DE4319813A1 - Process for the production of sterile milk by dynamic microfiltration - Google Patents

Description

The invention relates to a method for producing Milk, either whole milk or skimmed milk, with a reduced bacterial content, the product of this Procedure and procedure for distributing milk to the Consumer.

The well-known pasteurization process for killing Bak teries in milk have been used for many decades. Al However, they affect the pasteurization process high temperatures required the taste of milk. Furthermore, in the pasteurization process even at An high temperatures not all unwanted bacteria eliminates what leads to a short shelf life of most Leads dairy products.

Bacillus cereus is often the predominant bacterium in ver equally old milk that is treated in the conventional way delt because it outlives the pasteurization process ben and thrives at low temperatures, which Ver coarsens the milk. There is a general need for a method for reducing the bacterial content in Milk, both whole milk and skimmed milk, to increase the shelf life of the product and its ge taste by dispensing with the pasteurization process improve.  

Of great economic importance is the need the very expensive and labor intensive distribution process that is currently required to bring the milk to the consumer bring to make redundant. It is currently for every mole required after processing the raw milk Homogenize and other stages of milk for distribution to put consumers in containers and this milk un to transport cooling. This requires it for everyone Dairy to purchase a significant number of refrigerated trucks and to entertain the processed milk at the place of Ver transport division to the consumer. By providing would be a sterile or almost sterile milk product it possible to take the need to transport the milk under to make such cooling unnecessary. However, with the pasteurization process only milk with a decrease bacterial content, but not a sterile one Product.

If a sterile milk product could be made it would also be possible to store milk on Dispense place of distribution with cooling. It would be if of considerable economic advantage if large refrigerated compartments in typical grocery stores are eliminated could.

Even when using today's pasteurization process it is of particular interest in some cases before Pasteurization of a milk with a reduced bacteria to get salary. For example, a certain amount Raw milk must be so contaminated that the mere Pasteuri not to an adequate shelf life based on today's standards, leads.

For some applications, it is also desirable to provide a treated milk in which the bacteria content very strong, e.g. B. to 1/100 of the original value, is reduced. It is particularly important to use milk comparatively low bacterial content for manufacturing  of cheese because wrong bacterial cultures the Can destroy cheese. It’s usually not convenient the milk for use in cheese production simply in to be treated with heat to a sufficient extent, since one of the like heat treatment lead to a smaller amount of cheese and adversely affect the coagulation time can. Additives have conventionally been used to achieve this Lessen problem. In many cases, however, it would be nice it is worth avoiding the use of such additives.

Different methods of reducing the number of bacteria in Milk by filtration is known to those skilled in the art, but none the process has found general acceptance. The Prior art methods either result in a low flow rate, which is the process at An on a large scale makes it uneconomical, or it affect the quality of the milk, so that consumption not accept the product.

The use of conventional filtration devices for manufacturing milk with a reduced bacterial content been tried. The Swedish patent publication 380 422 describes a process in which whole milk by Mi crofiltration divided into filtrate and concentrate fractions becomes. The filtrate that passes through the pores of the filter (the The size of the pores is generally in the range from 0.1 μm to 10 µm), consists of milk with a largely reduced Fat content, and the concentrate that is on the surface of the Filters held back consists of cream, as not only Bacteria, but also largely by the fat balls Filters are retained.

The published Swedish patent application SE-A-67 15 081 describes a method for sterilizing milk in which the fat is first separated from the whole milk. Then the fat fraction is sterilized by heat and the Ma Germ milk fraction is steri by filtering the bacteria lized (no filter pore sizes are specified). Close  The sterilized fat and skim milk fractions become again mixed together, taking a sterile milk product receives. To filter the skimmed milk fraction To sterilize the bacteria, the pore size must be in the filter be so small that no bacteria can pass through it, what too low throughput speeds and the undesirable Retention of fat balls and proteins from milk leads.

U.S. Patent 5,064,674 relates to a method of manufacture hypoallergenic milk using ultrafiltration methods Use of membranes that allow the passage of molecules a molecular weight of about 5 kDa or less chen. The excluded components by the membrane retained, include milk protein, viable and non-viable bacteria, bacterial protein antigens and milk fat. That with the ultrafiltration process captured filtrate is therefore not only free of bacteria and bacterial protein antigens, but also of fat and of Milk protein, what the product as such is unsuitable for Makes use as milk.

So it is obvious that the pores of this Bacterial filters used in the field Sterilization of milk are effective, not just the bacteria remove but also the fat globules and at least some of the proteins. Such filters are quickly passed through retained material clogged; therefore the falls Flow rate through the filter quickly, and the Filters must be cleaned or replaced frequently. The high Prevent costs of such an inefficient procedure in general its application. Because the filter is also fat globules proteins and proteins, the quality of the Milk compromised.

From the discussion above it is evident that a ongoing need for improved milk filtration procedure exists with which a sterile or almost sterile  Product can be provided that is an improved Has durability, the process the quality of Milk not affected.

So far, some attempts have been made to cross-flow or Tangential flow filtration devices for treatment use of milk, such devices in the are known in this field.

Several types of filtration devices are described that allow such a tangential current or Perform cross-flow filtration. Maybe the older one most known such device, which in the Soviet Pa tent 142 626 (Zhevnovatyi, A.I.) is described in a tube of porous material that is inside a second Pipe is attached, formed, the one to be filtered Suspension under a load at high speed in the annular space occurs between the two tubes and that Filtrate flows inside the porous tube. With improved Devices of a similar construction will concentrate on two trical cylinder used, the inner cylinder through a microporous membrane is formed and the liquid a forced helicoidal flow around the inner zy linder is subjected.

Other crossflow filtration devices include a number of filter elements in the form of plates or disks are arranged one above the other. On both surfaces of it are microporous membranes, e.g. B. a filtrate manifold, arranged, the suspension to be filtered a disc one after another in a helicoidal way.

Many other forms of cross flow filtration systems are available has been developed. For example, U.S. Patent 5,009,781 relates a cross-flow filtration device with a filtrate network plant, which is a series of fil stepping chambers and one or more filtrate channels, which the Cut chambers, includes. U.S. Patent 5,035,799 relates to one  Cross-flow filter arrangement with filter sheet arrangements, the par allel are arranged within a filter tank, the incoming liquid is under pressure to a door to generate bulent cross-flow of the liquid via the media gene.

U.S. Patent 5,015,397 relates to cross-flow filtration device and method using a tube made of helicoidally rolled profile wire. Contaminated rivers liquidity occurs at one end. When flowing through the pipe their concentration of contaminants increases while clarified liquid passes through the pipe wall. U.S. patent 5 047 154 relates to a method and an apparatus for Increasing the flow rate of Cross flow filtration systems. U.S. Patent 4,569,759 relates a tangential flow filtration device and a plant, which comprises such a device.

Cross flow filtration differs from through running filtration basically that the liquid supplied speed parallel to the filter surface and the Filtration in a direction perpendicular to the direction of the Current of the supplied liquid takes place. With crossflow fil tration systems is generally the enrichment of ab filtered solids on the filter medium through the shear effect of the flow is reduced because the direction of flow of the supplied liquid is tangential to the membrane surface. Cross flow filtration therefore enables a quasi-statio nary operation with a nearly constant flow when the Drive pressure difference is kept constant. However this theoretical possibility in practice so far not he been enough. In conventional cross-flow filtration systems there is the problem of the decrease in the filtration through river. Much of the suspended solids will be on retained the wall of the tube and it forms quickly a dynamic membrane (also called "filter cake" or "Filter residue" is called). The dynamic membrane  is largely responsible for the following occurring Filtration.

