RELATIVE CONTRIBUTION OF PROTEINS TO CONDUCTIVITY CHANGES IN SKIM MILK DURING CHEMICAL ACIDIFICATION

As pH decreases, protein charges change and their contribution to electrical conductivity varies. In this work, the contribution of charged species in milk to the change in conductivity during acidification by HCl was modeled. The model predicts that the ionic species contributing to the conductivity change during HCl acidification were potassium, sodium, and chloride in the soluble phase of skim milk, chloride added by HCl acidification and calcium solubilized from micelles. Furthermore, this model showed that the proteins contribute about 40% of the initial conductivity of milk and their contribution was lowest at pH 4.4 at about 26.7%. The protein contribution calculated seems to be overestimated due probably to the viscosity correction factor (Fc) evaluated from literature and the electric mobility (.) values, which are from dilute and non-complex solution. However, the trends in the contribution of protein to conductivity obtained by calculation were in agreement with changes in .-potential reported in the literature. Our model, although limited by exclusion of the interactions of cations with phosphate, citrate, and casein phosphoseric should be considered as a start to the construction of a more complete model involving those interactions and electric mobility values calculated from milk.