the combination of the process steps , in particular the sequence of ultra - and microfiltration steps , which is preferably also still performed at low temperatures , prevents the growth of thermophilic microbes , which cannot be completely killed by heat treatment . insofar as growth of mesophilic microbes occurs , these are completely removed in the pasteurization step . this leads to a microbially excellent product . in the following table a , the typical specification requirements for a near sterile whey protein concentrate and the results achieved with the process according to the invention are summarized : the core of the process according to the invention is the sequence of first ultrafiltration , microfiltration and second ultrafiltration . the essential difference between micro - and ultrafiltration lies in the different pore sizes and in the different membrane structure such as the materials and the filter materials involved . a filtration through membranes with a pore size & lt ; 0 . 1 μm is as a rule described as ultrafiltration , while filtration at pore sizes & gt ; 0 . 1 μm is usually described as microfiltration . in both cases , purely physical , i . e . mechanical membrane separation processes are involved , which operate on the principle of mechanical size exclusion : all particles in the fluids which are larger than the membrane pores are held back by the membrane . the driving force in both separation processes is the differential pressure between inflow and outflow of the filter surface , which lies between 0 . 1 and 10 bar . depending on the use field , the material of the filter surface can consist of stainless steel , plastic , ceramic or textile fabric . there are various forms of filter element : cartridge filters , flat membranes , spirally wound modules , bag filters and hollow fibre modules which are all in principle suitable in the sense of the present invention . in the dairy industry , the preconception has long prevailed that for the removal or microorganisms in milk fractions the pore diameter should in general not be below a value of 0 . 5 μm . however , the invention includes the discovery that for the production of a microbially excellent whey protein concentrate a diameter in the range from 0 . 8 to even 1 . 6 pm and preferably 1 . 1 to 1 . 4 μm in the microfiltration step is entirely sufficient , if the majority of the microbes have previously been removed by ultrafiltration . in combination of this comparatively larger pore diameter with a microfiltration unit which essentially consists of a ceramic membrane , the problem of frequent blocking is simultaneously solved . furthermore , there is the preconception that the removal of microbes by means of filtration steps requires a temperature of at least 55 ° c ., since only under these conditions can adequate throughputs of about 450 to 550 lm 2 hr be achieved , while at temperatures of for example 20 to 30 ° c ., only flows of at most 100 l / m 2 hr can be achieved . hot filtration has however the substantial disadvantage that after about 4 hours filtration time , the heat - resistant microbes and spores begin to grow through the membrane and to proliferate again in the permeate . in the context of the process according to the invention , a particular advantage therefore consists in that the ultrafiltration is performed in the cold , that is at 4 to 25 and in particular 6 to 12 ° c . and the microfiltration also at low temperatures of about 6 to about 30 ° c . and in particular about 12 to about 25 ° c ., since the growing through of the microbes is in this way prevented and surprisingly a flow rate of 200 to 300 l / m 2 hr is nonetheless achieved . the heat treatment of the permeate from the last filtration step preferably takes place in heat exchangers , for which plate heat exchangers in particular have proved especially suitable . a temperature gradient is present on the heat exchangers , which is however selected such that the permeate is heated to a temperature of about 70 to 80 ° c . and in particular about 72 to 74 ° c . for a residence time of at least 20 and at most 60 seconds , preferably about 30 seconds . in a first alternative embodiment , the permeate can also be pasteurized by direct steam injection ( dsi ). this has the advantage that the slow passage through a temperature range in which mesophilic and thermophilic spores find optimal growth conditions is significantly shortened by flash heating . this is achieved by the direct injection of hot or even superheated steam , which can have a temperature of 100 to about 250 ° c . this is usually effected by means of nozzles which either dip directly into the product or are built into a side arm of the heat exchanger . the principle of dsi consists in that a superheated jet of steam under pressure is passed into a nozzle chamber and then decompresses through a perforated pipe (“ radial steam jet diffuser ”) into the liquid product to be heated . the high pressure flow creates a rapidly expanding radial heat exchange field as a result of which uniform heating of the product is achieved in very short periods . as explained at the start , the purpose consists in adjusting the milk product to an exact temperature in a very short time , preferably 1 to about 5 seconds and in particular 1 to 2 seconds . for this , it is necessary to pass a precise as possible a volume of steam into the product at high speed . if the steam volume is controlled via a pressure reducing valve , the velocity of the steam as a rule falls below the speed of sound , which leads to the product not heating up sufficiently fast . in order to prevent this , in the sense of the process according to the invention , the steam is preferably fed in under so - called “ choke - flow ” conditions , since this makes it possible to introduce the steam even at ultrasonic velocity directly into the product to be heated . this is understood to be the phenomenon of increasing the steam velocity by creating a pressure difference by mans of a special nozzle . suitable components are for example obtainable commercially from the firm prosonics . dsi requires no preheating of the substance used , i . e . the permeate from step ( c ) can be used directly . however , the smaller the temperature differences are , the more precise is the temperature control . in a second alternative embodiment , the permeate can also be pasteurized by ( steam ) infusion . this process has been known since the 1960 &# 39 ; s . essentially , the heating can be performed in two steps , wherein the material to be heated is sprayed into a pressure chamber filled with hot steam and the heating or pasteurization takes place as the droplets fall . however , since the year 2000 , the so - called pdx process has gained in importance . in this , the material to be heated is vaporized and abruptly heated in a flow of superheated steam . the steam flow advancing at ultrasonic velocity homogeneously distributes the product droplets so that a multiphase flow is created , in which the heating gently takes place only at the boundaries of the droplets . in this way , condensation of the droplets is also effected . here the steam can have a temperature of about 100 to about 250 ° c . and in particular about 120 to about 150 ° c ., and the infusion requires a time typically of 1 to 5 and in particular about 2 to 3 seconds . in a further preferred configuration , the infusion heating takes place in such a manner that product and steam are alternately sprayed into a reactor via concentric annular nozzles , so that a steam pressure gradient from inside to outside is produced . as a result , the droplets are held away from the walls and cannot overheat . it is likewise desirable during the cooling also to pass through the temperature range critical for microbial growth as quickly as possible . for this , flash cooling has proved especially effective . this is understood to mean a process in which the hot liquid product is “ flashed ” under turbulent flow conditions into a reactor which is under reduced pressure , so that the boiling point of water is lowered below 30 ° c . in support , the jacket of the flash reactor can additionally be further cooled . the cooling of the pasteurized product requires about 1 to 5 seconds , with the final temperature usually lying at about 25 to about 30 ° c . the drying of the pasteurized product can be effected in a manner known per se . preferably spray drying is used for this , wherein the temperature in the inlet is typically about 180 to about 260 ° c . and at the outlet about 80 to about 105 ° c . low temperatures are preferred since in this way the danger of the proteins denaturing is decreased . alternatively , the products can also be dewatered by freeze - drying . further additives , such as for example lecithins , vitamins or food emulsifiers [ ep 1314367 a1 , nestle ] and the like , can also be added to the homogenized concentrates before the spraying . the whey protein concentrates obtained in this manner have a protein content of at least 60 wt . % and preferably about 65 to about 90 wt . % and in particular about 70 to about 85 wt . %. the process is shown again schematically in fig1 . the meanings of the abbreviations in this are : uf 1 = 1 st ultrafiltration mf = microfiltration uf 2 = 2 nd ultrafiltration uht = ultra - high temperature heating = pasteurization spt = spray drying mpc85 = whey protein concentrate with 85 wt . % protein content 1 , 000 kg of whey were subjected to an ultrafiltration at a temperature of 8 ° c ., in which a spiral wound membrane with a pore diameter of 0 . 05 μm was used . lactose , ash and urea were removed with the permeate and discarded , while the retentate , after passage through a heat exchanger in which it was preheated to 25 ° c ., was fed into a microfiltration . here a ceramic membrane with a pore diameter of 1 . 1 μm was used . the retentate , which contained fat and casein , was discarded , while the permeate at 25 ° c . was subjected to a second ultrafiltration , which once again was performed with a spiral wound membrane with a pore diameter of 0 . 05 μm . the permeate was discarded , but the retentate was fed into a pasteurization in an ultra high temperature heater , in which it was heated to 72 ° c . in 30 seconds . next , the pasteurized product was transferred into a spray tower , in which with an inlet temperature of 200 to 220 ° c . ( outlet temperature : 80 ° c .) it was freed from water . ca . 4 . 5 kg of a sterile , pourable whey protein concentrate were obtained , which had a protein content of 85 wt . %. the service life of the microfiltration membrane here was at least 24 hours . example 1 was repeated , but the pasteurization performed by means of a dsi . for this hot steam at 220 ° c . was injected into the product for 2 seconds , as a result of which it heated up to ca . 75 ° c . 1 , 000 kg of whey were fed at a temperature of 8 ° c . into a plate heat exchanger and heated to 55 ° c . next the product was subjected to an ultrafiltration in which a spiral wound membrane with a pore diameter of 0 . 05 μm was used . lactose , ash and urea were removed with the permeate and discarded , while the retentate was fed into a microfiltration . here a ceramic membrane with a pore diameter of 1 . 1 km was used . the retentate , which contained fat and casein , was discarded , while the permeate still at 55 ° c . was subjected to a second ultrafiltration , which once again was performed with a spiral wound membrane with a pore diameter of 0 . 05 μm . the permeate was discarded , but the retentate fed into a pasteurization in a high temperature heater , in which it was heated to 72 ° c . in 30 seconds . next , the pasteurized product was transferred into a spray tower , in which with an inlet temperature of 200 to 220 ° c . ( outlet temperature : 80 ° c .) it was freed from water . ca . 4 . 5 kg of a sterile , pourable whey protein concentrate were obtained , which had a protein content of 67 wt . %. the service life of the microfiltration membrane was however only 6 hours , after which the process had to be interrupted and the membrane cleaned . example 1 shows that , in comparison with the prior art , according to the process according to the invention a larger quantity of concentrate with higher protein content is obtainable and this is associated with the additional advantageous effect of markedly longer membrane service lives .
a method for production of near sterile whey protein concentrates is proposed , which comprises the following steps : ultrafiltration of whey at a temperature of about 2 to about 25 ° c . to produce a first retentate r 1 and a first permeate p 1 ; microfiltration of the retentate r 1 from step at a temperature of about 2 to about 35 ° c . to produce a second retentate r 2 and a second permeate p 2 ; ultrafiltration of the second permeate p 2 from step at a temperature of about 6 to about 25 ° c . to produce a third retentate r 3 and a third permeate p 3 ; pasteurization of the retentate r 3 from step drying of the pasteurized product from step .