Method for extracting citrulline from watermelon

Abstract

The present invention relates to the technical field of natural substance extraction. Disclosed is a method for extracting Citrulline from a watermelon. The method for extracting Citrulline from a watermelon in the present invention comprises Raw material pretreatment, ultrasound-enzymatic hydrolysis assisted solvent leaching, and purification steps. The purification step comprises microbial fermentation, ion-exchange resin purification, macroporous adsorption resin discoloration, and crystallization and recrystallization. The method for extracting Citrulline in the present invention is simple, requires a mild condition, and has a good extraction effect on Citrulline. The purity of Citrulline after purification is more than 90%. In addition, the Citrulline extracted by the method in the present invention meets the related health requirements and product quality standards, can be applied to food and health food industries as a raw material, and has natural security advantages.

Claims

1. A method for extracting Citrulline from watermelon, comprising the steps of pretreating the watermelon, ultrasound-enzymatic hydrolysis assisted solvent leaching and purification; the step of purification includes: (1) microbial fermentation: adding 5% (v/v) yeast to a Citrulline extract and conducting a fermentation for 24 hours to remove the amount of sugar in the Citrulline extract; (2) ion-exchange resin purification: filtering the Citrulline extract to remove the yeast, passing the Citrulline extract over an HD-8 activated wet resin to adsorb the Citrulline, and eluting the HD-8 activated wet resin with 0.5 mol/L ammonia solution at an elution rate of 2 BV/h to obtain a Citrulline eluent; (3) macroporous adsorption resin discoloration: mixing a XAD-761 activated wet resin with the Citrulline eluent at a ratio of 1:20 (g/mL), and performing a static adsorption at 100-150 r/min for 2 hours at room temperature to obtain a crude Citrulline extract; (4) crystallization and recrystallization: a. concentrating the crude Citrulline extract under vacuum to obtain a concentrated solution with a soluble solid content 30%, adjusting the pH of the concentrated solution to 5.97, and precipitating at 4 C., centrifuging, washing and drying to obtain a white powdered solid of Citrulline crystals, b. dissolving the white powered solid of step (a) with water, adjusting the pH to 5.97, adding 0.1% Citrulline crystals as seed crystals, precipitating at 4 C., and centrifuging to obtain a precipitate, c. recrystallizing the precipitate from step (4)b by dissolving the precipitate with water, adjusting the pH to 5.97, adding 0.1% Citrulline seed crystal, precipitating and centrifuging to obtain a refined solid powder of Citrulline.

2. The method for extracting Citrulline from watermelon according to claim 1, wherein the step of the ultrasound-enzymatic hydrolysis assisted solvent leaching includes adding 0.1-0.2% biological enzyme to the pretreated watermelon.

3. The method for extracting Citrulline from watermelon according to claim 2, wherein the biological enzyme is pectinase, cellulase, or a combination thereof.

4. The method for extracting Citrulline from watermelon according to claim 1, wherein the ultrasonic-enzymatic hydrolysis assisted solvent leaching is conducted twice at a material-liquid ratio of 1:10-1:20 (kg/L), an ultrasonic power of 100-140 W, an extraction temperature of 30-50 C., and an extraction time of 60-120 min.

5. The method for extracting Citrulline from watermelon according to claim 1, wherein: pretreating the watermelon includes: removing an outer skin of the watermelon to obtain a watermelon rind, squeezing the watermelon rind and filtering to obtain a filtered residue or grounding the watermelon rind into a powder; ultrasound-enzymatic hydrolysis assisted solvent leaching includes: adding water to the filtered residue or the powder at a material-liquid ratio of 1:10-1:20 (kg/L) to form a mixture, and then adding 0.1% (w/w) of pectinase and 0.1% (w/w) of cellulose to the mixture; adjust pH to 4.0, sonicating the mixture twice at an ultrasonic power of 100-140 W, at an extraction temperature of 30-50 C., for 60-120 min to obtain the Citrulline extract.

