A method for improving the starch structure and digestibility of sprouted corn flour, the sprouted corn flour prepared therefrom, and its applications.

Abstract

This invention relates to the field of food processing technology, specifically to a method for improving the starch structure and digestibility of sprouted corn flour, the prepared sprouted corn flour, and its applications. A method for improving the starch structure and digestibility of sprouted corn flour includes the following steps: S1, preparation of sprouted corn: soaking and germinating corn kernels to obtain sprouted corn; S2, microwave treatment: subjecting the sprouted corn to microwave treatment; S3, forced-air drying: subjecting the microwave-treated sprouted corn to forced-air drying until constant weight, obtaining dried sprouted corn; S4, pulverization: pulverizing and sieving the dried sprouted corn to obtain sprouted corn flour. This method not only significantly improves the drying efficiency of sprouted corn but also improves the starch structure characteristics of the sprouted corn flour, particularly increasing the content of resistant starch and reducing in vitro digestibility, thereby providing a high-quality raw material for developing corn-based foods with low digestibility or low glycemic index.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, specifically to a method for improving the starch structure and digestibility of sprouted corn flour, the sprouted corn flour prepared therefrom, and its applications. Background Technology

[0002] Corn can germinate under suitable temperature and humidity conditions. During germination, its internal endogenous enzymes are activated, breaking down macromolecules such as starch, non-starch polysaccharides, and proteins, and generating various bioactive compounds, thus enhancing its nutritional value and making it easier for the human body to absorb. However, freshly germinated corn has a high water content and is highly susceptible to mold, requiring drying to extend its shelf life.

[0003] Microwave drying, as a highly efficient technology combining heat and non-heat treatment, is frequently used for grain drying due to its speed and energy efficiency. Current research on microwave treatment of germinated grains largely focuses on its effects on conventional nutrients, drying rate, and color; however, the mechanism by which microwave treatment affects the starch structure and digestibility of germinated corn remains unclear. Therefore, developing a method to improve the starch structure and digestibility of germinated corn flour and enhance drying efficiency is of great significance for developing high-value-added, highly functional corn staple food products. Summary of the Invention

[0004] This invention provides a method for improving the starch structure and digestibility of sprouted corn flour. This method can not only significantly improve the drying efficiency of sprouted corn, but also improve the starch structure characteristics of sprouted corn flour, especially increasing the content of resistant starch and reducing the in vitro digestibility, thereby providing high-quality raw materials for developing corn foods with low digestibility or low glycemic index.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for improving the starch structure and digestibility of sprouted corn flour includes the following steps:

[0007] S1, Preparation of germinated corn: Soak and germinate corn kernels to obtain germinated corn;

[0008] S2, Microwave treatment: Microwave treatment of sprouted corn;

[0009] S3, forced air drying: The sprouted corn after microwave treatment is dried by forced air drying to constant weight to obtain dried sprouted corn;

[0010] S4, Grinding: Grind and sieve the dried sprouted corn to obtain sprouted corn flour.

[0011] Further, in step S1, the corn kernels are soaked in a 1% sodium hypochlorite solution for 40 minutes, and then soaked in distilled water for 8 hours.

[0012] Furthermore, in step S1, the germination conditions are: germination for 48 hours in a dark environment at 28°C and 75% relative humidity.

[0013] Furthermore, the distilled water is changed every 12 hours during the germination process.

[0014] Furthermore, in step S2, during microwave treatment, the sprouted corn is laid flat with a thickness of 5-7 mm, the microwave power is 100 W, and the microwave treatment time is 1-5 min.

[0015] Furthermore, in step S2, the microwave treatment time is 2 minutes.

[0016] Furthermore, in step S3, the temperature for blower drying is 55°C.

[0017] Furthermore, in step S4, the material is sieved through a 100-mesh sieve.

[0018] The present invention also provides germinated corn flour prepared by the above method.

[0019] The present invention further provides the application of the germinated corn flour in the preparation of low-digestibility foods or low glycemic index foods.

