KR100527412B1 - Method for increase resistant starch content of cross-linked starch using acid treatment - Google Patents

Abstract

The present invention relates to a method for increasing the resistance starch content of crosslinked starch by acid treatment.

An object of the present invention is to provide a method for producing crosslinked starch which can increase the resistance starch content by performing acid treatment and heat treatment on the starch.

The method of increasing the resistance starch content of the crosslinked starch using the acid treatment of the present invention

Reacting by adding acid to the starch and then neutralizing by adding a base;

Heat treating the neutralized starch;

Crosslinking the starch by adding a crosslinking agent and a base after heat treatment;

Neutralization by addition of acid after base addition followed by removal of salt and unreacted crosslinker and drying.

Description

Method for increase resistant starch content of cross-linked starch using acid treatment}

It relates to a method for increasing the resistance starch content of crosslinked starch by acid treatment.

Resistant starch (RS) refers to starch and starch products that are resistant to starch degrading enzymes and are not digested and absorbed in the small intestine of humans. More widely, they are fermented in the large intestine without providing glucose to human tissues. It means starch to produce gas or short chain fatty acid. In the present invention, starch having resistance to starch degrading enzyme is briefly referred to as resistance starch.

Resistant starch is a starch particle that is hard to be decomposed by enzymes and has a B-type crystalline form such as partially starched grains or seeds and physically difficult to access enzymes1, bananas, potatoes and high amylose cornstarch2. , Resistance starch formed by aging, and resistance starch, which is chemically modified starch, are divided into four types.

Resistant starch has a physiological activity similar to that of dietary fiber in that it is not digested and absorbed in the human small intestine.

Resistant starch is not digested and absorbed in the small intestine, which can lower insulin and blood sugar levels in the postprandial blood, resulting in a decrease in energy density. May affect energy loss in the small intestine. Therefore, the addition of resistance starch is useful in the manufacture of diet foods as well as foods for adult diseases such as diabetes and obesity. In addition, there are reports that the physical properties are improved when added to bread, noodles, crackers, etc., it can exhibit a good effect on the quality of food manufacturing as well as the physiological activity of the human body.

Starch including resistance starch is already produced and sold in USA, Europe, Australia and Japan, all of which use high amylose corn starch. However, in Korea, high amylose-containing corn is not produced and the price is very expensive. Therefore, it is thought that a method for increasing the resistance starch content using starch containing amylose content is required. When manufacturing a large amount of resistance starch, economic aspects should be prioritized. Among the various types of resistance starch, production of chemically modified starch 4 is more economical than other types, and the process of manufacturing resistance starch will be simpler. do.

The present inventors have made efforts to increase the resistance starch content in the above-mentioned crosslinked starch, and it has been found that the resistance starch content of the crosslinked starch can be increased by performing acid treatment and heat treatment on the starch during the preparation of the crosslinked starch. .

Accordingly, an object of the present invention is to provide a method for preparing crosslinked starch, which can increase the resistance starch content by performing acid treatment and heat treatment on starch.

The method for increasing the resistance starch content of the cross-linked starch of resistance starch 4 using the acid treatment process of the present invention

Reacting by adding acid to the starch and then neutralizing by adding a base;

Heat treating the neutralized starch;

Crosslinking the starch by adding a crosslinking agent and a base after heat treatment;

Neutralization by addition of acid after base addition followed by removal of salt and unreacted crosslinker and drying.

In the present invention, starch may be used as a general starch as well as powder of grains. As an example of such starch, the present invention may use any one selected from wheat starch, waxy starch, rice starch, glutinous rice starch, corn starch, waxy corn starch, tapioca starch, sweet potato starch and potato starch.

Starch used in the acid treatment of starch in the present invention may be used any acid, including organic acids and inorganic acids. For example, when using any one inorganic acid selected from hydrochloric acid, nitric acid, and carbonic acid, the acid is preferably added in an amount of 0.005 to 1.0% based on the starch weight. In addition, when using any one organic acid selected from citric acid, acetic acid, lactic acid, tartaric acid and tartaric acid, the acid is preferably added to 1% or less by weight of starch.

When the acid is added to the starch, the yield of the starch is reduced to less than 30%, and the yield of the resistant starch is reduced. It is preferable to add so that it may become-50%. In addition, the acid treatment time is measured for various times, it is preferable that the acid treatment time of starch is carried out for 2 to 10 hours.

