Long-shaped rice starch-citrus pectin gel, preparation method thereof and long-shaped rice starch food

Abstract

The invention discloses long-shaped rice starch-citrus pectin gel, a preparation method thereof and long-shaped rice starch food. The preparation method comprises the following steps: selecting long-shaped rice to prepare long-shaped rice starch; mixing the prepared long-shaped rice starch with citrus pectin with the DE value of 38-73% according to the mass ratio of (0.4-0.5): 100, and uniformly stirring to obtain mixed powder; adding water into the mixed powder to prepare a 10% suspension, and heating in a water bath kettle at 95 DEG C for 30 minutes; and cooling the gelatinization system to room temperature to obtain the composite gel. The pectin with different esterification degrees interacts with the starch through hydrogen bonds, so that the gel property of the long-shaped rice starch is improved. The high-ester pectin improves the thermal stability of the starch gel and the compactness of a network structure. The low-ester pectin improves the water-retaining property and the storage stability of the starch gel. The research result encourages the pectin to be used in the long-shaped rice starch-based gel food, and the long-shaped rice starch-based gel food has good economic benefits and is easy for industrialized production.

Description

Technical Field

[0001] The present invention relates to the technical field of starch gel processing, and particularly to an indica rice starch - citrus pectin gel, a preparation method thereof, and an indica rice starch food. Background Art

[0002] More than half of the world's population regards rice as the main food source, and Asia contributes 90% of the world's rice production. Approximately one - third of the rice is indica rice, which is usually used to make gel - based foods such as rice noodles. The main component of rice is starch, and the production of starch gel mainly depends on the gelatinization and retrogradation of starch, which affects the quality of rice products. However, due to the poor gelatinization stability of natural indica rice starch under long - term heating, strong shear, or acidic environment, the gel structure is often damaged, and it has a strong tendency to retrograde, resulting in limited application in the food industry. Summary of the Invention

[0003] To solve the technical problems existing in the above - mentioned technology, in view of this, it is necessary to provide a preparation method of an indica rice starch - citrus pectin gel.

[0004] A preparation method of an indica rice starch - citrus pectin gel includes the following steps,

[0005] Step S1: Select indica rice containing 78.23% total starch content, 8.3% protein, 0.54% fat, 10.63% moisture, 0.51% ash, and 16.78% amylose to prepare indica rice starch;

[0006] Step S2: Mix the prepared indica rice starch with citrus pectin having a DE value of 38% - 73% in a mass ratio of 0.4 - 0.5:100 and stir evenly to obtain a mixed powder;

[0007] Step S3: Add water to the mixed powder to prepare a 10% suspension, and heat it in a water bath at 95°C for 30 minutes;

[0008] Step S4: Cool the gelatinization system to room temperature to obtain a composite gel.

[0009] Preferably, in step S1, the indica rice starch is obtained by the following method,

[0010] S11: Grind the indica rice into powder with a particle size not greater than 80 mesh, and degrease it according to the ratio of petroleum ether of 1:2 (g / mL);

[0011] S12: Disperse the degreased sample in 0.2% NaOH solution (1:4, g / mL) and soak it, discard the supernatant, and then wash the indica rice powder multiple times until white starch is obtained in the precipitate;

[0012] S13: Dry in an oven at 40 °C and grind to pass through a 100-mesh sieve to obtain indica rice starch.

[0013] Preferably, during soaking, use a soaking device to soak the defatted sample in a 0.2% NaOH solution for 24 h, stir once every 5 h, and stir for 10 min each time.

[0014] Preferably, during washing, use a washing device to centrifuge and wash the indica rice flour 2 - 3 times, with a washing time of 20 min.

[0015] Preferably, in step S2, the DE value of the citrus pectin is 38% - 48%.

[0016] Preferably, in step S2, the DE value of the citrus pectin is 48% - 57%.

[0017] Preferably, in step S2, the DE value of the citrus pectin is 57% - 73%.

[0018] It is also necessary to provide an indica rice starch - citrus pectin gel.

[0019] An indica rice starch - citrus pectin gel is prepared by using the preparation method of the indica rice starch - citrus pectin gel described above.

[0020] An indica rice starch food includes this indica rice starch - citrus pectin gel and indica rice starch.

