FIELD OF THE INVENTION

[0001] The invention relates to a process for separating milk components into individual components, and a low-factose or lactose-free milk composed of these components. The invention relates particularly to using nanofiltration technology in the separation of milk components.

BACKGROUND OF THE INVENTION

[0002] Several processes for producing low-iactose and !actose-free milk by using membrane techniques are known. A conventional enzymatic process for splitting iactose is aiso generally known in the field, the process comprising the step of adding lactase from fungus or yeast into milk in such a manner that lactose is split into monosaccharides, i.e. glucose and galactose, in over 80%.

[0003] Several membrane filtration process solutions have been presented for removing lactose from milk raw material. Four basic membrane filtration processes are generally used: reverse osmosis (RO), nanofiitration (NF), ultrafiltration (UF), and mtcrofiitrøtion (MF). Of these, UF is mainly suitable for separating lactose from milk. Reverse osmosis is generaily applied to concentration, ultra- and microfiltration to fractionation, and nanofiltration to both concentration and fractionation. A lactose removal process based on a membrane technique is described in WO publication 00/45643, for instance, wherein lactose is removed by ultrafiltration and diafiitration.

[0004] tt is known in the field that a problem with membrane techniques in genera! is that during ultrafiltration not only lactose is removed from the milk, but also some of the minerals that are significant for the taste of milk and milk products prepared thereof. Controlling the mineral content and especially bivalent minerals, such as calcium and magnesium, is particularly problematic in the field, and extensive loss results from the known processes, which is why these bivalent minerals must often be returned or added separately.

[0005] Often membrane processes aiso produce, for instance, mineral-containing secondary flows, which cannot be exploited efficiently and which aiso increase waste water load, require further processing and add to the costs. It would thus be useful to provide processes, by which bivalent minerals in particular may be controlled in the process and recovered more efficiently, thus aiiowing the circulation of process waters without producing secondary flows.

[0006] WO publication 03/094623 A1 discloses a process in which a milk product is ultrafiitered, nanofiltered, and concentrated by reverse osmosis, after which the minerals removed during ultrafiltration are returned to the UF retentate. The residual lactose of the thus obtained low-lactose milk product is hydroiyzed with a lactase enzyme into monosaccharides, whereby an essentially lactose-free milk product is obtained. With this process, lactose is removed from milk without affecting the organoleptic properties of the milk product being prepared. In this process, the loss of bivalent minerals, such as calcium and magnesium, may be significant. Also, the process produces minerals containing secondary flows, which cannot be utilized in the process and which require post-processing. To solve these problems, simpler and more efficient aitemative processes are needed.

[0007] Lactose can also be specifically separated from milk by chromatography. However, many problems differing from the processing of whey are associated with the processing of milk, such as easy precipitation of casein, maintaining the micellar structure of casein, behaviour of fat, and extremely strict hygiene requirements. For instance EP publication 226035 B1 describes a lactose separation process in which milk is fractionated in such a manner that the lactose fraction is separated and the minerals are in the protein fraction or protein-fat fraction. The process is characterized by balancing cation exchange resin by making its cation composition correspond to that of milk, and milk is separated chrornatographtcally in a column with the balanced cation exchange resin at a temperature of approximately 50 to 8O ⁰ C by using water in eiution. An advantage of the process is that all compounds essential to taste remain in the milk. However, chromatographic lactose separation is a slow and complex process that cannot be directiy applied to conventional dairies without expensive equipment investments. Another problem is a high consumption of water and a large amount of chemicals.

[0008] Patent publication KR20040103818 describes a process for the production of low-lactose rniik, comprising nanofiltering milk hydroiyzed with lactase to partly remove galactose and glucose, and adding water into the nanofiltration retentate to achieve a suitable sweetness. Choi et al. (Asian- Aust. J. Anim. Sci 20 (6) (2007) 989 - 993) describe a process for the production of lactose-hydrolyzed milk, wherein raw milk is hydroiyzed with .β- galactosidase (5 000 lactase activity unit/g, Vaiidase, Valley Research) partly (0,03%; 4 ⁰ C, 24 hours) or "completely ¹ (0.1 %; 40 h), heat-treated to inactivate the enzyme (72 ⁰ C, 5 min), cooled to 45 to 5O ⁰ C, and nanofiitered at a pressure of approximately 9 to 10 bars (130 to 140 psi; concentration factor 1.6). Water was added into the NF retentate and the heat treatment was performed at 65 ⁰ C for 30 min. The lactose-hydroiyze milk consisted of protein (3.1%), fat (3.5%), lactose (0.06%), glucose (1.45%), and galactose (1.29%). Sn the processes described in said publications and comprising a single-phase nanofiltration, all of the monovalent minerals are not yet returned to milk efficiently enough.

