A method for preparing fresh wet rice noodles

Abstract

The present invention provides a method for preparing fresh wet rice noodles, belonging to the field of food processing technology. The method uses rice flour, corn starch, and cassava starch as raw materials for slurry mixing, and adds linear polysaccharides to the raw materials to prepare the fresh wet rice noodles. The method utilizes the gelling properties of the linear polysaccharides to improve the quality and heat-resistant sterilization performance of the fresh wet rice noodles, reduce the breakage rate and cooking loss of the rice noodles, and simultaneously maintain high sensory quality.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, and in particular relates to a method for preparing fresh wet rice noodles. Background Art

[0002] Rice noodles are a traditional starchy food with a long history. They are popular among consumers for their ease of cooking, convenience, ease of seasoning, and smooth, elastic texture. They are also a key source of carbohydrates for energy. Rice noodles, also known as rice vermicelli or rice noodles, are made from rice through processes such as starch gelatinization, molding, and aging. Rice's primary component is starch, accounting for approximately 80%, followed by approximately 8% protein, small amounts of lipids, cellulose, and trace elements. Rice noodles are categorized as dry, semi-dry, and fresh wet rice noodles. Fresh wet rice noodles have a higher moisture content than the other two types. Unlike wheat, rice lacks gluten, a network-forming protein. Therefore, rice noodles rely on gelatinization and retrogradation of rice starch to form a gel. However, starch gels have poor extensibility and require a high moisture content to form, resulting in poor mechanical properties and prone to breakage. Furthermore, the high moisture content makes them susceptible to microbial growth, leading to spoilage and a short shelf life. Therefore, maintaining the freshness of fresh wet rice noodles is crucial to the rice noodle industry.

[0003] Heat sterilization is one of the most important methods used in food processing to extend the shelf life of food. It kills microorganisms within the food and packaging and inactivates enzyme activity, extending shelf life. Due to the characteristics of rice noodles, starch regelatinizes at higher temperatures, disrupting the gel network. This causes the noodles to break easily and clumping together. Therefore, high temperatures and high pressures cannot be used for heat sterilization of fresh wet rice noodles. Rice noodles are typically sterilized at 95°C for 30 minutes under atmospheric pressure, but this method also significantly affects their quality. Therefore, addressing the quality degradation of fresh wet rice noodles after heat sterilization is of great significance. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a method for preparing fresh wet rice noodles, wherein the prepared fresh wet rice noodles can still maintain better quality after heat sterilization.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides a method for preparing fresh wet rice noodles, comprising the following steps: slurrying a linear polysaccharide aqueous solution with rice noodles, corn starch and cassava starch, ripening the rice slurry and then extruding and molding the slurry to obtain molded rice noodles; the amount of the linear polysaccharide added is 1 to 1.13% of the total mass of the rice noodles and the starch.

[0007] Preferably, the mass ratio of rice flour: corn starch: tapioca starch is 1:0.15-0.25:0.3-0.4.

[0008] Preferably, the moisture content of the rice milk is 52-56%.

[0009] Preferably, the cooking temperature is 85-95° C., and the diameter of the formed rice noodles is 1.7-1.9 mm.

[0010] Preferably, the linear polysaccharide is agglutinated polysaccharide or sodium alginate.

[0011] Preferably, when the linear polysaccharide is a coagulated polysaccharide, the rice flour is sequentially aged, re-steamed, washed, cooled, and drained.

[0012] Preferably, the aging time is 6 to 9 hours, the aging temperature is 20 to 25° C., and the re-steaming time is 2 to 4 minutes.

[0013] Preferably, when the linear polysaccharide is sodium alginate, the rice flour is cross-linked, washed with water, and drained in sequence.

[0014] Preferably, the rice flour is immersed in a calcium chloride solution for cross-linking, and the cross-linking time is 8 to 15 minutes.

[0015] The invention also provides fresh wet rice noodles prepared by the method.

[0016] Beneficial effects of the present invention:

[0017] The present invention adds linear polysaccharides and utilizes the gelling properties of the linear polysaccharides to work together with starch gel to form an interpenetrating network, which can significantly improve the cooking quality and tensile properties of rice noodles, reduce the impact of heat sterilization on the quality of fresh wet rice noodles, and at the same time maintain a high sensory quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 : Extensibility curves of fresh wet rice noodles with different addition amounts of coagulant polysaccharides;

[0019] Figure 2 : Tensile properties of fresh wet rice noodles strengthened by cross-linking with different amounts of sodium alginate;

[0020] Figure 3 : Effects of coagulant polysaccharides on the gelatinization properties of rice flour;

[0021] Figure 4 : Effect of sodium alginate on the gelatinization properties of rice flour;

[0022] Figure 5 : Fourier transform infrared spectra of rice noodles with different coagulant polysaccharide contents;

[0023] Figure 6: Second derivative spectra of rice noodles with different coagulant polysaccharide contents;

[0024] Figure 7 :Ca 2+ -Infrared spectrum of SA rice flour;

[0025] Figure 8 :Ca 2+ -Infrared second derivative spectrum of SA rice flour;

[0026] Figure 9 : Cross-sectional SEM images of rice noodles with different coagulant polysaccharide contents;

[0027] Figure 10 : Cross-sectional SEM images of rice noodles with different sodium alginate contents;

[0028] Figure 11 : Contact angle change curves of rice flour with different curdlan contents;

[0029] Figure 12 : Contact angle change curves of rice noodles with different sodium alginate contents. DETAILED DESCRIPTION

[0030] The invention provides a method for preparing fresh wet rice noodles, comprising the following steps: slurrying a linear polysaccharide aqueous solution with rice noodles, corn starch and cassava starch, ripening the rice slurry and then extruding and molding the slurry to obtain molded rice noodles; the amount of the linear polysaccharide added is 1 to 1.13% of the total mass of the rice noodles and the starch.

