Brown Rice Slow-Digesting Nutritional Food Base Based on Hierarchical Filling Structure and Its Preparation Method

Abstract

This invention discloses a method for preparing a slow-digesting brown rice nutritional food base based on a graded filling structure, comprising the following steps: S1: Mixing brown rice flour, whey protein powder, and pullulanase evenly, then feeding the mixture into a twin-screw extruder for extrusion; collecting the extruded material to obtain a primary extrusion complex, namely, a brown rice-whey protein complex; S2: Drying and pulverizing the primary extrusion complex to obtain a primary extrusion complex dry powder; S3: Mixing the primary extrusion complex dry powder with soybean peptides evenly, feeding the mixture into a twin-screw extruder for extrusion; collecting the extruded material to obtain a secondary extrusion complex, namely, a brown rice-whey protein-soybean peptide complex forming a graded filling structure; S4: Drying and pulverizing the secondary extrusion complex to obtain a slow-digesting brown rice nutritional food base. This invention also discloses that the slow-digesting brown rice nutritional food base prepared by the above method slows down the digestion of brown rice and reduces the glycemic index.

Description

Technical Field

[0001] This invention relates to the field of food processing, specifically to a slow-digesting brown rice nutritional food base based on a graded filling structure and its preparation method. Background Technology

[0002] As a typical whole grain food, increasing the proportion of brown rice in daily diets is an important measure to actively respond to the national health strategy and effectively improve the nutritional health of residents. However, the promotion of brown rice still faces significant challenges at present. Although brown rice has better nutritional components and a lower glycemic index (GI) than refined white rice, it is still a staple food in the medium-to-high GI category, with a significant postprandial blood sugar response. Therefore, it is urgent to explore and optimize suitable physical, chemical, or biological processing modification technologies for brown rice. By regulating its starch structure and digestive characteristics, the digestion rate in the gastrointestinal tract can be effectively slowed down, thereby further reducing its postprandial blood sugar response. Ultimately, the goal is to develop a whole grain staple food base that combines good eating quality with low glycemic burden, providing practical theoretical and practical support for implementing the "Healthy China" strategy.

[0003] Starch can be classified into rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) based on its digestion rate. Increasing the content of SDS and RS is currently the goal of slowly digestible starch food processing. Current research indicates that proteins can effectively delay starch digestion through their physical barrier function, interactions with starch molecules such as hydrogen bonds, and inhibition of amylases. Therefore, constructing starch-protein complexes is considered an effective strategy for regulating starch digestion. However, the effectiveness of existing starch-protein complexes in delaying digestion still has room for improvement. This is because the three-dimensional network structure formed when a single protein molecule (such as β-lactoglobulin, the main component of whey protein, with a molecular weight of approximately 18.3 kDa) is complexed with amylose is not completely dense at the microscopic level, containing nanometer or micrometer-scale gaps. Key digestive enzymes in the human body, due to their specific molecular conformation and hydrodynamic dimensions, can still partially penetrate these gaps and bind to active sites on the starch chain, thereby catalyzing hydrolysis. Therefore, it is still necessary to further improve the delayed digestion effect of starch-protein complex.

[0004] Extruders, as commonly used industrial continuous processing equipment in grain ripening and modification, offer the possibility of achieving efficient compounding of proteins and starches. This invention systematically explores the process flow and parameters of brown rice-protein compounding based on extrusion technology, designs and develops slow-digestible brown rice nutritional food base materials, expands the application prospects of brown rice in the food industry, and is of great significance for meeting the nutritional and health needs of different populations and contributing to the implementation of the Healthy China strategy. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a slow-digesting brown rice nutritional food base based on a graded filling structure, which slows down the digestion of brown rice and reduces the glycemic index.

[0006] The present invention also aims to provide a slow-digesting nutrient food base of brown rice prepared by the above-mentioned preparation method.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing a slow-digesting brown rice nutritional food base based on a graded filling structure includes the following steps:

[0009] S1: Mix brown rice flour, whey protein powder and pullulanase evenly, then put them into a twin-screw extruder for extrusion; collect the extruded material to obtain a primary extrusion complex, which is the brown rice-whey protein complex.

[0010] S2: Dry and pulverize the primary extrusion compound to obtain primary extrusion compound dry powder;

[0011] S3: Mix the dry powder of the primary extrusion complex with soybean peptides evenly, feed it into a twin-screw extruder, and extrude it; collect the extruded material to obtain the secondary extrusion complex, which is the brown rice-whey protein-soybean peptide complex that forms a graded filling structure.

[0012] S4: Dry and pulverize the secondary extrusion complex to obtain the base material for slow-digesting brown rice nutritional food.

[0013] To overcome the limitations of existing starch-protein complexes in delaying digestion, this invention designs and constructs a ternary starch-protein "hierarchical filling structure," establishing a starch-protein composite technology based on a "hierarchical filling" strategy. Specifically, it utilizes macromolecular whey protein and small-molecule soybean peptides to synergistically fill brown rice flour in a hierarchical manner, obtaining a slow-digestible brown rice nutrient base.