[0009} WO publication 2007/076873 describes low-carbohydrate milk containing essentially all of the caicium and protein of the original milk, and a process for the production thereof. In this process, the pH of milk is adjusted to an aikafine value of 7.0 to 9.5, the milk is ultrafiltered, the UF permeate is nanofiitered preferably at a temperature of approximately 1O ⁰ C to minimize the microbioiogicai risk, the NF permeate, UF retentate and water are combined, and the pH is adjusted to the pH value of the original milk (pH 6.7) by adding acid, preferably citric acid or phosphoric acid. The energy content of the product is 90 to 250 kJ/100g. The process comprises a plurality of steps and requires strong chemicals to adjust the pH and to minimize the calcium and protein loss.

[0010] WO publication 2004/019693 describes a process for separating different components with membrane techniques (ultrafiltration, nanofϋtration and reverse osmosis) and combining these components info miik products, such as ice cream, yogurt and miik drink.

[0011] It is also known to use milk after lactose removal as a raw material in the production of low-carbohydrate dairy products. For instance WO publication 2006/087409 A1 describes a low-energy skim miik drink rich in added calcium, containing a low-energy milk base, which consists of skim miik or a whey protein solution or a mixture thereof and from which carbohydrates have been removed either completely or partly by ultrafiltration or chromatography according to the previously known processes. The energy content of the product is 20 kcal/100g at most. [0012] Recent studies have concentrated on membrane filtration of miik and on the use of such filtered, low-carbohydrate rniik in the preparation of dairy products, such as cheese, ice cream and yogurt. Common to the known multi-step membrane filtration processes comprising several different processes, one sub-phase of which is nanofϋtration, for preparing iow- carbohydrate milk products is that residual lactose is not removed from the milk raw materia! until it has undergone membrane filtration.

[0013] It is very challenging to achieve products that are completely flawless in taste and structure, that meet the consumers' expectations on an organoleptically competent miik product, and that are produced economically and simply without losing polyvalent minerals.

[0014] A process for the production of low-lactose and lactose-free mϋk products that are completeiy flawless in their organoleptic properties without any extra costs has now been unexpectedly invented. The process of the invention makes it possible to contra! bivalent minerals more efficiently and simpler than in conventional processes without any extra costs, and allows to minimize losses. In addition, the process of the invention does not produce secondary flows requiring post-processing, which makes the process more efficient.

BRIEF DESCRIPTION OF THE INVENTION

[0015] The present invention provides a new solution for avoiding calcium and protein losses that have proven problematic in the production of both low-lactose and lactose-free and low-carbohydrate milk products and problems associated with organoleptic properties, especially the taste, of such milk products by providing a process comprising hydrolyzing the lactose of a milk raw material, separating proteins, sugars and minerals from the obtained, hydrolyzed milk raw material into different fractions by phasing nanofiltration conditions according to membrane type, temperature, pressure and/or diafiitration and also applying membrane techniques and/or chromatographic separation processes in a feasible further separation. From the separated fractions, a desired milk product can be prepared.

[0016] As an aspect, the invention provides a process for separating milk components into individual components, the process being characterized by what is stated in the independent claim. The invention also provides a low- lactose and a lactose-free milk product, which are made from these components, and a process for the production of such a miik product. With the process of the invention, it is possible to simplify and enhance the production of low-lactose and lactose-free milk products, whereupon the ioss of especially bivalent minerals, particularly calcium and magnesium, is minimized and minerals and/or protein need not be supplemented/added separately,

[0017] All by-products obtained as a result of the process according to the invention are common dairy products and the secondary flows produced in the process can be further exploited in the process of the invention. The process does not lead to products or secondary flows, which should be processed or separated in an exceptional way, which means that the waste water load is minimized.

[0018] In addition, protein and mineral losses typical of lactose-free and low-lactose milk products in particular are avoided, and especially the recovery of bivalent minerals becomes more effective.

[0019] The invention also provides a process that is simple, economic, industrially applicable on a large scaie, and does not cause additional costs.

[0020] It was unexpectedly found that by hydrolyzing the lactose of a miik raw material completely or partly and phasing the nanofiltration of the hydrolyzed milk raw material in at feast two different nanofiltration conditions, such as at a temperature and/or pressure, and/or by diafiitration step, and/or with at least two different nanofiltration membrane types, the loss of minerais was minimized and the ratio between calcium and protein was controlled efficiently. The invention thus provides a process for separating the miik raw material components of hydrolyzed skim milk by benefiting from different permeability properties of nanofiltration membranes and different process conditions. A condition change may occur immediately or steadily or step by step at a certain speed, whereby the desired change/changing phase in the condition profile may also be understood as one sub-phase.

[0021] A milk product produced with the process of the invention has desired organoleptic properties, contains little carbohydrates, and contains a comparable amount of calcium as normal miik.

