Crosslinking strengthened rice flour as well as preparation method and application thereof

Abstract

The invention relates to cross-linking strengthened rice flour as well as a preparation method and application thereof, and belongs to the technical field of food processing. According to the preparation method, sodium alginate with high thermal stability is added, and the rice flour containing the sodium alginate is soaked in a calcium chloride solution, so that a dual physical crosslinking gel network (SA-Ca < 2 + > egg box structure) is constructed, the network structure of the fresh and wet rice flour is strengthened, and compared with products in the market, the fresh and wet rice flour is more stable in structure, better in quality and lower in breakage rate. And based on the change of the network structure, the heat-resistant sterilization capability of the rice noodles is also improved, the rice noodles are not easy to break after being recooked with hot water, the taste is smooth, tough and elastic, the breaking rate and the cooking loss rate of the fresh and wet rice noodles after thermal sterilization are reduced, and the quality of the fresh and wet rice noodles after thermal sterilization is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, and in particular relates to cross-linked strengthened rice flour and a preparation method and application thereof. Background Art

[0002] Rice noodles are not only easy to cook, convenient to eat, high in yield, and can provide high energy for the human body, but are also considered an important alternative food for patients with gluten intolerance. However, compared with wheat products, rice lacks gluten protein that can form a network, so rice noodles need to rely on the gelatinization and regeneration of rice starch to form gels. However, starch gels have poor extensibility and require high water content to form. This also leads to poor mechanical properties of rice noodles, easy to break, and unable to withstand high temperatures and pressures. On this basis, if the rice noodles are sterilized by heat, the quality of the rice noodles will be further affected, the phenomenon of rice noodles breaking will be aggravated, and the noodles will be easy to stick together, thus limiting the production process of rice noodles. Therefore, improving the physical properties of rice noodles is of great significance to the production and process development of rice noodles. Summary of the invention

[0003] The object of the present invention is to provide a cross-linked and strengthened rice flour and a preparation method and application thereof. The preparation method of the cross-linked and strengthened rice flour of the present invention can improve the physical properties of the rice flour and enhance the edible quality of the rice flour.

[0004] The present invention provides a method for preparing cross-linked fortified rice noodles, comprising the following steps:

[0005] mixing the crushed rice with starch to obtain a mixture of rice and starch;

[0006] The mixture of rice and starch is mixed with the sodium alginate solution, and slurry is prepared to obtain rice slurry containing sodium alginate;

[0007] The sodium alginate-containing rice slurry is subjected to a aging treatment and extruded into wires to obtain rice flour containing the sodium alginate;

[0008] The obtained rice flour containing sodium alginate is mixed with a calcium chloride solution and cross-linked to obtain cross-linked reinforced rice flour.

[0009] Preferably, the rice includes indica rice; and the crushed rice has a particle size of 60 to 100 meshes.

[0010] Preferably, the water content of the rice milk containing sodium alginate is 55% to 60%.

[0011] Preferably, the amount of sodium alginate added to the sodium alginate-containing rice milk is 0.33% to 1.33%.

[0012] Preferably, the starch comprises corn starch and / or tapioca starch.

[0013] Preferably, the cross-linking treatment time is 5 to 30 minutes.

[0014] Preferably, the calcium chloride solution is an aqueous solution; the concentration of calcium chloride in the calcium chloride solution is 0.05-0.2 mol / L.

[0015] The present invention also provides cross-linked and strengthened rice noodles prepared by the preparation method described in the above technical scheme.

[0016] The present invention also provides application of the preparation method of rice noodles described in the above technical solution in improving the physical properties of rice noodles.

[0017] The present invention also provides the application of the rice flour preparation method described in the above technical solution in improving the edible quality of rice flour;

[0018] The edible quality includes any one or more of ① to ③:

[0019] ①The color of rice noodles;

[0020] ② The organizational morphology of rice noodles;

[0021] ③The taste of rice noodles.

[0022] The present invention provides a method for preparing cross-linked and strengthened rice noodles. The method for preparing cross-linked and strengthened rice noodles of the present invention constructs a green double physically cross-linked starch hydrogel by adding sodium alginate and soaking in a calcium chloride solution, thereby improving the physical properties and edible quality of the prepared rice noodles. Specifically, as the amount of sodium alginate (SA) added increases, the hardness and chewiness of the rice noodles increase accordingly, and the sensory quality first increases and then decreases. The sensory quality of the sample with 1.00% alginate is the best according to the added amount; the cooking quality improves with the increase in the amount of sodium alginate added, and the cooked breakage rate of the samples with 1.00% SA and 1.33% SA is 0, and the cooking loss rate is significantly reduced compared with the control sample. The results of the Rapid Visco Analyzer (RVA) show that sodium alginate competes with starch for water during gelatinization, inhibits the swelling and breakage of starch granules, and improves the thermal stability of starch paste; infrared spectroscopy results show that sodium alginate combines with starch molecules through hydrogen bonds, reducing the number of hydrogen bonds inside the gel; SEM images show that as the amount of sodium alginate added increases, the rice flour network becomes denser and the continuity of the gel matrix increases, indicating that the gelling properties are enhanced, which improves the stretchability and cooking quality of the rice flour. In summary, the present invention uses cross-linked sodium alginate with high thermal stability to prepare rice flour containing cross-linked sodium alginate, and uses calcium chloride to soak the obtained rice flour containing sodium alginate to construct a double physical cross-linked gel network (SA-Ca 2+The egg box structure) strengthens the network structure of fresh wet rice noodles, and compared with the products on the market, the structure is more stable, the quality is better, and the breaking rate is lower. Based on the change of this network structure, the invention also improves the heat-resistant sterilization ability of rice noodles, and it is not easy to break after repeated boiling in hot water, and the taste is smooth and elastic. The breaking rate and cooking loss rate of fresh wet rice noodles after thermal sterilization are reduced, and the quality of thermally sterilized fresh wet rice noodles is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 The Ca provided by the present invention 2+ -SA effect on the tensile properties of rice noodles;

