Microwave synergistic hydrophilic colloid modified low-digestibility corn flour and preparation method thereof

Abstract

The invention discloses microwave synergistic hydrophilic colloid modified low-digestibility corn flour and a preparation method thereof, and belongs to the technical field of grain deep processing. The method solves the problems that the corn flour is poor in digestion resistance, the single microwave treatment effect is limited, excessive starch gelatinization is easily caused, the traditional modification technology is high in cost, not environmentally friendly, harsh in condition and unstable in modification effect, and digestion characteristics and application quality are difficult to consider after modification. The corn flour is used as a raw material, the digestion characteristic of the corn flour is regulated and controlled through cooperation of the hydrophilic colloid and the microwave treatment, the corn flour is used for the corn dough, the microwave and the hydrophilic colloid can improve the SDS content and the RS content of starch in the corn flour, and meanwhile the processing quality of the corn dough is improved; the water absorption rate and the freeze-thaw stability of the dough are improved, and the cooking loss rate is reduced. The preparation process is green and environment-friendly, no chemical reagent residues exist, the modification effect is stable and controllable, and the prepared low-digestibility corn flour has a wide application prospect as a functional food raw material.

Description

Technical Field

[0001] This invention belongs to the field of deep grain processing technology, specifically relating to microwave-assisted hydrophilic colloid modification of low-digestibility corn flour and its preparation method. Background Technology

[0002] With the high incidence of metabolic diseases such as obesity and diabetes, the development of low-digestibility foods has become a key research focus in the field of food science. Corn, as one of the world's three major food crops, has a starch content of about 70% in corn flour. However, natural corn flour has a high proportion of rapidly digestible starch (RDS) and a low content of slowly digestible starch (SDS) and resistant starch (RS), making it difficult to meet the specific raw material requirements of current functional foods. To effectively improve the digestibility of corn flour, researchers have developed various techniques, including physical modification, chemical modification, biological modification, and composite modification.

[0003] However, current corn flour modification technologies still have many shortcomings, with the limitations of single modification technologies being particularly prominent. For example, microwave treatment has a limited effect on increasing the SDS and RS content in corn flour starch, and prolonged treatment can easily lead to excessive gelatinization of the corn flour, damaging the product's texture and quality. Existing composite modification technologies also have significant drawbacks. For instance, some processes in physical-physical composite modification technologies, such as wet heat treatment, are time-consuming and energy-intensive. Physical-chemical composite modification technologies introduce chemical reagents, posing a risk of residue, requiring strict control of reagent dosage and reaction conditions. Some chemical reagents are expensive, increasing production costs. The process steps are relatively complex, placing more stringent requirements on equipment and operations. Physical-biological composite modification technologies involve expensive enzyme preparations and strains, and have stringent requirements for reaction temperature, pH, and other conditions. Biological reaction cycles are long, resulting in low processing efficiency and making them difficult to adapt to high-speed industrial production. The modification effect is easily affected by enzyme activity and strain vigor, resulting in insufficient stability. Currently, most modifications to corn flour focus on the methods listed above (single modification, physical-physical modification, physical-chemical modification, and physical-biological modification). Although these modification techniques have a certain effect on increasing the SDS and RS content in corn flour starch, this invention provides an environmentally friendly, low-energy-consumption, and simple process modification technique that has a better effect on increasing the SDS and RS content in corn flour compared to single modification techniques. It also improves the digestibility of corn flour while enhancing its processing applicability. Summary of the Invention

[0004] This invention addresses the problems of high RDS content, low SDS and RS content in existing corn flour starch, limited improvement effect of single microwave treatment on SDS and RS content and easy to cause excessive starch gelatinization, and the high energy consumption, chemical residue risk, high cost, harsh reaction conditions, unstable modification effect, poor processing applicability of modified corn flour and difficulty in balancing digestibility and actual application quality. It provides microwave-assisted hydrophilic colloid modification of low digestibility corn flour and its preparation method.

[0005] The technical solution of the present invention is as follows: One of the objectives of this invention is to provide a method for preparing low-digestibility corn flour modified by microwave synergistic hydrophilic colloid. The preparation method is as follows: the hydrophilic colloid is mixed evenly with corn flour, the moisture content of the mixture is adjusted, and then the moisture is balanced at 4 °C to obtain a corn flour-hydrophilic colloid mixture. The corn flour-hydrophilic colloid mixture is microwave-treated, dried, ground, and sieved to obtain low-digestibility corn flour.

[0006] Preferably, the hydrophilic colloid is konjac colloid, guar colloid, or arabinocolloid.

[0007] Preferably, the hydrophilic colloid is 2-6 wt% of corn flour, preferably 6 wt%.

[0008] Preferably, the moisture content is 10-40%, more preferably 20%.

[0009] Preferably, the equilibration time is 0-24 h, more preferably 12 h.

[0010] Preferably, the microwave processing power is 100-800 W and the time is 1-5 min, more preferably the power is 400 W and the time is 2 min.

[0011] Preferably, the drying temperature is 30-60 °C and the drying time is 12-48 h, more preferably 45 °C and 48 h.

[0012] The second objective of this invention is to provide a low-digestibility corn flour modified by microwave synergistic hydrophilic colloids obtained by the above preparation method.

