Method for improving pH and stability of crystal xylitol
阅读说明：本技术 一种提升晶体木糖醇pH和稳定性的方法 (Method for improving pH and stability of crystal xylitol ) 是由 吴强 毛宝兴 吴爱娟 魏子尧 林翠 石丽华 徐伟冬 秦淑芳 于 2020-12-29 设计创作，主要内容包括：本发明公开一种提升晶体木糖醇pH和稳定性的方法,采用碱液调节木糖醇离交液pH,提高晶体木糖醇的pH,并降低晶体木糖醇的水分活度；具体包括如下步骤：取木糖醇离交液,利用碱液调节其pH,碱液调节后的木糖醇离交液pH为6.9～7.1,折光率为50％～55％,电导率≤50μs/cm；将碱液调节后的木糖醇离交液进行真空浓缩,得到浓缩液；将浓缩液进行降温结晶,然后进行离心分离、热风干燥、冷风干燥,最终得到晶体木糖醇。本发明采用碱液调节木糖醇离交液的pH,不仅能够明显提高晶体木糖醇的pH,而且能够极大地简化操作、降低生产成本；同时,碱液调节后制备的晶体木糖醇水分活度更低,稳定性更好。(The invention discloses a method for improving the pH and stability of crystal xylitol, which adopts alkali liquor to adjust the pH of xylitol ion exchange liquid, improves the pH of the crystal xylitol and reduces the water activity of the crystal xylitol; the method specifically comprises the following steps: taking xylitol ion-exchange liquid, adjusting the pH of the xylitol ion-exchange liquid by using alkali liquor, wherein the pH of the xylitol ion-exchange liquid after being adjusted by the alkali liquor is 6.9-7.1, the refractive index is 50-55%, and the conductivity is less than or equal to 50 mus/cm; carrying out vacuum concentration on the xylitol ion-exchange liquid regulated by the alkali liquor to obtain a concentrated solution; and (3) cooling and crystallizing the concentrated solution, and then carrying out centrifugal separation, hot air drying and cold air drying to finally obtain the crystal xylitol. The method adopts alkali liquor to adjust the pH of the xylitol ion-exchange liquid, not only can obviously improve the pH of the crystal xylitol, but also can greatly simplify the operation and reduce the production cost; meanwhile, the crystal xylitol prepared after the alkali liquor is adjusted has lower water activity and better stability.)
1. A method for improving the pH and stability of crystalline xylitol is characterized in that an alkali liquor is adopted to adjust the pH of a xylitol ion-exchange liquid, improve the pH of the crystalline xylitol and reduce the water activity of the crystalline xylitol;
the method specifically comprises the following steps:
taking xylitol ion-exchange liquid, and adjusting the pH of the xylitol ion-exchange liquid by using alkali liquor, wherein the pH of the xylitol ion-exchange liquid adjusted by the alkali liquor is 6.9-7.1, the refractive index is 50-55%, and the conductivity is less than or equal to 50 mu s/cm;
step two, carrying out vacuum concentration on the xylitol ion-exchange liquid adjusted by the alkali liquor to obtain a concentrated solution;
and step three, cooling and crystallizing the concentrated solution obtained in the step two, and then carrying out centrifugal separation, hot air drying and cold air drying to finally obtain the crystal xylitol.
2. The method for improving the pH and stability of crystalline xylitol according to claim 1, wherein the refractive index of the xylitol ion-exchange liquid before being adjusted by alkali liquor in the first step is 50-55%, and the conductivity is less than or equal to 50 mus/cm.
3. The method for improving the pH and stability of crystalline xylitol according to claim 1, wherein the step-one alkaline solution comprises NaOH solution, KOH solution or Na solution2CO3And (3) solution.
4. The method for improving the pH and stability of crystalline xylitol according to claim 3, wherein the NaOH solution is a 1-4 wt% NaOH solution, the KOH solution is a 1-4 wt% KOH solution, Na is2CO3The solution is 4 to 10 weight percent of Na2CO3And (3) solution.
5. The method for improving the pH and the stability of the crystalline xylitol according to claim 1, wherein the second step is carried out vacuum concentration under the conditions of a vacuum degree of-0.085 MPa to-0.095 MPa and a temperature of 55 ℃ to 70 ℃ until the refractive index of the concentrated solution is 75 percent to 83 percent.