6. The purification method of Citrulline according to claim 1, wherein the ion-exchange resin purification is a shaker static adsorption or a dynamic exchange adsorption.

7. The purification method of Citrulline according to claim 6, wherein: the shaker static adsorption includes mixing the HD-8 activated wet resin and the Citrulline extract in a ratio of 1:15-20 (g/mL), and then performing a static adsorption at 100-150 r/min for 15 min; and the dynamic exchange adsorption includes packing 180 g of HD-8 activated wet resin in a glass chromatography column with an inner diameter of 26 mm and a height of 400 mm, and passing the Citrulline extract through the glass chromatography column at a speed of 2-6 BV/h to adsorb the Citrulline.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIG. 1 shows the effect of temperature and time on Citrulline extraction.

(2) FIG. 2 shows the effect of different extraction methods on Citrulline extraction.

(3) FIG. 3 shows the effect of adsorption time on HD-8 resin exchange adsorption of Citrulline.

(4) FIG. 4 shows the dynamic exchange adsorption curve of Citrulline with HD-8 resin.

DETAILED DESCRIPTION OF THE INVENTION

(5) Terms used in the present invention have the meanings generally understood by those of ordinary skill in the art unless otherwise specified.

(6) The present invention will be described in further detail with reference to specific embodiments and with reference to data. The following examples are only for the purpose of illustrating the present invention, and are not intended to limit the scope of the present invention in any way.

Embodiment 1

(7) A method for extracting Citrulline from watermelon, the steps are as follows:

1. Raw Material Pretreatment

(8) After the outer skin of the watermelon rind is removed, the rind is squeezed and filtered to obtain filter residue or the rind which is dried is ground into a powder;

2. Ultrasound-Enzymatic Hydrolysis Assisted Solvent Leaching

(9) Water was added to the pretreated material at a material-liquid ratio of 1:10 (kg/L), and then 0.1% (m/m) of pectinase and 0.1% (m/m) of cellulose were also added to the above pretreated material. Adjusted the pH of the enzymatic hydrolysis to 4.0, ultrasonic power to 100 W, extraction temperature to 50 C., extraction time to 90 min, and extraction times twice to obtain an extract.

3. Purification

(10) (1) Microbial fermentation: 5% (v/v) yeast was added to the extract or mixed solution of the extract and melon peel juice to ferment for 24 hours to remove sugar.

(11) (2) Ion-exchange resin purification: the liquid of Citrulline extract after microbial fermentation was filtered to remove yeasts, and added to HD-8 activated wet resin to perform the dynamic exchange adsorption of Citrulline, and then eluted with 0.5 mol/L ammonia solution to obtain Citrulline eluent; the elution rate is 2 BV/h;

(12) The dynamic exchange adsorption is that 180 g of activated wet resin was packed in a glass chromatography column with an inner diameter of 26 mm and a height of 400 mm, and the Citrulline extract solution after fermentation by microorganisms was passed through the resin column at a rate of 2 BV/h to adsorb Citrulline.

(13) (3) Macroporous adsorption resin discoloration: mixed XAD-761 activated wet resin with Citrulline eluent at 1:20 (g/mL), and performed static adsorption on condition of 100-150 r/min for 2 hours at room temperature.

(14) (4) Crystallization and recrystallization.

(15) a. The crude Citrulline extract was concentrated under vacuum to a soluble solid with the content 30%, the pH of the concentrated solution was adjusted to 5.97, and the Citrulline crystals were precipitated at 4 C. The precipitate was centrifuged, washed, and dried to obtain a white powdered solid of Citrulline crystals.

(16) b. Dissolved the Citrulline powder of step (a) with water, adjusted the pH to 5.97, added 0.1% Citrulline crystals as seed crystals, precipitated the Citrulline crystals at 4 C., and centrifuged to separate the precipitates.

(17) c. Repeated step (b) 1-2 times, centrifuged the precipitate, washed, and dried to obtain a refined solid powder of Citrulline.

(18) It is determined that the extraction rate of Citrulline in the above method was 93.43%, and the purity of the Citrulline extract after purification was 99.35%.

