A method for preparing isomerized lactose solution by isomerization of alkali solution

Abstract

The invention discloses a method for preparing isomerized lactose liquid by alkali liquid isomerization, which belongs to the technical field of functional sugars and specifically comprises the following steps: (1) isomerization reaction: preparing isomerized lactose reaction liquid; (2) nanofiltration: using a nanofiltration membrane to reduce monosaccharides and conductivity in the isomerized lactose solution; (3) granular carbon decolorization: the nanofiltration concentrate is subjected to granular carbon decolorization to obtain a decolorized liquid; (4) centrifugation: the decolorized liquid is subjected to a continuous centrifugation method to reduce conductivity and obtain a centrifugation liquid; (5) simulated moving bed chromatographic separation: obtaining a high-purity isomerized lactose liquid product through refining and purification; (6) the lactose separated by chromatography is recycled to the batching process to achieve efficient utilization of raw materials and reduce product production costs; and (7) the nanofiltration permeate obtained in step (2) is used to prepare a high-purity galactose product. The invention realizes the preparation of isomerized lactose liquid by alkali liquid isomerization and the co-production of galactose.

Description

Technical Field

[0001] The invention relates to the technical field of functional sugar preparation, and in particular to a method for preparing isomerized lactose liquid through alkaline solution isomerization. Background Art

[0002] Isomerized lactose is a disaccharide composed of galactose and fructose connected by β-(1→4) glycosidic bonds. It is also called isomerized lactose. It is obtained by isomerization reaction of lactose under alkaline conditions after heat treatment. Isomerized lactose is a functional disaccharide prebiotic with extremely high safety and convenient use. It currently exists in two physical states, namely, isomerized lactose liquid and isomerized lactose powder. Isomerized lactose liquid is a colorless to dark yellow liquid; isomerized lactose powder is a white or nearly white crystalline powder. Both physical states are highly stable, low in sweetness, low in calories, and easily soluble in water. Isomerized lactose is a bifidobacterium factor that can significantly promote the proliferation of bifidobacteria in the human body, inhibit the growth of spoilage bacteria, and thus regulate the balance of intestinal flora; at the same time, it can be metabolized by intestinal microorganisms, and the short-chain fatty acids produced can reduce the intestinal pH value, increase the intestinal osmotic pressure, promote intestinal peristalsis, shorten the intestinal running time, and achieve the effect of preventing, relieving and treating constipation. Isomerized lactose is the only prebiotic that can be used as both medicine and food. In the pharmaceutical industry, it is often called isomerized lactose concentrated solution, which is used to treat constipation and hepatic encephalopathy. In the food field, it is mainly used in infant formula milk powder, middle-aged and elderly milk powder, biscuits, beverages and dietary supplements. As people's understanding of it continues to deepen, isomerized lactose will be more and more widely used in the food field; adding isomerized lactose to animal feed can enhance the animal's resistance to intestinal flora. Therefore, isomerized lactose has broad application prospects and huge demand.

[0003] The production of isomerized lactose by catalyzing lactose with chemical isomerization is the only form of commercial production of isomerized lactose. The preparation of isomerized lactose by chemical isomerization has gone through three different stages, from the single use of strong alkaline reagents such as NaOH, KOH or strong organic bases such as tertiary amines, to the use of composite catalysts such as MgO and NaHSO3, and then to the use of complex catalysts such as NaAlO2 and H3BO3 / NaOH. The conversion rate of isomerized lactose has also increased from about 10% to about 75%. Although the chemical method, especially the use of complex catalysts represented by boric acid and sodium aluminate, can greatly improve the conversion rate of isomerized lactose, the removal of the complex catalyst is cumbersome, there are risks such as environmental pollution and food safety, and the large amount of catalyst, the large number of reaction by-products, the high energy consumption, and the complex separation and purification of the final product have seriously restricted the further development of the preparation of isomerized lactose by chemical isomerization.