[0021] Compared with the prior art, for the indica rice starch - citrus pectin gel and its preparation method provided by the present invention, pectins with different degrees of esterification in the present invention interact with starch through hydrogen bonds, improving the gel properties of indica rice starch. High - ester pectin improves the thermal stability of the starch gel and the compactness of the network structure. Low - ester pectin improves the water - holding capacity and storage stability of the starch gel. The research results will encourage the use of pectin in gel foods based on indica rice starch, with good economic benefits and easy for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for describing the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 It is the ATR - FTIR spectrogram of the gel.

[0024] Figure 2 It is the composite index (CI) diagram of the gel.

[0025] Figure 3 SEM image of the gel.

[0026] Figure 4 X-ray pattern of the gel.

[0027] Figure 5 Transverse relaxation time T of the gel 2 curve graph.

[0028] Figure 6 Influence diagram of the gel moisture distribution.

[0029] Figure 7 Schematic structural diagram of the immersion device of the present invention.

[0030] Figure 8 For the present invention Figure 7 Schematic cross-sectional structural diagram of A-A in the present invention.

[0031] Figure 9 For the present invention Figure 7 Schematic structural diagram from another angle.

[0032] Figure 10 Schematic structural diagram of the stirring mechanism of the present invention.

[0033] Figure 11 Schematic structural diagram of the stirring part of the present invention.

[0034] Figure 12 Schematic structural diagram of the washing device of the present invention.

[0035] Figure 13 For the present invention Figure 10 Schematic structural diagram from another angle.

[0036] In the figure: base 01, support seat 11, support roller 12, immersion tank 02, support ring 21, discharge port 22, material collection tank 23, discharge pipe 24, stirring mechanism 03, rotating shaft 31, stirring part 32, bushing 33, connecting rod 34, inner cylinder 04, middle cylinder 05, outer cylinder 06, discharge hole 61, first cavity 07, second cavity 08, cover plate 09, feed hole 91, dispersion cap 10. Specific embodiments

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0038] In the description of the present invention, it should be understood that the terms "upper", "middle", "outer", "inner", "lower", etc. indicating orientation or positional relationship are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the components or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation on the present invention.

[0039] The embodiment of the present invention provides a preparation method of indica rice starch - citrus pectin gel. Among them, the indica rice flour is prepared by grinding the indica rice variety "Quanyou 9028" from Anhui, containing 78.23% total starch content, 8.3% protein, 0.54% fat, 10.63% moisture, 0.51% ash, and 16.78% amylose; the citrus pectin is purchased from St. Louis, Missouri, USA, P9135, DE = 73%, methoxy ≥ 6.7%, galacturonic acid ≥ 74.0%, and other pectins with different DE values are prepared from the pectin with DE = 73% as raw material according to the published method (Cui, Chen, and Zhang 2023); all solutions are prepared with distilled water; all other chemicals and reagents are of analytical grade.

[0040] The specific preparation method includes the following steps.

[0041] Step S1: Select indica rice containing 78.23% total starch content, 8.3% protein, 0.54% fat, 10.63% moisture, 0.51% ash, and 16.78% amylose to prepare indica rice starch.

[0042] Step S2: Mix the prepared indica rice starch with citrus pectin with a DE value of 38% - 73% according to a mass ratio of 0.4 - 0.5:100 and stir evenly to obtain a mixed powder.

[0043] Step S3: Add water to the mixed powder to prepare a 10% suspension and heat it in a water bath at 95°C for 30 minutes.

[0044] Step S4: Cool the gelatinized system to room temperature to obtain a composite gel.

[0045] Among them, in step S1, the indica rice starch is obtained in the following manner.

[0046] S11: Grind the indica rice into powder with a particle size not greater than 80 mesh and degrease it according to a petroleum ether ratio of 1:2 (g / mL).

[0047] S12: Disperse the degreased sample in 0.2% NaOH solution (1:4, g / mL), discard the supernatant, and then wash the indica rice flour multiple times until white starch is obtained in the precipitate.

[0048] S13: Dry in an oven at 40 °C and grind through a 100-mesh sieve to obtain indica rice starch.

[0049] Among them, during soaking, the defatted sample is soaked in a 0.2% NaOH solution for 24 h using a soaking device, stirred every 5 h for 10 min each time.

[0050] Among them, during washing, the indica rice flour is centrifuged and washed 2 - 3 times using a washing device, with a washing time of 20 min.

[0051] Among them, in step S2, the DE value of the citrus pectin is 38% - 48%.

[0052] Among them, in step S2, the DE value of the citrus pectin is 48% - 57%.

