Slowly digestible food and a method for preparing the same

Abstract

This invention belongs to the field of food processing technology, specifically relating to a slowly digestible food and its preparation method. The invention provides a method for preparing a slowly digestible food, in which a blended liquid is continuously extruded into a calcium ion solution. The shear force during extrusion causes suspended starch particles to align orderly along the flow direction. Simultaneously, the ionic cross-linked colloids in the blended liquid rapidly cross-link with calcium ions to form a continuous, dense gel, which fixes and encapsulates the orderly arranged starch particles, achieving continuous and tight encapsulation. This actively blocks digestive enzymes from contacting the starch in physical space, forming more tortuous diffusion channels for digestive enzymes and affecting the particle expansion behavior during subsequent heating and gelatinization. The preparation method described in this invention achieves instantaneous gel setting within minutes, overcoming the limitations of traditional methods for preparing slowly digestible foods, such as the long cycles required for starch retrogradation and moist heat treatment, significantly improving preparation efficiency.

Description

Technical Field

[0001] This invention belongs to the field of food processing technology, specifically relating to a slow-digesting food and its preparation method. Background Technology

[0002] Noodles and vermicelli products are a staple food worldwide, widely popular for their smooth texture and ease of preparation. However, these products are primarily made from refined starch and are considered fast-digesting foods. Their high glycemic index has become a significant public health issue, posing a particular health risk to people with diabetes and those managing their blood sugar.

[0003] Slow-digesting foods are those that are digested and absorbed at a slower rate, releasing energy steadily and avoiding sharp fluctuations in blood sugar while prolonging satiety. Currently, strategies to reduce the glycemic index (GI) of such products mainly include: (1) blending with whole grains or legumes, which are rich in dietary fiber, but this often results in a rough texture and poor taste; (2) directly adding resistant starch or enzyme inhibitors, but this has limitations such as high cost and potential flavor distortion; and (3) adding edible gums (such as konjac gum and xanthan gum) to improve texture and hoping to delay digestion by forming a starch-colloid mixed network. However, conventional blended networks have limited effect on reducing digestibility, mainly because they fail to effectively construct a physical barrier that prevents digestive enzymes from contacting starch. Therefore, developing new starch-based staple food products that combine excellent taste and low GI characteristics is of urgent practical significance. Summary of the Invention

[0004] The purpose of this invention is to provide a slow-digesting food and its preparation method. The method of this invention utilizes ion-crosslinked colloids and calcium ions to encapsulate starch, which can effectively block or delay the penetration and diffusion of digestive enzymes into the interior, thereby significantly reducing the hydrolysis rate of starch.

[0005] This invention provides a method for preparing a slow-digesting food, comprising the following steps: continuously extruding a blended liquid into a calcium ion solution and solidifying it for 10-40 minutes to obtain the slow-digesting food; The blend liquid comprises: ion-crosslinked colloid, starch-based raw material, and water.

[0006] As a preferred embodiment, the slow-digesting food may be in the shape of strips, filaments, flakes, or blocks.

[0007] As a preferred embodiment, the blend liquid comprises, by weight, 0.5 to 2 parts of ion-crosslinked colloid, 10 to 40 parts of starch raw material, and 100 parts of water.

[0008] As a preferred embodiment, the ion-crosslinked colloid comprises sodium alginate and / or gellan gum.

[0009] As a preferred embodiment, the extrusion speed is 0.2~0.6 mL / s; during extrusion, the outlet of the extrusion device is placed in a calcium ion solution.

[0010] As a preferred embodiment, the concentration of calcium ions in the calcium ion solution is 0.0901~0.3604 mol / L.

[0011] As a preferred embodiment, before extrusion, the mixture is further subjected to a process of allowing it to stand.

[0012] As a preferred embodiment, the settling time is 2 to 5 minutes.

[0013] As a preferred embodiment, after obtaining the slow-digesting food, the method further includes: removing residual calcium ions from the surface of the slow-digesting food.

[0014] The present invention also provides a slowly digestible food prepared by the preparation method described above, wherein the slowly digestible food has a rapidly digestible starch content of <51%.

[0015] Beneficial Effects: This invention provides a method for preparing a slowly digestible food, comprising the following steps: continuously extruding a blended liquid into a calcium ion solution and solidifying it for 10-40 minutes to obtain the slowly digestible food; the blended liquid comprises: an ion-crosslinked colloid, starch-based raw materials, and water. Upon encountering calcium ions, the blended liquid prepared by the ion-crosslinked colloid and starch-based raw materials rapidly crosslinks to form a dense three-dimensional gel network, simultaneously encapsulating starch granules within the formed chambers. During subsequent gelatinization (the process of cooking the slowly digestible food), the dense gel network effectively protects the starch granules, confining them within the limited space of the chambers, preventing the diffusion and contact of enzyme molecules such as α-amylase to the starch substrate in the digestive system, and reducing the effective binding sites between enzymes and starch molecules. Simultaneously, the continuous gel framework restricts the swelling and disintegration of starch during digestion, maintaining the integrity of the system and slowing down the enzymatic hydrolysis rate of starch. Based on the protective effect of the three-dimensional gel network, the content of rapidly digestible starch that can be quickly hydrolyzed by enzymes is significantly reduced in the obtained slowly digestible food system, thereby achieving the slow digestibility of starch. The preparation method described in this invention achieves instant gel setting within minutes, overcoming the long cycle required by traditional methods for preparing slow-digestible foods, such as starch retrogradation and moist heat treatment, and has significant advantages in process efficiency. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly described below.