[0004] Aiming at the problems of many by-products in the catalytic process, difficulty in separating and removing the catalyst, low recovery rate, large consumption of organic reagents, high cost, long time and food safety hazards in the separation and purification process of high-purity isomerized lactose, the present invention adopts the alkali solution method to isomerize lactose to obtain isomerized lactose liquid, does not use a catalyst, avoids the problem of difficult catalyst separation and food safety problems caused by catalyst residues; the present invention adopts nanofiltration technology to reduce the monosaccharide content in the reaction liquid, and the monosaccharide content is reduced from 8-15% after isomerization to less than 2.5%, and at the same time, the conductivity of the reaction liquid is reduced to less than 2000us / cm. The light transmittance of the alkali isomerized liquid is increased to 99.0% by using granular carbon decolorization and continuous cross-linking coupling technology, which solves the problem of difficult decolorization of the alkali isomerized liquid in the industry, and at the same time, the cross-linking yield of the isomerized lactose liquid is increased by 5-10%; the lactose in the reaction liquid is separated by simulated moving bed chromatography separation technology, and a high-purity isomerized lactose liquid product with a purity of >92% isomerized lactose is prepared by one-step chromatography, which solves the problem of first performing lactose crystallization and then performing two-step chromatography separation to prepare isomerized lactose liquid. In addition, the nanofiltration permeate obtained contains a high-content galactose product, and a high-purity galactose product is prepared after electrodialysis, cross-linking, and chromatography, realizing the preparation of isomerized lactose liquid and galactose co-production by alkali isomerization. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention provides a method for preparing isomerized lactose solution by isomerization of alkali solution, which specifically comprises the following steps:

[0006] Step 1: preparing a lactose solution under temperature and environmental conditions, adjusting the pH value with liquid alkali, and performing an isomerization reaction to obtain an isomerized lactose reaction solution;

[0007] Step 2: using a nanofiltration membrane to reduce the monosaccharide and conductivity in the isomerized lactose reaction liquid of step 1 to obtain a nanofiltration concentrate and a nanofiltration permeate; the feed liquid that passes through the nanofiltration membrane is the nanofiltration permeate; the feed liquid that does not pass through the nanofiltration membrane is the nanofiltration concentrate;

[0008] Step 3: Decolorizing the nanofiltration concentrate obtained in step 2 with granular carbon to obtain a decolorized liquid;

[0009] Step 4: performing centrifugation on the decolorized liquid obtained in step 3 to obtain a centrifugation liquid;

[0010] Step 5: Concentrating the liquid after the separation in step 4 and purifying it by simulated moving bed chromatography to separate the chromatographic AD liquid and the chromatographic BD liquid;

[0011] Step 6: Purifying the chromatographic AD liquid after chromatographic separation in step 5 to obtain a high-purity isomerized lactose liquid;

[0012] Step 7: reusing the chromatographic BD liquid obtained in step 5 to the ingredients in step 1 to recycle the lactose;

[0013] Step 8: subjecting the nanofiltration permeate in step 2 to electrodialysis to reduce the conductivity of the permeate, decolorizing and centrifuging after concentration, and preparing high-purity galactose by simulated moving bed chromatography.

[0014] Furthermore, in step 1, 20-30% of the lactose solution is prepared at a temperature of 50-60°C, the pH is adjusted to 10.7-11.0 with liquid alkali, and the isomerization reaction is carried out at 60-70°C for 60-90 minutes to obtain the isomerized lactose reaction liquid with a conductivity of 8000-10000us / cm.

[0015] Furthermore, in step 2, the molecular weight of the nanofiltration membrane is 200Da, the concentration is 16-18%, the amount of water added is 2.5-3.0 times the mass of the feed liquid, the conductivity after nanofiltration is <2000us / cm, and the monosaccharide content is less than 2.5%.

[0016] Furthermore, the decolorization in step three adopts granular carbon decolorization, the decolorization temperature is 70-75° C., the flow rate adopted for decolorization is 0.5-1.0 BV / h, and the light transmittance after decolorization is greater than 40%.

[0017] Furthermore, the centrifugation in step 4 is carried out in a continuous centrifugation mode, the feed sugar concentration is 20%, the centrifugation flow rate is 2.0-2.8BV / h, the conductivity of the feed liquid after centrifugation is less than 20us / cm, and the transmittance is greater than 95%.

[0018] Furthermore, the temperature of the simulated moving bed chromatography purification in step 5 is 50-60° C., the feed concentration is 38-40%, the resin is a calcium-type strongly acidic cation exchange resin, and the eluent is deionized water.

[0019] Furthermore, the purification in step six includes sequentially performing secondary decolorization, secondary ion exchange, and secondary concentration on the chromatographic AD separation liquid obtained in step five.

[0020] Furthermore, the chromatographic BD liquid in step seven has a lactose purity of ≥85%, and the chromatographic BD liquid is a lactose solution.