[0025] Figure 2 This is a graph showing the effect of sodium alginate provided by the present invention on the gelatinization properties of rice flour;

[0026] Figure 3 The Ca provided by the present invention 2+ -Infrared spectrum of SA rice flour;

[0027] Figure 4 The Ca provided by the present invention 2+ -SA rice flour infrared second-order derivative spectrum; where a is the wave number range 3460cm -1 ~3580cm -1 Infrared second-order derivative spectrum; b is the wave number range 3250cm -1 ~3350cm -1 Infrared second derivative spectrum;

[0028] Figure 5 The cross-sectional SEM images of rice noodles with different sodium alginate addition amounts provided by the present invention; wherein a is 0.33% SA; b is 0.67% SA; c is 1.00% SA; d is 1.33% SA;

[0029] Figure 6 The Ca provided by the present invention 2+ -Results of the effect of SA on the contact angle of rice flour. DETAILED DESCRIPTION

[0030] The present invention provides a method for preparing cross-linked fortified rice noodles, comprising the following steps:

[0031] The crushed rice is mixed with starch to obtain a mixture of rice and starch; the mixture of rice and starch is mixed with a sodium alginate solution, and a slurry treatment is performed to obtain rice slurry containing sodium alginate; the rice slurry containing sodium alginate is ripened, extruded into threads, and rice flour containing sodium alginate is obtained; the obtained rice flour containing sodium alginate is mixed with a calcium chloride solution, and a cross-linking treatment is performed to obtain cross-linked reinforced rice flour.

[0032] The present invention mixes the crushed rice with starch to obtain a mixture of rice and starch. In a specific embodiment, the rice is de-stoned and cleaned. In a specific embodiment, the rice can be rice soaked in water. In a specific embodiment, the soaking time can be 4 to 6 hours. In a specific embodiment, the mass volume ratio of the soaked rice and water can be 1:1.5 g / mL. In a specific embodiment, the crushed rice can be obtained by grinding rice with water and then drying and grinding. In a specific embodiment, the amount of water added in the grinding operation can be 80% to 90% of the dry basis mass of the rice. In a specific embodiment, the drying temperature of the drying operation can be 45 to 55°C. In a specific embodiment, the rice includes indica rice; the crushed rice has a particle size of 60 to 100 meshes. In a specific embodiment, the starch includes corn starch and / or cassava starch. In a specific embodiment, when the mixture of rice and starch includes crushed rice, corn starch and tapioca starch, the mass ratio of the crushed rice, corn starch and tapioca starch can be 1:0.2:0.4.

[0033] A mixture of rice and starch is obtained. The present invention mixes the mixture of rice and starch with a sodium alginate solution, performs a slurry adjustment process, and obtains rice milk containing sodium alginate. In a specific embodiment, the sodium alginate solution can be an aqueous solution of sodium alginate. In a specific embodiment, the concentration of sodium alginate in the aqueous solution of sodium alginate can be 0.3% to 1.2%. In a specific embodiment, the moisture content of the rice milk containing sodium alginate can be 55% to 60%, and further 56%. In a specific embodiment, the amount of sodium alginate added to the rice milk containing sodium alginate is 0.33% to 1.33%.

[0034] After obtaining the rice slurry containing sodium alginate, the present invention performs a aging treatment on the rice slurry containing sodium alginate, and performs extrusion molding to obtain rice noodles containing sodium alginate. In a specific embodiment, the aging treatment can make the mixture of rice and starch in the rice slurry form a rice-starch-sodium alginate molecular network together with sodium alginate. In a specific embodiment, the aging temperature can be 90 to 105° C. In a specific embodiment, the setting of the aging temperature can make the starch fully gelatinized to form a starch three-dimensional network. In a specific embodiment, the aging and extrusion molding operations can be completed by an extruder. In a specific embodiment, the extrusion die head diameter of the extruder can be 1.2 to 2.0 mm.

[0035] After obtaining the rice flour containing sodium alginate, the present invention mixes the obtained rice flour containing sodium alginate with a calcium chloride solution and performs a cross-linking treatment to obtain cross-linked strengthened rice flour. In a specific embodiment, the cross-linking treatment time is 5 to 30 minutes. In a specific embodiment, after the cross-linking treatment, SA-Ca 2+ The egg box structure further strengthens the three-dimensional network matrix. In a specific embodiment, the calcium chloride solution is an aqueous solution; the concentration of calcium chloride in the calcium chloride solution can be 0.05-0.2 mol / L, and further 0.1 mol / L. In a specific embodiment, the cross-linked and strengthened rice noodles are fully washed with water and drained for packaging to obtain commercial cross-linked and strengthened rice noodles. In a specific embodiment, the commercial cross-linked and strengthened rice noodles can be sterilized in a water bath at 95°C for 30 minutes to obtain a heat-sterilized fresh wet rice noodle sample.