[0017] Figure 1The digestibility curves of the matured samples in Examples 9-13 are shown. Figure 2 The images are SEM images of the wet and cooked samples of raw vermicelli in Example 9, magnified 50 times. Figure 3 SEM images of the wet and cooked samples of raw vermicelli in Example 10, magnified 200 times; Figure 4 The images are SEM images of the wet and cooked samples of raw vermicelli in Example 11, magnified 200 times. Figure 5 SEM images of the wet and cooked samples of raw vermicelli in Example 12, magnified 200 times; Figure 6 SEM images of the wet and cooked samples of raw vermicelli in Example 13, magnified 200 times; Figure 7 The shear curves of the matured samples in Examples 9-13 are shown. Figure 8 The images show the stress-strain curves of the aged samples in Examples 1-13; from left to right, they are the aged samples of Examples 9-13, the aged samples of Examples 1-4, and the aged samples of Examples 5-8. Figure 9 A schematic diagram illustrating the laboratory preparation of slowly digestible foods; Figure 10 A photograph of a slow-digesting food prepared in the laboratory. in, Figures 2-6 , Figure 10 The image on the left shows a wet sample of raw vermicelli, and the image on the right shows a cooked sample. Detailed Implementation

[0018] This invention provides a method for preparing a slow-digesting food, comprising the following steps: continuously extruding a blended liquid into a calcium ion solution and solidifying it for 10-40 minutes to obtain the slow-digesting food; The blend liquid comprises: ion-crosslinked colloid, starch-based raw material, and water.

[0019] Unless otherwise specified, all raw materials involved in this invention are obtained through commercial means.

[0020] As one implementation method, the slow-digesting food can be in the form of strips, filaments, flakes, or blocks. When preparing strip or filament products, a linear gel structure can be formed through continuous extrusion; when preparing flake or block products, the corresponding shape can be obtained by adjusting the extrusion nozzle shape, mold, or receiving method. The core remains the rapid cross-linking and shaping of the blended liquid after contact with calcium ions. This invention constructs an actively isolating physical barrier in a macroscopic food system to regulate starch digestibility. A three-dimensional gel network formed by ion-crosslinked colloids and calcium ions serves as an artificially designed cell wall mimic, achieving continuous and tightly sealed encapsulation of starch granules, actively blocking enzyme-substrate contact in physical space. According to in vitro digestion results, the food prepared using the method described in this invention has a lower content of rapidly digestible starch and a higher content of slowly digestible components, showing potential for developing low-GI starch-based foods.

[0021] This invention involves continuously extruding a blend into a calcium ion solution. The blend comprises an ion-crosslinked colloid, starch-based raw materials, and water. Upon contact with calcium ions, the blend prepared by the ion-crosslinked colloid and starch-based raw materials rapidly crosslinks to form a dense three-dimensional gel network, simultaneously encapsulating starch granules within the formed chambers. During subsequent gelatinization (the process of cooking slowly digestible foods), the dense gel network effectively protects the starch granules, confining them within the limited space of the chambers. This prevents the diffusion and contact of enzyme molecules such as α-amylase to the starch substrate, reducing the effective binding sites between enzymes and starch molecules. Simultaneously, the continuous gel framework restricts the swelling and disintegration of starch during digestion, maintaining the integrity of the system and slowing down the enzymatic hydrolysis rate. Based on the protective effect of the three-dimensional gel network, the content of rapidly digestible starch that can be quickly hydrolyzed by enzymes is significantly reduced in the resulting slowly digestible food system, thus achieving the slow digestibility of starch.

[0022] In one embodiment, the ionic crosslinking colloid includes sodium alginate and / or gellan gum. When the ionic crosslinking colloid is sodium alginate, the blend is continuously extruded into a calcium ion solution. Sodium alginate crosslinks with calcium ions, rapidly reacting to form an egg-box structure, and subsequently forming a sodium alginate-calcium gel that encapsulates the starch granules. Furthermore, when the blend is extruded into the calcium ion solution, a concentration difference exists between the sodium ions inside the blend and the calcium ions in the calcium ion solution. Calcium ions rapidly diffuse from the high-concentration calcium ion solution into the low-concentration sodium alginate droplets. During this diffusion process, the sodium alginate in contact immediately crosslinks and solidifies, forming a gel layer that propagates from the outside in, achieving instantaneous gel setting within minutes.

[0023] When the ionic cross-linked colloid is gellan gum, the carboxyl groups on the molecular chains are negatively charged in water, repelling each other and forming a disordered coil. When calcium ions (Ca) are added... 2+Afterward, calcium ions shield the electrostatic repulsion between negative charges and act as a specific ionic cross-linking bridge. At the same time, they form ionic bonds with the carboxyl groups on two adjacent gellan gum molecular chains, causing the molecular chains to change from disordered coils to ordered double helix structures, and further aggregate into a stable three-dimensional network, thereby instantly locking in a large number of water molecules and forming a tough gel.

[0024] In one embodiment, the blend liquid comprises, by weight, 0.5-2 parts of ionic crosslinking colloid, 10-40 parts of starch raw material, and 100 parts of water. In a specific embodiment of the present invention, the weight of the ionic crosslinking colloid can be any value from 0.5 to 2 parts, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2 parts; the weight of the starch can be any value from 10 to 40 parts, for example, 10, 11, 12, 13, 14, 15, 17, 19, 20, 22, 25, 28, 30, 33, 35, 37, 39, or 40 parts. The suitable concentration of the ionic crosslinking colloid in the present invention can form a sodium alginate-calcium gel network with calcium ions, achieving physical encapsulation of starch particles. When the water content is 100 parts, it is difficult to mix and form a uniform suspension when the starch content exceeds 50 parts by mass. When the concentration of the ion-crosslinked colloid is fixed, as the starch content increases, the content of rapidly digestible starch decreases, and the elasticity and toughness gradually improve.

