Electrical conductivity of milk

Gerber, V. 1927. The significance of the specific electrical conductivity of milk and a new practical procedure for its determination. Z. Untersuch Lebensm. 54, 257-270. 

Muller, W. 1931. Contribution to the electrical conductivity of milk. Milchwiss. Forsch. 11, 243-251. 

Puri, B. R. and Parkash, S. 1963. Studies in physico-chemical properties of milk. XIII. Electrical conductivity of milk. Ind. J. Dairy Sci. 16, 47-50. 

Ruge-Lenartowiz, R. 1955. The influence of acidity on the electrical conductivity of milk. Roczn. Zalk. Hig Warsz 5, 91-102. In DSA 17, 613, 1955. 

Temperature control is important in conductivity measurements, since the conductivity of milk increases by about 0.0001 ohm 1cm 1 per degree Celsius rise in temperature (Gerber 1927 Muller 1931 Pinkerton and Peters 1958). Increased dissociation of the electrolytes and decreasing viscosity of the medium with increasing temperature are undoubtedly responsible for this effect. An investigation (Sudheendra-nath and Rao 1970) of the viscosity and electrical conductivity of skim milk from cows and buffaloes failed to reveal a simple relationship. The authors attributed the lack of linear correlations to variations in casein structure and its hydration. 

Fredholm, H. 1942. The specific electrical conductivity of Swedish cow milk, with special reference to the diagnosis of udder disease. Nord. Jordburgsforskning 1942, 195-213. 

Subheendranath, C. S. and Rao, M. B. 1970. The relationship between relative viscosity and electrical conductivity of skim milk. Proc. 18th Int. Dairy Congr. IE, 89. 

The carbonation was carried out using a mixture of 20% CO2 and 80% air. PCC morphology was controlled through crystallisation of intermediary phases as described by Yamada and Hara (1987). This study details the phase changes that occur over a period of time during the carbonation process, with respect to the reaction of milk of lime and carbon dioxide. The reaction was monitored using electrical conductivity of the remaining milk of lime and pH. 

The fat globules of milk reduce the conductivity by occupying volume and by impeding the mobility of ions. Thus the conductivity of whole milk is less than that of skim milk by about 10%, and that of cream varies with the fat content (Gerber 1927 Muller 1931 Prentice 1962). Homogenization of milk does not measurably influence conductivity (Prentice 1962). The conductivity of whey and ultrafiltrate is slightly greater than that of skim milk (Schulz 1956 Schulz and Sydow 1957). A possible relationship between the electrical conductivity and physical stability of evaporated milk and concentrated infant milk products has been reported (Hansson 1957). Samples of poor physical stability tended to have relatively low conductivity values compared to those of the more stable products. 

Schulz, M. E. and Sydow, G. 1957. The electrical conductivity (chloride-free) of milk and dairy products. Milchwissenschaft 12, 174-184. 

As in any electrochemical process, the products to be treated by EDBM must possess a relatively high mineral content to allow a good electrical conductivity to decrease the global resistance of the electrodialysis cell. Moreover, Bazinet et al. [108] demonstrated that the electrical efficiency of skim milk electroacidification is decreased, due to a lack of sufficiently mobile ions such as potassium (Figure 21.17). Consequently, H ions have to migrate across the CEM to ensure the electroneutrality. 

Electrostatic interactions in air are very different compared to the electrostatic interactions in aqueous systems, as there is no ion solubility and no double layer is formed. The source of the surface charges is also different. In air, there are no possibilities for acid-base interactions or for ion disassociation. Charging in air is caused by static electricity and is stable for non-conducting particles. This makes the interaction coulombic in nature, with a range comparable to the radius of the particle. The electrostatic interactions easily dominate when the particle size is large, the density is low, and there is a low water content (low conductivity). Typical examples could be during the drying of milk powder or the transport of coffee powder. 

NIR spectra of cow s composite and udder quarter milk subjected to multivariate data analysis contain information about milk abnormality and cow health disorders. Models for NIRS measurement of SCC in composite and udder quarter cow s milk have been developed. Models for simultaneous measurement of electrical conductivity and somatic cell count, as well as for identification of the main bacterial pathogens causing mastitis are described further. NIR spectroscopy has proved to be a valuable tool for mastitis diagnosis and for milk quality evaluation. 

MgO conducts heat well, but electricity only poorly, and is used as an insulator in electric heaters. Mg(OH)2 is a base. It is not very soluble in water but forms instead a white colloidal suspension, which is used as a stomach antacid called milk of magnesia. A side effect of stomach acid neutralization is the formation of MgCL, which acts as a purgative. 

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