[0013] Preferably, the starch in low-digestible corn flour contains ≤50% rapidly digestible starch (RDS), ≥27% slowly digestible starch (SDS), and ≥23% resistant starch (RS).

[0014] A third objective of this invention is to provide the application of the above-mentioned microwave-assisted hydrophilic colloid modified low-digestibility corn flour in the preparation of corn dough.

[0015] The beneficial effects of this invention are as follows: This invention provides a highly efficient, green, and controllable method for preparing low-digestibility corn flour using microwave-assisted hydrophilic colloids. Using corn flour as the raw material, hydrophilic colloids such as konjac gum, guar gum, or gum arabic are compounded. Through the synergistic effect of microwaves and hydrophilic colloids, the digestibility and physicochemical properties of corn flour are regulated. This significantly increases the content of SDS and RS in the starch of corn flour while reducing the content of RDS, achieving precise control over the digestibility of corn flour and effectively reducing its digestibility. Simultaneously, the hydration, gelatinization, thermal stability, rheological properties, and textural properties of the corn flour are optimized, ensuring the processing applicability of the product while reducing digestibility. This invention also applies the modified corn flour to corn dough products, improving the cooking characteristics, rheological properties, textural properties, and freeze-thaw stability of the dough products. Compared with existing technologies, this invention also has the following advantages: (1) Corn starch is an important component of corn flour. This invention significantly increases the content of SDS and resistant starch (RS) in corn starch through the synergistic effect of hydrocolloids and microwaves. Specifically, microwave-assisted guar gum treatment increases the RS content in corn starch to 32.18%, which is more than twice that of natural corn flour, while reducing the RDS content to 39.53%. Therefore, this invention can provide high-quality low-GI (glycemic index) food ingredients for special populations such as diabetics and obese individuals, expanding the application scope of corn flour in the field of functional foods.

[0016] (2) The microwave-assisted hydrophilic colloid of this invention not only improves the physicochemical properties of corn flour, but also significantly optimizes the cooking characteristics, textural properties, and freeze-thaw stability of corn dough when applied to it. Regarding cooking characteristics, compared to corn dough treated with microwave alone, the corn dough treated with the hydrophilic colloid of this invention exhibits a maximum water absorption rate of 73.26% and a minimum cooking loss rate of 6.48%, effectively solving the problems of corn dough easily becoming cloudy and having a loose structure during cooking. Regarding textural and rheological properties, the dough prepared from corn flour treated with microwave and with added guar gum has a hardness of 929.94 g and a significantly increased storage modulus, enhancing the dough's resistance to deformation and chewiness, and improving the defects of corn dough without corn flour, such as being brittle and crumbling. Regarding freeze-thaw stability, the addition of the hydrophilic colloid effectively reduces the water loss and separation rate during the freeze-thaw process, enhancing the freeze-thaw stability of the dough and improving the quality stability of the corn dough during cold chain storage and transportation.

[0017] (3) The present invention adopts a green process of physical modification and natural hydrophilic colloid compounding, with no chemical reagent residue, and the modification effect is stable and controllable. It solves the problem of limited effect and poor product quality of single modification technology. The low digestibility corn flour prepared has broad application prospects as a functional food raw material in the fields of low GI food and gluten-free food.

[0018] (4) This invention can regulate the physicochemical properties of corn flour by selecting different types of hydrocolloids according to food processing needs. When konjac gum or guar gum is selected, the peak viscosity, storage modulus and hardness of corn flour can be improved, enhancing the gel strength and structural stability of the system, and meeting the processing requirements of raw materials for gel foods, meat products and other products. When gum arabic is selected, the gelatinized viscosity and textural hardness of corn flour can be reduced, improving the fluidity of the system, and making it suitable for processing products such as sauces and baking batters. At the same time, microwave-assisted hydrocolloid treatment can improve the thermal stability of corn flour, with the gelatinization initiation temperature increasing to a maximum of 65.19 ℃, enhancing the structural stability of corn flour during high-temperature processing. Attached Figure Description

[0019] Figure 1 Gelatinization curves of natural corn flour, corn flour from Examples 1-3, and corn flour from Comparative Examples 1-4; Figure 2 Dynamic rheological parameter curves for natural corn flour, corn flour from Examples 1-3, and corn flour from Comparative Examples 1-4; Figure 3 The results show the solubility and swelling power of natural corn flour, corn flour from Examples 1-3, and Comparative Examples 1-4. Figure 4 The dynamic rheological parameter curves are shown for corn dough prepared using natural corn flour, corn flour from Examples 1-3 and Comparative Examples 1-4. (A) represents the storage modulus (G'), and (B) represents the loss modulus (G''). Figure 5 The water loss rate and water separation rate of corn dough prepared using natural corn flour, corn flour from Examples 1-3 and Comparative Examples 1-4, after freeze-thaw cycles. Detailed Implementation

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0021] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0022] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0023] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0024] In the following examples, konjac gum is abbreviated as KGM, guar gum as GG, and gum arabic as GA.

[0025] Example 1 Natural corn flour was dried, and hydrophilic konjac gum powder (Shanghai Aladdin Biochemical Technology Co., Ltd., K303576) was mixed evenly with corn flour at 6% of the corn flour mass (dry basis). The moisture content of the mixture was adjusted to 20%, and the moisture was equilibrated at 4 ℃ for 12 h to obtain a corn flour-hydrophilic colloid mixture. The mixture was placed in a glass petri dish and heated in a microwave oven at 400W for 2 min. After microwave treatment, it was dried in an oven at 45 ℃ for 48 h. The dried sample was ground and passed through a 100-mesh sieve to obtain low-digestibility corn flour with synergistic microwave treatment of hydrophilic colloid, denoted as M-KGM-CF.

