Method for preparing anti-retrogradation low-viscosity starch by extruding and activating citric acid

Abstract

The invention provides a method for preparing anti-retrogradation low-viscosity starch by extruding and activating citric acid, which comprises the following steps: fully mixing citric acid and starch which are weighed in proportion in a mixer, then activating the citric acid by using an extrusion technology and promoting the citric acid to be combined with starch molecules for extrusion, and then drying the extrudate in an infrared drying oven to obtain the anti-retrogradation low-viscosity starch. And drying and grinding to obtain the anti-retrogradation low-viscosity starch. The method provided by the invention effectively delays the retrogradation of starch, reduces the viscosity of starch after gelatinization, and solves the industrial problems of harsh reaction conditions and low reaction efficiency of citric acid modified starch, and the preparation process does not generate wastewater and is simple to operate.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, in particular to a method for preparing anti-retrogradation low-viscosity starch by extruding activated citric acid. Background Art

[0002] As a renewable resource, starch is widely used in both food and non-food fields due to its advantages such as low price, biodegradability, safety and non-toxicity. However, its inherent defects of easy regeneration after gelatinization, high viscosity and low fluidity limit the application of starch in certain fields. For example, in food processing, the high viscosity of starch will affect the processing performance and sensory evaluation of food. In the papermaking industry, starch is required to have better fluidity, otherwise it may cause uneven sizing. In the pharmaceutical industry, high-viscosity starch is used as a wall material for drug embedding, which will affect the release rate and bioavailability of the drug. Therefore, modifying starch to reduce starch viscosity is of great significance to broaden the application of starch.

[0003] Traditional starch modification methods mainly include physical modification, chemical modification and enzyme modification. Among them, chemical modification is widely used in starch modification due to its good modification effect and stable product properties. Citric acid, as an organic acid naturally present in many kinds of fruits, is widely regarded as a safe food additive and has very good solubility in water. Therefore, it is widely used in the food field. Citric acid can break the long chains of amylopectin, resulting in a decrease in the molecular weight of starch. Since the smaller molecules interact less in the solution, it plays a role in reducing the viscosity of the starch paste. However, the traditional citric acid starch modification process has the disadvantages of long reaction time, harsh reaction conditions and high production cost. Therefore, it is urgent to find new methods to simplify the reaction conditions while improving the reaction efficiency of citric acid and starch. Summary of the invention

[0004] In view of this, the present invention provides a method for preparing anti-retrogradation low-viscosity starch by extrusion-activating citric acid, so as to solve the problems of harsh reaction conditions and low modification efficiency of citric acid-modified starch in the prior art.

[0005] The present invention provides a method for preparing anti-retrogradation low-viscosity starch by extruding activated citric acid, comprising:

[0006] Step 1: Evenly mix starch and citric acid powder to obtain a starch and citric acid dry powder mixture;

[0007] Step 2: extruding the dry powder mixture to obtain a starch extrudate;

[0008] Step 3: cutting the starch extrudate to obtain a starch extrudate with a regular shape;

[0009] Step 4: Drying the regularly shaped starch extrudate by infrared radiation, cooling it, crushing it, and sieving it to obtain the low-viscosity starch with resistance to retrogradation.

[0010] Preferably, the starch includes at least one of rice starch, wheat starch, corn starch, potato starch and sweet potato starch.

[0011] Preferably, the mass ratio of the starch to the citric acid powder mixed in step 1 is 1:0.04-0.13.

[0012] Preferably, the starch and citric acid are mixed by a stirring mixer, wherein the rotation speed of the stirring mixer is 500-1000 r / min and the stirring time is 5-15 min.

[0013] Preferably, step 2: extruding the dry powder mixture through an extruder to obtain a starch extrudate after plasticization through an extruder die;

[0014] The parameters of the extruder are set as follows: solid feeding rate is 10-15 kg / h, feeding zone temperature is fixed at 25°C, melting zone temperature is set at 80-160°C, cooling zone temperature is 45°C, screw speed is 80-200 r / min, and liquid feeding rate is 5-8 kg / h;

[0015] The extruder adopts a 6-hole cylindrical die with a diameter of 0.5 cm.

[0016] Preferably, the regularly shaped starch extrudate in step 3 is a cylindrical strip, wherein the strip has a length of 3 to 5 cm and a diameter of 0.3 to 0.6 cm.

[0017] Preferably, the infrared radiation drying in step 4 is carried out by placing the regularly shaped starch extrudate in an infrared drying oven for drying at a drying temperature of 40 to 55° C. for a drying time of 10 to 50 min.

[0018] Preferably, in step 4, the sieved particle size is 80-200 mesh.