The particles that initially enter the wall matrix are eventually caught in it because of the irregular and serpentine nature of the Pore structure. As microfiltration progresses, it will Penetration of further small particles into the wall matrix inhibited the presence of the dynamic membrane. The education the dynamic membrane, together with a possible ver blockage of the pore structure of the tube by trapped part Chen, leads to a drop in the filtration flow. At In conventional systems, this waste is roughly in one exponential relationship to filtration time.

Cross-flow filtration of milk has been tried however, is due to the problems discussed above has not been widely accepted. U.S. Patent 5,028,436 applies a procedure to separate the dissolved and unsolved Ingredients of milk, using an mi Croporous membrane with a pore size in the range of 0.1 to 2 microns with an aqueous solution, a dispersion or an emulsion of lipids or peptides that is. The patent also applies to the pretreated mem bran separated milk. In the process of this patent, a first filtration stage using a microporous Membrane used in a tangential current mode. You get a clear filtrate and a thickly flowing concentrate. The filtrate contains all salts, lactose, amino acids, oligo peptides and low molecular weight polypeptides in the natural, non-denatured form, and the concentrate contains practically all of the casein and fat components the milk. The filtrate can therefore not be considered as "milk" be removed as all fatty substances have been removed from it are.

U.S. Patent 4,876,100 relates to a cross flow filtration ver continue to produce milk with a reduced bak  serial salary. Raw milk is separated by centrifugation a faction consisting of cream and another, from Skim milk existing fraction separated. The Skimilchfrak tion is passed into a microfilter, in which a part of the Fat globules, proteins and bacteria separated becomes. A filtrate is obtained from the microfilter Skimmed milk with a reduced content of fat, proteins and bacteria, and a concentrate with an elevated Content, fat, proteins and bacteria. The concentrate will then sterilized. The filtration process of the U.S. patent 4,876,100 decreases in addition to the bacterial content in the filtrate also its fat and protein content, it changes the properties of the filtrate compared to those of the original skim milk.

So far, the use of cross-flow filtration has so often Obviously not an acceptable procedure for verrin bacterial contamination in milk.

It became a way to overcome the classic problems associated with cross-flow filtration technology developed which is known as dynamic microfiltration. The dynamic filtration process overcomes the disadvantages the classic cross flow technology, because the one to be filtered Liquid is not simply tangent to the membrane surface che is headed. The membrane surface or a solid body are moved near the membrane surface so that the Liquid at the interface between the rotor and the Stator is subjected to a shear effect. The shear effect causes the membrane surface to "scrub" what keeps it comparatively free of particulate matter and prevents a filter cake from sticking to the mem branch surface forms. The particulate material that is otherwise would accumulate on the membrane surface, remains suspended, and it is eventually replaced by a se secondary stream, which is generally a concentrate stream is removed.  

Dynamic microfiltration systems can take various forms accept. For example, U.S. Patents 5,037,562 relate to 3,997,447 and 4,956,102 dynamic microfiltration plates systems.

U.S. Patents 4,956,102, 4,900,440, 4,427,552, 4,093,552, 4,066,554 and 3,797,662 as well as many others teach cylindri dynamic microfiltration devices.

No one has dynamic microfiltration on that yet Processing milk applied, and the application of the cross Stream filtration on milk was limited and is mainly for the fractionation of milk into components based on the Fat content has been applied.

It has now surprisingly been found that the dynamic microfiltration of milk successfully without the im Prior art problems of deterioration milk quality, premature constipation of the milk Filters and insufficient removal of bacteria by using the method according to the invention can be led.

According to the invention, milk is either whole milk or Skimmed milk, first homogenized and then a fil subjected to tration. Through the first homogeneity The particle size of the fat globules and other large, suspended milk constituents Lich reduced what a microfiltration of milk without we substantial removal and entrainment of grease or other com components.

Milk is an emulsion of fat and protein particles in What ser. Homogenization is a process for reducing tion of the emulsion particle size to prevent the passage through a microporous membrane with a suitable pore size enable and retain bacteria contained therein,  without undesirably reducing the fat and protein content of the Remove milk.

After homogenization, the milk is made using the filtered dynamic microfiltration. The invention provides in this way an improved method of manufacture of milk with a reduced bacterial content ready without that pasteurization is required. The part of the Milk fraction, which is retained by the microfilter, (the concentrate fraction), can be part of the supplied mate rials can be returned, or they can be discarded or in other methods can be used.

In one aspect, the invention thus provides a method for treating raw milk for producing treated milk with a lower bacterial content than raw milk. The method involves homogenizing the milk and dynamic microfiltration of the milk within about 5 minutes after homogenization by passing the milk through a medium pore size microfilter sufficient to reduce the bacterial content of the milk flowing therethrough to obtain a filtrate with a reduced bacterial content compared to the raw milk used and a concentrate with a higher bacterial content compared to the raw milk used. The milk obtained has a very low bacterial content, e.g. B. about 10 ³ bacteria per milliliter or less, and it keeps more organoleptic components than be found in pasteurized milk with the same bacterial content.

The milk obtained by the method according to the invention is generally more storable than milk made by conventional Pasteurization has been obtained. Considerable remaining Bacterial concentrations remain after pasteurization in milk, since milk naturally contains certain bacteria holds that survive the pasteurization process. Therefore Pasteurized milk continues to be chilled to the bacts reduce growth and prevent spoilage.  

However, some are bacteria present in raw milk both heat resistant (bacteria that cause pasteurization survive) as well as psychrotroph (bacteria that thrive at temperatures below 15 ° C), like Bacillus cereus. The presence of heat-resistant, psychrotro phen bacteria in packaged milk products is very harmful Lich, since their rapid growth, even under cooling, into one Spoilage of milk leads.

With the present invention it is possible to make sterile milk manufacture that even at room temperature for long periods of time tension, e.g. B. 30 days or more can be stored. The sterile milk according to the invention can by the absence of Bacteria in general and especially through the absence of bacteria and pathogenic microorganisms that follow the following are characterized:

Heat resistant bacteria:

Micrococcus
M. luteus, M. roseus

Streptococcus
S. pneumoniae, S. lactis, S. faecalis

Lactobacillus
L. delbrueckii, L. lactis, L. helveticus, L. casei, L. trichodes

Staphylococcus
S. aureus, S. epidermidis

Bacillus
B. cereus, B. subtilis, B. macerans, B. stearothermophilus

Clostridium
C. butyrium, C. pasteurianum, C. botulinum, C. perfringens, C. tetani

Psychotrophic bacteria:

Pseudomonas
P. aeruginosa, P. fluorescens, P. pseudomallei, P. mallei

Archnomobacter
Alcaligenes

Acientobacter
A. lignieressii, A. equirli

Flavobacterium
F. aquatile, F. menigosepticum

Bacillus
B. cereus, B. subtilis, B. macerans, B. stearothermophilus

Coliform bacteria:

Enterobacter
E. coli, Salmonella Typhi, Shigella Dysenteriae, Klebsiella Pneumoniae

Various:

Listeria
L. monocytogenes

The milk according to the invention fulfills and exceeds more typically the requirement that pasteurized milk of high quality When examined on a plate, a number of bacteria appears points that does not exceed 30,000 per milliliter, and one Number of coliform bacteria has 10 per milliliter does not exceed, these values being according to standard methods be true.