[0053] Among them, in step S2, the DE value of the citrus pectin is 57% - 73%.

[0054] Please refer to Figures 7 to 9 , in one embodiment, the soaking device includes a base 01 and a soaking tank 02; support seats 11 are oppositely arranged on the base 01, and four support rollers 12 evenly distributed on the top of the base 01 are arranged between the two support seats 11; the support rollers 12 on the same side can be synchronously driven by independent drive motors. A support ring 21 adapted to the support rollers 12 is arranged on the outer wall of the soaking tank 02, so that after the soaking tank 02 is installed on the support rollers 12, it can rely on the support rollers 12 to drive the soaking tank 02 to rotate circumferentially along its own axis. A discharge port 22 is opened on the outer wall of the soaking tank 02, and the discharge port 22 is blocked by a sealing door; during discharging, the soaking tank 02 rotates to make the discharge port 22 located at the lowest point, and at this time the soaking tank 02 stops rotating, then the sealing door is opened, and only by keeping the stirring mechanism 03 rotating can the defatted sample be quickly discharged.

[0055] A stirring mechanism 03 capable of stirring the defatted sample inside the soaking tank 02 is installed inside the soaking tank 02. Stirring makes the defatted sample form a turnover inside the soaking tank 02. The two ends of the stirring mechanism 03 are rotationally connected to the soaking tank 02, and the two ends of the stirring mechanism 03 extend outward and are rotationally installed on the two support seats 11; the stirring mechanism 03 is rotated circumferentially along the axis of the soaking tank 02 by a variable-frequency motor installed on the base 01. The stirring mechanism 03 and the soaking tank 02 rotate circumferentially separately, and the rotation direction of the soaking tank 02 is opposite to that of the stirring mechanism 03; for example, when the soaking tank 02 rotates clockwise, the stirring mechanism 03 rotates counterclockwise. In this way, when the stirring mechanism 03 stirs the defatted sample, the defatted sample can be fully turned over from the bottom up, promoting the precipitated defatted sample to come into full contact and mixing with the NaOH solution again.

[0056] Specifically, in order to better receive the degreased samples after soaking, a material receiving trough 23 with an arc-shaped structure is arranged below the soaking tank 02, and a discharge pipe 24 is arranged at the bottom of the material receiving trough 23.

[0057] Please refer to Figure 10 , specifically, the stirring mechanism 03 includes a rotating shaft 31 and stirring parts 32 evenly installed on the rotating shaft 31; among them, the rotating shaft 31 is arranged along the axis of the soaking tank 02, and the rotating shaft 31 is rotationally connected to the soaking tank 02; the two ends of the rotating shaft 31 are respectively rotationally installed on the support base 11 through bearings. A shaft sleeve 33 is key-connected to the rotating shaft 31, and connecting rods 34 for connecting the stirring parts 32 are evenly distributed along the circumferential direction of the shaft sleeve 33.

[0058] Please refer to Figure 11 , specifically, the surface of the stirring part 32 in contact with the degreased sample is of an arc-shaped structure, and this side surface is gradually inclined from one end to the other end with the axis of the stirring part 32 as the reference. When the stirring part 32 contacts the degreased sample, the arc-shaped side surface will drive the degreased sample, causing the degreased sample to be stirred from one end to the other end along the stirring part 32, so that the degreased sample is turned to one side, and further enabling the degreased sample to be fully contacted and mixed with the NaOH solution.

[0059] For further explanation, each stirring part 32 is staggeredly distributed with the rotating shaft 31 as the center; that is, the inclination direction of the arc surface of the previous stirring part 32 is opposite to the inclination direction of the arc surface of the next stirring part 32. When the stirring part 32 contacts the degreased sample, it can cause the degreased sample to be stirred left and right inside the soaking tank 02, thereby ensuring that the degreased sample is fully contacted and mixed with the NaOH solution.

[0060] Please refer to Figure 12 , Figure 13 , in an implementation manner, the washing device includes an inner cylinder 04, a middle cylinder 05, and an outer cylinder 06; the middle cylinder 05 is coaxially sleeved outside the inner cylinder 04, there is a spacing between the middle cylinder 05 and the inner cylinder 04, a first cavity 07 is formed between the bottom inside the middle cylinder 05 and the bottom of the inner cylinder 04, and the bottom of the inner cylinder 04 is rotatably connected to the bottom inside the middle cylinder 05; the inner cylinder 04 is rotated circumferentially through a first driving motor installed in the first cavity 07. The outer cylinder 06 is coaxially sleeved outside the middle cylinder 05, there is a spacing between the outer cylinder 06 and the middle cylinder 05, a second cavity 08 is formed between the bottom of the outer cylinder 06 and the bottom of the middle cylinder 05, and the bottom of the middle cylinder 05 is rotatably connected to the bottom of the outer cylinder 06; the middle cylinder 05 is rotated circumferentially through a second driving motor installed in the second cavity 08. There is a discharge hole 61 at the lower part of the outer cylinder 06 to facilitate the discharge of the washed starch.