Embodiment 2

(19) A method for extracting Citrulline from watermelon, the steps are as follows: the ratio of resin to Citrulline extract is 1:15 (g/mL).

1. Raw Material Pretreatment

(20) After the outer skin of the watermelon rind is removed, the rind is squeezed and filtered to obtain filter residue or the rind which is dried is ground into a powder;

2. Ultrasound-Enzymatic Hydrolysis Assisted Solvent Leaching

(21) Water was added to the pretreated material at a material-liquid ratio of 1:15 (kg/L), and then 0.1% (m/m) of pectinase and 0.1% (m/m) of cellulose were also added to the above pretreated material. Adjusted the pH of the enzymatic hydrolysis to 4.0, ultrasonic power to 120 W, extraction temperature to 30 C., extraction time to 60 min, and extraction times to twice to obtain an extract.

3. Purification

(22) (1) Microbial fermentation: 5% (v/v) yeast was added to the extract or mixed solution of the extract and melon peel juice to ferment for 24 hours to remove sugar.

(23) (2) Ion-exchange resin purification: the liquid of Citrulline extract after microbial fermentation was filtered to remove yeasts, and added to HD-8 activated wet resin to perform the dynamic exchange adsorption of Citrulline, and then eluted with 0.5 mol/L ammonia solution to obtain Citrulline eluent; the elution rate is 2 BV/h.

(24) The dynamic exchange adsorption is that 180 g of activated wet resin was packed in a glass chromatography column with an inner diameter of 26 mm and a height of 400 mm, and the Citrulline extract solution after fermentation by microorganisms was passed through the resin column at a rate of 2 BV/h to adsorb Citrulline.

(25) (3) Macroporous adsorption resin discoloration: mixed XAD-761 activated wet resin with Citrulline eluent at 1:20 (g/mL), and performed static adsorption on condition of 100-150 r/min for 2 hours at room temperature.

(26) (4) Crystallization and recrystallization.

(27) a. The crude Citrulline extract was concentrated under vacuum to a soluble solid with the content 30%, the pH of the concentrated solution was adjusted to 5.97, and the Citrulline crystals were precipitated at 4 C. The precipitate was centrifuged, washed, and dried to obtain a white powdered solid of Citrulline crystals.

(28) b. Dissolved the Citrulline powder of step (a) with water, adjusted the pH to 5.97, added 0.1% Citrulline crystals as seed crystals, precipitated the Citrulline crystals at 4 C., and centrifuged to separate the precipitates.

(29) c. Repeated step (b) 1-2 times, centrifuged the precipitate, washed, and dried to obtain a refined solid powder of Citrulline.

(30) It is determined that the extraction rate of Citrulline in the above method was 79.87%, and the purity of the Citrulline extract after purification was 97.65%.

Embodiment 3

(31) A method for extracting Citrulline from watermelon, the steps are as follows:

1. Raw Material Pretreatment

(32) After the outer skin of the watermelon rind is removed, the rind is squeezed and filtered to obtain filter residue or the rind which is dried is ground into a powder;

2. Ultrasound-Enzymatic Hydrolysis Assisted Solvent Leaching

(33) Water was added to the pretreated material at a material-liquid ratio of 1:20 (kg/L), and then 0.1% (m/m) of pectinase and 0.1% (m/m) of cellulose were also added to the above pretreated material. Adjusted the pH of the enzymatic hydrolysis to 4.0, ultrasonic power to 140 W, extraction temperature to 40 C., extraction time to 120 min, and extraction times to twice to obtain an extract.

3. Purification

(34) (1) Microbial fermentation: 5% (v/v) yeast was added to the extract or mixed solution of the extract and melon peel juice to ferment for 24 hours to remove sugar.

