Method for improving tensile property of cassava starch gel, cassava starch gel and application of cassava starch gel

Abstract

The invention provides a method for improving the tensile property of cassava starch gel, the cassava starch gel and application of the cassava starch gel, and relates to the technical field of food material processing. The method for improving the tensile property of the cassava starch gel comprises the following steps that cassava starch and a magnesium chloride solution are mixed, steamed and cooled, the cassava starch gel is obtained, and the concentration of the magnesium chloride solution is 2.1-2.8 M. According to the invention, the structure and physicochemical properties of the obtained cassava starch gel, including gelatinization property, stretchability, thermal property, microstructure property and crystallization property, are represented, which indicates that the tensile property of the cassava starch gel prepared by the method is significantly improved, and the cassava starch gel is simple and convenient to operate, low in cost, significant in effect and safe.

Description

Technical Field

[0001] This invention belongs to the field of food material processing technology, specifically relating to a method for improving the stretchability of cassava starch gel, cassava starch gel and its applications. Background Technology

[0002] Cassava starch has advantages such as wide availability, low cost, and moderate gelatinization temperature, making it widely used in the food industry. However, due to its molecular structure, cassava starch presents significant drawbacks when preparing starch-based products requiring high tensile properties. The tensile properties of starch gels directly affect the texture of food, such as toughness, elasticity, processing adaptability (e.g., moldability, fracture resistance), and shelf stability, and are key indicators determining product quality.

[0003] Starch modification methods typically employ physical modification, enzymatic modification, and the addition of plasticizers. Physical modification is energy-intensive and costly, and for some temperature- and pressure-sensitive starch raw materials or specific formulations, it may damage the properties of other components, negatively impacting product quality stability. Enzymatic modification has stringent selection and application conditions; different types and sources of enzymes have significantly different effects on starch, and the enzyme-catalyzed reaction is slow, resulting in low production efficiency. Furthermore, enzymes are relatively expensive, limiting their application in large-scale industrial production. Some plasticizers may raise safety concerns, and long-term consumption of foods containing certain plasticizers may pose potential health risks.

[0004] In the development of various starch-based products such as noodles, vermicelli, candies, pastries, and surimi products, the stretchability of cassava starch gel is crucial to ensure good taste, elasticity, and structural stability, thereby enhancing product quality and market competitiveness. Therefore, developing a simple, low-cost, effective, and safe method to improve the stretchability of cassava starch gel has become a pressing technical problem in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a method for improving the tensile properties of cassava starch gel, cassava starch gel and its application, which significantly improves the tensile properties of cassava starch gel.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for improving the stretchability of cassava starch gel, the method comprising the following steps:

[0008] Tapioca starch and magnesium chloride solution are mixed, steamed, and cooled to obtain tapioca starch gel. The concentration of the magnesium chloride solution is 2.1-2.8 M.

[0009] Preferably, the mass-to-volume ratio of the cassava starch to the magnesium chloride solution is 2:3 (g:mL).

[0010] Preferably, the steaming is carried out at room temperature and pressure.

[0011] Preferably, the steaming time is 3 to 8 minutes.

[0012] Preferably, the cooling process involves cooling to room temperature, which is 20–25°C.

[0013] The present invention also provides a cassava starch gel prepared by the method described above.

[0014] The present invention also provides the application of the method or the cassava starch gel in the preparation of products with tensile properties.

[0015] Preferably, the product includes food.

[0016] The present invention also provides the application of magnesium chloride solution as a crosslinking agent in improving the strain and flexibility of starch-based composite materials, wherein the magnesium chloride solution is a magnesium chloride solution with a concentration of 2.1 to 2.8 M.

[0017] Preferably, the starch-based composite material is prepared by mixing cassava starch and sweet potato starch.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention provides a method for improving the stretchability of cassava starch gel by mixing magnesium chloride with cassava starch. The method is simple to operate, low in cost, effective and safe, and has good strain and stress properties. Attached Figure Description

[0020] Figure 1 The RVA curves are for cassava starch containing different MgCl2 concentrations in Example 1.

[0021] Figure 2 The storage modulus G'(A), loss modulus G'(B), and loss factor tanδ(C) of cassava starch gel under different MgCl2 concentrations in Example 1 are given.

[0022] Figure 3 The thermograms of cassava starch in Example 1 at different magnesium chloride concentrations are shown.

[0023] Figure 4 The results show the tensile properties of cassava starch gel under different magnesium chloride concentrations in Example 1.

[0024] Figure 5The XRD patterns of cassava starch at different magnesium chloride concentrations in Example 1 are shown.

[0025] Figure 6 The images show SEM images of cassava starch treated with different concentrations of magnesium chloride in Example 1.

[0026] Figure 7 The images show cross-sectional SEM images of cassava starch gels at different concentrations of MgCl2 solution in Example 1.

[0027] Figure 8 The images show the FTIR spectra of cassava starch gels at different concentrations of MgCl2 solution in Example 1.

