Rice noodles as well as preparation method and application thereof

Abstract

The invention belongs to the field of food processing, and particularly relates to rice noodles as well as a preparation method and application thereof. The method comprises the following steps: sieving rice flour, uniformly compounding and mixing with citric acid or malic acid rice starch ester, regulating moisture, extruding, forming and drying. The invention also explores the influence of 0-40% of modified starch on the physicochemical properties of the mixed powder and the quality of the rice noodles, and finds that by adding 5-20% of modified starch, the cooking, texture, color and sensory quality of the rice noodles can be obviously improved, the aging of starch is inhibited, the glossiness is improved, and the glycemic index is effectively reduced. The effect is optimal under the addition amount of 20%, the sensory score of the rice noodles is high, the GI value is remarkably reduced, the RS content is increased, and preparation of the medium / low GI rice noodles is facilitated.

Description

Technical Field

[0001] The invention belongs to the field of food processing, and particularly relates to rice noodles and a preparation method and application thereof. Background Art

[0002] In recent years, with the public's growing concern for health and nutrition, people have not only increased their food intake but also actively sought technological means to reduce food digestibility. Rice noodles, a common rice product in the daily diet of Chinese residents, are widely popular due to their ease of preparation, ease of consumption, quick cooking, affordable price, and long shelf life. However, while rice noodles provide dietary convenience, they also pose certain health risks. Specifically, rice noodles are rapidly digested and absorbed in the human body, rapidly releasing glucose. This rapid release mechanism is not conducive to blood sugar stability and may exacerbate the occurrence and development of health problems such as high blood pressure, high cholesterol, and high blood sugar. Therefore, it is necessary to improve the production process of rice noodles to reduce their digestibility and better meet the modern demand for a healthy diet. Summary of the Invention

[0003] The present invention aims to provide rice noodles and a preparation method and application thereof. The method can significantly improve the physical and chemical properties of mixed rice flour and the cooking, texture, color and sensory quality of rice noodles, inhibit starch retrogradation, improve the glossiness of rice noodles, and effectively reduce the glycemic index of rice noodles, thereby facilitating the preparation of medium / low GI rice noodles.

[0004] The object of the present invention is achieved through the following technical solutions:

[0005] The present invention provides a rice noodle and a preparation method thereof, comprising the following steps:

[0006] (1) weighing the ground rice flour and sieving it, composite the rice starch ester with the sieved rice flour, and mixing them thoroughly to obtain a mixed powder;

[0007] (2) Adjust the moisture content, then place the mixed powder in a feeding hopper, and then extrude and shape the rice noodles. After the noodles are made, dry and store them.

[0008] Furthermore, in step (1), the sieving is through a 100-mesh sieve.

[0009] Furthermore, in step (1), the rice starch ester is rice starch citric acid ester or rice starch malic acid ester.

[0010] Furthermore, the preparation method of the rice starch ester comprises the following steps:

[0011] (1) Dissolve citric acid or malic acid in distilled water, adjust the pH to 3.5 with sodium hydroxide, and then dilute with distilled water to obtain an acid solution;

[0012] (2) uniformly mixing the prepared acid solution and rice starch, taking out and letting it stand at room temperature, and then drying it in a forced air drying oven to a water content of 5% to 10%, thereby obtaining a mixture;

[0013] (3) The crushed mixture was placed in a forced air drying oven and reacted at 130° C. for 6 h. The reaction mixture was washed with a large amount of distilled water to remove unreacted citric acid and malic acid. The washed starch was dried at room temperature and then ground and passed through an 80-mesh sieve to obtain a finished product.

[0014] Furthermore, in step (1), the amount of rice starch ester added is 0-40%.

[0015] Furthermore, in step (1), the amount of rice starch ester added is 20%.

[0016] Furthermore, in step (2), the moisture content is adjusted to 38%, the feeding speed of the mixed powder into the feeding hopper is 16 kg / h, and the extrusion molding is performed by a twin-screw two-stage extruder, the extrusion stage temperature is 90°C, and the molding stage temperature is 60°C.

[0017] The present invention also provides rice noodles prepared by the preparation method, wherein the rice noodles are medium / low GI rice noodles.

[0018] The present invention also provides an application of rice starch ester in improving the physical and chemical properties of rice noodle raw material powder and improving the quality of rice noodles. The improvement of the physical and chemical properties of the rice noodle raw material powder includes reducing the solubility, swelling degree, starch paste peak viscosity, minimum viscosity, final viscosity and regeneration value of the rice noodle raw material powder system, increasing the gelatinization temperature, and improving the aging resistance and elasticity; the improvement of the rice noodle quality includes inhibiting starch aging, reducing the hardness, chewiness and adhesiveness of the rice noodles, reducing the GI value of the rice noodles, and increasing the RS content of the rice noodles.

[0019] Furthermore, the rice starch ester is citric acid rice starch ester or malic acid rice starch ester, and the rice starch ester accounts for 5%-20% of the rice noodle raw material flour.

[0020] The beneficial effects of the present invention are:

[0021] This study investigates the effects of varying modified starch addition levels on the physical and chemical properties of mixed rice flour and the quality of rice noodles. The study focuses on the effects of modified starch additions within a range of 0% to 40% on the hydration, gelatinization, rheological, and thermomechanical properties of the mixed flour, as well as the cooking characteristics, texture, color, and sensory qualities of rice noodles. The glycemic index of the rice noodles is also predicted. The results are as follows:

[0022] (1) The results of the physical and chemical properties of the mixed powder showed that with the addition of starch citric acid ester and starch malic acid ester, the solubility and swelling of the mixed powder system decreased significantly (p < 0.05), the peak viscosity, minimum viscosity, final viscosity and regeneration value of the starch paste showed a significant downward trend, and the gelatinization temperature of the entire system increased significantly (p < 0.05). At the same time, the rheological results showed that the addition of modified starch had a greater effect on the elastic properties of rice gel. In comparison, starch citric acid ester had a better effect on improving the anti-aging and elasticity of the mixed powder, which was also related to its higher degree of esterification. In addition, both modified starches showed a good improvement effect on the mixed powder system at a 20% replacement amount, and the mixed powder system of the two modified starches had a good correlation with the quality of their respective rice noodles.

