Method for producing alkyl metal salt of ascorbyl 2-glucoside

Abstract

To provide a method for producing a stable alkali metal salt of ascorbyl 2-glucoside without browning.SOLUTION: The present invention provides a method for producing an alkali metal salt of ascorbyl 2-glucoside that involves reacting ascorbyl 2-glucoside and an alkali metal bicarbonate or alkali metal carbonate in an aqueous solution and adjusting the pH to 5-8, wherein the reaction is performed while introducing nitrogen gas into the aqueous solution from before the reaction.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing a stable alkyl metal salt of ascorbic acid 2-glucoside. [Background technology]

[0002] Ascorbic acid acts as a reducing agent, a collagen synthesis promoter, and an antioxidant. In particular, the excellent antioxidant effect of ascorbic acid suppresses melanin production in the skin and is known as an ingredient that prevents pigmentation such as age spots and freckles, and is widely used in medicines, foods, cosmetics, etc. However, ascorbic acid is unstable in its raw powder form when it is hygroscopic or alkaline, and an aqueous solution of ascorbic acid is not only highly acidic and irritating, but also easily oxidizes and browns due to the Maillard reaction caused by typical amines involved in decomposition, and the browning reaction progresses. For these reasons, cosmetics containing ascorbic acid and products containing water are prone to browning and develop unpleasant odors, losing their value as a product, and the amount of ascorbic acid added to the product is restricted, which inevitably affects its effectiveness (Non-Patent Document 1). From this perspective, a technique of blending flavonoid glycosides with ascorbic acid to suppress browning of ascorbic acid has been reported (Patent Documents 1 and 2). It has also been reported that ascorbic acid 2-glucoside is used instead of ascorbic acid.

[0003] However, the aqueous solution of ascorbic acid 2-glucoside has a low pH and, although its stability is improved slightly, the drawback of browning remains. Therefore, techniques of blending a strong base, lecithin, an ether compound, an ester compound, citric acid, etc. with ascorbic acid 2-glucoside have been reported (Patent Documents 3 to 6). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 04-099771 [Patent Document 2] Japanese Patent Application Publication No. 04-099730 [Patent Document 3] JP 2001-199863 A [Patent Document 4] JP 2002-265344 A [Patent Document 5] JP 2005-220029 A [Patent Document 6] JP 2012-246248 A [Non-patent literature]

[0005] [Non-Patent Document 1] Journal of the Japanese Society for Food and Nutrition, Vol. 26, No. 1, 7-10 (2015) Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for producing a stable alkali metal salt of ascorbic acid 2-glucoside which does not undergo browning. [Means for solving the problem]

[0007] Therefore, the present inventors have discovered that when ascorbic acid 2-glucoside is reacted with an alkali metal hydrogencarbonate or an alkali metal carbonate to produce an alkali metal ascorbic acid 2-glucoside, by introducing nitrogen gas into the aqueous solution from the beginning and adjusting the pH to 5 to 8, the pH after completion of the reaction is stable and a stable alkali metal ascorbic acid 2-glucoside that does not turn brown can be obtained, thereby completing the present invention.

[0008] That is, the present invention provides the following inventions [1] to [4]. [1] A method for producing an alkali metal ascorbic acid 2-glucoside by reacting ascorbic acid 2-glucoside with an alkali metal hydrogencarbonate or an alkali metal carbonate in an aqueous solution and adjusting the pH to 5 to 8, characterized in that the reaction is carried out while introducing nitrogen gas into the aqueous solution before the reaction. [2] The method according to [1], wherein the pH of an aqueous solution of ascorbic acid 2-glucoside is adjusted to 5 to 8 by adding an alkali metal hydrogencarbonate or an alkali metal carbonate while introducing nitrogen gas into the aqueous solution. [3] The method according to [1] or [2], wherein nitrogen gas is introduced into the aqueous solution at a rate of 100 mL / min or more. [4] The method according to any one of [1] to [3], wherein the pH is adjusted to 5 to 7. Effect of the Invention

[0009] According to the method of the present invention, a stable alkali metal ascorbic acid 2-glucoside salt which has a stable pH after completion of the reaction and does not turn brown can be obtained. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Terms used in this specification are used in the same manner as commonly used in the art unless otherwise specified.

[0011] In this specification, "ascorbic acid" is an organic compound named (R)-3,4-dihydroxy-5-((S)-1,2-dihydroxyethyl)furan-2(5H)-one in the IUPAC nomenclature system, which acts as vitamin C for humans and is used as an antioxidant food additive. In addition, the excellent antioxidant effect of ascorbic acid is known as an ingredient that inhibits melanin production in the skin and prevents pigmentation such as age spots and freckles, and is widely used in cosmetics. In this specification, "ascorbic acid 2-glucoside" is a compound in which glucose is bound to the carbon at the 2nd position of ascorbic acid, and is an ascorbic acid derivative with improved stability. It is approved as an active whitening ingredient in quasi-drugs and as a food additive. It is also called stable vitamin C or sustained-release vitamin C.