[0014] The whey protein described in this invention is an easily digestible and nutritionally complete protein that can delay starch digestion through multiple mechanisms. These mechanisms include: physical barrier effects, non-covalent interactions with starch molecules such as hydrogen bonds, and covalent complexation. The covalent complexation mechanism refers to the initial stage of the Maillard reaction between the aldehyde group at the end of the amylose chain and the amino group in whey protein, forming a stable starch-protein complex that effectively inhibits enzymatic hydrolysis.

[0015] The soybean peptides described are small molecular fragments obtained from soybean protein through enzymatic hydrolysis. Their core structural characteristic lies in their molecular weight being much smaller than the parent protein, short peptide chains, and simple spatial structure. This structural feature directly determines their excellent physicochemical properties. This invention utilizes the small molecular weight and high reactivity of soybean peptides to effectively penetrate and fill the microscopic gaps in the brown rice-whey protein complex, forming spatial occupancy sites. This more thoroughly hinders the contact between digestive enzymes and starch, synergistically enhancing the slow digestibility of the product.

[0016] Since the starch-protein complex is formed by the covalent bonding of the aldehyde groups at the ends of amylose and the amino groups in the protein, a higher amylose content is more conducive to the formation of the starch-protein complex. Therefore, this invention utilizes pullulanase's debranching enzymatic hydrolysis to provide more amylose raw materials for protein complex formation. Furthermore, pullulanase removes the side-chain structures of starch in brown rice flour, generating medium- and short-chain amylose and dextrin-like products. This further adjusts the ratio of crystalline to amorphous regions during starch retrogradation, hindering the diffusion rate and binding of digestive enzymes in the matrix, ultimately reducing starch digestibility.

[0017] Therefore, this invention first mixes brown rice flour with whey protein powder and pullulanase. Through a single extrusion process, under the synergistic effect of enzymatic hydrolysis, the starch is pregelatinized, debranched, and initially compounded with whey protein, effectively disrupting the starch crystalline structure and increasing the amylose content, laying the foundation for subsequent compounding. Subsequently, small-molecule soybean peptides are innovatively introduced and subjected to a second extrusion with the primary extrusion complex. During this process, the small-molecule soybean peptides can precisely embed into the gaps left by the framework constructed by the large-molecule whey protein, achieving graded and precise filling. This invention, through the above-mentioned dual compounding effect, precisely regulates the microstructure of the complex, constructing a dense "graded filling structure," which significantly enhances the inhibitory effect on amylase. Finally, after drying and pulverizing, a brown rice nutritional base with excellent slow-digestion characteristics is obtained.

[0018] Preferably, the amount of whey protein powder added according to the present invention is 20-30% of the mass of brown rice flour, that is, the whey protein content in the final product is 16-21%.

[0019] Preferably, the molecular weight of the soybean peptides described in this invention ranges from 800 to 1200 Da, and the amount added is 8 to 12% of the mass of brown rice flour. That is, the soybean peptide content in the final product is 6 to 8%.

[0020] Preferably, the pullulanase used in this invention is food-grade pullulanase, and its addition amount is 0.4-0.7% of the mass of brown rice flour, with an enzyme concentration of 500-1000 U / g (converted based on the mass of brown rice flour). As a specific embodiment, the pullulanase used in this invention has an enzyme activity of 1×10⁻⁶. 5 U / g.

[0021] In steps S1 and S3, brown rice flour or one-time extrusion compound dry powder is used for extrusion processing to increase the effective specific surface area accessible to the enzyme or soybean peptides, thereby improving enzymatic hydrolysis efficiency and peptide compounding efficiency. Theoretically, the finer the particle size, the larger the effective specific surface area accessible to the enzyme or soybean peptides, which is more conducive to the reaction. However, in actual production, the time cost and energy consumption limitations of the pulverization process must be comprehensively considered to determine the economically feasible pulverization fineness. Therefore, preferably, in step S1, brown rice is pulverized through an 80-mesh sieve to obtain brown rice flour; in step S2, the one-time extrusion compound is dried and then pulverized through an 80-mesh sieve to obtain one-time extrusion compound dry powder.