After the starch is acidified, the base is used to neutralize the starch. When neutralizing starch, the base is not specific, and any base may be used as long as it can neutralize the acidity of starch. After neutralizing the acidified starch using a base, the starch is shaken at 40 to 60 ° C. for 10 to 14 hours to perform heat treatment. After heat treatment under various conditions, in order to increase the resistance starch yield in the starch, it is preferable to shake the mixture at 40 to 60 ° C. for 10 to 14 hours.

After the heat treatment, the starch is prepared using a crosslinking agent. The crosslinking agent is added 10 to 14% by weight of a mixture of 99 to 99.9 parts by weight of sodium trimetaphosphate (STMP) and 0.1 to 1.0 part by weight of sodium tripolyphosphate (STPP) to the starch weight, and preferably for a predetermined time. Make it shake for 20 to 40 minutes. At this time, in order to suppress the gelatinization of the starch before adding the crosslinking agent to the starch solution, 10-12% sodium sulfate is added to the starch weight and shaken for about 30 minutes.

After adding and shaking the crosslinking agent, the base is added to bring the pH to 10-12, and the reaction is performed within 3 hours. In this case, a general base may be used. In the present invention, any one selected from sodium hydroxide, potassium hydroxide, barium hydroxide and calcium hydroxide may be used as an example of the base.

After the reaction is completed, the acid is added to the starch solution and neutralized. The neutralized starch is washed with water to wash off the salt produced by the reaction of the unreacted crosslinker with the base and the acid, and dried slowly at 40 to 60 ° C. The starch is ground after drying to obtain crosslinked starch having an increased resistance starch content.

On the other hand, if the acid used in the acid treatment of the starch is weak acid can be subjected to heat treatment immediately without undergoing a neutralization process. At this time, the acid used in the acid treatment may use the inorganic or organic acid mentioned in the foregoing, and by treating the acid so that the starch concentration is 30-50% with an acid concentration of 0.005 to 0.02N, and then heat-treated for 8 to 16 hours. Crosslinked starch with high yield of resistance starch can be obtained.

Hereinafter, the present invention will be described by the following comparative examples, examples and test examples. However, they are not limited to the scope of the present invention as an example of the present invention.

Comparative Example 1

After dissolving 100 g of wheat starch in 100 ml of distilled water, 10% sodium sulfate was mixed with respect to the weight of wheat starch and shaken at 45 ° C. for 30 minutes. After shaking, a mixture of 99 parts by weight sodium trimethaphosphate and 1 part by weight sodium tripolyphosphate (STPP) as a crosslinking agent was added 12% by weight of the wheat starch and shaken at 45 ° C. for 20 minutes. After shaking, 1M sodium hydroxide was added to make the pH of the solution 11.5, followed by reaction for 3 hours. After completion of the reaction, the starch was neutralized with 1M hydrochloric acid, and the crosslinking agent and the salt which were not reacted with water were repeatedly washed four more times, dried at 40 ° C., and crushed with 100 mesh to prepare crosslinked starch containing resistance starch.

Comparative Example 2

100 g of wheat starch was dissolved in 100 ml of distilled water, and then crosslinked starch was prepared in the same manner as in Comparative Example 1, except that heat treatment was performed while shaking in a constant temperature water bath at 50 ° C. for 12 hours.

<Example 1>

To 100 g of wheat starch, 100 mL of 0.1 N hydrochloric acid was added so that the starch concentration was 50%, and acidified for 2, 6, and 10 hours, respectively, and neutralized with 1 M sodium hydroxide. After neutralization, heat treatment (annealing) was performed while shaking in a constant temperature water bath at 50 ° C. for 12 hours.

The heat-treated suspension was mixed with 10% sodium sulfate by weight of wheat starch and shaken at 45 ° C. for 30 minutes. After shaking, a mixture of 99 parts by weight sodium trimethaphosphate and 1 part by weight sodium tripolyphosphate (STPP) as a crosslinking agent was added 12% by weight of the wheat starch and shaken at 45 ° C. for 20 minutes.

After shaking, 1M sodium hydroxide was added to make the pH of the solution 11.5, followed by reaction for 3 hours. After completion of the reaction, the starch was neutralized with 1M hydrochloric acid, and the crosslinking agent and the salt which were not reacted with water were repeatedly washed four more times, dried at 40 ° C., and crushed with 100 mesh to prepare crosslinked starch containing resistance starch.