[0020] The present invention has the following beneficial effects:

[0021] 1. This invention significantly improves the drying efficiency of sprouted corn by controlling the microwave treatment time and combining it with forced-air drying, reaching up to 80.22%, effectively solving the problem of sprouted corn being prone to mold.

[0022] 2. The method of the present invention can optimize the crystal structure of starch in germinated corn, reduce the gelatinization enthalpy, increase the degree of gelatinization, and improve the thermodynamic properties of starch.

[0023] 3. The method of the present invention can significantly increase the content of resistant starch and reduce the in vitro digestibility of starch, which helps to develop low digestibility foods or low glycemic index foods and is suitable for the processing of functional staple foods.

[0024] 4. The method of the present invention is simple to operate, low in cost, and suitable for industrial production. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 A schematic diagram illustrating the effect of different microwave treatment times on the drying characteristics of germinated corn.

[0027] Figure 2 Infrared spectra of germinated corn flour after different microwave treatment times;

[0028] Figure 3 X-ray diffraction patterns of germinated corn flour under different microwave treatment times;

[0029] Figure 4 Scanning electron microscope images of germinated corn flour under different microwave treatment times, showing the changes in the microscopic morphology of starch granules;

[0030] Figure 5 A graph showing the effect of different microwave treatment times on the gelatinization degree of germinated corn flour.

[0031] Figure 6 The graph shows the effect of different microwave treatment times on the digestibility of germinated corn flour (A. digestion curve; B. starch content). Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. The following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention.

[0033] Example

[0034] S1: 180 g of corn kernels were soaked in a 1% sodium hypochlorite solution for 40 min, then transferred to a 35×28×4 cm tray and soaked in distilled water for 8 h. Germination was carried out in a dark incubator at 28℃ and 75% relative humidity. The water was changed every 12 h to ensure optimal conditions, and germination time was 48 h.

[0035] S2: Take 100 g of sprouted corn and spread it evenly on a 32×25 cm (material thickness is about 6 mm) ceramic baking pan. Place it in a microwave oven and set the power to 100 W. Process for 0, 1, 2, 3, 4 and 5 minutes respectively.

[0036] S3: Dry the microwave-treated sprouted corn in a 55℃ forced-air drying oven until constant weight, and record the drying time.

[0037] S4: Grind the dried sprouted corn using a high-speed blender and pass it through a 100-mesh sieve for later use.

[0038] The germinated corn flour prepared in the examples was subjected to thermal property analysis, infrared spectroscopy analysis, X-ray diffraction analysis, microstructure observation, gelatinization degree determination, and in vitro digestibility determination. The results are analyzed as follows:

[0039] 1. Effect of different microwave treatment times on the drying characteristics of germinated corn flour

[0040] Depend on Figure 1 It can be seen that the longer the microwave treatment time, the significantly lower the drying time of sprouted corn, and the lower the moisture content in the corn. When the microwave treatment time is 0 min, the time required for the corn to reach constant weight is 180 min. As the microwave time increases, the drying time decreases by 20.34%, 28.98%, 45.56%, 56.17%, and 80.22%, respectively. Therefore, increasing the microwave treatment time can significantly accelerate the drying process.

[0041] 2. Analysis of the effect of different microwave treatment times on the thermodynamic properties of germinated corn flour

[0042] Thermodynamic properties are one of the key factors affecting food processing, and are closely related to starch interactions, crystallinity, and water absorption capacity. Table 1 below shows the effect of different microwave treatment times on the thermodynamic properties of corn flour.

[0043]

[0044] Note: The values ​​in the table are mean ± standard deviation. Different letters in the same column indicate significant differences (P < 0.05).