[0025] In one embodiment, the starch raw material includes plant starch and / or cereal flour. This invention does not specifically limit the type and source of the plant starch; it can be obtained through conventional commercial methods in the art. In a specific embodiment of this invention, the starch can be at least one of potato starch, corn starch, and cassava starch. This invention does not specifically limit the type and source of the cereal flour; it can be obtained through conventional commercial methods in the art. In a specific embodiment of this invention, the cereal flour can be one or more of wheat flour, rice flour, corn flour, oat flour, and buckwheat flour. The starch raw materials of this invention are all based on natural starch as the main component, possessing good water dispersibility and matrix compatibility, and can be uniformly blended with sodium alginate. These raw materials themselves have a fast digestion rate and strong glycemic index, and are a major source of carbohydrates in food. After extrusion and orientation arrangement, they can all be completely encapsulated and fixed by a dense gel network formed by sodium alginate-calcium ion crosslinking, limiting the gelatinization and expansion rupture of starch granules upon heating, effectively delaying the starch hydrolysis process, thereby achieving the effect of reducing the digestion rate and preparing slowly digestible foods. Therefore, as long as the starch raw material can form an extrudable suspension system in the aqueous phase and can be embedded and fixed by an ion-crosslinked colloidal network, it can be applied to the method of the present invention; different starch sources may affect the final texture and digestion rate, but do not change the basic mechanism of the present invention to delay starch enzymatic hydrolysis by constructing a physical barrier through an ion-crosslinked network.

[0026] In one embodiment, the preparation of the blend includes: mixing an ionically cross-linked colloidal solution with a starch-based raw material to obtain the blend. Taking sodium alginate as an example, the preparation process of the ionically cross-linked colloidal solution includes: mixing and stirring sodium alginate and water to obtain a sodium alginate solution, i.e., the ionically cross-linked colloidal solution. In one embodiment, the stirring temperature is 25°C; the stirring time is 4 hours. The suitable stirring time and temperature of the present invention allow the ionically cross-linked colloid to dissolve completely. After obtaining the sodium alginate solution, a starch-based raw material is added to obtain the blend. In one embodiment, after obtaining the blend, the process further includes: standing; the standing time is 2-5 minutes. In a specific embodiment of the present invention, the standing time can be any value within 2-5 minutes, for example, 2, 2.5, 3, 3.5, 4, 4.5, or 5 minutes. The settling process described in this invention helps remove air bubbles from the blended solution. Air bubbles increase the surface area of ​​the same volume of vermicelli in contact with the enzyme solution, and the enzyme may also penetrate the vermicelli more quickly. If air bubbles are not removed, it will affect the physical properties of the vermicelli, such as texture and stretchability, and may also affect digestion. If the settling time is too short, the air bubbles will not be completely eliminated; if the settling time is too long, the starch will sink to the bottom, and the vermicelli will not be able to present a uniform solution when extruded.

[0027] This invention involves continuously extruding the blended liquid into a calcium ion solution for solidification. Continuous extrusion, as described in this invention, refers to continuously injecting the blended liquid into the calcium ion solution in a fluid form, causing the blended liquid to continuously solidify upon contact with calcium ions, thereby obtaining a uniformly shaped gel-like food. The fluid form described in this invention includes a liquid column and / or filaments. Taking sodium alginate as an ion-crosslinked colloid as an example, the continuous extrusion of the blended liquid into the calcium ion solution utilizes the shear force during extrusion to align the suspended starch particles along the flow direction. Simultaneously, the sodium alginate in the blended liquid rapidly crosslinks with calcium ions to form a continuous, dense gel, fixing and encapsulating the ordered starch particles. This achieves continuous and tight encapsulation of the starch particles, actively blocking digestive enzymes from contacting the starch in physical space, forming more tortuous diffusion channels for digestive enzymes, and affecting the particle expansion behavior during subsequent heating and gelatinization.

[0028] In one embodiment, the concentration of calcium ions in the calcium ion solution is 0.0901~0.3604 mol / L. In a specific embodiment of the present invention, the concentration of calcium ions in the calcium ion solution can be any value within the range of 0.0901~0.3604 mol / L, for example, 0.0901, 0.1, 0.12, 0.13, 0.15, 0.20, 0.22, 0.25, 0.28, 0.30, 0.33, 0.35, 0.36, or 0.3604 mol / L. In another embodiment, the calcium ion solution includes either calcium chloride solution or calcium lactate solution. Taking calcium chloride as an example, the concentration of calcium ions in the calcium ion solution can be any value within the range of 1%~4% (w / v), for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, or 4%. This invention allows for the simultaneous and precise control of the product's texture (such as elasticity and toughness) and nutritional function (digestion rate) by adjusting the concentration of ion-crosslinked colloids and the ratio of starch. This provides a universal and designable platform for developing functional convenience foods that meet the needs of different population groups.

[0029] In one embodiment, the extrusion speed is 0.2~0.6 mL / s. In a specific embodiment of the present invention, the extrusion speed can be any value within the range of 0.2~0.6 mL / s, for example, 0.2, 0.3, 0.4, 0.5, or 0.6 mL / s. In one specific embodiment of the present invention, the extrusion rate is 30 mL / min, i.e., 0.5 mL / s. Taking the preparation of a strip-shaped slow-digesting food (gel strip) as an example, if the extrusion speed is too fast, the diameter of the formed gel strip will decrease; if it is too slow, it will stagnate at the tip of the syringe, forming lumps that cannot be extruded further. At this extrusion speed, the gel diameter and overall uniformity can be guaranteed.

[0030] In one embodiment, during extrusion, the outlet of the extrusion device is placed in a calcium ion solution. Compared to the preparation of slowly digested starch granules (applicant's prior patent 202110760532.5), during extrusion, the outlet of the extrusion device does not come into contact with the calcium ion solution, and the slowly digested starch granules are formed in a static state, resulting in a looser structure. In contrast, in this invention, the outlet of the extrusion device is placed in a calcium ion solution. At the moment of extrusion, the molecular chains of the ion-crosslinked colloid are stretched and oriented under shear force, and then instantly crosslink. This results in a higher density and smaller pore size in the formed three-dimensional network. The denser gel network means stronger physical binding of the starch granules, which can more effectively delay the penetration of water molecules and the attack of amylase.