[0028] Figure 9 The tensile stress-strain test results of the composite starch gel under different concentrations of MgCl2 solution in Example 1 are shown. Detailed Implementation

[0029] This invention provides a method for improving the stretchability of cassava starch gel, the method comprising the following steps:

[0030] Tapioca starch and magnesium chloride solution are mixed, steamed, and cooled to obtain tapioca starch gel. The concentration of the magnesium chloride solution is preferably 2.1–2.8 M, more preferably 2.1–2.5 M, and most preferably 2.1 M. Distilled water is used as the solvent for the magnesium chloride solution.

[0031] In this invention, the preferred mass-to-volume ratio of the cassava starch to the magnesium chloride solution is 2:3 (g:mL).

[0032] In this invention, when the potato starch and magnesium chloride solution are mixed evenly and then steamed, the process is carried out at room temperature and pressure. The steaming time is preferably 3 to 8 minutes, more preferably 4 minutes. During cooling, the mixture is cooled to room temperature, which is 20 to 25°C.

[0033] In this invention, high concentrations of MgCl2 solutions of 2.1M and 2.8M reduce the number of pores in the hydrogel of cassava starch. The addition of MgCl2 can give the starch gel better tensile properties. Under the condition of 2.1M concentration, the cassava starch gel has an optimal strain of 1590%.

[0034] The present invention also provides a cassava starch gel prepared by the method described above. The cassava starch gel exhibits good stretching properties.

[0035] This invention also provides the application of the method or the cassava starch gel in the preparation of products with tensile properties. The products preferably include food products, such as vermicelli, rice noodles, candies, pastries, surimi products, etc.

[0036] This invention also provides the application of magnesium chloride solution as a crosslinking agent in improving the strain and flexibility of starch-based composite materials. The starch-based composite material is preferably a composite starch gel prepared by mixing cassava starch and sweet potato starch, wherein the mass ratio of cassava starch to sweet potato starch is 9:1.

[0037] In this invention, the preparation of the composite starch gel includes mixing a mixture of cassava starch and sweet potato starch in a mass ratio of 9:1 with a magnesium chloride solution, followed by steaming and cooling to obtain the starch gel. The concentration of the magnesium chloride solution is preferably 2.1–2.8 M, more preferably 2.1–2.5 M, and most preferably 2.1 M. The solvent for the magnesium chloride solution is distilled water. The mass-to-volume ratio of the cassava starch and sweet potato starch mixture in a mass ratio of 9:1 to the magnesium chloride solution is preferably 2:3 (g:mL).

[0038] In this invention, when the potato starch and magnesium chloride solution are mixed evenly and then steamed, the process is carried out at room temperature and pressure. The steaming time is preferably 3 to 8 minutes, more preferably 4 minutes. During cooling, the mixture is cooled to room temperature, which is 20 to 25°C.

[0039] In this invention, after induction treatment with magnesium chloride salt solution, the strain and flexibility of the composite starch gel are significantly improved. The tensile strain of the gel increases from 890% (0M) to 1496% (2.1M), and the tensile stress decreases from 0.019MPa (0M) to 0.013MPa (2.1M).

[0040] In the following embodiments of the present invention, the cassava starch was purchased from Shanghai Taihua Co., Ltd., and the sweet potato starch was purchased from Shucheng Dahai Starch Co., Ltd.

[0041] In the following embodiments of the present invention, anhydrous magnesium chloride was purchased from Sinopharm Chemical Reagent Co., Ltd., anhydrous ethanol was purchased from Tianjin Fuyu Fine Chemical Co., Ltd., and other reagents were of analytical grade.

[0042] In the following embodiments of the present invention, the experimental instruments used include: a grinding mill purchased from Guangzhou Xuzhong Food Equipment Co., Ltd.; a texture analyzer (TA.XT Plus C) purchased from Stable Micro Systems, UK; a rapid viscosity analyzer (RVA-TecMaster) purchased from Xinhang Technology Co., Ltd.; a scanning electron microscope (S-3400N) purchased from Hitachi Instruments Ltd., Japan; an X-ray diffractometer (AxSD8) purchased from Bruker AXS GmbH, Germany; an interfacial rheometer (Anton Paar MCR102) purchased from Anton Paar GmbH, Austria; a Fourier transform infrared spectrometer (FTIR-8400) purchased from Shimadzu Corporation, Japan; a differential scanning calorimeter (DSC-204F1) purchased from Mettler Toledo International Trading Co., Ltd., Switzerland; a two-dimensional small-angle X-ray scattering instrument (Nano-inXider) purchased from Xenocs Ltd., France; and a vacuum freeze dryer (SCIENTZ-18N / A) purchased from Ningbo Xinzhi Biotechnology Co., Ltd.

[0043] To further illustrate the present invention, the invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the invention.

[0044] Unless otherwise specified, the experimental methods used in the following examples are conventional preparation methods; the materials and equipment used are commercially available unless otherwise specified.