[0061] Specifically, through holes allowing the degreased sample to flow out are provided on the side walls of the inner cylinder 04 and the middle cylinder 05, and filter meshes or filter membranes capable of filtering impurities are installed on the inner walls of the inner cylinder 04 and the middle cylinder 05. When the inner cylinder 04 and the middle cylinder 05 rotate circumferentially, washing of the degreased sample can be achieved through the action of centrifugation, and impurities and the sample can be separated successively; moreover, the rotation directions of the inner cylinder 04 and the middle cylinder 05 are opposite, which can cancel out the inertial force between the inner cylinder 04 and the middle cylinder 05. During washing, washing is first performed through the inner cylinder 04 and then through the middle cylinder 05. In this process, the sample thrown out by the centrifugal force of the inner cylinder 04 will enter the middle cylinder 05 rotating in the opposite direction to the inner cylinder 04. At this time, the throwing direction of the sample is exactly opposite to the rotation direction of the middle cylinder 05, so that the middle cylinder 05 can be used to disperse the sample for the second time to improve the washing effect.

[0062] Certainly, for the filter meshes or filter membranes installed on the inner walls of the inner cylinder 04 and the middle cylinder 05, a cylindrical structure can be adopted, and its size is adapted to the inner cylinder 04 and the middle cylinder 05. The filter meshes or filter membranes can be correspondingly installed on the inner walls of the inner cylinder 04 and the middle cylinder 05 in a detachable manner. Usually, the filter meshes or filter membranes can be fixed on the inner cylinder 04 and the middle cylinder 05 by means of bolt connection. After a large amount of impurities adhere to the filter meshes or filter membranes, the filter meshes or filter membranes can be disassembled, cleaned, and then reinstalled. The filter meshes or filter membranes adopting a cylindrical structure can enable them to have better overall stress performance when bearing radial centrifugal force, so as to prevent deformation due to uneven stress, thereby affecting the washing effect.

[0063] Specifically, a cover plate 09 is fixedly arranged on the top of the outer cylinder 06. The cover plate 09 entirely covers the inner cylinder 04, the middle cylinder 05, and the outer cylinder 06, and a feed hole 91 communicating only with the inner cylinder 04 is provided on the cover plate 09; the top of the inner cylinder 04 and the top of the middle cylinder 05 are respectively rotatably connected to the cover plate 09.

[0064] Specifically, a dispersion cap 10 with a conical structure is arranged in the upper part of the inner cylinder 04. The dispersion cap 10 is fixedly connected to the bottom of the cover plate 09. Through the dispersion cap 10, the degreased sample entering the inner cylinder 04 can be dispersed around, and combined with the circumferential rotation of the inner cylinder 04, rapid dispersion of the degreased sample can be achieved.

[0065] The present invention also provides an indica rice starch - citrus pectin gel, which is prepared by using the preparation method of the indica rice starch - citrus pectin gel.

[0066] The present invention also provides an indica rice starch food, including the indica rice starch - citrus pectin gel and indica rice starch.

[0067] Comparative Example:

[0068] (1) Extraction of indica rice starch: Grind indica rice into powder with a particle size not greater than 80 mesh, add petroleum ether for degreasing (with a petroleum ether ratio of 1:2 (g / mL)), disperse the degreased sample in 0.2% (g / mL) NaOH solution (1:4, g / mL) and soak for 24 hours, stir every 5 h for 10 min each time, discard the supernatant, then wash and centrifuge the indica rice powder 2 - 3 times to remove impurities, with a washing time of 20 min and a centrifugal acceleration of 4000 g for 20 min to obtain a white starch precipitate. Finally, dry it in an oven at 40 °C and grind it to pass through a 100 - mesh sieve to obtain indica rice starch;

[0069] (2) Preparation of indica rice starch gel: Add water to indica rice starch and homogenize to prepare a suspension with a concentration of 10% (g / mL), and heat it in a water bath at 95 °C for 30 minutes, then cool the gelatinized system to room temperature to obtain indica rice starch gel.