[0031] The rice flour of the present invention is preferably indica rice flour. As an optional embodiment, the present invention comprises washing the indica rice and soaking it in water for 4 hours (the mass-to-volume ratio of indica rice to water being approximately 1:1.5 g / mL). After soaking, the water is drained and the rice is ground with water representing approximately 80% of the dry weight of the indica rice. After grinding, the rice is dried at 45°C, ground using a high-speed mill, and passed through an 80-mesh sieve to produce the indica rice flour.

[0032] The present invention uses rice flour, corn starch, and tapioca starch as raw materials for slurry mixing, wherein the mass ratio of rice flour: corn starch: tapioca starch is 1:0.15-0.25:0.3-0.4, preferably 1:0.2:0.4, and the moisture content of the rice slurry after slurry mixing is 52-56%. The rice slurry obtained by slurry mixing is poured into an extruder for maturation and extrusion molding, wherein the maturation temperature is 85-95°C, preferably 90°C, the diameter of the extrusion die is 1.7-1.9 mm, preferably 1.8 mm, and the diameter of the extruded wire is 1.8 mm. The shaped rice noodles are obtained after maturation and extrusion, and the shaped rice noodles are subsequently processed.

[0033] In the present invention, when the linear polysaccharide is a coagulant polysaccharide, the formed rice noodles are sequentially aged, re-steamed, washed, cooled, and drained to obtain a final fresh wet rice noodle product. The rice noodles are immediately placed in a room temperature environment for aging after extrusion, wherein the aging temperature is 20-25° C., preferably 22-23° C., and the aging time is 6-12 hours, preferably 9-10 hours. After aging, the noodles are re-steamed in boiling water in a steamer for 2-4 minutes, preferably 3 minutes, thoroughly washed, cooled, drained, and packaged. The noodles are then sterilized in a water bath at 95° C. for 30 minutes to obtain the fresh wet rice noodle product.

[0034] In the present invention, when the linear polysaccharide is sodium alginate, the formed rice noodles are sequentially crosslinked, washed, and drained. Immediately after extrusion, the rice noodles are immersed in a calcium chloride solution for crosslinking for 15 minutes. After thorough washing, the noodles are drained and packaged, and sterilized in a water bath at 95°C for 30 minutes to obtain a fresh wet rice noodle product. The concentration of the calcium chloride solution is 0.1±0.02 mol / L.

[0035] The present invention adds linear polysaccharides to rice flour, corn starch and cassava starch raw materials, utilizes the gelling properties of the linear polysaccharides, and works together with starch gel to form an interpenetrating network, which can significantly improve the cooking quality and tensile properties of the rice flour, reduce the impact of heat sterilization on the quality of fresh wet rice flour, and at the same time maintain a high sensory quality, thereby greatly improving the quality of the rice flour.

[0036] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0037] In the following examples, unless otherwise specified, all methods are conventional.

[0038] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0039] In a specific embodiment of the present invention, indica rice was purchased from Guilin Dingyin Food Co., Ltd., corn starch was purchased from Zhucheng Xingmao Corn Development Co., Ltd., cassava starch was purchased from Shanghai Miruini Food Co., Ltd., coagulant polysaccharide (CUR) was purchased from Haiaos Biotechnology Co., Ltd., medium viscosity sodium alginate (SA) was purchased from Qingdao Mingyue Seaweed Co., Ltd., and anhydrous calcium chloride was purchased from Sinopharm Chemical Reagent Co., Ltd.; a grinder and a self-cooking extruder were purchased from Guangzhou Xuzhong Food Equipment Co., Ltd., a texture analyzer (TA.XT PlusC) was purchased from Stable Micro System, UK, a rapid viscosity analyzer (RVA-Tec Master) was purchased from Xingang Technology Co., Ltd., a Fourier transform infrared spectrometer (FTIR-8400) was purchased from Shimadzu Corporation, Japan, a scanning electron microscope (JSM-7500F) was purchased from JEOL Ltd., and an optical contact angle meter (DSA100S) was purchased from Krug GmbH, Germany.

[0040] In the specific examples of the present invention, all experiments were repeated at least three times, and the results are presented as mean values ​​and standard deviations. SPSS 17.0 (SPSS Inc., Chicago, USA) was used to perform variance analysis on the experimental data, and the significance of each mean was determined using Duncan's multiple range test (p < 0.05). Graphical analysis was performed using Origin 2018 (OriginLab Inc., USA).

[0041] Example 1

[0042] This embodiment provides a production process of fresh wet rice noodles:

[0043] Indica rice → remove sand and stones → wash rice → crush and grind → dry → dry grind and sieving → adjust the slurry (add starch and coagulant polysaccharide) → mature → shred → age → re-steam → cool and wash → drain water → bag and seal → sterilize.

[0044] Specific process: After washing the indica rice, soak it in water for 4 hours (the mass volume ratio of indica rice to water is 1:1.5g / mL). After soaking, drain the water and add 80% of the dry mass of the indica rice for grinding. After grinding, dry it at 45℃, grind it into powder using a high-speed grinder and pass it through an 80-mesh sieve. The coagulant polysaccharide is dispersed in distilled water, and the added amount of the coagulant polysaccharide is 1.13% of the total mass of rice flour and starch. Indica rice flour, corn starch and tapioca starch are added to prepare the slurry (the mass ratio of indica rice flour: corn starch: tapioca starch is 1:0.2:0.4), so that the moisture content of the final rice slurry is 52%; the rice slurry is poured into an extruder for maturation and extrusion molding, wherein the maturation temperature is 95°C and the extrusion die head diameter is 1.8mm; after the rice flour is extruded, it is immediately placed in a 25°C environment for aging for 6 hours; after the aging is completed, it is re-steamed in boiling water in a steamer for 3 minutes, and the residual starch is fully rinsed with cold water. The starch is cooled and then sealed and packaged, and sterilized in a water bath at 95°C for 30 minutes to obtain fresh wet rice flour.