[0045] Example 1

[0046] 1.1 Preparation of magnesium chloride solutions of different concentrations and magnesium chloride starch gel

[0047] 12g of cassava starch was added to 18mL of magnesium chloride solutions of different concentrations (0, 0.35, 0.7, 1.05, 2.1, and 2.8M). After mixing thoroughly, a suspension was obtained. The suspension was poured into a silicone mold (8cm × 1.8cm × 0.2cm), steamed in boiling water for 4 minutes, and then cooled to room temperature (20–25℃) before demolding to obtain magnesium chloride starch gel samples of different concentrations. The samples were named 0M, 0.35M, 0.7M, 1.05M, 2.1M, and 2.8M. Here, 0, 0.35, 0.7, 1.05, 2.1, and 2.8 represent the concentrations of magnesium chloride, and distilled water was used as the solvent to prepare the magnesium chloride solutions.

[0048] 1.2 Treatment of cassava starch with different concentrations of magnesium chloride

[0049] Following the method of Li et al. (Li Y, Liu P, Ma C, et al. Structural Disorganization and Chin Aggregation of High-Amylose Starch in Different Chloride Salt Solutions[J]. ACS Sustainable Chemistry & Engineering, 2020, 8: 4838-4847.), 3g of cassava starch was mixed with 28mL of magnesium chloride solutions of different concentrations (0, 0.35, 0.7, 1.05, 2.1, and 2.8M) (the solvent for the magnesium chloride solutions was distilled water). The mixture was vortexed at room temperature for 5min to ensure thorough mixing. Four times the volume of anhydrous ethanol was added to terminate the reaction. The mixture was centrifuged at 3000r / min for 5min, and the supernatant was removed. The precipitate was washed three times with anhydrous ethanol. The obtained starch samples were dried in an oven at 50℃ for 12h and ground into powder to obtain cassava starch treated with different concentrations of magnesium chloride.

[0050] The obtained cassava starches treated with different concentrations of magnesium chloride were further analyzed. In addition, untreated cassava starch was used as a control sample and dried in an oven at 50°C for 12 hours.

[0051] 1.3 Analysis of Gelatinization Characteristics

[0052] The gelatinization characteristics of cassava starch in different concentrations of magnesium chloride were determined using a rapid viscosity analyzer, according to the method of Xiao et al. (Xiao,W.,Shen,M.,Ren,Y.,Wen,H.,Li,J.,Rong,L.,Liu,W.,&Xie,J.(2022).Controlling the pasting, rheological, gel, and structural properties of corn starch incorporation of debride-anched waxycorn starch. Food Hydrocolloids,123,107-136.).

[0053] Different concentrations of MgCl2 (0, 0.35, 0.7, 1.05, 2.1, and 2.8 M) were mixed with cassava starch (3 g) to achieve a total mixture weight of 28 g. The resulting sample suspension was stirred uniformly at 160 rpm using a plastic propeller, heated from 50 °C to 95 °C at a rate of 12.0 °C / min, and then cooled to room temperature. Each test was repeated at least three times, and the Regression Variation (RVA) curve was recorded to obtain the peak viscosity (PV), valley viscosity (TV), final viscosity (FV), decay value (BD = PV - TV), and reversion value (SB = FV - TV).

[0054] 1.4 Dynamic Rheological Properties

[0055] The rheological properties of fresh hydrogels were determined using an interfacial rheometer, following the method described by Feng et al. (Feng Y, Wang S, Li Y, et al. Entanglement in Smart Hydrogels: Fast Response Time, Anti-Freezing and Anti-Drying[J]. Advanced Functional Materials, 2023, 33). All experimental samples were derived from starch gels prepared in section 1.1, and the resulting circular gel samples, with a diameter of 50 mm and a thickness of 2 mm, were immediately subjected to rheological measurements after cooling to room temperature. Specifically, a rheometer equipped with a PP50 probe was used for the rheological experiments. The measurements were conducted at 25℃, with a range of 0.1–100 rad·s. -1 Frequency scanning was performed within the test frequency range. A lid was placed on the sample to reduce moisture loss. The storage modulus (G') and loss modulus (G") of the hydrogel were obtained as a function of angular frequency at 1% strain.

[0056] 1.5 Thermal properties of starch in magnesium chloride solution

[0057] The method was followed according to that of Wang et al. (Wang J, Zhao X, Zhou C, et al. Effects of gellan gum and dinulin on mixed-gel properties and molecular structure of gelatin[J]. Food Science Nutrition, 2021, 9: 1336-1346.). 3 mg of dry cassava starch sample was placed in a crucible, and twice the weight of the cassava starch sample was added to MgCl2 solution (0, 0.35, 0.7, 1.05, 2.1, and 2.8 M). The crucible was covered and sealed, and the cassava starch-MgCl2 mixture was equilibrated at 25 °C for 5 min before being sealed in an aluminum tray. Under nitrogen atmosphere, the temperature was increased from 25 °C to 125 °C at a rate of 10 °C / min. The onset temperature (To), peak temperature (Tp), termination temperature (Tc), and enthalpy (ΔH) of starch gelatinization were tested and analyzed. ΔH was calculated based on the weight of the dry starch.