[0022] In steps S1 and S3, the twin-screw extruder is set with five temperature zones, the feed rate is set to 5 kg / h, the water flow rate is set to 50% of the feed rate, and the screw speed is set to 50 rpm. Specifically, in step S1, to ensure the enzymatic hydrolysis effect and avoid excessive starch chain degradation, the extrusion temperature is preferably set within the optimal temperature range for pullulanase, i.e., between 50 and 60°C. This temperature range maintains the high catalytic activity of pullulanase while effectively preventing starch chain breakage or enzyme protein denaturation and inactivation caused by high temperatures. In step S3, to ensure the cross-linking effect between starch and peptides while avoiding the adverse effects of high temperatures on peptide activity, the extruder temperature range is preferably set between 60 and 80°C. This temperature range is conducive to the extension of starch molecular chains and the hydrogen bonding and hydrophobic interactions between starch and peptides, forming a dense composite network structure to achieve graded filling, while avoiding excessive temperature damage to the molecular conformation of peptides or excessive thermal cross-linking. The final temperature zone is set at 100-110°C to terminate the reaction and mature the material. Therefore, in step S1, the preferred temperature range of the twin-screw extruder is set to 50~60℃, 50~60℃, 50~60℃, 50~60℃, and 100~110℃; in step S3, the preferred temperature range of the twin-screw extruder is set to 60~80℃, 60~80℃, 60~80℃, 60~80℃, and 100~110℃. For the sake of process simplification, steps S1 and S3 both use the same temperature range setting. As a specific embodiment, the temperature range of the twin-screw extruder is set to 60℃, 60℃, 60℃, 60℃, and 100℃; this setting is for illustrative purposes only and does not constitute a limitation on the scope of protection of this invention. In practical applications, the temperature range can be flexibly adjusted within each preferred temperature range according to specific needs.

[0023] Preferably, in steps S2 and S4, a heat pump dryer is used to dry the extruded material to reduce the moisture content through the drying operation, and the drying temperature is 60°C.

[0024] The present invention also provides a slow-digesting brown rice nutritional food base prepared by the above preparation method, which is a low-GI starch food base.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The core advantage of this invention lies in the simultaneous gelatinization, enzymatic hydrolysis, and compounding achieved using a twin-screw extruder; it innovatively introduces soybean peptides of specific molecular weights to form a dual-protein system with whey protein: during extrusion, whey protein first combines with amylose produced by pullulan enzymatic hydrolysis to form a macroscopic framework; subsequently, small-molecule soybean peptides are effectively embedded in the gaps of the network structure, forming a denser composite network. This hierarchical filling effect can more effectively delay starch digestion and reduce the glycemic index, while the process is continuous and efficient, suitable for large-scale production.

[0027] (2) The present invention adopts an extrusion coupled enzymatic hydrolysis process to ensure that the enzymatic hydrolysis reaction is carried out effectively under suitable temperature conditions, and achieves the ideal enzymatic debranching effect by optimizing process parameters; by using the extrusion shearing action to destroy the natural structure of starch, the accessibility of enzyme and substrate is improved, thereby significantly improving the enzymatic hydrolysis efficiency and greatly shortening the time required for enzymatic hydrolysis.

[0028] (3) The preparation method of the slow-digestible brown rice nutritional food base material based on the graded filling structure described in this invention slows down the digestion rate of the processed brown rice flour. At the same time, the addition of whey protein and soybean peptides further optimizes the amino acid composition and achieves nutritional complementarity. It can be used as a low-GI starch base material for other product applications. Attached Figure Description

[0029] Figure 1 The images show a 500x electron microscope image and a 630x laser confocal microscope image of the slow-digesting brown rice nutrient substrate from Example 1.

[0030] Figure 2 The images show a 500x electron microscope image and a 630x laser confocal microscope image of the slow-digesting brown rice nutrient substrate from Example 2.

[0031] Figure 3 The images are 500x electron microscope images and 630x laser confocal microscope images of the slow-digesting brown rice nutrient substrate of Comparative Example 1.

[0032] Figure 4 The images are 500x electron microscope images and 630x laser confocal microscope images of the slow-digesting brown rice nutrient substrate of Comparative Example 2.

[0033] Figure 5 The images are 500x electron microscope images and 630x laser confocal microscope images of the slow-digesting brown rice nutrient substrate of Comparative Example 3.

[0034] Figure 6 The images are 500x electron microscope images and 630x laser confocal microscope images of the slow-digesting brown rice nutrient substrate of Comparative Example 4.

[0035] Figure 7 The images are 500x electron microscope images and 630x laser confocal microscope images of the slow-digesting brown rice nutrient substrate of Comparative Example 5.

[0036] Figure 8 The images are 500x electron microscope images and 630x laser confocal microscope images of the slow-digesting brown rice nutrient substrate of Comparative Example 6.

[0037] Figure 9 The images show a 500x electron microscope image and a 630x laser confocal microscope image of the slow-digesting brown rice nutrient substrate used in Comparative Example 7. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer and more explicit, the invention is further illustrated below through embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the application of this invention. Unless otherwise specified, all materials used in the following embodiments are commercially available products.

[0039] Example 1

[0040] Brown rice slow-digestible nutritional base was prepared based on 1 kg of brown rice. The proportions of other ingredients added (based on the weight of brown rice) are as follows:

[0041] Whey protein powder: 30%, soybean peptides: 12%, pullulanase: 0.7%; wherein, the pullulanase concentration is 1000 U / g, and the molecular weight of soybean peptides is 800~1200 Da.

[0042] The preparation method in this embodiment is as follows:

[0043] S1: Grind brown rice through an 80-mesh sieve. Mix brown rice flour, whey protein powder, and pullulanase evenly according to the above proportions. Then, feed the mixture into a twin-screw extruder for one extrusion. Collect the extruded material to obtain a one-extrusion composite. The feed rate of the twin-screw extruder is set to 5 kg / h, the water content is set to 50% (based on material mass), the screw speed is set to 50 rpm, and the temperature zones of the twin-screw extruder are set to 60 ℃, 60 ℃, 60 ℃, 60 ℃, and 100 ℃.