[0045] Example 2

[0046] The difference between this embodiment and embodiment 1 is that the added amount of the coagulant polysaccharide is 0.38% of the total mass of the rice flour and starch.

[0047] Example 3

[0048] The difference between this embodiment and embodiment 1 is that the added amount of the coagulant polysaccharide is 0.63% of the total mass of the rice flour and starch.

[0049] Example 4

[0050] The difference between this embodiment and embodiment 1 is that the added amount of the coagulant polysaccharide is 0.88% of the total mass of the rice flour and starch.

[0051] Comparative Example 1

[0052] The difference between this embodiment and embodiment 1 is that the added amount of coagulant polysaccharide is 0% of the total mass of rice flour and starch.

[0053] Example 5

[0054] This embodiment provides a production process of fresh wet rice noodles:

[0055] Indica rice → remove sand and stones → wash rice → crush and grind → dry → dry grind and sieving → dissolve sodium alginate → prepare slurry (add starch and sodium alginate solution) → mature → extrude → cross-link → wash with water → drain water → bag and seal → sterilize.

[0056] The specific process is as follows: After washing, indica rice is soaked in water for 4 hours (the mass-to-volume ratio of indica rice to water is 1:1.5 g / mL). After soaking, the water is drained and 80% of the dry weight of the indica rice is added for grinding. After grinding, the rice is dried at 45°C, ground using a high-speed grinder, and passed through an 80-mesh sieve. Sodium alginate solutions of 0.3%, 0.6%, 0.9%, and 1.2% are prepared and stirred at high speed at room temperature to fully dissolve the sodium alginate until the solution is completely transparent. These solutions are then used to prepare fresh wet rice noodle samples with different sodium alginate addition levels. Indica rice flour, corn starch and tapioca starch are added to prepare the rice slurry (the mass ratio of indica rice flour: corn starch: tapioca starch is 1:0.2:0.4) so ​​that the moisture content of the final rice slurry is 52%, and the amount of sodium alginate added is 1% of the total mass of the rice flour and starch; the rice slurry is poured into an extruder for maturation and extrusion molding, wherein the maturation temperature is 95°C and the extrusion die head diameter is 1.8 mm; after the rice noodles are extruded, they are immersed in a calcium chloride solution (concentration of 0.1±0.02 mol / L) for cross-linking for 15 minutes, and then washed thoroughly with water, drained and packaged, and sterilized in a water bath at 95°C for 30 minutes to obtain fresh wet rice noodles.

[0057] Example 6

[0058] The difference between this embodiment and embodiment 5 is that the amount of sodium alginate added is 0.33% of the total mass of rice flour and starch.

[0059] Example 7

[0060] The difference between this embodiment and embodiment 5 is that the amount of sodium alginate added is 0.67% of the total mass of rice flour and starch.

[0061] Example 8

[0062] The difference between this embodiment and embodiment 5 is that the amount of sodium alginate added is 1.33% of the total mass of rice flour and starch.

[0063] Example 9

[0064] The fresh wet rice noodle samples obtained from each group of the embodiment and the comparative example 1 group (control group) were placed at room temperature for 24 hours and then subjected to relevant quality measurements:

[0065] (1) Determination of moisture content of fresh wet rice noodles

[0066] The moisture content of fresh wet rice noodles was determined using the direct drying method, i.e., the 105°C constant weight method. Take a clean glass dish and place it in an electric blast drying oven at 105°C and dry it for 0.5h to constant weight (m1). Weigh about 5g (m2) of rice noodle sample and place it in a glass dish, place it in an electric blast drying oven at 105°C and dry it for 3-4h, take it out and place it in a desiccator to cool to room temperature, and weigh it; place it in a 105°C drying oven again and dry it for 1h, take it out and place it in a desiccator to cool to room temperature and weigh it again. Repeat the weighing until the difference between the two masses is less than 2mg, which is constant weight (m3). Calculate the moisture content of fresh wet rice noodles according to the following formula:

[0067]

[0068] The moisture content of fresh wet rice noodles was calculated to be 52-56%.

[0069] (2) Determination of tensile properties

[0070] The tensile properties of rice noodles were measured using the tensile mode of the texture analyzer. The prepared fresh wet rice noodles were cooked in boiling water for 2 minutes to re-cook (the rice noodles were completely dispersed and there was no hard core inside). After cooling to room temperature, a certain length of rice noodles was cut and fixed using the A-TG probe fixture of the texture analyzer. The initial strain was 30mm and the tensile test was performed at a tensile rate of 1mm / s. The elongation at break and tensile strength of the rice noodles were obtained based on the stress-strain curve. The results are shown in Figure 2. Figures 1-2 . Figure 1 To study the effect of coagulant polysaccharides on the tensile properties of rice noodles; Figure 2 Ca 2+ -Effect of SA on the tensile properties of rice noodles.