[0058] 1.6 Tensile properties of magnesium chloride starch gel

[0059] The stress-strain properties of starch gel were determined using the preparation method described in 1.1. The determination method is as follows:

[0060] The stress-strain characteristics of various starch gel samples were determined under the optimal cooking time. Freshly prepared magnesium chloride starch gel samples were cooked in boiling water for 2 minutes until fully cooked (completely transparent with no hard core). After cooling to room temperature, a piece of magnesium chloride starch gel (0.2 cm thick) of a certain length was cut. The tensile properties of the magnesium chloride starch gel were measured using a texture analyzer equipped with an A / TGP probe. The experimental conditions were: a speed of 3 mm / s before and after measurement, a speed of 1 mm / s during measurement, and a probe distance of 10 mm.

[0061] The stress-strain curves of magnesium chloride starch gel were obtained by repeating the experiment at least 10 times.

[0062] 1.7 XRD Crystallization Characteristics

[0063] The crystal structure of cassava starch treated with different concentrations of magnesium chloride prepared in 1.2 was determined using a wide-angle X-ray polycrystalline diffractometer (D8ADVANCE). The moisture content of the sample was balanced to above 20%. An appropriate amount of starch powder was placed in a measuring glass container, and the parameters were set to scan the sample with a scanning range of 4°-40° (20) and a step size of 0.1° to obtain the XRD images of all starch samples.

[0064] 1.8 Microstructure of starch treated with different concentrations of magnesium chloride

[0065] The microstructure of starch was observed using a scanning electron microscope. For example, the starch prepared according to 1.2 was attached to a sample stage with conductive tape, sputtered with gold three times, and then images of the powder microstructure were captured on the microscope to observe the morphological characteristics of the powder particles.

[0066] 1.9 Microstructure of magnesium chloride starch gel

[0067] The magnesium chloride starch gels of different concentrations prepared in 1.1 were cooled to room temperature, then rapidly frozen in liquid nitrogen, freeze-dried at -80℃ for 36 hours, cut to appropriate sizes, fixed on the sample stage, sputtered with gold, and then observed on an instrument.

[0068] 1.10 Fourier Transform Infrared Spectroscopy (FTIR)

[0069] FTIR determination method for starch gel samples: The concentrations of magnesium chloride starch gels prepared in 1.1 were recorded at 400-4000 cm⁻¹ using a Nicolet 6700 FTIR spectrometer. -1 Infrared spectra within the specified range. The sample was mixed with KBr (1% w / w) and pressed into a pellet. Spectra were plotted against a KBr background at 4 cm⁻¹. -1 High-resolution collection was performed, with an average of 64 scans per sample to obtain the spectrum.

[0070] 1.11 Effect of magnesium chloride on the tensile properties of composite starch gel

[0071] To further verify the strategy of salt solution induction to improve starch gelation, cassava starch and sweet potato starch were mixed in a 9:1 mass ratio and a composite starch gel was prepared according to method 1.1. The stress-strain characteristics of the composite starch gel were measured according to method 1.6.

[0072] 1.12 Data Statistical Analysis

[0073] All experiments were performed at least three times. Data are reported as mean ± standard deviation and analyzed using one-way ANOVA with SPSS V.27 software (IBM, Armonk, NY, USA). The significance of each mean at the 95% (p<0.05) level was determined according to Duncan's test range.

[0074] 2 Results and Discussion

[0075] 2.1 Gelatinization Characteristics Determination

[0076] The gelatinization characteristics of starch under MgCl2 conditions were elucidated using RVA. Figure 1 As shown in Table 1.

[0077] Table 1 Gelatinization characteristics of cassava starch at different MgCl2 concentrations

