Ultrasonic-sodium citrate composite modification method of lotus root whole powder and modified lotus root whole powder

Abstract

The invention belongs to the field of starch modification, and discloses an ultrasonic-sodium citrate composite modification method of lotus root whole powder and modified lotus root whole powder. The modification method comprises the following steps: mixing lotus root whole powder, sodium citrate and water to obtain a mixture; and sequentially carrying out ultrasonic treatment, freeze-drying and grinding treatment on the mixture to obtain the modified lotus root whole powder. According to the method disclosed by the invention, multi-scale regulation and control on a starch particle crystal structure, an intermolecular acting force, a gelatinization characteristic and a gel network are realized through cooperative treatment of ultrasonic (physical field) and sodium citrate (chemical environment), the modification effect of the lotus root whole powder is remarkably improved, and starch retrogradation is effectively inhibited.

Description

Technical Field

[0001] This invention belongs to the field of starch modification, and more specifically, relates to an ultrasonic-sodium citrate composite modification method for lotus root powder and the modified lotus root powder. Background Technology

[0002] Traditional lotus root starch production processes primarily extract starch granules, resulting in the loss of most dietary fiber, protein, vitamins, minerals, and functional components through water runoff or waste disposal, causing significant nutritional losses. The byproducts, lotus root residue (containing fiber, residual starch, and protein) and lotus root juice, have low utilization rates and are mostly used as animal feed or discharged as wastewater. Large amounts of washing water mixed with lotus root juice form high-concentration organic wastewater, which pollutes water bodies if directly discharged. In contrast, whole lotus root powder is produced by processing whole lotus roots into powder without separation or extraction, preserving almost all nutritional components (lotus root powder contains 8-12% moisture, 30% fiber, 0.5-1% fat, 5-6% protein, and 50% starch), making it a complete nutritional base that meets the requirements of healthy food. The whole lotus root powder production process generates no waste residue, significantly improves raw material utilization and product yield, and drastically reduces wastewater discharge at the source, offering both environmental and economic advantages.

[0003] However, during processing and storage, lotus root powder often suffers from starch retrogradation and insufficient heat processing tolerance, leading to a decline in product quality, such as hardening, deteriorated taste, and decreased stability, severely impacting its industrial application value and limiting its large-scale application in the food industry. In existing technologies, physical modification methods (such as ultrasonic treatment) mainly utilize cavitation effects to disrupt the crystalline structure of starch granules, improving their gelatinization properties to obtain modified lotus root powder and delay starch retrogradation. Chemical modification methods often employ reagents such as salts, borax, and sodium citrate to interfere with intermolecular hydrogen bonds or form new chemical bonds, thus delaying the retrogradation process and obtaining modified lotus root powder. However: Physical modification methods utilize the ultrasonic cavitation effect to mechanically disrupt the starch crystal structure and molecular chain entanglement. The product is obtained through "preparation of an aqueous dispersion system - ultrasonic treatment - gelatinization". This method can improve the solubility and gelatinization properties of starch. However, the depth of control is limited and the stability is easily affected. Specifically, mechanical disruption is achieved only through physical cavitation, lacking the precise reconstruction of the starch molecular network by chemical action. This results in insufficient depth of control over the multi-scale structure of starch (crystallinity, intermolecular forces, and micro-network). Furthermore, high-power processing can easily cause excessive damage to the starch structure, thereby affecting the processing stability of the product. Chemical modification methods, which disrupt the hydrogen bond network between starch molecules through ionic effects and hydrogen bonding, and produce products through "mixing, homogenization, and gelatinization," can improve the thermal stability and water-holding capacity of starch. However, this method cannot substantially destroy the physical structure of starch granules and is unable to break through the original rigid network constraints of starch, resulting in limited improvement in core properties such as anti-retrogradation and gelatinization stability. In addition, some chemical modification methods pose environmental risks or have complex processes.