[0071] Figure 1 The results showed that with the increase of the amount of polysaccharide added, the elongation at break of rice noodles showed a trend of first decreasing and then increasing. The elongation at break of rice noodles with a polysaccharide addition of 0.38% was about 78%, and the tensile strength was 2.7 g·mm -2 When the amount of coagulant polysaccharide added increased to 1.13%, the elongation at break was about 147% and the tensile strength was 3 g·mm -2When the amount of curdlan added reached and exceeded 0.63% by mass, the elongation at break of fresh wet rice noodles was significantly higher than that of the control sample (91%). The decrease in the tensile strength of the sample may be because the addition of curdlan as a hydrophilic colloid inhibited the short-term retrogradation of starch to a certain extent, resulting in a decrease in gelation and a decrease in tensile strength. The elongation at break showed a trend of first decreasing and then increasing compared with the control. The reason may be that the curdlan inhibited the short-term retrogradation of starch, resulting in a decrease in gelation. At a low addition amount, curdlan failed to form a continuous network in the rice noodles and could not improve the tensile properties of the rice noodles. When the curdlan addition amount was increased, it formed a starch-curdlan double network structure with the rice noodles, which played a role in strengthening the gelation of the rice noodles.

[0072] Figure 2 The results show that with the increase of sodium alginate addition, the elongation at break and tensile strength of rice noodles gradually increase. The elongation at break of rice noodles with 0.33% sodium alginate addition is only about 56%, and the tensile strength is 1.5g·mm -2 When the addition amount of sodium alginate increases to 1.33%, the elongation at break and tensile strength increase significantly, reaching 112% and 7.8 g·mm, respectively. -2 . Because the rice noodle sample production process does not involve an aging process, the starch network and sodium alginate network of the rice noodle with a lower sodium alginate addition are insufficiently strong, and the elongation at break and tensile strength are both at a low level. The strength of the cross-linked sodium alginate network is closely related to the concentration and moisture content of the sodium alginate. In the rice noodle system, starch, protein, and sodium alginate compete with each other for water, which further reduces the strength of the sodium alginate network. As the amount of sodium alginate added increases, the tensile strength and elongation at break of the rice noodle increase significantly, indicating that the gel network in the rice noodle is significantly enhanced.

[0073] (3) Determination of texture properties (TPA)

[0074] The texture characteristics of rice noodles were measured using the TPA mode of the texture analyzer. Sample preparation was the same as in (2). Samples of uniform thickness were selected, and two 2.5 mm long strips were cut and placed parallel to each other on the test bench. A P / 36R probe was used, with a pre-test speed of 1 mm / s, a mid-test speed of 1 mm / s, and a post-test speed of 1 mm / s. The compression ratio was 50%, the trigger force was 5 g, and the interval between the two compressions was 5 s. The results are shown in Tables 1 and 2.

[0075] Table 1 Effects of coagulant polysaccharides on the texture characteristics of rice noodles

[0076]

[0077]

[0078] As shown in Table 1, the hardness of the control sample was 1481.14±84.53 g, while that of the sample containing 1.13% coagulant was 1419.67±75.16 g. The hardness of the samples containing coagulant was lower than that of the control sample, showing a trend of initially decreasing and then increasing. The chewiness of the samples also showed a trend of initially decreasing and then increasing, with the sample containing 1.13% coagulant having higher chewiness than the control sample. The sample containing 0.63% coagulant had the lowest hardness and chewiness. This is because coagulant inhibits starch retrogradation in rice flour, resulting in reduced gelation and hardness. Greater hardness indicates a higher degree of starch retrogradation in starchy foods. As the coagulant addition level increases, it forms a double network gel with starch in the rice flour, strengthening the gel. No significant differences were observed in the viscosity and elasticity of any of the samples. The cohesion and resilience of the samples increased with increasing amounts of coagulant polysaccharide added, indicating that the addition of coagulant polysaccharide forms a certain number of hydrogen bonds with starch, resulting in a certain degree of cohesion and improving the resilience of rice noodles. The results show that at low addition levels, coagulant polysaccharide fails to form a gel network within the rice noodles, resulting in reduced gelation and poor quality. However, as the addition level increases, coagulant polysaccharide forms a gel network within the rice noodles, improving their quality. Generally, fresh wet rice noodles experience a certain degree of hardness increase after heat sterilization, which is related to changes in the network formed by the short-term retrogradation of amylose in starch after high-temperature sterilization. The addition of coagulant polysaccharide reduces the hardness of rice noodles and can, to a certain extent, improve the sensory quality of fresh wet rice noodles after heat sterilization.

[0079] Table 2Ca 2+ Effects of -SA on the textural properties of rice flour

[0080]

[0081]

[0082] As shown in Table 2, rice noodles with a 0.33% sodium alginate addition exhibit lower hardness, springiness, and chewiness, but higher viscosity. This is due to the lack of retrogradation and the low sodium alginate addition, resulting in lower crosslinking strength and a looser gel network. Viscosity is related to the cooked breakage rate; a higher cooked breakage rate indicates greater stickiness, a finding consistent with cooking characteristics. Furthermore, no significant differences in cohesion or resilience were observed among the samples. With increasing sodium alginate addition, the hardness, springiness, and chewiness of rice noodles with a 1.33% addition gradually increased, increasing by 88.43% and 74.72%, respectively, compared to the control, while viscosity decreased by 61.56%. This indicates increased gel strength and improved quality, indicating that the sodium alginate network plays a dominant role in the rice noodles. The increases in hardness and springiness are consistent with the results obtained for tensile properties; the increase in hardness indirectly reflects an increase in gel strength and tensile strength. The hardness and chewiness of the control sample were slightly higher than those of the sample containing 0.33% sodium alginate, and the viscosity was slightly lower, indicating that aging can significantly improve the quality of rice noodles.

