The Electrical Conductivity of Milk—The Effect of Dilution and Temperature

Figures & data

Table 1 Some of the most common ions present in milk and their concentration, valence, and limiting molar conductivity

Ion	Concentrationa (mM)	Valencea	Limiting molar conductivityb (S cm^2 mol^−1)
Na^+	21.0	1	50.1
K^+	36.4	1	73.5
Ca^2+	2.1	2	119
Mg^2+	0.8	2	106
Cl^−	30.7	1	76.3
	0.9	2	160
Others	29.0	1.3	85c
Sum conc	120.9
Representative value	1.1d	75d

^aValues taken from Walsta.[9]

^bValues taken from Atkins.[11]

^cEstimated from experimental data (Fig. 3).

^dConcentration weighted values.

Figure 1 Experimental results from the conductivity measurements. Temperature range 2–70°C.

Figure 2 The relation between the conductivity of undiluted fat-free milk (K ₀) and temperature. The experimental results from both milk batches are compared with Prentice's result.[6]

Figure 3 The experimental values at 2, 30, och 60°C in relation to Kohlrausch law and the Debye-Hückel-Onsager theory, assuming a molar concentration of 120.9 mmol L⁻¹, an ion valence of 1.1, and a limiting molar conductivity of 75 S cm² mol⁻¹. Pronounced deviation from linearity is seen at 0.2 M^1/2, corresponding to about 25% milk in water.

Figure 4 The predicted values from the model (Eqs. (8)–(10)) vs. all the measured values.

Walsta , P. , Geurts , T.J. , Noomen , A. , Jellema , A. and Van Boekel , M.A.J.S. 1999 . “ Milk Components ” . In Dairy Technology , Food Science and Technology 45 New York : Marcel Dekker, Inc. .

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Atkins , P.W. 1994 . Physical Chemistry, , 5th Ed. 834 – 846 . Oxford, , Great Britain : Oxford University Press . C28 pp

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Prentice , J.H. 1972 . The temperature coefficient of electrolytic conductivity of milk . Journal of Dairy Research , 39 : 275 – 278 .

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