<Example 2>

0.1 N hydrochloric acid was added to 100 g of wheat starch, and crosslinked starch containing resistance starch was prepared in the same manner as in Example 1 except for acid treatment for 2, 6, and 10 hours.

<Example 3>

120 mL of 0.1 N hydrochloric acid was added to 100 g of wheat starch, and a crosslinked starch containing resistance starch was prepared in the same manner as in Example 1 except that acid treatment was performed for 2, 6, and 10 hours.

<Example 4>

Citric acid (citric acid) was added to 30 g of wheat starch and 1% of the starch weight, acidified for 2 hours, and neutralized with sodium hydroxide. After neutralization, heat treatment (annealing) was performed while shaking in a constant temperature water bath at 50 ° C. for 12 hours.

After the process was prepared in the same way as in Example 1 cross-linked starch.

Example 5

Cross-linked starch was prepared in the same manner as in Example 4, except that acetic acid was added 1% to starch weight in 30 g of wheat starch.

<Test Example 1>

Resistive starch yield, swelling force at 95 ° C, and solubility at 95 ° C were measured for the crosslinked starch prepared in Comparative Example 1, Comparative Example 2 and Example 1 and the results are shown in Table 1 below. The crosslinked starch prepared in Example 1 is prepared by heat treatment for 12 hours after acid treatment for 2 hours.

As shown in Table 1, the resistance starch yields of the crosslinked starch of Comparative Example 1, which were not subjected to acid treatment and heat treatment, were 16.4% and 85.0%, and the yield of resistance starch of the crosslinked starch of Example 1, which was subjected to acid treatment and heat treatment, was 37.8%. And increased to 99.7%. This is because the branched portion of amylopectin in the starch particles is hydrolyzed by the acid during the acid treatment of the starch, so that the molecules are easily rearranged during the heat treatment and crosslinking occurs efficiently.

On the other hand, in the crosslinked starch prepared in Comparative Examples 1,2 and Example 1, the swelling power did not show a large difference, but it can be seen that the solubility is slightly different from each other.

Table 1.Resistant starch yield, swelling force, solubility results of Comparative Example 1,2 and Example 1 crosslinked starch

Item Comparative Example 1 Comparative Example 2 Example 1 Resistance starch yield (%) P / G 16.4 24.2 39.3 AOAC 85.0 96.9 99.7 Swelling force (95 ℃) 4.34 5.59 4.29 Solubility (95 ℃) 0.84 1.25 1.50

On the other hand, the measurement of the resistance starch yield, swelling power, and solubility of the crosslinked starch was measured by the following method.

(1) resist starch yield (P / G)

Pancreatin-gravimetric method uses pancreatin, an enzyme similar to human enzymes, and measures the residue after degradation. 1 g of sample starch (per building) and 20 mL of acetate buffer solution (pH 5.2) were added to a 50 mL centrifuge tube, mixed well, and heated with stirring in a boiling water bath. This was rapidly cooled, and placed in a constant temperature water bath at 37 ° C. to make the temperature the same. Then, 2 mL of enzyme solution (Pancreatin) was added and reacted for 16 hours. After the reaction, ethanol was added to allow the total solution to have an alcohol concentration of 80%, and left for 1 hour or more, and then filtered through crucible (2G3, IWAKI) containing celite, which was previously dried and weighed. 78% ethanol, 95% ethanol, acetone was washed in order and the insoluble residue was dried for 16 hours in a 105 ℃ oven, the weight was measured and the yield of the resistance starch was calculated by the difference from the crucible weight before filtration.

Enzyme solution was added to 1 mL of pancreatin in 12 mL secondary distilled water and stirred for 10 minutes, followed by centrifugation at 3000 rpm for 10 minutes to mix supernatant 10 mL, 0.2 mL pullulanase and 1.8 mL secondary distilled water. Enzyme solution was prepared just before use and enzymatic reaction was carried out under the same conditions without addition of starch.