[0070] Example 1

[0071] (1) Extraction of indica rice starch: Grind indica rice into powder with a particle size not greater than 80 mesh, add petroleum ether for degreasing (with a petroleum ether ratio of 1:2 (g / mL)), disperse the degreased sample in 0.2% (g / mL) NaOH solution (1:4, g / mL) and soak for 24 hours, stir every 5 h for 10 min each time, discard the supernatant, then wash and centrifuge the indica rice powder 2 - 3 times to remove impurities, with a washing time of 20 min and a centrifugal acceleration of 4000 g for 20 min to obtain a white starch precipitate. Finally, dry it in an oven at 40 °C and grind it to pass through a 100 - mesh sieve to obtain indica rice starch;

[0072] (2) Preparation of indica rice starch - citrus pectin mixture: Mix indica rice starch with citrus pectin with a DE value of 38% according to a mass ratio of 0.5:100 and stir to obtain an indica rice starch - citrus pectin mixture;

[0073] (3) Preparation of indica rice starch - citrus pectin gel: Add water to the mixture and homogenize to prepare a mixed suspension with a concentration of 10% (g / mL), and heat it in a water bath at 95 °C for 30 minutes, then cool the gelatinized system to room temperature to obtain indica rice starch - citrus pectin gel.

[0074] Example 2

[0075] The difference between Example 2 and Example 1 is that the DE value of citrus pectin is 48%.

[0076] Example 3

[0077] The difference between Example 3 and Example 1 is that the DE value of citrus pectin is 57%.

[0078] Example 4

[0079] Example 4 is different from Example 1 in that the DE value of citrus pectin is 64%.

[0080] Example 5

[0081] Example 5 is different from Example 1 in that the DE value of citrus pectin is 73%.

[0082] The above comparative examples and the gel samples obtained in Examples 1-5 were respectively labeled as RS, RS-38P, RS-48P, RS-57P, RS-64P, and RS-73P. The preparation method of indica rice starch-citrus pectin gel and the quality of its gel were evaluated by the following experimental methods. Each experiment was carried out at least three times, and the results were presented in the form of mean ± standard deviation. The variance of the data was tested using SPSS 27.0, showing significant differences at p < 0.05.

[0083] 1. Determination of swelling power, solubility, and leached amylose content

[0084] (1) Determination method

[0085] Determination of swelling power and solubility: First, 0.4 g of the mixed powder and 20 mL of distilled water were placed in a pre-weighed centrifuge tube, heated in a water bath at 80 °C for 30 min, centrifuged (8000 g, 10 min), and then the supernatant was collected and the swollen precipitate was weighed. Subsequently, the collected supernatant was dried to a constant weight in an air drying oven at 105 °C and weighed. SP (g / g) and S (%) were calculated by the following formulas.

[0086] SP (g / g) = m 1 / [m × (1 - S)] (1)

[0087] S (%) = (m 2 / m) × 100 (2)

[0088] Where m represents the weight of the complex, m 1 represents the weight of the swollen precipitate, and m 2 represents the weight of the dried supernatant.

[0089] Determination of the leached amylose content: The amount of amylose leached from the complex was determined by the iodine-binding method. First, 0.4 g of the complex and 20 mL of distilled water were placed in a centrifuge tube and heated in a water bath at 80 °C for 30 min. After centrifugation (8000 g, 10 min), 0.1 mL of the supernatant was taken and mixed with 1 mL of glacial acetic acid (1 mol / L) and 2 mL of iodine solution (0.01 mol / L). Then, the absorbance of the supernatant was measured at 620 nm using a microplate reader (Synergy H1, made in the United States). The leached amylose content (C A , %) was calculated according to the fixed equation (3).

[0090] A 620 = 18.6×10 -3 C A + 9.5×10 -3 (3)

[0091] (2) Experimental results

[0092] The swelling power, solubility, and leached amylose of the complex are shown in Table 1. Both high-ester and low-ester pectins inhibited the swelling of indica rice starch granules, and among them, low-ester pectin (DE = 38%) showed a more significant inhibitory effect. The reason may be that the low-ester pectin has a larger number of carboxyl groups, making it more hydrophilic, thus reducing the water available for the complex to gelatinize. The solubility (S) of the complex showed a similar trend to the swelling power. The reason is that the limited swelling power of the complex led to a reduction in the diffusion of amylose and amylopectin. During the starch gelatinization process, the content of leached amylose is a key parameter. The addition of pectin restricted the leaching of amylose from indica rice starch, and the inhibitory effect of low-ester pectin was more significant.