[0012] In the present specification, the term "alkali metal" refers to an element belonging to Group 1 of the periodic table excluding hydrogen, and includes lithium, sodium, potassium, rubidium, cesium, and francium. In the present invention, sodium and potassium are preferred, and sodium is more preferred.

[0013] In this specification, the term "alkali metal hydrogen carbonate" refers to a hydrogen carbonate of the alkali metal. Specific examples include sodium hydrogen carbonate and potassium hydrogen carbonate, with sodium hydrogen carbonate being more preferred. The "alkali metal carbonate" is a carbonate of the alkali metal. Specific examples include sodium carbonate and potassium carbonate, with sodium carbonate being more preferred.

[0014] In this specification, "pH" refers to the hydrogen ion concentration index of an aqueous solution, and can be measured using a commercially available pH meter. "Dissolved oxygen concentration" is also called the amount of dissolved oxygen, and can be measured using a commercially available dissolved oxygen meter.

[0015] One aspect of the present invention is a method for producing an alkali metal ascorbic acid 2-glucoside by reacting ascorbic acid 2-glucoside with an alkali metal hydrogencarbonate or an alkali metal carbonate. A preferred embodiment of the present invention is a method for producing an alkali metal ascorbic acid 2-glucoside by reacting ascorbic acid 2-glucoside with an alkali metal hydrogencarbonate or an alkali metal carbonate in an aqueous solution and adjusting the pH to 5 to 8, characterized in that the reaction is carried out while introducing nitrogen gas into the aqueous solution before the reaction.

[0016] Specifically, while introducing nitrogen gas into an aqueous solution of ascorbic acid 2-glucoside, an alkali metal hydrogen carbonate or an alkali metal carbonate is added to adjust the pH to 5 to 8.

[0017] The concentration of ascorbic acid 2-glucoside in the aqueous solution is not particularly limited, but is preferably from 1% by mass to 50% by mass.

[0018] In the present invention, it is preferable to introduce nitrogen gas into the aqueous solution of ascorbic acid 2-glucoside from the beginning in order to stabilize the pH after neutralization during the reaction. The rate of introduction of nitrogen gas into the aqueous solution is preferably 100 mL / min or more, more preferably 120 mL / min or more, and even more preferably 150 mL / min or more in order to prevent browning of the resulting alkali metal salt of ascorbic acid 2-glucoside. The introduction of this nitrogen gas is preferably performed so that the dissolved oxygen concentration (DO) in the aqueous solution is 5 ppm or less, and more preferably 4 ppm or less. The method of introducing nitrogen gas into the aqueous solution is preferably performed by blowing nitrogen gas into the aqueous solution. The introduction of nitrogen gas into the aqueous solution is preferably performed until the end of the reaction, that is, until the end of the adjustment of the pH to 5 to 8.

[0019] Next, the pH of the aqueous solution of ascorbic acid 2-glucoside is adjusted to 5 to 8 by adding an alkali metal hydrogen carbonate or an alkali metal carbonate. The alkali metal hydrogen carbonate to be added is preferably sodium hydrogen carbonate or potassium hydrogen carbonate, more preferably sodium hydrogen carbonate.The alkali metal carbonate to be added is preferably sodium carbonate or potassium carbonate, more preferably sodium carbonate. The addition of the alkali metal hydrogen carbonate or the alkali metal carbonate is continued until the pH of the aqueous solution is stabilized between 5 and 8. The rate at which the alkali metal hydrogen carbonate or the alkali metal carbonate is added is preferably gradual so as not to cause a large change in pH. The amount of the alkali metal hydrogen carbonate or the alkali metal carbonate added is until the pH of the aqueous solution is stabilized between 5 and 8, and is theoretically considered to be equimolar to that of ascorbic acid 2-glucoside. The pH is preferably 5 to 7, more preferably 5 to 6, and even more preferably 5 to 5.5. The above reaction is preferably carried out under atmospheric pressure at room temperature, for example, from 5°C to 40°C.

[0020] After completion of the reaction, the resulting aqueous solution of alkali metal ascorbic acid 2-glucoside may be used as is, but it can also be isolated as an alkali metal ascorbic acid 2-glucoside powder by freeze-drying.

[0021] The resulting aqueous solution of alkali metal ascorbic acid 2-glucoside or powder of alkali metal ascorbic acid 2-glucoside is stable and does not brown even when stored for a long period of time. The aqueous solution of alkali metal ascorbic acid 2-glucoside does not change in pH and is stable. Therefore, the aqueous solution of alkali metal ascorbic acid 2-glucoside or the powder of alkali metal ascorbic acid 2-glucoside obtained by the method of the present invention can be widely used in cosmetics, medicines, foods, etc. EXAMPLES

[0022] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples in any way.

[0023] Comparative Example 1 (without N2 purging) 100 g of purified water was weighed into a 200 mL glass beaker. 9.05 g of ascorbic acid 2-glucoside powder was weighed and gradually added to the beaker while stirring with a magnetic stirrer, and completely dissolved at room temperature. Sodium bicarbonate powder was gradually added to the beaker to adjust the pH of the solution to the range of 5.0-8.0. A dissolved oxygen measuring electrode was inserted into the beaker from the beginning, and the dissolved oxygen concentration (DO) in the solution was measured over time. After adjusting the pH, stirring was stopped and the solution was left to stand for 60 minutes, and the pH of the solution was measured.