[0036] The present invention also provides cross-linked and strengthened rice noodles prepared by the preparation method described in the above technical scheme.

[0037] The present invention also provides the application of the preparation method of rice noodles described in the above technical solution in improving the physical properties of rice noodles. In a specific embodiment, the physical properties include any one or more of tensile properties, texture properties, cooking properties, viscosity properties, microstructure and hydrophilicity.

[0038] The present invention also provides an application of the rice flour preparation method described in the above technical solution in improving the edible quality of rice flour; the edible quality includes any one or more of the items shown in ① to ③:

[0039] ①The color of rice noodles;

[0040] ② The organizational morphology of rice noodles;

[0041] ③The taste of rice noodles.

[0042] In order to further illustrate the present invention, a cross-linked and fortified rice flour provided by the present invention and a preparation method and application thereof are described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0043] The test materials used in the present invention are as follows:

[0044] Indica rice-Guilin Dingyin Food Co., Ltd.;

[0045] Corn starch-Zhucheng Xingmao Corn Development Co., Ltd.;

[0046] Cassava starch-Shanghai Miruini Food Co., Ltd.

[0047] Medium viscosity sodium alginate (SA) - Qingdao Mingyue Seaweed Co., Ltd.;

[0048] Anhydrous Calcium Chloride-Sinopharm Chemical Reagent Co., Ltd.

[0049] The test instrument used in the present invention is as follows:

[0050] Milling machine-Guangzhou Xuzhong Food Equipment Co., Ltd.

[0051] Self-cooking shredded wire extruder-Guangzhou Xuzhong Food Equipment Co., Ltd.

[0052] Texture Analyzer (TA.XTPlusC) - Stable Micro System, UK;

[0053] Rapid Viscosity Analyzer (RVA-Tec Master) - Xingang Technology Co., Ltd.;

[0054] Fourier transform infrared spectrometer (FTIR-8400) - Shimadzu Corporation, Japan;

[0055] Scanning electron microscope (JSM-7500F) - JEOL Ltd.;

[0056] Optical contact angle measuring instrument (DSA100S) - Krues GmbH, Germany.

[0057] Example 1

[0058] Screening the optimal extrusion hole diameter for preparing heat-sterilized rice noodles.

[0059] (1) Preparation of heat-sterilized rice noodles with different diameters: 500 g of a mixture (rice flour: corn starch: tapioca starch = 5:1:2) was weighed and mixed with sodium alginate solution of different concentrations to make the addition of sodium alginate 0.33%, 0.67%, 1.00%, and 1.33% of the mass of the rice noodles, respectively. 1.2 mm, 1.5 mm, 1.8 mm, 2.0 mm, and 2.3 mm extrusion ports were selected, respectively, and the rice noodles were gelatinized at 95°C by single screw extrusion. After extrusion, the rice noodles were immersed in calcium chloride solution for cross-linking for 15 minutes, washed thoroughly with water, drained, and packaged, and sterilized in a water bath at 95°C for 30 minutes to obtain heat-sterilized fresh wet rice noodles.

[0060] (2) Steaming and tensile properties test: Take 20 20cm long heat-sterilized rice noodles and heat them in boiling water until there is no hard core inside. This is the optimal steaming time. The ratio of the number of broken rice noodles (less than 10cm) to the number of original rice noodles during this time is the broken rate. Use a clamp to pinch the two ends of the rehydrated rice noodles and stretch them outward from 1cm. The elongation at break is calculated as the ratio of the extended length to the initial length. By comparing the quality and performance of different direct heat sterilized rice noodles, it is believed that the rice noodles prepared with a 1.8mm extrusion port have the best quality, so the subsequent experiments all use a 1.8mm extrusion port to prepare the required rice noodles.

[0061] Example 2

[0062] Screening the optimal cross-linking time for soaking in calcium chloride solution for preparing heat-sterilized rice noodles.

[0063] (1) Preparation of heat-sterilized rice noodles with different soaking time in calcium chloride solution: Weigh 500g of the mixture (rice flour: corn starch: tapioca starch = 5:1:2) and mix with sodium alginate solution of different concentrations. The amount of sodium alginate added is 0.33%, 0.67%, 1.00% and 1.33% of the mass of the rice noodles. Use a 1.8mm extrusion port to gelatinize and form the rice noodles at 95℃ through a single screw extruder. After extrusion, immerse the rice noodles in calcium chloride solution for cross-linking for 5min, 10min, 15min, 20min, 25min and 30min, rinse thoroughly with water, drain and package, and sterilize in a water bath at 95℃ for 30min to obtain heat-sterilized fresh wet rice noodles.

[0064] (2) Steaming and tensile properties test: Take 20 20 cm long heat-sterilized rice noodles and heat them in boiling water until there is no hard core inside. This is the optimal steaming time. The ratio of the number of broken rice noodles (less than 10 cm) to the number of original rice noodles during this time is the breakage rate. Use a clamp to pinch the two ends of the rehydrated rice noodles and stretch them outward from 1 cm. The elongation at break is calculated as the ratio of the extended length to the initial length. By comparing the quality and performance of different direct heat sterilized rice noodles, it is believed that the rice noodles prepared by soaking in calcium chloride solution for 15 minutes have the best quality, so subsequent experiments all use soaking for 15 minutes to prepare the required rice noodles.