[0004] Therefore, existing technologies (physical modification methods and chemical modification methods) can usually only delay starch retrogradation in isolation, lacking the synergistic regulation of "physical field-chemical environment". Furthermore, they have not conducted systematic research on the core issue of starch retrogradation (starch retrogradation refers to the phenomenon that gelatinized starch molecules (mainly amylose) re-aggregate, form a double helix structure and crystallize during cooling or storage, resulting in hardening of starch quality, deterioration of taste and decrease in processing stability). They cannot simultaneously optimize multiple key physicochemical indicators such as anti-retrogradation, texture and water distribution, nor can they achieve synergistic optimization of the multi-scale structure of starch. Summary of the Invention

[0005] The purpose of this invention is to address the technical shortcomings of existing technologies that fail to solve the core problem of starch retrogradation, and to propose an ultrasonic-sodium citrate composite modification method for lotus root powder and the resulting modified lotus root powder. This invention achieves multi-scale regulation of the crystal structure, intermolecular forces, gelatinization characteristics, and gel network of starch granules through the synergistic treatment of ultrasound (physical field) and sodium citrate (chemical environment), significantly improving the modification effect of lotus root powder and effectively inhibiting starch retrogradation.

[0006] To achieve the above objectives, the present invention provides a method for ultrasonic-sodium citrate composite modification of lotus root powder, the modification method comprising: Lotus root powder, sodium citrate, and water were mixed to obtain a mixture; the mixture was then subjected to ultrasonic, freeze-drying, and crushing processes to obtain modified lotus root powder.

[0007] According to the present invention, preferably, the method for preparing the lotus root powder includes the following steps: cutting the washed and peeled fresh lotus root into thin slices, drying with hot air, crushing and sieving to obtain the lotus root powder.

[0008] In this invention, the thickness of the sheet is 2-3 mm.

[0009] In this invention, the hot air drying temperature is 70°C and the time is 8 hours.

[0010] According to the present invention, preferably, the sieving is a sample sieve passing through a 100-140 mesh sieve.

[0011] According to the present invention, preferably, the method further includes: stirring and homogenizing the ultrasonically treated mixture to obtain a homogenate; subjecting the homogenate to heating and gelatinizing, freeze-drying and crushing treatments in sequence to obtain the modified lotus root powder.

[0012] According to the present invention, preferably, the stirring and homogenizing speed is 8000-12000 r / min and the time is 0.5-1.5 min.

[0013] According to the present invention, preferably, the temperature of the heating and gelatinization treatment is 85-95°C and the time is 10-20 min.

[0014] According to the present invention, preferably, the freeze-drying temperature is -85°C to -75°C and the time is 12-36 hours.

[0015] According to the present invention, preferably, the mass ratio of lotus root powder to sodium citrate is 100:(0.6-12.2). In the present invention, as a preferred embodiment, 100g of lotus root powder, 0.6-12.2g of sodium citrate, and 500g of water (preferably distilled water) are used.

[0016] According to the present invention, preferably, the concentration of sodium citrate in the mixture is 0.1-2.0%.

[0017] According to the present invention, preferably, the ultrasonic treatment time is 15-25 minutes and the power is 200-800W.

[0018] Another aspect of the present invention provides modified lotus root powder obtained by the ultrasonic-sodium citrate composite modification method of the aforementioned lotus root powder.

[0019] The beneficial effects of the technical solution of this invention are as follows: This invention achieves multi-scale regulation of the crystal structure, intermolecular forces, gelatinization characteristics, and gel network of starch granules through the synergistic treatment of ultrasound (physical field) and sodium citrate (chemical environment), significantly improving the modification effect of lotus root powder, effectively inhibiting starch retrogradation, optimizing the gel network and moisture distribution, and improving the processing stability of lotus root powder. Through the method of this invention, high-quality lotus root powder products suitable for complex processing scenarios can be developed. Specifically: 1. This invention overcomes the shortcomings of existing single ultrasonic modification, which can only physically destroy the starch structure, and single sodium citrate modification, which can only chemically regulate molecular effects. Neither of these can solve the starch retrogradation problem from the dual dimensions of "structural destruction-network reconstruction". The invention opens the starch particle channels through the ultrasonic cavitation effect, allowing sodium citrate ions to penetrate deeply. The two work together to destroy the starch crystal structure and reorganize the molecular network, reducing the aggregation of amylose and double helix reconstruction. This significantly reduces the starch retrogradation value and increases the disintegration value. The anti-retrogradation effect is far superior to that of single technologies, effectively inhibiting the retrogradation behavior of starch and extending the shelf life of the product.