(35) (2) Ion-exchange resin purification: the liquid of Citrulline extract after microbial fermentation was filtered to remove yeasts, and added to HD-8 activated wet resin to perform the dynamic exchange adsorption of Citrulline, and then eluted with 0.5 mol/L ammonia solution to obtain Citrulline eluent; the elution rate is 2 BV/h;

(36) The dynamic exchange adsorption is that 180 g of activated wet resin was packed in a glass chromatography column with an inner diameter of 26 mm and a height of 400 mm, and the Citrulline extract solution after fermentation by microorganisms was passed through the resin column at a rate of 2 BV/h to adsorb Citrulline.

(37) (3) Macroporous adsorption resin discoloration: mixed XAD-761 activated wet resin with Citrulline eluent at 1:20 (g/mL), and performed static adsorption on condition of 100-150 r/min for 2 hours at room temperature.

(38) (4) Crystallization and recrystallization.

(39) a. The crude Citrulline extract was concentrated under vacuum to a soluble solid with the content 30%, the pH of the concentrated solution was adjusted to 5.97, and the Citrulline crystals were precipitated at 4 C. The precipitate was centrifuged, washed, and dried to obtain a white powdered solid of Citrulline crystals.

(40) b. Dissolved the Citrulline powder of step (a) with water, adjusted the pH to 5.97, added 0.1% Citrulline crystals as seed crystals, precipitated the Citrulline crystals at 4 C., and centrifuged to separate the precipitates.

(41) c. Repeated step (b) 1-2 times, centrifuged the precipitate, washed, and dried to obtain a refined solid powder of Citrulline.

(42) It is determined that the extraction rate of Citrulline in the above method was 86.58%, and the purity of the Citrulline extract after purification was 98.11%.

COMPARATIVE EXAMPLE 1

(43) A method for extracting Citrulline from watermelon, the steps are as follows:

1. Raw Material Pretreatment

(44) After the outer skin of the watermelon rind is removed, the rind is squeezed and filtered to obtain filter residue or the rind which is dried is ground into a powder;

2. Ultrasound-Enzymatic Hydrolysis Assisted Solvent Leaching

(45) Water was added to the pretreated material at a material-liquid ratio of 1:10 (kg/L), and then 0.1% (m/m) of pectinase and 0.1% (m/m) of cellulose were also added to the above pretreated material. Adjusted the pH of the enzymatic hydrolysis to 4.0, ultrasonic power to 100 W, extraction temperature to 50 C., extraction time to 90 min, and extraction times to twice to obtain an extract.

3. Purification

(46) (1) Microbial fermentation: 5% (v/v) yeast was added to the extract or mixed solution of the extract and melon peel juice to ferment for 24 hours to remove sugar.

(47) (2) Ion-exchange resin purification: the Citrulline extract after microbial fermentation was filtered to remove yeasts, and added to HD-8 activated wet resin to perform the dynamic exchange adsorption of Citrulline, and then eluted with 0.1 mol/L ammonia solution for 2 BV/h of the elution rate.

(48) The dynamic exchange adsorption is that 180 g of activated wet resin was packed in a glass chromatography column with an inner diameter of 26 mm and a height of 400 mm, and the Citrulline extract solution after fermentation by microorganisms was passed through the resin column at a rate of 2 BV/h to adsorb Citrulline.

(49) (3) Macroporous adsorption resin discoloration: mixed XAD-761 activated wet resin with Citrulline eluent at 1:20 (g/mL), and performed static adsorption on condition of 100-150 r/min for 2 hours at room temperature.

(50) (4) Crystallization and recrystallization.

(51) a. The crude Citrulline extract was concentrated under vacuum to a soluble solid with the content of 30%, the pH of the concentrated solution was adjusted to 5.97, and the Citrulline crystals were precipitated at 4 C. The precipitate was centrifuged, washed, and dried to obtain a white powdered solid of Citrulline crystals.

(52) b. Dissolved the Citrulline powder of step (a) with water, adjusted the pH to 5.97, added 0.1% Citrulline crystals as seed crystals, precipitated the Citrulline crystals at 4 C., and centrifuged to separate the precipitates.