BRIEF DESCRIPTION OF THE FIGURES

[0022] Figure 1a shows chromatographic separation of a mineral- sugar fraction at 65 ⁰ C (Finex CS09GC resin, flow rate 160 ml/h, feed 20 mf, NF retentate of the second nanofiltration, °Brix 16%). [0023] Figure 1b shows chromatographic separation of a mineraf- sugar fraction at 1O ⁰ C (Finex CS09GC resin, flow rate 160 ml/h, feed 20 mi, NF retentate of the second nanofiitration, Brix ^D 16%).

DETAILED DESCRIPTION OF THE INVENTION

[0024] As an aspect, the invention relates to a process for separating milk components, the process being characterized by a) hydrolyzing the lactose of a rnilk raw material, thus obtaining hydroiyzed milk raw materia!, and b) performing a phased nanofiitration for the hydroiyzed milk raw materia! in at least two sub-phases, whereby at least a portion of a nanofiitration retentate NF Ret I and/or a nanofϊftration permeate NF Perm I received from a first sub-phase is subjected to a second sub-phase to obtain a nanofiitration retentate NF Ret Il and nanofiitration permeate NF Perm Il of the second sub-phase, and optional subsequent nanofiitration sub-phases are performed on at least a portion of some nanofiltratiαn retentates and/or permeates of the preceding sub-phases, or a combination thereof, to obtain nanofiitration retentate fractions NF Ret ill etc. and nanofiitration permeate fractions NF Perm HI etc., respectively, of said subsequent sub-phases, to separate proteins, sugars and minerals into these different fractions.

[0025] In the context of the present invention, a miik raw material refers to miik, whey, and combinations of milk and whey as such or as a concentrate. The mϋk raw material may be supplemented with ingredients generally used in the preparation of milk products, such as fat, protein or sugar fractions, or the like. The milk raw material may thus be, for instance, full-fat milk, cream, low-fat miik or skim miik, uitrafiltered milk, diafiStered miik, microfiltered miik, lactose-free or low-lactose milk, protease treated milk, recombined miik from mϋk powder, organic milk or a combination of these or a dilution of any of these. Preferably the milk raw material is skim miik.

[0026] in step a) of the process of the invention, the lactose of the milk raw material is hydroiyzed into monosaccharides, as is known in the fieid. !n an embodiment of the process according to the invention, the hydrolysis is performed in its entirety (compiete hydrolysis) prior to phased nanofiitration. In a second embodiment of the process of the invention, the hydrolysis is performed partly before the phased nanofiitration, and the lactose hydrolysis of the partially hydroiyzed milk raw material Is continued simultaneously with the phased nanofiltration of the partially hydrolyzed milk raw materia!. The lactose hydrolysis can continue as long as the lactase enzyme is inactivated, for example by a heat treatment of a miik product composed at a iater stage of various fractions received in the invention.

[0027] Complete hydrolysis means that the lactose content of the hydrolyzed miik raw materia! is less than 0.5%. Partial hydrolysis means that the lactose content of the hydroiyzed milk raw materia! is more than 0.5%.

[0028] In step b) of the process of the invention, the hydrolyzed milk raw material obtained in the previous step a) undergoes a phased nanofiltration to separate proteins, sugars and minerals into different fractions, in the context of the present invention, a phased nanofϊftratiσn means that nanofiitration comprises at least two sub-phases. Each sub-phase is carried out under different process conditions and/or by using different membrane types. A variable condition may be, for instance, fiitration temperature, filtration pressure, diafϋtration, and/or concentration factor of filtration. In each sub- phase, conditions can be changed with regard to one or more variabies. A condition change may happen immediately or steadily or step by step at a certain speed, whereby the desired change/changing phase in the condition profile refers to a sub-phase, in an embodiment of the invention, the phased nanofiltration comprises a change in temperature conditions and/or membrane type, in a second embodiment of the invention, the nanofiitration is combined with diafiltration (DF), wherein diawater is added into the nanofiitration retentate in at feast one sub-phase of nanofiitration.

[0029] The phased nanofiltration of the invention, comprising at least two sub-phases, produces two or more nanofiitration, i.e. NF, retentates, which are marked with NF Ret I, NF Ret ii, NF Ret ill, etc. in the following, and two or more nanofiltration, i.e. NF, permeates, which are marked with NF Perm !, NF Perm ii, NF Perm 111, etc. in the following. The serial number refers to the number of nanofiltration sub-phases carried out in the process. Thus

- NF Ret 1 refers to a retentate obtained in the first sub-phase of nanofiltration

- NF Ret I! refers to a retentate obtained in the second sub-phase of nanofiitration

- NF Ret HI refers to a retentate obtained in the third sub-phase of nanofϋtration, etc. - NF Perm 1 refers to a permeate obtained in the first sub-phase of naπofiltration

- NF Perm Il refers to a permeate obtained in the second sub-phase of nanofϋtration

- NF Perm Ii! refers to a permeate obtained in the third sub-phase of nanofiltration, etc.