6. The method for improving the pH and stability of crystalline xylitol according to claim 1, wherein the temperature of step three is reduced at 40-65 ℃ for crystallization for 6-24 h.
7. The method for improving the pH and stability of crystalline xylitol according to claim 1, wherein the centrifugation in step three is carried out at 600-1000 rpm for 1-5 min.
8. The method for improving the pH and the stability of the crystalline xylitol according to claim 1, wherein the third step is carried out by hot air drying at 50 to 70 ℃ for 5 to 30 min.
9. The method for improving the pH and stability of crystalline xylitol according to claim 1, wherein the third step is carried out by cold air drying at 15-25 ℃ for 5-20 min.
Technical Field
The invention relates to the technical field of xylitol preparation, in particular to a method for improving the pH and stability of crystalline xylitol.
Background
Xylitol is a five-carbon sugar, has the same sweetness as sucrose, emits a large amount of heat when dissolved in water, is a natural sweetener with wide prospect, and has good application in the fields of food, beverage, medicine and the like. At present, xylose is mainly used as a raw material in industry, and a xylitol solution is obtained through catalytic hydrogenation reaction; then the xylitol solution is subjected to the working procedures of decolorization, ion exchange, concentration, crystallization and the like to obtain the crystal xylitol. In the ion exchange process, the xylitol solution can remove impurity ions in the feed liquid and can also play a role in adjusting the pH of the feed liquid after passing through the anion and cation exchange columns. In the industrial production of the crystal xylitol, an ion exchange column generally adopts a mode of connecting an anode column and an cathode column in series, and whether a feed liquid is qualified is judged by measuring the pH and the conductivity of the discharged material of the cathode column; however, the crystalline xylitol prepared by connecting the positive column and the negative column in series has low pH and high water activity, the pH is about 5.0 generally, and the water activity reaches over 0.53, which not only causes the stability of the crystalline xylitol to be reduced, but also greatly limits the application of the xylitol.
To raise the pH of crystalline xylitol, there are currently two main methods: firstly, adding an alkaline solution to adjust the pH of a feed solution to 6.0-7.5 after corncobs are hydrolyzed, decoloring, ion exchange, concentrating and crystallizing the feed solution to obtain xylose, dissolving and hydrogenating the xylose to obtain a xylitol hydrogenated solution, and decoloring, ion exchange, concentrating, crystallizing and the like the hydrogenated solution to obtain crystal xylitol, wherein the method can improve the pH of the crystal xylitol to a certain extent, but the pH of the feed solution is easy to reduce due to the fact that the ion exchange process exists after the alkaline solution is adjusted, and the pH of the crystal xylitol is unstable; and secondly, a group of strong base resin or mixed bed resin is added behind an anion column in the ion exchange process so as to achieve the purpose of increasing the pH value of the crystal xylitol. While reducing the water activity in food products is mostly achieved by adding some food additives or by extending the drying time, this method tends to result in unacceptable food properties. Therefore, there is an urgent need to find a method which is inexpensive, simple to operate, and capable of improving the pH and stability of crystalline xylitol.
Disclosure of Invention
The invention aims to provide a method for improving the pH and stability of crystalline xylitol so as to overcome the defects of the prior art.
The invention adopts the following technical scheme:
a method for improving the pH and stability of crystalline xylitol adopts alkali liquor to adjust the pH of xylitol ion-exchange liquid, improve the pH of the crystalline xylitol and reduce the water activity of the crystalline xylitol;
the method specifically comprises the following steps:
taking xylitol ion-exchange liquid, and adjusting the pH of the xylitol ion-exchange liquid by using alkali liquor, wherein the pH of the xylitol ion-exchange liquid adjusted by the alkali liquor is 6.9-7.1, the refractive index is 50-55%, and the conductivity is less than or equal to 50 mu s/cm;
step two, carrying out vacuum concentration on the xylitol ion-exchange liquid adjusted by the alkali liquor to obtain a concentrated solution;
and step three, cooling and crystallizing the concentrated solution obtained in the step two, and then carrying out centrifugal separation, hot air drying and cold air drying to finally obtain the crystal xylitol.
Further, the refractive index of the xylitol ion-exchange liquid before the adjustment of the alkali liquor in the step one is 50-55%, and the conductivity is less than or equal to 50 mus/cm.
Further, the alkali solution of step one comprises NaOH solution, KOH solution or Na2CO3And (3) solution.