According to another embodiment of the present invention a process for the treatment of raw milk position of treated milk with a compared to Raw milk provided lower bacterial content, the fol The following stages include: (1) The milk is broken down into a fat fraction with a minimum fat content of around 10% and a lean milk fraction separated; (2) the skimmed milk fraction becomes homo genized and within about 5 minutes of homogeneity subjected to dynamic microfiltration by the skimmed milk fraction through a microfilter with a average pore size, which is sufficient to contain the bacteria to reduce milk flowing through, is directed to a Filtrate with a lower bacterial content than the one put skimmed milk fraction and a concentrate with a height  ren bacterial content than the skimmed milk fraction used receive; (3) the bacterial content of the fat fraction is in reduced to a separate level; and (4) the skim milk fraction after microfiltration and the fat fraction with the reduced bacterial content are combined.

According to another embodiment of the present invention a method for the production of milk with a Fat content of about 2% is provided, the following stages comprises: (1) a skimmed milk fraction is homogenized; (2) within about 5 minutes after homogenization the skim milk fraction of a dynamic microfiltration posed by the skim milk fraction through a microfil ter with an average pore size that is sufficient, the bacteria rien content of the milk flowing through is used to a filtrate compared to the Skim milk fraction lower bacterial content and a concentration occurred with a compared to the skim milk frak used tion to get higher bacterial content; (3) the bacteria content of the cream fraction with a minimum fat content of about 10% is reduced; and (4) the skimmed milk fraction after the Microfiltration and the cream fraction with the decreased Bacteria content are combined.

According to the invention, a method for processing Milk provided for consumption by a consumer, comprising the following stages: the raw milk is obtained; the Milk is homogenized and within about 5 minutes after the homogenization of a dynamic cross-flow micro subjected to filtration by passing the milk through a microfil ter with an average pore diameter sufficient to reduce the bacterial content of the milk flowing through, is passed to a filtrate with a lower bacteria content to get than the raw milk used; the milk is placed in a container for consumer use packed; and the milk is brought to the place of cooling without cooling Distribution transported to the consumer.  

According to the invention, a method for Distribution of milk for consumption by a consumer which comprises the following stages: the raw milk is receive; the bacterial content of the milk is reduced to a concentration reduction of 10³ bacteria per milliliter or less device; the milk is put into a container for use packed the consumer; and the milk is turned on without cooling transported the place of distribution to the consumer. This makes the need for refrigerated transportation and distribution vehicles superfluous.

Figure 1 is a schematic diagram of the equipment used in the method of the invention.

Figure 2 is a graphical representation of particle sizes in milk after homogenization.

The material used is fresh, un treated raw milk from a pet like a cow. The The method according to the invention can also be applied to processed milk, like pasteurized milk, then who which, however, does not realize all the advantages as the Her Providing milk with improved organoleptic properties compared to milk that has not been pasteurized that is.

The raw milk to be processed can first be heated exchangers are directed to a suitable temp rature set, and then if necessary be passed through a centrifugal separator to the ge whole cream fraction or a part thereof on conventional ones Way to remove.

The raw milk is homogenized and passed through pretty quickly a dynamic microfilter, where one fil receives fraction and a concentrate fraction. The size the pores of the microfilter is chosen so that at least some of the bacteria is retained. The filtrate, then the proportion of the milk fraction caused by the retention upper  surface of the microfilter consists of milk with none or a reduced bacterial content (based on the Milk before microfiltration), essentially none Change in fat and protein content occurs. The filtrate fraction can then be used directly to manufacture other products, such as milk powder, or it can be used without further ado Treatment to be packaged.

The filtrate fraction is cheaper than that for many reasons milk obtained by conventional pasteurization. You be holds more organoleptic components than milk, the pasteu What has been standardized from the point of view of the consumer improved from taste. Furthermore, the fiction milk obtained has a much longer shelf life, because bacteria, like psychrophilic bacteria, in particular Bacillus cereus, can be completely removed according to the invention can, which is impossible with conventional pasteurization.

The concentrate fraction, i.e. the proportion of the milk fraction, from the retention membrane surface of the microfilter retained and recovered consists of milk with a increased bacterial content (based on the milk used before microfiltration) and one essentially unchanged content of fat globules and proteins. The concentrate fraction can then be discarded or used in other processes be used.

The filtrate may contain some bacteria, the smaller the less but the number of bacteria, the more durable the product. The complete sterilization is desirable, but the at catchy growth rate of a small number ver permanent bacteria is usually low enough to a significantly increased durability of the resulting Lead milk product.

The shelf life of milk produced according to the invention is compared to conventional pasteurized milk  increases because in particular the concentration of Bacillus cereus is significantly reduced.

Since the milk according to the invention can be made sterile, while using conventional pasteurization techniques milk is not really sterile, the milk has one extremely high durability when cooled or at room temperature especially when the milk is under aseptic conditions is filled into a container. One way to to achieve this is to use the "form-fill-seal" technique, which is known in the packaging industry. This technique is often used when packaging sterile solutions and the like, e.g. B. applied in the pharmaceutical industry. The milk produced according to the invention can be used the "form-fill-seal" technique, and such Milk shows an extremely long time even at room temperature Durability.

The exact process or the machinery used to filling is not critical. Only as an example and as an explanation of how the "form-fill-seal" technique can be used, the following Be submitted letter.

Some vertical packaging machines that after the "Form-Fill-Seal" technology (form, fill and welding technology) ten, use a web made of a synthetic thermo plastic film that unrolled from a roll and through Welding the longitudinal edges of the film in a tube formation unit is formed into a continuous tube. At at their machines will use the pipe at the time of use extruded from a resin melt. This is how it is done The pipe is transported to a filling station, where it is in Cross direction is buckled. This section is located in a welding device below the filling station. in the kinked section of the pipe is the pipe using the Welding device welded, making an airtight seal is created across the pipe. After ver  will weld a lot of material that will be packaged should, e.g. B. a liquid, filled into the tube, namely in the filling station. The material fills the tube upwards from the aforementioned seal. The pipe will then turn on predetermined piece moved down and on a second cross Section cut in the transverse direction and welded.

Such a vertical, according to the "form-fill-seal" technique working machine as described above, is commercially available under the trademark PREPAC. A others are described in U.S. Patent 5,038,550.

The milk fraction is first preferably one for the Homogenization suitable temperature heated or cooled, after the centrifugal separation that may have taken place tion and before homogenization. The milk is then in passed a homogenizer in which the fat emulsion size is reduced to a sufficient size to pass occurs through the membrane to allow. Is preferably the size of all suspended particles less than about 1 µm. It is important that the milk is relatively soon after the homogeneity is filtered. The filtration is preferably carried out in less than about 5 minutes, especially in less than about 2 minutes, and most preferably in less than about 30 Seconds.

The important factor is not the time before the filtra tion, but the fact that the filtration before any an essential agglomeration to form spheres a substantial number of particles larger than about 1 µm are done.

Homogenization of skimmed milk or whole milk before Filtration in a cylindrical dynamic microfiltrati Unit is essential to the fat inventory parts and other components of milk are sufficient to emul yaw and suspend and the particle size is sufficient to reduce, so that he has good filtration  is aimed. However, a rotating disc filter develops a noteworthy shear rate immediately on the surface of the rotating disc. So there can be a certain degree of homo Geneticization of milk essentially at the same time as Filtration done. Such a "self emulsification" of Milk made possible by the action of the dynamic microfilter light skim milk with a rotating disc filter process without the need for a separate Homogenizer exists.

The environment of the rotating disc causes both a homogenization and a simultaneous filtering of the milk, which is not achieved by a rotating cylindrical filter unit. A rotating disc filter can produce a shear rate of approximately 200,000 sec ^-1 , while a rotating cylindrical unit can only produce a shear rate of 10,000 sec ^-1 . Although the shear force in a rotating disc filter unit is considerable, it is believed that in most cases it is not sufficient to homogenize whole milk sufficiently.