[0065] Example 3

[0066] Screen the optimal sterilization time for preparing heat-sterilized rice noodles.

[0067] (1) Preparation of heat-sterilized rice noodles with different sterilization times: Weigh 500g of a mixture (rice flour: corn starch: tapioca starch = 5:1:2) and mix it with sodium alginate solution of different concentrations. The amount of sodium alginate added is 0.33%, 0.67%, 1.00%, and 1.33% of the mass of the rice noodles, respectively. Use a 1.8mm extrusion port to gelatinize and form the rice noodles at 95℃ through a single screw extruder. After extrusion, immerse the rice noodles in a calcium chloride solution for cross-linking for 15 minutes, rinse them thoroughly with water, drain the water, and package them. Sterilize them in a water bath at 95℃ for 15 minutes, 30 minutes, 45 minutes, and 60 minutes, respectively, to obtain heat-sterilized fresh wet rice noodles.

[0068] (2) Steaming and tensile properties test: Take 20 20cm long heat-sterilized rice noodles and heat them in boiling water until there is no hard core inside. This is the optimal steaming time. The ratio of the number of broken rice noodles (less than 10cm) to the number of original rice noodles during this time is the breakage rate. Use a clamp to pinch the two ends of the rehydrated rice noodles and stretch them outward from 1cm. The elongation at break is calculated as the ratio of the extended length to the initial length. By comparing the quality and performance of different direct heat sterilized rice noodles, it is believed that the rice noodles prepared by sterilization for 30 minutes have the best quality, so subsequent experiments all use sterilization for 30 minutes to prepare the required rice noodles.

[0069] Example 4

[0070] Screen the optimal mixed powder ratio for preparing heat-sterilized rice noodles.

[0071] (1) Preparation of heat-sterilized rice noodles with different mixed powder ratios: Weigh 500g of the mixture, in which the ratios of rice flour: corn starch: tapioca starch are 5:1:2, 5:2:1, and 5:1.5:1.5, respectively, and use different concentrations of sodium alginate solution for slurry adjustment, with the addition amount of sodium alginate being 0.33%, 0.67%, 1.00%, and 1.33% of the mass of the rice noodles, respectively. Use a 1.8mm extrusion port to extrude the rice noodles through a single screw extruder at 95°C for gelatinization. After extrusion, immerse the rice noodles in a calcium chloride solution for cross-linking for 15 minutes, rinse them thoroughly with water, drain the water, and package them. Sterilize them in a water bath at 95°C for 30 minutes to obtain heat-sterilized fresh wet rice noodles.

[0072] (2) Steaming and tensile properties test: Take 20 20cm long heat-sterilized rice noodles and heat them in boiling water until there is no hard core inside. This is the optimal steaming time. The ratio of the number of broken rice noodles (less than 10cm) to the number of original rice noodles during this time is the breaking rate. Use a clamp to pinch the two ends of the rehydrated rice noodles and stretch them outward from 1cm. The elongation at break is calculated as the ratio of the extended length to the initial length. By comparing the quality and performance of different direct heat sterilized rice noodles, it is believed that the rice noodles prepared with a mixed powder ratio of 5:1:2 have the best quality. Therefore, subsequent experiments all use a mixed powder ratio of 5:1:2 to prepare the required rice noodles.

[0073] Test Example 1

[0074] 1.1 Preparation of cross-linked sodium alginate fresh wet rice noodles.

[0075] According to the optimal conditions provided in Examples 1 to 4, cross-linked sodium alginate fresh wet rice noodles were prepared. The general process is as follows:

[0076] Indica rice → remove sand and stones → wash rice → crush and grind → dry → dry grind and sieve → dissolve sodium alginate → adjust the slurry (add starch and sodium alginate solution) → mature → extrude → cross-link (soak in chlorine CaCl2 solution) → wash with water → drain water → bag and seal → sterilize.

[0077] Specific process: After the indica rice is de-stoned and washed, it is soaked in water for 4 hours (the mass volume ratio of indica rice to water is about 1:1.5g / mL). After soaking, the water is drained, and water of about 80% of the dry weight of the indica rice is added for grinding. After grinding, it is dried at 45°C, ground with a high-speed grinder and passed through an 80-mesh sieve; 0.3%, 0.6%, 0.9%, and 1.2% sodium alginate solutions are prepared respectively, and a stirrer is used to stir at high speed at room temperature to fully dissolve the sodium alginate until the solution is completely transparent; starch (indica rice flour / corn starch / cassava starch ratio is 1 / 0.2 / 0.4) and sodium alginate solution are added for slurry adjustment, so that the moisture content of the final rice slurry is about 56%; the amount of sodium alginate added is 0.33%, 0.67%, 1.00%, and 1.33% of the mass of the rice flour, respectively. The prepared rice slurry is poured into an extruder for maturation and extrusion molding, wherein the temperature is 95°C and the diameter of the extrusion die is 1.8 mm; after the rice noodles are extruded, they are immersed in a calcium chloride solution for cross-linking for 15 minutes, and then they are thoroughly washed with water and drained for packaging, and sterilized in a water bath at 95°C for 30 minutes to obtain a heat-sterilized fresh wet rice noodle sample.