Furthermore, the NaOH solution is 1 to 4 weight percent of NaOH solution, the KOH solution is 1 to 4 weight percent of KOH solution, and Na2CO3The solution is 4 to 10 weight percent of Na2CO3And (3) solution.
Further, the second step is carried out vacuum concentration under the conditions of vacuum degree of-0.085 MPa to-0.095 MPa and temperature of 55 ℃ to 70 ℃ until the refractive index of the concentrated solution is 75 percent to 83 percent.
And further, cooling and crystallizing for 6-24 h at 40-65 ℃.
And further, centrifuging and separating at 600-1000 rpm for 1-5 min.
And further, drying the mixture in the third step for 5-30 min by hot air at 50-70 ℃.
And further, drying the third step for 5-20 min by cold air at 15-25 ℃.
The invention has the beneficial effects that:
compared with the method that the NaOH solution is adopted to adjust the corncob hydrolysate or the strong base resin or the mixed bed resin is adopted to improve the pH value of the crystalline xylitol, the method adopts the alkali solution to adjust the pH value of the xylitol ion-exchange liquid, not only can obviously improve the pH value of the crystalline xylitol, but also can greatly simplify the operation and reduce the production cost; meanwhile, the crystal xylitol prepared after the alkali liquor is adjusted has lower water activity and better stability.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
A method for improving the pH and stability of crystalline xylitol adopts alkali liquor to adjust the pH of xylitol ion-exchange liquid, improve the pH of the crystalline xylitol and reduce the water activity of the crystalline xylitol;
the method specifically comprises the following steps:
step one, taking xylitol ion-exchange liquid (xylitol ion-exchange liquid obtained by ion-exchanging decolorized xylitol liquid by adopting strong acid cation resin and weak base anion resin) which is subjected to a conventional ion-exchange procedure: the refractive index is 50-55%, the conductivity is less than or equal to 50 mu s/cm, the pH value is adjusted by using alkali liquor, and the alkali liquor comprises 1-4 wt% of NaOH solution, 1-4 wt% of KOH solution or 4-10 wt% of Na2CO3The pH value of the solution, the xylitol ion-exchange liquid after the adjustment of the alkali liquor is 6.9 to 7.1, the refractive index is 50 to 55 percent, and the conductivity is less than or equal to 50 mu s/cm ((No matter adding strong alkali liquor or weak alkali liquor, the influence on the conductivity is not great because the amount of the alkali liquor added is small when the required pH value is increased, and the amount of the alkali liquor can be ensured to be within 50 us/cm);
step two, carrying out vacuum concentration on the xylitol ion-exchange liquid after alkali liquor adjustment under the conditions of vacuum degree of-0.085 MPa to-0.095 MPa and temperature of 55 ℃ to 70 ℃ until the refractive index of the concentrated solution is 75 percent to 83 percent;
and step three, cooling and crystallizing the concentrated solution obtained in the step two at 40-65 ℃ for 6-24 h, then centrifugally separating at 600-1000 rpm for 1-5 min, drying with hot air at 50-70 ℃ for 5-30 min, and drying with cold air at 15-25 ℃ for 5-20 min to finally obtain the crystalline xylitol.
Example 1
Taking 1000ml of xylitol ion-exchange liquid: refraction is 52%, pH is 3.91, and conductivity is 3.859 mus/cm; adopting 1 wt% NaOH solution to adjust the pH, and adjusting the properties of the xylitol ion-exchange liquid by alkali liquor: the refractive index is 52%, the pH value is 6.94, and the electric conductivity is 2.022 mu s/cm; then carrying out vacuum concentration on the xylitol ion-exchange liquid regulated by the alkali liquor at-0.095 MPa and 60 ℃ until the refractive index is 80%; then cooling and crystallizing the concentrated solution for 24 hours at 50 ℃; and finally, carrying out centrifugal separation at the rotating speed of 800rpm for 2min, drying by hot air at 50 ℃ for 30min, and drying by cold air at 15 ℃ for 15min to obtain the crystal xylitol.
The acidity of the crystalline xylitol was determined according to the chinese pharmacopoeia method, using fresh ultrapure water, according to 10g crystalline xylitol: xylitol solution was prepared at a ratio of 20ml of ultrapure water, and the pH of the xylitol solution of this example was measured to be 6.36. After the crystalline xylitol was left standing at normal temperature for one week, the pH of the xylitol solution was measured to be 6.29 by the same method. After the crystalline xylitol was left to stand at normal temperature for one month, the pH of the xylitol solution was measured to be 6.27 by the same method.
