A simple cryoscopic method for the prediction of water activity in butter

1. Introduction

Water activity (aw) is an importante fator in the stability of many food systems and its determination is of importance to the food industry (6, 7, 9). Some Years ago investigations were carried out on the analytical potential of a thermistor cryoscope besides its well known use to detect fraud by water admixture to milk in the Dairy laboratory practice (11). Although the physicochemical relastionship between freezing point depression (FPD) and water activity of aqueous solutions and liquid foods is well known (5), it seems that only recently a direct cryoscopic approach to aw measurement in a non-liquid food system (cheese) has been accomplished (1, 3). Using own published data (12) on cryoscopic salt content determination in butter, and Raoult’s law, the aw of some samples of salted and unsalted butter was calculated and found to be comparable to dats available in the literature (10).

Furthermore, comparative analysis of some butter samples for water activity determination using a standard hygrometer confirmed the applicability of the method. The presente paper reports on this simple cryoscopic approach to aw prediction in butter.

5. References

(1) CABEZAS, L.; MARCOS, A.; ESTEBAN, M. A.; FERNANDEZ SALGUERO, J.; ALCALÁ, M. Food Chem., v. 30, p. 59-66, 1988.

(3) ESTEBAN, M. A.; MARCOS, A.; FERNANDEZ SALGUERO, J. Food Chem., v. 25, p. 31-39, 1987.

(5) LERICI, C. R.; PIVA, M.; DALLA ROSA, M. J. Food Sci., v. 48, n. 6, p. 1667-1669, 1983.

(6) PRIOR, B. A. J. Food Prot., v. 42, n. 8, p. 668-674, 1979.

(7) SPERBER, W. H. J. Food Prot., v. 46, n. 2, p. 142-150, 1983.

(9) TROLLER, J. J. Food Prot., v. 46, n. 2, p. 129-134, 1983.

(10) WALSTRA, P.; JENNESS, R. Dairy chemistry and Physics. Wiley Interscience Publ., 1984.

(11) WOLFSCHOON-POMBO, A. F. Deutsche Molkerei-Zeitung, v. 107, n. 3, p. 36-43, 1986.

(12) WOLFSCHOON-POMBO, A. F.; DE LIMA, A.; EMALDI, G. C. Milchwissenschsfat, v. 38, n. 6, p. 349-351, 1983.

6. Summary

After melting a butter sample at 60ºC and centrifugationof the extracted water phase, freezing point depression determinations are carried out in a diluted aqueous extract.

Using Raoult’s law the effective mumber of

moles of solute (n2) which affects the vapor pressure of the aqueous phase of butter is estimated freezing point depression                and know n1 (number

of moles of solvent in the system = g1/18, Where g1, means the water content of butter/kg and 18 the molecular weight of water). The water activity (aw) of butter can be predicted. Water activity values of salted and unsalted butter were calculated and found to range from 0.925 to 0.995 aw units, respectively. Comparative water activity determinations (cryoscopy vs hygrometer) in 6 unsalted butter samples showed that the mean difference between the methods was 0.017 aw units. aw in butter depends mainly on moisture and salt content of the sample.     

[101] WOLFSCHOON-POMBO, A. F. A simple cryoscopic method for the prediction of water activity in buttter. Milchwissenschaft, v. 46, n. 2, p. 98-100, 1991.