According to the invention, the filtration is called dynamic filtration carried out, d. that is, the filtration medium itself becomes constant kept moving so that the effective flow rate milk is very high in the medium. The spe The physical physical form of the dynamic membrane is not critical. So the membrane medium z. B. the shape of shit ben or accept cylinders. Such dynamic microfilm tration devices have already been explained, and they are suitable for the practice of the present invention. Generally, the dynamic microfilter comprises a cylinder drical or disc-shaped membrane element, which is in rotates within an impermeable outer cylinder. At a cylindrical dynamic microfilter, if too filtering liquid in the space between the Stator and the rotating membrane is inserted, pulse transferred from the rotating membrane to the liquid The liquid near the inner cylinder experiences one  higher centrifugal force than the liquid near the outside Cylinder. This phenomenon creates under certain conditions against a flow pattern known as the Taylor vortex this phenomenon being the development of a noteworthy Prevents residue on the membrane surface.

The dynamic filtration process takes advantage of Generation of Taylor vortices around the surface of the membrane to keep free of possible residues, their Components then suspended in the filtered liquid stay. The process splits the material used a filtrate (the portion of the liquid that is bran occurs) and a concentrate (the fraction that the contains suspended particles that are normally on the Surface of the membrane would be deposited, the Mem bran would clog). This way a high Flow rate through the membrane for a long time Period of time can be maintained. The amount of wagered Material and concentrate must be controlled in a way the one that leads to a stable fluid flow. Self at low concentrate flow rates it is possible to have a stable flow of liquid to the surface surface of the membrane.

The dynamic microfiltration enables a wide range rich in effective surface speeds of the fil trationsmediums relative to the milk used. E.g. can an effective surface speed of about 3 m / sec up to about 50 m / sec, preferably from about 5 m / sec to about 30 m / sec and in particular from about 8 m / sec to about 20 m / sec be turned.

To achieve the desired surface speeds, must be a representative filter medium in the form of a cylinder approximately 6.35 cm (2.5 inches) in diameter with a Speed from about 1000 to about 6000 revolutions per Minute (rpm) are rotated, with a speed of about 5000 rpm is typical.  

When a dynamic disk filtration device is used, a typical disk filtration medium is from about 5 cm (2 inches) to about 120 cm (48 inches) in diameter. Such discs can e.g. B. with speeds from about 1000 rpm to about 8000 rpm and typically from about 3000 rpm to about 6000 rpm, depending on the design of the special dynamic microfilter that is used. The shear rates of such disk filters are typically in the range from about 100,000 sec ^-1 to about 400,000 sec ^-1 . The preferred disk filters include disk filters of the type described in US patent application 07/812 123 filed on December 24, 1991.

The size of the microfilter pores is chosen so that bacteria present in the milk are retained while still maintaining a sufficient flow rate through the microfilter. Suitable membranes include hydrophilic microporous membranes with good flow properties, a narrow pore size distribution and constant usage properties when removing relevant bacteria. The pore size of the microfilter membrane should be about 0.01 to about 5.0 µm, the value according to a method known to the person skilled in the art, such as the bubble point test (ASTM F316-86) or the K _L method (US Pat. No. 4,340,479 ) is determined. Preferably, the pore size is about 0.1 to about 1 micron. In particular, filters are used which have a pore size of approximately 0.2 to approximately 0.5 μm. Microporous filters of this type are known and readily available.

Preferred microporous membranes that can be set according to the invention is, are those sold by Pall Corporation under the trademarks Ultipor _N66 ®, Fluorodyne® and Posi dyne®, by the company Cuno Corporation under the Wa Renz calibrate Zetapor® and by the company Millipore membranes sold under the trademark Durapore®.

The cylindrical membrane elements suitable according to the invention comprise membrane elements which, according to a person skilled in the art known methods are tightly connected to a carrier.

Finally, the bacteria should be enriched in a stream be made up of less than about 5% of the feed makes, and more than about 95% of what is normally found in milk Solids and proteins found should cross the membrane for longer periods of time happen.

The dynamic microfilter can be in a single pass be driven without the need for repatriation of the concentrate. If necessary, the concentrate be returned to the feed. If a cylin dynamic dynamic microfilter is used, then can he ge at different ratios of filtrate flow together with the feed stream (concentration factors) be. The cylindrical dynamic microfilter is ever but advantageously with a ratio of filtrate to Feed material of over 90%, in particular of over 95% and very particularly preferably operated by over 98%, as above a filtrate with a very low bacterial content as to produce the desired product.

Similarly, a rotating dynamic disc microfilter at different ratios of filtrate flow operated on the entire feed stream. The out choosing a high ratio is reduced in a simple manner the throughput while operating at a low ver ratio leads to higher throughput. It is believed that operation at a ratio of about 40% is advantageous is to ensure a stable flow rate through the fil maintenance, although other conditions are also appropriate can be turned.

The filtration of freshly homogenized milk can be warm 40 ° C to 60 ° C can be done, which is at or slightly above  half the crystallization temperature of about 40 ° C the higher melting components of milk fat is. This is under half the temperature of conventional thermal Pasteurization can be applied. Alternatively, the Milk with a certain reduction in the flow rate at much lower temperatures, such as about 15 to about 35 ° C and especially from about 20 to about 25 ° C be filtered.

After microfiltration, the concentrate can be in a ge discarded as appropriate, further processing under thrown or used directly.

The method according to the invention can advantageously be used be implemented if it is the desired end product Whole milk, discontinued milk or skimmed milk.

Restrain the flow rates through the bacteria diaphragm of milk with a reduced fat content are usually higher than the flow rate of Milk with a high fat content. In some cases it is economically more advantageous, a milk with a higher Fat content, like milk with 2% fat, by mixing a fil skimmed milk with a filtered fat fraction put. This fat fraction can be a cream fraction with a minimum fat content of around 10%.

The filtration of the cream fraction can e.g. B. after the procedure of the US application with the serial no. 07/952 337 or under Use of a bacteria-retentive dead-end filtrate on cartridge. The filtration can be carried out in a large-scale nisch appropriate way by heating the fat composition to a point where it is in the liquid state located and easily filtered through a microporous membrane can be done. The preheated fat can be in front of the fil tration be homogenized. Alternatively, the fat can composition to be subjected to pasteurization in order to reduce their bacterial content, or it can be a combination  nation from pasteurization and microfiltration the.

If it is also the aim of the method, protein con centrates, e.g. B. from milk from a transgenic animal such as one transgenic cow, then get the dynamic micro filtration carried out to a high concentration of Kon to reach the center, using a micro porous membrane with a pore size of about 0.2 microns or we Niger.

Suitable devices for carrying out the This method can be achieved by connecting conventional equipment equipment including centrifugal separators, Microfilters, sterilization units, heat exchangers and Pumps are constructed. The skilled person is able to Ven tile for the control of current and pressure and others to provide necessary auxiliary equipment to make the device functional, and then others conventional modifications to such a device perform that required in a special case are.

The following examples are provided for further explanation special embodiments.

The following general methods were used in the examples applied.

Method A: Setting the temperature of the milk

Unless otherwise stated, it was the milk used in the following examples is commercially available Retail milk. The temperature of the Milk was subjected to an appropriate procedure prior to filtration temperature set. The preferred operating temperature (40 up to 60 ° C) was used because the majority of the fats in the Milk at this temperature did not crystallize Condition. A 35 l jacketed fermenter  (Type 3000 from Chemap A.G.) served as the working container. The container was filled with milk and the contents were heated to about 50 ° C using the hot water jacket, if nothing else is specified. The milk was made during the Er warm stirring to improve heat transfer.