The water activity of the crystalline xylitol was measured by a water activity tester, and the water activity of the crystalline xylitol of this example was 0.4811.
Example 2
Taking 1000ml of xylitol ion-exchange liquid: the refraction is 53 percent, the pH value is 3.92, and the electric conductivity is 4.309 mu s/cm; adopting 1 wt% NaOH solution to adjust the pH, and adjusting the properties of the xylitol ion-exchange liquid by alkali liquor: the refractive index is 53 percent, the pH value is 7.06, and the electric conductivity is 2.397 mu s/cm; then, carrying out vacuum concentration on the ion exchange liquid adjusted by the alkali liquor at 60 ℃ under the pressure of-0.095 MPa until the refractive index is 80.5%; then cooling and crystallizing the concentrated solution for 24 hours at 50 ℃; and finally, carrying out centrifugal separation at the rotating speed of 600rpm for 5min, drying by hot air at 60 ℃ for 15min, and drying by cold air at 20 ℃ for 8min to obtain the crystal xylitol.
The acidity of the crystalline xylitol was determined according to the chinese pharmacopoeia method, using fresh ultrapure water, according to 10g crystalline xylitol: xylitol solution was prepared at a ratio of 20ml of ultrapure water, and the pH of the xylitol solution of this example was measured to be 6.41. After the crystalline xylitol was left standing at normal temperature for one week, the pH of the xylitol solution was measured to be 6.34 by the same method. After the crystalline xylitol was left to stand at normal temperature for one month, the pH of the xylitol solution was measured to be 6.30 by the same method.
The water activity of the crystalline xylitol was measured by a water activity tester, and the water activity of the crystalline xylitol of this example was 0.4802.
Example 3
Taking 1000ml of xylitol ion-exchange liquid: the refraction is 50.5%, the pH value is 4.05, and the conductivity is 2.465 mu s/cm; adopting 1 wt% NaOH solution to adjust the pH, and adjusting the properties of the xylitol ion-exchange liquid by alkali liquor: the refractive index is 50.5%, the pH is 6.95, and the conductivity is 1.544 mu s/cm; then, carrying out vacuum concentration on the ion exchange liquid adjusted by the alkali liquor at 60 ℃ under the pressure of-0.095 MPa until the refractive index is 79%; then cooling the concentrated solution at 50 ℃ and crystallizing for 24 h; and finally, centrifugally separating at the rotating speed of 1000rpm for 1min, drying by hot air at 70 ℃ for 5min, and drying by cold air at 25 ℃ for 5min to obtain the crystal xylitol.
The acidity of the crystalline xylitol was determined according to the chinese pharmacopoeia method, using fresh ultrapure water, according to 10g crystalline xylitol: xylitol solution was prepared at a ratio of 20ml of ultrapure water, and the pH of the xylitol solution of this example was measured to be 6.26. After the crystalline xylitol was left to stand at normal temperature for one week, the pH of the xylitol solution was measured to be 6.18 by the same method. After the crystalline xylitol was left to stand at normal temperature for one month, the pH of the xylitol solution was measured to be 6.15 by the same method.
The water activity of the crystalline xylitol was measured by a water activity tester, and the water activity of the crystalline xylitol of this example was 0.4829.
To further illustrate the improvement effect of the present invention, the following comparative experiment was performed.
Comparative example 1
Taking 1000ml of xylitol ion-exchange liquid: the refractive index is 53%, the pH value is 4.11, and the electric conductivity is 3.998 mu s/cm; directly carrying out vacuum concentration on the xylitol ion-exchange liquid at-0.095 MPa and 60 ℃ without adding alkali liquor to adjust the pH value until the refractive index is 80%; then cooling the concentrated solution at 50 ℃ and crystallizing for 24 h; and finally, carrying out centrifugal separation at the rotating speed of 800rpm for 2min, drying by hot air at 50 ℃ for 30min, and drying by cold air at 15 ℃ for 15min to obtain the crystal xylitol.