[0023] (2) The effect of modified starch on the quality characteristics of rice noodles showed that when the two modified starches replaced 5% to 20%, it was helpful for the formation of the gel network of rice noodles and made them have better cooking quality. With the addition of modified starch, starch aging could be inhibited, and the hardness, chewiness and adhesiveness of rice noodles were significantly reduced (p<0.05), while the elasticity, viscosity, recovery and cohesion did not change significantly (p>0.05). Moreover, when the replacement amount was 20%, the sensory score of rice noodles was the highest, which were 90.0 points and 88.7 points respectively, indicating that the consumer acceptance of rice noodles was the best at this addition amount. In addition, the L value of rice noodles increased significantly, and the a and b* values ​​decreased significantly (p<0.05), indicating that the addition of modified starch was beneficial to the gloss of rice noodles. At the same time, the hydrolysis index and glycemic index of rice noodles were measured, and it was found that the GI values ​​of rice noodles replaced with 20% citric acid starch ester and 20% malic acid starch ester were 58.5 and 66.0, respectively, which were significantly lower than those of the control group rice noodles (p<0.05), and had a higher RS ​​content than the control group rice noodles, which is conducive to the preparation of medium / low GI rice noodles. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a diagram showing the effect of different starch ester addition amounts on the hydration properties of mixed powder, where A refers to the addition of citric acid starch ester, and B refers to the addition of malic acid starch ester. Different letters in the same indicator indicate significant differences at p<0.05.

[0025] Figure 2 The figure shows the effect of starch ester addition on the loss modulus, storage modulus and loss coefficient of the mixed powder, where AA1, B1, and C1 represent different CRS addition amounts, and A2, B2, and C2 represent different MRS addition amounts;

[0026] Figure 3 This is a diagram showing the effect of different amounts of citric acid starch ester addition on the cooking characteristics of rice noodles, where different letters in the same indicator indicate significant differences (p<0.05);

[0027] Figure 4 This is a diagram showing the effect of different malic acid starch ester addition amounts on the cooking characteristics of rice noodles, where different letters in the same indicator indicate significant differences (p<0.05);

[0028] Figure 5 The figure shows the effect of starch ester addition on rice noodle color, where A1, B1, and C1 represent different CRS addition amounts, and A2, B2, and C2 represent different MRS addition amounts. Different letters indicate significant differences at p < 0.05.

[0029] Figure 6 Macroscopic images of rice noodles before and after adding modified starch, where Figure A is the control group, Figures BE are the addition amounts of 5%, 10%, 20%, and 40% citric acid starch ester, and Figure FI is the addition amount of 5%, 10%, 20%, and 40% malic acid starch ester;

[0030] Figure 7 Figure 1 is the effect of different modified starch addition amounts on the microstructure of rice noodles, where Figure A is the control group, Figures BE are 5%, 10%, 20%, and 40% citric acid starch ester addition amounts, and Figure FI is 5%, 10%, 20%, and 40% malic acid starch ester addition amounts;

[0031] Figure 8 Figure 2 is the content of RDS, SDS, RS in different samples (A) and the starch hydrolysis rate curve (B), where different letters in the same component indicate significant differences (p < 0.05);

[0032] Figure 9 This is a correlation analysis chart between the physical and chemical properties of mixed flour and rice noodle quality. Figure A shows the addition of citric acid starch ester, and Figure B shows the addition of malic acid starch ester. *p<0.05, **p<0.01. DETAILED DESCRIPTION

[0033] Example 1 Effect of Rice Starch Ester Addition Amount on Mixed Flour

[0034] 1. Experimental Materials

[0035] The rice adopted in the present embodiment is from Wuchang Jinhe Rice Industry Co., Ltd., and is long-grain fragrant; Rice flour, citric acid rice starch ester, and malic acid rice starch ester are all homemade by the laboratory, and the related specific instruments are as shown in Table 1, and the related specific experimental reagents are as shown in Table 2.

[0036] Table 1 Specific instruments

[0037] name model Manufacturer electronic balance JA2003 Shanghai Puchun Measuring Instrument Co., Ltd. Digital constant temperature water bath LKTC-B1-T Changzhou Ronghua Instrument Manufacturing Co., Ltd. Rapid Viscosity Analyzer TCW3.17.3.509 Perton Ruihua Scientific Instruments (Beijing) Co., Ltd. Visible spectrophotometer 722 Tianjin Tester Analytical Instrument Co., Ltd. Thermal collector constant temperature heating magnetic stirrer DF-101S Henan Yuhua Instrument Co., Ltd. High-speed centrifuge TJ16 Shanghai Luxiang Instrument Centrifuge Instrument Co., Ltd. Rheometer MCR102 Austrian Anton Paar Field emission scanning electron microscopy SU8010 Hitachi Corporation Colorimeter NH300 Kruide Instrument Co., Ltd. Mixing tester Mixolab2 French Chopin Instrument Company Texture Analyzer TMS-Touch250 American Food Technology Corporation Water bath constant temperature oscillator SHA-C Hangzhou Jingfei Instrument Technology Co., Ltd. microplate reader M2e Meigu Molecular Instruments (Shanghai) Co., Ltd. Freeze dryer SCIENTZ-12N Ningbo Xinzhi Biotechnology Co., Ltd. Twin-screw extruder FT Jinan Zhennuo Machinery Co., Ltd.