[0044] S2: The primary extrusion compound is dried in a heat pump drying system at 60 ℃, then pulverized and sieved through an 80-mesh sieve to obtain the primary extrusion compound dry powder;

[0045] S3: Thoroughly mix the dry powder of the primary extrusion complex with soybean peptides, and feed it into a twin-screw extruder for secondary extrusion; collect the extruded material to obtain the secondary extrusion complex; wherein, the feed rate of the twin-screw extruder is set to 5 kg / h, the water content is set to 50% (based on material mass conversion), the screw speed is set to 50 rpm, and the temperature zones of the twin-screw extruder are set to 60℃, 60℃, 60℃, 60℃, and 100℃;

[0046] S4: The secondary extrusion composite is dried in a heat pump drying system at 60 ℃, pulverized and sieved through an 80-mesh sieve to obtain the slow-digesting brown rice nutritional food base.

[0047] Example 2

[0048] Brown rice slow-digestible nutritional base was prepared based on 1 kg of brown rice. The proportions of other ingredients added (based on the weight of brown rice) are as follows:

[0049] Whey protein powder: 20%, soybean peptides: 8%, pullulanase: 0.4%; wherein, the pullulanase concentration is 500 U / g, and the molecular weight of soybean peptides is 800~1200 Da.

[0050] The preparation method in this embodiment is as follows:

[0051] S1: Grind brown rice through an 80-mesh sieve. Mix brown rice flour, whey protein powder, and pullulanase evenly according to the above proportions. Then, feed the mixture into a twin-screw extruder for one extrusion. Collect the extruded material to obtain a one-extrusion composite. The feed rate of the twin-screw extruder is set to 5 kg / h, the water content is set to 50% (based on material mass), the screw speed is set to 50 rpm, and the temperature zones of the twin-screw extruder are set to 60 ℃, 60 ℃, 60 ℃, 60 ℃, and 100 ℃.

[0052] S2: The primary extrusion compound is dried in a heat pump drying system at 60 ℃, then pulverized and sieved through an 80-mesh sieve to obtain the primary extrusion compound dry powder;

[0053] S3: Thoroughly mix the dry powder of the primary extrusion complex with soybean peptides, and feed it into a twin-screw extruder for secondary extrusion; collect the extruded material to obtain the secondary extrusion complex; wherein, the feed rate of the twin-screw extruder is set to 5 kg / h, the water content is set to 50% (based on material mass conversion), the screw speed is set to 50 rpm, and the temperature zones of the twin-screw extruder are set to 60℃, 60℃, 60℃, 60℃, and 100℃;

[0054] S4: The secondary extrusion composite is dried in a heat pump drying system at 60 ℃, pulverized and sieved through an 80-mesh sieve to obtain the slow-digesting brown rice nutritional food base.

[0055] This invention fully verifies the feasibility and superiority of the technical solutions described in this invention by designing comparative examples from multiple dimensions (processing technology, formulation composition, and molecular weight of soybean peptides). It is noteworthy that in all comparative examples, the amount of raw materials added is the same as in the examples used as controls. The specific comparative example settings are shown in Tables 1-3 below.

[0056] Table 1 Comparative examples set according to different processing methods

[0057]

[0058] Table 2 Comparative ratios set according to different formulation compositions (+ indicates addition, -- indicates no addition)

[0059]

[0060] Table 3 Comparative proportions based on different molecular weights of soybean peptides

[0061]

[0062] The following is an explanation of each comparative example:

[0063] Comparative Example 1

[0064] The difference between this comparative example and Example 2 is that all raw materials are compounded through a single extrusion process:

[0065] The slow-digestible brown rice nutrient base mentioned in this invention was prepared based on 1 kg of brown rice. The proportions of other ingredients added (based on the mass of brown rice) are as follows:

[0066] Whey protein powder: 20%, soybean peptides: 8%, pullulanase: 0.4%; wherein, the pullulanase concentration is 500 U / g, and the molecular weight of soybean peptides is 800~1200 Da.

[0067] The preparation method for this comparative example is as follows:

[0068] S1: Grind brown rice through an 80-mesh sieve. Mix brown rice flour, whey protein powder, soybean peptides, and pullulanase evenly according to the above proportions. Then feed the mixture into a twin-screw extruder, collect the extruded material, and obtain the extrusion complex. The feed rate of the twin-screw extruder is set to 5 kg / h, the water content is set to 50% (based on material mass), the screw speed is set to 50 rpm, and the temperature zones of the twin-screw extruder are set to 60 ℃, 60 ℃, 60 ℃, 60 ℃, and 100 ℃ for one extrusion.

[0069] S3: The extrusion compound is dried in a heat pump drying system at 60 ℃, pulverized and sieved through an 80-mesh sieve to obtain brown rice food base material.