(53) c. Repeated step (b) 1-2 times, centrifuged the precipitate, washed, and dried to obtain a refined solid powder of Citrulline.

(54) It is determined that the extraction rate of Citrulline in the above method was 74.28%, and the purity of the Citrulline extract after purification was 95.74%.

COMPARATIVE EXAMPLE 2

(55) A method for extracting Citrulline from watermelon, the steps are as follows:

1. Raw Material Pretreatment

(56) After the outer skin of the watermelon rind is removed, the rind is squeezed and filtered to obtain filter residue or the rind which is dried is ground into a powder;

2. Ultrasound-Enzymatic Hydrolysis Assisted Solvent Leaching

(57) Water was added to the pretreated material at a material-liquid ratio of 1:10 (kg/L), and then 0.1% (m/m) of pectinase and 0.1% (m/m) of cellulose were also added to the above pretreated material. Adjusted the pH of the enzymatic hydrolysis to 4.0, ultrasonic power to 100 W, extraction temperature to 50 C., extraction time to 90 min, and extraction times to twice to obtain an extract.

3. Purification

(58) (1) Microbial fermentation: 8% (v/v) yeast was added to the extract or mixed solution of the extract and melon peel juice to ferment for 24 hours to remove sugar.

(59) (2) Ion-exchange resin purification: the Citrulline extract after microbial fermentation was filtered to remove yeasts, and added to HD-8 activated wet resin to dynamically exchange and adsorb Citrulline, and then eluted with 1.0 mol/L ammonia solution for 2 BV/h of the elution rate.

(60) The dynamic exchange adsorption is that 180 g of activated wet resin was packed in a glass chromatography column with an inner diameter of 26 mm and a height of 400 mm, and the Citrulline extract solution after fermentation by microorganisms was passed through the resin column at a rate of 2 BV/h to adsorb Citrulline.

(61) (3) Macroporous adsorption resin discoloration: mixed XAD-761 activated wet resin with Citrulline eluent at 1:20 (g/mL), and performed static adsorption on condition of 100-150 r/min for 2 hours at room temperature.

(62) (4) Crystallization and recrystallization.

(63) a. The crude Citrulline extract was concentrated under vacuum to a soluble solid with the content of 30%, the pH of the concentrated solution was adjusted to 5.97, and the Citrulline crystals were precipitated at 4 C. The precipitate was centrifuged, washed, and dried to obtain a white powdered solid of Citrulline crystals.

(64) b. Dissolved the Citrulline powder in step (a) with water, adjusted the pH to 5.97, added 0.1% Citrulline crystals as seed crystals, precipitated the Citrulline crystals at 4 C., and centrifuged to separate the precipitates.

(65) c. Repeated step (b) 1-2 times, centrifuged the precipitate, washed, and dried to obtain a refined solid powder of Citrulline.

(66) It is determined that the extraction rate of Citrulline in the above method was 79.73%, and the purity of the Citrulline extract after purification was 92.47%.

COMPARATIVE EXAMPLE 3

(67) A method for extracting Citrulline from watermelon, the steps are as follows:

1. Raw Material Pretreatment

(68) After the outer skin of the watermelon rind is removed, the rind is squeezed and filtered to obtain filter residue or the rind which is dried is ground into a powder;

2. Ultrasound-Enzymatic Hydrolysis Assisted Solvent Leaching

(69) Water was added to the pretreated material at a material-liquid ratio of 1:10 (kg/L), and then 0.1% (m/m) of pectinase and 0.1% (m/m) of cellulose were also added to the above pretreated material. Adjusted the pH of the enzymatic hydrolysis to 4.0, ultrasonic power to 100 W, extraction temperature to 50 C., extraction time to 90 min, and extraction times to twice to obtain an extract.

3. Purification

(70) (1) Microbial fermentation: 3% (v/v) yeast was added to the extract or mixed solution of the extract and melon peel juice to ferment for 24 hours to remove sugar.