[0078] sample 0M 0.35M 0.7M 1.05M 2.1M 2.8M PV(cP) <![CDATA[4730.67±14.01 d ]]> <![CDATA[4571.33±22.81 e ]]> <![CDATA[4809.00±112.58 d ]]> <![CDATA[5183.33±138.54 c ]]> <![CDATA[6711.33±61.21 b ]]> <![CDATA[7050.00±16.97 a ]]> TV(cP) <![CDATA[2113.67±97.65 e ]]> <![CDATA[2389.00±92.00 d ]]> <![CDATA[2763.00±22.27 c ]]> <![CDATA[3238.67±112.62 b ]]> <![CDATA[4095.67±198.09 a ]]> <![CDATA[3966.50±170.41 a ]]> FV(cP) <![CDATA[3035.33±29.87 f ]]> <![CDATA[3372.33±120.87 e ]]> <![CDATA[3865.67±95.55 d ]]> <![CDATA[4413.33±67.87 c ]]> <![CDATA[5275.00±64.37 b ]]> <![CDATA[5554.00±25.46 a ]]> BV(cP) <![CDATA[2617.00±106.89 b ]]> <![CDATA[2182.33±74.38 c ]]> <![CDATA[2046.00±92.15 c ]]> <![CDATA[1944.67±54.20 c ]]> <![CDATA[2615.67±223.16 b ]]> <![CDATA[3083.50±187.38 a ]]> SV(cP) <![CDATA[921.67±74.04 c ]]> <![CDATA[983.33±76.51 bc ]]> <![CDATA[1102.67±86.75 bc ]]> <![CDATA[1174.67±64.94 b ]]> <![CDATA[1179.33±207.23 b ]]> <![CDATA[1587.50±195.87 a ]]> PT (°C) 83.95±2.81c 89.72±3.33b 92.07±1.63ab 94.47±0.78a 93.15±2.30ab 89.06±2.26c

[0079] Note: Mean ± SD indicates replication of the three experiments; values ​​with different superscript letters (af) in the same column are significantly different (p < 0.05). PV represents peak viscosity, TV represents valley viscosity, FV represents final viscosity, BV represents decay viscosity, SV represents retrogradation viscosity, and PT represents gelatinization temperature.

[0080] Depend on Figure 1 As shown in Table 1, the viscosity curves exhibited an upward trend with increasing MgCl2 concentration. The peak viscosity increased from 4730.67±14.01 cP (0M) to 7050.00±16.97 cP (2.8M), and the final viscosity increased from 3035.33±29.87 cP (0M) to 5554.00±25.46 cP (2.8M). This may be because the higher magnesium chloride concentration accelerates the breakage of starch granules during gelatinization. The final viscosity of all samples was significantly higher than that of the control. During this stage, MgCl2... 2+ Induced starch molecule aggregation ions become the dominant effect, with a large amount of Mg 2+ It interacts more directly with starch molecules to form Mg 2+ Starch complex. As the concentration increased from 0 M to 1.05 M, the gelatinization temperature increased from 83.95℃ to 94.47℃, indicating that MgCl2 increases the gelatinization temperature. Under high concentration conditions (2.1 M and 2.8 M), the gelatinization temperature decreased. This is because salt ions disrupt the starch granule structure, enhancing water absorption and swelling, leading to a lower gelatinization temperature. The increased retrogradation value during cooling indicates that MgCl2 promotes the rearrangement of starch molecules during cooling, resulting in enhanced intermolecular interactions.

[0081] 2.2 Dynamic Rheological Properties

[0082] The dynamic frequency scanning test results of the composite gel and the control cassava starch gel are as follows: Figure 2As shown, within the measurement frequency range, the storage modulus (G') is greater than the loss modulus (G”) and tanδ < 1, indicating that the starch-based hydrogel exhibits a solid state and elastic behavior. G' reflects the elastic properties of the material. G' decreases in the range of 0.35M-1.05M, indicating that low concentrations of MgCl2 cause the starch-based gel to transition from elastic to viscous. The elastic properties decrease with increasing concentration because MgCl2 disrupts the hydrogen bonds between starch molecules, leading to a looser gel network structure and affecting the structure and stability of the gel. Under low concentration conditions (0.35M), the G” value also shows a decreasing trend. When the concentration increases to (0.7-2.8M), the G” value gradually increases. The change in G” indicates that the viscous properties of the cassava starch gel first decrease (0.35M) and then increase (0.7M-2.8M) with increasing MgCl2 concentration. High concentrations of MgCl2 may increase the mobility of starch molecules, thereby reducing energy dissipation. High concentrations of MgCl2 may further weaken the interactions between starch granules, leading to a significant decrease in the elastic properties of the gel, which gradually increased in the 2.1M group. Furthermore, the dynamic modulus of the gel containing MgCl2 also increased with increasing frequency, indicating a significant frequency dependence. The addition of MgCl2 made the viscous properties of the cassava starch gel more prominent than its elastic properties; MgCl2 altered the interactions between starch molecules, causing the gel to exhibit viscous behavior. These results indicate that MgCl2 significantly affects the rheological properties of cassava starch gel, especially at high concentrations of 2.1 and 2.8M, where the elastic and viscous properties of the gel changed significantly.

[0083] 2.3 Thermal performance analysis of starch in magnesium chloride solution

[0084] The changes in the thermal properties of starch in a MgCl2 environment were studied, and the corresponding curves are shown below. Figure 3 As shown in Table 2.