[0083] (4) Determination of cooking characteristics

[0084] Determination of the breakage rate of fresh wet rice noodles: Take 20 pieces of fresh wet rice noodles 20 cm long and cook them in 500 mL of boiling water for 2 minutes. Then remove the rice noodles and rinse them with cold water to drain. Record the mass m1 and m2 of the rice noodles with a length of less than 10 cm and more than 10 cm respectively. Calculate the breakage rate according to the following formula:

[0085]

[0086] Determination of the cooking loss rate and rehydration rate of fresh wet rice noodles: Take 20 20cm long fresh wet rice noodles, weigh them before testing (m0), and measure the moisture content M. After cooking in 500mL of boiling water for 2 minutes, remove the rice noodle sample and rinse it thoroughly with distilled water. Weigh the mass of the fresh wet rice noodles after cooking (m1). Then cool the rice noodle soup to room temperature, transfer it to a 1000mL volumetric flask, make up the volume, shake it well, transfer 100mL to a constant weight glass dish (m2), and place it in a 105℃ electric heated forced air drying oven to dry to constant weight (m3). Calculate the cooking loss rate and rehydration rate according to the following formula:

[0087]

[0088]

[0089] The results are shown in Tables 3-4.

[0090] Table 3 Effects of coagulant polysaccharides on the cooking properties of rice flour

[0091]

[0092] Table 3 shows that compared with the control, the breakage rate and cooking loss rate of the fresh wet rice noodle sample with 0.38% CUR significantly increased, and the water absorption rate slightly increased. This indicates that the low addition of coagulant polysaccharide prevents gel formation and also has a certain impact on the short-term recovery of starch, reducing the gelation properties of the rice noodles, negatively affecting the quality of the rice noodles and reducing the cooking quality of the fresh wet rice noodles. With further increase in the addition of coagulant polysaccharide, the breakage rate and cooking loss rate gradually decreased. The breakage rate and cooking loss rate of the 0.63% CUR sample were 17.90% and 1.14%, respectively, close to those of the control sample. The breakage rate and cooking loss rate of the 0.88% CUR and 1.13% CUR samples were significantly lower than the control sample, while the water absorption rate significantly increased. Coagulant polysaccharide is a hydrophilic colloid with high hydrophilicity and water-binding properties. With increasing addition, the water absorption rate of the fresh wet rice noodles gradually increased. Generally, higher water absorption rate results in better elasticity and smoothness of the rice noodles. Curative polysaccharides form heat-irreversible gels above 80°C, which can improve the quality of fresh wet rice noodles after heat sterilization. Results showed that samples with a 1.13% CUR content had lower breakage rates and cooking loss rates, and relatively higher water absorption rates, indicating that curative polysaccharides have a significant effect on improving the quality of fresh wet rice noodles.

[0093] Table 4Ca 2+ Effect of -SA on cooking properties of rice flour

[0094]

[0095] As shown in Table 4, compared with the control, the breaking rate and cooking loss rate of the fresh wet rice noodles sample with 0.33% SA increased significantly, the water absorption rate increased slightly but not significantly, and the quality was low; when the addition amount increased to 0.67% SA, the breaking rate and cooking loss rate of the fresh wet rice noodles decreased significantly, indicating that cross-linked sodium alginate played a role in strengthening the quality of rice noodles, and soaking in Ca 2+ After solution, Ca 2+ It slowly penetrates into the rice noodles from the surface, causing sodium alginate to cross-link and form a network, which has the effect of strengthening the quality of rice noodles. 2+ The cross-linked sodium alginate gel network has good heat resistance, so during the cooking process of fresh wet rice noodles, it can reduce the breakage rate, prevent the loss of starch inside the rice noodles, reduce the cooking loss rate, and prevent the occurrence of soupiness; the breakage rate of the sample with 1.00% SA is reduced to 0, the cooking loss rate is further reduced, and the water absorption rate decreases with the increase of SA addition. This is because the stronger SA network will prevent the entry of water, but it will make the hardness of the fresh wet rice noodles too high, which is not conducive to the sensory quality. Therefore, the rice noodles with 1.00% SA addition have both a lower breakage rate and cooking loss rate, and have appropriate hardness and chewiness, and the overall quality is the best.

[0096] (5) Determination of viscosity characteristics (RVA)

[0097] The viscosity properties of linear polysaccharides on rice flour, starch, and their mixtures were analyzed using a rapid viscosity analyzer (RVA). a. Corn starch, tapioca starch, and indica rice flour samples were weighed into aluminum cans at a mass ratio of 1:0.2:0.4 for indica rice flour: corn starch: tapioca starch, totaling 3 g. Coagulant polysaccharides were added at mass fractions of 0.38%, 0.63%, 0.88%, and 1.13%, respectively, and distilled water was added to bring the total weight to 28 g. b. Corn starch, tapioca starch, and indica rice flour samples were weighed into aluminum cans at a mass ratio of 1:0.2:0.4 for indica rice flour: corn starch: tapioca starch, totaling 3 g. Sodium alginate at mass fractions of 0%, 0.33%, 0.67%, 1.00%, and 1.33%, respectively, and distilled water was added to bring the total weight to 28 g.

[0098] The test method adopts the standard procedure in the RVA instrument. Each starch suspension is stirred in the instrument at a speed of 960 rpm for the first 10 seconds, and then continuously stirred at a speed of 160 rpm until the test is completed; the sample is kept at 50°C for 60 seconds, then heated to 95°C at a constant speed for 240 seconds and kept for 150 seconds, and then cooled to 50°C at a constant speed for 240 seconds and kept for 90 seconds, and the test is completed. The RVA curve is recorded to obtain the peak viscosity, valley viscosity, final viscosity, attenuation value (the difference between the peak viscosity and valley viscosity), and regeneration value (the difference between the final viscosity and valley viscosity). The results are shown in Tables 5 to 6 and Figures 3-4 . Figure 3 To investigate the effect of polysaccharides on the gelatinization properties of rice flour, Figure 4 The effect of sodium alginate on the gelatinization properties of rice flour.