[0030] Sf desired, two or more retentate and permeate fractions obtained from the phased nanofiltration can be combined for the subsequent nanofiltration sub-phase.

[0031] In an embodiment of the invention, the NF retentate and NF permeate fractions obtained from the phased nanofiitration, or a combination thereof, are further processed by membrane techniques and/or by chromatography to further improve the separation of proteins, sugars and minerals. Further processing may concern either one or more NF retentates or NF permeates obtained from any of the nanofiitration sub-phases. Also, the retentates and permeates can be combined in any manner for said subsequent processes, A membrane technique particularly suitable to be used in further processing is reverse osmosis (RO). In the following, RO Ret refers to a retentate obtained by reverse osmosis, and RO Perm refers to a permeate obtained by reverse osmosis. The various fractions obtained in the separation processes can also be subjected to evaporation.

[0032J Different separation processes may also be combined as desired in one or more phases. In an embodiment of the invention, the protein, sugars and minerals of the hydrolyzed milk raw material are separated by membrane techniques, by performing a phased nanofiltration preferably in the first phase under conditions, in which monosaccharides are retained in the retentate to a low extent, and in the second phase under conditions, in which monosaccharides are retained in the retentate to a high extent. In a specific embodiment of the invention, the phased nanofiitration is performed in the first phase in warm conditions, at approximately more than 25 to 5O ⁰ C, in particular at approximately 42 to 51 ⁰ C, and in the second phase in cold conditions, at approximately 5 to 25 ⁰ C, in particular at approximately 10 to 18 ⁰ C. According to a second embodiment of the invention, the nanofiltration may alternatively be performed first in cold conditions and then in warm conditions. In membrane techniques, usually a temperature of for instance 1O ⁰ C is known to be used as an industrial process temperature to avoid microbiological problems. [0033] Suitable nanofiltratlon membranes include, for instance, Desa! 5 DL (GE Osmonics, USA), Desai 5 DK (GE Osmonics, USA), TFC® SR3 (Koch membrane systems, Inc., USA), FiLMTEC™ NF (Dow, USA). Suitable reverse osmosis membranes include, for instance, TFC® HR (Koch membrane systems, Inc., USA) and FILMTEC FT30 (Dow, USA).

[0034] In an embodiment of the invention, a further chromatographic separation is performed for one or more NF retentates. in a preferred embodiment of the invention, the separation is performed for the retentate obtained in the second sub-phase of nanofϋtration.

[0035] A concentration factor (K) refers to the weight ratio between the liquid to be fed to the filtration and the retentate, and it is determined by the following formula:

K- feed (kg)Zretentate (kg)

[0036] in the process of the invention, preferably a concentration factor K = 1 to 10, more preferably K ~ 2 to 6, is used in the nanofiitration. if diafiltration is employed in the phased nanofϋtration according to the invention, the concentration factor may be considerably bigger.

[0037] The process of the present invention may be applied to both batch and continuous production. Preferably, the process of the invention is performed as a batch process.

[0038] In a specific embodiment of the process according to the invention, wherein the phased nanofiitration of lactose-hydrolyzed skim milk is carried out by performing the first phase in warm conditions (K=3) and nanofiStering the NF permeate (NF Perm i) obtained in the first phase in cold conditions (K=6) in the second phase to recover minerals, the NF retentate of the first nanofiitration phase (NF Ret I) contains glucose 2.5%, galactose 2.5%, and ash 1.4% and has a dry matter content of 15.5%, and the permeate of the second nanofiitration phase (NF Perm Ii) contains glucose 0.2%, galactose 0.2%, and ash 0.2% and has a dry matter content of 0.5%. By composing a lactose-free milk of said NF retentate (21.3%), said NF permeate (35.4%), and the hydrolyzed skim milk (43.2%), a product with desired organoleptic properties couid be obtained. The amount of eaicium was exactly the same as in the originai milk (1100 mg/kg). The milk contained 3.3% protein, 1.6% glucose, 1 ,6% galactose, 0.7% ash, and had a dry matter content of 7.3%. This embodiment of the invention will be described in example 3, and the composing of the miik from said fractions will be illustrated in example 8, [0039] In a second specific embodiment of the process according to the invention, wherein reverse osmosis was performed after the phased nanofϋtration and diafiltration, the second sub-phase of the nanofiStration provided an NF permeate U containing glucose 0.7%, galactose 0.7%, and ash 0.2% and having a dry matter content of 2.0%, and, respectively, an NF retentate IE (K=3) containing glucose 3.1%, galactose 3.1 %, and ash 1.1 % and having a dry matter content of 14.4%. The miik composed of said NF retentate and RO retentate of the hydrolyzed skim milk (50:50) corresponded to normal rniik in other respects except for the carbohydrates (protein 3.3%, glucose 1.7%, galactose 1.6%, ash 0.7%, dry matter 7.5%, calcium 1100 ml/kg). This embodiment of the invention will be described in example 2, and the composing of the milk from said fractions in example 6.