[0085] Table 2 Thermal properties of cassava starch in magnesium chloride solutions of different concentrations

[0086] sample To / ℃ Tp / ℃ Tc / ℃ <![CDATA[ΔH / Jg -1 ]]> 0M <![CDATA[65.71±0.41 c ]]> <![CDATA[70.34±0.47 d ]]> <![CDATA[80.14±0.26 d ]]> <![CDATA[12.65±1.34 a ]]> 0.35M <![CDATA[74.73±0.43 b ]]> <![CDATA[79.25±0.11 c ]]> <![CDATA[89.15±0.09 c ]]> <![CDATA[10.69±0.38 ab ]]> 0.7M <![CDATA[78.73±0.07 a ]]> <![CDATA[83.67±0.00 b ]]> <![CDATA[94.19±0.32 ab ]]> <![CDATA[10.35±0.50 bc ]]> 1.05M <![CDATA[79.34±0.28 a ]]> <![CDATA[83.75±0.11 b ]]> <![CDATA[92.94±0.53 b ]]> <![CDATA[9.28±0.68 c ]]> 2.1M <![CDATA[79.55±0.01 a ]]> <![CDATA[80.28±0.12 a ]]> <![CDATA[90.27±1.01 a ]]> <![CDATA[4.49±0.40 d ]]> 2.8M - - - -

[0087] Note: Mean ± SD indicates replication of three experiments; values ​​with different superscript letters (ad) in the same column are significantly different (p < 0.05).

[0088] according to Figure 3 As shown in Table 2, starch typically requires high-temperature heating to disrupt its crystal structure. The To, Tp, Tc, and ΔH values ​​of natural cassava starch are 65.71℃, 70.34℃, 80.14℃, and 12.65 J·g, respectively. -1Compared to 0 M, cassava starch treated with MgCl2 at a concentration of 0.35 M exhibited higher To, Tp, and Tc, but ΔH gradually decreased, and the initial gelatinization temperature gradually increased with increasing concentration. When MgCl2 exceeded 0.7 M, Mg... 2+ The interaction between ions and starch dominates, accelerating the disruption of existing hydrogen bond structures in starch granules, leading to a decrease in ΔH. With further increases in MgCl2 concentration, the size of To increases significantly, while Tp and Tc gradually increase and then decrease. This is attributed to Mg... 2+ and Cl - Ions alter the structure of water in low-concentration MgCl2 solutions, leading to a decrease in the proportion of free water and reducing diffusion into starch granules, thereby stabilizing the starch granules. Furthermore, the enthalpy of starch gradually decreases with increasing MgCl2 content; when the MgCl2 concentration reaches 2.8 M, the ΔH value drops from 22.28 J / g (0 M) to 0 J / g (2.8 M). This indicates that high MgCl2 concentrations cause starch to completely lose its crystalline structure without heating, thus gelatinizing the starch at lower temperatures.

[0089] 2.4 Tensile properties of magnesium chloride starch gel

[0090] The stress-strain curves of cassava starch gel at different magnesium chloride concentrations are shown below. Figure 4 As shown, the control pure cassava starch gel exhibited excellent tensile properties, with a strain of 1290% and a stress of 0.015 MPa. Starch gels with low MgCl2 concentrations (0.35-1.05 M) showed a significant increase in stress, ranging from 0.015 to 0.02 MPa. Higher MgCl2 concentrations (2.1 M) resulted in a significant decrease in tensile strength, reaching only 0.0125 MPa with a strain of 1550%. Starch hydrogels with added MgCl2 exhibited higher elongation at break, with a maximum strain of 1550% at 2.1 M, significantly higher than the control (0 M). The stress in gels with high magnesium chloride concentrations (0.35-2.8 M) initially increased and then gradually decreased with increasing elongation, while the stress in low-concentration (0-1.05 M) gels increased with increasing elongation. In summary, adding 0.35M MgCl2 to cassava starch gel can achieve a high stress of 0.018MPa while maintaining a tensile strength of 1550%, and the magnesium ions (MgCl2) contribute to this effect. 2+ The coordination bonds formed between MgCl2 and the hydroxyl groups (-OH) in starch molecules promote intermolecular cross-linking, contributing to the construction of a dense and stable network structure. Adding a high concentration of 2.1M MgCl2 resulted in an optimal strain of 1590% while maintaining a low stress of 0.013 MPa. The tensile behavior is attributed to the breaking of hydrogen bonds and the formation of amorphous MgCl2 chains, leading to slippage between starch chains. This excellent mechanical property greatly expands the potential applications of starch hydrogels.

[0091] 2.5 Crystalline structure of starch treated with different concentrations of magnesium chloride

[0092] The long-range crystal structure of starch treated with MgCl2 solution was analyzed using XRD. The crystallinity of starch granules was analyzed, and starch was isolated from the solution and its structure was characterized. Figure 5 As shown, the peak positions remained unchanged after treatment with different concentrations of MgCl2, indicating that MgCl2 does not alter the basic crystal structure of cassava starch. The control cassava starch exhibited strong crystallization peaks, with A-type crystallization peaks at 15°, 17°, 18°, and 23°. When the MgCl2 concentration ranged from 0.35M to 0.7M, the crystallinity changed slightly. As the concentration gradually increased to 2.8M, the diffraction pattern showed that the crystallization area began to decrease, and the diffraction peak intensity significantly weakened, indicating a gradual decrease in starch crystallinity. This decrease in crystallinity is due to the addition of MgCl2 reducing the ordered arrangement between starch molecules, disrupting the hydrogen bonds between starch molecules, altering the ordered arrangement between starch molecules, reducing the orderedness of the crystal structure, lowering the peak values, and gradually weakening the crystal structure, thus destroying the ordered structure. The decrease in crystallinity means that the crystalline regions are destroyed, and the amorphous regions (non-crystalline regions) increase.