[0099] Table 5 Effects of coagulant polysaccharides on the gelatinization properties of rice flour

[0100]

[0101]

[0102] From Table 5 and Figure 3 It can be seen that 1.13% CUR reduces the overall viscosity of the rice flour system. This is likely because curdlan is a hydrophilic colloid. When added to a certain level, it inhibits the swelling of starch granules, reduces the peak viscosity, and improves the thermal stability of starch granules. It also reduces the retrogradation value, indicating that a certain amount of curdlan inhibits the short-term retrogradation of amylose to a certain extent. Although inhibiting short-term retrogradation may have a negative impact on rice flour, curdlan forms a thermally irreversible gel after heating above 80°C, improving the gel strength of the rice flour and compensating for the negative impact of inhibiting short-term retrogradation.

[0103] Table 6 Effect of sodium alginate on the gelatinization properties of rice flour

[0104]

[0105] From Table 6 and Figure 4 As can be seen, with increasing sodium alginate addition, the system's peak viscosity, trough viscosity, and final viscosity all show a trend of first decreasing and then increasing. This indicates that the addition of hydrophilic colloids such as sodium alginate inhibits the swelling and fragmentation of starch granules, and the degree of inhibition is closely related to the hydrophilic colloid addition level. During the initial gelatinization phase, starch granules absorb water and swell upon heating. The viscosity at maximum swelling is the peak viscosity. Hydrophilic colloids such as sodium alginate compete with starch granules for water, weakening the hydration of starch. The inhibitory effect is highest at an addition level of 1.00%. The retrogradation value, which reflects the increase in starch viscosity during cooling, decreased for samples with varying sodium alginate addition levels.

[0106] (6) Fourier transform infrared spectroscopy (FT-IR)

[0107] The samples were analyzed using a Fourier transform infrared spectrometer with an ATR accessory. The prepared samples were completely frozen in liquid nitrogen (-196°C) and immediately placed in a freeze dryer at -80°C for freeze drying. The freeze-dried samples were crushed and passed through an 80-mesh sieve. The powder samples were scanned at 4000-400 cm -1 Infrared spectrum in the range, scanning rate is 4cm -1 , the number of scans was 64. The spectral deconvolution method was used to calculate R 1047 / 1022 The second-order derivative of infrared spectroscopy was used to analyze the changes in hydrogen bonds inside rice flour gels. The second-order derivative was obtained by 7-point smoothing using the Savitzky-Golay method and a three-term polynomial (Lu et al., 2021). Figures 5 to 8 .

[0108] Figure 5 Infrared spectra (a), deconvolution spectra (b), R 1047 / 1022 Relationship with the content of coagulant polysaccharides (c). Figure 5 It can be seen that compared with the infrared spectrum of the control rice flour, no new absorption peaks appeared after the addition of coagulant polysaccharide. The overall infrared spectrum skeleton is the same as that of the control rice flour, which is a typical starch infrared spectrum skeleton, indicating that there is no covalent bond between rice flour and coagulant polysaccharide. The glucose unit of starch contains multiple hydroxyl groups, and coagulant polysaccharide is a linear glucose composed of several D-glucose residues connected by β-1,3-D-glucosidic bonds. It also has a large number of hydroxyl groups, so the interaction between starch and coagulant polysaccharide should be mainly hydrogen bond interaction. The infrared spectrum shows that at 3300cm -1 A broad peak appears on the left and right, which is a typical hydroxyl stretching vibration absorption peak. The infrared spectrum of starch is analyzed by spectral deconvolution, and R is obtained by calculation.1047 / 1022 All rice noodle samples were aged for 6 h, and the R 1047 / 1022 is 0.58. With the increase of the content of coagulant polysaccharide, the ratio gradually decreases. The R 1047 / 1022 was 0.50, which was about 13.8% lower than that of the control sample, indicating that the coagulant polysaccharide had a certain degree of inhibitory effect on the aging of rice noodles.

[0109] Figure 6 The second derivative spectra of rice noodles with different CUR contents, wave number range 3500 cm -1 ~3600cm -1 (a) and wave number range 3250cm -1 ~3350cm -1 (b) By Figure 6 It can be seen that the wave number of the free hydrogen bond of the control sample is 3543 cm -1 The wave number of hydrogen bond between double helices is 3286 cm -1 With the increase of the amount of coagulant polysaccharide added, 3543cm -1 The band at 1.13% CUR sample shifts to higher frequencies, and the wave number of 1.13% CUR sample shifts to 3548 cm -1 This indicates that the coagulated polysaccharide will bind to the amylose molecules through hydrogen bonds, reducing the number of free hydrogen bonds; wave number 3286 cm -1 The band at 3289 cm-1 gradually shifted to higher frequencies with the increase of the coagulant polysaccharide content, and the 1.13% CUR sample shifted to 3289 cm-1. -1 This indicates that the addition of coagulant polysaccharide will inhibit the short-term retrogradation of amylose and reduce the number of hydrogen bonds between double helices.

