Characterizing deterioration of milk through bioimpedance spectroscopy

Abstract

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.

Caption of Graphical Abstract

Cole equivalent circuit is considered for the bioimpedance spectroscopy (BIS) study of milk. All Cole parameters are experimentally estimated to characterize the state of the milk undergoing natural adulteration process. Relative changes in relaxation-time is considered as the monitoring parameter for adulteration. In order to gain statistical relevance, multiple measurement (replica) is conducted and ANOVA is incorporated in the BIS study. A simple, low-cost and cylinder-in-cylinder type sample holder is fabricated to study BIS of liquid sample. As an alternative to traditional pathological test, shelf-life of milk is estimated by electrical test.