Method for preparing pyrazine mixture based on Maillard reaction

Abstract

The invention relates to the field of organic synthesis, in particular to a method for preparing a pyrazine mixture based on a Maillard reaction, which comprises the following steps: carrying out the Maillard reaction in a buffer solution by taking amino acid and reducing sugar as reaction raw materials and ammonium salt as a catalyst, stopping the reaction when the content of the pyrazine mixture in the reaction solution does not change any more, and then purifying and separating to obtain the pyrazine mixture containing 2, 4-diazabicyclo [3, 4-b] pyridine. The invention relates to a pyrazine mixture of 2, 5-dimethylpyrazine, 2, 6-dimethylpyrazine and 2, 3-dimethylpyrazine. Compared with a traditional Maillard reaction, the ammonium salt is introduced into a Maillard reaction system of amino acid and reducing sugar for the first time to serve as the catalyst, and the content of pyrazine in the Maillard product can be remarkably increased.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis, and more specifically to a method for preparing pyrazine mixtures based on Maillard reaction. Background Technology

[0002] The Maillard reaction is a non-enzymatic, brown reaction between amino compounds and reducing sugars. The reaction proceeds through a complex process, ultimately producing a brown or even black mixture containing various small and large molecules, with the high-molecular-weight products also known as melanoidins. The Maillard reaction generates a large number of aroma-producing components and has been used to prepare various fragrances, flavorings, and flavor enhancers. Because both the reaction and the products of the Maillard reaction can be considered natural, these flavor bases have been recognized as "natural" by international authoritative organizations, thus their applications have attracted widespread attention and become a research hotspot in fields such as organic chemistry, food chemistry, flavor chemistry, the food industry, and the tobacco industry.

[0003] In the field of flavor chemistry, many researchers have conducted studies on the preparation of flavorings using various sugar and nitrogen sources through Maillard reactions. For example, patent application CN 109161440 A discloses a method for obtaining Maillard reaction products by reacting reducing sugars and amino acids; patent application CN 104194938 A discloses a method for preparing Maillard reaction flavorings for tobacco using glucose and phenylalanine; patent application CN 112980580 A discloses a Maillard reaction flavoring, its preparation method, and its applications; patent application CN 114947099 A discloses Maillard reaction intermediates, their synthesis methods, and uses; and patent application CN11374342 A discloses a Maillard reaction product, its preparation method, and its applications.

[0004] Although there are many studies on the preparation of fragrances via the Maillard reaction, there are few reports on the preparation and separation of pyrazine mixture fragrances via the Maillard reaction. Moreover, the current process for preparing pyrazine fragrances using the Maillard reaction is relatively crude, mostly using the traditional "one-pot" method to obtain Maillard reaction products, which are then directly applied to the blending of fragrances and flavorings without separation treatment. This results in the limited application and insignificant effects of the Maillard reaction products. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing pyrazine mixtures based on Maillard reaction, wherein the pyrazine mixtures prepared by the method provided by the present invention have good aroma.

[0006] This invention provides a method for preparing a pyrazine mixture based on the Maillard reaction. Using amino acids and reducing sugars as reactants and an ammonium salt as a catalyst, the Maillard reaction is carried out in a buffer solution. The reaction is stopped when the content of the pyrazine mixture in the reaction solution no longer changes. Subsequent purification yields a pyrazine mixture containing 2,5-dimethylpyrazine, 2,6-dimethylpyrazine, and 2,3-dimethylpyrazine. The amino acids are at least one selected from glycine, alanine, lysine, histidine, arginine, valine, leucine, serine, proline, aspartic acid, and asparagine. The reducing sugars are at least one selected from xylose, arabinose, glucose, fructose, and galactose. The ammonium salts are at least one selected from ammonium acetate, ammonium chloride, ammonium sulfate, diammonium hydrogen phosphate, and ammonium citrate.