As soon as the milk reaches the desired process temperature milk was at a rate of about 1 l / min pumped into a homogenizer.

Method B: homogenization of milk

When entering the homogenizer (Model 15 MR from the company APV Gaulin, Inc.) the milk was subjected to a two-stage homo generation process, initially at about 17.2 MPa (2500 psi) and then at about 3.4 MPa (500 psi). Start and operation were performed as described in the APV Gaulin operating manual is described for this unit. Typically, the Transfer the milk to a buffer tank after homogenization leads, which was provided with a coat and at the ge desired process temperature was maintained. That tank acted as a liquid buffer between the outlet of the Homoge nisators and the inlet of the filter. If necessary, could the homogenized milk returned through the homogenizer leads to a constant volume in the buffer tank right to maintain.

Method C: introduction of bacteria into the used Milk flow

In some experiments, the milk stream was artificially inoculated with bacteria to show the very high titer reduction possible according to the invention. The bacterial vaccination culture was added to the feed stream via a metering pump between the work tank and the homogenizer. The flow rate of the inoculum was adjusted so that a desired concentration of bacteria of about 10 ⁶ bacteria per milliliter of milk was achieved. Since the bacteria were introduced before the homogenizer, the bacteria were mixed well with the process liquid before they entered the filtration device. In most cases the E. coli strain ATCC 15224 was used.

An alternative method of inoculating milk with bacteria would be added directly to the bacteria desired concentration in the working container. A Such method is not preferred because it is the bacteria a long dwell time at temperatures above the reverse exposure temperature. This could, depending on the one set trunk, to an undesirable growth or killing the bacteria before entering the filtra lead device.

Method D: Bacterial Assay

Mesophile: Bacterial concentrations were determined by dilution series of samples determined. Appropriate dilutions were made passed through a sterile membrane with pores of 0.2 µm and grown on Mueller-Hinton agar for 24 hours at 32 ° C. These Procedures are detailed in a publication with the Title "Manual of Clinical Microbiology", 2nd edition (1974), ASM, Washington DC.

Listeria monocytogenes ATCC 43256 was the patho examined The populations of samples were determined using the method of Agello et al. (G. Agello, P. Hayes and J. Feeley, Abstracts of the Annual Meeting (1986), ASM, Washington DC, p. 5) and tries.

Method E: cleaning procedure

Disinfection and sterilization were carried out before each Ver such as carried out using 0.1 N sodium hydroxide. In the sterilization process, the membrane and all were there with connected equipment, first with water rinses and then with 0.1 N sodium hydroxide at 50 ° C for treated for about half an hour. The alkaline solution was then neutralized with phosphoric acid. This neutral The solution was then flushed through the system until all Sections were neutral. Filtration attempts were immediately carried out  telbar carried out according to this procedure. The entire equipment and the membrane elements were removed using Ste Disinfection procedure after the completion of each test graces.

Method F: Check the integrity

Each membrane element was put on before the bacteria were used Integrity examined. A forward current test like that in the publication NM 900a, "The Pall Ultipor membrane fil ter guide ", 1980 (available from Pall Corporation), has been described to check the integrity agile.

Description of the filtration device

• 1. The cylindrical dynamic microfilter
  The cylindrical dynamic microfilter (cylindrical DMF) used for these investigations was a device with the designation BDF-01, which was manufactured by Sulzer Brothers Limited, Winterthur, Switzerland. The equipment is from Rebsamen et al. (Dynamic Microfiltration and Ultrafiltration in Biotechnology, E. Reb samen and H. Zeigler, Proceedings of the World Filtration Congress IV, 1986, Ostend, Belgium). In this context, reference is also made to U.S. Patents 4,066,554 and 4,093,552.
• 2. Description of the membrane filter elements
  The membrane filter elements used in these experiments were typically nylon membranes of various qualities, such as Ultipor N ₆₆ ® and Posidyne ®, which are commercially available from Pall Corporation, Glen Cove, NY. The pore sizes were 0.2, 0.30, 0.45 and 0.65 µm. The membrane elements had a surface area of 0.04 m ² .
• 3. The dynamic microfilter in disc format
  The disc format consisted of a 15.24 cm (6 inch) diameter membrane support disc, which was placed on a hollow shaft and was in a sealed housing, with the required fluid inlet and outlet connections. The carrier disc had means for attaching the membranes to its surface in a sealed manner and contained drainage spaces to carry the filtrate flow through the membrane and the disc and out through the shaft. The effective membrane area was 0.014 m ² , and rotation speeds of up to 4500 rpm were possible.
• Any dynamic microfiltration disc units that have been explained above, can in the execution of the Invention are used. In connection with a wide dynamic microfiltration device in the disc form mat incorporated in the practice of the present invention can be set, is on the US patent application no. 07/812 123, which was filed on December 24, 1991 pointed.
• 4. Description of membrane filter elements
  The membrane filter elements were membranes of the same quality as described in the section on the cylindrical DMF. Typically, they were circular flat membranes that were cut to fit the disc DMF. When inserted into the dynamic microfilter, the filtrate chamber was sealed from the feed using a Q-ring. The membrane filter elements had a surface area of 0.014 m ² .

Method G1: Operation of the cylindrical dynamic microfilm ters

Before filtration, a filter element was used as in section described about the filter arrangements in the cylindrical dynamic microfilter (DMF) arranged. Disinfect and Sterilization was carried out using the method described as E written procedures performed. After observing the Method G2 described starting procedure was to filter  milk from the buffer tank via a positive displacement pump pumped the cylindrical DMF. The amount of concentrate was by a second pump or by a pressure relief valve til, which were connected to the concentrate outlet, control ert. Temperatures and flow rates of the application materials, the filtrate and the concentrate and the pressure of the Feed materials were at various times in the Ver run of the experiment, typically at intervals of 10 minutes ten, measured. The standard operating conditions of the cylindri DMF consisted of a rotation speed of 5000 rpm, a ratio of filtrate to feed of more than 95% and a feed pressure of about 0.13 to 0.20 MPa (1.3 to 2.0 bar). All examples with the This device were at a constant flow rate of the feed material.

Method G2: Start the dynamic filter

Before the introduction of milk into the dynamic filter warm, deionized, through a filter with a pore 0.2 µm filtered water through the system to start up the system. The Rotationsge Speed of the dynamic filter was on the operating brought speed while water through the system streamed. When the system reached equilibrium the milk flow switched on. The milk replaced the water in the system and the filtration started.

Method H: Operation of the dynamic disk microfilter

The one described in the section on filter arrangements Disk DMF filter element was inserted into the disk DMF puts. Disinfection and sterilization were carried out according to the Method E described procedures performed. After observing the starting procedure described for method G2 the milk to be filtered from the buffer tank in the disk DMF pumped. The amount of concentrate and feed pressure were arranged in the concentrate opening Valve controlled. Temperatures and flow rates of feed, filtrate and concentrate as well as the pressure  of the feed were at different times in the Ver run of the experiment, typically at intervals of 10 minutes ten, measured. A feed speed of around 960 ml / min was maintained for all examples. With the other given filtrate flow rates the values that were obtained when the current in the fil tration unit had stabilized.