[0026] Example 2 The difference between this embodiment and Example 1 is that the hydrophilic colloid is guar gum (Shanghai Aladdin Biochemical Technology Co., Ltd., G109238), while the rest of the process operations and parameter settings are the same as in Example 1. The resulting low-digestibility corn flour is denoted as M-GG-CF.

[0027] Example 3 The difference between this embodiment and Example 1 is that the hydrophilic colloid is gum arabic (Shanghai Aladdin Biochemical Technology Co., Ltd., A108976), while the rest of the process operations and parameter settings are the same as in Example 1. The resulting low-digestibility corn flour is denoted as M-GA-CF.

[0028] Comparative Example 1 The difference between this comparative example and Example 1 is that no hydrophilic colloid was added, but the remaining process operations and parameter settings are the same as in Example 1. The microwave-treated corn flour obtained is denoted as MCF.

[0029] Comparative Example 2 The difference between this comparative example and Example 1 is that no microwave treatment was performed, and the corn flour-hydrophilic colloid mixture was directly dried. The remaining process operations and parameter settings were the same as in Example 1. The resulting konjac gum-treated corn flour was denoted as KGM-CF.

[0030] Comparative Example 3 The difference between this comparative example and Example 2 is that no microwave treatment was performed, and the corn flour-hydrophilic colloid mixture was directly dried. The remaining process operations and parameter settings were the same as in Example 1. The guar gum-treated corn flour obtained was denoted as GG-CF.

[0031] Comparative Example 4 The difference between this comparative example and Example 3 is that no microwave treatment was performed, and the corn flour-hydrophilic colloid mixture was directly dried. The remaining process operations and parameter settings were the same as in Example 1. The resulting gum arabic-treated corn flour was denoted as GA-CF.

[0032] Performance testing (I) Characterization of corn flour treated with hydrophilic colloids in a synergistic microwave process 1. Determination of the gelatinization characteristics of corn flour treated with hydrophilic colloids via microwave. The gelatinization characteristics of corn flour were determined using a rapid viscosity analyzer (RVA): 2 g of corn flour sample was added to an RVA test aluminum can, and 25 mL of distilled water was added to ensure uniform mixing before starting the test.

[0033] The gelatinization characteristics of corn flour are a key factor determining the sensory quality of the product, and also have a decisive impact on the choice of production process and the stability of the product during storage. The gelatinization curves of natural corn flour (CF), corn flour from Examples 1-3, and Comparative Examples 1-4 are shown below. Figure 1 As shown, the gelatinization characteristic parameters are shown in Table 1.

[0034] Table 1. Gelatinization characteristics of natural corn flour, corn flour from Examples 1-3, and corn flour from Comparative Examples 1-4

[0035] Note: The values ​​in the table are mean ± standard deviation. Different letters in the same column of each table indicate significant differences. p <0.05.

[0036] from Figure 1As shown in Table 1, comparing natural corn flour with microwave-treated corn flour, microwave treatment significantly altered the gelatinization characteristics of the corn flour. The peak viscosity, trough viscosity, and final viscosity of MCF were all lower than those of CF. This is because the crystalline regions of some starch granules were slightly damaged, resulting in impaired water absorption and swelling capacity during the initial heating phase of RVA, preventing the formation of a peak viscosity as high as that of untreated granules. Compared to natural corn flour and microwave-treated corn flour, the addition of KGM and GG in the co-treatment of both led to an increase in the peak viscosity, trough viscosity, and final viscosity of the corn flour. This is because KGM and GG are highly efficient thickeners; they rapidly hydrate and form a high-viscosity solution during the initial heating phase. This viscosity, combined with the viscosity generated during subsequent corn flour gelatinization, results in an extremely high apparent viscosity value. KGM and GG have strong hydrophilicity; during the initial heating phase, they hydrate with free water molecules in the system, thus limiting the amount of water available for swelling and gelatinization of the starch granules in the corn flour. This increases the gelatinization viscosity of the corn flour. The high viscosity of starch paste effectively limits the site of action and diffusion rate of amylase, leading to an increase in RS content. Compared with KGM and GG, GA is a polysaccharide with a relatively low molecular weight and highly branched structure, and its thickening ability is far less than that of linear colloids. The addition of GA reduces the peak viscosity, valley viscosity, and final viscosity of the system. This indicates that GA has a weak competitive hydration ability; instead, it acts more like a filler and stabilizer. During gelatinization, GA molecules can fill the starch gel network, playing a certain stabilizing role. This is reflected in its lower disintegration value (BD) compared to natural corn flour, indicating that the thermal stability of M-GA-CF has been improved to some extent.

[0037] 2. Determination of rheological properties of corn flour treated with hydrophilic colloids in conjunction with microwave treatment After RVA testing, the samples were transferred to the rheometer platform and allowed to stand at 25 °C for 1 min before testing. A 40 mm aluminum plate was used for testing, with a plate spacing of 1 mm. The shear rate for the static rheological experiments was set to 0.01–100 s⁻¹. -1 Furthermore, at 25 °C, with 1-100 rads -1 Dynamic scanning was performed using the angular frequency of the sample. The storage modulus (G'), loss modulus (G"), and loss factor (tan δ) of the sample were measured.