[0038] Table 2 Experimental reagents

[0039] name Manufacturer Sodium hydroxide Tianjin Continental Chemical Reagent Factory hydrochloric acid Xilong Chemical Co., Ltd. Glucoamylase Beijing Yita Biological Co., Ltd. Pepsin Beijing Yita Biological Co., Ltd. Trypsin Beijing Yita Biological Co., Ltd. Glucose test kit Nanjing Jiancheng Bioengineering Institute

[0040] 2. Experimental Methods

[0041] 2.1 Preparation of rice starch ester

[0042] Dissolve 8g of citric acid / malic acid in 20mL of distilled water, adjust the solution's pH to 3.5 with 10mol / L sodium hydroxide, and dilute to 50mL with distilled water. Mix the prepared acid solution with 50g of rice starch, let it sit at room temperature for 16 hours, and then dry it in a 50°C air drying oven for 12 hours to a moisture content of 5% to 10%. The crushed mixture is placed in a 130°C air drying oven for 6 hours. The resulting mixture is then washed with plenty of distilled water to remove unreacted citric and malic acid. The washed starch is dried at room temperature, ground, and passed through an 80-mesh sieve to yield finished citric acid rice starch ester (CRS) and malic acid rice starch ester (MRS).

[0043] 2.2 Effect of CRS / MRS addition on the solubility and swelling of mixed powder

[0044] CRS / MRS was mixed with rice flour at replacement levels of 0%, 5%, 10%, 20%, and 40%, and its solubility and swelling properties were measured.

[0045] 2.3 Effect of CRS / MRS addition on the gelatinization properties of mixed powder

[0046] CRS / MRS was mixed with rice flour at replacement levels of 0%, 5%, 10%, 20%, and 40%, and its gelatinization properties were measured.

[0047] 2.4 Effect of CRS / MRS addition on rheological properties of mixed powder

[0048] CRS / MRS was mixed with rice flour at replacement levels of 0%, 5%, 10%, 20%, and 40%, and its rheological properties were measured.

[0049] 2.5 Effect of CRS / MRS addition on the thermomechanical properties of mixed powder

[0050] The thermomechanical properties of mixed rice dough were measured using a Mixolab analyzer. The test parameters were set as follows: different amounts of CRS / MRS (0%, 5%, 10%, 20%, and 40%) were added to the rice flour, and the mixture was placed in a mixing bowl for stirring. The moisture base was the actual moisture content, and a certain amount of water was added according to the requirement of achieving the maximum torque (C1 = 1.1 ± 0.05 Nm). The instrument has automatic water addition and temperature control functions. The initial test temperature was set to 30°C, and the insulation duration was 8 minutes. Subsequently, the temperature was increased to 90°C at a rate of 4°C / min and maintained for 8 minutes. Finally, the temperature was reduced to 50°C at a rate of 4°C / min, and the stirring speed was maintained at 80 r / min. The measurement was completed after 45 minutes, and the indicators were measured.

[0051] 3. Experimental Conclusion

[0052] 3.1 Effect of CRS / MRS addition on hydration properties of mixed powder

[0053] The cooking loss and water absorption of rice products during cooking are related to solubility and swelling. The solubility and swelling of the mixture of rice flour and modified starch measured at 95 °C are as follows: Figure 1 shown.

[0054] Swelling power and solubility can reflect the dispersion and gelatinization of starch granules when heated in water. Figure 1 As the content of CRS and MRS in the mixed flour increased from 0% to 40%, the solubility and swelling capacity of the mixed flour decreased significantly (p < 0.05). The solubility of the mixed flour of CRS and MRS with rice flour decreased from 7.4% to 4.1% and 4.0%, respectively, and the swelling capacity decreased from 8.0% to 4.2% and 4.4%, respectively. This may be due to the high content of amylose in the modified starch, the strong intermolecular interaction and dense arrangement, which inhibits the interaction between starch molecules and water molecules, subsequently limiting their water absorption and swelling. After the amylose dissolves, the starch granules absorb water and swell. In addition, the swelling capacity of starch mainly reflects the insolubility of amylopectin, which is mainly caused by the formation of hydrogen bonds between the side chains of amylopectin. Its swelling properties are also related to the chain length of amylopectin. After CA treatment, the amylose content of native starch increases and more long amylopectin chains are converted to short chains, disrupting the hydrogen bonds between amylopectin side chains. This results in a lower swelling degree for the CRS mixed powder system compared to the MRS mixed powder system. Solubility is the result of amylose leaching during swelling. Reduced solubility means a lower solids content dispersed in the solution, likely due to the high density of the starch structure. This may lead to less disintegration of starch granules during gelatinization. The disintegration values ​​of CRS itself and its mixed powder system are lower than those of MRS, which is consistent with the results of related research.

[0055] 3.2 Effect of CRS / MRS addition on the gelatinization properties of mixed powder

[0056] The gelatinization properties of the mixed powder gel samples with two different addition amounts of modified starch and rice flour analyzed by rapid visco analyzer (RVA) are shown in Tables 3-4.

[0057] Table 3 Effect of citric acid starch ester addition on the gelatinization properties of mixed powder

[0058]

[0059] Note: The values ​​marked with different letters in the same column are significantly different (p<0.05).

[0060] Table 4 Effect of malic acid starch ester addition on the gelatinization properties of mixed powder

[0061]

[0062] Note: The values ​​marked with different letters in the same column are significantly different (p<0.05).

