استفاده از اندازه گیری پذیرش الکتریکی برای کنترل کیفیت شیر

The method of electrical admittance spectroscopy has been used to study the water and fat content of milk. Over the frequency range 5 Hz to 1 MHz, the electrical circuit was dominated by a single time constant. To eliminate the effect of electrode polarisation, the conductance of the milk was measured at high frequencies where it showed a saturation value. The characteristics at 100 kHz and 8 °C for all milk samples revealed a linear decrease in conductance with increasing water content. Admittance data for full fat, semi-skimmed and skimmed milk showed an increase in milk conductance with decreasing fat content.

Valuable information about the electrical conduction behaviour of solid or liquid materials may be obtained by performing electrical admittance measurements over a wide range of frequencies. Admittance spectroscopy can also be used for gas and vapour sensing [1] and [2] and for quality control of a variety of foodstuffs [3] and [4]. The electrical conductivity of dairy products has been studied for more than 40 years to provide accurate values of the fat and protein content [5], [6] and [7]. Recently, adulteration has led to considerable problems in the milk industry and it has become necessary to develop new and improved instrumentation for the rapid and reliable detection of fraud. Several standard methods can be used to detect the concentration of water or fat content in milk. These techniques are based on the changes in freezing point of the milk (cryoscopic method) or on changes in refraction of light of the whey component of milk after the removal of the fat components. Here, we apply the technique of admittance spectroscopy to investigate the fat and water content in different types of milk.

The work described in this study shows the possibility of the development of a reusable device for the detection of water in milk based on admittance measurements. Over the frequency range 5 Hz to 1 MHz, the electrical circuit was dominated by a single time constant. If the fat content of the milk is known, then the observed conductance results at 100 kHz may be used to estimate the water content (or vice versa), providing that the measurements take place under accurate temperature control. Further work will focus on the use of the entire admittance spectrum (i.e. rather than a single frequency measurement) to obtain a more detailed analysis of the milk. This may be achieved, for example, by modifying the surface of the Au electrodes and studying the resulting capacitance characteristics.