Homogenisation of dairy products at high fat content using the valve technology
Special Symposium - Innovations in Food Technology (LMC Congress)
Innovations in Food Technology - Poster Session (Food - P2)
Keywords: milk, high-pressure homogenisation, micro-structured system, partial homogenisation, dairy products
High pressure homogenisation is a unit operation widely used in the production of emulsions in the submicron range. In food industry it is used for the homogenisation of e.g. dairy products. An emulsion premix is pressurised to several hundred bars and then pumped through homogenising valves where droplets are disrupted (full stream homogenisation). Product properties such as colour, consistency, taste, and creaming stability can be improved by homogenisation [Kessler 1996, Schuchmann et al. 2005]. Besides conventional flat valves (as used for dairy products) a simple orifice may also serve as homogenisation valve [Stang 1998]. Recently we investigated the homogenisation efficiency of orifice-type valves on several emulsion-based products.
In most homogenising devices droplets are not only deformed and disrupted by one single mechanism. Usually, different mechanisms affect the droplets simultaneously. In a simple orifice valve droplets are deformed in a laminar elongational flow partially superimposed by shear flow in front of the borehole, whereas behind the borehole forces in turbulent flow predominate. Furthermore, cavitation phenomena may occur.
The research was focused on the influence of parameters like the homogenisation pressure, temperature and the valve geometry on the particle size distribution of the product. Flow patterns within the homogenisation valves were determined. The influence of flow patterns on droplet deformation and disruption was investigated. Based on these results, impingement jet deflection valves were developed, and scale-up rules were established [Aguilar et al. 2006]. In emulsions containing slow adsorbing emulsifiers (as milk and cream), droplets formed in homogenisation tend to aggregate and coalesce. For these systems, a micro-structured system was developed in cooperation with the Forschungszentrum Karlsruhe. This micro-structured system (‘combi-valve’) combines a homogenisation valve (of orifice type) with a T-shaped micro-mixer. The micro-mixer allows adding a second, emulsifier containing phase to the first one being just homogenised.
In the combi-valve only one component is high-pressure homogenised. In the case of dairy products, the first component stream is cream coming from the separator. The cream contains most of the fat globules, especially the big ones. The second component, skimmed milk, enters the valve at significantly reduced pressure. Skimmed milk contains high amounts of dairy proteins being able to adsorb at the new fat globule interfaces. Fat globule aggregation or coalescence - as it is usually found in homogenisation of cream at fat contents above 17 % - can thus be suppressed efficiently. Thus cream of a fat content up to 42 vol.-% can be efficiently homogenised. In the same time, the fat content is adjusted to the target product value. Hence, the volume to be high-pressure homogenised is significantly reduced without loosing product quality resulting in huge energy savings. In order to realise this, the second component stream has to be mixed to the high-pressure homogenised stream within milliseconds resulting in three effects: First, an intense and fast mixing is realised as the second stream enters in a region of high turbulent flow. Secondly, the intruding second component stream influences positively the homogenising effect taking place mainly after the homogenising valve by applying back-pressure and inducing additional kinetic turbulent energy [Aguilar et al. 2004]. Thirdly, additional emulsifier molecules can be added via the second component stream directly into the zone of droplet break-up, enabling to improve the stabilisation of new droplets.
Aguilar, F. A.; Freudig, B.; Schuchmann, H. P.: Chemie Ingenieur Technik Vol. 76 (4), 2004, 396-399.
Aguilar, F. A.; Schuchmann, H. P.; Schubert, H.: 3. Jahresbericht AiF-Projekt Nr. 13731 N 2006.
Kessler, H. G.: Lebensmittel- und Bioverfahrenstechnik - Molkereitechnik, Verlag A. Kessler, München, 1996.
Schuchmann, H. P.; Danner, T.: Chemie Ingenieur Technik Vol. 76 (4), 2005, 364-375.
Stang, M.: Dissertation, Universität Karlsruhe (TH), 1998.
Presented Thursday 20, 13:30 to 14:40, in session Innovations in Food Technology - Poster Session (Food - P2).