[0063] As shown in Tables 3-4, with the increase in the addition of CRS and MRS, the peak viscosity, minimum viscosity, final viscosity, and regeneration value of the mixed flour showed a significant downward trend, and the gelatinization temperature of the entire system increased significantly (p<0.05). The gelatinization characteristics depend on the rigidity of the starch granules, which in turn affects the granule swelling potential and the amount of amylose leached into the solution. The pure rice flour sample in the control group had a higher peak viscosity, and the high viscosity of rice flour was related to its high swelling power. This may be because pure rice flour has a lower amylose content than the modified starch mixed flour, which leads to a higher swelling power, which is consistent with the results of related studies. Its higher swelling power and water solubility make it show a higher peak viscosity in the gelatinization curve. This is consistent with the researchers' research on potato starch, which found that the gelatinization behavior of potato starch showed a lower amylose content associated with a higher peak viscosity. After modification with CA and MA, the strong intermolecular forces between starch molecules result in lower water-holding capacity, making it less likely to disperse throughout the system. This weakens the hydrogen bonding forces between rice starch and water molecules, thereby reducing the swelling rate of rice starch granules in water and, in turn, causing a decrease in the viscosity of the entire mixed flour. Furthermore, the increased gelatinization temperature of the mixed flour system may be due to the high amylose content in the modified starch, which promotes the formation of double helices in the amorphous regions of the starch granules. This dense crystalline structure is thermally stable and requires more energy to break down. Similar findings have been observed in the modification of natural cassava starch: dough containing 20% ​​starch acetate has a lower gelatinization peak temperature, which can be used in noodle production to delay noodle aging. Furthermore, studies have found that starch esters with high DS levels significantly slow aging, and similar results were observed in this example. The peak viscosity, disintegration value, and reversion value of the high-DS CRS mixed rice flour were all lower than those of the MRS mixed rice flour, indicating that CRS is more effective in improving the aging resistance of the mixed flour system. Therefore, the results of this study on gelatinization properties can provide a reference for improving the thermal processing quality of rice products.

[0064] 3.3 Effect of CRS / MRS addition on rheological properties of mixed powder

[0065] For viscoelastic substances, G' represents solid state (elasticity) and G" represents liquid state (viscosity). The rheological properties of rice gel samples containing CRS and MRS were analyzed to reflect the viscoelasticity of the mixed gel samples. The changes in storage modulus (G'), loss modulus (G") and loss coefficient (tanδ) of the mixed powder system with angular frequency at different modified starch addition amounts are shown in Figure 2 middle.

[0066] Depend on Figure 2As shown in (A, B), during the deformation of the gel structures of native starch and modified starches (citric acid and malic acid treated starch), all mixed powder gels exhibited weak gel behavior, as evidenced by positive tan δ and G' values ​​significantly higher than G". Furthermore, G' values ​​for all samples were higher than G" across the entire frequency range, and both G' and G" gradually increased with increasing frequency, consistent with the researchers' finding that high amylose content contributes to gel firmness and stability. Furthermore, G' and G" were frequency-dependent and did not cross over the entire frequency range, showing a sharp increase in G' and a moderate increase in G". However, the rates of increase varied among samples with different modified starch contents, with higher modified starch content resulting in higher G' and G" values. This is likely due to the aggregation and ordering of amylose chains and the further formation of hydrogen bonds between chains. Furthermore, polymerization reactions between starch granules, forming double helical segments, are a primary driver of gel formation, similar to the readily hydrogen-bonded formation of amylose when it diffuses into solution, producing rigid, opaque gelatin. After adding modified starch to rice flour, the change in G' value was more obvious than that in G", and there was a large difference between them, indicating that the modified starch had a more significant effect on the elastic properties of rice flour gel than on the viscosity properties. Therefore, the modified starch-rice flour complex was added to the formulation of rice noodles to improve their quality properties, especially the elasticity of rice noodles.

[0067] At the same time, Figure 2 As can be seen in (C), values ​​of tanδ<1 indicate a predominantly elastic behavior, while values ​​greater than 1 reflect the viscous behavior of the starch gel. The control rice flour and all mixed flours showed tanδ values ​​ranging from 0.12 to 0.29, indicating that all samples were more elastic than viscous. The significant difference in viscoelastic properties between mixed flour and rice flour alone also suggests that the addition of modified starch can provide the rheological properties required for a wide range of food industry applications. In addition, as the amount of starch citric acid ester added increased, the G' of the mixed flour increased significantly, while there was no significant difference in G' between different amounts of starch malic acid ester added, and starch citric acid ester had a higher G' between the two, indicating that the addition of starch citric acid ester can better improve the elasticity of the mixed flour gel system. Therefore, in food industry applications, the addition of this modified starch to rice flour can be used to increase the elastic properties of rice flour-based products (such as rice noodles and rice cakes).

[0068] 3.4 Effect of CRS / MRS addition on the thermomechanical properties of mixed powder

[0069] The thermomechanical properties of rice dough are mainly dominated by protein denaturation and starch gelatinization. In this example, the effect of the addition amount of CRS and MRS on the thermomechanical properties of rice dough was measured using a Mixolab device. The results are shown in Tables 5-6.

[0070] Table 5 Effect of citric acid starch ester addition on the thermomechanical properties of mixed powder

[0071]

[0072] Note: The values ​​marked with different letters in the same column are significantly different (p<0.05).

[0073] Table 6 Effect of malic acid starch ester addition on the thermomechanical properties of mixed powder

[0074]

[0075] Note: The values ​​marked with different letters in the same column are significantly different (p<0.05).

[0076] As shown in Tables 5-6, with increasing addition levels of CRS and MRS, the water absorption rate and stability time of rice dough both showed an initial upward and then downward trend. At a 20% addition level, the water absorption rate reached peak values ​​of 73.1% and 72.8%, respectively, while the stability time reached peak values ​​of 1.12 min and 0.85 min, respectively. This indicates that the appropriate addition of these two modified starches can effectively enhance the processing properties and improve the quality of rice dough. This phenomenon may be due to the excellent hydration properties of modified starches (especially chemically modified ones). Appropriate addition of these starches facilitates binding with proteins to form a tight network structure, thereby enhancing the toughness of rice dough. This is consistent with the research results of modified starches in gluten-free food systems. Furthermore, the weakening degree of rice dough, which reflects the degree to which rice dough can withstand mechanical agitation during mixing, increases when the addition level of CRS and MRS ranges from 0% to 20%. This may be due to the interaction between the modified starch and rice flour, forming a holistic structure, thereby improving the kneading and stirring resistance of the rice dough. Starch retrogradation refers to the gradual reduction in molecular kinetic energy during the cooling of gelatinized starch, resulting in a loss of solubility in the tightly packed, highly crystallized starch microbundles between adjacent molecules. It is commonly used to describe the recrystallization of amylose. A lower retrogradation value indicates a lower likelihood of starch retrogradation. As shown in the table, after adding modified starches, the starch retrogradation properties gradually decreased at substitution levels of 0% to 20%, indicating that the appropriate addition of these two modified starches can inhibit starch retrogradation, consistent with previous research results. Therefore, a 20% addition level can moderately improve the processing properties of rice dough. Overall, at the same addition level, the effect of citric acid starch ester on rice dough processing properties was slightly stronger than that of malic acid starch ester, but the difference between the two was not significant, and both significantly outperformed the blank control (p < 0.05).