[0007] In some embodiments, the purification includes the following steps: (1) The pyrazine mixture was distilled from the reaction solution using molecular distillation equipment; (2) The pyrazine mixture obtained in (1) is first neutralized with an alkaline substance, and then extracted with an organic solvent; (3) The organic phase of the pyrazine-containing mixture obtained in (2) is distilled to recover the organic solvent, and crude pyrazine mixture is obtained; (3) Purification is carried out by distillation.

[0008] In some embodiments, high performance liquid chromatography is used to detect the content of the pyrazine mixture in the reaction solution.

[0009] In some embodiments, the buffer solution is used to maintain a pH of 6-7, such as 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, or 7.0.

[0010] In some embodiments, the buffer solution is a NaH2PO4-Na2HPO4 buffer solution.

[0011] In some embodiments, the Maillard reaction time is 3-6 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours.

[0012] In some embodiments, the amino acids are preferably leucine, serine, and proline.

[0013] In some embodiments, the reducing sugar is preferably xylose and glucose.

[0014] In some embodiments, the ammonium salt is preferably ammonium acetate and diammonium hydrogen phosphate.

[0015] In some embodiments, the amount of ammonium salt used is 10%-100% of the molar equivalent of amino acids, for example 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%.

[0016] In some embodiments, the Maillard reaction temperature is 90°C-150°C, for example 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C or 150°C.

[0017] In some embodiments, the alkaline substance is selected from one or more of sodium carbonate, potassium carbonate, sodium hydroxide, or potassium hydroxide.

[0018] In some embodiments, the organic solvent is selected from one or more of cyclohexane, n-hexane, ethyl acetate, butyl acetate, benzene, or toluene.

[0019] In some embodiments, the molar ratio of the amino acid to the reducing sugar is 1.0:(1.0-2.0), for example 1.0:1.0, 1.0:1.1, 1.0:1.2, 1.0:1.3, 1.0:1.4, 1.0:1.5, 1.0:1.6, 1.0:1.7, 1.0:1.8, 1.0:1.9 or 1.0:2.0.

[0020] Compared with the prior art, a certain embodiment of the present invention includes at least one of the following beneficial effects: 1. Compared with the traditional Maillard reaction, the content of pyrazine in the Maillard product can be significantly increased by selecting specific amino acid combinations and introducing ammonium salts as catalysts.

[0021] 2. Compared to traditional separation methods, this method is the first to use molecular distillation equipment to separate Maillard reaction products, followed by neutralization, extraction, concentration, and distillation to obtain a pyrazine mixture. The preparation process is simple, easy to operate, and can achieve continuous industrial production.

[0022] In the context of this invention, all figures disclosed herein are approximate values, regardless of whether words such as "approximately" or "about" are used. The value of each figure may vary by 1%, 2%, 5%, 7%, 8%, 10%, 15%, or 20%, etc. Whenever a figure with a value of N is disclosed, any figure having a value of N+ / -1%, N+ / -2%, N+ / -3%, N+ / -5%, N+ / -7%, N+ / -8%, N+ / -10%, N+ / -15%, or N+ / -20% is explicitly disclosed, where "+ / -" indicates addition or subtraction. Whenever a lower limit, RL, and an upper limit, RU, of a numerical range are disclosed, any value within that disclosed range is explicitly disclosed. In particular, the following value is included within this range: R = RL + K * (RU - RL), where K is a variable increasing in 1% increments from 1% to 100%. For example: 1%, 2%, 3%, 4%, 5%, 50%, 51%, 52%, 95%, 96%, 97%, 98%, 99%, or 100%. In addition, the numerical ranges defined by the two R numbers disclosed herein are also specifically included. Detailed Implementation

[0023] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0024] The following examples use the following liquid chromatography parameters: LC-1260 high-performance liquid chromatograph; Shim-pack Scepter C18-120 column (4.6 mm × 250 mm); column oven temperature: 30°C; mobile phase V(methanol):V(water) = 20:80; flow rate: 0.5 mL / min; injection volume: 5.0 μL; detection wavelength: 254 nm.