(2) Resistance Starch Yield (AOAC)

Dissolve well by adding 40 mL of MES-Tris buffer (pH 8.2) to 1.0 g of starch sample, add 0.1 mL of heat-safe alpha-amylase (Cat No. A-3306, Sigma) and stir in a boiling water bath (100 ° C). After reacting for 15 minutes (850 rpm), the reaction mixture was cooled to room temperature. After cooling, add 0.1 mL (50 mg / mL MES-Tris buffer) of protease (Cat No. P-3910), react for 30 minutes in a 60 ℃ constant temperature shaker, add 5 mL of 0.567N HCl, and adjust the pH to 4.6. 0.1 mL of amyloglucosidase (Cat No. A-9913, Sigma) was added and the reaction was continued at 60 ° C for 30 minutes. In order to stop the reaction, 95% ethanol was added to make the total alcohol concentration 80%, and left for at least 1 hour, and the resultant was filtered with a glass filter (2G3, IWAKI) containing 0.5 g of a known acid washed celite. Washing with 78%, 95% ethanol and acetone and drying the insoluble residue until constant in an oven at 105 ° C. was calculated by weight.

(3) swelling power

The swelling power was added 0.5 g of starch into a 50 mL centrifuge tube and dispersed well in 40 mL of distilled water, then stirred for 30 minutes with a stirrer at 100 ° C. for 30 minutes at 3000 rpm, and the swelling force was calculated by the following equation from the precipitated weight.

(4) solubility

For solubility, add 0.5 g of starch to a 50 mL centrifuge tube, disperse well in 40 mL of distilled water, stir for 30 minutes at 100 ° C with a stirrer, and centrifuge at 3000 rpm for 30 minutes. The total sugar standard curve was calculated by the phenol-sulfuric acid method using glucose.

<Test Example 2>

Resistance starch yield, swelling power, and solubility of the crosslinked starch prepared according to the acid treatment time and the amount of hydrochloric acid used in Examples 1 to 3 were measured using the method described in Test Example 1, and the results were measured. It is shown in Tables 2-1 to 2-3 below.

Table 2-1. Resistance starch yield, swelling force, solubility of Example 1

Starch 100 (g) / 0.1N HCl 100mL Acid Treatment Time (hr) 2 6 10 Resistance starch yield (%) P / G 39.3 38.5 37.8 AOAC 99.7 Swelling force (%) 30 ℃ 2.82 1.34 3.19 95 ℃ 4.42 4.23 4.29 Solubility (%) 30 ℃ 0.83 0.78 0.50 95 ℃ 1.30 1.26 1.50

Table 2-2. Resistance starch yield, swelling force, solubility of Example 2

Starch 100 (g) / 0.1N HCl 110mL Acid Treatment Time (hr) 2 6 10 Resistance starch yield (%) P / G 30.9 33.9 32.6 AOAC 95.9 Swelling force (%) 30 ℃ 3.13 2.92 2.81 95 ℃ 4.67 4.44 4.51 Solubility (%) 30 ℃ 0.80 1.22 0.54 95 ℃ 1.68 1.38 1.32

Table 2-3. Resistance starch yield, swelling force and solubility of Example 3

Starch 100 (g) / 0.1N HCl 120mL Acid Treatment Time (hr) 2 6 10 Resistance starch yield (%) P / G 28 31.8 32.7 AOAC Swelling force (%) 30 ℃ 2.72 2.76 2.96 95 ℃ 3.79 3.92 3.43 Solubility (%) 30 ℃ 0.64 1.02 0.76 95 ℃ 2.82 1.62 1.26

In Table 2-1 to Table 2-3, all of the results of the resistance starch yield (P / G) analysis showed a high yield of 30% or more, except that the acid was treated with 120 ml of hydrochloric acid for 2 hours with respect to 100 g of starch. Among them, the yield of resistance starch of the crosslinked starch prepared in Example 1 having the highest starch concentration was different depending on the heat treatment time, but showed a high yield close to 40% at 37.8 to 39.3%.

<Test Example 3>

Resistance starch of crosslinked starch subjected to acid treatment for 2 hours without heat treatment, resist starch of crosslinked starch subjected to acid treatment for 2 hours in Example 1 (B), acid treatment for 6 hours in Example 1 Resistance starch of one crosslinked starch (C), resistance starch of crosslinked starch subjected to acid treatment in Example 1 for 10 hours (D), resistance starch of crosslinked starch subjected to acid treatment in Example 2 ( E), the resistance starch (F) of the cross-linked starch subjected to acid treatment for 2 hours in Example 3 was used as a sample and the results according to the diffraction angle were measured using an X-ray diffractometer for these samples and shown in FIG. .