[0093] 2.6 Determination of starch microstructure

[0094] Scanning electron microscopy (SEM) was used to further verify the structural changes of starch granules in MgCl2 solution, observing the microstructure of natural cassava starch and starch samples treated with MgCl2. Figure 6 As shown, untreated cassava starch (0M) samples all exhibited spherical or semi-spherical structures of varying sizes with smooth surfaces. At lower MgCl2 concentrations (0.35M), the starch granules developed pores and deformed, but retained their intact granular structure. At MgCl2 concentrations (0.7M), fine cracks appeared on the surface of the starch granules, meaning that most starch granules showed numerous cracks. The cracks were more pronounced at 1.05M, wrinkling appeared on the surface of the starch granules at 2.1M, and the starch granules broke at 2.8M. The hard outer layer of the starch granules behaved like MgCl2. 2+ and Cl - The semi-permeable membrane of ions restricts the entry of low-concentration ions. When the MgCl2 concentration reaches 2.1M, the particle structure exhibits varying degrees of structural collapse. The disintegration of the outer layer of starch requires a higher ion concentration. For starch in MgCl2 solution at a concentration of 2.8M, almost no intact particle shape is visible, indicating complete structural disintegration. Unlike gelatinization induced by heating or high pressure, gelatinization occurs under these conditions without heating.

[0095] 2.7 Microstructural characteristics of gels

[0096] To investigate the differences in the effects of different concentrations of MgCl2 on improving the mechanical properties of cassava starch gel, such as... Figure 7 Cross-sectional SEM images of all cassava starch gel samples are shown. The cross-section of the control cassava starch gel shows a honeycomb-like pore structure with relatively uniformly arranged pores. The pores are small and evenly distributed, and the significant microstructural feature of starch gels is generally a porous structure. When the concentration increases to 0.35 M, the gel pore structure becomes more obvious, the pore size increases, and the pore walls thicken, while still maintaining a certain degree of uniformity. This is due to the interaction between salt ions in MgCl2 and starch molecules, and the presence of Mg ions in the salt solution. 2+ and Cl - This is related to electrostatic interactions with charged groups (such as hydroxyl groups) on starch molecules. Compared to pure starch hydrogels, 0.7M gels exhibit thicker pore walls, larger pore sizes, more uniform pore distribution, and a dendritic structure in some areas. This effect reduces the distance between starch molecular chains, promoting the formation of a gel network and resulting in a denser gel structure. When the MgCl2 concentration increases to 1.05M, the network structure changes significantly; the gel loses its obvious honeycomb-like pore structure, the number of pores inside the hydrogel is greatly reduced, and the structure becomes even denser. When the MgCl2 concentration increases to 2.1M and 2.8M, a small number of pores appear, and smooth planes emerge. This result can be attributed to the interaction between starch and MgCl2. 2+ A strong hydrogel network structure is formed between the aggregates. At high concentrations, the tendency for aggregation and the high melt viscosity of the polymer promote starch aggregation. This aggregation occupies a large amount of space, leading to a reduction in the number of pores. The formation of this structure is related to the strong cross-linking that occurs under higher concentration conditions, under which the starch gel structure exhibits high density. This indicates that different MgCl2 concentrations can alter the morphology and microstructure of cassava starch hydrogels.

[0097] 2.8 Short-range ordered structure of starch gel

[0098] FTIR spectra of cassava starch gel at different concentrations of MgCl2 solution are as follows: Figure 8 As shown, the study investigated changes in the starch molecular structure. No new absorption bands appeared after MgCl2 treatment; only changes in the intensity of some absorption peaks were observed, indicating that the interaction between MgCl2 and starch is a physical interaction, not a chemical reaction. With increasing MgCl2 concentration, starch showed changes in intensity at 1200-800 cm⁻¹. -1 The absorption peak intensity at this location significantly decreased after processing, and this region was more sensitive to short-range structural changes in the CC and CO stretching regions, indicating that increased MgCl2 concentration reduced the ordered structure of the region, which is consistent with the trend of XRD crystal structure changes. The CO stretching vibration peak may shift or change in intensity due to enhanced intermolecular interactions. (1500-1750 cm⁻¹) -1The peak intensity changed significantly, and Mg was formed in the cassava starch gel. 2+ The starch complex underwent cross-linking. This is likely because the addition of MgCl2 disrupts the existing hydrogen bond network, forming new hydrogen bonds, which is most pronounced in the OH stretching vibration region. This is particularly evident in the 3700-3000 cm⁻¹ region. -1 A broad absorption band was detected, which is related to the stretching vibration of the OH bond, indicating an enhancement of hydrogen bonding interactions in the system. The addition of MgCl2 reduces the formation of intramolecular and intermolecular hydrogen bonds between starch chains, disrupting the original hydrogen bond network and inhibiting the formation of an ordered structure. The hydroxyl groups in the MgCl2 starch molecule interact, and this disruptive effect becomes more significant with increasing concentration, resulting in a marked change in the OH stretching vibration peak. This may be due to the disruption of more hydrogen bonds or the formation of new hydrogen bonds, affecting the formation of the ordered structure of starch.