Examples example 1

Skimmed milk was passed at room temperature at a rate of about 600 ml / min into a cylindrical DMF equipped with an Ultipor N ₆₆ ® membrane with a pore size of 0.45 µm. Operating conditions in the DMF were maintained as indicated for Method G1 and are summarized in Table I. Feed pressure began to rise rapidly a few minutes after the start of the test, indicating clogging of the microporous membrane.

Example 2

Skimmed milk was heated to 50 ° C according to method A and homogenized according to method B. The homogenized milk was then stored in a buffer tank for about 4 hours while the temperature of the milk was kept at about 50 ° C for this period. After this 4 hour delay, the milk was pumped into a cylindrical DMF equipped with an Ultipor N ₆₆ ® membrane with a pore size of 0.45 µm at a feed rate of approximately 600 ml / min. The preferred conditions of DMF operation as given in Method G1 have been maintained. The feed pressure started to increase rapidly after only a few minutes of operation, indicating clogging of the microporous membrane, and the test had to be stopped.

Example 3

Skimmed milk heated to 50 ° C by Method A and homogenized by Method B was placed in a cylindrical DMF equipped with an Ultipor N ₆₆ ® membrane with a pore size of 0.45 µm within no more than 5 minutes after Pump homogenization. The preferred conditions of DMF operation as set forth in Method G1 have been maintained. A stable filtrate flow rate of 1080 l / h / m ² was achieved until the milk supply was exhausted. No increase in feed pressure was observed in the course of the experiment.

After all the milk had been processed, the feed was turned on non-homogenized skimmed milk at 50 ° C without disturbing the System operation changed. That fell within a few minutes Milk filtrate flow rate drops rapidly, and the Sy stem pressure rose, indicating that constipation of the mem bran had occurred. This example clearly shows the need maneuverability to homogenize milk to a significant To achieve flow through the microfiltration membrane.

Examples 1-3 show that it is necessary to refer to the Enough shear (in this case by the homogenization), namely before the filtration in order to sufficiently reduce the emulsion particle size of the milk gladly, so that a passage through the microporous membrane is possible Lich and in this way a perfect filtration he is aimed. In particular, Example 2 shows that the particles size distribution to larger particle sizes within one returns shortly after homogenization. For Correct filtration therefore requires homogenization within a short period of time before filtration, so about in less than 5 minutes and preferably in shorter time.

Example 4

Skimmed milk was preheated according to method A and pumped into a disc DMF equipped with an Ultipor F ₆₆ ® membrane with a pore size of 0.45 μm. The method described in Method H was used. A steady flow of filtrate quickly established and was maintained for about 100 minutes until the milk supply was exhausted.

The operating conditions of the disc DMF produce a calculated shear rate of approximately 200,000 sec ^-1 in the space between the rotating disc and the membrane. This shear is in the range of the shear rates generated by homogenizers under the conditions of Method B.

This example shows that the required shear before filtration can be achieved in one step, ie without the need for a separate homogenizer. This example clearly shows that the membrane was not blocked by solids from the milk and that the shear of about 200,000 sec ^-1 generated by the rotation of the disk was sufficient to reduce the particle size in the skim milk so that it could pass through the microfilter membrane was made possible, which ensured perfect filtration.

Table 1 summarizes the results of Examples 1-4; the data show that a steady flow of filtrate is achieved through the membrane when sufficient Sche on the milk within a short time before the fil tration is exercised.

Table 1

Example 5

The relationship between particle size and time after to determine the homogenization, skim milk according to Me Method A heated and according to the method B described Process homogenized. The particle size distribution in be pull after the homogenization was determined. The Particle size distribution was determined using a Be drawing "Integrated Micro-Optical Liquid Volumetric Sensor" (IMOLV-.2), manufactured by Particle Measurement Systems, Colorado, is available, measured. This laser particle tough ler is designed to have the particle size distribution measures in the range of about 0.1 to 5.0 microns.

The milk samples were diluted in a ratio of 1: 300,000 and then subjected to the analysis as it is in the business book for the IMOLV device is specified. About a mem bran with a pore size of 0.04 µm filtered, deionized water with an electrical resistance of 18 Megaohm and a particle number of less than 50 per milli liter was used to dilute the milk samples.

Fig. 2 shows the results of the particle analysis. A graphical representation of the number of particles, based on the number of particles after 5 seconds, against the particle size is shown in the figure. The figure clearly shows that the number of larger particles increases with the time after homogenization. Since the number of small particles decreases simultaneously over this period, it is evident that the small particles agglomerate over time to form larger particles.

Examples 6 to 9

Membranes of various pore sizes and bacterial retention properties were tested in a cylindrical DMF to determine what size of stationary filtrate flow milk can be obtained. The general method that  for Examples 6 to 9 was used below specified.

• 1. The desired membrane filter element was in the zylindri arranged DMF.
• 2. An integrity test as described in method F. has been carried out. The membrane filter element was not used if it meets the requirements of the test not satisfied.
• 3. The equipment was disinfected according to Method E.
• 4. The milk to be filtered was prepared according to the method A described method preheated.
• 5. The milk was homogenized according to method B.
• 6. The starting procedure described in method G2 was carried out.
• 7. The milk was poured from the buffer tank into the cylindrical one DMF with the desired flow rate leads.
• 8. The operating parameters were determined using the parameters from Me method G1 specified guidelines set.
• 9. Appropriate measurements were made.

Typically, the cylindrical DMF was operated at 5000 rpm, which corresponded to a shear rate of approximately 10,000 sec ^-1 in the filter. The feed temperature was 50 ° C and the feed pressure varied from 0.13 to 0.20 MPa (1.3 to 2.0 bar). The filtrate to feed ratio was maintained above 95% in each of these examples. The flow rate shown in Table 2 is the steady flow of filtrate typically achieved 15 minutes after the start of the filtration. The total time of the experiment varied from case to case since the volume of filtered milk was constantly 30 l.

Example 6

In this example, an Ultipor N ₆₆ ® membrane with a pore size of 0.2 µm was used. A feed rate of 250 ml / min was chosen in order to obtain a stationary filtrate flow of 300 l / h / m ² . The filtration lasted about 130 minutes with no noticeable drop in the filtrate flow rate, at which point there was no more milk in the working container.

Example 7

In this example, an Ultipor N ₆₆ ® membrane with a pore size of 0.30 µm was used. A feed rate of about 550 ml / min was chosen to achieve a steady flow of 775 l / h / m ² for about 60 minutes, after which the experiment was stopped.

Example 8

In this example, an Ultipor N ₆₆ ® membrane with a pore size of 0.45 µm was used. A feed rate of 740 ml / min was chosen to achieve a steady flow of 1080 l / h / m ² . Filtration lasted about 40 minutes with no apparent drop in flow rate, after which the milk supply was exhausted and the experiment ended.

Example 9

In this example, an Ultipor N ₆₆ ® membrane with a pore size of 0.65 µm was used. A task speed of 1100 ml / min was chosen to achieve a steady flow of 1680 l / h / m ² . Filtration lasted approximately 30 minutes, after which the milk supply was exhausted and the experiment ended.

Examples 6-9 are summarized in Table 2. The Data show that by using the Fil stable filtrate flow rates can be achieved using ver different qualities of bacteria retaining membranes. The table shows that Mem branches with smaller pores and thus with larger back sustainability for bacteria can be used, and at the expense of filtrate flow rates.  

Table 2

Flow of milk using different membranes in a cylindrical DMF

Example 10

In this example, a Posidyne® membrane with a po sititive surface charge and a pore size of 0.2 µm used. The pore surface of the membrane used is che occupied by quaternary ammonium groups. She assigns one high absorption capacity for biological material.

