Method and system for directly heating a protein-enriched milk product by introducing steam into said milk product

Abstract

Directly heating a protein-enriched milk product occurs by introducing steam, the direct heating taking the form of an infusion or injection method. The described technique significantly extends service time, ensuring a content of non-denatured whey proteins in the treated protein-enriched milk product greater than that obtained in the prior art. The milk product, which is preheated and kept at temperature is indirectly cooled before direct heating by a recuperative cooling step from the preheating temperature to a cool-down temperature with a temperature difference ranging from 5 K to 10 K. The direct heating from the cool-down temperature to the high pasteurization temperature is controlled by direct heating setting parameters which are known per se. Finally, the milk product is cooled by flash cooling from the high pasteurization temperature to a necessarily required exit temperature.

Claims

1. A method for directly heating a protein-enriched milk product by introducing steam into the protein-enriched milk product, wherein: (a) during direct heating, the steam heats the protein-enriched milk product to produce a high-temperature pasteurized protein-enriched milk product by means of direct high-temperature pasteurization to a high pasteurization temperature, (b) before the direct heating, the protein-enriched milk product is preheated indirectly to a preheating temperature and, following on from the preheating when viewed in a direction of flow of the protein-enriched milk product, a first instance of keeping the protein-enriched milk product at the preheating temperature is carried out for a defined and controlled first dwell time, (c) following on from the direct heating to the high pasteurization temperature when viewed in the direction of flow of the protein-enriched milk product, a second instance of keeping the protein-enriched milk product at the preheating temperature is carried out for a defined and controlled second dwell time, (d) flash cooling the protein-enriched milk product by means of decompression of the steam from a first pressure to a lower pressure, and removal of water from the high-temperature pasteurized protein-enriched milk product in an amount corresponding to that of the steam supplied to the high-temperature pasteurized protein-enriched milk product that has been kept at the preheating temperature, the protein-enriched milk product that is preheated indirectly and kept at the high pasteurization temperature is indirectly cooled before the direct heating by means of a recuperative cooling step so that a temperature difference between the preheating temperature and a cool-down temperature is in a range from 5 K to 10 K, the direct heating from the cool-down temperature to the high pasteurization temperature is controlled by means of adjusting direct heating setting parameters, and in accordance with the feature (d), the protein-enriched milk product is cooled by flash cooling from the high pasteurization temperature to an exit temperature.

2. The method according to claim 1, wherein: the temperature difference is 10 K.

3. The method according to claim 1, wherein: the direct heating setting parameters are pressure, temperature, and a duration of action of the steam.

4. The method according to claim 1, wherein: the direct heating is achieved by means of an infusion method.

5. The method according to claim 1, wherein: the direct heating is achieved by means of an injection method.

6. The method according to claim 2, wherein: the direct heating setting parameters are pressure, temperature, and a duration of action of the steam.

7. The method according to claim 6, wherein: the direct heating is achieved by an infusion method.

8. The method according to claim 2, wherein: the direct heating is achieved by an injection method.

9. The method according to claim 3, wherein: the direct heating is achieved by an infusion method.

10. The method according to claim 3, wherein: the direct heating is achieved by an injection method.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is represented in more detail by the following description and the appended figures of the drawing and the claims. While the invention is realized in a wide variety of embodiments of a method of the generic type and in a wide variety of embodiments of a system of the generic type for carrying out the method, a preferred exemplary embodiment of the method according to the invention and of the system according to the invention are described in the following based on the drawing.

(2) FIG. 1 is a schematic representation of a system according to the prior art for directly heating a protein-enriched milk product by introducing steam into said milk product.

(3) FIG. 2 is a schematic representation, proceeding from the known system according to FIG. 1, of the system according to the invention having a cooler arranged according to the invention.

(4) FIG. 3 is a block diagram of the method according to the prior art (Experiment I).

(5) FIG. 3A is a block diagram of the method according to the invention comprising cooling by ?TK=5 K (Experiment II).

(6) FIG. 3B is a block diagram of the method according to the invention comprising cooling by ?TK=10 K (Experiment III).

(7) FIG. 4 shows a detail from the system according to FIG. 2 in the region upstream of a direct heating apparatus for carrying out the method according to the prior art, without cooling of or a cooling procedure performed on the milk product that has been preheated and kept at temperature.