As shown in FIG. 1, the crystal structure of Form A showing peaks at 15, 17, and 24 ° at the diffraction angle (2θ) was not different from raw starch. As the acid treatment time increased and the ratio of acid added to starch increased, the peak area of the crystalline form decreased, and as the degree of acid treatment increased, the crystal portion decreased.

X-ray diffraction measurement of the resistive starch of FIG. 1 was obtained by diffraction using a X-ray diffractometer (D / Max 1200, Rigaku Co., Japan) to a diffraction angle (2θ) of 40 to 5 ° and peaks according to the diffraction angle. The degree of crystallinity was compared by the position and intensity of. The equipment conditions used at this time are as follows. Target: Cu-Kα, Filter: Ni, Voltage: 40kV, Current: 20mA, Scanning speed: 8 ° / min

<Test Example 4>

For the sample mentioned in Test Example 3, the particle surface of the sample was observed using a scanning electron microscope, and this is shown in FIG. 2.

As shown in FIG. 2, the particle shape of the starch was maintained intact in both the crosslinked samples after the acid treatment and heat treatment. However, the acid treatment and the annealing treatment appeared to cause some damage to the surface of the particles.The longer the acid treatment time or the higher the amount of acid addition, the lower the resistance starch content and the more dents appeared on the surface of the particles. A flat dent was found.

The particle surface observation of the sample using the scanning electron microscope was performed by adding acetone to each sample to disperse the particles and plating them with gold to make them conductive, and then scanning electron microscopy (Scanning Electron Microscope, JEOL JSM-5400, Japan). Using 25 kV of acceleration voltage, 85 seconds of Phototimes, 2000 times magnification was observed.

<Test Example 5>

Regarding the crosslinked starch prepared in Examples 4 and 5, the resistance starch yield, swelling degree, and solubility were measured using the measuring method described in Test Example 1, and the results are shown in Table 3 below.

Table 3. Resistance starch yield, swelling and solubility results of Examples 4 and 5

Item Resistance starch yield (%) Swelling degree Solubility P / G AOAC 30 ℃ 95 ℃ 30 ℃ 95 ℃ Example 4 29.2 99.7 2.01 3.11 1.07 1.47 Example 5 32.8 100 1.69 3.10 0.97 1.04

As shown in Table 3, the resistance starch yield of crosslinked starch prepared by adding citric acid and acetic acid to 1% of starch weight, neutralized and heat treated was 29.2% and 32.8% when P / G method, and AOAC method The resistance starch yield is high at 99.7% and 100.0%. On the other hand, the addition of citric acid in the production of crosslinking not only increases the yield of resistive starch, but also affects the color of the prepared starch. The crosslinking starch contains a high yield of resistive starch by controlling the concentration of citric acid. It is believed that you will get.

<Test Example 6>

In Example 1, the yield of the resistance starch of the crosslinked starch could be greatly increased, but since the neutralization process was included after the acid treatment, it was cumbersome to use in the manufacturing process, so that the neutralization process was omitted by lowering the concentration of hydrochloric acid during the acid treatment. Bound starch was prepared.

Crosslinked starch was prepared in the same manner as in Example 1, except that the concentration of hydrochloric acid, starch concentration, and heat treatment time were adjusted as shown in Table 4, and the heat treatment was performed immediately after the acid treatment without neutralization. The resistance starch yield and swelling force at 95 ° C. of the crosslinked starch were measured and the results are shown in Table 4 below.

Resistance starch yield and swelling force were measured using the method mentioned in Test Example 1.

Table 4.

Hydrochloric acid concentration (N) Starch concentration (%) Heat treatment time (hr) Resistance starch yield (%) Swelling force (95 ℃) P / G AOAC 0 40 12 24.1 -* 5.13 0.005 35 8 18.7 - 5.81 35 16 20.0 - 6.73 45 8 22.1 - 5.22 45 16 23.9 - 5.52 0.01 30 12 16.8 - 5.59 40 4 20.4 - 5.27 40 12 20.8 - 5.24 40 20 25.4 78.5 5.73 50 12 26.4 98.3 4.69 0.015 35 8 21.4 - 5.53 35 16 20.5 - 5.95 45 8 24.3 - 5.86 45 16 24.4 - 5.18 50 12 29.7 98.9 0.02 40 12 19.9 - 5.68

