A Comparative Study of pH and Temperature Effects on the Acidic Coagulation of Milks from Cows, Goats, and Sheep

Abstract

The acidic coagulation of milk from cows, goats, and sheep was studied at various temperatures by a turbidimetric method based on light reflection and capillary viscosimetry. Milk was acidified by hydrolysis of a defined amount of glucono-δ-lactone. Two characteristic behaviors of milk were distinguished by turbidimetry. The first was observed at 15 and 20°C for the three types of milk and at 30°C for goat milk. The typical turbidimetric pattern as a function of pH could be divided into three stages. The first stage, from initial pH of milk to approximately pH 5.9, showed an initial increase in turbidity and a decrease in viscosity. The second stage, from pH 5.9 to approximately pH 5.2, corresponded to a decrease of milk turbidity associated with an increase in viscosity. The third stage was a logarithmic increase in turbidity. The second typical behavior of milk during acidification was obtained at 30 and 40°C for cow and sheep milks and at 40°C for goat milk. The turbidimetric and pH profiles could be divided into two parts: a slight turbidity increase and a rise in turbidity until a plateau was reached. © 1995, American Dairy Science Association. All rights reserved.