A feed rate of 260 ml / min was chosen to achieve a steady flow of 360 l / h / m ² . The filtrate flow was of the same order of magnitude as that obtained with the uncharged membrane described in Example 6. Filtration lasted approximately 120 minutes with no discernible drop in filtrate flow rate, at which point there was no milk in the working container. A filtrate to feed ratio above 97% was maintained throughout the experiment. Further experimental conditions are given in Table 3.

It was expected that a large amount of proteins from the Milk form a bond with the membrane surface and it would eventually clog. This example shows that at a dynamic mode a membrane that is normally a Affinity for proteins shows is well suited.

Example 11

A feed rate of 740 ml / min of whole milk was chosen and a stable filtrate flow of 1130 l / h / m ² was achieved. Further experimental conditions are given in Table 3. Filtration lasted approximately 40 minutes, after which the milk supply was exhausted and the experiment ended.

This example shows that whole milk using the he inventive method can be filtered. The observ eighth difference in filtrate flow rates between whole milk and skimmed milk (as in Example 9) mainly due to the differences in their viscosities to be traceable. The ratio of the filtrate flow rate Speed for whole milk to skim milk is approximate equal to the ratio of the viscosities of whole milk and Ma germilch.

Table 3

Examples 12 to 16

Examples for the determination of the filtrate flows through ver different membranes with bacterial retention using the dynamic disc microfilter again get. The general procedure for Examples 12-16 is described below. The conditions described generally apply to any example, unless from something else is expressly stated.

• 1. The desired membrane filter element was in the disc DMF arranged.
• 2. An integrity test as described in method F. has been carried out. The membrane filter element was not used if it meets the requirements of the test not satisfied.
• 3. The equipment was disinfected according to Method E.
• 4. The milk to be filtered was prepared according to the method A pre-warmed procedures.
• 5. The milk was homogenized according to method B.
• 6. The general starting procedure described in method G2 was carried out.
• 7. The milk was taken from the buffer tank into the disk DMF the desired flow rate transferred.
• 8. Appropriate measurements were made.

Typically, the disk DMF was held at 3500 rpm, which corresponds to a calculated shear rate of approximately 200,000 sec ^-1 . The feed temperature was 50 ° C and the feed pressure was maintained at about 0.02 MPa (0.2 bar). Milk was pumped into the filter at a rate of 960 ml / min to maintain a high cross-flow rate across the membrane. The ratio of filtrate to feed material was set specifically for the membrane pore size, the application temperature and the rotor speed. The unfiltered portion of the feed was returned to the work tank. The flow rate given below is a stationary filtrate flow rate which was achieved through the membrane, typically half an hour after the start of the filtration.

Example 12

An Ultipor N ₆₆ ® membrane with a pore diameter of 0.2 µm was used for this example. A stationary Fil flow rate of 850 l / h / m ² was achieved.

Example 13

An Ultipor N ₆₆ ® membrane with a pore diameter of 0.45 µm was used for this example. A steady flow rate of 1600 l / h / m ² was achieved.

Example 14

A Posidyne® membrane with a pore diameter of 0.45 µm was used for this example. A stationary filtrate flow of 1600 l / h / m ² was achieved.

The data shown in Table 4 summarize Examples 11 to 13 together. The data show that by using the invented Filtration method according to the invention stable filtrate flow restrain speeds using bacteria tendency membranes with different quality can be achieved can while using a disc DMF. The table shows that membranes with smaller pores and consequently increased bacterial retention (titer reduction) according to the invention at the expense of the filtrate flow rate ten can be used.  

Table 4

Example 15

Skimmed milk homogenized according to Method B at 18 ° C was pumped into a disc DMF which was equipped with an Ultipor N ₆₆ ® membrane with a pore size of 0.45 µm. The filtration was carried out at a feed rate of 860 ml / min, a stationary filtrate flow of about 860 l / h / m ^{2 being} achieved through the membrane. The filtered milk was measured at 25 ° C. Further conditions for this example are given in Table 5.

This example shows that chilled skimmed milk at about 18 ° C according to the inventive method with a membrane Bacterial retention can be processed. One takes indicates that the reduced filtrate flow at this tempera the higher viscosity of the milk at this temperature, compared to higher temperatures.

Example 16

A disc DMF was equipped with an Ultipor N ₆₆ ® membrane with a pore size of 0.45 µm. Whole milk was fed to the slices of DMF at a rate of 900 ml / min and a stationary filtrate flow of about 850 l / h / m ^{2 was} achieved through the membrane. This experiment was carried out without recycling the unfiltered portion of the feed stream.

This example shows that whole milk can be filtered according to the method of the invention using a disc DMF. Skim milk led to an almost stationary filtrate flow of approximately 1600 l / h / m ² under essentially identical conditions. The observed difference in the filtrate flow rates between skim milk and whole milk can be roughly attributed to the differences in the viscosities of the liquids.

Example 17

Using the methods described above, a filtration experiment was carried out with a disk DMF while maintaining a high ratio of filtrate to feed material. An Ultipor N ₆₆ ® membrane with a pore diameter of 0.45 µm was used in this experiment. The skim milk feed rate was maintained at 115 ml / min and a rotational speed of 2100 rpm was used. A filtrate flow of 460 l / h / m ^{2 was} achieved.

Table 5

Example 18

In order to show a longer operation, a test was carried out with a large amount (500 l) of raw, unpasteurized skimmed milk. The milk was preheated to 50 ° C by passing it through a plate heat exchanger. It was then homogenized according to method B and then pumped into a cylindrical DMF, which was equipped with a membrane with a pore diameter of 0.65 μm. Typically, the dynamic microfilter was held at 5000 rpm for this example. The feed pressure varied from 0.13 to 0.15 MPa (1.3 to 1.5 bar) at a feed rate of approximately 1300 ml / min. The ratio of filtrate to feed was kept above 95%. A stationary filtrate flow of about 1680 l / h / m ² was achieved. There was no drop in the flow rate of filtered milk and no increase in feed pressure during the 6 hours of continuous operation required to process the 500 liters.

This example shows that it is possible that the fiction use appropriate filtration processes for longer periods.

Example 19

This example shows that it is possible that the fiction Moderate method of filtering milk using a disc DMF for the purpose of obtaining proteins from to apply the milk. Proteins in milk generally show a size range of about 0.02 to about 0.30 µm (D.G. Schmidt, P. Walstra and W. Buchheim, Neth. Milk Dairy J., Vol. 27 (1973), p. 128) on what they have to gain after makes accessible method according to the invention. This is especially true especially for the production of biologically important proteins transgenic animals such as transgenic cows, sheep and the like, which have been genetically engineered to be according to those skilled in the art already known techniques for the production of such Pro stimulate teine, important.  

A disc DMF was used which was equipped with a nylon filter with a pore size of 0.2 µm. The filtration of the milk was carried out at a feed rate of 840 ml / min, a stationary permeate flow of about 850 l / h / m ^{2 being} achieved through the membrane, namely at a rotor speed of 3500 rpm, the retentate being recycled while the permeate was discarded in the present method. Samples of the feed, permeate and retentate were taken periodically, which were then analyzed for the total protein content according to the Kjeldahl method. It was found that the protein content in the retentate was initially the same as in the feed, but increased with a longer-lasting return of the retentate (retentate: 4.9%, feed material: 3.1%).

The use of a membrane with a smaller pore size should have an even better concentration of protein in the Allow concentrate flow.

Examples 20 and 21

These examples were performed to show that none Fractionation of components in the milk during the Filtration method according to the invention occurs. In these Examples were samples from the feed, the filtrate and the concentrate at different times during the Filtration analyzes the protein concentrations after the Kjeldahl method and the total solids content by Determine evaporation.

