A PROCESS FOR THE SPECIFIC SEPARATION OF LACTOSE FROM MILK

Abstract: The invention relates to a process for accom­ plishing specific chromatographic separation of lactose from milk. Milk is treated in a column with a cation exchange resin balanced in such a manner that its cationic composition corresponds to the cationic compo­ sition of milk at a temperature of about 50 to about 80°C, and the column is eluted with water to recover a protein containing fraction and lactose fraction.

Description: The present invention relates to a process for accomplishing specific chromatographic separation of lactose from milk. In the production of cheese, curd, and milk protein powders, a process stage of essential importance is the separation of the main components of milk from each other, i.e. the separation of fat and protein - or in fatless products the separation of protein only - from lactose. Traditionally, this has been carried out by pre­ cipitating casein or a mixture of casein and fat by means of a rennet enzyme or by adjusting the pH by means of an acid to the isoelectric point (pH about 4.5). Whey pro­ teins as well as lactose and salts normally remain in the solution, i.e. the whey. Consequently, several processes have been developed for improving the protein yield. By the use of heat treat­ ment or calcium addition, the whey proteins are caused to precipitate with casein. Besides lactose and salts, only low molecular weight nitrogenous compounds remain in the solution part. The utilization of this kind of proteinless whey is very difficult. New processes have been developed besides the pre­ cipitation processes. In the early 1970's, the gel filtra­ tion was believed to offer a satisfactory technical solu­ tion to the recovery of milk proteins in a soluble form (U.S.Patent No. 3,547,900). In the gel filtration, the protein fraction of milk is separated from the lactose and the salts of milk. However, the industrial applica­ tions of the process have been prevented by the high price and difficulties in the treatment of the gel material as well as hygiene problems. The ultrafiltration, too, developed strongly in the 1970's, and has been applied industrially especially in the production of Feta cheese, curd, and a whey protein powder. The most important reason why the ultra­ filtration has not become more general is that its by­ product, permeate, is difficult to utilize. The permeate contains the components which have gone through the ultrafiltration membrane, such as lactose, salts, and low molecular weight nitrogenous compounds. Another problem with ultrafiltration is that it is very difficult as well as expensive to obtain a high protein content (over 80 per cent of the dry substance). Unexpectedly, it has now been found that the chromatographic separation makes it possible to fraction milk in such a manner that lactose is separated as a pure fraction while the salts remain in the protein fraction or in the protein/fat fraction. In this way a fraction nearly free from lactose and having a high protein con­ tent is obtained; on the other hand, a pure lactose solution much easier to utilize is obtained in place of the permeate. If the salts in the protein fraction are disadvantageous in view of the intended use, the protein fraction can be concentrated by ultrafiltration in place of evaporation, so that the salts are removed together with water. Chromatographic separation by means of a cation exchange resin is a process known per se and it is an industrially applied process e.g. for the separation of saccharose from molasses and for the separation of fructose from a mixture of glucose and fructose. U.S. Patent No. 3,969,337 describes the chromatographic fractionation of whey by means of a cation exchange resin. However, the treatment of milk includes many problems different from those connected with the treat­ ment of whey; e.g. the susceptibility of casein to precipitate, the preservation of the micellic structure of casein, the behaviour of fat, and the extremely high hygiene requirements. Therefore, this per se known process for the separation of whey cannot be applied in the treatment of milk. So the invention is concerned with an improved, hygienic, industrially applicable process for accomplish­ ing specific chromatographic separation of lactose from milk, said process comprising the steps of (a) packing a column with a particulate cation exchange resin, (b) balancing said cation exchange resin in such a manner that its cationic composition corresponds to the cationic composition of milk, (c) treating milk in a column with said balanced cation exchange resin at a temperature of about 50 to about 80°C, and (d) eluting the column with water to recover successively a protein containing fraction and lactose fraction from the bottom of the column. The cation exchange resin can be e.g. a strong cation exchange resin manufactured by Suomen Sokeri Oy (a resin having a polystyrene divinyl benzene skeleted and containing sulphonic acid groups). The resin has a structure of the same type as e.g. the resin "Duolite C 204 F" (manufacturer Duolite International S.A.), and it is used industrially for the separation of saccharose from molasses. A suitable mean particle size of resin is 0.06 to 0.6 mm. Preferably the mean