[0025] The following are the parameters of the molecular distillation equipment in each embodiment: The FMD-100 molecular distillation equipment features a split-type double-layer feed tank with a sample preheating system and an automatic sample feeding system; the main evaporator system has an outer jacket with heat transfer oil and an inner condenser coil, with an evaporation area of ​​0.15 m². 2 Built-in condenser area ≥0.2m² 2 The magnetic stirring and scraping film system uses a high-efficiency, high-temperature resistant, and corrosion-resistant SS316 scraping film basket and PTEE scraper. During use, the molecular distillation cooling system is turned on, the cooling temperature is set, the vacuum system is turned on, liquid nitrogen is added to the cold trap, and the heater is turned on for heating. Once the vacuum and evaporation temperature reach the required experimental conditions, Maillard reaction solution is added, and distillation separation is performed at the set temperature, vacuum, and feed rate.

[0026] The gas chromatography parameters for the following examples are as follows: injection port temperature 250°C, temperature program: initial temperature 70°C, hold for 3 min, then increase at 5°C / min. -1 Heat to 230°C. Use high-purity nitrogen as the carrier gas (purity ≥99.99%) at a flow rate of 1 mL / min. -1 The injection volume was 0.2 μL, and the split ratio was 50:1. The area normalization method was used for analysis.

[0027] In the following examples, all reducing sugars mentioned are D-type sugars, and all amino acids are α-L-type amino acids.

[0028] 1. Selection of amino acid type The preparation methods of Examples 1-9 are as follows: (1) Mix different amino acids with 500g glucose, 21g ammonium acetate (the molar ratio of the amount of added amino acids to the amount of added glucose is 1:1, and the amount of added amino acids is converted to grams accordingly, and the value is rounded to the nearest whole number), and 5kg of NaH2PO4-Na2HPO4 buffer solution with pH=6-7. Heat the mixture in an oil bath to reflux reaction. The reaction temperature is 110°C and the reaction time is 3 hours. Stop the reaction when the content of the pyrazine mixture no longer changes as detected by liquid chromatography. (2) The reaction solution was directly added to the sample feed tank of the molecular distillation apparatus at a feed rate of 20 mL / min, a sample preheating temperature of 45°C, an evaporation temperature of 90°C, an internal condensation temperature of 5°C, a heavy phase heat exchanger temperature of 60°C, a sample loading vacuum of 10–20 Pa, and a scraper rotation speed of 200 r / min. The light and heavy phases of the pyrazine-containing mixture were separated. (3) The light phase of the pyrazine mixture was first neutralized to pH=10 with 10 wt% NaOH, and then extracted three times with ethyl acetate; (4) Combine the extracted organic phases, distill to recover the solvent ethyl acetate, and then continue distilling to obtain the crude pyrazine mixture; (5) The crude pyrazine mixture is further purified by distillation to obtain the corresponding pyrazine mixture; (6) Gas chromatography was used to determine the proportion of the peak areas of 2,5-dimethylpyrazine, 2,6-dimethylpyrazine and 2,3-dimethylpyrazine in the pyrazine mixture to the total peak area of ​​the three pyrazines.

[0029] The amino acids used in Examples 1-11 and the preparation results are shown in Table 1.

[0030] Table 1

[0031] Conclusion: As can be seen from Table 1, the selected amino acids can all yield the corresponding pyrazine mixtures by Maillard reaction with glucose. Among them, proline, leucine and serine have higher yields and are the preferred amino acids.