(71) (2) Ion-exchange resin purification: the Citrulline extract after microbial fermentation was filtered to remove yeasts, and added to HD-8 activated wet resin to dynamically exchange and adsorb Citrulline, and then eluted with 0.5 mol/L ammonia solution for 1 BV/h of the elution rate.

(72) The dynamic exchange adsorption is that 180 g of activated wet resin was packed in a glass chromatography column with an inner diameter of 26 mm and a height of 400 mm, and the Citrulline extract solution after fermentation by microorganisms was passed through the resin column at a rate of 4 BV/h to adsorb Citrulline.

(73) (3) Macroporous adsorption resin discoloration: mixed XAD-761 activated wet resin with Citrulline eluent at 1:20 (g/mL), and performed static adsorption on condition of 100-150 r/min for 2 hours at room temperature.

(74) (4) Crystallization and recrystallization.

(75) a. The crude Citrulline extract was concentrated under vacuum to a soluble solid with the content of 30%, the pH of the concentrated solution was adjusted to 5.97, and the Citrulline crystals were precipitated at 4 C. The precipitate was centrifuged, washed, and dried to obtain a white powdered solid of Citrulline crystals.

(76) b. Dissolved the Citrulline powder of step (a) with water, adjusted the pH to 5.97, added 0.1% Citrulline crystals as seed crystals, precipitated the Citrulline crystals at 4 C., and centrifuged to separate the precipitates.

(77) c. Repeated step (b) 1-2 times, centrifuged the precipitate, washed, and dried to obtain a refined solid powder of Citrulline.

(78) It is determined that the extraction rate of Citrulline in the above method was 84.77%, and the purity of the Citrulline extract after purification was 97.63%.

Effect of Different Temperature and Time on Citrulline Extraction

(79) Based on the extraction method of Example 1, in the process of ultrasound-assisted solvent extraction, three different extraction temperatures such as 30, 40, and 50 C. were used, and different extraction times (30, 60, 90, 120, 180 min) were set at each extraction temperature to study the effect of different temperature and time on the effect of Citrulline extraction. The results are shown in FIG. 1.

(80) It can be seen from FIG. 1 that increasing the temperature can accelerate the extraction of Citrulline, and also has a certain effect on improving the extraction rate. However, with the increase of temperature, the solubility of other ingredients in watermelon rind will increase, and the Maillard reaction will intensify, which will cause difficulties in subsequent purification work. Therefore, the extraction temperature should not exceed 50 C. At the same time, it can be seen from FIG. 1 that with the increase of extraction time, the amount of Citrulline extracted increase slightly, but it can be extracted completely after 1.5 hours, and further extension of the extraction time has little effect on the increase of extraction rate. Therefore, 1.5-2 hours is chosen as the better extraction time.

Effect of Different Methods on Citrulline Extraction

(81) Based on the extraction method of Citrulline in Example 1, without ultrasound-assisted extraction (complex enzymatic method), without enzymatic hydrolysis (ultrasonic method), the solvent extraction method (control) with neither ultrasound-assisted extraction nor enzymatic hydrolysis and the extraction method (ultrasound-enzymatic method) of Example 1 were used to extract Citrulline in watermelon. The extraction effect was measured as shown in FIG. 2.

(82) It can be seen from FIG. 2 that both the ultrasonic extraction and the complex enzymatic treatment can improve the extraction effect of Citrulline. In addition, the ultrasound-enzymatic method has the best extraction effect on Citrulline.

Effect of Different Enzyme Treatments on the Citrulline Extraction

(83) Based on the Citrulline extraction method in Example 1, different biological enzymes were added to perform enzymolysis treatment on rind with outer skin was removed, and the effect of different enzyme treatments on the Citrulline extraction was measured. The results are shown in Table 1.

(84) TABLE-US-00001 TABLE 1 Effect of different enzyme treatments on Citrulline extraction in watermelon rind Concentration of Citrulline in Treatment Addition extract (mg/mL) Pectinase 0.2% 1.227 Cellulase 0.2% 1.205 Pectinase + Cellulase 0.1% + 0.1% 1.278 Control (not processed) 1.114

(85) The results in Table 1 show that the addition of pectinase and cellulase towards raw materials of watermelon rind to perform pretreatment is beneficial to the extraction of Citrulline, and the effect of the combined enzyme treatment is better than that of any single enzyme treatment.