[0024] Example 1 (with N2 purging from the beginning) The same operation as in Comparative Example 1 was carried out. At this time, from the beginning of the operation, pure nitrogen gas was blown into the solution at a flow rate of 150 mL / min from a nitrogen cylinder via a regulator, and the nitrogen gas was stopped at the stage where the pH adjustment was completed. After the pH adjustment, the stirring was stopped, the solution was left to stand for 60 minutes, and the pH of the solution was measured.

[0025] Table 1 shows the changes in pH and dissolved oxygen concentration (DO) over time.

[0026] [Table 1]

[0027] In Comparative Example 1, the pH rose significantly after standing for 60 minutes, and the DO rose to a level exceeding 7 ppm. In contrast, in Example 1, the pH barely rose after standing for 60 minutes, and the DO was lower than initially, remaining at a low level of 3 ppm or less even after standing for 60 minutes after neutralization.

[0028] About 15 mL of each of the solutions of Comparative Example 1 and Example 1 was measured and placed in a 30 mL glass vial, and after closing the lid, the vial was stored in a thermostatic chamber at 40° C., and the degree of discoloration over time was visually confirmed. As a result, when observed after one month, slight yellowing was observed in Comparative Example 1, but no discoloration was observed in Example 1, demonstrating that Example 1 had good stability.

[0029] The following examples (Comparative Examples 2 and 3 and Example 2) were carried out under conditions in which the solid content was higher than in Comparative Example 1 and Example 1.

[0030] Comparative Example 2 (without N2 purging) 200 g of purified water was weighed into a 500 mL glass beaker. 34.2 g of ascorbic acid 2-glucoside powder was weighed and gradually added to the beaker while stirring with a magnetic stirrer, and completely dissolved at room temperature. Sodium bicarbonate powder was gradually added to the beaker to adjust the pH of the solution to the range of 5.0-8.0. After the pH adjustment, stirring was stopped and the solution was left to stand for 60 minutes, and the pH of the solution was measured.

[0031] Comparative Example 3 (N2 purging started after neutralization) The same operation as in Comparative Example 2 was carried out. After adjusting the pH, pure nitrogen gas was blown into the solution from a nitrogen cylinder via a regulator at a flow rate of 150 mL / min, and the nitrogen gas was stopped at the stage where the pH adjustment was completed. After adjusting the pH, the stirring was stopped, the solution was left to stand for 60 minutes, and the pH of the solution was measured.

[0032] Example 2 (N2 purging started from the beginning) 200 g of purified water was weighed into a 500 mL glass beaker. 34.2 g of ascorbic acid 2-glucoside powder was weighed and gradually added to the beaker while stirring with a magnetic stirrer, and completely dissolved at room temperature. Sodium bicarbonate powder was gradually added to the beaker to adjust the pH of the solution to 5.0-8.0. At the beginning of the operation, pure nitrogen gas was blown into the solution from a nitrogen cylinder via a regulator at a flow rate of 150 mL / min, and the nitrogen gas flow was stopped when the pH adjustment was completed. After the pH adjustment, the stirring was stopped, the solution was left to stand for 60 minutes, and the pH of the solution was measured.

[0033] The change in pH over time is shown in Table 2.

[0034] [Table 2]

[0035] In Comparative Example 2, the pH increased slightly after standing for 60 minutes. In contrast, in Comparative Example 3, in which nitrogen purging was performed immediately after the pH adjustment, the dissolved carbon dioxide was suddenly removed, and the pH rose significantly toward the alkaline side. In Example 2, in which nitrogen purging was performed from the beginning, almost no increase in pH was observed.

[0036] The aqueous solutions after the reaction in Examples 1 and 2 and Comparative Examples 1 to 3 were freeze-dried to obtain sodium ascorbic acid 2-glucoside powder. The NMR of the obtained powder was measured, and it was confirmed that it was sodium ascorbic acid 2-glucoside.

Claims

1. A method for producing an alkali metal ascorbic acid 2-glucoside by reacting ascorbic acid 2-glucoside with an alkali metal hydrogencarbonate or an alkali metal carbonate in an aqueous solution and adjusting the pH to 5 to 8, characterized in that the reaction is carried out while introducing nitrogen gas into the aqueous solution before the reaction.

2. 2. The process according to claim 1, wherein the pH of the aqueous solution of ascorbic acid 2-glucoside is adjusted to 5 to 8 by adding an alkali metal hydrogencarbonate or an alkali metal carbonate while introducing nitrogen gas into the aqueous solution.

3. 3. The process according to claim 1, wherein nitrogen gas is introduced into the aqueous solution at a rate of 100 mL / min or more.

4. The process according to any one of claims 1 to 3, wherein the pH is adjusted to 5 to 7.

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