[0093] Table 1 Swelling power (SP), solubility (S), and leached amylose content (C A )

[0094]

[0095] a - e represent significant differences (p < 0.05) in the SP, S, and C A of the complex.

[0096] 2. Thermal properties of the complex

[0097] (1) Determination method

[0098] The thermal properties of the complex were measured using a differential scanning calorimeter (DSC). 3 mg of the dry sample was mixed with water at a weight ratio of 1:3, and then the crucible was sealed and equilibrated at 4 °C for 12 h. During the test, an empty crucible was used as a control. The temperature was raised from 30 °C to 100 °C at a rate of 10 °C / min, and the gelatinization onset temperature (To), peak temperature (Tp), conclusion temperature (Tc), and gelatinization enthalpy (ΔH) were calculated from the DSC curve.

[0099] (2) Experimental results

[0100] The thermal parameters of the complex are shown in Table 2. Pectin slightly increased the To, Tp, and Tc of indica rice starch, which may be due to the interaction between pectin and indica rice starch. Low-ester pectin decreased the gelatinization enthalpy (ΔH), while high-ester pectin had the opposite effect, because the addition of low-ester pectin inhibited the penetration of water molecules into the interior of starch granules, reducing the energy required to break the starch chains. The increased number of hydrogen bonds formed between high-ester pectin and starch increased the short-range order, resulting in an increase in ΔH, which was supported by the FT-IR results.

[0101] Table 2 Thermal properties of the complex

[0102]

[0103]

[0104] a - b represents the significant difference in the gelatinization temperature and ΔH of the complex (p < 0.05).

[0105] 3. ATR-FTIR spectral analysis of the gel

[0106] (1) Measurement method

[0107] The starch gel was freeze-dried, ground, and sieved through a 100-mesh sieve. The freeze-dried powder of the gel was tested using a Fourier transform infrared spectrometer (ATR-FTIR). The spectral scanning range was 4000 - 650 cm -1 , with a resolution of 4 cm -1 , and the number of scans was 8 times.

[0108] (2) Experimental results

[0109] The ATR-FTIR spectrum of the gel is as Figure 1 shown. Due to the low concentration of pectin with different degrees of esterification (DE) added, no new spectral bands appeared. 3300 cm -1The bands at [specific position] shifted to lower wavenumbers after adding pectins with different DE values, indicating that more hydrogen bonds were formed by pectins in the starch gel. In addition, high-ester pectin led to a greater number of hydrogen bonds formed in the starch gel than low-ester pectin, which might be due to the significantly higher interaction between high-ester pectin and indica rice starch than that between low-ester pectin and indica rice starch. 1640 cm -1 The band at [specific position] represents the bound water in the amorphous region. Adding pectins with different DE values did not change the position of this peak, but its intensity increased from 0.009 (RS) to 0.023 (RS-38P). This indicates that low-ester pectin can inhibit the movement of water molecules inside starch, which is consistent with the findings of LF-NMR.

[0110] The infrared spectrum of the gel was deconvoluted, and the value of 1047 / 1022 cm -1 reflects the short-range ordered structure of the sample. As Figure 1 shown in B, the short-range order of all composite gels increased compared with RS, and the short-range ordered structure of RS-73P increased from 0.627 to 0.730. This is because high-ester pectin increased the short-range order of indica rice starch by forming hydrogen bonds with free amylose.

[0111] Figure 1 is the ATR-FTIR spectrogram of the gel. A. Wavenumber range (4000 cm -1 -800 cm -1 ); B. Wavenumber range (1200 cm -1 -800 cm -1 )

[0112] 4. Composite index of the gel

[0113] (1) Measurement method

[0114] Add 0.1 g of freeze-dried gel to 9 mL of distilled water and vortex for 3 min. Then add 100 μL of iodine reagent (2% KI and 1.3% I 2 ) to the dispersion. Next, centrifuge the dispersion at 8000 r / min for 15 min and measure the absorbance of the supernatant at 690 nm. Calculate the CI using the following formula.

[0115] CI (%) = [(A c - A m ) / A c × 100 (4)

[0116] In the formula, Ac is the absorbance of RS, and Am is the absorbance of the composite gel.