The acidity of the crystalline xylitol was determined according to the chinese pharmacopoeia method, using fresh ultrapure water, according to 10g crystalline xylitol: xylitol solution was prepared at a ratio of 20ml of ultrapure water, and the xylitol solution pH of this comparative example was measured to be 5.02. After the crystalline xylitol was left to stand at normal temperature for one week, the pH of the xylitol solution was measured to be 4.85 by the same method. After the crystalline xylitol was left to stand at normal temperature for one month, the pH of the xylitol solution was measured to be 4.60 by the same method.
The water activity of the crystalline xylitol was measured by a water activity tester, and the water activity of the crystalline xylitol of this comparative example was 0.5358.
Comparative example 2
Taking 1000ml of xylitol ion-exchange liquid: the refractive index is 51%, the pH value is 3.98, and the conductivity is 3.763 mu s/cm; directly carrying out vacuum concentration on the xylitol ion-exchange liquid at-0.095 MPa and 60 ℃ without adding alkali liquor to adjust the pH value until the refractive index is 81%; then cooling the concentrated solution at 50 ℃ and crystallizing for 24 h; and finally, carrying out centrifugal separation at the rotating speed of 600rpm for 5min, drying by hot air at 60 ℃ for 15min, and drying by cold air at 20 ℃ for 8min to obtain the crystal xylitol.
The acidity of the crystalline xylitol was determined according to the chinese pharmacopoeia method, using fresh ultrapure water, according to 10g crystalline xylitol: xylitol solution was prepared at a ratio of 20ml of ultrapure water, and the xylitol solution pH of this comparative example was measured to be 5.00. After the crystalline xylitol was left standing at normal temperature for one week, the pH of the xylitol solution was measured to be 4.84 by the same method. After the crystalline xylitol was left to stand at normal temperature for one month, the pH of the xylitol solution was measured to be 4.62 by the same method.
The water activity of the crystalline xylitol was measured by a water activity tester, and the water activity of the crystalline xylitol of this comparative example was 0.5336.
Comparative example 3
Taking 1000ml of corncob hydrolysate (which is obtained by taking corncobs as raw materials and sulfuric acid as a catalyst and hydrolyzing for 2-3 h at 125 ℃), and adjusting the pH value to 7.0 by adopting 1 wt% of NaOH solution; then, obtaining xylose by the corncob hydrolysate through the steps of conventional decolorization, ion exchange, evaporation, crystallization and the like, carrying out hydrogenation reaction on the dissolved xylose under the catalysis condition of a nickel catalyst, decolorizing until the light transmittance is more than or equal to 95%, carrying out filter pressing under the pressure less than or equal to 0.5MPa, and carrying out ion exchange on the xylose by a cation exchange column and an anion exchange column to obtain xylitol ion exchange liquid: the refractive index is 53 percent, the pH value is 5.38, and the conductivity is 4.136 mu s/cm; directly carrying out vacuum concentration on the ion exchange liquid at-0.095 MPa and 60 ℃ until the refractive index is 80%; then cooling the concentrated solution at 50 ℃ and crystallizing for 24 h; and finally, carrying out centrifugal separation at the rotating speed of 1000rpm for 1min, drying by hot air at 70 ℃ for 5min, and drying by cold air at 25 ℃ for 5min to obtain the crystal xylitol.
The acidity of the crystalline xylitol was determined according to the chinese pharmacopoeia method, using fresh ultrapure water, according to 10g crystalline xylitol: xylitol solution was prepared at a ratio of 20ml of ultrapure water, and the xylitol solution pH of this comparative example was measured to be 5.77. After the crystalline xylitol was left to stand at normal temperature for one week, the pH of the xylitol solution was measured to be 5.65 by the same method. After the crystalline xylitol was left to stand at normal temperature for one month, the pH of the xylitol solution was measured to be 5.50 by the same method.
The water activity of the crystalline xylitol was measured by a water activity tester, and the water activity of the crystalline xylitol of this comparative example was 0.5276.
The results of pH and water activity measurements of the crystalline xylitol prepared in each of the above examples and comparative examples were summarized to obtain table 1: as can be seen from Table 1, the pH values of examples 1 to 3 are all above 6.0, the pH value after one month changes from 0.09 to 0.11, and the water activity after one month is below 0.49, while the pH values of comparative examples 1 to 3 are all below 6.0, the pH value after one month changes from 0.27 to 0.42, and the water activity after one month is above 0.52.
TABLE 1
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.