[0032] 2. Selection of Ammonium Salt Type The preparation methods for Examples 10-17 and Comparative Examples 1-4 are as follows: (1) Mix 500g glucose, 320g proline (the molar ratio of glucose to proline is 1:1) and 5kg of NaH2PO4-Na2HPO4 buffer solution with pH=6-7, add a certain percentage of ammonium salts of amino acid molar equivalents, heat in an oil bath to reflux reaction, the reaction temperature is 110°C, the reaction time is 3 hours, and stop the reaction when the content of pyrazine mixture no longer changes as detected by liquid chromatography; (2) The reaction solution was directly added to the sample feed tank of the molecular distillation apparatus at a feed rate of 20 mL / min, a sample preheating temperature of 45°C, an evaporation temperature of 90°C, an internal condensation temperature of 5°C, a heavy phase heat exchanger temperature of 60°C, a sample loading vacuum of 10–20 Pa, and a scraper rotation speed of 200 r / min. The light and heavy phases of the pyrazine-containing mixture were separated. (3) The light phase of the pyrazine mixture was first neutralized to pH=10 with 10 wt% NaOH, and then extracted three times with ethyl acetate; (4) Combine the extracted organic phases, distill to recover the solvent ethyl acetate, and then continue distilling to obtain the crude pyrazine mixture; (5) The crude pyrazine mixture was further purified by distillation to obtain the corresponding pyrazine mixtures; (6) Gas chromatography was used to determine the proportion of the peak areas of 2,5-dimethylpyrazine, 2,6-dimethylpyrazine and 2,3-dimethylpyrazine in the pyrazine mixture to the total peak area of ​​the three pyrazines.

[0033] The ammonium salts used in Examples 12-15 and Comparative Examples 1-4, the amount of ammonium salts added, and the preparation results are shown in Table 2.

[0034] Table 2

[0035] Conclusion: As can be seen from Table 2, the yield of the pyrazine mixture produced by the Maillard reaction is significantly improved after the addition of ammonium salts, and ammonium acetate and diammonium hydrogen phosphate have better catalytic effects than ammonium chloride and ammonium sulfate, making them the better ammonium salts.

[0036] 3. Selection of reducing sugar type The preparation methods of Examples 16-25 are as follows: (1) Different types of reducing sugars were mixed with 21g ammonium acetate, 320g proline (the molar ratio of added amino acids to added glucose was 1:1, and the amount of added reducing sugar was converted to grams accordingly, and the value was rounded to the nearest whole number), and 5Kg NaH2PO4-Na2HPO4 buffer solution with pH=6-7. The mixture was heated in an oil bath to reflux reaction at a reaction temperature of 110°C for 3 hours. The reaction was stopped when the content of the pyrazine mixture was no longer changed by liquid chromatography. (2) The reaction solution was directly added to the sample feed tank of the molecular distillation apparatus at a feed rate of 20 mL / min, a sample preheating temperature of 45°C, an evaporation temperature of 90°C, an internal condensation temperature of 5°C, a heavy phase heat exchanger temperature of 60°C, a sample loading vacuum of 10–20 Pa, and a scraper rotation speed of 200 r / min. The light and heavy phases of the pyrazine-containing mixture were separated. (3) The light phase of the pyrazine mixture was first neutralized to pH=10 with 10 wt% NaOH, and then extracted three times with ethyl acetate; (4) Combine the extracted organic phases, distill to recover the solvent ethyl acetate, and then continue distilling to obtain the crude pyrazine mixture; (5) The crude pyrazine mixture was further purified by distillation to obtain the corresponding pyrazine mixtures; (6) Gas chromatography was used to determine the proportion of the peak areas of 2,5-dimethylpyrazine, 2,6-dimethylpyrazine and 2,3-dimethylpyrazine in the pyrazine mixture to the total peak area of ​​the three pyrazines.

[0037] Table 3

[0038] Conclusion: As shown in the table, all selected reducing sugars can undergo a reverse Maillard reaction with proline to yield the corresponding pyrazine mixtures. Xylose and glucose show better reaction results, yielding higher pyrazine mixtures, and are therefore preferred reducing sugars. Furthermore, the yields of the examples with a proline to reducing sugar molar ratio of 1:2.0 are slightly higher than those with a ratio of 1:1.5.