[0031] The curing time described in this invention is 10-40 minutes. In specific embodiments of this invention, the curing time can be any value within the range of 10-40 minutes, such as 10, 15, 20, 23, 25, 28, 30, 35, 37, or 40 minutes. When the slow-digesting food is in the form of strips or filaments, the curing time can be any value within the range of 10-20 minutes, such as 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 minutes. When the slow-digesting food is in the form of flakes, the curing time can be any value within the range of 10-40 minutes, such as 10, 15, 20, 23, 25, 28, 30, 35, 37, or 40 minutes. When the slow-digesting food is in block form, the curing time can be any value between 20 and 40 minutes, such as 20, 22, 23, 25, 26, 27, 29, 30, 33, 35, 36, 38, or 40 minutes. In this invention, the blended liquid is extruded into a calcium ion solution, and the network of the gel-like food begins to form. However, the reaction rate on the outside of the gel-like food is faster than on the inside. As the curing time increases, the crosslinking density continues to increase, but the network is basically formed within 20 minutes of curing. Therefore, limiting the curing time to 10-40 minutes is beneficial for gel network formation, enabling instantaneous curing and shaping of the gel-like food, greatly shortening the production cycle. The curing time in this invention starts from the moment the blended liquid is extruded and contacts the calcium ion solution. For each 1.5 minutes of gel-like food produced, the curing time needs to be recalculated separately.

[0032] As one implementation method, after obtaining the slow-digesting food, the process further includes removing residual calcium ions from the surface of the slow-digesting food. As one implementation method, the removal includes rinsing the gel strip with deionized water. Residual calcium ions can undergo secondary excessive cross-linking with sodium alginate on the material surface, forming a dense, hard, but brittle outer layer that easily produces a sudden breaking sensation when bitten. Furthermore, calcium chloride has a bitter and astringent taste. If not thoroughly rinsed after solidification, the residual calcium ions on the food surface will directly contribute to an unpleasant taste. A schematic diagram of the preparation of slow-digesting food using sodium alginate as an ion-crosslinking colloid in the laboratory is shown below. Figure 9 As shown; a physical image of the prepared slow-digesting food is shown below. Figure 10 As shown.

[0033] Unlike traditional passive methods that rely on starch retrogradation, the method described in this invention actively creates a physical encapsulation environment for starch granules by constructing an ion-crosslinked colloidal-calcium ion crosslinking network. Results show that this technology can significantly reduce the rapidly digestible starch (RDS) content in the final product, from approximately 74% in ordinary potato noodles to 28%. This demonstrates the great potential for preparing starch-based foods with low GI potential through physical means.

[0034] This invention also provides a slowly digestible food prepared by the method described above, wherein the rapidly digestible starch content of the slowly digestible food is <51%. As one embodiment, the rapidly digestible starch content of the slowly digestible food is <35%. The slowly digestible food prepared using the method of this invention exhibits a tensile strain of up to 180% and a stress range of 8000 Pa to 80000 Pa, demonstrating good taste and chewiness. Furthermore, the rapidly digestible starch content of the obtained slowly digestible food is reduced from 74% in ordinary potato vermicelli to 28%, significantly increasing its slow digestibility. Compared to the slowly digestible starch granules prepared by the applicant's prior patent (202110760532.5), which are dropped into a calcium ion solution in droplet form, resulting in a disordered starch arrangement and a particle size of 1-2 mm, most of the starch cannot be directly coated, leading to a higher rapidly digestible starch content. Moreover, using slowly digestible starch granules as a raw material results in a poorer taste; furthermore, crushing them reduces their anti-digestion effect. The slow-digesting food obtained by the preparation method described in this invention is a macroscopic food. The dense three-dimensional gel network can effectively block or delay the penetration and diffusion of digestive enzymes into the interior, thereby significantly reducing the hydrolysis rate of starch and ultimately obtaining a product with low fast-digesting starch content and low GI potential.

[0035] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0036] The materials and reagents used in the embodiments of this invention are as follows: Sodium alginate (SA), food grade, purchased from Qingdao Mingyue Seaweed Group Co., Ltd. Potato starch, purchased from Gansu Lantian Potato Industry Development Co., Ltd.; Tapioca starch, purchased from Thai Hua Co., Ltd., Thailand; Pea starch, purchased from Yantai Shuangta Food Co., Ltd.; Anhydrous calcium chloride (food grade); the experimental water was deionized water.

[0037] Example 1 A slow-digesting food, prepared by the following steps: (1) Accurately weigh 0.8 g sodium alginate powder, dissolve it in 100 mL of deionized water, and stir continuously at 25°C for 4 hours on a magnetic stirrer to ensure complete dissolution. Prepare a 0.8% SA solution for later use.

[0038] (2) Add 10 g of potato starch to a 0.8% SA solution, and then let it stand for 5 minutes to remove air bubbles, to obtain a uniform starch / SA mixed suspension, which is called the mixed solution.

[0039] (3) Prepare a 2% (w / v) calcium chloride aqueous solution as a coagulation bath; use a 50 mL syringe (equipped with a round needle with an inner diameter of 2.0 mm) to draw up the blend and squeeze the blend vertically into the coagulation bath at a constant speed (30 mL / min). The extrusion time is <1.5 min. The extruded linear gel strip is left to stand and solidify in the coagulation bath for 20 minutes to ensure complete ionic crosslinking reaction. Then, remove the gel strip, rinse it with deionized water to remove residual calcium ions on the surface, and drain it to obtain the raw starch strip wet sample.