[0040] Fractions obtained by the process of the invention may be used particularly for producing lactose-free skim milk with desired organoleptic properties, the composition of which corresponds to that of the hydrolyzed milk, with the exception of carbohydrates, by combining the NF retentate i (K=1.5) (66.6%) of the first nanoftitration phase of the hydrolyzed skim milk, the NF permeate Il (27.7%) of the second nanofiltration phase, and the mineral fraction (5.7%) separated in a chromatography column. The amount of calcium was exactly the same as in the original milk (1100 mg/kg). The milk contained protein 3.3%, glucose 1.6%, galactose 1.6%, ash 0.7%, and had a dry matter content of 7.5%. The composing of this milk will be described in example 7.

[0041] As a second aspect, the invention thus relates to a lactose- free or low-lactose milk product comprising at least one NF retentate fraction NF Ret II, NF Ret 111, etc. or NF permeate fraction NF Perm Ii, NF Perm 111, etc., which are obtained by nanofiltration of the hydrolyzed milk raw material, comprising at ieast two sub-phases.

[0042] in a second embodiment of the invention, the milk product of the invention is produced by combining two or more of the fractions: retentate and permeate fractions of a first sub-phase of nanofiitration NF Ret I and NF Perm I, respectively, retentate fractions of a second and subsequent nanofiitration sub-phases NF Ret II, NF Ret IiI, etc., permeate fractions of a second and subsequent nanofiltration sub-phases NF Perm I!, NF Perm IiI, etc., a retentate fraction RO Ret a permeate fraction RO Perm received from reverse osmosis of said permeate fractions of any nanofiltration sub-phase, or a combination thereof, and a chromatographically separated mineral and sugar-containing fractions of the retentate fractions NF Ret I, NF Ret II, NF Ret IK, etc.

[0043] The lactose-free or iow-lactose milk product of the invention can be liquid or in the form of a concentrate or powder.

[0044] As an aspect, the invention also relates to a process for the production of lactose-free or iow-iactose milk product, the process comprising a) hydroiyzing the lactose of a milk raw material, thus obtaining hydrolyzed milk raw material, and b) performing a phased nanofϊitration for the hydrolyzed milk raw materia! in at least two sub-phases, whereby at least a portion of a nanofiltration retentate NF Ret I and/or a nanofiltration permeate NF Perm I received from a first sub-phase is subjected to a second sub-phase to obtain a nanofiltration retentate NF Ret Il and nanofiitration permeate NF Perm Il of the second sub-phase, and optional subsequent nanofiltration sub-phases are performed on at least a portion of some nanofiltration retentates and/or permeates of the preceding sub-phases, or a combination thereof, to obtain nanofiitration retentate fractions NF Ret HI etc. and nanofiitration permeate fractions NF Perm III etc., respectiveiy, of said subsequent sub-phases, to separate proteins, sugars and minerais into these different fractions, c) further processing, if desired, one or more of any of the NF retentate fractions NF Ret !, NF Ret II, NF Ret III, etc. and the NF permeate fractions NF Perm I, NF Perm El, NF Perm III, etc., or a combination thereof, by a membrane technique, and/or evaporation, and/or chromatography, d) composing a product with a desired composition from one or more of the retentate and permeate fractions received from nanofiltration comprising at least two sub-phases, and, if desired, from the retentate and/or permeate fraction obtained from the first nanofiltration sub-phase, obtained from step b), and, if desired, from one or more fractions obtained from step c) and possibly other ingredients, e) if desired, concentrating the product obtained from step d) to a concentrate or a powder.

[0045] The milk product according to the present invention is a low- lactose or lactose-free product, in the present invention the term low-lactose means that the lactose content of the milk product is not more than 1.0%. The term lactose-free means that the milk product does not contain lactose more than 0.5 g/serving (e.g. 0.5 g/244g for liquid milks, the lactose content being 0.21% at most), however, not more than 0.5%. In accordance with the invention, it is also possible to produce low-carbohydrate milks with flawless organoleptic properties. In addition, the loss of calcium and protein contained in the milk raw material is minimized and a separate supplementation/addition of minerals and/or protein is not necessary.

[0046] The following examples illustrate the invention but do not limit the invention to the embodiments mentioned.

Example 1 : Single-phase nanofiltration of hydrolyzed skim milk with Desal 5 DL membrane (K~3)

[0047] Skim milk (20 I) was hydrolyzed (9 ⁰ C, 18 h) by Godo YNL2 lactase (Godo Shusei Company, Japan) with a dosage of 0.08% and nanofiltered with a Desal 5 DL membrane (GE Osmonics, USA) at a temperature of 10 to 18 ⁰ C and a pressure of 12 to 21 bar. The permeate flow was 5.7 to 9.6 l/m ² h. The nanofiltration was continued until the concentration factor was 3 and the retentate volume 6.7 ! and the permeate volume 13.3 I.