[0039] Maillard reactions were carried out using more preferred amino acids (serine, leucine, and proline), more preferred reducing sugars (glucose and xylose), and more preferred ammonium salts (ammonium acetate and diammonium hydrogen phosphate) at different reaction temperatures and at different reaction times, resulting in Examples 26-30.

[0040] Example 26 (1) Mix 292g serine, 750g glucose, 103g ammonium acetate and 5kg NaH2PO4-Na2HPO4 buffer solution with pH=6-7, heat in an oil bath to reflux reaction, the reaction temperature is 120°C, the reaction time is 4 hours, and stop the reaction when the content of pyrazine mixture no longer changes as detected by liquid chromatography. (2) The reaction solution was directly added to the sample feed tank of the molecular distillation apparatus at a feed rate of 20 mL / min, a sample preheating temperature of 45°C, an evaporation temperature of 90°C, an internal condensation temperature of 5°C, a heavy phase heat exchanger temperature of 60°C, a sample loading vacuum of 10–20 Pa, and a scraper rotation speed of 200 r / min. The light and heavy phases of the pyrazine-containing mixture were separated. (3) The light phase of the pyrazine mixture was first neutralized to pH=10 with 10wt% NaOH, and then extracted three times with ethyl acetate; (4) Combine the extracted organic phases, distill to recover the solvent ethyl acetate, and then continue distilling to obtain the crude pyrazine mixture; (5) The crude pyrazine mixture was further purified by distillation to obtain 43g of pyrazine mixture, with a yield of 14.3%. Gas chromatography was used to determine the peak areas of 2,5-dimethylpyrazine, 2,6-dimethylpyrazine and 2,3-dimethylpyrazine in the pyrazine mixture to the total peak area of ​​the three pyrazines: 23% 2,5-dimethylpyrazine, 71% 2,6-dimethylpyrazine and 6% 2,3-dimethylpyrazine.

[0041] Example 27 (1) Mix 364g leucine, 1000g glucose, 206g ammonium acetate and 5kg NaH2PO4-Na2HPO4 buffer solution with pH=6-7, heat in an oil bath to reflux reaction, the reaction temperature is 130°C, the reaction time is 6 hours, and stop the reaction when the content of pyrazine mixture no longer changes as detected by liquid chromatography. (2) The reaction solution was directly added to the sample feed tank of the molecular distillation apparatus at a feed rate of 20 mL / min, a sample preheating temperature of 45°C, an evaporation temperature of 90°C, an internal condensation temperature of 5°C, a heavy phase heat exchanger temperature of 60°C, a sample loading vacuum of 10–20 Pa, and a scraper rotation speed of 200 r / min. The light and heavy phases of the pyrazine-containing mixture were separated. (3) The light phase of the pyrazine mixture was first neutralized to pH=10 with 10wt% NaOH, and then extracted three times with ethyl acetate; (4) Combine the extracted organic phases, distill to recover the solvent ethyl acetate, and then continue distilling to obtain the crude pyrazine mixture; (5) The crude pyrazine mixture was further purified by distillation to obtain 45.2 g of pyrazine mixture, with a yield of 15.1%. Gas chromatography was used to determine the peak areas of 2,5-dimethylpyrazine, 2,6-dimethylpyrazine and 2,3-dimethylpyrazine in the pyrazine mixture to the total peak area of ​​the three pyrazines: 21% 2,5-dimethylpyrazine, 72% 2,6-dimethylpyrazine and 7% 2,3-dimethylpyrazine.