[0040] (4) Take an appropriate amount of raw vermicelli wet sample and cook it in boiling water for 1 minute and 30 seconds. After taking it out, quickly immerse it in ice water to cool for 10 seconds to stop the residual heat effect, drain the water, and it is the cooked sample to be tested.

[0041] Example 2 A slow-digesting food, prepared in the same way as in Example 1, except that in step (2), 20 g of potato starch is added to a 0.8% SA solution.

[0042] Example 3 A slow-digesting food, prepared in the same way as in Example 1, except that in step (2), 30 g of potato starch is added to a 0.8% SA solution.

[0043] Example 4 A slow-digesting food, prepared in the same way as in Example 1, except that in step (2), 40 g of potato starch is added to a 0.8% SA solution.

[0044] Test Example 1 Using the cooked samples prepared in Examples 1-4 as the test subjects, the contents of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) in each sample were determined.

[0045] (1) Disperse 3 g of trypsin (product number: P7545, Sigma-Aldrich Ltd., CAS No.: 8049-47-6) in 20 mL of deionized water and vortex for 5 min. After vortexing, transfer 15 mL of the supernatant to a centrifuge tube and add 1.1 mL of α-glucosidase (product number: A7095, Sigma-Aldrich Ltd., CAS No.: 9032-08-0; EC No.: 232-877-2, enzyme activity: ≥260 U / mL) to prepare an enzyme solution. Note that the enzyme solution should be prepared and used immediately.

[0046] (2) After cooking the samples separately, weigh 0.2 g of the sample (converted dry weight) and 18 mL of acetate buffer (pH 5.20) and add them to a centrifuge tube. Then cool to 37°C, add 20 glass beads and 2 mL of enzyme solution to the centrifuge tube to obtain the hydrolysate. The mass of the sample (converted dry weight) is calculated according to the following formula: Sample mass = 0.2 / (1 - moisture content); where the moisture content is the water content of the fresh powder after cooking.

[0047] (3) Incubate the centrifuge tubes in a shaking water bath at 37°C for 0, 20, 60, 90, 120 and 180 min. At each time point, take 0.1 mL of the hydrolysate from the centrifuge tube and mix it with 0.9 mL of 90% ethanol solution.

[0048] (4) The content of hydrolyzed glucose in the supernatant after centrifugation was determined using the K-GLUC kit (purchased from Megazyme, Ireland, K-GLUC). The concentrations were measured at t=0 min (G0) and t=20 min (G...). 20 ), t=120 min (G 120 When calculating the content of RDS, SDS, and RS, use the total starch mass (S, mg) of the sample as an example, and calculate using the following formula: RDS (%) = (G 20 -G0)×0.9×100 / S; SDS (%) = (G 120 -G 20 ) × 0.9 × 100 / S; RS(%)=100-RDS(%)-SDS(%); Where G0 represents the absorbance of 100 μg of the mixed solution at 0 min / the absorbance of 100 μg of glucose); G 20 This represents the absorbance of 100 μg of the mixed solution at 20 min / the absorbance of 100 μg of glucose; G 120 1 represents the absorbance of 100 μg of the mixed solution at 120 min / absorbance of 100 μg of glucose; S represents the total starch mass in the sample; 0.9 is the stoichiometric constant of starch extracted from glucose.

[0049] The test results are shown in Table 1. Meanwhile, the content of various starches in ordinary potato starch noodles was used as a comparison. For relevant data on potato starch noodles, please refer to "Effects of peanut oligopeptides on the pasting properties of potato starch and digestive characteristics of dry, flat potato starch noodles".

[0050] Table 1. RDS, SDS, and RS contents in the ripened samples tested in Examples 1-4

[0051] Experimental results showed that, under the same sodium alginate concentration, the content of rapidly digestible starch decreased significantly with the increase of starch concentration, from 74% in the control to 30%.

[0052] Example 5 A slow-digesting food, the steps are as follows: (1) Accurately weigh 1.2 g sodium alginate powder, dissolve it in 100 mL of deionized water, and stir continuously at 25°C for 4 hours on a magnetic stirrer to ensure complete dissolution, and prepare a 1.2% SA solution for later use.

[0053] (2) Add 40 g of potato starch to a 1.2% SA solution, and then let it stand for 5 minutes to remove air bubbles, to obtain a uniform starch / SA mixed suspension, which is called the mixed solution.

[0054] (3) Prepare a 2% (w / v) calcium chloride aqueous solution as a coagulation bath; use a 50 mL syringe (equipped with a round needle with an inner diameter of 2.0 mm) to draw up the blend and squeeze the blend vertically into the coagulation bath at a constant speed (30 mL / min). The extruded linear gel strip is left to stand and solidify in the coagulation bath for 10 minutes to ensure complete ionic crosslinking reaction. Then, the gel strip is taken out, rinsed with deionized water to remove residual calcium ions on the surface, and drained to obtain a raw starch strip wet sample.

[0055] (4) Take an appropriate amount of raw vermicelli wet sample and cook it in boiling water for 1 minute and 30 seconds. After taking it out, quickly immerse it in ice water to cool for 10 seconds to stop the residual heat effect, drain the water, and it is the cooked sample to be tested.

[0056] Example 6 A slow-digesting food, prepared in the same way as in Example 5, except that: in step (3), it is cured for 20 minutes.

[0057] Example 7 A slow-digesting food, prepared in the same way as in Example 5, except that: in step (3), it is cured for 40 minutes.

[0058] Example 8 A slow-digesting food, prepared in the same way as in Example 5, except that: in step (3), it is cured for 60 minutes.

[0059] Test Example 2 Using the cooked samples prepared in Examples 5-8 as the test subjects, the contents of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) in each sample were determined. The method was the same as in Test Example 1, and the results are shown in Table 2.