[0048] Samples were taken from the feed, which consisted of hydrolyzed skim milk, obtained NF retentate and NF permeate, and protein, dry matter, glucose, galactose, ash, and calcium were determined on the basis of the samples (table 1).

Table 1: Nanofiltration retentate and permeate compositions

[0049] On the basis of the results it can be stated that in practice, calcium was not lost to the permeate but it remained in the same fraction as protein (table 1). in addition, monosaccharides permeate through the membrane to a great extent. When the retentate was diluted to the original protein content of the milk, the taste was considered "empty", i.e. untypical of milk, The reason for this are the minerals of the milk which were lost to the permeate during nanofiltration, providing the milk with an important property of saity taste. Thus, by nanofiltering hydrolyzed milk only in one phase, it is not possible to produce lactose-free or low-iactose milk tasting iike normal milk.

Example 2: Three-phase nanofHtration {membrane DesaJ DK + dla- fiϊtration and membrane Fiimtec NF) of hydroSyzed skim milk combined with RO filtration

[0050] 0.06% of Godo YNL2 lactase (Godo Shusei Company, Japan) was added into skim milk (20 I) and hydrolyzed for 18 h at 1 O ⁰ C. The residual lactose content of the skim milk was then 0.03%. The thus obtained hydrolyzed skim milk was nanofiltered at 10 to 15°C. The filtration membrane was Desal 5 DK (GE Osmonics, USA) and the pressure was 13 to 19 bar, the permeate flow being 8.4 to 10.5 l/m ² h. The hydroiyzed skim milk was first filtered with a concentration factor 2, which means that an amount of 10 i of permeate altogether was removed from the apparatus. This was followed by diafiltration, i.e. diawater (5 I) was added to the NF retentate I (10 !) at the same speed at which NF permeate Il was produced. The permeate from the first nanofϋtration phase and the permeate obtained from the diafiltration were recovered and combined. The combined permeate fraction is called an NF permeate H in the following.

|0051] Samples were taken from the feed, which was hydrolyzed skim milk, NF permeate !i and retentate obtained from the diafiltration, called an NF retentate il in the following, and protein, dry matter, giucose, galactose and ash and calcium were determined from the samples (table 2). After 4 hours, the lactose content of the NF retentate was < 0.01%, so the hydrolysis continued during and after the nanofiltration. Table 2: First rtanofiltration of hydrolyied skim milk combined with diafiltration. Feed, reteπtate and permeate compositions. In addition to the volumes in the table, an amount of 5 I of diawater was fed into the apparatus.

[0052] The experiment was continued in the third sub-phase by nanofϋteriπg the NF permeate Il with a concentration factor 10 by Filmtec NF membranes (Dow, USA) at a filtration temperature of 10 to 2O ⁰ C. The permeate flow was 5.3 to 9.4 l/m ² h and the pressure 10 to 21 bar.

[0053] The obtained NF permeate ill was further concentrated by reverse osmosis (Fiimtec RO-390-FF, Dow, USA) at room temperature (about 25 ⁰ C) with a concentration factor 1.35.

[0054] On the basis of the NF permeate Ni and the NF reteπtate ill and the RO retentate i, dry matter, glucose and ash were determined. The results are shown in table 3.

Table 3: Second nanofHtratϊαn of hydrøϊyzed skiim milk and concentration by reverse osmosis. Feed, retentate and permeate compositions.

[0055] The second-phase retentate (NF retentate II; table 2) and the RO retentate (tabie 3) were used in composing a milk (example 6). The RO permeate can also be used in composing a milk.

Example 3: Two-phase nanofiJtration (membranes Desal 5 DL (K=3) and Filmtec NF (K=6)} of hydrolyzed skim milk

[0056] The phased nanofiltration of lactose-hydrolyzed skim milk was tested by performing the first phase in warm conditions, and nanofiltering in the second phase the NF permeate i obtained in the first phase in coid conditions to recover the minerais.

|0057] As described above, skim milk (40 !) was hydrolyzed (9 ⁰ C ₁ 18 h) with Godo YNL2 lactase (Godo Shusei Company, Japan) with a dosage of 0.08%. The hydrolyzed skim milk was nanofiltered at a temperature of 47 to 51 ⁰ C. The nitration membrane was Desai 5 DL (GE Osmonics, USA). The pressure was increased to keep the fiow constant. During the experiment, the permeate flow was 8.1 to 9.6 l/m ² h and the pressure 4 to 6.4 bar. The filtration was continued until the concentration factor was 3.

[0058] Samples were taken from the feed, retentate and permeate, and protein, dry matter, glucose, galactose and ash and calcium were determined on the basis of the samples (table 4). Table 4: First nanofiltration of hydrolyzed skim milk.

Feed, retentate and permeate compositions.

