Milk is a daily consumed product and its intriguing foaming properties are important e.g. when processing dairy-based foams such as whipped cream or cappuccino-style beverages. Dairy foams are colloidal systems formed by air bubbles, water, and surface active proteins. Temperature is a very important parameter influencing the foaming behavior of milks containing lipids[1,2]. We investigated the temperature dependence of foamability, foam stability and foam structure between 5 and 60°C for four types of milk: ultra-high temperature processed milk and pasteurized milk, each with 1.5 and 3.5% fat content. All foam measurements were performed using the KRÜSS DFA100. We found, that foamability and foam stability exhibit a strong minium at 25°C thereby extending the existing literature with novel data[3]. These and our temperature dependent dynamic surface tension data of the investigated milks support the idea[1], that the state of the milk-fat globule is responsible for detrimental effects on the foaming behaviour. In this talk, we explain how at ~25°C the partially crystalline state of the milk-fat globules negativly affects foaming properties.
Finally, we determined for the first time the temperature and time dependence of the foam structure (bubble size distribution) for all investigated milks[3]. With this the aging behaviour of the foams can be characterized and differences in foam structure‘s homogeneity can be related to foam stability.
References:
[1]S. Kamath et al., Intern. Dairy Jour. 18, 997-1002
[2]T. Huppertz, Intern. J. Dairy Techn. 63, 477-487
[3]K. Oetjen, T.Willers et al., Colloids Surf. A: Physicochem. Eng. Aspects (2014), (accepted, in Press)
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