[0060] Table 2. RDS, SDS, and RS contents in the ripened samples tested in Examples 5-8

[0061] During the process of extruding the mixed solution into calcium chloride, the network begins to form, but the reaction rate on the outside is still faster than that on the inside. As the curing time is extended, the crosslinking density continues to increase, but the network is basically formed in 20 minutes. Therefore, even if the time is extended to 60 minutes, the RDS content does not decrease much.

[0062] Example 9 A slow-digesting food, prepared by the following steps: (1) Accurately weigh 0.5 g sodium alginate powder, dissolve it in 100 mL of deionized water, and stir continuously at 25°C for 4 hours on a magnetic stirrer to ensure complete dissolution. Prepare a 0.5% SA solution for later use.

[0063] (2) Add 40 g of potato starch to a 0.5% SA solution, and then let it stand for 5 minutes to remove air bubbles, to obtain a uniform starch / SA mixed suspension, which is called the mixed solution.

[0064] (3) Prepare a 2% (w / v) calcium chloride aqueous solution as a coagulation bath; use a 50 mL syringe (equipped with a round needle with an inner diameter of 2.0 mm) to draw up the blend and squeeze the blend vertically into the coagulation bath at a constant speed (30 mL / min). The extruded linear gel strip is left to stand and solidify in the coagulation bath for 10 minutes to ensure complete ionic crosslinking reaction. Then, the gel strip is taken out, rinsed with deionized water to remove residual calcium ions on the surface, and drained to obtain a raw starch strip wet sample.

[0065] (4) Take an appropriate amount of raw vermicelli wet sample and cook it in boiling water for 1 minute and 30 seconds. After taking it out, quickly immerse it in ice water to cool for 10 seconds to stop the residual heat effect, drain the water, and it is the cooked sample to be tested.

[0066] Example 10 A slow-digesting food, prepared in the same way as in Example 9, except that: in step (1), an SA solution with a concentration of 0.8% is prepared.

[0067] Example 11 A slow-digesting food, prepared in the same way as in Example 9, except that: in step (1), an SA solution with a concentration of 1.2% is prepared.

[0068] Example 12 A slow-digesting food, prepared in the same way as in Example 9, except that: in step (1), an SA solution with a concentration of 1.6% is prepared.

[0069] Example 13 A slow-digesting food, prepared in the same way as in Example 9, except that: in step (1), an SA solution with a concentration of 2.0% is prepared.

[0070] Test Example 3 (1) Using the cooked samples prepared in Examples 9-13 as the test subjects, the contents of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) in each sample were determined. The method was the same as in Test Example 1, and the results are shown in Table 3. At the same time, the starch digestibility at 20, 60, 90, 120, and 180 min was determined. The method is described in [Zou, J., Zhang, K., Li, W., Qin, Y., Sun, Q., Ji, N., & Xie, F. (2024). Exploring the role of the thick and dense calcium alginate shell on the anti-digestibility mechanism of corn starch / carboxymethyl cellulose / calcium alginate liquid-core beads prepared by reverse spherification. Food Hydrocolloids, 156. https: / / doi.org / 10.1016 / j.foodhyd.2024.110357]. The detection results are shown in Table 3. Figure 1 As shown.

[0071] Table 3. Contents of RDS, SDS, and RS in Examples 9-13

[0072] Table 3 shows that, under the same starch concentration and curing time, RDS decreased significantly as the sodium alginate concentration increased from 0.5% to 0.8%. When the sodium alginate concentration continued to increase to 1.2%–2.0%, the RDS remained relatively stable at approximately 30%–32%, without further significant decrease. This indicates that under these starch addition and curing conditions, the encapsulation effect of the gel network on starch granules tended to stabilize. This may be because at a sodium alginate concentration of 0.5%, the number of sodium alginate molecular chains in the system was insufficient, and after calcium ion crosslinking, it mainly formed local gel regions, making it difficult to construct a continuous, complete, and dense calcium alginate network. Therefore, some starch granules could not be fully encapsulated, making them more prone to gelatinization, swelling, and enzymatic hydrolysis during subsequent ripening, resulting in a relatively high RDS content. When the sodium alginate concentration increased to 0.8%, the continuity and encapsulation coverage of the gel network tended to saturate. Further increasing the sodium alginate concentration had limited effect on improving the effective crosslinking density and enzyme diffusion barrier effect, thus the RDS stabilized at around 30% and no longer decreased significantly. When the sodium alginate concentration is fixed at 0.8%, as the starch concentration increases, the distance between starch molecules after gelatinization decreases and the interaction is enhanced. Under high starch concentration, the straight and branched chains of the broken starch granules become intertwined, restricting the free movement between starch chains. Digestive enzymes have difficulty breaking glycosidic bonds. Furthermore, as the amount of starch increases, the network gaps are filled, forming a denser gel system, which further inhibits enzyme activity.

[0073] according to Figure 1 It was found that different sodium alginate concentrations significantly modulate the in vitro digestion behavior of potato starch gel. With increasing sodium alginate concentration, the digestion curve of the starch gel system tended to flatten out, indicating that sodium alginate effectively slows down the enzymatic hydrolysis of starch. This is because sodium alginate forms an ion-crosslinked gel network under the action of calcium ions. This network can encapsulate and structurally restrict potato starch, reducing the direct contact between starch and digestive enzymes, and delaying the diffusion of digestive enzymes and hydrolysis products in the gel system. Higher concentrations of sodium alginate can enhance the density and stability of the gel network, thereby reducing the proportion of rapidly hydrolyzed starch and increasing the proportion of slowly digestible starch and resistant starch. These results demonstrate that by adjusting the sodium alginate concentration and combining it with calcium ion crosslinking, the digestion rate of potato starch gel can be effectively controlled, resulting in starch-based gel products with slow digestion and sustained release characteristics.