[0021] Furthermore, in step eight, the ratio of the nanofiltration permeate to pure water is 1:1, the test temperature is 30-35°C, the feed voltage is 30V, and the current drops to 0.1-0.2A before the test is completed.

[0022] Furthermore, the temperature of the simulated moving bed chromatography in step eight is 50-60° C., the feed concentration is 40-60%, the resin is a potassium-type strongly acidic cation exchange resin, and the eluent is deionized water.

[0023] The beneficial effects of the present invention are:

[0024] (1) The present invention adopts the alkaline solution method to isomerize lactose to obtain isomerized lactose liquid without using a catalyst, thereby avoiding the problem of catalyst separation difficulty and the food safety problem of catalyst residue.

[0025] (2) The present invention adopts nanofiltration technology to reduce the monosaccharide content in the reaction solution from 8-15% after isomerization to below 2.5%, and at the same time, the conductivity of the reaction solution is reduced to below 2000us / cm.

[0026] (3) The granular carbon decolorization and continuous cross-linking coupling technology are used to increase the light transmittance of the alkali isomerization liquid to 99.0%, solving the problem of difficult decolorization of the alkali isomerization liquid in the industry. At the same time, the cross-linking yield of the isomerized lactose liquid is increased by 5-10%.

[0027] (4) The lactose in the reaction solution is separated by one-step chromatography using simulated moving bed chromatography separation technology to prepare a high-purity isomerized lactose liquid product with an isomerized lactose purity of >92%, which solves the problem of first crystallizing lactose and then performing two-step chromatography to prepare isomerized lactose liquid.

[0028] (5) The permeate of the isomerized lactose solution nanofiltration contains a high content of galactose products. After electrodialysis to reduce the conductivity of the permeate, it is concentrated and then decolorized and demixed. The simulated moving bed chromatography separation technology is used to prepare a high-purity galactose product, realizing the co-production of isomerized lactose solution and galactose products by alkali isomerization. It has great industrial production and application value. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0030] Example 1

[0031] Step 1: First, prepare a 20% lactose solution at 50°C, adjust the pH to 10.7 with liquid alkali, and perform isomerization reaction at 60°C for 90 minutes to obtain an isomerized lactose reaction liquid with a conductivity of 8000us / cm.

[0032] Step 2: Using a nanofiltration membrane to reduce the monosaccharide and conductivity in the isomerized lactose reaction liquid of step 1 to obtain a nanofiltration concentrate and a nanofiltration permeate; the feed liquid that passes through the nanofiltration membrane is the nanofiltration permeate, and the feed liquid that does not pass through the nanofiltration membrane is the nanofiltration concentrate. The specific steps are: pouring the isomerized lactose reaction liquid into a nanofiltration membrane for nanofiltration purification, the molecular weight of the nanofiltration membrane is 200Da, the amount of water added is 3.0 times the mass of the feed liquid, and the monosaccharide content in the nanofiltration concentrate obtained after nanofiltration is reduced from 8.71% before nanofiltration to 2.39%, the conductivity is 1900us / cm, and the concentration of the nanofiltration concentrate is 16%;

[0033] Step 3: The concentrated nanofiltration solution after nanofiltration enters a granular carbon decolorization column. The temperature of the decolorization column is 75° C. The flow rate used for decolorization is 1.0 BV / h. The transmittance after decolorization is 48%.

[0034] Step 4: The decolorized liquid is purified by continuous centrifugation. The feed sugar concentration is 20%. The conductivity of the liquid after centrifugation is 18 us / cm, the transmittance is 98.9%, the centrifugation rate is 2.0 BV / h, and the yield of isomerized lactose liquid is 98.5%.

[0035] Step 5: The temperature of simulated moving bed chromatography purification is 60° C., the feed concentration is 40%, the resin is a calcium-type strongly acidic cation exchange resin, the eluent is deionized water, and the chromatography AD liquid and the chromatography BD liquid are separated after chromatography. The AD liquid is isomerized lactose with a purity of 90.06%, and the BD liquid is lactose with a purity of 90.04%;

[0036] Step 6: The chromatographic AD separation liquid obtained in step 5 is subjected to secondary decolorization, secondary ion exchange, and secondary concentration in sequence for purification to obtain an isomerized lactose liquid with a solid content of 68.9% and an isomerized lactose purity of 90.45%. The resin is a calcium-type strongly acidic cation exchange resin, and the eluent is deionized water.