[0020] 2. Meanwhile, given that high-power ultrasound alone can easily lead to excessive damage to the starch structure and sodium citrate alone cannot improve the physical structure of starch, this invention achieves synergistic complementarity between ultrasound and sodium citrate. Ultrasound moderately disrupts the structure while sodium citrate stabilizes the network, avoiding excessive damage or rigid network limitations. This enhances the gelatinization stability and shear resistance of the modified lotus root powder, making it suitable for complex processing scenarios.

[0021] 3. This invention addresses the shortcomings of existing technologies in simultaneously controlling multiple textural indicators. By synergistically regulating the intermolecular forces and gel network structure of starch, this invention makes the gel softer and with appropriate hardness, and a balance between elasticity and water retention, resulting in a better product texture and more reasonable moisture distribution, effectively improving the consumer experience.

[0022] 4. In addition, compared with the problems of some chemical modifications that may introduce harmful reagents and complex composite modification processes, this invention uses food-grade sodium citrate and green ultrasonic technology, which contains no toxic or harmful substances. It not only improves the modification efficiency, but also has a simple process flow (mixing and homogenizing - ultrasonication - gelatinization) and controllable parameters. It has the advantages of safety, environmental protection and controllable cost, and is easy to promote on a large scale in industry, which meets the requirements of modern food industry for green processing technology.

[0023] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0024] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0025] Figure 1 The results of scanning electron microscopy testing of the ultrasonic-modified lotus root powder sample of Test Example 2 are shown.

[0026] Figure 2 The optical microscope test results of the ultrasonic-modified lotus root powder sample of Test Example 3 are shown.

[0027] Figure 3 The results of polarized light microscopy testing of the ultrasonic-modified lotus root powder sample in Test Example 4 are shown.

[0028] Figure 4 The results of the texture test of the ultrasonic-modified lotus root powder sample in Test Example 5 are shown.

[0029] Figure 5 The diagram shows a flow chart of an ultrasonic-sodium citrate composite modification method for lotus root powder provided by the present invention. Detailed Implementation

[0030] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0031] Preparation Example

[0032] Preparation of lotus root powder: Fresh lotus root that has been washed and peeled is cut into thin slices (2-3 mm thick), spread out and dried in a 70℃ hot air drying oven for 8 hours. After drying, the slices are coarsely ground in a pulverizer and then passed through a 120-mesh sample sieve to obtain the lotus root powder.

[0033] Example 1

[0034] This embodiment provides a method for ultrasonic-sodium citrate composite modification of lotus root powder, comprising: mixing 100g of lotus root powder obtained in the preparation example with 3.6g of sodium citrate and 500g of distilled water to obtain a mixture; subjecting the mixture to ultrasonic (300W, 20min), freeze-drying (-80℃, 24h) and crushing treatments in sequence to obtain modified lotus root powder.

[0035] The differences between Examples 2-6 and Comparative Examples 1-6 and Example 1 are shown only in Table 1.

[0036] Table 1

[0037] Test Example 1: Gelatinization Performance Test

[0038] In this test example, the ultrasonically treated mixtures of the examples and comparative examples were stirred and homogenized (10000 r / min for 1 min) to obtain a homogenate. The homogenate was then heated and gelatinized (90°C for 15 min) to obtain a gelatinized sample.

[0039] The gelatinization characteristics of different examples and comparative examples were determined using a rapid viscosity analyzer. Specifically, the gelatinized samples were placed in the aluminum canister of the rapid viscosity analyzer, and the following procedures were followed: The measurement procedure was as follows: heating from 50°C to 95°C at a rate of 12°C / min, holding at 95°C for 2.5 min, and then cooling to 50°C at the same rate. Peak viscosity, valley viscosity, disintegration value, final viscosity, and recovery value were recorded.

