A cryoscopic method for salt (NaCl) content determination in butter

1. Introduction

In butter manufacture, the determination of the salt (sodium chloride) content plays an important role. Salt testing of butter is essential for both factory process control and legislative purposes. The commonly used Mohr procedure for the determination of the salt content of butter involves melting of the butter sample by adding boiling water, and titration of the chlorides in the mixture with a solution of silver nitrate, using potassium chromate as indicator. The Mohr procedure depends largely on the skill of the technician in determining When the end point has been reached; furthermmore, the method has the disadvantage of requiring the use of an expensive Chemical (AgNO3) reagent. In order o reduce this dependence on operator skills as well as on using silver nitrate, other methods can be developed. Measurement of the electrical conductivity of an aqueous extract of the butter has been suggested as a basis of a method of salt estimation (6). The present paper describes a method for the determination of the salt content of buther based on the measurement of the freezing point of the aqueous phase of butter, which is depressed as a consequence of the lowering of the vapor pressure by the addition of the non-volatile electrolyte, NaCl, during butter manufacture. Cryoscopic procedures are used nowadays for the determination of the degree of lactose hydrolysis in milk (7).

5. References

(6) PLYAKHIN, G. Mol. Prom., v. 11, n. 9, p. 30, 1950; Ref.: Chem. Abstracts, v. 45, p. 779, 1951.

(7) RAMET, J. P.; NOVACK, G.; EVERS, P. A.; NIJPELS, H. H. Le Lait, v. 59, n. 581-582, p. 46-55, 1979.

6. Summary

A new cryoscopic method for the determination of the sodium chloride content of butter was developed. The method is based on the fact, that addition of salt during buttermaking causes a depression of the freezing point of the aqueous phase of butter. The aqueous phase of butter is separated by placing a butter sample in a water bath or oven at 60ºC, followed by centrifugation at 20,000 rpm/10 min. Hereafter, 2.0ml are made up to 10.0 ml with distilled water. The depression of the freezing point of the diluted serum is then measured in a milk cryoscope. By means of a standard curve which relates freezing point depression with sodium chloride concentration (Raoult’s law), the salt content of butter is easily calculated; that values has to be corrected for the moisture content of butter. The method is suitable for “on line” factory control os salted butter (mean value = 1.81 % against 1,82 % by Mohr method, n = 15) as well as for rouine analysis of comercial salted butter samples (x = 1.44 % vs 1.47 % standard procedure, n = 5). Diferences between means were not significant at 5 % level of probability. 

[65] WOLFSCHOON-POMBO, A. F.; LIMA, A. de. A cryoscopic method for salt (NaCl) content determination in butter. Milchwissenschaft, v. 38, n. 6, p. 349-351, 1983.