[0019] The present invention provides a method for preparing low-viscosity starch with resistance to retrogradation by extruding activated citric acid. Aiming at the inherent defects of high gelatinization viscosity and easy retrogradation of starch, the present invention solves the industry problems of harsh reaction conditions and low modification efficiency of citric acid-modified starch. The method couples the pressure, high temperature, shear and other effects provided by extrusion, so that the reactive groups (-COOH) of citric acid are stretched and exposed, and there is no need to change external conditions such as pH, so that the reactive groups can react with the hydroxyl groups of starch in the hot and humid environment formed by extrusion, thereby reducing the viscosity of starch and delaying the retrogradation of starch.

[0020] The invention has a simple process, high reaction efficiency, can reduce the amount of chemical reagents used, uses less water, and can obtain anti-retrogradation low-viscosity starch after the extrudate is dried and crushed. The anti-retrogradation low-viscosity starch prepared by the method of the invention is not easy to retrograde in a short period of time and has the characteristics of low viscosity. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic flow chart of a method for preparing low-viscosity starch with resistance to retrogradation by extruding activated citric acid according to the present invention;

[0022] Figure 2 It is the gelatinization RVA spectra of the low-viscosity starch with anti-retrogradation prepared in Example 1 of the present invention, the single extruded starch and the native starch (corn starch);

[0023] Figure 3 This is a schematic diagram showing the fluidity comparison between the low-viscosity starch with anti-retrogradation properties prepared in Example 1 of the present invention and the gelatinized starch and native starch (corn starch) after extrusion alone;

[0024] Figure 4 Schematic diagram showing the comparison of the retrogradation values ​​of the low-viscosity starch paste with resistance to retrogradation prepared in Example 1 of the present invention, the extruded starch paste alone, and the native starch (corn starch) after gelatinization. DETAILED DESCRIPTION

[0025] In order to solve the problems of long reaction time, harsh reaction conditions, high production cost, etc. in the traditional citric acid modified starch process, this embodiment provides a method for preparing anti-retrogradation low-viscosity starch by extruding activated citric acid, comprising:

[0026] Step 1: Weigh an appropriate amount of starch into a high-speed stirring mixer, add citric acid and stir evenly in the mixer to obtain a starch and citric acid dry powder mixture; the selected citric acid has a wide range of sources and is a green food additive. There is no need to use additional processes to remove the citric acid, so it has a high safety factor and is healthy and environmentally friendly.

[0027] Step 2: The dry powder mixture obtained in step 1 is transferred to a solid feeder of an extruder, and the feeder feeds the mixture into the extruder at a uniform speed for extrusion, and a starch extrudate is obtained after being plasticized by the die head of the extruder;

[0028] Step 3: Cut the starch extrudate obtained in step 2 to obtain cylindrical strips.

[0029] Step 4: Place the strips obtained in step 3 in an infrared drying oven for drying, then cool and transfer to a universal grinder for crushing, and sieve to obtain low-viscosity starch that resists retrogradation. Infrared radiation drying can reduce the specific surface area of ​​starch, which is not conducive to the contact between starch and water molecules, so that the swelling degree of starch molecules during gelatinization is limited and the viscosity is reduced.

[0030] In step 1, the mass ratio of starch to citric acid is 1:0.04-0.13, the speed of the mixer is 500-1000 r / min, and the stirring time is 5-15 min. The above ratio can ensure that the carboxyl group of the extrusion-activated citric acid and the hydroxyl group of the starch can effectively undergo esterification reaction;

[0031] The extrusion parameters in step 2 are: solid feeding rate of 10-15 kg / h, feed zone temperature fixed at 25° C., melting zone temperature set at 80-160° C., cooling zone temperature of 45° C., the above extrusion temperature can make the starch undergo a certain degree of hydrogen bond stretching, but will not cause excessive breakage of the starch molecular chain; screw speed of 80-200 r / min, liquid feed rate of 5-8 kg / h; controlling the extrusion moisture can provide suitable moisture conditions for the esterification reaction between starch and citric acid.

[0032] The present invention adopts a 6-hole cylindrical die with a diameter of 0.5 cm. The small-aperture cylindrical die can further inhibit the expansion of starch during the extrusion process, avoid the reaggregation of partially gelatinized starch molecules, effectively delay the starch recovery speed, and reduce the starch recovery rate.

[0033] The strip in step 3 has a length of 3 to 5 cm and a diameter of 0.3 to 0.6 cm.

[0034] In step 4, the drying temperature is 40-55° C., and the drying time is 10-50 min; and the sieving is through a 80-200 mesh sieve.

[0035] Extrusion activation is a clean, efficient and mass-producible processing method. During the extrusion process, the extruder can provide multiple effects such as strong shear, high pressure, wet heat, kneading, etc., which can provide a variety of coupling reaction conditions for citric acid and starch.

[0036] Therefore, it is feasible in terms of process and technology to use extrusion technology to activate citric acid reactive groups and promote their reaction efficiency with starch.

