Dielectric behavior of adulterated milk with urea and water

Milk adulteration, especially by adding urea, is one of the major health concerns. In this work, we report a dielectric methodology to detect the existence of polar adulteration like urea and water in milk. The microwave dielectric spectra of whole milk, skim milk and their mixture with varying contents of water or urea was measured. An obvious dielectric relaxation was observed for these systems. The dielectric relaxations were well represented by the superposition of two relaxation processes which are attributable to free water and water adsorbed on protein, urea-water co-clusters and urea-water co-clusters adsorbed on protein for both milk-water systems, urea aqueous solution and both urea-milk systems respectively. The relaxation of lower frequency was identified as the dipole orientation polarization of water or urea-water co-clusters adsorbed on protein in milk mixtures. Significant differences in dielectric parameters, relaxation time and relaxation strength, between these systems were analyzed by comparing between skim and whole milk with different water contents and among water, skim and whole milk with different urea contents. The results show that microwave dielectric spectroscopy may provide a way or a choice for monitoring of water and urea in adulterated milk. (C) 2018 Elsevier B.V. All rights reserved.