[0078] Conventional rice noodles without sodium alginate and without cross-linking (soaking in CaCl2 solution) were used as control samples. The general process of the control sample rice noodles is: indica rice → sand and stone removal → rice washing → crushing and grinding → drying → dry grinding and sieving → slurry adjustment → maturation → extrusion → room temperature aging → re-steaming → bagging and sealing → sterilization.

[0079] Since the sodium alginate fortified rice noodles were not aged, the control samples without sodium alginate could not be tested, so the control samples were set as samples aged at room temperature for 3 hours and re-steamed at this moisture content. The prepared samples were placed at room temperature for 24 hours before relevant quality tests.

[0080] 1.2 Determination of moisture content

[0081] Use the direct drying method to determine the moisture content of fresh wet rice noodles, that is, the 105℃ constant weight method. Take a clean glass dish and place it in an electric blast drying oven at 105℃ and dry it for 0.5h to constant weight (m1). Weigh about 5.0g (m2) of rice noodle sample and place it in a glass dish, put it in a 105℃ electric blast drying oven and dry it for 3-4h, take it out and put it in a dryer to cool to room temperature, and weigh it; put it in a 105℃ drying oven again and dry it for 1h, take it out and put it in a dryer 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 the constant weight (m3). Calculate the moisture content of fresh wet rice noodles according to the following formula:

[0082] Moisture content (%) = (1-m3-m1) / m2×100%, formula I.

[0083] 1.3 Determination of tensile properties

[0084] The tensile properties of rice noodles were measured using the tensile mode of the texture analyzer. The prepared fresh wet rice noodles were boiled in boiling water for 2 minutes to make them cooked again (the rice noodles were completely dispersed and there was no hard core inside), then they were taken out and cooled 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 30 mm, and the tensile test was performed at a tensile rate of 1 mm / s. The elongation at break and tensile strength of the rice noodles were obtained according to the stress-strain curve.

[0085] 1.4 Determination of texture properties (TPA)

[0086] The texture characteristics of rice noodles were measured using the TPA mode of the texture analyzer. The sample processing method was the same as 4.2.3.3. Select samples with uniform thickness, cut two 2.5 mm long strips and place them parallel to the test bench, select the P / 36R probe, the speed was 1 mm / s before the test, 1 mm / s during the test, and 1 mm / s after the test. The compression ratio was 50%, the trigger force was 5g, and the time interval between the two compressions was 5s.

[0087] 1.5 Determination of cooking characteristics

[0088] (1) Determination of the breaking rate of fresh wet rice noodles

[0089] Take 20 fresh wet rice noodles with a length of 20 cm, cook them in 500 mL boiling water for 2 min, remove the rice noodles and drain them in cold water, record the weight m1 and m2 of the rice noodles with a length of less than 10 cm and more than 10 cm respectively, and calculate the breakage rate according to the following formula:

[0090]

[0091] (2) Determination of cooking loss rate and rehydration rate of fresh wet rice noodles

[0092] Take 20 20cm long fresh wet rice noodles, weigh them before testing (m0), and determine the moisture content M. After cooking in 500mL boiling water for 2min, remove the rice noodle sample and rinse it with distilled water. Weigh the mass of 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 blast drying oven to dry to constant weight (m3). Calculate the cooking loss rate and rehydration rate according to the following formula:

[0093]

[0094] 1.6 Determination of viscosity characteristics (RVA)

[0095] The effect of sodium alginate on the viscosity characteristics of rice flour and starch mixture was analyzed using a rapid viscosity analyzer (RVA). Indica rice flour, ordinary corn starch and cassava starch were weighed in a ratio of 1 / 0.2 / 0.4 and mixed into an aluminum can, with a total weight of 3g. Sodium alginate and distilled water with mass fractions of 0%, 0.33%, 0.67%, 1.00% and 1.37% were added to the mixture, respectively, to make a total weight of 28g. The test method adopted the standard procedure in the RVA instrument. Each starch suspension was stirred at 960rpm for the first 10s in the instrument, and then continuously stirred at 160rpm until the test was completed; the sample was kept at 50℃ for 60s, then heated to 95℃ at a constant speed for 240s and kept for 150s, then cooled to 50℃ at a constant speed for 240s and kept for 90s, and the test was completed. The RVA curve was recorded to obtain the peak viscosity, valley viscosity, final viscosity, decay value (the difference between the peak viscosity and the valley viscosity), and regeneration value (the difference between the final viscosity and the valley viscosity).

[0096] 1.7 Fourier transform infrared spectroscopy (FT-IR)

[0097] 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 through an 80-mesh sieve and 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 second-order derivative of infrared spectra was used to analyze the changes in hydrogen bonds inside rice flour gels, and the Savitzky-Golay method with 7-point smoothing and three-term polynomials was used to obtain the second-order derivative.

[0098] 1.8 Scanning Electron Microscope (SEM)

[0099] The cross-sectional morphology of fresh wet rice noodles was observed using a JSM-7500F scanning electron microscope. The prepared fresh wet rice noodles samples 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 gold spraying three times to make the fracture surface of the samples uniformly coated. All samples were observed at a magnification of 1000 times and an accelerating voltage of 10 kV.