[0070] Comparative Example 2

[0071] The difference between this comparative example and Example 2 is that the mixture is obtained solely through physical compounding:

[0072] Brown rice slow-digestible nutritional base was prepared based on 1 kg of brown rice. The proportions of other ingredients added (based on the weight of brown rice) are as follows:

[0073] Whey protein powder: 20%, soybean peptides: 8%, pullulanase: 0.4%; wherein, the pullulanase concentration is 500 U / g, and the molecular weight of soybean peptides is 800~1200 Da.

[0074] The preparation method for this comparative example is as follows:

[0075] S1: Grind brown rice through an 80-mesh sieve, and mix brown rice flour, whey protein powder, soy peptides and pullulanase evenly according to the above proportions to obtain a mixture.

[0076] S2: Place the mixture in a heat pump drying system and dry at 60 ℃ to obtain brown rice food base.

[0077] Comparative Example 3

[0078] The difference between this comparative example and Example 2 is that extrusion compounding was performed without the addition of pullulanase:

[0079] Brown rice slow-digestible nutritional base was prepared based on 1 kg of brown rice. The proportions of other ingredients added (based on the weight of brown rice) are as follows:

[0080] Whey protein powder: 20%, soybean peptides: 8%; the molecular weight of soybean peptides is 800~1200 Da.

[0081] The preparation method for this comparative example is as follows:

[0082] S1: Grind brown rice through an 80-mesh sieve. Mix brown rice powder and whey protein powder evenly according to the above ratio, and then feed the mixture into a twin-screw extruder for one extrusion. Collect the extruded material to obtain a one-extrusion composite. The feed rate of the twin-screw extruder is set to 5 kg / h, the water content is set to 50% (based on the material mass), the screw speed is set to 50 rpm, and the temperature zones of the twin-screw extruder are set to 60 ℃, 60 ℃, 60 ℃, 60 ℃, and 100 ℃.

[0083] S2: The primary extrusion compound is dried in a heat pump drying system at 60 ℃, then pulverized and sieved through an 80-mesh sieve to obtain the primary extrusion compound dry powder;

[0084] S3: Thoroughly mix the dry powder of the primary extrusion complex with soybean peptides, and feed it into a twin-screw extruder for secondary extrusion; collect the extruded material to obtain the secondary extrusion complex; wherein, the feed rate of the twin-screw extruder is set to 5 kg / h, the water content is set to 50% (based on material mass conversion), the screw speed is set to 50 rpm, and the temperature zones of the twin-screw extruder are set to 60℃, 60℃, 60℃, 60℃, and 100℃;

[0085] S4: The secondary extrusion composite is dried in a heat pump drying system at 60 ℃, pulverized and sieved through an 80-mesh sieve to obtain brown rice food base material.

[0086] Comparative Example 4

[0087] The difference between this comparative example and Example 2 is that extrusion compounding was performed without the addition of soybean peptides:

[0088] Brown rice slow-digestible nutritional base was prepared based on 1 kg of brown rice. The proportions of other ingredients added (based on the weight of brown rice) are as follows:

[0089] Whey protein powder: 20%, pullulanase: 0.4%; wherein, the pullulanase concentration is 500 U / g.

[0090] The preparation method for this comparative example is as follows:

[0091] S1: Grind brown rice through an 80-mesh sieve. Mix brown rice flour, whey protein powder, and pullulanase evenly according to the above proportions. Then, feed the mixture into a twin-screw extruder for one extrusion. Collect the extruded material to obtain a one-extrusion composite. The feed rate of the twin-screw extruder is set to 5 kg / h, the water content is set to 50% (based on material mass), the screw speed is set to 50 rpm, and the temperature zones of the twin-screw extruder are set to 60 ℃, 60 ℃, 60 ℃, 60 ℃, and 100 ℃.

[0092] S2: The primary extrusion compound is dried in a heat pump drying system at 60 ℃, then pulverized and sieved through an 80-mesh sieve to obtain the primary extrusion compound dry powder;

[0093] S3: The dry powder of the primary extrusion compound is fed into a twin-screw extruder for secondary extrusion; the extruded material is collected to obtain the secondary extrusion compound; wherein, the feed rate of the twin-screw extruder is set to 5 kg / h, the water content is set to 50% (converted according to the material mass), the screw speed is set to 50 rpm, and the temperature zones of the twin-screw extruder are set to 60 ℃, 60 ℃, 60 ℃, 60 ℃, and 100 ℃;

[0094] S4: The secondary extrusion composite is dried in a heat pump drying system at 60 ℃, pulverized and sieved through an 80-mesh sieve to obtain brown rice food base material.

[0095] Comparative Example 5

[0096] The difference between this comparative example and Example 2 is that extrusion compounding was performed without the addition of whey protein powder:

[0097] Brown rice slow-digestible nutritional base was prepared based on 1 kg of brown rice. The proportions of other ingredients added (based on the weight of brown rice) are as follows:

[0098] Soybean peptides: 8%, pullulanase: 0.4%; wherein, the pullulanase concentration is 500 U / g, and the molecular weight of soybean peptides is 800~1200 Da.

