Characterizing deterioration of milk through bioimpedance spectroscopy

Quality assessment and characterization of liquid milk by means of electronic sensor remains an intensive area of research. In this work, cylinder-in-cylinder type sample holder is fabricated to measure the bioimpedance of milk as a function of frequency. Experiments on bioimpedance spectroscopy were conducted during adulteration (at control temperature, 23°C) of branded (pasteurized) milk as well as raw milk. Cole equivalent circuit is considered as a characterizing model for milk. Cole parameters were extracted from the experimental data. From Cole parameters, relaxation-time was estimated and state of the milk sample has been expressed in terms of relaxation-time. Analysis of variance was performed on relaxation-time of the samples to gain statistical significance. Our method is capable to discriminate liquid milk from different commercial brands. It was found that the relaxation-time decreases monotonically with the progression of adulteration time for all kinds of milk considered in this study. From the changes in relaxation-time, the adulteration was found to be significant in the first three hours. Hence it is not advisable to consume milk after two hours of adulteration if kept at 23°C. Dominant biochemical pathways responsible for adulteration of milk are also presented.