[0100] 1.9 Determination of contact angle

[0101] 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 min (Zhang et al., 2022); 34 μL of water was dropped on the sample slice, and the contact angle was measured at 0 s, and then the contact angle was measured every 60 s for a cumulative measurement of 5 min. The contact angle change curve of the sample within 5 min was obtained.

[0102] 1.10 Sensory evaluation

[0103] Select 20 students from the food major to form two sensory evaluation groups, with 10 people in each group. Refer to the sensory scoring standards shown in Table 1 to conduct sensory evaluation on fresh wet rice noodles from four aspects: color, smell, tissue morphology, and taste. The full score for each indicator is 10 points, and the average value is taken as the final result.

[0104] Table 1 Sensory scoring criteria

[0105]

[0106] 1.11 Data Statistical Analysis

[0107] All experiments were repeated at least three times, and the results were expressed as mean and standard deviation. SPSS17.0 (SPSS Inc., Chicago, USA) was used to perform variance analysis on the experimental data, and Duncan's multiple range test was used to determine the significance of each mean (p < 0.05). Origin 2018 (OriginLab Inc., USA) was used for graphic analysis.

[0108] 2 Results Analysis and Discussion

[0109] 2.1 Analysis of tensile properties of cross-linked sodium alginate rice flour

[0110] Figure 1The tensile curves of fresh wet rice noodles strengthened by cross-linking with different amounts of sodium alginate are shown in Figure 2. It can be observed 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 amount of sodium alginate increased to 1.33%, the elongation at break and tensile strength increased significantly, reaching 112% and 7.8 g·mm, respectively. -2 . Since the aging process was not carried out in the production process of the rice noodle samples, the starch network and sodium alginate network of the rice noodles with a lower sodium alginate addition were insufficient in strength, and the elongation at break and tensile strength were both at a low level. The strength of the cross-linked sodium alginate network was 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 moisture, which further reduces the strength of the sodium alginate network. With the further increase in the amount of sodium alginate added, the tensile strength and elongation at break of the rice noodles increased significantly, indicating that the gel network in the rice noodles was significantly enhanced.

[0111] 2.2 Analysis of texture characteristics of cross-linked sodium alginate rice flour

[0112] Table 2Ca 2+ Effect of -SA on the textural properties of rice flour

[0113]

[0114] The data are expressed as mean ± standard deviation (n = 3), and the values ​​marked with different letters (ad) in the same column are significantly different (p < 0.05).

[0115] Table 2 shows the texture characteristics of fresh wet rice noodles strengthened by cross-linking with different addition amounts of sodium alginate. It can be observed from the table that the hardness, elasticity and chewiness of rice noodles with 0.33% sodium alginate addition are lower, and the viscosity is higher. This is because there is no retrogradation process, and the amount of sodium alginate added is small, the cross-linking strength is low, and the gel network is looser. The viscosity is related to the cooked breaking rate. The higher the cooked breaking rate, the greater the viscosity. This result is consistent with the cooking characteristics. In addition, there is no significant difference in cohesion and recovery between the samples. With the increase of sodium alginate addition, the hardness, elasticity and chewiness of rice noodles with 1.33% addition gradually increase, which are 88.43% and 74.72% higher than the control, respectively, and the viscosity decreases by 61.56%, indicating that the gel strength of rice noodles increases, the quality is improved, and the sodium alginate network plays a leading role in rice noodles. The increase in hardness and elasticity is consistent with the results in tensile properties. The increase in hardness reflects the increase in gel strength and tensile strength of rice noodles from the side. 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, which also shows that aging can significantly improve the quality of rice noodles.

[0116] 2.3 Analysis of cooking characteristics of cross-linked sodium alginate rice flour

[0117] Table 3Ca 2+ Effect of -SA on cooking characteristics of rice flour

[0118] sample Strip breaking rate (%) Cooking loss rate (%) Water absorption (%) Comparison <![CDATA[27.53±5.55 b ]]> <![CDATA[1.37±0.14 b ]]> <![CDATA[22.35±2.62 a ]]> 0.33%SA <![CDATA[83.14±7.78 a ]]> <![CDATA[1.96±0.10 a ]]> <![CDATA[23.18±1.51 a ]]> 0.67%SA <![CDATA[9.04±1.70 c ]]> <![CDATA[0.96±0.10 c ]]> <![CDATA[21.18±1.82 ab ]]> 1.00% SA <![CDATA[0.00±0.00 d ]]> <![CDATA[0.53±0.11 d ]]> <![CDATA[18.78±1.26 bc ]]> 1.33% SA <![CDATA[0.00±0.00 d ]]> <![CDATA[0.33±0.04 e ]]> <![CDATA[16.78±1.61 c ]]>

[0119] The data are expressed as mean ± standard deviation (n = 3). The values ​​marked with different letters (ae) in the same column are significantly different (p < 0.05).

[0120] The three indicators of cooking loss, breakage rate and water absorption rate are important indicators for evaluating the quality of fresh wet rice noodles. Among them, a lower breakage rate indicates that the rice noodles are not easy to break, have better quality and higher gel strength; a lower cooking loss rate indicates that less starch and other substances are lost during the cooking process, and it is not easy to become mushy; the water absorption rate indicates the amount of water absorbed by the rice noodles during the cooking process. Generally, the higher the water absorption rate, the better the elasticity and smoothness of the rice noodles; therefore, fresh wet rice noodles with better cooking quality should have a lower breakage rate, lower cooking loss and relatively higher water absorption rate.