(8) FIG. 5 shows the detail from the system according to FIG. 2 for carrying out the method according to the invention, with the cooling according to the invention of the milk product that has been preheated and kept at temperature by means of the cooler arranged according to the invention.

(9) FIG. 6 is a graphical, normalized representation of the measured values for the content of non-denatured ?-lactoglobulin, determined in Experiments I to III, from a protein-enriched milk product treated in the system according to the invention according to FIGS. 2, 4, and 5.

(10) FIG. 7 is a graphical, normalized representation of the measured values for the content of furosine, determined in Experiments I to III, from a protein-enriched milk product treated in the system according to the invention according to FIGS. 2, 4, and 5.

(11) FIGS. 8A-10B show photographs of product fouling or of the fouling layer in the inlet of the second conveying apparatus arranged downstream of the direct heating apparatus after a production time of 5 hours, wherein two photographs arranged vertically with respect to one another in each case are shown and assigned to the Experiments I to III in the order given.

DETAILED DESCRIPTION

(12) A system 100 known from the cited prior art according to FIG. 1 (insofar as it relates to an infusion apparatus and the other apparatuses arranged downstream hereof) is disclosed, for example, in EP 794 706 B1 and WO 2011/101077 A1. For carrying out the infusion method IFV, the system 100 includes a direct heating apparatus 8 in the form of an infusion apparatus 80 for carrying out high-temperature pasteurization HE within the scope of direct heating DE. The infusion apparatus 80 may comprise a product inlet 28 in its headspace (WO 2010/086082 A1), via which inlet the protein-enriched milk product P to be heat-treated is supplied to said infusion apparatus 80, for example and preferably centrally and annularly. Steam D is supplied to the supplied milk product P radially on the outside and at the same time radially from the inside, for example and preferably via an outer and an inner steam inlet 26, in order to directly heat said product, as a result of which high-temperature pasteurization HE from a preheating temperature T2=TVE to a high pasteurization temperature T4=THE takes place. With regard to the way in which the milk product P and the steam D is supplied, the prior art includes numerous other options that may also be used within the scope of the present invention. The infusion apparatus 80 is supplied with a first coolant K1 via a first coolant inlet 40 to a coolant chamber on the base of the container for cooling a base of the infusion apparatus 80. The first coolant K1 is discharged via a first coolant outlet 42.

(13) An outlet opening on the lower end of the infusion apparatus 80 is connected via an outlet pipe 30 to a first conveying apparatus 10, for example a rotating positive displacement pump or a centrifugal pump, which is connected via a third product line portion 32 to a second holding tube 12 for a second instance HH2 of keeping the product at temperature for the purpose of maintaining the high pasteurization temperature T5=THE for a second dwell time ?t2. The second holding tube 12 leads via a fourth product line portion 34 to a vacuum chamber 14. The second conveying apparatus 10 conveys the high-temperature pasteurized milk product P that has been kept at the high pasteurization temperature THE from the infusion apparatus 80 to the vacuum chamber 14. The vacuum chamber 14 is designed to remove, by means of so-called flash cooling FK, from the milk product P being cooled by means of a pressure drop, the amount of water W that is supplied to the infusion apparatus 80 as steam D in the form of exhaust vapors, and to discharge said vapors via a vapor outlet 38 preferably arranged in the upper region. A milk product P treated in this manner exits the vacuum chamber 14 at an exit temperature T6=TA via a discharge line 36, which is arranged in the lower region of said chamber on a tapering base and which leads through a second conveying apparatus 16.

(14) The milk product P to be heat-treated enters the system 100 via a milk product inlet 18 at a preheater 2 for preheating VE the product to the preheating temperature T1=TVE. The preheater 2 leads via a first product line portion 20 to a first holding tube 4 for the first instance HH1 of keeping the product at temperature for the purpose of maintaining the preheating temperature T2=TVE for a first dwell time ?t1. The first holding tube 4 opens out into the headspace of the infusion apparatus 80 via a second product line portion 22 and the product inlet 28 downstream thereof. The preheater 2 is fed with a preferably regenerative heat transfer medium M via a heat transfer medium inlet 2a and a heat transfer medium outlet 2b.

