The work described in this paper shows the possibility of the development of a reusable device for the detection of adulteration in milk based on admittance measurements. The AC electrical admittance spectra of different milk samples have been studied using uncoated and alkyl mercaptan coated gold electrodes. Uncoated gold electrodes exhibited a polarisation at around 250 Hz for full fat milk, while mercaptan coated gold electrodes showed a polarisation at around 1.1 kHz. Admittance data for full fat, semi-skimmed and skimmed milk showed an increase in milk conductance with decreasing fat content. A novel method to detect added water to full fat milk has been developed using single frequency electrical conductance measurements. The characteristics at 100 kHz and 8°C for all skimmed milk samples revealed a linear decrease in conductance with increasing water content over the entire range of water concentrations. In contrast, the conductance of full fat milk showed a linear decrease only at added water concentrations higher than 10%. At low added water concentrations full fat milk showed an increase in conductance at a point where the milk fat hydrolysed to produce fatty acids and glycerol. The lower limit of the detection is 1% change in water content, providing that the measurements take place under accurate temperature control.
展开▼