* Not measured

In Table 4, the concentration of hydrochloric acid is 0.005 to 0.02 N, the starch concentration is 30 to 50%, the heat treatment time is 8 to 16 hours, and the yield of resistance starch produced under these conditions is 16.8 to 29.7% when measured by the P / G method. The swelling force was 4.69 to 6.73, and there was no significant difference in the resistance starch prepared under each condition. The yield of resistive starch was the highest in starch yield of 29.7% of crosslinked starch prepared after heat treatment for 12 hours by adding 0.015N HCl to 50% starch concentration. Next, the resistance starch yield obtained after heat-treating 0.01N hydrochloric acid to 50% of starch concentration for 12 hours was 26.4%, and the yield of resistance starch when heat-treated for 20 hours with 0.01N hydrochloric acid to 40% of starch concentration. It was as high as 25.4%.

Although the yield of the resistive starch was lower than that of the crosslinked starch of Example 1 in the yield of the resistive starch, if the starch was pretreated with weak acid, the starch yield of about 30% could be obtained if the starch concentration and the heat treatment time were adjusted. It is feed.

It can be seen that the resistance starch content can be increased in the preparation of the crosslinked starch by performing acid treatment and heat treatment on the starch as in the test result.

Therefore, starch with increased starch content according to the present invention can be used as an excellent raw material of diet food production as well as food useful for adult diseases such as noodles, cookies, snacks, starch premix, diabetes or obesity.

1 is an X-ray diffraction graph of crosslinked starch using an X-ray diffractometer.

2 is a photograph of crosslinked starch using a scanning electron microscope.

Claims (8)

In increasing the resistance starch content of the crosslinked starch, Wheat starch, waxy starch, rice starch, glutinous rice starch, corn starch, waxy corn starch, tapioca starch, sweet potato starch, potato starch, any one selected from hydrochloric acid, nitric acid, carbonic acid, citric acid, acetic acid, Reacting with addition of any one organic acid selected from lactic acid, tartaric acid and tartaric acid, and then neutralizing by adding any base selected from sodium hydroxide, potassium hydroxide, barium hydroxide and calcium hydroxide, Heat treating the neutralized starch; Cross-linking the starch by adding a crosslinking agent consisting of a mixture of sodium trimethaphosphate and sodium tripolyphosphate and any base selected from sodium hydroxide, potassium hydroxide, barium hydroxide and calcium hydroxide after heat treatment; After crosslinking reaction, neutralize by adding any inorganic acid selected from hydrochloric acid, nitric acid, carbonic acid, or any organic acid selected from citric acid, acetic acid, lactic acid, tartaric acid, tartaric acid, and then removing salt and unreacted crosslinking agent and drying. Method for increasing the resistance starch content of crosslinked starch using an acid treatment, characterized in that it comprises a. delete The crosslinked starch using acid treatment according to claim 1, wherein the acid is added with any inorganic acid selected from hydrochloric acid, nitric acid, and carbonic acid at a starch concentration of 0.005 to 1.0% to a starch concentration of 30 to 50%. How to increase the resistance starch content The acid treatment method according to claim 1, wherein the acid is any one of an organic acid selected from citric acid, acetic acid, lactic acid, tartaric acid, and tartaric acid, which is 1% or less of starch weight and has a starch concentration of 30 to 50%. Method for increasing resistance starch content of crosslinked starch. The method of increasing the resistance starch content of crosslinked starch using an acid treatment according to claim 1, wherein the heat treatment is shaken at 40 to 60 ° C for 10 to 14 hours. The crosslinking agent according to claim 1, wherein 10 to 14% by weight of a mixture of 99 to 99.9 parts by weight of sodium trimetaphosphate and 0.1 to 1.0 part by weight of sodium tripolyphosphate is added to the starch weight. How to increase resistance starch content. The method of increasing the resistance starch content of crosslinked starch using acid treatment according to claim 1, wherein the crosslinking agent and a base are added to react the starch to crosslinking within 3 hours. 2. The resistance starch of the crosslinked starch using acid treatment according to claim 1, wherein any one base selected from sodium hydroxide, potassium hydroxide, barium hydroxide and calcium hydroxide is added so as to have a pH of 10 to 12 upon crosslinking of the starch. How to increase the content.