(15) As an alternative to the above-described infusion apparatus 80, the direct heating apparatus 8 of the system 100 (FIG. 1) may be designed in the form of an injection apparatus 800 for carrying out an injection method IJV. In this per se known design, the milk product P enters the injection apparatus 800 via the product inlet 28 for the purpose of high-temperature pasteurization HE and preferably forms a propulsive jet in said apparatus. The propulsive jet flows through a mixing chamber of the injection apparatus 800, wherein the heating medium, i.e., the steam D, is made to flow by a pressure drop caused by the speed of the milk product P in the form of a propulsive jet to be introduced into the milk product P. The steam inlet 26 also leads to the mixing chamber, where the steam D acts on the propulsive jet, preferably laterally.

(16) A system 1000 according to the invention (FIG. 2) for directly heating DE the protein-enriched milk product P by introducing steam D into said milk product P proceeds in an identical manner from the known system 100 according to FIG. 1, with the reference signs being carried over unchanged. In order to avoid repetitions, only the differences between the system 1000 according to the invention and the known system 100 will be described in the following.

(17) A cooler 6 designed as a recuperator is arranged between the direct heating apparatus 8, 80, 800 and the first holding tube 4, the product side of which cooler is guided via the second product line portion 22. The cooler 6 is supplied with a second coolant K2, preferably cold water, via a second coolant inlet 6a and a second coolant outlet 6b and it has the function of cooling down the milk product P that has been preheated and kept at temperature by a temperature difference ?TK from the preheating temperature T2=TVE to a cool-down temperature T3=TK by means of indirect cooling K.

(18) Experiments that serve to prove that the goals formulated with the object according to the invention have been achieved were carried out using the system 1000 according to the invention. Three of these experiments, which were carried out on consecutive days and which are denoted as Experiment I, II, and III, are referred to below with regard to a selection of relevant results and measured values.

Experiments I, II and IIIOverview

(19) The first experiment (without cooling K) used the process sequence according to FIGS. 3 and 4 and is referred to as Experiment I. The second experiment (with cooling K) used the process sequence according to FIGS. 3A and 5 and is referred to as Experiment II. The third experiment (with cooling K) used the process sequence according to FIGS. 3B and 5 and is referred to as Experiment III.

(20) In Experiment I, the milk product P that has been preheated to the preheating temperature T2=TVE and kept at temperature is guided through the inactive cooler 6 via the second product line portion 22 without cooling K and supplied to the direct heating apparatus 8 designed as an infusion apparatus 80 at the preheating temperature T2=TVE.

(21) In Experiments II and III, the milk product P that has been preheated to the preheating temperature T2=TVE and kept at temperature is in each case guided via the second product line portion 22 through the active cooler 6, where it is indirectly cooled K by the temperature difference ?TK to the cool-down temperature T3=TK. The temperature difference ?TK in Experiment II differs from that in Experiment III. The milk product P enters the direct heating apparatus 8 designed as an infusion apparatus 80 at the relevant cool-down temperature T3=TK.

(22) All relevant temperatures and dwell times in Experiments I to III for the heat treatment of the protein-enriched milk product P, from the preheating VE in the preheater 2 at the preheating temperature T1=TVE to the treated milk product P in the discharge line 36 at an exit temperature T6=TA (FIG. 1, 2), are compiled in the following Table 1. For the heat treatment, the following applies, among other things: Experiment I: TVE?TA=2 K; Experiment II: TK?TA=1.5 K; Experiment III: TK?TA=2 K.

(23) TABLE-US-00001 TABLE 1 TVE in TK in Experiment ? C. ?t1 in s ? C. THE in ? C. ?t2 in s TA in ? C. I 85 30 137.5 1 83 II 85 30 80 137.5 1 78.5 III 85 30 75 137.5 1 73

Experiment Results

(24) A selection of the measured values obtained in Experiments I to III is given in Table 2 below. The relevant heating indicators, namely non-denatured ?-lactoglobulin and furosine, for estimating and monitoring the actual thermal load on milk products and their significance for the nutritional and sensorial quality of said milk products have already been addressed above. The associated measured values obtained in Experiments I to III are highlighted in gray in Table 2.