[0077] Effect of the addition amount of rice starch ester on rice noodles

[0078] 1. Experimental Methods

[0079] 1.1 Preparation of Rice Noodles

[0080] 1500g of ground rice flour was weighed and passed through a 100 mesh sieve. Two kinds of rice starch ester were compounded with rice flour in different proportions (0%, 5%, 10%, 20%, and 40%), mixed thoroughly, and the moisture content was adjusted to 38%. The mixed powder was placed in a feeding hopper with a feed rate maintained at 16kg / h. The mixture was then extruded by a twin-screw two-stage extruder at 90°C and 60°C. After the noodles were made, they were dried and stored.

[0081] 1.2 Effect of CRS / MRS addition on cooking characteristics of rice noodles

[0082] Boil 20g of dry rice noodles (m0) in 400mL of water to ensure that there are no raw parts. After cooking, rinse the rice noodles with cold water, drain for 30s, and weigh them (m1) to determine the water absorption rate of the rice noodles. Cooking loss is the ratio of the weight of the residue in the water after cooking to the weight of the dry rice noodles. The residue in the water is obtained by drying in an oven at 105°C (m2) to determine the rice noodle cooking loss rate. Add 15 whole dry rice noodles to 1L of boiling water, increase the cooking time to 20min, and record the number of rice noodles (m3) to determine the rice noodle breakage rate. Use the following formulas to calculate water absorption rate, cooking loss rate, and breakage rate:

[0083] Water absorption rate = m1 / m0×100%

[0084] Cooking loss rate = m2 / m0×100%

[0085] Broken strip rate = (m3-15) / 15×100%.

[0086] 1.3 Effect of CRS / MRS addition on the texture characteristics of rice noodles

[0087] Nine rice noodles of uniform thickness and length, 4 cm, were placed in boiling water and boiled for 10 minutes. After boiling, the noodles were rinsed with cold water over a filter for 30 seconds, then placed on filter paper to absorb the surface moisture. Three rice noodles were placed on the test bench at the same distance and tested. In TPA mode, a P / 36R probe was selected with a compression ratio of 70%, a pre-test speed of 1 mm / s, a mid-test speed of 1 mm / s, a post-test speed of 2 mm / s, a trigger force of 5 g, and a parameter acquisition rate of 500 pps.

[0088] 1.4 Effect of CRS / MRS addition on rice noodle color

[0089] The color of the prepared rice noodles was measured using a colorimeter, and the results were expressed using lightness (L), redness (a), and yellowness (b*) values.

[0090] 1.5 Effect of CRS / MRS addition on the microstructure of rice noodles

[0091] The microstructure of rice noodle cross-sections was observed and analyzed using a scanning electron microscope. The prepared rice noodles were freeze-dried for 24 hours, cut into 1 mm thick sections, and secured to a sample stage with special double-sided tape. The sections were then placed in an ion sprayer and subjected to gold coating for 80 seconds. Scanning conditions were: 15 kV acceleration voltage, 600x magnification.

[0092] 1.6 Effect of CRS / MRS addition on sensory properties of rice noodles

[0093] Ten rice noodles of uniform thickness were selected and placed in 700 mL of boiling water, maintaining a slight boil. Once cooked, the noodles were removed from the water, placed in a strainer, and rinsed with cold water for 30 seconds to filter out excess water. The excess water was then absorbed with absorbent paper and placed on a plate for tasting. A sensory evaluation panel of six to eight trained experts tasted the rice noodles containing varying amounts of modified starch and scored them based on seven sensory criteria. The final results were calculated as the arithmetic mean, with appropriate modifications based on the specific scoring criteria used by Lu Yu.

[0094] Effects of 1.7 CRS / MRS on in vitro digestibility of rice noodles

[0095] Disperse 200 mg of starch sample with 5 mL of 0.5 mol / L sodium acetate buffer (pH 5.2) in a 50 mL centrifuge tube and mix thoroughly. Place the centrifuge tube in a boiling water bath for 20 minutes. Then, transfer the tube to a 37°C water bath shaker and shake at 170 rpm until it cools. Then, simulated gastric fluid solution [HCl (10 mL, 0.05 mol / L), pepsin (50 mg), guar gum (50 mg)] was added to the centrifuge tube, mixed well, and shaken for 30 minutes. Seven glass beads and 5 mL of sodium acetate buffer were added and the shaking continued for 30 minutes. After that, 10 mL of mixed enzyme solution [(porcine pancreatic α-amylase (290 U / mL), amyloglucosidase (260 U / mL))] was added to the tube. The tube was then shaken at 170 rpm in a 37°C water bath. Aliquots (0.5 mL) were taken at intervals of 20 and 120 minutes and mixed with 4 mL of 95% ethanol to inactivate the enzymes. The mixed solution was centrifuged at 10,000 rpm for 5 minutes, and the amount of glucose released at 20 and 120 minutes was measured using a glucose kit (POD-GOD method). The percentages of RDS, SDS, and RS in the sample were calculated using the following formula:

[0096] RDS (%) = [(G20-FG) / TS] × 0.9 × 100 (Formula 3-1)

[0097] SDS (%) = [(G120 - G20) / TS] × 0.9 × 100 (Formula 3-2)

[0098] RS(%)=[(TS-RDS-SDS) / TS]×100 (Formula 3-3)

[0099] Where:

[0100] G20 - the amount of glucose released within 20 min of hydrolysis, mg;

[0101] G120 - the amount of glucose released within 120 min of hydrolysis, mg;

[0102] FG——the amount of free glucose in starch, mg;

[0103] TS——total starch weight, mg.