particle size of resin is 0.4 mm. The column is filled with resin in the sodium form. The resin is balanced so that it obtains a balance with milk with respect to its ionic form. When the resin is balanced, fatless milk or con­ centrated milk is passed through the resin bed in an amount at least 10 times the volume of the resin bed. The balancing of resin can also be carried out by means of a salt solution the cationic composition of which corresponds to that of milk. For example, a water solution can be prepared from a salt mixture containing calciumchloride, calium chlor­ ide, sodium chloride, and magnesium chloride. The con­ centrations of said salts in the water solution are as follows: In the balancing of the resin, preferably one column volume of the water solution prepared from the salt mixture as described above is passed through the resin bed. If the chromatographic separation is carried out by means of a resin in the calcium form, milk is pre­ cipitated when it comes into contact with the resin, and the column is clogged. On the other hand, if the resin is in the sodium form, the micellic structure of casein is broken, and the casein dissolves into a sodium caseinate form. Milk thereby becomes transparent in appearance, and at the same time the taste and other properties thereof change. On the contrary, the casein preserves its micellic structure, but is not precipitated when a balanced cation exchange resin is used according to the present inven­ tion for the chromatographic treating of milk. In the treatment of milk, an extremely high hygiene is required. In general, this can be affected by a suitable choice of the pH and temperature. In the process according to the invention, the pH cannot be adjusted to any greater degree, because it is of advantage to keep the milk proteins in the anionic form (pH over 5) so as to prevent them from adhering to the resin. The temperature must be such that no bacterial growth occurs in the milk. For instance, the temperature used in the process for the chromatographic treatment of whey stated in U.S. Patent No. 3,969,337, i.e. 20°C, is impossible in practice because it is thereby not possible to control the bacterial growth. The ultra­ filtration, in turn, aims at as high temperatures as possible, although the resistance of the membranes sets the upper limit to about 50 to 55°C. At these temperatures the bacterial growth is already clearly slower than at 20°C. In the chromatographic treatment of milk, the starting point, however, is that no growth at all is allowed, and the microbiological quality should preferably be improved. It has been found that this is achieved by carrying out the chromatographic separa­ tion at a temperature within the range from 50 to 80°C, the preferred temperature range being from 55 to 70°C. Even chromatographing temperatures exceeding 80°C are possible in view of the resistance of resin; however, the whey proteins contained in the milk start to dena­ turate at such temperatures, as a result of which their properties change. The process according to the invention is suitable for the treatment of both fatless and fatty milk, because the milk fat melts completely at temperatures exceeding 40°C. Unexpectedly the separation of lactose from fatty milk takes place as specifically as from fatless milk. Thereby the fat, proteins and salts are separated as one fraction and the lactose as another. The water and waste water costs of the process according to the invention are extremely low, because the elution can be carried out with condensation water coming from the evaporator when milk is concentrated by evaporating before the chromatographic separation. The condensation water is more suitable for eluation than tap water, because the salt content thereof is very low. If the fractions are concentrated by evaporating, the same water can be circulated in the process. With the exception of the washing of the column, the process does not produce waste water to any greater degree. Test results show that the interval between two washings can be several days, provided that a daily washing is not required e.g. by legislation. The energy costs of new evaporators based on the mechanical compression of steam are so low that the only major disadvantage of the chromatographic separa­ tion, i.e. dilution, does not notably affect the profi­ tability of the process. In the process, the chromatography column can be charged with fairly large amounts of milk so that the dilution is insignificant. In practice, a suitable ratio of the volume of the milk to be treated to the volume of the balanced cation exchange resin contained in the column is from about 1:200 to about 1:4, preferably from about 1:50 to about 1:5. The following examples are illustrative of the invention. Example 1 A column having a height of 100 cm and a dia­ meter of 1.6 cm was filled with a strong cation exchange resin manufactured by Suomen Sokeri Oy and having a structure of the same type as e.g. Duolite C 204 F (Duolite International S.A.). The mean particle size of the resin was 0.4 mm. The resin volume of the column after it was ready packed was 160 ml. The column was provided with a heating jacket by means of which the temperature was maintained at 65°C. Two litres of fatless milk was first