[0038] The rheological behavior of corn flour in water is mainly determined by the swelling and interaction of starch granules, as well as the properties of the continuous phase. This invention employs a dynamic rheological method, using frequency scanning tests, to investigate the effects of microwave treatment and different types of hydrophilic colloids (konjac gum, guar gum, and gum arabic) on the storage modulus (G') and loss modulus (G'') of corn flour. The test results are as follows: Figure 2As shown, it can be seen that all samples exhibited weak gelation behavior in the angular frequency range (0.1-100 rad / s) during the frequency scanning test after gelatinization. Specifically, the storage modulus (G') was consistently higher than the loss modulus (G'') throughout the entire frequency range, and both showed a certain degree of frequency dependence. Figure 2 As shown, the rheological parameters of different sample groups exhibit significant differences. Compared with natural corn flour, the systems with microwave treatment and synergistic addition of konjac gum or guar gum showed increased G' and G'' values, while the systems with added gum arabic showed a significant decreasing trend in G' and G'' values. This is because konjac gum and guar gum, with their high molecular weight and linear chain structure, greatly enhance the gel strength and elasticity of the system by forming a strong self-network and synergistically working with starch granules. Conversely, gum arabic, due to its highly branched globular molecular conformation, weakens the continuity and strength of the starch network through steric hindrance and plasticizing effects, making the system softer and more fluid. Therefore, when a strong supporting structure is needed for corn flour-based food systems to improve viscosity and gel strength, linear colloids such as KGM and GG should be selected; while when the goal is to reduce system hardness or improve fluidity, the compact gum arabic can be chosen.

[0039] 3. Determination of the gel texture properties of corn flour treated with hydrophilic colloids in conjunction with microwave treatment The RVA-tested samples were stored at 4 °C for 24 h, and their gel texture properties were determined using a physical property analyzer. Measurement conditions: P / 0.5 probe was used; pre-test velocity was 1.0 mm / s; test velocity was 1.0 mm / s; post-test velocity was 1.0 mm / s; trigger force was 5.0 g; and compression was 50%.

[0040] Texture is a key macroscopic attribute that determines the final quality of starch-based foods. This study investigated the effects of microwave treatment and the addition of different hydrophilic colloids on the texture of cornstarch gel systems by measuring multiple parameters, including hardness, elasticity, cohesiveness, viscosity, and chewiness. The texture test results for each sample group are shown in Table 2.

[0041] Table 2. Texture properties of natural corn flour, corn flour from Examples 1-3, and corn flour from Comparative Examples 1-4

[0042] Note: The values ​​in the table are mean ± standard deviation. Different letters in the same column of each table indicate significant differences. p <0.05.

[0043] As can be seen from the data in Table 2, microwave treatment, as well as the type and addition of hydrocolloids, all had a significant impact on all textural parameters of corn starch gel. p<0.05). Comparing CF and MCF, microwave treatment reduced the hardness, elasticity, cohesiveness, viscosity, and chewiness of corn flour gels. This indicates that microwave heating and non-thermal effects damage the starch granules in corn flour, disrupting some of their crystalline structure and reducing particle integrity. During subsequent gelatinization and cooling, the gel network structure formed by these damaged starch granules is more porous. Compared to the control group CF, the corn flour gel treated with microwaves and synergistically with the addition of KGM or GG showed increased all textural parameters, improved elasticity and cohesiveness, and enhanced internal binding force, allowing the gel to better maintain structural integrity after the first compression, thus significantly improving cohesiveness. Simultaneously, this network endowed the gel with excellent deformation recovery ability, manifested as an increase in elasticity, which is of great significance for improving the fragility and poor texture of corn flour gel foods. Compared to CF, the samples GA-CF and M-GA-CF with added gum arabic exhibited reduced hardness, elasticity, cohesiveness, and viscosity. This indicates that the highly branched and compact spherical molecular conformation of gum arabic makes it difficult for it to form an effective network, hindering the recrystallization of amylose and the effective entanglement of molecular chains during cooling, thus reducing hardness, elasticity, cohesiveness, and viscosity.

[0044] 4. Determination of thermal stability of corn flour treated with hydrophilic colloids via microwave The thermodynamic properties of the samples were determined using differential scanning calorimetry (DSC). 3 ± 0.5 mg of sample was weighed into a crucible, and deionized water was added at a ratio of sample to deionized water of 1:3 (w / w, on a dry basis). The mixture was then allowed to equilibrate at room temperature for 24 h. The DSC test conditions were as follows: an empty crucible served as a blank control; the temperature range was 30–120 °C; and the heating rate was 10 °C / min.

[0045] Determine the initial gelatinization temperature (T) during the gelatinization process. o Peak gelatinization temperature (T) p Termination gelatinization temperature (T) c Thermodynamic parameters (ΔH) and gelatinization enthalpy (ΔH) can be used to assess the effect of the thermal stability of the crystalline region inside the starch granules on digestibility. See Table 3 for the thermodynamic parameters.