[0040] In this invention, the retrogradation value refers to the difference between the final viscosity and the valley viscosity of the starch paste during the cooling process, as measured by a rapid viscosity analyzer. It is the core indicator characterizing the tendency of starch retrogradation; the lower the value, the less starch retrogradation. In this invention, the disintegration value refers to the difference between the peak viscosity and the valley viscosity of starch gelatinization, as measured by a rapid viscosity analyzer. It reflects the stability of starch paste under high temperature and high shear conditions. The higher the value, the stronger the ability of the starch paste to resist structural damage during processing and the better the system uniformity is maintained.

[0041] The results are shown in Table 2.

[0042] Table 2

[0043] As shown in Table 2: Comparative Example 1 is untreated whole starch, with a lower peak viscosity and a higher rebound value. This is mainly because the natural starch has an intact structure, which limits water absorption during gelatinization, and the amylose is easy to rearrange and revert after cooling. Comparative Examples 4-6 showed that as the concentration of sodium citrate increased, the disintegration value increased while the recovery value decreased. This is mainly because the ionic effect of sodium citrate disrupts the hydrogen bonds between starch molecules, promotes water absorption and swelling during gelatinization, and makes the paste more easily broken. At the same time, the increased disintegration value inhibits the re-aggregation of amylose and delays retrogradation, which is reflected in the decrease in the recovery value. Based on Comparative Examples 2 and 3, it can be seen that as the ultrasonic power increases, the disintegration value increases while the retrogradation value decreases. Sodium citrate can effectively inhibit starch retrogradation, promote starch granules to absorb water and swell, making the structure more fragile at high temperatures and resulting in a higher disintegration value; high-power ultrasound destroys the starch structure and inhibits retrogradation. In the ultrasonic-sodium citrate synergistic treatment examples (Examples 1-6), it was found that the disintegration value was significantly higher than that of the single treatment, and the recovery value was significantly lower than that of the single treatment. Among them, Example 5 had a lower recovery value, a higher disintegration value, and the paste was more easily broken, showing the best performance.

[0044] Test Example 2: Scanning Electron Microscopy Test

[0045] This test example tests the sample before gelatinization and the sample after gelatinization. The samples in this test example before gelatinization are the modified lotus root powders obtained in Examples 2 and 5 and Comparative Examples 1, 2, 3, and 5 above. The gelatinized sample of this test example was obtained by stirring and homogenizing the mixture of ultrasonically treated Examples 2 and 5 and Comparative Examples 1, 2, 3 and 5 (10000 r / min, 1 min) to obtain a homogenate. The homogenate was then heated and gelatinized (90℃, 15 min) to obtain the gelatinized sample of this test example. After being freeze-dried (-80℃, 24 h), it was then brittle in liquid nitrogen and used for this test example.

[0046] In this test case, the microstructure of the ungelatinized and gelatinized samples was observed using a scanning electron microscope (SU8600, Hitachi, Japan). Micrographs were taken at 500× magnification with an accelerating voltage of 5 kV. The surface morphology and internal gel structure of the modified lotus root powder samples under different treatment conditions were tested.

[0047] See results Figure 1 ,like Figure 1 As shown: Comparative Example 1 after gelatinization exhibits a continuous and dense gel network with a small average pore size; Sodium citrate treatment (Comparative Examples 4-6) had no significant effect on the gel network structure. This is mainly because sodium citrate interferes with intermolecular hydrogen bonds primarily through ionic effects, and has a limited impact on the macroscopic structure of the formed gel network, without significantly altering the network porosity. The gel network structure became loose after only ultrasonic treatment (Comparative Examples 2-3), and the average pore size increased with increasing ultrasonic power (the average pore size of Comparative Example 2 after gelatinization was 22.1 μm, and the average pore size of Comparative Example 3 after gelatinization was 25.9 μm). The ultrasonic-sodium citrate synergistic treatment (Examples 1-6) resulted in the most porous gel network, with a significantly increased average pore size, making water distribution easier and allowing for faster water absorption during gelatinization. This also increased the disintegration value. The "pores and cracks" created by ultrasound provided channels for the penetration of sodium citrate small molecules, enabling them to more deeply disrupt the starch network structure from the inside, resulting in a more porous structure. This effectively inhibited amylose rearrangement and reduced the recovery value.