[0121] The present invention obtains Ca through the above cooking characteristics determination experiment 2+ The results of the effect of SA on the cooking properties of rice noodles are shown in Table 3. 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 make it less likely to become mushy; the breakage rate of the sample with 1.00% SA is reduced to 0, and the cooking loss rate is further reduced. 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 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.

[0122] 2.4 Analysis of viscosity characteristics of indica rice flour with sodium alginate

[0123] Table 4 Effect of sodium alginate on the gelatinization properties of rice flour

[0124]

[0125] The data are expressed as mean ± standard deviation (n = 3), and the values ​​marked with different letters (ad) in the same column are significantly different (p < 0.05).

[0126] Effects of different sodium alginate addition amounts (0.33%, 0.67%, 1.00%, 1.33%) on the RVA gelatinization properties of rice flour system Figure 2 As shown in Table 4, the parameters are shown in Table 4. It can be observed from the table that with the increase of the amount of sodium alginate added, the peak viscosity, valley viscosity and final viscosity of the system all show a trend of first decreasing and then increasing, which indicates that the addition of hydrophilic colloids such as sodium alginate will inhibit the swelling and breakage of starch granules, and the degree of inhibition is closely related to the amount of hydrophilic colloid added. In the early stage of gelatinization, starch granules absorb water and swell when heated. The viscosity when the maximum swelling degree is reached is the peak viscosity, while hydrophilic colloids such as sodium alginate will compete with starch granules for water and weaken the hydration degree of starch. The inhibition effect reaches the highest when the addition amount is 1.00%. The regeneration value reflects the increase in starch viscosity during the cooling process, and the regeneration values ​​of samples with different sodium alginate addition amounts all decrease. Hydrophilic colloids can significantly delay the short-term regeneration of various types of starch. The decrease in the regeneration value indicates that during the cooling process, the sodium alginate molecules interact with the starch molecules, interfering with the rearrangement of the amylose molecules, thereby delaying the short-term regeneration of starch to a certain extent.

[0127] 2.5 Infrared spectroscopy analysis of cross-linked sodium alginate rice flour

[0128] Fourier transform infrared spectroscopy (FTIR) can be used to test the interaction between sodium alginate and starch molecules in rice flour, to verify whether starch is compatible with sodium alginate and to determine whether new groups are generated in the mixed system.

[0129] The infrared spectra of rice flour with different sodium alginate addition amounts of the present invention are as follows: Figure 3 Compared with the infrared spectrum of the control rice flour, no new absorption peaks appeared after adding sodium alginate. The overall infrared spectrum skeleton was the same as that of the control rice flour, which was a typical starch infrared spectrum skeleton, indicating that there was no covalent bonding 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 wide peak appears around 3290cm, which is a typical hydroxyl stretching vibration absorption peak. The rice flour-sodium alginate system is mainly hydrogen bond interaction, but because 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. The hydrogen bond between the double helices is located at 3290cm-1 The position of free hydrogen bonds is usually around 3500 cm -1 The present invention Ca 2+ -SA rice flour infrared second-order derivative spectrum Figure 4 As shown, the wave number of the free hydrogen bond of the control sample is 3537 cm -1 Department Figure 4 a) The wave number of hydrogen bond between double helices is 3289 cm -1 Department Figure 4 b). 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 This indicates that free hydrogen bonds are reduced. Sodium alginate not only inhibits starch gelatinization, but also combines with amylose molecules through hydrogen bonds, reducing the number of free hydrogen bonds, enhancing the hydrogen bond interactions in the system, strengthening the three-dimensional gel network, and significantly improving the mechanical properties of rice noodles, thereby increasing the tensile properties of rice noodles. -1 There is no change in the bands at the positions, which indicates that all samples have not been aged and the number of hydrogen bonds between the double helices has not changed.

[0130] 2.6 Microstructure analysis of cross-linked sodium alginate rice flour

[0131] The scanning electron microscope images of fresh wet rice noodles with different sodium alginate additions were obtained. Figure 5 As shown. Using scanning electron microscopy, the internal network structure of different rice flour samples can be observed more intuitively. Four samples with 0.33% SA, 0.67% SA, 1.00% SA and 1.33% SA were observed respectively to analyze the direct differences between different samples. Figure 5 a) When the amount of sodium alginate added is small, the gel network is mainly formed by the short-term regeneration of starch 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 breaking rate and cooking loss rate, and low tensile strength. As the amount of sodium alginate added increases, such as Figure 5 c and 5d, the combination of short-term retrogradation of starch gelatinization and cross-linked sodium alginate formed a denser network with a smaller network pore size and increased matrix continuity. This can explain the Ca 2+ The reasons why cross-linked sodium alginate improves the cooking quality and sensory quality of rice noodles.

