demonstrated that there was a significant change in all spectra profiles due to the syrup additions, allowing a mathematical model to be adopted for practical application The effects indicated that there was a reduction in the electrical resistance of the samples and this is due to the reduction in viscosity and the consequent increase in ionic mobility in the medium. A modeling with equivalent circuits was realized to expand knowledge about the phenomena studied and all presented a correction factor above 0.96 and an error of less than 1,1%, indicating good adjustments. The results obtained demonstrate the potential of measuring electrical impedance as an alternative in the development of methodologies applied to the detection of adulteration in honey by syrup.