[0099] 2.9 Effect of magnesium chloride on the tensile properties of composite starch gel

[0100] To verify the universality of magnesium chloride salt solution-induced treatment in improving the tensile properties of starch gels and enhancing the mechanical properties of composite starch gels, this study further investigated the effect of magnesium chloride concentration on the tensile stress-strain of a composite starch gel made from cassava starch and sweet potato starch in a 9:1 ratio. Figure 9 The tensile strain of the gel increased from 890% (0M) to 1496% (2.1M), while the tensile stress decreased from 0.019 MPa (0M) to 0.013 MPa (2.1M). These results indicate that the strain and flexibility of the composite starch gel were significantly improved after treatment with magnesium chloride salt solution. This finding is of great significance for broadening the application of starch gels in food, biological, and packaging materials.

[0101] This study investigated the effects of MgCl2 salt solution on starch and starch gel properties. Different concentrations of salt ions can disrupt the crystal structure of starch granules, and magnesium chloride can alter the structure of starch gel, enabling cross-linking of starch molecular chains. The effects of different concentrations of MgCl2 on starch gelatinization and retrogradation were systematically studied. The results showed that MgCl2 treatment of cassava starch led to an increase in gelatinization temperature and a decrease in enthalpy. SEM microscopic results indicated the appearance of cracks in starch granules with increasing MgCl2 concentration. Subsequently, starch-based hydrogels were prepared, and their structure and physicochemical properties, including gelatinization characteristics, stretchability, thermal properties, microstructure, and crystallinity, were characterized. The microstructure of cassava starch hydrogels treated with MgCl2 solution was observed using scanning electron microscopy. The results showed that low concentrations (0.35M, 0.7M) of MgCl2 solution caused the hydrogel to absorb water and swell, resulting in larger pores and thicker pore walls. High concentrations (2.1M and 2.8M) of MgCl2 solution reduced the number of pores in the hydrogel. The addition of MgCl2 imparted better tensile properties to the starch gel, and the 2.1M concentration resulted in an optimal strain of 1590%. Magnesium ions (MgCl2) were also present. 2+ The coordination bonds formed between MgCl2 and the hydroxyl groups (-OH) in starch molecules can promote intermolecular cross-linking, thereby improving the mechanical strength of the material. 0.35M MgCl2 can exhibit a high stress of 0.018 MPa while also possessing a tensile strength of 1550%. Furthermore, the chloride ions (Cl-) in the MgCl2 solution... - Magnesium chloride (MgCl2) helps to construct a dense and stable network structure by inhibiting the charge repulsion between starch molecules, thereby enhancing the mechanical properties of starch-based materials. Magnesium chloride also shows significant improvement effects on pure cassava starch and compounded cassava starch (90% sweet potato starch, 10% added) starch gels. Therefore, MgCl2 solution, as an effective crosslinking agent, demonstrates significant application potential in the modification of starch-based composite materials.

[0102] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for improving the stretchability of cassava starch gel, characterized in that, The method includes the following steps: Tapioca starch and magnesium chloride solution are mixed, steamed, and cooled to obtain tapioca starch gel. The concentration of the magnesium chloride solution is 2.1-2.8 M.

2. The method according to claim 1, characterized in that, The mass-to-volume ratio of the cassava starch to the magnesium chloride solution is 2:3 (g:mL).

3. The method according to claim 1, characterized in that, Steaming is carried out at room temperature and pressure.

4. The method according to claim 1, characterized in that, Steaming time is 3 to 8 minutes.

5. The method according to claim 1, characterized in that, During cooling, the material is cooled to room temperature, which is 20–25°C.

6. Cassava starch gel prepared by any one of claims 1 to 5.

7. The application of the method according to any one of claims 1 to 5 or the cassava starch gel according to claim 6 in the preparation of products with tensile properties.

8. The application according to claim 7, characterized in that, The products include food.

9. The application of magnesium chloride solution as a crosslinking agent in improving the strain and flexibility of starch-based composite materials, characterized in that, The magnesium chloride solution is the magnesium chloride solution of claim 1.

10. The application according to claim 9, characterized in that, The starch-based composite material is prepared by mixing cassava starch and sweet potato starch.

Images