[0104] 1.8 Data Statistics and Analysis

[0105] The experimental data were statistically analyzed using SPSS22.0 in the calculation format of mean ± standard deviation, and one-way analysis of variance (ANOVA) was performed with a significance level of p < 0.05. The obtained data were plotted using Origin2021. All experiments were repeated three times.

[0106] 2. Experimental Results

[0107] 2.1 Effect of CRS / MRS addition on cooking characteristics of rice noodles

[0108] Cooking quality is related to high water absorption and low cooking loss. By analyzing the cooking characteristics of rice noodles, the effects of modified starch on rice noodle quality are summarized, which can also provide some references for the process quality control of rice noodle preparation. The results of the effects of different modified starch addition amounts on rice noodle water absorption, cooking loss and cooked breakage rate are shown in the figure. Figure 3-4 As shown. Cooking loss and breaking rate are indicators reflecting the cooking quality of rice noodles. The cooking loss and breaking rate of rice noodles are negatively correlated with the quality of rice noodles. Figure 3As the amount of CRS added increased (5% to 20%), the cooking loss and breakage rates of rice noodles first decreased and then increased, reaching a minimum of 8.5% and 7.3%, respectively, which were 7.1% and 19.4% lower than those of the control group and significantly lower than those of regular rice noodles (p < 0.05). The water absorption rate of rice noodles also increased and then decreased with increasing CRS addition, reaching a maximum of 118.8% at a 5% addition, 1.3 times the 88.1% of the control group. The main principles of rice noodle production are starch gelatinization and retrogradation, with amylose content playing the most important role in the cooking quality of rice noodles. Solids loss during cooking is primarily due to the solubilization of loosely bound gelatinized starch on the product surface and is dependent on the strength of the retrograde starch network. The addition of 5% to 20% CRS promotes the formation of a gelatin network in rice noodles, increasing water absorption and reducing cooking loss and breakage rates. The study found that cooking loss of rice noodles is primarily due to the dissolution of the gelatinized starch network, which is loose in structure. Therefore, when the starch ester content exceeds 20%, the gelatinization and aging processes of the starch are severely disrupted, resulting in poor gelatinization of the rice noodle gel network. This impact outweighs the modified starch's promotion of the gel network during the rice noodle cooking process, leading to increased cooking loss and breakage. Furthermore, the study found that higher gelatinization temperatures and incomplete gelatinization lead to the formation of more starch residues, which also results in higher cooking loss rates. Therefore, when the CRS addition level is 20% or less, the cooking properties of rice noodles can be effectively improved.

[0109] Depend on Figure 4 As the addition level of MRS increases, its water absorption and cooked breakage rate show similar trends to those of CRS. However, the cooking loss rate initially increases, then decreases to 9.4% at a 20% addition level, before continuing to rise. This increased cooking loss rate makes the rice noodles more likely to become soupy. This may be due to the increased dissolution of starch and other substances during the cooking process, coupled with its relatively high gelatinization temperature, which hinders the formation of the starch gel network, resulting in a less dense rice noodle structure and reduced quality. Alternatively, the low free amylose content may be insufficient to promote gel network formation, leading to higher cooking loss in rice noodles. Overall, however, rice noodles prepared with 20% MRS exhibit better cooking quality. Furthermore, a comparison of the effects of CRS and MRS on the cooking properties of rice noodles shows that CRS, due to its higher anti-aging properties, amylose content, and lower swelling capacity, has a greater effect on improving the cooking properties of rice noodles.

[0110] 2.2 Effect of CRS / MRS addition on the texture characteristics of rice noodles

[0111] The texture of rice noodles is the most important characteristic that determines consumer acceptance of the product. The effects of different modified starch addition levels on the texture of rice noodles are shown in Tables 7-8.

[0112] Table 7 Effect of citric acid starch ester addition on texture characteristics of rice noodles

[0113]

[0114] Note: The values ​​marked with different letters in the same column are significantly different (p<0.05).

[0115] Table 8 Effect of malic acid starch ester addition on texture characteristics of rice noodles

[0116]

[0117]

[0118] Note: The values ​​marked with different letters in the same column are significantly different (p<0.05).

[0119] As shown in Tables 7-8, with increasing amounts of CRS and MRS, the hardness, chewiness, and gummy properties of rice noodles all decreased significantly (p < 0.05), while elasticity, viscosity, resilience, and cohesion did not change significantly (p > 0.05). In texture quality analysis, hardness and elasticity are generally considered to characterize the overall quality of rice noodles. With increasing amounts of CRS and MRS, the hardness of rice noodles was significantly lower than that of pure rice noodles (p < 0.05). The hardness of cooked rice noodles is affected by the amylose content, which causes aging during gel formation. Therefore, the hardness of rice noodles can reflect the degree of aging after cooking. This is consistent with previous studies of gelatinization properties, which showed that the regeneration value of mixed flours decreased, and the regeneration and coagulation of starch gel was inhibited, thus affecting the aging of rice noodles. Therefore, the addition of CRS and MRS inhibits the aging of rice noodles, thereby reducing their hardness.

[0120] Furthermore, the addition of CRS and MRS had little effect on the elasticity of rice noodles, with no significant change. However, the addition of 40% MRS did improve the elasticity of rice noodles. Therefore, the results indicate that the addition of both modified starches can improve the textural properties of their respective rice noodles to some extent, with CRS and MRS having a greater impact on the firmness and elasticity of rice noodles, respectively.

[0121] 2.3 Effect of CRS / MRS addition on rice noodle color

[0122] The color of rice noodles affects consumers' choice and consumption of rice noodles. The color parameters (L, a, b) of rice noodles with different addition amounts of citric acid starch ester and malic acid starch ester are shown in Figure 5 middle.