[0117] (2) Experimental results

[0118] The composite index of the gel is as shown in Figure 2As shown in the figure, when the degree of esterification increased from 38% to 73%, the CI significantly increased from 9.36% to 22.25%. The reason is that high-ester pectin enhanced the leaching of amylose, thus promoting the interaction between high-ester pectin and indica rice starch.

[0119] Figure 2 is the complex index (CI) of the gel. a - d represent significant differences in the CI of the gels (p < 0.05).

[0120] 5. Microstructure Observation of Gels

[0121] (1) Measurement Method

[0122] The freeze-dried gel was cut into thin slices, sputter-coated with gold, and the microstructure of the gel was observed by a scanning electron microscope (EM30 +, China) at an accelerating voltage of 8.0 kV.

[0123] (2) Experimental Results

[0124] Images of the gel under a scanning electron microscope (SEM) at 400 times magnification are shown as Figure 3 follows. All gels exhibited an obvious "honeycomb" structure, which was also observed in pectin - wheat starch gels, Mesona chinensis polysaccharide - rice starch gels, and oat β - glucan - rice starch gels. Compared with the pure indica rice starch gel, all composite gels presented a continuous and relatively ordered layered network structure. With the increase in the DE value of pectin, the stability of the composite gel network structure gradually enhanced, showing a denser, more continuous, more regular, and relatively ordered layered network structure. This may be related to the interaction between high-ester pectin and the leached amylose.

[0125] Figure 3 are the SEM images of the gel (×400)

[0126] 6. Crystal Structure of Gels

[0127] (1) Measurement Method

[0128] Before XRD analysis, the samples were freeze-dried and passed through a 200-mesh sieve. The freeze-dried gels were scanned from 5° to 40° at a rate of 2° min -1 using an X-ray diffractometer (Rigaku D / MAX2500VL / PC, Japan). The relative crystallinity was calculated using MDI-Jade6.0 software.

[0129] (2) Experimental Results

[0130] Figure 4The X-ray diffraction patterns and relative crystallinity of the gels were shown. Diffraction peaks appeared at 13° and 20° for all gels. The addition of pectin had no obvious effect on the diffraction peak positions of indica rice starch, indicating that pectin had little influence on the crystal structure of indica rice starch. The calculation of relative crystallinity showed that the area of the crystallization peak gradually increased during storage. Compared with RS, the relative crystallinity of other samples decreased, and the effect of RS-38P was the most significant, with the relative crystallinity decreasing by 1.3% and 1.68% at 7 d and 14 d, respectively. This was consistent with the inhibitory effect of low-ester pectin on the recrystallization of glutinous rice starch and corn starch.

[0131] Figure 4 was the X-ray pattern of the gel. (A: The gel was stored at 4 °C for 7 d, B: The gel was stored at 4 °C for 14 d)

[0132] 7. Water mobility analysis of the gels

[0133] (1) Measurement method

[0134] Low-field nuclear magnetic resonance (LF-NMR): LF-NMR (NMI20-015V-I, Suzhou Newmed Electronic Technology Co., Ltd., Suzhou, China) was used. The sample (1.6 g) was placed in 2 mL of liquid phase and then transferred to an NMR tube. Measurements were carried out using the Carr-Purcell-Meiboom-Gill sequence, with the set parameters of an echo time (TE) of 0.2 ms, 12,000 echoes (NECH), and 8 scans (NS).

[0135] (2) Experimental results

[0136] Figure 5 showed the T 2 relaxation time curve of the gel, and the LF-NMR parameters are shown in Table 3. According to the mobility, the water molecules in the gel were divided into strongly bound water (T 21 ), weakly bound water (T 22 ), and free water (T 23 ), and the corresponding peak areas were labeled as A 21 , A 22 , and A 23 . The addition of pectin significantly decreased the T 21 value and increased the A 21 value, and the effect of low-ester pectin was more obvious. This indicated that low-ester pectin better restricted the water mobility, which might be due to the de-esterification of pectin in the side chain, making the carboxyl groups formed after de-methoxylation more likely to bind to water.

[0137] With the extension of storage time, T 21The peak gradually shifted to the right, resulting in a decrease in peak area, indicating that long-term retrogradation would reduce the water-holding capacity of starch. However, the RS-38P and RS-48P samples showed a larger bound water area, increasing from 0.57% to 1.04% and 1.07% respectively. In summary, low-ester pectin enhanced the water-binding ability, while high-ester pectin showed poor hydrophilicity. The research results indicated that the water-holding capacity of pectin might be the reason for inhibiting starch retrogradation.