(25) In FIG. 6, the normalized content of non-denatured ?-lactoglobulin L/Lo [1] in the treated milk product P is shown for the Experiments I to III. Here, L represents the relevant measured value (?-LG) for the non-denatured ?-lactoglobulin in g/kg protein (*) in the treated milk product P, which is based on Lo, wherein Lo is the reference value for the normalization and denotes the relevant measured value for the non-denatured ?-lactoglobulin in the untreated milk product P (raw milk).

(26) TABLE-US-00002 TABLE 2 Experiment I II III Without cooling With cooling With cooling TVE = 85? C./ TVE = 85? C./ TVE = 85? C./ ?t1 = 30s/without ?t1 = 30s/TK = 80? C./ ?t1 = 30s/TK = 75? C./ Raw K/THE = 137.5? C./ Raw THE = 137.5? C./ Raw THE = 137.5? C./ Constituents milk ?t2 = 1s/TA = 83? C. milk ?t2 = 1s/TA = 78.5? C. milk ?t2 = 1s/TA = 73? C. pH 6.75 6.77 6.75 6.78 6.76 6.80 (12? C.) (9? C.) (10? C.) (02? C.) (11? C.) (11 ? C.) Dry matter DM in % 12.15 11.47 11.67 11.01 11.49 10.33 Fat in % 0.08 0.161 0.08 0.13 0.09 0.11 Ash in % 0.96 0.90 0.93 0.86 0.91 0.81 Protein in % 6.38 5.98 6.11 5.72 6.02 5.38 ?-LG in g/kg milk (*) 8.35 1.92 6.90 2.20 6.85 2.55 ?-LG in g/kg protein (*) 130.9 32.1 112.9 38.5 113.8 47.4 Furosine in mg/kg milk Furosine in mg/100 g protein 2.66 9.44 2.78 9.39 2.66 8.36 Lactulose in mg/kg milk 9 53 8 44 6 50 (*): P-lactoglobulin (acid-soluble)

Result

(27) The experiment results (Table 2) show that the indirect cooling K according to the invention in Experiment II (?TK=5 K.fwdarw.L/Lo=0.34) and in Experiment III (?TK=10 K.fwdarw.L/Lo=0.42) results in a desirable, unexpected, and surprising increase in the content of non-denatured ?-lactoglobulin compared with Experiment I (without cooling K; ?TK=0 K.fwdarw.L/Lo=0.25), wherein, under the other given process conditions in the system 1000, the cooling by ?TK=10 K in Experiment III produces an optimal result (FIG. 6).

(28) In FIG. 7, the normalized content of furosine F/Fo [1] in the treated milk product P is shown for the Experiments I to III. Here, F represents the relevant measured value for the furosine in mg/100 g protein in the treated milk product P, which is based on Fo, wherein Fo is the reference variable for the normalization and denotes the relevant measured value for the furosine in the untreated milk product P (raw milk).

Result

(29) The experiment results (Table 2) show that the indirect cooling K according to the invention in Experiment II (?TK=5 K.fwdarw.F/Fo=3.38) and in Experiment III (?TK=10 K.fwdarw.F/Fo=3.14) results in a desirable, unexpected, and surprising decrease in the content of furosine compared with Experiment I (without cooling K; ?TK=0 K.fwdarw.F/Fo=3.55), wherein, under the other given process conditions in the system 1000, the cooling by ?TK=10 K in Experiment III produces an optimal result.

(30) It cannot be established with certainty based on Experiments I to III whether the increase in the content of ?-lactoglobulin and the decrease in the content of furosine are solely attributable to the indirect cooling K according to the invention prior to the direct heating DE. It cannot be excluded that the observed differences, which are desirable, unexpected, and surprising, are predominantly attributable to the indirect cooling K according to the invention and, if anything, to a rather small extent on the required stronger cooling of the protein-enriched milk product P during the flash cooling FK (different exit temperatures 78.5? C. and 73? C. for Experiments II and III, respectively, compared with TA=83? C. for Experiment I).

(31) However, this uncertainty does not appear to be essential to the invention, especially because Experiments II and III must necessarily end at different exit temperatures TA with respect to each other and in each case with respect to Experiment I. Said exit temperatures necessarily result from the condition set wherein water in an amount corresponding to that of previously supplied steam is removed from the high-temperature pasteurized milk product that has been kept at temperature by flash cooling by means of decompression to a lower pressure. Ultimately, the indirect cooling according to the invention is also the cause of this situation and is responsible for its possible effects.