[0123] Depend on Figure 5It can be seen that with the increase in the amount of modified starch added, the L value increased significantly, and the a and b values ​​decreased significantly. The maximum L values ​​of CRS and MRS were 72.3 and 72.1, respectively. The L value is an important parameter reflecting the color of rice noodles and represents the brightness of rice noodles. The gradual increase in the L value is beneficial to the gloss of the rice noodles, indicating that the addition of modified starch has increased the brightness of the rice noodles, which means that consumer favorability has increased. At the same time, the color, water content and water absorption of rice noodles will also affect the brightness of rice noodles. This is mainly because the introduction of carbonyl groups improves the transparency and water absorption of starch. The addition of modified starch promotes the water absorption of rice dough, thereby further increasing the L value of rice noodles. The color of the modified starch itself is greater than the whiteness of rice flour, which leads to a decrease in the a and b values ​​of rice noodles. In addition, the addition of both esterified starches is beneficial to improving the color of rice noodles, but the numerical differences between the parameters are small. In addition, in Figure 6 The macroscopic images of the rice noodles show that the color of the rice noodles slightly improves with the increase of the modified starch addition. The rice noodles prepared with 20% CRS and MRS addition have better quality, which is conducive to the industrial production of rice noodles.

[0124] 2.4 Effect of CRS / MRS addition on the microstructure of rice noodles

[0125] The microstructure of rice noodles has a great influence on their physical properties, such as cooking properties and texture. In order to observe the changes in starch granule morphology, the effects of native rice starch and two esterified starches on the microstructure of rice noodles were scanned and characterized by scanning electron microscopy. The results are shown in Figure 2. Figure 7 shown.

[0126] Depend on Figure 7As can be seen, the cross-section of the rice noodles in the control group exhibits a relatively smooth and dense structure, indicating that the starch has been fully gelatinized and the noodle structure is quite dense. However, when the starch ester addition level is between 5% and 10%, the cross-section of the rice noodles begins to show unevenness, accompanied by unevenly distributed particles. This is likely due to the fact that the internal interaction forces of the modified starch molecules are much stronger than those of rice starch molecules, resulting in a significant difference in structure from rice starch, thus losing the original gelatinization properties of rice starch. The presence of this structure has a certain impact on the gelatinization and aging processes of rice starch. When the starch ester addition level is between 20% and 40%, the cross-section of the rice noodles is relatively rough, with uneven particle distribution and the appearance of large voids. In this case, the gelatinization process of the rice noodles is severely impaired, voids appear in the cross-section, and more particles begin to distribute and aggregate on the surface. In summary, as the ratio of CRS to MRS gradually increased, the rice noodles exhibited a rougher cross-section and texture. Simultaneously, the number of cavities and pores within them increased and became unevenly distributed, indicating that a complete gel structure had not formed within the rice noodles. This is consistent with the results of a study on the cooking properties of rice noodles, which showed that the cooking loss of rice noodles increased and the hardness and elasticity of the rice noodle texture decreased.

[0127] 2.5 Effect of CRS / MRS Addition Amount on Sensory Properties of Rice Noodles

[0128] Sensory properties are an important indicator of potential consumer preference. The differences in sensory properties between pure rice flour (control) and rice noodles prepared with starch citric acid ester and starch malic acid ester at 5%, 10%, 20% and 40% substitution levels are presented in Tables 9-10.

[0129] Table 9 Effect of citric acid starch ester addition on sensory properties of rice noodles

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[0131] Note: The values ​​marked with different letters in the same column are significantly different (p<0.05).

[0132] Table 10 Effect of malic acid starch ester addition on sensory properties of rice noodles

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[0134]

[0135] Note: The values ​​marked with different letters in the same column are significantly different (p<0.05).

[0136] Tables 9-10 show that, when modified starch addition levels ranged from 5% to 20%, the addition of starch esters of citric acid and malic acid increased the overall sensory evaluation score of rice noodles compared to conventional rice noodles, significantly improving all sensory characteristics (p < 0.05), particularly the appearance, palatability, and toughness of the rice noodles. This indicates that rice noodles containing esterified starches exhibited better taste and appearance than conventional rice noodles. This may be due to the esterification reaction introducing new functional groups into the starch molecules, forming a stable cross-linked structure, which improves the water-holding capacity, transparency, and toughness of the rice noodles. Furthermore, at a 20% substitution level, the two starch esters showed the greatest effect on the sensory properties of rice noodles, increasing sensory scores by 14.1% and 12.4%, respectively. This decreased at a 40% addition level, with a significant decrease in toughness and elasticity, consistent with the results observed in the macroscopic images of the rice noodles. Therefore, the addition of 20% starch esters of citric acid showed the greatest improvement in the sensory properties of rice noodles.

[0137] Effect of 2.6 CRS / MRS on in vitro digestibility of rice noodles

[0138] Starch digestibility is related to human health. Increased digestibility promotes increased blood sugar levels after meals, which in turn induces the occurrence of certain diseases. A decrease in rice noodle digestibility is beneficial for the prevention and treatment of diabetes and other chronic diseases. From the above experimental results, it can be seen that when the CRS and MRS replacement amount is 20%, the properties of the mixed flour and the quality of rice noodles are better. Therefore, the effects of the addition of different modified starches on the starch composition RDS, SDS, RS percentages and hydrolysis curves of the prepared rice noodle samples were compared. Figure 8 shown.