[0042] Example 28 (1) Mix 320g proline, 416g xylose, 37g diammonium hydrogen phosphate and 5kg NaH2PO4-Na2HPO4 buffer solution with pH=6-7, heat in an oil bath to reflux reaction, the reaction temperature is 110°C, the reaction time is 3 hours, and stop the reaction when the content of pyrazine mixture no longer changes as detected by liquid chromatography. (2) The reaction solution was directly added to the sample feed tank of the molecular distillation apparatus at a feed rate of 20 mL / min, a sample preheating temperature of 45°C, an evaporation temperature of 90°C, an internal condensation temperature of 5°C, a heavy phase heat exchanger temperature of 60°C, a sample loading vacuum of 10–20 Pa, and a scraper rotation speed of 200 r / min. The light and heavy phases of the pyrazine-containing mixture were separated. (3) The light phase of the pyrazine mixture was first neutralized with 10% NaOH to pH=10, and then extracted three times with ethyl acetate; (4) Combine the extracted organic phases, distill to recover the solvent ethyl acetate, and then continue distilling to obtain the crude pyrazine mixture; (5) The crude pyrazine mixture was further purified by distillation to obtain 43.5 g of pyrazine mixture, with a yield of 14.5%. Gas chromatography was used to determine the peak areas of 2,5-dimethylpyrazine, 2,6-dimethylpyrazine and 2,3-dimethylpyrazine in the pyrazine mixture to the total peak area of ​​the three pyrazines: 20% 2,5-dimethylpyrazine, 71% 2,6-dimethylpyrazine and 9% 2,3-dimethylpyrazine.

[0043] Example 29 (1) Mix 292g serine, 624g xylose, 183g diammonium hydrogen phosphate and 5kg NaH2PO4-Na2HPO4 buffer solution with pH=6-7, heat in an oil bath to reflux reaction, the reaction temperature is 120°C, the reaction time is 4 hours, and stop the reaction when the content of pyrazine mixture no longer changes as detected by liquid chromatography. (2) The reaction solution was directly added to the sample feed tank of the molecular distillation apparatus at a feed rate of 20 mL / min, a sample preheating temperature of 45°C, an evaporation temperature of 90°C, an internal condensation temperature of 5°C, a heavy phase heat exchanger temperature of 60°C, a sample loading vacuum of 10–20 Pa, and a scraper rotation speed of 200 r / min. The light and heavy phases of the pyrazine-containing mixture were separated. (3) The light phase of the pyrazine mixture was first neutralized with 10% NaOH to pH=10, and then extracted three times with ethyl acetate; (4) Combine the extracted organic phases, distill to recover the solvent ethyl acetate, and then continue distilling to obtain the crude pyrazine mixture; (5) The crude pyrazine mixture was further purified by distillation to obtain 44.5 g of pyrazine mixture, with a yield of 14.8%. Gas chromatography was used to determine the peak areas of 2,5-dimethylpyrazine, 2,6-dimethylpyrazine and 2,3-dimethylpyrazine in the pyrazine mixture to the total peak area of ​​the three pyrazines: 23% 2,5-dimethylpyrazine, 70% 2,6-dimethylpyrazine and 7% 2,3-dimethylpyrazine.

[0044] Example 30 (1) Mix 364g leucine, 832g xylose, 367g diammonium hydrogen phosphate and 5kg NaH2PO4-Na2HPO4 buffer solution with pH=6-7, heat in an oil bath to reflux reaction, the reaction temperature is 130°C, the reaction time is 6 hours, and stop the reaction when the content of pyrazine mixture no longer changes as detected by liquid chromatography. (2) The reaction solution was directly added to the sample feed tank of the molecular distillation apparatus at a feed rate of 20 mL / min, a sample preheating temperature of 45°C, an evaporation temperature of 90°C, an internal condensation temperature of 5°C, a heavy phase heat exchanger temperature of 60°C, a sample loading vacuum of 10–20 Pa, and a scraper rotation speed of 200 r / min. The light and heavy phases of the pyrazine-containing mixture were separated. (3) The light phase of the pyrazine mixture was first neutralized with 10% NaOH to pH=10, and then extracted three times with ethyl acetate; (4) Combine the extracted organic phases, distill to recover the solvent ethyl acetate, and then continue distilling to obtain the crude pyrazine mixture; (5) The crude pyrazine mixture was further purified by distillation to obtain 45.5 g of pyrazine mixture, with a yield of 15.2%. Gas chromatography was used to determine the peak areas of 2,5-dimethylpyrazine, 2,6-dimethylpyrazine and 2,3-dimethylpyrazine in the pyrazine mixture to the total peak area of ​​the three pyrazines: 20% 2,5-dimethylpyrazine, 72% 2,6-dimethylpyrazine and 8% 2,3-dimethylpyrazine.