Example 20

Samples of feed, filtrate and concentrate were added different times during the be in Example 18 written test and on their total content Solids analyzed in every stream. The data in Table 6 show that there is no substantial depletion at the entire festival substances from the filtrate when using a membrane a pore size of 0.65 µm occurred.  

Example 21

Samples of feed, filtrate and concentrate were added different times during the execution of Bei taken from game 13 and the total solids content and analyzed proteins in each stream. The dates are in Table 6 shown. Again, no major deception solids and / or proteins from the filtrate milk when using a membrane with a pore size of 0.45 µm detected.

Table 6

Examples 22 to 28

Examples 22 through 28 were performed to show that it is possible with the method according to the invention, Bak remove terie from milk. The general procedure ent said that applied in the experiments of Examples 6 to 18 procedures, with the exception that bacteria according to method C were added to the working current. E. coli bacteria that were usually found in milk in these versu Chen used as vaccine cultures, unless otherwise stated ben is. Samples of feed, filtrate and Bacterial concentrate was selected at different times filtration using sterile techniques taken. These samples were applied to the bacteria Method D explained above was examined. The results are given in Table 7.  

As shown in this table, it is in accordance with the invention possible a dramatic reduction in the bacterial content of milk. The high proportion of E. coli bacteria removed is directly more distant Bacillus cereus bacteria transferable using conventional pasteurization not completely removed can be. E. coli is known to be a rod structure with dimensions of approximately 1.1 to 1.5 µm by 2 to 6 µm, while Bacillus bacteria such as Bacillus cereus have similar dimensions, and they also have Rod structures with dimensions of approximately 1.0 to 1.2 µm times 3 to 5 µm. The ability to remove E. coli as indicated in Table 7, also means that the Ver is able to drive the very undesirable Bacillus remove cereus bacteria, resulting in a milk with a very long shelf life even at room temperature.

Examples 22, 23 and 24

Examples 6, 8 and 9 were repeated with the exception that that E. coli was introduced into the working stream according to method C. has been. Samples of feed, filtrate and concentrate were taken for bacterial analysis. The data for ver Reduction in titer are shown in Table 7.

Example 25

Example 13 was repeated, except that bacteria were introduced into the Method C feed stream and that the bacterial concentrate was not returned to the process vessel. A stationary milk flow of approximately 1600 l / h / m ^{2 was} achieved. The microbiological data are shown in Table 7.

The filtered milk contained only very low concentrations of 7 to 10 bacteria per milliliter of milk, which was dramatically below the concentration of the feed of 10 ⁶ per milliliter. The reduction in titer in this case was more than 10 ⁵ . For comparison, only reductions in the titer of about 10 ² to 10 ^{3 are} achieved in the conventional pasteurization of milk.

Example 26

The experimental conditions and procedures of Example 12 were repeated in this experiment, except that E. coli was added to the Method C feed stream and the concentrate was not returned to the process vessel. A steady milk flow of about 850 l / h / m ² was achieved. Samples of feed, filtrate and concentrate were taken for bacterial analysis. The data listed in Table 7 show a reduction in the titre of more than 10⁶. The fact that no bacteria were detected in the filtered milk shows that it has been able to produce sterile milk.

This example shows that with the Ver is possible to drive bacteria out essentially completely Remove milk using a disc DMF and a suitably chosen membrane. In this way can be made sterile milk.

Example 27

Unpasteurized raw milk contains a variety of org nisms, including coliform bacteria such as E. coli, and pathogens such as Listeria and Campylo bacteria, and Bacillus cereus. In this example, the Raw milk is not inoculated with bacteria from the outside, but the Rather, milk was based on the inherent or "native" bacteria rien examined.

Samples of feed, filtrate and concentrate were used Bacterial analysis during the execution of experiment 18 ent taken and analyzed for native bacteria according to method D.

Only 14 bacteria per milliliter were found in the filtrate. The feed had 2500 bacteria per milliliter and the concentrate 2 × 10 ⁴ bacteria per milliliter.

Furthermore, no psychrophilic bacteria were found in the filtrate posed. Psychrophilic bacteria are Bak teries that grow at low temperatures and a ver cause chilled milk.

Table 7 summarizes experiments 22 to 27. The data show that both when using cylinders and Slices an improved reduction in titer at the expense of the filtrate flow can be achieved. The table also shows that it is possible by choosing the right one Membrane to obtain a sterile milk filtrate.

Table 7

Example 28

In addition to bacteria (E. coli), for which the reduction of the Ti t has been investigated, there is a pathogenic organism in milk men, like Listeria, which are of practical importance for whey are crying. These pathogens pose a greater challenge tion as the coliform bacteria (E. coli), which are also found in dynamic filters were examined. The investigations were carried out according to Method D to determine whether the  membrane filter elements used these pathogens effectively remove. This test was carried out in an off-line test device and not in a dynamic filter guided.

The data shown in Table 8 clearly show that a Ulti por N ₆₆ ® membrane microns with a pore size of 0.45 and a specific bubble point (ASTM F316-86) enables complete removal of Listeria.

Table 8

Reductions in titer of pathogenic organisms in milk using Pall membranes

Example 29

Filtered Ma prepared according to the method of Example 16 Germ milk is collected in a disinfected container.

Commercially available cream is heated to 65 ° C and .mu.m by a Ultipor N ₆₆ ® filter cartridge with a pore size of 0.2, which is obtained from Pall Corporation, East Hills, NY Lich, filtered, with a minimum reduced copy titer on E. coli bacteria of 10 ⁶ . The filtered cream is largely depleted of bacteria and is collected in a disinfected container.

The filtered skimmed milk and the filtered cream are ver unites and homogenizes to a milk with a fat content of 2% and a reduced bacterial content.

Claims (4)

1. Process for the treatment of raw milk for the production of treated milk with a lower bacterial content than the raw milk, characterized by the following stages:

• (1) the milk is separated into a fat fraction with a minimum fat content of about 10% and a skimmed milk fraction;
  (2) the skimmed milk fraction is homogenized and subjected to dynamic microfiltration within about 5 minutes after homogenization by passing the skimmed milk fraction through a microfilter with a medium pore size sufficient to reduce the bacterial content of the milk flowing through, to obtain a filtrate with a lower bacterial content compared to the skimmed milk fraction used and a concentrate with a higher bacterial content compared to the skimmed milk fraction used;
  (3) the bacterial content of the fat fraction is reduced in a separate step; and
  (4) the skimmed milk fraction after microfiltration and the fat fraction with the reduced bacterial content are combined.

2. The method according to claim 1, characterized in that that the bacterial content of the fat fraction by dynamic Mi crofiltration is reduced. 3. The method according to claim 1, characterized in that the bacterial content of the fat fraction by pasteurization is reduced. 4. Process for the production of milk with a fat content of about 2%, characterized by the following stages:
(1) a skimmed milk fraction is homogenized;
(2) within about 5 minutes after homogenization, the skimmed milk fraction is subjected to dynamic microfiltration by passing the skimmed milk fraction through a microfilter with a medium pore size sufficient to reduce the bacterial content of the milk flowing through to carry a filtrate to obtain a lower bacterial content compared to the skimmed milk fraction used and to obtain a concentrate with a higher bacterial content compared to the skimmed milk fraction used;
(3) the bacterial content of the cream fraction with a minimum fat content of about 10% is reduced; and
(4) the skimmed milk fraction after the microfiltration and the cream fraction with the reduced bacterial content are combined.