[0139] Depend on Figure 8 (A) It can be seen that with the addition of CRS and MRS, the content of RDS and SDS in rice noodles decreased significantly, while the content of RS increased significantly (p<0.05). The postprandial blood sugar response is largely determined by the content of RDS, while the content of RS and SDS controls the increase in GI value. The increase in RS content indicates an increase in digestibility. Figure 8 As can be seen from the starch digestibility curve in (B), the starch hydrolysis rate increases rapidly in the first 20 minutes of intestinal digestion, then gradually stabilizes and basically reaches equilibrium after 90 minutes. With the addition of starch citric acid ester and starch malic acid ester, the RDS and SDS contents decrease, the RS content increases, and the overall starch hydrolysis rate of rice noodles decreases. At 180 minutes, the hydrolysis rates of rice noodles prepared by adding 20% ​​CRS and MRS reached 51.7% and 59.8%, respectively, which were 14.5% and 6.4% lower than those of the ordinary rice noodle control group, respectively. This indicates that modified starch may have a certain degree of effect on regulating the postprandial blood sugar response of rice products. The hydrolysis index and glycemic index of rice noodles before and after the addition of modified starch were predicted, and the results are shown in Table 10.

[0140] Table 10 Starch hydrolysis index and glycemic index in different samples

[0141]

[0142]

[0143] Note: The values ​​marked with different letters in the same column are significantly different (p<0.05).

[0144] Table 10 shows that compared to ordinary rice noodles, partially replacing raw materials with modified starch facilitates slower digestion in the human body. The addition of both CRS and MRS significantly reduced the HI and GI values ​​of rice noodles (p < 0.05), with GI values ​​decreasing by 23.3% and 13.5%, respectively. This indicates that CRS is more effective in reducing the GI value of rice noodles than MRS. This decrease in GI may be due to the swelling properties of resistant starch during food digestion, which converts it into a highly viscous sol, thereby enhancing satiety and helping to delay the rise in postprandial blood glucose levels. Furthermore, multiple factors, such as the ratio of amylose to amylopectin, the crystallinity of starch granules, the starch gelation process, and food processing methods, all influence the GI value of starchy foods. The higher amylose content and lower crystallinity of CRS demonstrate its superior digestibility in rice noodles.

[0145] 2.7 Correlation between rice noodle quality evaluation indices and physical and chemical properties of mixed flour

[0146] Correlation analysis between the physical and chemical properties of mixed flours of esterified starch and rice flour with different substitution amounts and the quality of rice noodles prepared as raw materials Figure 9 shown.

[0147] Depend on Figure 9Overall, the mixed flour systems containing starch citric acid ester and starch malic acid ester samples showed a good correlation with the quality of their respective rice noodles. Specifically, the hydration properties of the starch citric acid ester and starch malic acid ester mixed flours showed a significant positive correlation with the peak viscosity, final viscosity, and regeneration value of their starch pastes (p < 0.01), and a negative correlation with the gelatinization temperature. Furthermore, with the exception of the dough regeneration value, the thermomechanical properties of the mixed doughs showed a significant positive correlation with each other, while the dough regeneration value showed a highly significant negative correlation with the other thermomechanical properties (p < 0.01). The cooking properties of rice noodles, including water absorption, cooking loss, and breakage, showed a negative correlation with their textural properties (hardness and springiness) (p < 0.05). Therefore, when the hardness of rice noodles is low, the intermolecular forces in the starch are weak, the gel network structure is not compact, the rice noodles are thermally unstable during cooking, and the amylose is easily dissolved, resulting in a high cooking loss and breakage rate. In addition, the correlation between individual indicators of samples with starch citric acid ester was general, while the correlation of samples with starch malate ester was slightly stronger, and they were basically significant or extremely significant positive and negative correlations.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be covered by the scope of the claims of the present invention.

Claims

1. A rice noodle and a preparation method thereof, characterized in that: The following steps are involved: (1) weighing the ground rice flour and sieving it, composite the rice starch ester with the sieved rice flour, and mixing them thoroughly to obtain a mixed powder; (2) Adjust the moisture content, then place the mixed powder in a feeding hopper, and then extrude and shape the rice noodles. After the noodles are made, dry and store them.

2. The preparation method according to claim 1, wherein In step (1), the sieving is through a 100-mesh sieve.

3. The preparation method according to claim 1, wherein In step (1), the rice starch ester is rice starch citric acid ester or rice starch malic acid ester.

4. The preparation method according to claim 3, wherein The preparation method of the rice starch ester comprises the following steps: (1) Dissolve citric acid or malic acid in distilled water, adjust the pH to 3.5 with sodium hydroxide, and then dilute with distilled water to obtain an acid solution; (2) uniformly mixing the prepared acid solution and rice starch, taking out and letting it stand at room temperature, and then drying it in a forced air drying oven to a water content of 5% to 10%, thereby obtaining a mixture; (3) The crushed mixture was placed in a forced air drying oven and reacted at 130° C. for 6 h. The reaction mixture was washed with a large amount of distilled water to remove unreacted citric acid and malic acid. The washed starch was dried at room temperature and then ground and passed through an 80-mesh sieve to obtain a finished product.

5. The preparation method according to claim 1, wherein In step (1), the amount of rice starch ester added is 0-40%.

6. The preparation method according to claim 5, wherein In step (1), the amount of rice starch ester added is 20%.

7. The preparation method according to claim 5, wherein In step (2), the moisture content is adjusted to 38%, the feeding speed of the mixed powder into the feeding hopper is 16 kg / h, and the extrusion molding is performed by a twin-screw two-stage extruder, the extrusion stage temperature is 90°C, and the molding stage temperature is 60°C.

8. Rice noodles prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The rice noodles are medium / low GI rice noodles.

9. The application of rice starch ester in improving the physicochemical properties of rice noodle raw material powder and improving the quality of rice noodles is characterized in that, The improvement of the physical and chemical properties of the rice noodle raw material flour is to reduce the solubility, swelling, peak viscosity, minimum viscosity, final viscosity and regeneration value of the rice noodle raw material flour system, increase the gelatinization temperature, and improve the aging resistance and elasticity; the improvement of the quality of the rice noodles is to inhibit starch aging, reduce the hardness, chewiness and adhesiveness of the rice noodles, reduce the GI value of the rice noodles, and increase the RS content of the rice noodles.

10. The use according to claim 9, characterized in that The rice starch ester is citric acid rice starch ester or malic acid rice starch ester, and the rice starch ester accounts for 5%-20% of the rice noodle raw material flour.

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