[0045] As can be seen from Examples 1, 8, 9, 12, 13, 16, 17, 20, 21, and 26-30, the yields of pyrazine mixtures of more preferred amino acids (serine, leucine, and proline), more preferred reducing sugars (glucose and xylose), and more preferred ammonium salts (ammonium acetate and diammonium hydrogen phosphate) undergoing Maillard reactions at different reaction temperatures and times are approximately 14.06%-15.20%. The yields of pyrazine mixtures in other examples are approximately 4.17%-9.17%, which are significantly higher than the 1.20%-2.07% of the comparative examples. This indicates that ammonium salts do indeed have a strong catalytic effect in Maillard reactions.

[0046] In each embodiment, the peak area of ​​2,5-dimethylpyrazine, 2,6-dimethylpyrazine, and 2,3-dimethylpyrazine was not significantly different from that of the comparative example in terms of the proportion of the total peak area of ​​the three pyrazines.

[0047] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a mixture of pyrazines based on Maillard reaction, comprising: using an amino acid and a reducing sugar as raw materials for reaction, using an ammonium salt as a catalyst, carrying out Maillard reaction in a buffer solution, stopping the reaction when the content of the mixture of pyrazines in the reaction solution no longer changes, and then purifying to isolate a mixture of pyrazines containing 2,5-dimethylpyrazine, 2,6-dimethylpyrazine and 2,3-dimethylpyrazine; the amino acid is at least one of glycine, alanine, lysine, histidine, arginine, valine, leucine, serine, proline, aspartic acid and asparagine; the reducing sugar is at least one of xylose, arabinose, glucose, fructose and galactose; the ammonium salt is at least one of ammonium acetate, ammonium chloride, ammonium sulfate, diammonium hydrogen phosphate and ammonium citrate.

2. The method of claim 1, wherein, the purifying comprises the following steps: (1) distilling the mixture of pyrazines from the reaction solution using a molecular distillation device; (2) neutralizing the mixture of pyrazines obtained in (1) with an alkaline substance and then extracting with an organic solvent; (3) distilling the organic phase containing the mixture of pyrazines obtained in (2) to recover the organic solvent and obtain a crude product of the mixture of pyrazines; (3) purifying by rectification.

3. The method according to claim 2, wherein: the content of the mixture of pyrazines in the reaction solution is detected using high performance liquid chromatography; and / or the buffer solution is used to maintain pH = 6-7; and / or the buffer solution is NaH2PO4-Na2HPO4 buffer solution; and / or the Maillard reaction time is 3-6 hours. the amino acid is leucine, serine and proline; and / or the reducing sugar is xylose and glucose; and / or the ammonium salt is ammonium acetate and diammonium hydrogen phosphate. the amount of the ammonium salt is 10%-100% of the molar equivalent of the amino acid. the Maillard reaction temperature is 90°C-150°C. the alkaline substance is selected from one or more of sodium carbonate, potassium carbonate, sodium hydroxide or potassium hydroxide; and / or the organic solvent is selected from one or more of cyclohexane, n-hexane, ethyl acetate, butyl acetate, benzene or toluene.

4. The method of claim 1, wherein: the molar ratio of the amino acid to the reducing sugar is 1.0: (1.0-2.0). ​ ​ 5. The method of claim 1, wherein: ​ 6. The method of claim 1, wherein: ​ 7. The method of claim 2, wherein: ​ ​ 8. The method of any one of claims 1-7, wherein: ​

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