[0099] The preparation method for this comparative example is as follows:

[0100] S1: Grind brown rice through an 80-mesh sieve. Mix the brown rice powder and pullulanase evenly according to the above ratio, and then feed the mixture into a twin-screw extruder for one extrusion. Collect the extruded material to obtain a one-extrusion composite. The feed rate of the twin-screw extruder is set to 5 kg / h, the water content is set to 50% (based on the material mass), the screw speed is set to 50 rpm, and the temperature zones of the twin-screw extruder are set to 60 ℃, 60 ℃, 60 ℃, 60 ℃, and 100 ℃.

[0101] S2: The primary extrusion compound is dried in a heat pump drying system at 60 ℃, then pulverized and sieved through an 80-mesh sieve to obtain the primary extrusion compound dry powder;

[0102] S3: Thoroughly mix the dry powder of the primary extrusion complex with soybean peptides, and feed it into a twin-screw extruder for secondary extrusion; collect the extruded material to obtain the secondary extrusion complex; wherein, the feed rate of the twin-screw extruder is set to 5 kg / h, the water content is set to 50% (based on material mass conversion), the screw speed is set to 50 rpm, and the temperature zones of the twin-screw extruder are set to 60℃, 60℃, 60℃, 60℃, and 100℃;

[0103] S4: The secondary extrusion composite is dried in a heat pump drying system at 60 ℃, pulverized and sieved through an 80-mesh sieve to obtain brown rice food base material.

[0104] Comparative Example 6

[0105] The difference between this comparative example and Example 2 is that it uses soybean peptides with a smaller molecular weight for compounding:

[0106] Brown rice slow-digestible nutritional base was prepared based on 1 kg of brown rice. The proportions of other ingredients added (based on the weight of brown rice) are as follows:

[0107] Whey protein powder: 20%, soybean peptides: 8%, pullulanase: 0.4%; wherein, the pullulanase concentration is 500 U / g, and the molecular weight of soybean peptides is 200~500 Da.

[0108] The preparation method of this comparative example is the same as that of Example 2, and brown rice food base is obtained.

[0109] Comparative Example 7

[0110] The difference between this comparative example and Example 2 is that it uses soybean peptides with a larger molecular weight for compounding:

[0111] Brown rice slow-digestible nutritional base was prepared based on 1 kg of brown rice. The proportions of other ingredients added (based on the weight of brown rice) are as follows:

[0112] Whey protein powder: 20%, soybean peptides: 8%, pullulanase: 0.4%; wherein, the pullulanase concentration is 500 U / g, and the molecular weight of soybean peptides is 1500~2000 Da.

[0113] The preparation method of this comparative example is the same as that of Example 2, and brown rice food base is obtained.

[0114] Test case

[0115] The digestibility and other experiments conducted on the food base samples prepared in the above embodiments and comparative examples further demonstrated the digestion-delaying effect of the brown rice slow-digesting nutrient base designed and constructed based on the "graded filling structure" of the present invention.

[0116] I. In vitro digestion assay

[0117] By simulating the enzymatic digestion of food in the human gut, and measuring the amount of glucose released from brown rice flour and food base samples from the examples and comparative examples during a 2-hour digestion process, the contents of RDS, SDS, and RS, and the predicted glycemic index (eGI) were calculated. The testing procedure is as follows:

[0118] Disperse 600 mg of usable sample in 20 mL of sodium acetate buffer solution at pH 5.2. For uncooked samples (such as brown rice flour and Comparative Example 2), pregelatinization is required in a 95 °C boiling water bath for 20 min. Then, under 37 °C incubation conditions, gently stir and enzymatically digest the sample using a mixture of trypsin and amylose-glucose hepatase for 2 hours. At 0, 10, 20, 40, 60, 80, 100, and 120 min, 100 μL of the sample extracted from the digest is added to 2.9 mL of anhydrous ethanol to inactivate the enzymes. The supernatant is then collected by centrifugation, and the glucose concentration is analyzed using a glucose oxidase-peroxidase kit.

[0119] The conversion formulas for RDS, SDS, and RS are as follows:

[0120] RDS=(G 20 -G0)×0.9

[0121] SDS=(G 120 -G 20 ) × 0.9

[0122] RS = TS - (RDS + SDS)

[0123] Among them, G0, G 20 G 120 The glucose content was measured at 0, 20, and 120 min, respectively, and TS was the total starch content of the sample.

[0124] Hydrolysis rate curves were plotted based on the starch hydrolysis rate at different time points, and the eGI was calculated from the hydrolysis rate curves. The eGI conversion formula is as follows:

[0125] Hydrolysis rate (%) = G t ×0.9 / TS×100%

[0126] eGI = 0.862 × (Auc 样品 / Auc 白面包 +8.198

[0127] Among them, G t Let Auc be the amount of glucose hydrolyzed at time t. 样品 and Auc 白面包 The figures represent the areas under the hydrolysis rate curves for the sample and white bread, respectively.