[0045] Table 1 shows that microwave treatment significantly affected the thermal properties of germinated corn flour. The initial temperature, peak temperature, and termination temperature of the untreated sample were 102.40℃, 109.92℃, and 113.21℃, respectively. With prolonged microwave treatment time, the initial and termination temperatures showed a trend of first increasing and then decreasing. The increase in termination temperature indicates that the relatively fragile starch crystals may be preferentially destroyed after microwave treatment, while the relatively stable crystals are preserved. The increase in initial temperature may be due to the dissociation and rearrangement of starch chains during microwave treatment, and the enhanced interaction between adjacent chains, resulting in the formation of some more stable crystals and helical structures. However, the initial and termination temperatures gradually decreased with increasing microwave time, possibly because the prolonged microwave energy destroyed most of the starch crystal structure, leading to a decrease in temperature. The rearrangement of starch molecules during microwave radiation may lead to the formation of crystals with different stabilities. The changes in thermodynamic properties also indicate that the destruction of weak crystals, the rearrangement of dissociated starch chains, and the enhancement of interactions between adjacent chains may occur simultaneously.

[0046] The endothermic henryi value represents the energy required to decompose the double helix structure, reflecting the double helix structure and molecular order of the starch microcrystalline region. A higher endothermic henryi value indicates better thermal stability of the starch structure; a lower value indicates smaller crystalline regions, increasing structural disorder and decreasing the stability of both crystalline and amorphous regions. With increasing microwave time, the endothermic henryi value significantly decreases, possibly because the activation of amylase during corn germination disrupts starch crystals, thereby altering their surface properties and stability. Simultaneously, microwave treatment reduces the order of the starch crystalline region and disrupts the double helix structure between the crystalline and amorphous regions. The thermal properties of germinated corn can serve as an important reference indicator for assessing the degree of starch gelatinization.

[0047] 3. Effects of different microwave treatment times on the Fourier transform infrared (FTIR) spectra of germinated corn flour

[0048] Depend on Figure 2 It can be seen that the characteristic absorption peaks of the control group (0 min) are located at 3144, 2929, 2370, 1650 and 1016 cm⁻¹. −1 3144 cm −1 The broad peak nearby corresponds to the stretching vibration of the hydroxyl bond. 2929 cm⁻¹ −1 The peaks at 2370 and 1650 cm⁻¹ correspond to the asymmetric stretching vibrations of the carbonyl bond. −1 The peak at 1016 cm⁻¹ corresponds to the stretching vibration of a saturated carbonyl bond. −1 The peak at 763 cm⁻¹ corresponds to the bending vibration of the carbonyl-hydroxyl bond. −1The peak at that location corresponds to the stretching vibration of the carbon-carbon bond. During the first 2 minutes of microwave treatment, the chemical bonds remained unchanged, and the spectrum showed no significant difference. However, as the treatment time increased, the intensity of the characteristic spectral peaks gradually decreased. Microwave treatment may have disrupted the network structure associated with the functional groups, altering their vibrational environment and consequently changing the intensity and shape of the absorption peaks.

[0049] In FTIR spectra, the absorption peak near 1047 cm⁻¹ is characteristic of the starch crystalline region, while the absorption peak near 1022 cm⁻¹ is unique to the starch amorphous region. Therefore, the ratio of peak intensities at 1047 and 1022 cm⁻¹ can be used to characterize the change in starch double helixity; the larger the value, the more ordered the starch structure, with values ​​of 1.037, 1.054, 1.015, 1.013, 1.000, and 0.999, respectively. The double helixity generally shows a decreasing trend, indicating that the structural characteristics of the starch crystalline region are weakened to some extent after microwave treatment. This is because microwave treatment disrupts the amorphous and crystalline structure of starch and reduces the crystalline regions within the starch granules.