Effect of the Number of Extractions on Citrulline Extraction

(86) Based on the Citrulline extraction method of Example 1, the amount of Citrulline was detected for each extraction, and the total extraction was performed 3 times. The results are shown in Table 2:

(87) TABLE-US-00002 TABLE 2 Effect of extraction times on extraction rate Number of extractions 1 2 3 Concentration of Citrulline 1.412 0.410 0.089 in extract (mg/mL) Extraction rate (%) 72.41 21.02 4.72

(88) As can be seen from Table 2, the method of the present invention can efficiently extract Citrulline from watermelon rind. After three extractions, more than 98% of Citrulline can be extracted from watermelon rind. Among them, the first two extraction rates reach 93.43%. So in the extraction of Citrulline from watermelon rind, it is sufficient to extract twice.

Effect of Microbial Fermentation on Citrulline Content

(89) 5% (v/v) yeast was added to the crude Citrulline extract to ferment for 24 hours. The changes in sugar and Citrulline content before and after fermentation were compared. The results are shown in Table 3.

(90) TABLE-US-00003 TABLE 3 Comparison of sugar and Citrulline content before and after fermentation Test items Before fermentation After fermentation Total sugar (mg/mL) 12.90 2.31 Citrulline concentration 1.56 1.52 (mg/mL)

(91) As can be seen from Table 3, after the crude Citrulline extract is fermented by yeast, the total sugar content decreases sharply, but the Citrulline content changes little, indicating that the microbial fermentation method can effectively remove the sugar in it, and has little effect on the Citrulline content.

Effect of Different Ion-Exchange Resins on the Adsorption of Citrulline

(1) Static Adsorption

(92) Took 5 g each of five types of activated wet resins, put them in 250 mL stoppered conical flasks, and added 100 mL of crude Citrulline extract to perform static adsorption on a shaker at room temperature. Determined the content of residual Citrulline of extraction after 8 hours, and then investigated the adsorption effect of different resins on Citrulline. The results are shown in Table 4.

(93) TABLE-US-00004 TABLE 4 Adsorption effect of Citrulline by different resins Resin model D001 D113 HD-8 732 252H Content of Citrulline in 5.26 5.26 5.26 5.26 5.26 the original extract (mg/mL) Citrulline content after 4.20 4.79 3.43 3.83 4.33 adsorption (mg/mL) Equilibrium adsorption 21.18 9.33 36.69 28.55 18.49 capacity (mg/g wet resin) Adsorption percentage (%) 20.13 8.87 34.88 27.14 17.58

(94) As the results in Table 4, it is known that the selected cationic resins can exchange and adsorb Citrulline in the crude Citrulline extract. Among them, strong acid ion-exchange resins such as D001, HD-8, 732, and 252H have a stronger exchange adsorption capacity, while D113 is a weak acid ion exchange resin, which has a weaker exchange adsorption capacity for Citrulline. In addition, among the four strong acid ion exchange resins, HD-8 resin has the strongest exchange capacity for Citrulline in the crude Citrulline extract, and its equilibrium adsorption capacity reaches 36.69 mg/g wet resin.

(2) Effect of Adsorption Time on HD-8 Resin Exchanging Citrulline

(95) Took 10 g of activated HD-8 wet resin, put it in a 250 mL stoppered conical flask, and added 150 mL of crude Citrulline extract to perform static adsorption in a shaker under normal temperature conditions, and periodically sampled to determine the remaining concentration of Citrulline in the supernatant to investigate the dynamic equilibrium time of HD-8 resin exchange adsorption of Citrulline. The results are shown in FIG. 3.