[0074] (2) Using the raw vermicelli wet samples and the cooked samples to be tested prepared in Examples 9-13 as the subjects, the cross-sections of the raw vermicelli wet samples and the cooked samples to be tested were observed using a scanning electron microscope (SEM). The results are as follows: Figures 2-6 As shown.

[0075] Scanning electron microscopy can display the particle arrangement of starch in gels, the network distribution after gelatinization, and the particle morphology, showing cross-sections of sodium alginate gels at different concentrations. According to... Figures 2-6 It is known that when the gel is fresh and has not been cured, the thin film formed by calcium alginate coats the surface of starch granules, forming small chambers. However, the size of these chambers is uncertain, depending on the concentration of sodium alginate molecules and their distribution during extrusion. Inside the fresh gel, there are gaps between the calcium alginate network and the starch. This may be because, during the instantaneous formation of a single network of calcium alginate-coated starch by calcium chloride upon the entry of the sodium alginate-starch mixed solution into the gel, some of the solution is directly encapsulated within the calcium alginate. This water sublimates from the gaps in the gel network during freeze-drying, leaving voids inside the gel. The interior of the fresh gel is basically composed of a single network, with calcium alginate chambers encapsulating raw starch granules in varying numbers, possibly related to the initial solution mixing conditions. In contrast, the cured gel exhibits a continuous network structure, and some granular starch granules can be observed, along with the thickened pore walls formed by calcium alginate.

[0076] As the sodium alginate concentration increases, the amount of starch that retains the granular morphology after gelatinization increases, which is why the RDS decreases subsequently.

[0077] (3) Using the cooked samples prepared in Examples 9-13 as the test subjects, the toughness, textural hardness, chewing hardness, and chewiness of the samples were determined. The method is described in [Lobato-Calleros C, Escalona-Buendia H, et al. Effect of the weight ratio of alginate-modified tapioca starch on the physicochemical properties and release kinetics of chlorogenic acid containing beads[J]. FoodHydrocolloids, 2015, 48: 301-11]. The results are as follows: Figure 7 As shown in Table 4.

[0078] Table 4. Texture properties of the ripened samples tested in Examples 9-13

[0079] Toughness typically refers to the area under the curve formed by the force (vertical axis) and distance (horizontal axis) from the start of shearing until complete sample fracture, representing the total energy required to completely sever the gel. It includes not only the effect of hardness but also the energy absorbed by the sample during deformation before fracture. Increased sodium alginate concentration leads to a denser and more ordered network, potentially causing the gel to transition from brittle fracture to ductile fracture, thus increasing toughness. This change is related to an increase in bound water in the water distribution; the more bound water, the more energy the gel typically requires to be severed.

[0080] Texture hardness occurs immediately after the blade cuts the sample, typically referring to the maximum peak force reached by the shear probe during sample cutting, representing the ultimate strength of the gel network. Texture hardness gradually increases with increasing sodium alginate concentration, possibly because the higher sodium alginate concentration leads to increased network cross-linking density and a stronger network skeleton. Table 4 shows that there were no significant differences in toughness, texture hardness, chewiness, and chewiness among samples with different sodium alginate concentrations. However, texture hardness and chewiness generally increased with increasing sodium alginate concentration, indicating that higher concentrations of sodium alginate are beneficial for improving the support and chewiness of the gel network.

[0081] Test Example 4 The stress-strain changes of samples in Examples 1-13 were measured using methods described in [Effects of erythritolon rheological properties of rice flour and structural characteristics of extruded dried rice noodles with rapid rehydration behaviors[J]. FoodHydrocolloids, 2023, 144: 109007.;Improvement of pasting and gelling properties of potato starch using a direct vapor-heat moisture treatment[J]. International Journal of Biological Macromolecules, 2022a, 219: 1197-207.;Effects of sweet potato starch on the physicochemical properties and edible qualities of instant fresh rice noodles[J]. International Journal of Biological Macromolecules, 2025, 286: 138553]. The results are as follows. Figure 8 As shown.

[0082] Calcium alginate initially forms the first network, thus serving as the continuous phase in the integrated gel system and providing the basic elastic framework, determining the gel's rigidity. Starch granules merely act as fillers. During cooking, the starch gelatinizes and breaks down, acting as a dispersed phase in the system. Both the broken starch granules and the dissolved branched and linear starch fill the pores of the framework, playing a role in transferring and dispersing stress. Furthermore, the starch occupies a certain amount of space, compressing the mobility of the calcium alginate segments, forcing them into a more extended and tensile conformation. Deforming this network requires overcoming greater energy, thus macroscopically manifesting as increased stress.

[0083] As the external force gradually increases, stress is transferred from the continuous phase (calcium alginate) to the dispersed phase (starch). If the interfacial bonding force is just right, when the stress reaches a certain critical value, starch granules or starch micro-regions will begin to undergo minute interfacial debonding from the calcium alginate network. This debonding process requires energy. Moreover, after debonding, the starch granules may undergo minute displacement or rotation within the pores of the network, generating friction with the surrounding molecular chains. This friction is a process that consumes mechanical energy and converts it into heat energy, effectively delaying the initiation and propagation of macroscopic cracks, thereby increasing the fracture strain.

[0084] The hydrogen bonds formed within gelatinized starch molecules and between starch and sodium alginate have lower bond energies than the ionic cross-links of calcium alginate. During deformation, these weaker hydrogen bonds (called sacrificial bonds) break or dissociate before the main chain network of calcium alginate. This pre-breakage behavior acts as a buffer at the microscopic level, consuming a large amount of energy through its own breakage and protecting the main calcium alginate network from instantaneous destruction.

