Abstract
The main aim of this research is to investigate the characteristics of milk and milk proteins as natural emulsifiers. It is still largely unclear how the two main fractions of the milk proteins behave as emulsifier in highly concentrated emulsions. The surface-active effect of these is determined experimentally for emulsions with a high oil content (φ > 0.7), in this case fully refined rapeseed oil. Recent publications have not yet sufficiently investigated how proteins from native milk behave in emulsions in which a jamming transition is observed. In addition, scientific measurements comparing fresh milk emulsions and emulsions of dried milk protein powders based on rheological and thermal properties are pending and unexamined. The emulsions, prepared with a rotor-stator disperser, are investigated by their particle size and analysed by microscopy, characterised by their rheological properties. The behaviour under shear is directly observed by rheo-optical methods, which enables the direct observation of the dynamic behaviour of the oil droplets undergoing a size selective jamming transition. For a better understanding of the contributions of the different emulsifying proteins, oil-in-water emulsions have been prepared by using whey protein isolates and sodium casinates. Their different role (and function) on the interface activity can be assigned to the droplet sizes and mechanical behaviour during increasing shear deformation. In addition, solid (gelled) emulsions are prepared by heating. It is shown that the cysteine-containing whey proteins are mainly responsible for the sol–gel transition in the continuous water phase and the formation of soft solids.
Highlights
In the food and cosmetics industry, milk proteins are used as natural products in a variety of products [1]
Milk proteins consist of two main fractions: caseins by about 80% and whey proteins by around 20%
Increase of the storage modulus G’ between 70/71% and 72/73% compares directly to the corresponding microscopy shown in Figure 8, where the increasing concentration shows the nature of the jamming transition
Summary
In the food and cosmetics industry, milk proteins are used as natural products in a variety of products [1]. The proteins contained in fresh milk are obtained by the membrane process or by precipitation [2]. As fresh milk and its proteins are natural products, no declaration with E-numbers is required, which, in turn, corresponds to the trend towards “clean labelling”. Milk proteins consist of two main fractions: caseins by about 80% and whey proteins by around 20%. The different structural and functional properties of the two fractions allow them to be used in a wide range of applications. Caseins are very heat stable, but denature at a pH value of approximately 4.6. Heat-sensitive milk proteins include whey proteins, which begin to denature partially at temperatures above 65 ◦ C [3]
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