(32) Water in an amount corresponding to that of previously supplied steam is removed from the high-temperature pasteurized milk product that has been kept at temperature by flash cooling by means of decompression to a lower pressure can only be fulfilled depending on the amount of steam (preferably saturated steam) supplied in each case during the direct heating DE in Experiments I to III and thus necessarily with accordingly assigned, different exit temperatures TA. The flash cooling FK also includes the removal of the amount of water that is necessarily required as compensation by the relevant indirect cooling K process from the preheating temperature TVE to the cool-down temperature TK (enthalpy decrease), again in the form of an adequate amount of steam D during the direct heating DE from the cool-down temperature TK to the high pasteurization temperature THE (enthalpy increase).

(33) The exit temperatures TA assigned to Experiments I to III (see Table 1) must necessarily be different to fulfill the condition set wherein water in an amount corresponding to that of previously supplied steam is removed from the high-temperature pasteurized milk product that has been kept at temperature by flash cooling by means of decompression to a lower pressure.

Experiment I (without Cooling)

(34) In order to remove the amount of water W that corresponds to the amount of previously supplied steam D for the heating, from the preheating temperature TVE=85? C. to the high pasteurization temperature THE=137.5? C., from the high-temperature pasteurized milk product P during flash cooling FK, a saturation pressure p.sub.s or corresponding absolute pressure (low pressure with respect to atmospheric pressure) that allows the milk product P to boil at a saturation temperature T.sub.s(p.sub.s)=83? C., which also corresponds to the exit temperature TA, must be set in the vacuum apparatus 14 (see FIG. 2).

Experiment II (with Cooling; Cooling from TVE=85? C. to TK=80? C.; ?TK=5 K)

(35) The cooling of the milk product P by a temperature difference ?TK=5 K requires a corresponding dissipation of heat or enthalpy decrease from or in the milk product P. This enthalpy decrease in Experiment II must be compensated during the direct heating DE by an additional supply of steam, preferably saturated steam, compared with Experiment I in order to arrive at the same high pasteurization temperature THE as in Experiment I (THE=137.5? C.).

(36) To prevent the milk product P from being watered down by the additional supply of steam in Experiment II, an amount of water corresponding to the additional amount of steam must be removed from the milk product P in the vacuum chamber 14 by means of the so-called flash cooling FK in the form of vapors. This process takes place when the milk product P is in a state of saturation.

Experiment III (with Cooling; Cooling from TVE=85? C. to TK=75? C.; ?TK=10 K)

(37) The cooling of the milk product P by a temperature difference ?TK=10 K requires a corresponding dissipation of heat or enthalpy decrease from or in the milk product P. This enthalpy decrease in Experiment III must be compensated during the direct heating DE by an additional supply of steam, preferably saturated steam, in an even higher amount compared with Experiment I and thus in a higher amount than in Experiment II to arrive at the same high pasteurization temperature THE as in Experiment I and Experiment II (THE=137.5? C.).

(38) To prevent the milk product P from being watered down by the additional supply of steam in Experiment III to an even greater extent than in Experiment II, an amount of water corresponding to the additional amount of steam must be removed from the milk product P in the vacuum chamber 14 by means of the so-called flash cooling FK in the form of vapors. This process takes place when the milk product P is in a state of saturation.

(39) FIGS. 8A-10B qualitatively show, for Experiments I to III, in each case after a production time of 5 hours, the extent of the product fouling or of the fouling layer in the region of the system 1000 that is generally most critical, i.e., downstream of the outlet of the direct heating apparatus 8, 80 and, in this case, in the suction nozzle of the second conveying apparatus 10 (FIG. 2), which is easily accessible from a disassembly point of view. The photographs in FIGS. 8A and 8B are assigned to Experiment I, those in FIGS. 9A and 9B to Experiment II, and those in FIGS. 10A and 10B to Experiment III.