[0128] Table 4 shows the evaluation results of Examples 1-2 and Comparative Examples 1-7.

[0129] Table 4. RDS, SDS, RS content and eGI results of the examples and comparative examples.

[0130]

[0131] In the in vitro digestion model, starch digestible within 0–20 min is classified as rapidly digestible starch (RDS), starch digestible within 20–120 min as slowly digestible starch (SDS), and starch indigestible within 120 min as resistant starch (RS). The predicted glycemic index (eGI) represents the predicted blood glucose fluctuations within 2 hours postprandial under in vitro digestion conditions. Table 4 shows that the SDS and RS contents of samples 1 and 2 were significantly higher, while their eGI was significantly lower than that of brown rice flour and other comparative samples. Sample 1 showed the most significant effect in delaying starch digestion, resulting in smaller blood glucose fluctuations, followed by Sample 2. Both fall into the category of low-GI food bases. This result confirms the feasibility and superiority of the "hierarchically filled" starch gel network structure constructed based on secondary extrusion in regulating digestion rates.

[0132] From a processing perspective, Comparative Example 1 (single extrusion) lacked an orderly "step-by-step" filling process, resulting in a chaotic and disordered compounding process between the large-molecule whey protein and the small-molecule soybean peptides. Consequently, the digestibility of the final product was not as good as that of Example 2. Comparative Example 2 (physical mixing), lacking the thermal-mechanical driving force and Maillard reaction during the extrusion process to achieve covalent bonding of protein and starch, failed to form an effective starch-protein complex. Its digestibility characteristics were no different from ordinary extruded brown rice flour, classifying it as a high-GI food base.

[0133] From a formulation perspective, Comparative Example 3 lacked pullulanase, resulting in insufficient amylose content for compounding within the system, thus limiting the compounding effect and leading to poor delayed digestion. This confirms that native brown rice starch needs enzymatic debranching modification to expose more linear segments, providing a structural and raw material basis for subsequent efficient compounding. A comparison between Example 2 and Comparative Examples 4 (whey protein only) and 5 (soybean peptides only) clearly reveals the necessity of the synergistic effect of large-size and small-size dual-protein systems. Although small-molecule soybean peptides can more easily penetrate the starch network due to their size advantage, when acting alone, the lack of a pre-constructed macroscopic framework from large-molecule whey protein for support and anchoring causes the peptide molecules to distribute randomly and disordered within the network, failing to form a continuous, dense barrier layer. Conversely, when whey protein first constructs the macroscopic network, soybean peptides of specific molecular weights can precisely embed themselves into the nanoscale gaps left by the former during secondary extrusion. This hierarchical strategy of filling gaps after framework construction achieves multi-scale barrier construction from macro to micro, which can more effectively prevent the approach and penetration of α-amylase and other enzymes, thus exhibiting the best digestion delay effect.

[0134] From the perspective of the molecular weight of key components, Comparative Examples 6 and 7 used soybean peptides with molecular weights that were too small (<500 Da) and too large (>1500 Da), respectively. However, their digestibility data still differed from that of Example 2, and both fell into the category of medium-GI food base materials. The reason for this is that in Comparative Example 6, the steric hindrance effect of the excessively small peptides was weak, making it difficult to form an effective physical barrier, and they might be hydrolyzed prematurely by peptidases in the gastrointestinal tract. In Comparative Example 7, the molecular flexibility of the excessively large peptides decreased, making it difficult to effectively embed into the gaps in the network constructed by whey protein and starch. As a result, their filling efficiency and final effect were not as good as the preferred molecular weight range used in Example 2.

[0135] II. Complexation Index (CI)

[0136] Disperse 1 g of sample into 9 mL of distilled water and let stand for 6 h. Then, take 0.2 mL of the suspension and add 4.8 mL of deionized water and 0.5 mL of iodine reagent (2% KI, 0.2% I2), vortex to mix. Finally, centrifuge the mixed sample solution at 6000 g for 15 min, and measure the absorbance of the supernatant at 690 nm using a UV spectrophotometer. The complexation index is calculated according to the following formula:

[0137] CI (%) = (Aref-Amix) / Aref×100

[0138] In the formula, Aref is the absorbance of the control sample (starch), and Amix is ​​the absorbance of the complex.

[0139] Table 5 shows the complexation index results for Examples 1-2 and Comparative Examples 1-7.

[0140] Table 5. Complexation index of the examples and comparative examples

[0141]

[0142] The complexation index (CI) effectively characterizes the interaction strength between protein and starch. The results, along with in vitro digestion data, confirm the formation effects of different complex structures. Furthermore, the scanning electron microscope (SEM) and laser confocal microscope (LCM) images in the accompanying figures also demonstrate the microscopic morphology of the starch-protein complex. As shown in Table 5, the complexation indices of Examples 1 and 2 are significantly higher than those of the other groups. This indicates that the graded filling processing strategy—first constructing a complex framework from macromolecular whey protein, and then secondary embedding with soybean peptides of specific molecular weights—successfully achieves the most complete and orderly binding between starch, protein, and peptides. Simultaneously, the SEM images show that Examples 1 and 2 exhibit a typical microscopic morphology of starch-protein crystals and molten states coexisting, indicating the formation of a dense and ordered complex network. In the LCM images, the composite fluorescence orange-red signal of Examples 1 and 2 is the most significant and continuously distributed, further confirming the high degree of binding between starch and protein / peptide.