[0037] Step 7: The chromatographic BD liquid obtained in step 5 is recycled to the batching process in step 1 with a lactose purity of 90.04%, thereby reusing the lactose and reducing the production cost of the product;

[0038] Step eight: subjecting the nanofiltration permeate of step two to electrodialysis, wherein the ratio of the nanofiltration permeate to pure water is 1:1, the feed concentration is 60%, the feed voltage is 30 V, and the conductivity in the permeate is reduced by electrodialysis, the temperature is 30° C., and the measurement is terminated when the current is 0.1 A. A high-value product with a galactose purity of ≥95% is prepared by decolorization, ion exchange and simulated moving bed chromatography separation technology, thereby realizing the isomerization of alkali solution to prepare the co-production of isomerized lactose solution and galactose product, the temperature of the simulated moving bed chromatography is 50° C., the resin is a potassium-type strong acid cation exchange resin, and the eluent is deionized water.

[0039] Example 2

[0040] Step 1: First, prepare a 30% lactose solution at 60°C, adjust the pH to 11.0 with liquid alkali, and perform isomerization reaction at 70°C for 60 minutes to obtain an isomerized lactose reaction liquid with a conductivity of 10000us / cm.

[0041] Step 2: Use a nanofiltration membrane to reduce the monosaccharide and conductivity in the isomerized lactose reaction liquid of step 1 to obtain a nanofiltration concentrate and a nanofiltration permeate; the feed liquid that passes through the nanofiltration membrane is the nanofiltration permeate, and the feed liquid that does not pass through the nanofiltration membrane is the nanofiltration concentrate. The specific steps are: pouring the reaction liquid into a nanofiltration membrane for nanofiltration purification, the molecular weight of the nanofiltration membrane is 200Da, and the amount of water added is 2.5 times the mass of the feed liquid. After nanofiltration, the monosaccharide content is reduced from 9.39% before nanofiltration to 1.99%, the concentration of the nanofiltration concentrate is 18%, and the conductivity is 1800us / cm.

[0042] Step 3: The concentrated nanofiltration solution after nanofiltration enters a granular carbon decolorization column. The temperature of the decolorization column is 70° C. The flow rate used for decolorization is 0.5 BV / h. The transmittance after decolorization is 52%.

[0043] Step 4: The decolorized liquid is purified by continuous centrifugation. The feed sugar concentration is 20%. The conductivity of the liquid after centrifugation is 15 us / cm, the transmittance is 99.2%, the centrifugation rate is 2.8 BV / h, and the yield of centrifugation isomerized lactose liquid is 98.0%.

[0044] Step 5: The temperature of simulated moving bed chromatography purification is 50° C., the feed concentration is 38%, the resin is a calcium-type strongly acidic cation exchange resin, and the eluent is deionized water. After chromatography, chromatography AD liquid) and chromatography BD liquid (lactose purity 89.73%) are separated; the AD liquid is isomerized lactose with a purity of 92.11%, and the BD liquid is lactose with a purity of 89.73%;

[0045] Step 6: The chromatographic AD separation liquid obtained in step 5 is subjected to secondary decolorization, secondary ion exchange, and secondary concentration in sequence for purification to obtain an isomerized lactose liquid with a solid content of 67.9% and an isomerized lactose purity of 92.35%.

[0046] Step 7: The chromatographic BD liquid obtained in step 5, with a lactose purity of 89.73%, is recycled to the batching process in step 1 to reuse the lactose and reduce the production cost of the product;

[0047] Step eight: subjecting the nanofiltration permeate of step two to electrodialysis, wherein the ratio of the nanofiltration permeate to pure water is 1:1, the feed concentration is 40%, the feed voltage is 30V, and the conductivity in the permeate is reduced by electrodialysis, and the temperature is 30°C, and the current is terminated at 0.1A. A high-value product with a galactose purity of ≥98% is prepared by decolorization, ion exchange and simulated moving bed chromatography separation technology, thereby realizing the isomerization of alkali solution to prepare the co-production of isomerized lactose solution and galactose product, the temperature of the simulated moving bed chromatography is 60°C, the resin is a potassium-type strong acid cation exchange resin, and the eluent is deionized water.

