Applicability of electrical parameters for controlling the quality of skim milk with various dry matter contents

Abstract

The aim of the present study was to determine the effect of concentrating skim milk (10–50 g 100 g−1) on changes in contents of minerals as well as values of physicochemical and structural parameters (pH, total protein, micro- and macro-mineral content, viscosity, particle diameter, micrographs by fractal dimension), electrical parameters: conductivity (Z, G), and dielectric parameters (Cp, Cs). Statistical analysis was conducted to determine the applicability and limitations of electrical parameters as tools for controlling the quality of concentrated skim milk.The obtained results show that as the dry matter content increases, the particle diameter and viscosity increase linearly, while the pH value decreases. The trends for electrical parameters and microstructure, as described by the fractal dimension, were less clear-cut. The electrical parameters suited to control the quality (Cluster 1 and 2 parameters) of concentrated skim milk turned out to be the dielectric parameter (Cs 100 Hz, p < 0.001, r ≈ (−0.8) to 0.9), followed by the conductivity parameter (Z – Cluster 1: p < 0.05, r ≈ 0.38; Cluster 2: p < 0.01, r ≈ −0.52) measured at f = 100 Hz, 1 kHz, and 100 kHz. Parameters Cs and Z at f = 100 Hz can be harnessed in practice to develop a simple and cost effective measurement device, which could replace time-consuming and costly assays done using reference methods.