[0110] Figure 7 Ca 2+ -Infrared spectrum of SA rice flour. Figure 7 It can be seen that compared with the infrared spectrum of the control rice flour, no new absorption peaks appeared after adding sodium alginate. The overall infrared spectrum skeleton is the same as that of the control rice flour, which is a typical starch infrared spectrum skeleton, indicating that there is no covalent bond between rice flour and sodium alginate. Since the glucose unit of starch contains multiple hydroxyl groups, and the G / M segment of sodium alginate also contains a large number of hydroxyl groups, the interaction between starch and sodium alginate should be mainly hydrogen bonding. The infrared spectrum shows that at 3300cm -1 A broad peak appears on the left and right, which is a typical hydroxyl stretching vibration absorption peak. The rice flour-sodium alginate system is mainly characterized by hydrogen bonding. However, since multiple hydroxyl absorption peaks overlap to form a broad peak, the original infrared spectrum cannot directly reflect the changes in various hydrogen bonds in the rice flour system.

[0111] Figure 8 Ca 2+-Infrared second-order derivative spectrum of SA rice noodles, wave number range 3460cm -1 ~3580cm -1 (a) and wave number range 3250cm -1 ~3350cm -1 (b) By Figure 8 It can be seen that the wave number of the free hydrogen bond of the control sample is 3537 cm -1 The wave number of hydrogen bond between double helices is 3289 cm -1 With the increase of sodium alginate addition, 3537cm -1 The band at 1.33% sodium alginate moved to a higher frequency, and the wave number of the sample with 1.33% sodium alginate added moved to 3547 cm -1 Sodium alginate not only inhibits starch gelatinization, but also combines with amylose molecules through hydrogen bonds, reducing the number of free hydrogen bonds. -1 There was no change in the bands at the bottom, indicating that all samples were not aged and the number of hydrogen bonds between the double helices did not change.

[0112] (7) Scanning electron microscopy (SEM)

[0113] The cross-sectional morphology of fresh wet rice noodles was observed using a JSM-7500F scanning electron microscope. The prepared fresh wet rice noodles were quickly frozen in liquid nitrogen, and after applying external force to produce a fracture surface, they were immediately placed in a freeze dryer at -80°C for freeze drying. The freeze-dried samples were taken out and subjected to three gold spraying treatments to ensure that the fracture surface of the samples was evenly coated. All samples were observed at a magnification of 2000 times and an accelerating voltage of 10kV. The results are shown in Figures 9-10 .

[0114] Figure 9 Cross-sectional SEM images of rice noodles with different curdlan content. a: control; b: 0.38% CUR; c: 0.63% CUR; d: 0.88% CUR; e: 1.13% CUR. Figure 9Compared to the control sample, the 0.38% CUR rice noodle sample exhibited larger pores. Due to the low addition of coagulant polysaccharide, the rice noodle gel network is primarily formed by the short-term retrogradation of the starch paste. Coagulant polysaccharide inhibits this short-term retrogradation, leading to larger pores and a looser gel network. This reduces the gel strength of the rice noodles, resulting in increased noodle breakage and cooking loss. As shown in Figure c, with increasing coagulant polysaccharide addition, the gel pores of the 0.63% CUR sample become denser compared to the 0.38% CUR sample, indicating that coagulant polysaccharide begins to strengthen the rice noodle network. Figures d and e show even denser gel pores, indicating that increasing coagulant polysaccharide content enhances the continuity of the gel matrix and strengthens the rice noodle network structure. These results indicate that a low addition level (0.38% CUR) results in a looser gel network and poorer gelation. However, with increasing coagulant polysaccharide addition, the gel network becomes denser, strengthening the rice noodle network and improving the quality of fresh wet rice noodles.

[0115] Depend on Figure 10 It can be seen that when the amount of sodium alginate added is small, the formation of the gel network is mainly based on the gel network formed by the short-term retrogradation of starch after gelatinization. The network pores are large, the network is relatively loose, the gel matrix continuity is poor, and the strength is insufficient, resulting in a high rice noodle breakage rate and cooking loss rate, and low tensile strength. With the increase of the amount of sodium alginate added, the short-term retrogradation of starch after gelatinization and the cross-linking of sodium alginate combine to form a denser network, the network pore size decreases, and the matrix continuity increases. This can explain the Ca 2+ The reasons why cross-linked sodium alginate improves the cooking quality and sensory quality of rice noodles.

[0116] (8) Determination of contact angle

[0117] The hydrophilicity of the sample was measured using an optical contact angle meter. The freeze-dried sample was crushed and passed through an 80-mesh sieve. 1.5 g of the sample was weighed and a powder tablet press was used to prepare a sample slice at a pressure of 8 t for 2 minutes (Zhang et al., 2022). 34 μL of water was dropped on the sample slice and the contact angle was measured at 0 s. The contact angle was then measured every 60 s for a total of 5 minutes. The contact angle change curve of the sample within 5 minutes was obtained. The results are shown in Figures 11-12 .

[0118] Depend on Figure 11The initial contact angle of the control sample was 42.8°. After adding 0.38% CUR, 0.63% CUR, 0.88% CUR, and 1.13% CUR, the initial contact angles decreased to 37.6°, 33.8°, 32.3°, and 31.6°, respectively. This significant decrease in the initial contact angle indicates that the addition of coagulant polysaccharide increased the hydrophilicity of the rice flour system. Over time, the contact angle of the control sample decreased by 25.2% to 32.0° at 5 minutes. The contact angle of the 0.38% CUR sample decreased by approximately 26.3% to 27.7° at 5 minutes, a decrease of approximately 30.1% compared to 0 minutes. The contact angle of the 1.13% CUR sample decreased by approximately 30.1% to 22.1° at 5 minutes. The data indicate that the addition of coagulant polysaccharide significantly increased the rate of contact angle decrease, indicating that the hydrophilicity of rice flour increased and the water absorption rate accelerated. Better water holding capacity and hydrophilicity are beneficial for rice noodles to absorb water after re-cooking, and are beneficial for rice noodles to maintain higher elasticity and smooth taste.

