EP1497020B1 - Method and device for homogenizing emulsions - Google Patents

Abstract

Method and device for homogenizing emulsions, especially milk, wherein an emulsion is subjected to a high shearing force in a homoginizer equipped with microstructures.

Description

The invention relates to a method for homogenizing emulsions, in particular milk, with which it is possible to crush the fat droplets by a homogenizer equipped with special microstructures at a substantially lower operating pressure than has hitherto been possible.

Homogenizing is an essential process step for milk processing. In order to obtain a supernatant or weeks stable emulsion, the fat droplets contained in the milk must be small and evenly distributed. In addition, a more full-bodied taste is achieved by this fine distribution. The homogenization of milk today is done exclusively with high-pressure homogenizers. In this process, the milk is conveyed through a narrow gap with very high pressure in a process that has been tried and tested over the past 100 years, thereby reducing the fat globules to sizes in the range of 0.3 to 0.4 μm.

The energy required to break up the fat droplets is three orders of magnitude higher than the theoretically necessary energy required to increase the surface area of the fat phase. Assuming a uniform energy input over the volume, the actual energy input is still two orders of magnitude above the theoretical minimum. Despite continuous improvement of the process, most of the energy stored in the milk only causes warming.

So is in the German patent application 197 00 810 a method for the homogenization of milk is described, in which the milk is conveyed through a single- or multi-stage Düsendispergiervorrichtung. Shearing forces, the caused by multiple flow deflections in tight microstructures or holes with a diameter of less than 1 micron, find no application. Rather, there is the homogenization at Düsendurchmessem about 100 microns by the nozzle flow, but not by the shearing of the droplets.

One method of reducing the droplet size of photoemulsions is in US Pat US-A-5811227 described in which a raw emulsion is pressed through a fiber filter.

An improvement of the efficiency would lead to a very decisive technical progress. In addition to lowering the specific energy consumption, in particular a substantial simplification of the technical design of the homogenization plant could be achieved, which would lead to considerable savings in the production and maintenance costs.

So far, microtechnology has been used successfully in many areas of industry. Due to the small structural dimensions, high heat transfer rates, fast mixing processes and very precise flow guidance are achieved. In the food industry, the particular advantages of microtechnology for process improvements, in particular for the improvement of fluid processes, have hitherto hardly been used.

Microstructures for the treatment of liquid samples are in US-B-6,368,871 described. These structures make it possible to combine the most diverse material flows and the treatment of sensitive macromolecules (DNA, proteins, ...).

It was therefore an object to develop a method and an apparatus for homogenizing emulsions, in particular for homogenizing milk, by which the technical advantages of the use of microstructures can be used and the fat droplets in emulsions, especially in milk, can be uniformly comminuted and For this purpose, a considerably lower operating pressure than before, preferably an operating pressure below 50 bar, is required.

It has now been found that this object is achieved by a method according to claim 1 and a device according to claim 5.

The staggered flow obstacles formed as microstructures preferably have the shape of rhombuses, triangles, sickles or other sharp-edged structures.

As materials, for example corrosion-resistant steels, but also ceramic materials can be used. The production can be carried out with standard production methods of microtechnology such. B. LIGA technique, deep etching, spark erosion, laser ablation or mechanical micro-machining done. The structures can be positively, materially or non-positively connected, for example by diffusion soldering, diffusion welding, Etektronenstrahlschweißen, gluing or pressing. Another method to inexpensively produce structures with fine flow obstructions is to use thin metal wires with another metal layer, e.g. As a silver layer to coat galvanically, then pressed in parallel and to fix on a support plate, for example by welding. The outer metal layer is then removed again by an etching solution, so that the desired structure is formed.

Fig.1

zeigt eine Anordnung der erfindungsgemäß besonders bevorzugten rhombischen Mikrostrukturen, die zur Erhöhung der Scherkräfte gegeneinander versetzt sind.

Fig. 2

zeigt die für die Erzeugung optimaler Scherkräfte wichtigen geometrischen Abmessungen (a), (b), (α), die entsprechend den Eigenschaften der zu homogenisierenden Emulsion und der zu erzielenden Fetttröpfchengröße variiert werden können. Weitere Variationsmöglichkeiten ergeben sich durch die Höhe der Mikrostrukturen und durch die Anzahl der hintereinander angeordneten Reihen der Mikrostrukturen.

Fig.3

zeigt den Aufbau eines erfindungsgemäße Mikrostrukturen enthaltenden Homogenisators. Dabei sind in der Homogenisiereinheit eine oder mehrere mikrostrukturierte Platten übereinander geschichtet, in denen die rhombischen Aussparungen am Rand scharfkantige Erhebungen zeigen, die für die Ausbildung erheblicher Scherkräfte verantwortlich sind. Gleichzeitig wird dargestellt, wie die Emulsion den Plattenstapel anströmt und wie sie ihn nach erfolgter Homogenisierung wieder verlässt. Dabei wird die Rohemulsion, also z.B. die Milch, mittels einer Pumpe durch die Homogenisiereinheit gedrückt und kann anschließend weiter verarbeitet werden.