[0048] Test Example 3: Optical Microscope Test

[0049] The test sample in this test example is the gelatinized sample from Test Example 2.

[0050] The morphology of starch granules in the test samples of this test example was analyzed using an optical microscope (ICX41). After rehydration of the freeze-dried samples treated under each condition, a small amount was taken and evenly dispersed on a glass slide. A coverslip was placed on the slide and gently pressed to remove air bubbles, ensuring a clear field of view. The objective lens was 40× and the eyepiece was 10×. The morphology, surface structure, swelling, and degree of breakage of starch granules in the modified samples under different treatment conditions were observed under the optical microscope.

[0051] See results Figure 2 ,like Figure 2 As shown: In the untreated sample Comparative Example 1, the natural starch granules were slender and oval in shape, with a smooth surface, no cracks, and an intact structure. However, after treatment with sodium citrate (Comparative Examples 4-6), the starch granules showed significant swelling, increased diameter, and surface cracks. This was attributed to sodium citrate entering the granule surface through ionic effects and osmosis, breaking some hydrogen bonds, promoting water absorption and swelling, and causing the granules to expand and the surface structure to loosen. After ultrasonic treatment (Comparative Examples 2-3), the particles broke apart, and a clear cross-sectional shadow was visible. This is because the microjets and shock waves generated by the ultrasonic cavitation effect exerted mechanical shearing and collision effects on the starch particles, directly causing particle breakage or surface damage. The particles treated with ultrasound and sodium citrate synergistically (Examples 1-6) were finer and exhibited the highest degree of fragmentation. Example 5 showed the most significant improvement, primarily because ultrasound first opened micro-cracks on the particle surface or inside, providing channels for sodium citrate penetration. Sodium citrate then penetrated deep into the particle, further disrupting the starch structure at the molecular level and promoting particle disintegration. Ultimately, the combined effect of physical fragmentation and chemical swelling resulted in a significant reduction in particle size and the most porous structure.

[0052] Test Example 4: Polarizing Microscopy Test

[0053] The test sample in this test example is the gelatinized sample from Test Example 2.

[0054] The crystal morphology of starch granules in the test samples of this example was analyzed using a polarizing microscope (CX40P). After rehydrating the freeze-dried sample, a small amount was evenly dispersed on a glass slide, covered with a coverslip and gently pressed to remove air bubbles, ensuring a clear field of view. The "Maltese cross" feature of the modified samples under different treatments was observed under a polarizing microscope (200×) to determine the integrity and order of the internal crystal structure of the starch granules.

[0055] See results Figure 3 ,like Figure 3 As shown: Comparative Example 1 shows a clear and bright Maltese cross, which is attributed to the highly ordered crystalline structure of the natural starch granules, which exhibits typical birefringence under polarized light, forming a clear Maltese cross. The brightness and clarity of the Malta Cross were slightly reduced after treatment with sodium citrate (Comparative Examples 4-6). This was attributed to the fact that sodium citrate entered the starch granules through ionic effects and osmosis, partially disrupting the intermolecular hydrogen bonds and slightly interfering with the orderly arrangement of the crystals, but not completely destroying the crystalline structure. The cavitation effect of ultrasound directly disrupts the continuity of the crystal structure of starch granules. In the ultrasound-treated group (Comparative Examples 2-3), the brightness and clarity of the Malta Cross were significantly reduced, and the degree of damage increased with increasing power. In cases of synergistic treatment with ultrasound and sodium citrate (Examples 1-6), a complete Maltese cross is almost impossible to observe in the field of view. This indicates that the "chemical softening" effect of sodium citrate and the "physical disruption" effect of ultrasound work synergistically to dismantle the crystalline order of starch at a deeper level. The inability of starch molecular chains to rearrange and recrystallize further inhibits retrogradation.

[0056] Test Example 5: Texture Test

[0057] The test sample in this test example is the gelatinized sample from Test Example 2.