[0143] In contrast, although Comparative Examples 1, 6, and 7 used the same raw materials, their composite effects were significantly inferior to Example 2 due to deviations in processing methods or the molecular weight of key components. Specifically, Comparative Example 1 (single extrusion) lacked an orderly grading step, resulting in a chaotic composite process and a low complexation index. Its microscopic image showed only scattered fluorescence signals, and almost all of it was in a molten state. Comparative Examples 6 and 7, on the other hand, failed to achieve effective gap filling due to either excessively small (insufficient filling efficiency) or excessively large (poor molecular flexibility, difficult to embed) soybean peptides, respectively, thus reducing the final complexation index and resulting in uneven fluorescence distribution. From the perspective of the reaction substrate, Comparative Example 3 had a limited content of amylose in its system because pullulanase was not added. As the main carrier for hydrophobic interactions and hydrogen bonding with proteins, the insufficient amount of amylose directly limited the total amount and stability of the complex, leading to a decrease in the degree of complexation and making it difficult to form a regular crystalline-molten coexistence morphology at the microscopic level.

[0144] More importantly, the results of Comparative Examples 4 and 5 reveal the limitations of single protein components. While Comparative Example 4 (whey protein only) could form a preliminary complex network, the remaining nanoscale voids could not be effectively shielded; although fluorescence signals were present in the laser confocal image, voids existed, and the crystalline regions were isolated. Comparative Example 5 (soybean peptides only), lacking the guidance and anchoring of a macromolecular backbone, showed peptide molecules randomly distributed within the starch network, making it difficult to construct a continuous, dense barrier layer; the fluorescence signal was diffuse and weak. Both examples, unable to form a complete multi-level barrier from macroscopic framework to microscopic filling, exhibited low complexation indices. Comparative Example 2, being a physical mixture without extrusion, had the lowest complexation index, consistent with expectations.

Claims

1. A method for preparing a slow-digesting nutritional food base of brown rice based on a graded filling structure, characterized in that, Includes the following steps: S1: Mix brown rice flour, whey protein powder and pullulanase evenly, then feed them into a twin-screw extruder for extrusion; collect the extruded material to obtain a primary extrusion complex; S2: Dry and pulverize the primary extrusion compound to obtain primary extrusion compound dry powder; S3: Mix the dry powder of the primary extrusion complex with soybean peptides evenly, feed it into a twin-screw extruder, and extrude it; collect the extruded material to obtain the secondary extrusion complex; S4: Dry and pulverize the secondary extrusion complex to obtain brown rice slow-digesting nutritional food base.

2. The method for preparing brown rice slow-digesting nutritional food base according to claim 1, characterized in that, The molecular weight range of the soybean peptide is 800~1200 Da, and the amount added is 8~12% of the mass of brown rice flour.

3. The method for preparing brown rice slow-digesting nutritional food base according to claim 2, characterized in that, The amount of whey protein powder added is 20-30% of the mass of brown rice flour.

4. The method for preparing brown rice slow-digesting nutritional food base according to claim 3, characterized in that, The pullulanase mentioned is a food-grade pullulanase, and its addition amount is 0.4~0.7% of the mass of brown rice flour, with an enzyme concentration of 500~1000 U / g.

5. The method for preparing brown rice slow-digesting nutritional food base according to claim 4, characterized in that, In step S1, the temperature zones of the twin-screw extruder are set to 50~60℃, 50~60℃, 50~60℃, 100~110℃, the feed rate is set to 5 kg / h, the water flow rate is set to 50% of the feed rate, and the screw speed is set to 50 rpm.

6. The method for preparing brown rice slow-digesting nutritional food base according to claim 5, characterized in that, In step S3, the temperature zones of the twin-screw extruder are set to 60~80℃, 60~80℃, 60~80℃, 100~110℃, the feed rate is set to 5 kg / h, the water flow rate is set to 50% of the feed rate, and the screw speed is set to 50 rpm.

7. The method for preparing brown rice slow-digesting nutritional food base according to claim 6, characterized in that, In steps S1 and S3, the temperature zones of the twin-screw extruder are set to 60°C, 60°C, 60°C, 60°C, and 100°C.

8. The method for preparing brown rice slow-digesting nutritional food base according to claim 7, characterized in that, In step S1, brown rice is pulverized through an 80-mesh sieve to obtain brown rice flour; in step S2, the primary extrusion compound is dried and then pulverized through an 80-mesh sieve to obtain primary extrusion compound dry powder.

9. The method for preparing brown rice slow-digesting nutritional food base according to claim 8, characterized in that, The drying temperature in steps S2 and S4 is 60°C.

10. The slow-digesting brown rice nutritional food base prepared by the method of claim 1.

Images