(96) It can be seen from FIG. 3 that the rate of exchanging and adsorbing Citrulline by HD-8 resin is very fast, and the Citrulline in the adsorption extract is quickly exchanged within the first 5 minutes. The rate becomes slowly after 5 minutes, and then reaches equilibrium after 15 minutes.

(3) Dynamic Exchange Adsorption

(97) 180 g of activated wet resin was packed in a glass chromatography column with an inner diameter of 26 mm and a height of 400 mm, and the crude Citrulline extract was passed through the resin column at room speeds of 2, 4, and 6 BV/h respectively. The residual Citrulline content in the effluent was collected and measured to investigate the dynamic exchange adsorption effect of HD-8 resin on Citrulline. The results are shown in FIG. 4.

(98) It can be seen from FIG. 4 that with the increase of the volume of the effluent, the concentration of residual Citrulline in the column solution also gradually increases, indicating that the adsorption percentage of Citrulline in the extract by the HD-8 resin gradually decreases. In addition, as the flow velocity of the column is reduced, the leakage rate of Citrulline is also greatly reduced, and the rate of decrease of the adsorption percentage is significantly slower, indicating that appropriately reducing the flow rate of the column can increase the dynamic adsorption effect. This is because when the flow velocity through the column is too large, the Citrulline in the extraction solution has no time to diffuse to the inner surface of the resin, which causes the HD-8 resin to rapidly decrease the adsorption percentage of Citrulline in the extraction solution. Therefore, a flow rate of 2 BV/h is more appropriate. At this flow rate, when the effluent volume is 2000 mL, the adsorption percentage can still reach more than 50%.

Decoloration Effect of Citrulline Eluent with Different Macroporous Adsorption Resins

(99) Weighed 5 g of XDA-5, XAD-761, AB-8, HZ-803 activated wet resin into 250 mL stoppered triangle flasks respectively, and added 100 mL Citrulline eluent to perform static adsorption on the condition of 100-150 r/min at room temperature. After 2 hours, the light transmittance and Citrulline concentration were measured after filtration and sampling to investigate the effect of different macroporous adsorption resins on the removal of pigment from the Citrulline eluate under static adsorption conditions. The results are shown in the Table 5.

(100) TABLE-US-00005 TABLE 5 Decolorization effect of Citrulline eluent with different macroporous adsorption resins Citrulline Light concentration transmittance (mg/mL) Resin Before After Before After model adsorption adsorption adsorption adsorption XDA-5 78.2 97.4 7.26 7.15 XAD-761 78.2 98.2 7.26 7.22 AB-8 78.2 98.7 7.26 7.06 HZ-803 78.2 97.9 7.26 7.18

(101) It can be known from Table 5 that the four macroporous adsorption resins tested can effectively remove the pigment in the Citrulline eluent, and the adsorption of Citrulline is less. Considering the decolorization effect and the adsorption of Citrulline, it is better to use XAD-761 macroporous adsorption resin to decolor the Citrulline eluent.

Analysis Results of Citrulline Extract of the Present Invention

(102) The physicochemical properties and hygienic indicators of the Citrulline extract extracted in Example 1 were analyzed and compared with the quality standards of commercially available Citrulline products. The results are shown in Table 6.

(103) TABLE-US-00006 TABLE 6 Physicochemical properties and hygienic indicators of Citrulline extract Commercial product Test item Unit Test result standard Citrulline content % 92.48 Ammonium content % <0.02 0.02 (NH.sub.4) Chloride % <0.02 0.02 Sulfate (SO.sub.4) % <0.02 0.02 Iron mg/kg <10 10 Arsenic mg/kg 2.7 10.sup.2 1 Lead mg/kg Not 10 detected

(104) From the test results in Table 6, it can be known that the heavy metal and microbe indexes of the Citrulline extract extracted by the method of the present invention meet the relevant sanitary requirements and product quality standards.

(105) The above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, the technical solutions described in the embodiments are still possibly modified, or some of the technical features are equivalently replaced by those skilled in the art by referring to the foregoing. These modifications or replacements do not depart from the spirit and scope of the technical solutions claimed in the present invention.