Rapid impedance method for predicting the potential shelf life of packaged pasteurized milk

The potential shelf life of packaged pasteurized milk was studied using a rapid impedance method. The results showed a high correlation between the shelf life of Fengxing and Xiang Man-lou pasteurized milks and between the detection time and the logarithm of colony-forming units per milliliter. The impedance detection time was measured after preliminary incubation at 30 degrees C for 6 h for 100 and 200 microL milk samples, or at 37 degrees C for 6 h for 100-400 microL milk samples for Fengxing pasteurized milk, and after 6 h preliminary incubation at 30 degrees C for 300 and 400 microL milk samples or 6 h at 37 degrees C for 100-400 microL milk samples for Xiang Man-lou pasteurized milk. Regressive equations were then constructed to predict the potential shelf life. Compared with the traditional method, the impedance method plus pre-incubation of milk at elevated temperatures (30 and 37 degrees C) was rapid, accurate, and convenient. The entire estimation process was completed within 11-14 and 14-20 h for Fengxing and Xiang Man-lou pasteurized milks, respectively.