[0048] Table 1 Example 1 Example 2 Experimental measurement results Isomerized lactose components (area percentage)

[0049]

[0050]

[0051] Although the present invention has been described in detail by way of embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention or any person skilled in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and shall be within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for preparing isomerized lactose solution by alkali isomerization, characterized in that: The steps include: Step 1: preparing a lactose solution under temperature and environmental conditions, adjusting the pH value with liquid alkali, and performing an isomerization reaction to obtain an isomerized lactose reaction solution; Step 2: using a nanofiltration membrane to reduce the monosaccharide and conductivity in the isomerized lactose reaction liquid of step 1 to obtain a nanofiltration concentrate and a nanofiltration permeate; the feed liquid that passes through the nanofiltration membrane is the nanofiltration permeate; the feed liquid that does not pass through the nanofiltration membrane is the nanofiltration concentrate; Step 3: Decolorizing the nanofiltration concentrate obtained in step 2 with granular carbon to obtain a decolorized liquid; Step 4: performing centrifugation on the decolorized liquid obtained in step 3 to obtain a centrifugation liquid; Step 5: Concentrating the liquid after the cross-exchange in step 4 and purifying it by simulated moving bed chromatography to separate and obtain chromatographic AD liquid and chromatographic BD liquid; Step 6: Purifying the chromatographic AD liquid after chromatographic separation in step 5 to obtain a high-purity isomerized lactose liquid; Step 7: reusing the chromatographic BD liquid obtained in step 5 to the ingredients in step 1 to recycle the lactose; Step 8: subjecting the nanofiltration permeate in step 2 to electrodialysis to reduce the conductivity of the permeate, decolorizing and centrifuging after concentration, and preparing high-purity galactose by simulated moving bed chromatography.

2. The method for preparing isomerized lactose solution by alkali isomerization according to claim 1, characterized in that: In step 1, 20-30% of the lactose solution is prepared at a temperature of 50-60° C., the pH is adjusted to 10.7-11.0 with liquid alkali, and the isomerization reaction is carried out at 60-70° C. for 60-90 minutes to obtain the isomerized lactose reaction liquid with a conductivity of 8000-10000 us / cm.

3. The method for preparing isomerized lactose solution by alkali isomerization according to claim 1, characterized in that: In step 2, the molecular weight of the nanofiltration membrane is 200Da, the concentration is 16-18%, the amount of water added is 2.5-3.0 times the mass of the feed liquid, the conductivity after nanofiltration is <2000us / cm, and the monosaccharide content is less than 2.5%.

4. The method for preparing isomerized lactose solution by alkali isomerization according to claim 1, characterized in that: The decolorization in step 3 adopts granular carbon decolorization, the decolorization temperature is 70-75°C, the flow rate adopted for decolorization is 0.5-1.0BV / h, and the light transmittance after decolorization is greater than 40%.

5. The method for preparing isomerized lactose solution by alkali isomerization according to claim 1, characterized in that: The centrifugation in step 4 is carried out in a continuous centrifugation mode, the feed sugar concentration is 20%, the centrifugation exchange rate is 2.0-2.8BV / h, the conductivity of the feed liquid after centrifugation is <20 us / cm, and the transmittance is >95%.

6. The method for preparing isomerized lactose solution by alkali isomerization according to claim 1, characterized in that: The temperature of the simulated moving bed chromatography purification in step 5 is 50-60° C., the feed concentration is 38-40%, the resin is a calcium-type strongly acidic cation exchange resin, and the eluent is deionized water.

7. The method for preparing isomerized lactose solution by alkali isomerization according to claim 1, characterized in that: The purification in step six includes sequentially performing secondary decolorization, secondary ion exchange, and secondary concentration on the chromatographic AD separation liquid obtained in step five.

8. The method for preparing isomerized lactose solution by alkali isomerization according to claim 1, characterized in that: The chromatographic BD liquid in step 7 has a lactose purity of ≥85%, and the chromatographic BD liquid is a lactose solution.

9. The method for preparing isomerized lactose solution by alkali isomerization according to claim 1, characterized in that: In step eight, the ratio of nanofiltration permeate to pure water is 1:1, the test temperature is 30-35°C, the feed voltage is 30V, and the current drops to 0.1-0.2A before the test is completed.

10. The method for preparing isomerized lactose solution by alkaline solution isomerization according to claim 1, characterized in that: The temperature of the simulated moving bed chromatography in step eight is 50-60° C., the feed concentration is 40-60%, the resin is a potassium-type strongly acidic cation exchange resin, and the eluent is deionized water.

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