[0059] The NF permeate I (20 !) of hydrofyzed skim mϋk was further nanofiitered with a concentration factor 6, as a result of which NF retentate il and NF permeate !l were obtained. The nanofiltration membrane was Filmtec NF (Dow, USA) and the filtration temperature was 10 to 25 ⁰ C. The permeate flow was 4.3 to 9.6 i/m ^z h and the filtration pressure 10 to 26 bar.

[0060] Samples were taken from the feed (NF permeate I), NF retentate Il and NF permeate Ii, and protein, dry matter, glucose, galactose and ash were determined on the basis of the samples (table 5).

Table 5: Second nanofiltration of hydrolyzed skim milk.

Feed, retentate and permeate compositions.

[0061] The first-phase retentate (NF retentate I; table 4) and the second-phase permeate (NF permeate Ii; table 5) were used in composing a milk (example 8). The NF retentate I was also used in composing a milk containing whey protein (exampie 10). Example 4: Two-phase nanofϋtratϊon of hydrolyzed skim milk (membranes Desal 5 DL (K= ¹ LS) and Filmtec MF (K=6))

[0062] The lactose of skim milk was hydrolyzed like in example 3, The first phase of the phased nanofiltration of the hydrolyzed skim milk was performed at 5O ⁰ C like in example 3, except that the concentration factor was 1.5. The NF permeate I obtained in the first phase was nanofiltered in the second phase at 10 to 25 ⁰ G with a concentration factor 6 to recover the minerals, as is described in example 3.

[0063] Protein, dry matter, glucose, galactose and ash and calcium were determined on the basis of the feed (hydrolyzed skim milk), NF retentate i and NF permeate I of the first nanofiltration phase {table 6). Dry matter, glucose, galactose and ash were determined on the basis of the feed (NF permeate !}, NF retentate ii and NF permeate Il of the second nanofiltration phase (table 7).

[0064] Sugars and minerals in the NF retentate il were separated from one another by chromatography, which will be described in example 5.

Tafoϊe 6: First nanofiltration of hydrolyzed skim milk.

Feed, retentate and permeate compositions.

Table 7: Second nanofiftration of hydrolyzed skim miSk.

Feed, retentate and permeate compositions.

[0065J The first-phase retentate (NF retentate I) (table 6) and the second-phase permeate (NF permeate Ii) were used in composing a milk (example 7),

Example 5: Recovery of minerals from concentrated nanofiltration permeate

[0066] The concentrated NF permeate of hydrolyzed skim milk, i.e. the retentate of the second nanofiltration phase (NF retentate II), was further processed in a chromatography column in order to separate the mineral fraction and the sugar fraction.

[0067] A cation-exchange resin (Finex CS 09 GC, Finex Oy, Finland, Na form) was mixed with skim milk (1 litre/50 mi of resin) for 30 minutes. The skim milk was flushed clean from the resin with ion-exchanged water. The balanced resin (180 to 200 ml) was packed in a column with a heating jacket (height 100 cm, diameter 1 ,5 cm) at 65 ⁰ C. 20 mi of NF retentate concentrate (NF retentate II) was fed into the column (°Brix about 16; example 4). The flow rate was 160 ml/h, the temperature 65 ⁰ C, and tap water was used as an eluant. Fractions of 5 mi were collected and combined into two fractions: a mineral fraction and a sugar fraction. A similar separation was also performed at 10 ⁰ C.

[0068] Ash, galactose and glucose were determined on the basis of the fractions.

[0069] In practice, a complete separation of the milk minerals and the monosaccharides in the concentrated NF permeate (NF retentate H) of skim milk was achieved (tabies 8 and 9). The sugars were separated more efficiently at a temperature of 65 ⁰ C. [0070] The mineral fraction separated at a temperature of 65 ^P C (fractions 0 to 50; table 8) was used in composing the lactose-free milk (example 7).

Table 8: ⁰ BrIx and conductivity of fractions separated by chromatography from concentrated NF permeate of skim milk

Table 9: Galactose, glucose and ash content of fractions separated by chromatography from concentrated NF permeate of skim milk

Example 6: Composing of tactose-free milk from nanofiltratton retentate and RO retentate of hydrolyzed skim miJk

[0071] A iactose-free mifk was composed of the NF retentate H and RO retentate I of the hydroiyzed skim miik of example 2. The compositions and proportions of the fractions in the composite as weli as the composition of the lactose-free milk are shown in table 10. The composition of the lactose-free skim miik corresponds to that of normal milk, except for carbohydrates.

Table 10: Composing of lactose-free skϊnn milk from NF retentate and RO reteπtate of hydrolyzed skrm milk

Example 7: Composing of lactose-free milk from nanøfiltratiora and chromatography fractions of hydrolyzed skϊm milk

[0072] A lactose-free milk drink composed of the fractions of examples 4 and 5, i.e. the retentate of the first nanofiltration of hydrolyzed skim miik (NF retentate I), the NF permeate of the NF permeate derived from the first nanofiltration (NF permeate II), and the mineral fraction separated by chromatography from the NF retentate of the second nanofiltration. The compositions and proportions of the fractions in the composed milk as well as the composition of the composed product are shown in table 11. (The liquid contained in the lactose-free milk is derived from the process, and water need not be added separately.)