pumped through the column for the achievement of an ionic balance. After a flushing with water, 5 ml of fatless concentrated milk (pH ad­ justed to 6.7 with NaOH, the dry content 27%) was fed into the column. The elution was carried out with demineralized water. The flow rate was 150 ml/h. The fractions were gathered every two minutes. The fractio­ nation of fatless milk under these conditions is pre­ sented in Tables 1 and 2. Table 1 Fractionation of fatless concentrated milk under the conditions of Example 1 Table 2 Distribution of the other components of fatless milk into a protein and a lactose fraction under the conditions of Example 1 Example 2 The test arrangements were the same as in Example 1 except that now 2 ml of concentrated milk (dry content 36%) prepared from whole milk (3.9% fat) was fed into the column containing the balanced cation exchange resin. The results are shown in Table 3. Table 3 Fractionation of fatty concentrated milk under the conditions of Example 2 Example 3 The test arrangements were the same as in Example 1 except that 15 ml of fatless concentrated milk (dry content 29%) was fed into the column containing the balanced cation exchange resin. As appears from Table 4, the separation was still fairly good, and the dilution insignificant. Table 4 Fractionation of fatless concentrated milk Example 4 The hygiene of the separation column was observed by determining the microbe amounts of fractions obtained from the column by means of the total colony determina­ tion. The influence of temperature was clearly brought out when fatless concentrated milk of low quality was chromatographed at 50°C and 65°C with the test arrange­ ments of Example 1. Table 5 shows the results of the first run. With a longer run at 50°C, the column was contaminated even more clearly, whereas the column remained clean at 65°C. Table 5 The influence of temperature on the microbio­ logical quality of the fractions Example 5 The balancing of resin by means of a salt mixture corresponding to the cationic composition of milk: A water solution was prepared from a salt mixture containing calcium chloride, calium chloride, sodium chloride, and magnesium chloride. The concentration of said salts in the water solution were as follows: The resin used in Example 1 was balanced similarly as in Example 1 except that the balancing was carried out by using, instead of fatless milk, one column volume of the water solution prepared from the salt mixture as described above. When the separation of lactose from milk was carried out with a resin balanced in this way, the results obtained were similar to those obtained with a resin balanced with milk.

Claims: 1. A process for accomplishing specific chroma­ tographic separation of lactose from milk, charac­ terized in, that (a) a column is packed with a particulate cation exchange resin, (b) said cation exchange resin is balanced in such a manner that its cationic composition corresponds to the cationic composition of milk, (c) milk is treated in a column with said balanced cation exchange resin at a temperature of about 50 to about 80°C, and (d) the column is eluted with water to recover successively a protein containing fraction and lactose fraction from the bottom of the column. 2. A process according to claim 1, charac­ terized in, that chromatographic separation is carried out at a temperature of about 55 to about 70°C. 3. A process according to claim 1 or 2,characterized in, that the cation exchange resin is balanced with fatless milk or concentrated milk by using said milk in a volume amount at least 10 times the volume amount of the resin contained in the column. 4. A process according to claim 3, charac­ terized in, that the cation exchange resin is a resin having a polystyrene divinyl benzene skeletal and containing sulphonic acid groups. 5. A process according to any of thepreceding claims characterized in, that the pH of the milk is over 5. 6. A process according to claim 5, charac­ terized in, that the milk is concentrated milk having a dry content of at least 20%. 7. A process according to claim 6, charac­ terized in, that the concentrated milk is pre­ pared from fatless milk and has a dry content of at least 20%. 8. A process according to claim 6, charac­ terized in, that the concentrated milk is pre­ pared from fatty milk and has a dry content of at least 20%. 9. A process according to any of the preceding claims, characterized in, that the ratio of the volume of the milk to be treated to the volume of the balanced cation exchange resin contained in the column is from about 1:200 to about 1:4. 10. A process according to claim 9, charac­ terized in, that the ratio of the volume of the milk to be treated to the volume of the balanced cation exchange resin contained in the column is from about 1:50 to about 1:5. 11. A process according to any of the preceding claims, characterized in, that the elution is carried out with water obtained from the concentra­ tion of the milk to be treated. 12. A process according to any of the preceding claims, characterized in, that the mean particle size of the resin is 0.06 to 0.6 mm.

Inventors: HARJU, MATTI
Applicants: VALIO MEIJERIEN KESKUSOSUUSLIIKE
Application year: 1986
Main classification: A23C9
IPC codes: C13K5, A23C9, A23J1, B01D15