The Rapid and Simple Method for the Estimation of Titratable Acidity of Raw Milk

Abstract

The rapid and simple method for the estimation of the titratable acidity of raw milk was developed. As well known, the change of pH per unit volume of titre (pH/v) becomes largest in the neighbourhood of the equivalent point, when raw milk is neutralized with alkaline solution. Therefore, it is expected that the pH value of raw milk which was measured after addition of the equivalent amount of alkaline solution will be distributed in the wider pH-range according to the titratable acidity. The pH which was measured after addition of a defined volume of alkaline solution was named as the "Shifted pH". The titration curves were drawn for all raw milk samples and those containing known amount of added lactic acid or solids-not-fat. The correlation coefficient between the "Shifted pH" of each step of titre and titratable acidity was calculated. A plot of the correlation coefficient vs. the amount of titre also had a peak around the equivalent point. Linear regression formula was obtained between titratable acidity and the "Shifted pH" which had been measured after 8ml of 0.1N NaOH were added to 50g of raw milk sample. The titratable acidity was esimated by substitution of the "Shifted pH"-value of raw milk samples in the formula. The estimated values thus obtained coincided well with the values obtained by titration. Consequently, this method is effective for the rapid and simple estimation of the titratable acidity in raw milk, and is suitable for the automatic analysis.