[0037] In the above preparation method, there is no need to create an additional reaction environment for citric acid and starch (such as changing the pH), which greatly reduces the amount of chemical reagents used and does not generate waste water.

[0038] like Figure 2 As shown, compared with starch prepared by extrusion alone, after adding citric acid, extrusion activation can promote the grafting reaction of citric acid and starch, and the starch is not easy to regenerate after gelatinization and the viscosity is significantly reduced.

[0039] The preparation method provided in this embodiment is further verified below in conjunction with specific examples.

[0040] Example 1

[0041] Weigh 5kg of corn starch into a mixer, and add citric acid powder according to the mass ratio of starch: citric acid = 1:0.04. The mixer speed is 500r / min and stirred for 15min. Transfer the evenly mixed dry powder mixture to the feeder and feed the material into the extruder at a speed of 15kg / h for extrusion. The extrusion parameters are: the temperature of the feeding zone is 25℃, the temperature of the melting zone is set to 80℃, the temperature of the cooling zone is 45℃, the screw speed is 200r / min, and the liquid feed rate is 5kg / h. Cut the extrudate into strips with a length of 5cm and a diameter of 0.6cm. Transfer the obtained strips to a 40℃ infrared drying oven and dry them for 50min. Then crush the dried sample and pass it through an 80-mesh sieve to obtain a low-viscosity starch that resists retrogradation. Compared with native starch and extruded starch, its retrogradation values ​​are reduced by 71.5% and 23.1%, respectively (see Appendix). Figure 4 ), the peak viscosity decreased by 64.8% and 49.8% respectively (Appendix Figure 2 After the sample was gelatinized, the fluidity of the paste was significantly enhanced (see Appendix Figure 3 ), further confirming the low viscosity of the sample after gelatinization.

[0042] Example 2

[0043] Weigh 7kg of wheat starch in a mixer, and add citric acid powder according to the mass ratio of starch: citric acid = 1:0.06. The mixer speed is 800r / min and stirred for 12min. The uniformly mixed dry powder mixture is transferred to the feeder and fed into the extruder at a speed of 12kg / h for extrusion. The extrusion parameters are: the feeding zone temperature is 25℃, the melting zone temperature is set to 120℃, the cooling zone temperature is 45℃, the screw speed is 160r / min, and the liquid feed rate is 6kg / h. The extrudate is cut into strips with a length of 4cm and a diameter of 0.4cm. The obtained strips are transferred to a 45℃ infrared drying oven for drying for 40min, and then the dried sample is crushed through a 200-mesh sieve to obtain a low-viscosity starch that resists retrogradation. Compared with native starch and extruded starch, the retrogradation values ​​are reduced by 82.3% and 22.5%, respectively, and the peak viscosity is reduced by 71.2% and 45.6%, respectively.

[0044] Example 3

[0045] Weigh 8kg of potato starch in a mixer, and add citric acid powder according to the mass ratio of starch: citric acid = 1:0.08. The mixer speed is 700r / min and stirred for 13min. The uniformly mixed dry powder mixture is transferred to the feeder and fed into the extruder at a speed of 13kg / h for extrusion. The extrusion parameters are: the feeding zone temperature is 25℃, the melting zone temperature is set to 140℃, the cooling zone temperature is 45℃, the screw speed is 180r / min, and the liquid feed rate is 7kg / h. The extrudate is cut into strips with a length of 4.5cm and a diameter of 0.3cm. The obtained strips are transferred to a 50℃ infrared drying oven for drying for 38min, and then the dried sample is crushed through a 120-mesh sieve to obtain a low-viscosity starch that resists retrogradation. Compared with native starch and extruded starch, the retrogradation values ​​are reduced by 74.5% and 23.7%, respectively, and the peak viscosity is reduced by 67.9% and 42.3%, respectively.

[0046] Example 4

[0047] Weigh 6kg of rice starch in a mixer, and add citric acid powder according to the mass ratio of starch: citric acid = 1:0.11. The mixer speed is 650r / min and stirred for 12min. The uniformly mixed dry powder mixture is transferred to the feeder and fed into the extruder at a speed of 11kg / h for extrusion. The extrusion parameters are: the feeding zone temperature is 25℃, the melting zone temperature is set to 100℃, the cooling zone temperature is 45℃, the screw speed is 150r / min, and the liquid feed rate is 8kg / h. The extrudate is cut into strips with a length of 5.5cm and a diameter of 0.5cm. The obtained strips are transferred to a 55℃ infrared drying oven for drying for 32min, and then the dried sample is crushed through a 140-mesh sieve to obtain a low-viscosity starch that resists retrogradation. Compared with native starch and extruded starch, the retrogradation values ​​are reduced by 76.0% and 22.6%, respectively, and the peak viscosity is reduced by 61.2% and 42.5%, respectively.