[0050] 4. Effects of different microwave treatment times on the crystal structure of germinated corn flour

[0051] Figure 3 X-ray diffraction (XRD) patterns of germinated corn flour after microwave treatment for different times are shown. Figure 3 The X-ray diffraction pattern of corn germination powder exhibits typical A-type crystal structure characteristics. As shown in the figure, the XRD patterns for the first 3 minutes of microwave treatment all show diffraction peaks at 15°, 17°, 18°, and 23°, indicating that microwave treatment did not alter the crystal structure of the corn starch. When the microwave time exceeded 3 minutes, the diffraction peaks at 15°, 17°, 18°, and 23° gradually disappeared, possibly because microwave treatment causes the starch granules to absorb water and swell, disrupting the crystal structure. When the temperature reaches the gelatinization temperature, the double helix structure unwinds, the crystalline region disappears, and the diffraction peaks weaken or disappear.

[0052] Relative crystallinity, representing the relative proportion of crystalline to amorphous regions of starch, was 13.36%, 14.62%, 15.71%, 13.67%, 11.55%, and 11.63%, respectively. With increasing treatment time, the crystallinity initially increased and then decreased. The increase in crystallinity before 2 minutes may be related to the evaporation of moisture from the corn during microwave treatment, which leads to an increase in the relative proportion of crystalline starch in the system. This robust crystalline structure resists digestive enzyme decomposition, resulting in a simultaneous increase in resistant starch content. The decrease in crystallinity with prolonged treatment time indicates that prolonged microwave exposure disrupts the ordered crystalline structure of starch, causing the molecular chains to become disordered and resulting in partial starch gelatinization. Microwaves can induce the unwinding of some double-helix structures within the crystalline regions, causing irreversible damage to the crystal structure and thus reducing relative crystallinity. This result is consistent with the findings of infrared spectroscopy analysis.

[0053] 5. Effects of different microwave treatment times on the microstructure of germinated corn flour

[0054] Scanning electron microscope (SEM) is a microscopic observation device that falls between transmission electron microscope and optical microscope. Figure 4 Scanning electron micrographs of germinated corn flour treated with different microwave times show the changes in the microscopic morphology of starch granules. Figure 4 It was observed that in germinated corn flour that had not undergone microwave treatment, the starch granules maintained a plump and smooth morphology, exhibiting a porous characteristic. This is likely because germination enhances the activity and hydrolytic capacity of amylase, making it easier for amylase to hydrolyze the starch granules from within, thus damaging the entire granule and increasing porosity. After 1 minute of microwave treatment, the starch granule surface remained smooth and intact, with only an increase in porosity. After 3 minutes of microwave treatment, the starch granules in the corn flour became irregular in shape, with obvious surface depressions and adhesion between granules. This demonstrates that short-term microwave treatment does not cause significant damage to the starch granules in corn flour. However, prolonged microwave treatment can induce internal rearrangement of starch molecules, leading to changes in the surface morphology of the granules.

[0055] 6. Effect of different microwave treatment times on the gelatinization degree of germinated corn flour

[0056] Gelatinization degree reflects the extent to which water enters the microcrystalline bundle structure of starch in a hydrothermal environment, causing the amorphous regions of starch granules to expand and the original crystalline structure to be destroyed. Figure 5 This is a graph showing the effect of different microwave treatment times on the gelatinization degree of germinated corn flour. Figure 5It is known that microwave treatment increases the gelatinization degree of corn flour. The degree initially increases with prolonged treatment time and then gradually stabilizes. Initial microwave heating causes the starch in the corn flour to rapidly absorb energy, unwinding the double helix structure and rapidly increasing the gelatinization degree. As the treatment time continues, the moisture content in the corn decreases, preventing further starch gelatinization. Appropriate starch gelatinization enhances the viscosity and formability of corn flour, improving its palatability.

[0057] 7. Effects of different microwave treatment times on the digestibility of germinated corn flour

[0058] In vitro digestion curves can reflect the digestibility of germinated corn flour. Starches with different structures have different digestibility rates. Based on their metabolic rate in the human body, starches can be classified into three categories: rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS). Figure 6 The graph shows the effect of different microwave treatment times on the digestibility of germinated corn flour (A. digestion curve; B. starch content).