[0046] Table 3 Thermal property parameters of natural corn flour, corn flour from Examples 1-3 and Comparative Examples 1-4

[0047] Note: The values ​​in the table are mean ± standard deviation. Different letters in the same column of each table indicate significant differences. p <0.05.

[0048] As can be seen from the data in Table 3, the gelatinization temperature and gelatinization enthalpy of corn flour increased after microwave treatment in Examples 1-3. o T pT c The increase in ΔH and the decrease in ΔH are due to the destruction of some weak crystalline regions during microwave treatment, leading to a decrease in ΔH. The addition of hydrophilic colloids in Examples 1-3 all resulted in an increase in gelatinization temperature and a decrease in gelatinization enthalpy. o T p and T c The increase in gelatinization temperature is due to the strong water-binding capacity of hydrocolloids, which reduces the free water activity around starch granules in corn flour that is available for gelatinization. The hydration network layer formed by colloidal molecules on the surface of starch granules physically hinders heat conduction and water molecule penetration, thus delaying gelatinization. Among the three colloids, guar gum (GG) showed the most significant increase in gelatinization temperature, reflecting its superior hydration capacity and molecular structure that forms an effective barrier. However, there is a problem of weak binding between corn flour and hydrocolloids, so a two-pronged approach is needed. Microwave treatment and hydrocolloids have a synergistic effect in regulating the thermal properties of corn flour, with the M-GG-CF group exhibiting the highest gelatinization temperature (T0) among all samples. o 65.19 ℃; T c 74.43 ℃; T p (83.57 ℃) to maximize the thermal stability of starch granules. Increased thermal stability leads to decreased sensitivity to digestive enzymes such as α-amylase, resulting in reduced digestibility and increased resistant starch content.

[0049] 5. Determination of hydration properties of corn flour treated with hydrophilic colloids via microwave synergy Take 0.5 g (dry basis) of sample and mix it evenly with 25 mL of deionized water in a centrifuge tube. Place the mixture in a 90 ℃ water bath and heat continuously with stirring for 30 min. Then cool to room temperature and centrifuge at 5000 r / min for 20 min. After centrifugation, discard the supernatant, weigh the precipitate and dry it at 105 ℃ to constant weight. Calculate the solubility (S) and swelling power (SP) of starch in corn flour according to Equations (1) and (2), respectively.

[0050] (1) (2) In the formula, A is the mass of the precipitate after constant weight drying (g); W is the mass of the dry sample (g); and B is the mass of the precipitate after centrifugation (g).

[0051] Hydration properties are a fundamental functional attribute of cereal flour raw materials in food processing and applications. They directly determine the swelling capacity, water-holding capacity, and interaction with other components, thus affecting the product's processing performance, texture, and shelf-life stability. The solubility and swelling power test results for natural corn flour in Examples 1-3 and Comparative Examples 1-4 are as follows: Figure 3 As shown. By Figure 3 It is evident that MCF exhibits increased solubility and swelling power compared to CF. This is due to the damage to the corn flour particle structure caused by microwave treatment. In a microwave field, polar water molecules within the corn flour particles undergo high-speed rotation and friction. Microwave energy disrupts the hydrogen bonds that maintain the structure within the starch particles, making some amorphous regions more porous and even damaging the orderliness of some crystalline regions. This allows water molecules to more easily penetrate into the particle's interior during subsequent hydration, combining with exposed hydrophilic hydroxyl groups, resulting in higher solubility and swelling power. Corn flour treated with microwave treatment in conjunction with KGM or GG shows higher solubility and swelling power. This is due to the superior hydrophilicity and water-holding capacity of KGM and GG themselves. These two high-molecular-weight linear polysaccharides contain a large number of hydroxyl groups, which can form a strong hydration layer with water molecules through hydrogen bonds. Furthermore, after microwave treatment, the more porous surface structure of the corn flour particles, combined with the strong hydration network formed by KGM or GG, creates a stronger synergistic effect, constructing a composite system with strong water-holding capacity. This promotes the stability and densification of the corn flour structure, effectively delaying the digestion process. In contrast, M-GA-CF with added gum arabic shows a trend of reduced swelling power and solubility. This is because GA's compact, highly branched structure adsorbs onto the surface of corn flour particles. This adsorption forms a relatively dense shell or interacts with starch or protein through hydrogen bonds, restricting the free swelling of starch particles in hot water and hindering further water molecule penetration, thus reducing swelling power. Since GA adsorbs onto the surface of corn flour particles, it also hinders the contact between starch molecules and digestive enzymes to some extent, thereby reducing digestibility.

[0052] 6. Determination of in vitro digestion properties of corn flour treated with hydrophilic colloids and microwave synergistic effect Weigh 500 mg (dry basis) of each corn flour sample, add 10 mL of sodium acetate buffer solution (0.1 M, pH 5.2), shake well, and equilibrate in a 37 ℃ water bath for 10 min. Then add 2.5 mL of freshly prepared α-amylase and amyloglucosidase mixed digestion solution and 6 glass beads, and immediately transfer to a 37 ℃ constant temperature shaking incubator for enzymatic digestion. At 20 min and 120 min, aspirate 500 μL of the solution and add it to a centrifuge tube containing 20 mL of 66% anhydrous ethanol to inactivate the enzyme. Then centrifuge at 5000 r / min for 10 min. Glucose content G 20 and G 120The D-glucose assay was performed using the following method: After centrifugation, 0.1 mL of the supernatant was taken and 3 mL of GOPOD solution was added. Sodium acetate buffer and GOPOD solution were added to the blank control group. The mixture was incubated in a 45 ℃ water bath for 20 min, and the absorbance was measured at 510 nm using a microplate reader. The contents of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) were calculated according to formulas (3), (4), and (5), respectively. (3) (4) (5) In equations (3), (4), and (5), G0, G 20 and G 120 The values ​​represent the amount of glucose released at 0 min, 20 min, and 120 min of enzymatic hydrolysis, respectively. TS represents the total starch content (mg), and the coefficient 0.9 is the glucose conversion factor.