[0132] 2.7 Contact angle analysis of cross-linked sodium alginate rice powder

[0133] Hydrophilicity is an important factor affecting the rehydration ability of rice flour. In the experiment, the hydrophilicity of starch can be measured by the contact angle. The smaller the contact angle, the stronger the attraction between starch and water molecules. The contact angle measurement results of the rice flour sample of the present invention are as follows: Figure 6 As shown, the contact angles of all rice flour samples are less than 90°, indicating that rice flour is a hydrophilic material. This is due to the presence of many hydrophilic hydroxyl groups in natural starch molecules. In addition, sodium alginate is also a hydrophilic colloid with strong water absorption. Adding it to food can greatly improve the water retention of the product. The initial contact angle of the control sample was 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 was 46.4°, and it was 35.0° at 5 minutes, which was reduced by 24.6%. The initial contact angle of the 1.33% SA sample was 36.3°, and it was 19.9° at 5 minutes, which was reduced by 45.2%. From the data, it can be seen that the addition of sodium alginate significantly increased the rate of contact angle reduction, indicating that the hydrophilicity of rice flour increased, the water absorption rate accelerated, and it was more conducive to water retention during long-term storage, which was beneficial to improving the taste and flavor of rice flour.

[0134] 2.8 Sensory evaluation of cross-linked sodium alginate rice flour

[0135] The sensory evaluation results of rice noodles with different sodium alginate additions are shown in Table 5. It can be observed from the table that the color score of rice noodles gradually increases. This is because with the increase in the amount of sodium alginate added, the gelling property of rice noodles is enhanced, and the surface color is more uniform and has no variegated color. The odor difference of each sample is not significant, because the rice noodles and starch raw materials used are the same, and the odor difference is not significant. The tissue morphology score and taste score show a trend of first increasing and then decreasing with the increase in the amount of sodium alginate added. This is because cross-linked sodium alginate can enhance the gelling property of rice noodles, reduce the breaking rate and cooking loss, but too high an addition amount will make the rice noodles too gelling, the texture is stiff, which is not conducive to the taste, resulting in a lower score. Comprehensively considering various sensory indicators, rice noodles with 1.00% SA have the best sensory quality and the highest score.

[0136] Table 5 Sensory evaluation results of different rice flour samples

[0137]

[0138]

[0139] The data are expressed as mean ± standard deviation (n = 3). The values ​​marked with different letters (ae) in the same column are significantly different (p < 0.05).

[0140] In summary, the present invention strengthens the quality of fresh wet rice noodles by cross-linking by studying different addition amounts of sodium alginate, and characterizes the results of the samples by instruments and equipment such as texture analyzer, rapid viscosity analyzer, scanning electron microscope, Fourier transform infrared spectroscopy, etc. Compared with the control, with the increase of the addition amount of sodium alginate, the hardness and chewiness of the rice noodles increase accordingly, and the sensory quality first increases and then decreases. The sensory quality of the sample with 1.00% alginate is the best according to the addition amount. The cooking quality improves with the increase of the addition amount of sodium alginate. The cooked and broken strips rate of the samples with 1.00% SA and 1.33% SA is 0, and the cooking loss rate is significantly lower than that of the control sample. The RVA results show that sodium alginate competes with starch for water during gelatinization, inhibits the swelling and breakage of starch granules, and improves the thermal stability of starch paste. The infrared spectrum results show that sodium alginate combines with starch molecules through hydrogen bonds to reduce the number of hydrogen bonds inside the gel. SEM images show that with the increase of sodium alginate addition, the rice noodle network becomes denser and the continuity of the gel matrix increases, indicating that the gel property is enhanced, which improves the stretchability and cooking quality of the rice noodles. This chapter provides a method to use cross-linked sodium alginate with high thermal stability to strengthen the network structure of fresh wet rice noodles, improve the heat sterilization ability of rice noodles, reduce the breakage rate and cooking loss rate of fresh wet rice noodles after thermal sterilization, and improve the quality of thermally sterilized fresh wet rice noodles.

[0141] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creative work, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing cross-linked fortified rice flour, comprising the following steps: mixing the crushed rice with starch to obtain a mixture of rice and starch; The mixture of rice and starch is mixed with the sodium alginate solution, and slurry is prepared to obtain rice slurry containing sodium alginate; The sodium alginate-containing rice slurry is subjected to a aging treatment and extruded into wires to obtain rice flour containing sodium alginate; The obtained rice flour containing sodium alginate is mixed with a calcium chloride solution and cross-linked to obtain cross-linked reinforced rice flour.

2. The preparation method according to claim 1, characterized in that: The rice includes indica rice; the grain size of the crushed rice is 60 to 100 meshes.

3. The preparation method according to claim 1, characterized in that: The water content of the rice milk containing sodium alginate is 55% to 60%.

4. The preparation method according to claim 1, characterized in that: The added amount of sodium alginate in the sodium alginate-containing rice milk is 0.33% to 1.33%.

5. The preparation method according to claim 1, characterized in that: The starch includes corn starch and / or tapioca starch.

6. The preparation method according to claim 1, characterized in that: The cross-linking treatment time is 5 to 30 minutes.

7. The preparation method according to claim 1, characterized in that: The calcium chloride solution is an aqueous solution; the concentration of calcium chloride in the calcium chloride solution is 0.05-0.2 mol / L.

8. Cross-linked and fortified rice flour prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the preparation method according to any one of claims 1 to 7 in improving the physical properties of rice noodles.

10. Application of the preparation method according to any one of claims 1 to 7 in improving the edible quality of rice noodles; The edible quality includes any one or more of ① to ③: ①The color of rice noodles; ② The organizational morphology of rice noodles; ③The taste of rice noodles.

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