[0059] Depend on Figure 6 As shown in Figure A, with increasing enzymatic hydrolysis time, all samples exhibited similar digestion characteristics: the digestion rate increased significantly within the initial 30 minutes, then gradually slowed down between 30 and 180 minutes, eventually stabilizing. When the microwave treatment time was 2 minutes, the overall digestion curve of the corn flour was low, indicating that the in vitro digestibility of the germinated corn flour after 1 and 2 minutes of microwave treatment was lower than the control sample, and the resistant starch content was the highest. This may be because during short-term microwave treatment, the incompletely gelatinized starch granules in the germinated corn flour are prone to slight aggregation due to local thermal effects, forming a temporary dense structure that hinders enzyme contact. Furthermore, when the microwave treatment time was greater than 2 minutes, the in vitro digestibility of the germinated corn starch gradually increased, confirming... Figure 5 Increased starch gelatinization during prolonged microwave treatment, leading to partial starch gelatinization and internal rearrangement of starch molecules, promotes enzymatic hydrolysis of starch during in vitro digestion. Therefore, controlling the processing time can help increase the anti-digestive properties of sprouted corn flour. Research on starch anti-digestive properties is of significant reference value for assessing the glycemic index of grain products.

[0060] In summary, microwave treatment significantly improves the drying efficiency of sprouted corn, up to 80%. FTIR spectroscopy analysis shows that microwave treatment disrupts the crystal structure of starch in sprouted corn flour. Moderate microwave treatment does not change the peak positions of absorption peaks, nor does it add, subtract, or alter chemical bonds or functional groups; however, excessive microwave treatment weakens the characteristic peaks of the starch spectrum. XRD results indicate that microwave treatment does not change the crystal morphology of corn starch, but it initially increases and then decreases its relative crystallinity, leading to an initial increase followed by a decrease in its in vitro digestibility. A 2-minute treatment resulted in an 11.3% increase in resistant starch (RS) content and the lowest digestibility. Simultaneously, microwave treatment lowers the gelatinization enthalpy and increases the degree of gelatinization in sprouted corn flour. Microscopically, starch granules change from intact to concave and agglomerated. Therefore, appropriate microwave treatment can help increase the anti-digestibility properties of sprouted corn flour and improve its starch structural characteristics, providing a crucial theoretical basis for developing high-value-added, highly functional corn staple food products in the food industry.

[0061] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for improving the starch structure and digestibility of sprouted corn flour, characterized in that, Includes the following steps: S1, Preparation of germinated corn: Soak and germinate corn kernels to obtain germinated corn; S2, Microwave treatment: Microwave treatment of sprouted corn; S3, forced air drying: The sprouted corn after microwave treatment is dried by forced air drying to constant weight to obtain dried sprouted corn; S4, Grinding: Grind and sieve the dried sprouted corn to obtain sprouted corn flour.

2. The method according to claim 1, characterized in that, In step S1, corn kernels are soaked in a 1% sodium hypochlorite solution for 40 minutes, and then soaked in distilled water for 8 hours.

3. The method according to claim 1, characterized in that, In step S1, the germination conditions are: germination for 48 hours in a dark environment at 28℃ and 75% relative humidity.

4. The method according to claim 3, characterized in that, The distilled water should be changed every 12 hours during the germination process.

5. The method according to claim 1, characterized in that, In step S2, during microwave treatment, the sprouted corn is spread out evenly with a thickness of 5-7 mm, the microwave power is 100W, and the microwave treatment time is 1-5 minutes.

6. The method according to claim 5, characterized in that, In step S2, the microwave treatment time is 2 minutes.

7. The method according to claim 1, characterized in that, In step S3, the temperature for blower drying is 55°C.

8. The method according to claim 1, characterized in that, In step S4, the material is sieved through a 100-mesh sieve.

9. Germinated corn flour prepared by the method according to any one of claims 1 to 8.

10. The use of the germinated corn flour of claim 9 in the preparation of low-digestibility foods or low-glycemic index foods.

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