[0053] The RDS, SDS, and RS contents of natural corn flour, corn flour of Examples 1-3, and comparative examples 1-4 are shown in Table 4.

[0054] Table 4. RDS, SDS, and RS content of natural corn flour, corn flour from Examples 1-3, and comparative examples 1-4

[0055] Note: The values ​​in the table are mean ± standard deviation. Different letters in the same column of each table indicate significant differences. p <0.05.

[0056] As shown in Table 4, microwave treatment in Comparative Example 1 significantly improved the digestibility of corn flour paste, manifested as an increase in corn starch content and a corresponding decrease in SDS and RS content. The starch in the CF sample contained 10.50% RS, while after microwave treatment (MCF), this value decreased to 8.95%. This is because microwave treatment disrupts the starch crystal structure and physical barriers in corn flour, making it easier for enzymes to access and hydrolyze, thus improving the digestibility of corn flour. The addition of hydrophilic colloids in Comparative Examples 2-4 significantly reduced the digestibility of corn flour, i.e., increased the SDS and RS content in its starch. This effect was particularly pronounced in the corn flour of Examples 1-3. The SDS and RS content in the starch of the corn flour in Examples 1-3 were significantly higher than those of natural corn flour and microwave-treated corn flour only, with SDS being higher than or close to that of natural corn flour and RS being higher than that of corn flour treated only with hydrophilic colloids but not microwave-treated. This indicates that the synergistic effect of microwave treatment and GG can better improve the anti-digestion properties of corn starch. The antidigestion resistance of M-GG-CF was superior to that of M-KGM-CF and M-GA-CF, indicating that the synergistic effect of microwave treatment and GG can better enhance the antidigestion resistance of corn starch. GG, as a high molecular weight thickener, significantly increases the viscosity of the digestion system. This high-viscosity environment hinders the free diffusion of digestive enzymes (α-amylase) within the system and slows the release of the substrate (starch) into the supernatant, thus delaying the enzymatic hydrolysis process overall. In this invention, the flexible long-chain polysaccharide of the hydrophilic colloid forms an interpenetrating physical entanglement network with the starch molecular chains in corn flour during gelatinization. This network not only improves the water-holding capacity of corn flour and reduces the free water available for enzymatic hydrolysis, but also makes it difficult for the enzyme's active sites to access the substrate, thereby causing some corn starch to exhibit good antidigestion resistance. Microwave treatment alone increases the digestibility of corn flour, while the addition of guar gum effectively reverses this trend, significantly reducing the digestion rate. The combination of the two further enhances the synergistic effect, maximizing the slow-digesting and antidigesting components of the system.

[0057] (II) Characterization of corn dough The method for preparing corn dough is as follows: Take 1000 g of corn flour treated in each example or comparative example, add 50% of its mass of distilled water, mix evenly, and knead until the surface is smooth. Divide the dough into 5 g portions, wrap each portion in plastic wrap, and store at 25°C for later use. Natural corn flour is marked as CF, corn dough prepared with natural corn flour is marked as CD, corn dough prepared with corn flour from Comparative Example 1 is marked as MCD, corn dough prepared with corn flour from Comparative Examples 2-4 is marked as KGM-CD, GG-CD, and GA-CD, respectively, and corn dough prepared with corn flour from Examples 1-3 is marked as M-KGM-CD, M-GG-CD, and M-GA-CD, respectively.

[0058] 1. Determination of the cooking characteristics of corn dough ① Cooking loss rate Place the dough in boiling water at 100 ℃. When the white core of the dough disappears, remove it and transfer the water to a flat dish. Then, dry it in an oven at 105 ℃ until constant weight. Calculate the cooking loss rate according to formula (6): (6) In formula (6): M is the mass of the dough before cooking (g), G is the mass of the dry matter in the soup (g), and W is the moisture content of the dough before cooking (%).

[0059] ② Water absorption rate Place the dough in boiling water at 100℃. When the white core of the dough disappears, remove it, drain the water with filter paper, and weigh it. Calculate the water absorption rate according to formula (7): (7) In formula (7): M is the mass of the dough after cooking (g), N is the mass of the dough before cooking (g), and W is the moisture content of the dough before cooking (%).

[0060] The cooking quality of corn dough can be evaluated by measuring water absorption rate and cooking loss rate. Water absorption rate reflects the dough's ability to absorb water during cooking; ideal dough should have a high water absorption rate without losing its shape. Cooking loss rate measures the degree to which soluble solids inside the dough dissolve into the cooking water during cooking, and is a core parameter for evaluating the dough's structural integrity and cooking resistance. The test results of the cooking characteristics of each sample dough are shown in Table 5.

