Relationship between surface tension, free fatty acid concentration and foaming properties of milk

The relationship between surface tension, free fatty acid concentration and the foaming properties of milk was investigated. The surface tension of milk with varying free fatty acid concentration was determined using the Wilhelmy plate technique and the milks were subsequently foamed by steam injection using a commercial coffee machine and by air injection using a specially designed foaming apparatus. Foaming properties of milk in terms of initial foam volume, foam stability and visual appearance of foam as functions of free fatty acid concentration were determined. Surface tension of milk showed a negative relationship with its free fatty acid concentration and foaming properties. However, natural variations in the surface tension of milk due to other surface active components such as protein, fat and phospholipids made it difficult to determine an absolute surface tension value below which the foaming properties of milk are negatively affected.