[0138] Table 3 LF-NMR parameters of gels during storage

[0139]

[0140] a-e represent significant differences in the LF-NMR parameters of gel samples (p<0.05).

[0141] Figure 5 is the transverse relaxation time T of the gel 2 Curve graph (A: gels stored at 4°C for 7 days, B: gels stored at 4°C for 14 days)

[0142] 8. Water distribution analysis of gels

[0143] (1) Measurement method

[0144] Magnetic resonance imaging (MRI): The proton density of the sample was imaged using a spin echo imaging sequence. The scanning parameters were set as follows: echo time = 20 ms, average value = 4, repetition time = 500 ms. The obtained original grayscale image was converted into a pseudo-color image.

[0145] (2) Experimental results

[0146] The influence of the water distribution of gels is shown in Figure 6 . The color bar represents the relative proportion of water activity. The RS samples stored for the same time showed stronger relaxation signals than other samples, indicating that pectin restricted the free migration of water molecules. During storage, the red area of all samples increased steadily, indicating the gradual release of internal water molecules and the gradual increase in water activity. It is worth noting that the water activity of RS-38P and RS-48P was significantly lower than that of other samples, indicating that low-ester pectin effectively restricted the movement of water molecules, thus inhibiting the rearrangement of starch. This result was consistent with the changing trend of the peak area of water in different states. Therefore, low-ester pectin has been proven to enhance the water-holding capacity of indica rice starch gels, thereby improving their storage stability.

[0147] Figure 6 is the influence of the water distribution of gels (A: gels stored at 4°C for 7 days, B: gels stored at 4°C for 14 days)

[0148] The above-disclosed is only the preferred embodiment of the present invention. Of course, the scope of rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A method for preparing indica rice starch-citrus pectin gel, characterized in that: The following steps are included: Step S1: selecting indica rice containing 78.23% total starch content, 8.3% protein, 0.54% fat, 10.63% moisture, 0.51% ash, and 16.78% amylose to prepare indica rice starch; Step S2: mixing the prepared indica rice starch and citrus pectin with a DE value of 38%-73% at a mass ratio of 0.4-0.5:100 and stirring evenly to obtain a mixed powder; Step S3: adding water to the mixed powder to prepare a 10% suspension, and heating in a 95°C water bath for 30 minutes; Step S4: Cooling the gelatinization system to room temperature to obtain a composite gel.

2. The method for preparing the indica rice starch-citrus pectin gel according to claim 1, characterized in that: In step S1, indica rice starch is obtained by the following method: S11: grinding indica rice into powder with a particle size of no more than 80 mesh, and defatting the powder in a ratio of 1:2 (g / mL) of petroleum ether; S12: The defatted sample was dispersed in a 0.2% NaOH solution (1:4, g / mL) and soaked, the supernatant was discarded, and then the indica rice flour was washed several times until white starch was obtained in the precipitate; S13: Drying in an oven at 40° C. and grinding to pass through a 100-mesh sieve to obtain indica rice starch.

3. The method for preparing the indica rice starch-citrus pectin gel according to claim 2, characterized in that: During the soaking, the defatted sample was soaked in a 0.2% NaOH solution using a soaking device for 24 hours, stirred every 5 hours, and each stirring lasted for 10 minutes.

4. The method for preparing the indica rice starch-citrus pectin gel according to claim 3, characterized in that: During washing, the indica rice flour is centrifuged and washed 2-3 times using a washing device, and the washing time is 20 minutes.

5. The method for preparing the indica rice starch-citrus pectin gel according to claim 1, characterized in that: In step S2, the DE value of citrus pectin is 38%-48%.

6. The method for preparing the indica rice starch-citrus pectin gel according to claim 1, characterized in that: In step S2, the DE value of citrus pectin is 48%-57%.

7. The method for preparing the indica rice starch-citrus pectin gel according to claim 1, characterized in that: In step S2, the DE value of citrus pectin is 57%-73%.

8. An indica rice starch-citrus pectin gel, characterized in that: The gel is prepared by the method for preparing the indica rice starch-citrus pectin gel according to any one of claims 1 to 7.

9. A non-glutinous rice starch food, comprising the non-glutinous rice starch-citrus pectin gel and non-glutinous rice starch.

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