[0061] Table 5. Water absorption and cooking loss rates of corn dough prepared using natural corn flour, corn flour from Examples 1-3, and corn flour from Comparative Examples 1-4.

[0062] Note: The values ​​in the table are mean ± standard deviation. Different letters in the same column of each table indicate significant differences. p <0.05.

[0063] As shown in Table 5, microwave treatment alone (MCD) resulted in low water absorption and high cooking loss in the corn dough. This indicates that microwave treatment disrupts the structural integrity of starch granules in the corn flour, making the resulting dough network structure more porous and fragile. During cooking, this leads to increased cooking loss, as a large number of starch molecules (especially easily soluble amylose) and granular fragments detach from the dough surface and dissolve into the cooking water, causing severe turbidity. The reduced water absorption is due to the unstable structure dissolving after absorbing water, rather than expanding in an orderly manner. The addition of the three hydrophilic colloids in Examples 1-3 all improved the water absorption and reduced the cooking loss in the corn dough, demonstrating the significant potential of hydrophilic colloids in improving the cooking quality of gluten-free dough. The addition of hydrophilic colloids significantly reduced the cooking loss while increasing the water absorption. This is because these high molecular weight polysaccharides form a strong, continuous three-dimensional network in the dough, tightly encapsulating the starch granules and forming a stable structure. This effectively resists thermal damage during cooking, preventing excessive dissolution and loss of starch granules, thus significantly reducing the cooking loss. Meanwhile, this stable structure allows the dough to swell fully without disintegrating after absorbing water, resulting in a higher water absorption rate. Table 5 also shows that the water absorption rates of the M-KGM-CD, M-GG-CD, and M-GA-CD groups were all higher than their respective untreated groups, while the cooking loss rate was further reduced. This indicates that microwave treatment causes hydrogen bonding or physical entanglement between starch granules and hydrophilic colloidal molecules in the corn flour, thereby constructing a more efficient and synergistic composite network. This optimized network structure exhibits stronger resistance and water retention during cooking: on the one hand, it can more effectively lock in internal components, reducing the cooking loss rate to a lower level (M-KGM-CD group); on the other hand, its stable structure allows the system to absorb and retain more water, thus achieving a higher water absorption rate (M-GG-CD group). 2. Determination of the rheological properties of corn dough Take 5 g of corn dough sample and place it in the center of the sample stage. Then, use a scraper to remove the dough sample outside the parallel plate. Incubate at 25 °C with 1-100 rads. -1 The angular frequency was dynamically scanned. The storage modulus (G') and loss modulus (G") of the corn dough were measured.

[0064] The rheological properties of dough are a direct reflection of its internal three-dimensional network structure in macroscopic mechanical behavior. They comprehensively reflect the dough's strength, elasticity, and viscosity, and are key to predicting its processing performance and final product quality. Using a dynamic rheological method, the effects of microwave treatment synergistically with hydrocolloids on the storage modulus (G') and loss modulus (G'') of dough were investigated through frequency scanning tests. The dynamic rheological parameter curves are shown below. Figure 4As shown, all cornmeal dough samples exhibited typical solid-like behavior within the frequency scanning range (0.1-100 rad / s), i.e., the storage modulus (G') was consistently higher than the loss modulus (G''), and both increased with increasing frequency. This indicates that the formed cornmeal doughs all possessed a stable, predominantly elastic gel network structure. Figure 4 It can be seen that the doughs prepared using corn flour from Examples 1 and 2 exhibited increased G' and G'' values. This result indicates that the strong network formed by KGM or GG significantly restricts the free movement of starch granules and water molecules, reducing energy dissipation. This allows the dough to store energy more through elastic deformation when subjected to external forces, thus giving the dough stronger structural stability and resistance to deformation. Conversely, the dough prepared using corn flour from Example 3 showed a significant decrease in both storage modulus (G') and loss modulus (G''). GA molecules increased the average distance between starch granules, weakening the direct interactions between granules formed through hydrogen bonds, van der Waals forces, etc., which are the basis for the strength of gluten-free dough. Dough is a system with limited water content. Although GA's water-holding capacity is not as good as linear colloids, it still has good hydrophilicity.

[0065] 3. Determination of the textural properties of corn dough The textural properties of corn dough were determined using a physical property analyzer equipped with a P / 36R cylindrical probe. Test conditions: speed 1 mm / s before test, speed 5 mm / s during test, and speed 5 mm / s after test.

[0066] Texture analysis is an instrumental method that simulates the human oral chewing process, quantifying various physical properties of food through two compression cycles. The texture test results of dough samples for each group are shown in Table 6.

[0067] Table 6. Texture properties of corn dough prepared using natural corn flour, corn flour from Examples 1-3, and corn flour from Comparative Examples 1-4

[0068] Note: The values ​​in the table are mean ± standard deviation. Different letters in the same column of each table indicate significant differences. p <0.05.