[0119] Depend on Figure 12 It can be seen that the initial contact angle of the control sample is 47.8°. After adding 0.33% SA, 0.67% SA, 1.00% SA, and 1.33% SA, the initial contact angles decreased to 46.4°, 42.9°, 38.4°, and 36.3°, respectively. It can be seen that the initial contact angle has decreased significantly, indicating that the addition of sodium alginate significantly improves the hydrophilicity of the rice flour system. As time increases, the contact angle of the control sample at 5 minutes is 39.4°, a decrease of 17.6%. The initial contact angle of the 0.33% SA sample is 46.4°, and at 5 minutes it is 35.0°, a decrease of 24.6%. The initial contact angle of the 1.33% SA sample is 36.3°, and at 5 minutes it is 19.9°, a decrease of 45.2%. It can be seen from the data that the addition of sodium alginate significantly increases the rate of contact angle decrease, indicating that the hydrophilicity of rice flour increases and the water absorption rate is accelerated.

[0120] (9) Sensory evaluation

[0121] We recruited 20 students from the food science department to form two sensory evaluation groups, with 10 people in each group. Referring to the sensory scoring standards in Table 7, we conducted a sensory evaluation of fresh wet rice noodles from four aspects: color, smell, tissue morphology, and taste. Each indicator has a full score of 10 points, and the average value is taken as the final result, see Tables 8 and 9.

[0122] Table 7 Sensory evaluation of fresh wet rice noodles

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[0124] Table 8 Sensory evaluation results of rice noodles with different coagulant polysaccharide contents

[0125]

[0126] As shown in Table 8, the rice noodle color score initially decreased and then increased. This is likely because the gelling properties of the rice noodles initially decreased and then increased with increasing curdlan addition, indirectly leading to a change in color. The odor of each sample was not significantly different, as the rice flour and starch used were identical. The textural morphology and taste scores initially decreased and then increased with increasing curdlan addition. This is because curdlan causes the gelling properties of the rice noodles to initially decrease and then increase, resulting in an initial increase and then decrease in the breakage rate and cooking loss. Based on a comprehensive analysis of all sensory indicators, the rice noodles with 1.13% CUR had the best sensory quality and the highest score.

[0127] Table 9 Sensory evaluation results of rice noodles with different sodium alginate contents

[0128]

[0129] As shown in Table 9, the color score of rice noodles gradually increased. This is because the gelling properties of the rice noodles increased with the increase in sodium alginate addition, resulting in a more uniform surface color and no variegated color. The odor of each sample did not differ significantly, as the rice flour and starch used were the same, so the odor differences were not significant. The morphology score and taste score showed a trend of first increasing and then decreasing with the increase in sodium alginate addition. This is because cross-linked sodium alginate enhances the gelling properties of rice noodles, reducing the breakage rate and cooking loss. However, excessive addition of sodium alginate can lead to excessive gelling properties and a stiff texture, which is not conducive to taste and results in a lower score. Based on a comprehensive analysis of all sensory indicators, rice noodles with 1.00% SA had the best sensory quality and the highest score.

[0130] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing fresh wet rice noodles, characterized in that, The following steps are involved: The coagulant polysaccharide is dispersed in distilled water, and indica rice flour, corn starch, and tapioca starch are added to prepare the slurry so that the moisture content of the final rice slurry is 52%; the rice slurry is poured into an extruder for maturation and extrusion molding, wherein the maturation temperature is 95° C. and the extrusion die head has a diameter of 1.8 mm; the rice noodles are immediately placed in a 25° C. environment for aging after extrusion for 6 hours; after the aging is completed, the rice noodles are re-steamed in boiling water in a cooking pot for 3 minutes, rinsed with cold water to remove residual starch, and the rice noodles are cooled and then sealed and packaged, and sterilized in a water bath at 95° C. for 30 minutes to obtain fresh wet rice noodles; The added amount of the coagulant polysaccharide is 1.13% of the total mass of indica rice flour and starch, and the mass ratio of the indica rice flour: corn starch: cassava starch is 1:0.2:0.

4.

2. A method for preparing fresh wet rice noodles, characterized in that, The following steps are involved: Prepare a sodium alginate solution and use a stirrer to stir at high speed at room temperature to fully dissolve the sodium alginate until the solution is completely transparent; Indica rice flour, corn starch, and tapioca starch are added to the sodium alginate solution to prepare a slurry so that the moisture content of the final rice slurry is 52%; the rice slurry is poured into an extruder for aging and extrusion molding, wherein the aging temperature is 95° C. and the extrusion die head has a diameter of 1.8 mm; after extrusion, the rice flour is immersed in a calcium chloride solution for cross-linking for 15 minutes, thoroughly washed with water, drained, packaged, and sterilized in a water bath at 95° C. for 30 minutes to obtain fresh wet rice flour; The added amount of the sodium alginate is 1% of the total mass of the indica rice flour and starch; the mass ratio of the indica rice flour: corn starch: cassava starch is 1:0.2:0.4; and the concentration of the calcium chloride solution is 0.1±0.02 mol / L.

3. The method according to claim 1 or 2, characterized in that After washing, the indica rice is soaked in water for 4 hours, the water is drained, and 80% of the dry weight of the indica rice is added for grinding. After grinding, the indica rice is dried at 45° C., ground with a high-speed grinder, and passed through an 80-mesh sieve to prepare indica rice flour.

4. Fresh wet rice noodles prepared by the method according to any one of claims 1 to 3.

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