[0058] The full textural analysis of the test samples in this test example was performed using a texture analyzer (TMS-Pro, FTC, USA). The test parameters were set as follows: a P10 cylindrical probe equipped with a 25N load sensing element was used; the sample was equilibrated to 25°C before testing; the testing speed was 60 mm / min, the compression set was 50%, and the trigger force was 0.05 N. The measured parameters included key textural parameters such as hardness, resilience, elasticity, and cohesion.

[0059] See results Figure 4 ,like Figure 4 As shown: Untreated (Comparative Example 1) whole powder has moderate hardness, average resilience, and low elasticity and cohesion. This is mainly because the gel network structure formed by natural starch is relatively dense but lacks toughness, and the intermolecular forces are weak, making it easy for the structure to collapse after compression. Sodium citrate treatment alone (Comparative Examples 4-6) significantly reduced resilience and enhanced cohesion. This is attributed to sodium citrate disrupting some hydrogen bonds and introducing ionic interactions, making the gel network softer yet more tightly bound and less prone to disintegration. The ultrasonic treatment group (Comparative Examples 2-3) showed improved resilience, decreased elasticity, and weakened cohesion. This was mainly because ultrasound destroyed the starch granules and network structure, forming a more porous gel that was easier to recover its shape after compression, but its structural strength decreased. The synergistic effect of ultrasound and sodium citrate (Examples 1-6) reconstructed a denser and stronger novel gel network, resulting in the highest hardness, improved resilience and elasticity, and significantly enhanced cohesion in the gelatinized sample of Example 5. This is because ultrasound moderately disrupted the original network, while sodium citrate, through hydrogen bonding and ionic interactions, reconstructed a denser and stronger novel gel network based on the broken structure. The complementary physical disruption and chemical recombination resulted in an ideal texture that combines hardness, elasticity, and cohesion.

[0060] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for ultrasonic-sodium citrate composite modification of lotus root powder, characterized in that, The modification method includes: Lotus root powder, sodium citrate, and water were mixed to obtain a mixture; the mixture was then subjected to ultrasonic, freeze-drying, and crushing processes to obtain modified lotus root powder.

2. The ultrasonic-sodium citrate composite modification method for lotus root powder according to claim 1, wherein, The method for preparing the lotus root powder includes the following steps: fresh lotus root that has been washed and peeled is cut into thin slices, dried with hot air, pulverized and sieved to obtain the lotus root powder.

3. The ultrasonic-sodium citrate composite modification method for lotus root powder according to claim 2, wherein, The sieving process involves passing the sample through a 100-140 mesh sieve.

4. The ultrasonic-sodium citrate composite modification method for lotus root powder according to claim 1, wherein, The method further includes: stirring and homogenizing the ultrasonically treated mixture to obtain a homogenate; and sequentially subjecting the homogenate to heating and gelatinizing, freeze-drying, and crushing to obtain the modified lotus root powder.

5. The ultrasonic-sodium citrate composite modification method for lotus root powder according to claim 4, wherein, The stirring and homogenizing speed is 8000-12000 r / min, and the time is 0.5-1.5 min; The heating and gelatinization process is carried out at a temperature of 85-95℃ for 10-20 minutes.

6. The ultrasonic-sodium citrate composite modification method for lotus root powder according to claim 1 or 4, wherein, The freeze-drying process is carried out at temperatures ranging from -85℃ to -75℃ for 12-36 hours.

7. The ultrasonic-sodium citrate composite modification method for lotus root powder according to claim 1 or 4, wherein, The mass ratio of lotus root powder to sodium citrate is 100:(0.6-12.2).

8. The ultrasonic-sodium citrate composite modification method for lotus root powder according to claim 1 or 4, wherein, The concentration of sodium citrate in the mixture is 0.1-2.0%.

9. The ultrasonic-sodium citrate composite modification method for lotus root powder according to claim 1 or 4, wherein, The ultrasonic treatment time is 15-25 minutes, and the power is 200-800W.

10. Modified lotus root powder obtained by the ultrasonic-sodium citrate composite modification method for lotus root powder according to any one of claims 1-9.

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