[0073] in addition, a iactose-free milk was composed as in the above, except that instead of the mineral fraction separated by chromatography, water was added (table 12). Instead of water, an RO permeate fraction obtained from reverse osmosis may be used.

[0074] Except for carbohydrates, the composition of the milks corresponded to that of the hydrolyzed milk entirely. The amount of calcium (1100 mg/kg) was exactly the same as in the original milk. The products were also assessed organoleptically, and they were considered to have good properties and to taste like common skim milk. Table 11: Composing of lactose-free milk from NF retentate I, NF permeate I! and mineral fraction from chromatography. Compositions of fractions and praduGt, and proportion of fractions.

Table 12: Composing of lactose-free milk from NF retentate I, NF permeate H and water. Compositions of fractions and product, and proportion of fractions.

Example 8: Composing of low-lactose, lactose-free and ϊow-carbohydrate rnϊSks from nanofiltratϊon fractions of hydrolyzed skim milk

[0075] The lαw-iactose, iactose-free and low-carbohydrate milks according to the invention were composed of the fractions of example 3, i.e. the NF retentate i and the NF permeate II. In addition, hydroiyzed skim milk was used in composing a lactose-free miik (table 13), and skim miik in composing a iow-lactose, protein- and calcium-enriched miik (table 14). A low- carbohydrate iactose-free milk was composed of the NF fractions only (table 15). The compositions and proportions of the fractions In the composed milks as well as the composition of the product are shown in tables 13 to 15.

Table 13: Composing of lactose-free milk from nanofiltratiøn fractions, having the composition of a product corresponding to norma! miϊk.

[0076] Except for carbohydrates, the composition of the lactose-free skirn milk described in table 13 corresponded to that of the hydrolyzed milk entirely. What is noteworthy is that the amount of calcium was exactly the same as in the originai milk. The product was also assessed organoieptically. and it was considered to be good and taste like normal skim milk.

Tab!© 14: Composing of low-lactose protein- and calcium-enriched milk

[0077] The mifk described in table 14 has a protein content that is considerably higher than in normal miik, but the amount of monosaccharides is at a level, the sweetness of which corresponds to normal milk. In an organoleptic test it was observed that the milk tasted richer than normal skim milk but otherwise the taste was the same as in normal miik.

Table 15: Composing of low-carbohydrate lactose-free milk

[0078] The product described in table 15 had a similar composition as normal milk, but there was no lactose, and the amounts of glucose and galactose were very small. Despite its composition, the milk was unexpectedly rich in taste although it was not as sweet as normal milk.

Example 9; Single-phase nanofHtration of hydrαlyzed whey with Desal 5 DL membrane (K=7)

[0079] Skimmed whey (40 I) was hydro!yzed (9 ⁰ C ₁ 20 h) with Godo YNL2 lactase (Godo Shusei Company, Japan) with a dosage of 0.1%, and nanofiitered with a Desai 5 DL membrane (GE Osmonics, USA) at a temperature of 46 to 51 ⁰ C and a pressure of 3 to 6.5 bar. The permeate flow was 10.0 to 13.5 l/rn ² h. The nanofiitration was continued until the concentration factor was 7, the retentate volume 5.5 I and the permeate volume 34.5 I.

[0080] Samples were taken from the feed (hydrolyzed whey), retentate and permeate, and protein, dry matter, giucose, galactose, ash, and calcium were determined on the basis of the samples (table 16). Table 16: First naπofiϊtration of hydroSyzed whey. Feed, retentate and permeate compositions.

[0081] The composition of the NF permeate I separated from the hydrolyzed whey corresponded to the NF permeate separated from the hydrolyzed skim mϋk in corresponding conditions (example 3, table 4). if desired, the nanofϋtration of whey can be continued in the second phase in the same way as in example 3.

[0082] The NF retentate I was used in composing the miik (example 10).

Example 10; Composing of lactose-free milk containing whey protein from nanofiitratson fractions of hydroiyzed whey and skim milk

[0083| A lactose-free milk containing whey protein was composed of the NF retentate I of the hydrolyzed whey of example 9, the NF retentate ! of the hydrolyzed skim milk of example 3, hydrolyzed skim milk, and the RO permeate obtained in example 2. The compositions and proportions of the fractions in the composite as well as the composition of the lactose-free mϋk containing whey protein are shown in table 17. The lactose-free milk containing whey protein contained less carbohydrates and more calcium than normal miik, as well as whey protein, the proportion of which in the proteins of the milk is 40%. Table 17: Composing of lactose-free skim milk containing whey protein from nanofiStratϊon fractions and skim milk