Establishing Quantitative Standards for Residual Alkaline Phosphatase in Pasteurized Milk

Abstract

The alkaline phosphatase (ALP) assay is a rapid and convenient method for verifying milk pasteurization. Since colorimetric ALP assays rely on subjective visual assessments, their results are especially unreliable near the detection limits. In this study, we attempted to establish quantitative criteria for residual ALP in milk by using a more objective method based on spectrophotometric measurements. Raw milk was heat-treated for 0, 10, 20, 30, and 40 min and then subjected to ALP assays. The quantitative criteria for residual ALP in the milk was determined as 2 μg phenol/mL of milk, which is just above the ALP value of milk samples heat-treated for 30 min. These newly proposed methodology and criteria could facilitate the microbiological quality control of milk.

Keywords: alkaline phosphatase; milk; pasteurization; quantitative criteria; spectrophotometer.

Fig. 1.. Alkaline phosphatase standard curve. The standard curve was generated using a serially diluted phenol standard solution. Dilutions were incubated for 15 min at 40℃ prior to being mixed with CQC catalyst solution and extraction with butanol. The absorbance of the butanol extracts was measured using a spectrophotometer at 650 nm. The standard curve was plotted as μg phenol against absorbance and a linear function equation and correlation coefficient were calculated.