Foaming properties and foam structure of milk during storage

Changes in foaming properties and foam structure of raw whole, raw skim, pasteurised whole, and pasteurised skim milk during storage at 4 °C, evaluated by mechanical mixing, air and steam injection, were investigated. The results showed that storage of milk until the end of their shelf-life (day 3 for raw milk and day 21 for pasteurised milk) did not induce any significant change in pH, particle size, viscosity and their foaming properties (foaming capacity, foam stability and size of air bubbles) although there was a slight increase in free fatty acid content. Regarding foaming methods, the air injection method produced much less foam volume than mechanical mixing and steam injection, except for raw milk where mechanical mixing showed the least foamability. However, an opposite trend was observed for foam stability. Although air injection induced the largest size of air bubbles, it produced the most stable foam, which was much more stable than foam produced by mechanical mixing and steam injection.