[0048] Example 5

[0049] Weigh 6.5kg of sweet potato starch in a mixer, and add citric acid powder according to the mass ratio of starch: citric acid = 1:0.13. The mixer speed is 900r / min and stirred for 10min. The uniformly mixed dry powder mixture is transferred to the feeder and fed into the extruder at a speed of 14kg / h for extrusion. The extrusion parameters are: the feeding zone temperature is 25℃, the melting zone temperature is set to 150℃, the cooling zone temperature is 45℃, the screw speed is 170r / min, and the liquid feed rate is 5.5kg / h. The extrudate is cut into strips with a length of 3cm and a diameter of 0.3cm. The obtained strips are transferred to a 48℃ infrared drying oven for drying for 40min, and then the dried sample is crushed through a 170-mesh sieve to obtain a low-viscosity starch that resists retrogradation. Compared with native starch and extruded starch, the retrogradation values ​​are reduced by 70.1% and 21.0%, respectively, and the peak viscosity is reduced by 68.8% and 40.7%, respectively.

[0050] Example 6

[0051] Weigh 6kg of starch (wheat starch: rice starch = 1:3) and place it in a mixer, and add citric acid according to the mass ratio of starch: citric acid = 1:0.12. The mixer speed is 950r / min and stirred for 9min. The evenly mixed dry powder mixture is transferred to the feeder and fed into the extruder at a speed of 14kg / h for extrusion. The extrusion parameters are: the feeding zone temperature is 25℃, the melting zone temperature is set to 155℃, the cooling zone temperature is 45℃, the screw speed is 165r / min, and the liquid feed rate is 5.8kg / h. Cut the extrudate into strips with a length of 3.5cm and a diameter of 0.4cm. Transfer the obtained strips to a 50℃ infrared drying oven and dry them for 55min. Then crush the dried sample through a 120-mesh sieve to obtain a low-viscosity starch that resists retrogradation. Compared with native starch and extruded starch, the retrogradation values ​​were reduced by 77.0% and 21.5%, respectively, and the peak viscosities were reduced by 60.0% and 40.2%, respectively.

[0052] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0053] It should be understood that the present invention is not limited to what has been described above and that various modifications and changes may be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing anti-retrogradation low-viscosity starch by extrusion-activated citric acid, characterized in that: include: Step 1: Evenly mix starch and citric acid powder to obtain a starch and citric acid dry powder mixture; Step 2: extruding the dry powder mixture to obtain a starch extrudate; Step 3: cutting the starch extrudate to obtain a starch extrudate with a regular shape; Step 4: Drying the regularly shaped starch extrudate by infrared radiation, cooling it, crushing it, and sieving it to obtain the low-viscosity starch with resistance to retrogradation.

2. The method for preparing anti-retrogradation low-viscosity starch by extrusion-activated citric acid according to claim 1, characterized in that: The starch includes at least one of rice starch, wheat starch, corn starch, potato starch and sweet potato starch.

3. The method for preparing anti-retrogradation low-viscosity starch by extrusion-activated citric acid according to claim 1, characterized in that: The mass ratio of the starch and citric acid powder mixed in step 1 is 1:0.04-0.

13.

4. The method for preparing anti-retrogradation low-viscosity starch by extrusion-activated citric acid according to claim 1, characterized in that: The starch and citric acid are mixed by a stirring mixer, wherein the rotation speed of the stirring mixer is 500-1000 r / min and the stirring time is 5-15 min.

5. The method for preparing anti-retrogradation low-viscosity starch by extrusion-activated citric acid according to claim 1, characterized in that: Step 2: Extruding the dry powder mixture through an extruder to obtain a starch extrudate after being plasticized by the die head of the extruder; The parameters of the extruder are set as follows: solid feeding rate is 10-15 kg / h, feeding zone temperature is fixed at 25°C, melting zone temperature is set at 80-160°C, cooling zone temperature is 45°C, screw speed is 80-200 r / min, and liquid feeding rate is 5-8 kg / h; The extruder adopts a 6-hole cylindrical die with a diameter of 0.5 cm.

6. The method for preparing anti-retrogradation low-viscosity starch by extrusion-activated citric acid according to claim 1, characterized in that: The regularly shaped starch extrudate in step 3 is a cylindrical strip, wherein the strip has a length of 3 to 5 cm and a diameter of 0.3 to 0.6 cm.

7. The method for preparing anti-retrogradation low-viscosity starch by extrusion-activated citric acid according to claim 1, characterized in that: The infrared radiation drying method in step 4 is: placing the regularly shaped starch extrudate in an infrared drying oven for drying at a drying temperature of 40 to 55° C. for a drying time of 10 to 50 minutes.

8. The method for preparing anti-retrogradation low-viscosity starch by extrusion-activated citric acid according to claim 1, characterized in that: In step 4, the sieved particle size is 80 to 200 meshes.

Images