Fig. 4

zeigt eine scharfkantige Mikrostruktur, die aus einer Schicht von Metalldrähten hergestellt worden ist, die mit einem zweiten Metall überzogen und nach paralleler Verpressung auf eine oder zwischen mehreren Trägerplatten fixiert sind. Anschließend ist dann das zweite Metall herausgelöst worden. Für dieses Verfahren werden vorteilhafter Weise Metalldrähte mit einem Durchmesser von weniger als 3 µm eingesetzt. Besonders zu empfehlen ist es, die Metalldrähte beim Herstellungsverfahren mit Silber zu überziehen.

The cleaning of components has, especially in food technology, an important importance. For the homogenizer according to the invention, chemical cleaning agents can be used for this purpose. Another possibility is a construction that provides a mechanical cleaning. The microstructured plate is inserted through a plate with openings in the form of flow obstacles in the flow space, so that the cleaning can be done by lowering the microstructures.

Fig.1

shows an arrangement of the invention particularly preferred rhombic microstructures, which are offset from each other to increase the shear forces.

Fig. 2

shows the important for the generation of optimal shear geometric dimensions (a), (b), (α), which can be varied according to the properties of the emulsion to be homogenized and the fat droplet size to be achieved. Further variations result from the height of the microstructures and the number of successively arranged rows of microstructures.

Figure 3

shows the structure of a homogenizer according to the invention containing microstructures. In this case, one or more microstructured plates are stacked in the homogenizing unit, in which the rhombic recesses at the edge show sharp-edged elevations which are responsible for the formation of considerable shearing forces. At the same time it is shown how the emulsion flows against the plate stack and how it leaves it again after homogenization. Here, the raw emulsion, so for example the milk, pressed by a pump through the homogenizer and can then be further processed.

Fig. 4

shows a sharp-edged microstructure, which has been produced from a layer of metal wires, which are coated with a second metal and fixed after parallel pressing on one or more support plates. Then then the second metal has been dissolved out. Metal wires with a diameter of less than 3 μm are advantageously used for this method. It is especially recommended to coat the metal wires with silver during the manufacturing process.

The shear forces required to produce uniformly small droplets of fat in an emulsion can also be produced by differently designed microstructures. Particularly suitable for this purpose is a perforated plate proved, the holes have a diameter of less than 1 micron. This hole diameter is particularly suitable for the homogenization of milk, in which the fat droplets before the emulsion have a diameter of 3 to 25 microns and after passage through the homogenizer should have only a uniform droplet size of less than 1 micron. A comparable effect is also achieved by microchannels whose narrowest cross-section is smaller than 1 μm.

The use of femtosecond lasers is of particular interest for producing the apertured plate which can be used in accordance with the invention for homogenizing emulsions, since in the processing of materials with high thermal conductivity and comparatively low melting temperature (for example metals) the melt adhesions which generally occur when conventional laser beam sources are used can not significantly reduce the achievable precision. Even transparent materials such as organic materials can be processed with very little damage with these femtosecond lasers.

Such a perforated plate is preferably made of metal or of glass.

With the method according to the invention, it is possible to produce a uniformly homogenized emulsion, in particular milk with a particle size of less than 1 .mu.m, which is distinguished by a particularly high durability with a significantly reduced operating pressure of less than 50 bar compared to the current standard of about 200 bar.

Claims (6)

1. Method for homogenizing emulsions, wherein the emulsion is subjected to high shearing forces in a flow field by means of a homogenizer equipped with microstructures, characterized in that said shearing forces are generated by mutually offset flow obstacles in the shape of diamonds, triangles, crescents or other sharp-edged structures or by an apertured plate whose holes have a diameter of less than 1 µm.
2. Method according to Claim 1, characterized in that the holes in the apertured plate are generated by a femtosecond laser.
3. Method according to Claims 1 and 2, characterized in that it is used for milk homogenization so that the fat globules in the emulsion are reduced to a size of under 1 µm.
4. Method according to Claims 1 to 3, characterized in that the operating pressure is under 50 bar.
5. Device for milk homogenization according to Claims 1 to 4, characterized in that it has one or more microstructured, sharp-edged plates which are stacked on top of one another and which, as flow obstacles, exert high shearing forces on the stream of liquid, wherein the shearing forces are generated by offset flow obstacles in the shape of diamonds, triangles, crescents or other sharp-edged structures or by apertured plates whose holes have a diameter of less than 1 µm.
6. Device as according to Claim 5, characterized in that it has an apertured plate with micro channels whose narrowest cross section is less than 1 µm.

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