The Effect of Bronopol on the Freezing Point and Impedance of Milk Samples

Preferred sample-handling guidelines for the testing of raw milk samples cryoscopically require refrigeration followed by analysis within 24 hours. When this practice cannot be followed, the use of a broad-spectrum preservative, such as bronopol, is an acceptable alternative. Cryoscopy’s primary function is to detect added water in milk by measuring its freezing point.

This study was designed to quantify the effect of adding a preservative to a milk sample that will be tested cryoscopically. Using raw milk, pasteurized whole milk, and reagent grade water, 11 different concentrations of bronopol were tested 5 times each on a cryoscope, and these results were compared to the baseline readings of the unadulterated samples. The results show a direct, measurable correlation between bronopol concentration and freezing point depression of the samples. When used at the manufacturer’s suggested concentration of approximately 0.44 mg/mL, bronopol depresses the freezing point by 10 – 20 m°H.