(40) FIGS. 8A and 8B (Experiment I, without cooling K) show a continuous layer of fouling PF of a significant thickness after a production time of 5 hours, which impairs the transfer of heat and the general functioning of the system components in the high-temperature pasteurization regions in question. Production must be interrupted and the system 1000 cleaned after a production time of approximately 10 hours.

(41) FIGS. 9A and 9B (Experiment II, with cooling K; ?TK=5 K) show a circumferential colonization of the wall of the regions in question by a fouling layer PF of very moderate thickness that has a large number of island-like interruptions and that hardly impairs the transfer of heat and the general functioning of the system components in the high-temperature pasteurization regions in question, such that interruption to production and cleaning of the system 1000 is only required after a production time of up to 20 hours (production time approximately 2 to 3 times longer than in Experiment I).

(42) FIGS. 10A and 10B (Experiment III, with cooling K; ?TK=10 K) show an island-like colonization of a very limited surface area on the walls in question by a fouling layer PF of moderate thickness that hardly impairs the transfer of heat and the general functioning of the system components in the high-temperature pasteurization regions in question, such that interruption to production and cleaning of the system 1000 is only required after a production time of up to 20 hours (production time approximately 2 to 3 times longer than in Experiment I).

(43) The discernible darker areas on the end face of the suction nozzle in the black-and-white image in FIGS. 9A to 10B are slight deposits of the high-temperature pasteurized milk product P with brown or reddish-brown discolorations that are presumably caused by slight leaks at the flange connection and that point to a Maillard reaction MR of the milk product P.

(44) The facts and results presented above in relation to the direct heating apparatus 8 designed as an infusion apparatus 80 can be applied analogously to a direct heating apparatus 8 designed as an injection apparatus 800 (FIG. 1, 2). A person skilled in the art who is familiar with the solution to the object according to the invention, or a process engineer or technologist specializing in dairy science or food processing engineering or dairy technology will be able to apply the teaching of the present invention without exercising inventive skill even to an injection method not set out in detail in this application and will be able to optimize said teaching with regard to the process parameters, which then still have to be determined.

(45) The following is a list of reference numbers used in the drawings and this description, which reference to the figures in which they first appear.

FIG. 1 (PRIOR ART)

(46) 100 System according to the prior art 8 Direct heating apparatus 80 Infusion apparatus 800 Injection apparatus 2 Preheater 2a Heat transfer medium inlet 2b Heat transfer medium outlet 4 First holding tube 10 First conveying apparatus 12 Second holding tube 14 Vacuum apparatus 16 Second conveying apparatus 18 Milk product inlet (for milk product P to be treated) 20 First product line portion 22 Second product line portion 26 Steam inlet 28 Product inlet 30 Outlet pipe 32 Third product line portion 34 Fourth product line portion 36 Discharge line (for treated milk product P) 38 Vapor outlet 40 First coolant inlet 42 First coolant outlet D Steam DE Direct heating FK Flash cooling HE High-temperature pasteurization HH1 First instance of keeping at temperature HH2 Second instance of keeping at temperature IFV Infusion method IJV Injection method K1 First coolant M Heat transfer medium P Milk product (protein-enriched) TA Exit temperature (=T6) TVE Preheating temperature (=T1, T2) THE High pasteurization temperature (=T4, T5) VE Preheating W Water ?t1 First dwell time ?t2 Second dwell time

FIGS. 2 TO 4

(47) 1000 System 6 Cooler 6a Second coolant inlet 6b Second coolant outlet K Cooling K2 Second coolant TA Cool-down temperature (=T3) ?TK Temperature difference p.sub.s Saturation pressure T.sub.s Saturation temperature

FIGS. 6 TO 10B

(48) I First experiment (without cooling K) II Second experiment (with cooling K) III Third experiment (with cooling K) F Furosine (measured value in mg/100 g protein) Fo Furosine (measured value, reference value for normalization) F/Fo Furosine (Normalized measured values in [mg/100 g protein]/[mg/100 g protein]=[1]) L Non-denatured ?-lactoglobulin (measured value in g/kg protein) Lo becomes (Measured value, reference value for normalization) L/Lo Non-denatured ?-lactoglobulin (Normalized measured values in [g/kg protein]/[g/kg protein]=[1]) MR Maillard reaction (browning) PF Fouling layer (product fouling; formation of deposits)