[0069] The data in Table 6 show that microwave treatment and the type of hydrocolloid had a significant impact on all the textural parameters of corn dough. p<0.05). Compared with corn dough prepared using CD and MCD, microwave treatment reduced the hardness, elasticity, cohesiveness, stickiness, and chewiness of the corn dough. This is highly consistent with the aforementioned findings of reduced G' and G'' in rheology, indicating that microwave treatment weakens the internal network structure of the dough and destroys some of its crystal structure and particle integrity. This results in a looser overall dough structure, weaker resistance to external deformation, reduced cohesiveness, and weakened ability to recover from deformation. The doughs with KGM added in Example 1 and GG added in Example 2 showed an increase in all textural parameters, with the reinforcing effect of GG being particularly prominent (all parameters in the M-GG-CD group were the highest). The high molecular weight linear chains of KGM and GG formed a strong, continuous three-dimensional network in the dough, tightly binding the starch granules within it. This composite network greatly enhanced the dough's resistance to compression deformation, thus causing a sharp increase in hardness. The increase in chewiness, as a comprehensive indicator of hardness, elasticity, and cohesiveness, is an inevitable result of the strengthening of the overall dough structure. The significant improvement in elasticity and cohesiveness of cornmeal dough is due to its strong colloidal network, which endows the dough with excellent internal binding force. This allows the dough to maintain better structural integrity after the first compression, thus significantly improving cohesiveness and enhancing its recovery ability after deformation, manifested as increased elasticity. This is crucial for improving the fragility and crumbling of gluten-free dough. Therefore, cornmeal dough with added KGM and GG is more suitable for making cookies, chips, and low-moisture baked goods, improving the chewiness and structural integrity of the finished product. Conversely, cornmeal dough with added GA had the lowest textural parameters among all samples, with its hardness (294 g) even significantly lower than the control group CD (538 g) and the microwave-treated MCD group (429 g). This result indicates that the globular molecular structure of GA acts as a filler between corn flour particles, hindering the close packing and interaction between particles, disrupting the continuity of the corn flour's own network structure, resulting in an extremely soft dough structure with minimal hardness, cohesiveness, and chewiness. Therefore, cornmeal dough with added GA is more suitable for making softer, more delicate steamed or paste-like corn products.

[0070] 4. Determination of freeze-thaw stability of corn dough The corn dough was placed in a -20 ℃ freezer for 24 h and allowed to thaw naturally at room temperature for 1 h. After thawing, it was centrifuged at 3000 r / min for 20 min. The masses of the dough before and after freeze-thaw were determined as M0 and M1, respectively. The mass of the centrifuged dough sample was then weighed and recorded as M2. The water loss rate and water separation rate of the dough sample were calculated according to equations (8) and (9), respectively: (8) (9) The results of the determination of water loss rate and water separation rate of each dough sample are as follows: Figure 5As shown, compared with the control group (CD), the MCD group prepared from corn flour treated with microwave alone showed increased water loss and water separation rates, indicating that the physical disruption of the corn dough gel network by microwave treatment is the dominant factor affecting its freeze-thaw stability. The addition of hydrophilic colloids in Examples 1-3 effectively reduced the water loss and water separation rates of the dough, with GG showing particularly outstanding effects, closely related to its strong network-building and water-binding capabilities. Constructing a strong network within the starch network not only locks in a large amount of water but also reduces damage to starch granules, effectively maintaining their integrity and firmly locking in moisture, thus significantly reducing water loss. Comparing M-KGM-CD with KGM-CD, M-GG-CD with GG-CD, and M-GA-CD with GA-CD, it was found that the corn dough treated with microwave and hydrophilic colloid synergistically had lower water loss and water separation rates. This indicates that microwave damage to the surface structure of starch granules and increased exposure of molecular chains, while weakening the strength of the pure starch network, creates a tighter and more effective interaction between starch molecules and hydrophilic colloid molecules. This enhanced intermolecular interaction (such as hydrogen bonding or physical entanglement) constructs a more stable network structure. Therefore, microwave-assisted hydrophilic colloidal treatment leads to a further reduction in water loss and water separation rates, thereby improving freeze-thaw stability.

[0071] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing low-digestibility corn flour modified by microwave-assisted hydrophilic colloids, characterized in that, The preparation method is as follows: the hydrophilic colloid is mixed evenly with corn flour, the moisture content of the mixture is adjusted, and then the moisture is balanced at 4 ℃ to obtain a corn flour-hydrophilic colloid mixture. The corn flour-hydrophilic colloid mixture is microwave-treated, dried, ground and sieved to obtain low digestibility corn flour.

2. The preparation method according to claim 1, characterized in that, The hydrophilic colloids are konjac colloids, guar colloids, or arabinocolloids.

3. The preparation method according to claim 1, characterized in that, The hydrophilic colloid is 2-6 wt% of corn flour.

4. The preparation method according to claim 1, characterized in that, The moisture content is 10-40%.

5. The preparation method according to claim 1, characterized in that, The equilibration time is 0-24 hours.

6. The preparation method according to claim 1, characterized in that, The microwave processing power is 100-800 W, and the time is 1-5 min.

7. The preparation method according to claim 1, characterized in that, The drying temperature is 30-60 ℃, and the time is 12-48 h.

8. A microwave-assisted hydrophilic colloid modified low-digestibility corn flour obtained by the preparation method according to any one of claims 1-7.

9. The low-digestibility corn flour according to claim 8, characterized in that, The starch in corn flour contains ≤50% rapidly digestible starch, ≥27% slowly digestible starch, and ≥23% resistant starch.

10. The application of microwave-assisted hydrophilic colloid modified low-digestibility corn flour as described in claim 8 or 9 in the preparation of corn dough.

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