[0085] As starch content increases, the large number of expanded starch granules crowd out the space occupied by sodium alginate. The sodium alginate molecular chains are forced into the narrow gaps between the starch granules, leading to a localized increase in its effective concentration and enhanced rigidity. When the starch content reaches 40% (i.e., 40 g added), the granules may begin to contact and compress each other, forming a supportive network. This network itself can withstand a certain amount of external pressure and synergistically strengthens the sodium alginate network. Furthermore, the carboxyl and hydroxyl groups on the sodium alginate molecular chains can form numerous hydrogen bonds with the hydroxyl groups on the starch surface, increasing the interfacial area and allowing stress to be efficiently transferred from the sodium alginate network to the starch phase.

[0086] Example 14 A slow-digesting food, prepared by the following steps: (1) Accurately weigh 0.5 g of low acyl gellan gum powder (CG-LA, Shandong Fufeng Fermentation Co., Ltd.), dissolve it in 100 mL of deionized water, and stir continuously at 25 °C for 4 hours on a magnetic stirrer to ensure complete dissolution, and prepare a gellan gum solution with a concentration of 0.5% (w / v) for later use.

[0087] (2) Add 10 g of potato starch to a 0.5% (w / v) gellan gum solution, and then let it stand for 5 minutes to remove air bubbles, to obtain a uniform starch / gellan gum mixed suspension, which is referred to as the mixed solution.

[0088] (3) Prepare a 2% (w / v) calcium chloride aqueous solution as a coagulation bath; use a 50 mL syringe (equipped with a round needle with an inner diameter of 2.0 mm) to draw up the blend and squeeze the blend vertically into the coagulation bath at a constant speed (30 mL / min). The extrusion time is <1.5 min. The extruded linear gel strip is left to stand and solidify in the coagulation bath for 20 minutes to ensure complete ionic crosslinking reaction. Then, remove the gel strip, rinse it with deionized water to remove residual calcium ions on the surface, and drain it to obtain the raw starch strip wet sample.

[0089] (4) Take an appropriate amount of raw vermicelli wet sample and cook it in boiling water for 1 minute and 30 seconds. After taking it out, quickly immerse it in ice water to cool for 10 seconds to stop the residual heat effect, drain the water, and it is the cooked sample to be tested.

[0090] Example 15 A slow-digesting food, prepared in the same way as in Example 14, except that 20 g of potato starch is added in step (2).

[0091] Example 16 A slow-digesting food, prepared in the same way as in Example 14, except that 30 g of potato starch is added in step (2).

[0092] Example 17 A slow-digesting food, prepared in the same way as in Example 14, except that 40 g of potato starch is added in step (2).

[0093] Example 18 A slow-digesting food, prepared in the same way as in Example 14, except that 0.8 g gellan gum is added in step (1).

[0094] Example 19 A slow-digesting food, prepared in the same way as in Example 14, except that 1.0 g of gellan gum is added in step (1).

[0095] Example 20 A slow-digesting food, prepared in the same way as in Example 14, except that 1.2 g of gellan gum is added in step (1).

[0096] Example 21 A slow-digesting food, prepared in the same way as in Example 14, except that 1.5 g of gellan gum is added in step (1).

[0097] Example 22 A slow-digesting food, prepared in the same way as in Example 14, except that: Add 0.8 g of low-acyl gellan gum powder in step (1); Add 40 g of potato starch in step (2).

[0098] Test Example 5 Using the matured sample prepared in Example 22 as the subject, the contents of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) in the sample were determined using the same method as in Test Example 1. The results showed that the contents of RDS, SDS, and RS in the sample were 30.26±0.10%, 40.26±0.12%, and 29.49±0.18%, respectively. The cross-linked gel network formed by low-acyl gellan gum under the action of calcium ions can effectively encapsulate and structurally confine potato starch, reducing the direct contact between starch and digestive enzymes, delaying the diffusion of digestive enzymes in the gel system and the starch hydrolysis process, thereby reducing the proportion of rapidly digestible starch and increasing the proportion of slowly digestible starch and resistant starch. This technology can be used to prepare starch-based gel foods with slow-release digestibility properties.

[0099] In summary, the preparation method described in this invention achieves instantaneous gel setting within minutes, breaking through the traditional methods for preparing slow-digesting foods and demonstrating significant advantages in process efficiency.

[0100] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a slowly digestible food, characterized in that, Includes the following steps: The blend is continuously extruded into a calcium ion solution and solidified for 10-40 minutes to obtain the slow-digesting food. The blend liquid comprises: ion-crosslinked colloid, starch-based raw material, and water.

2. The preparation method according to claim 1, characterized in that, The slow-digesting food may be in one of the following shapes: strips, shreds, flakes, or blocks.

3. The preparation method according to claim 1, characterized in that, The blend comprises, by weight, 0.5 to 2 parts of ion-crosslinked colloid, 10 to 40 parts of starch raw material, and 100 parts of water.

4. The preparation method according to claim 1 or 3, characterized in that, The ion-crosslinked colloids include sodium alginate and / or gellan gum.

5. The preparation method according to claim 1, characterized in that, The extrusion speed is 0.2~0.6 mL / s; during extrusion, the outlet of the extrusion device is placed in a calcium ion solution.

6. The preparation method according to claim 1, characterized in that, The concentration of calcium ions in the calcium ion solution is 0.0901~0.3604 mol / L.

7. The preparation method according to claim 1, characterized in that, Before extrusion, the process also includes: allowing the blend to stand.

8. The preparation method according to claim 7, characterized in that, The settling time is 2-5 minutes.

9. The preparation method according to claim 1, characterized in that, After obtaining the slow-digesting food, the process further includes: removing residual calcium ions from the surface of the slow-digesting food.

10. The slowly digestible food prepared by the preparation method according to any one of claims 1 to 9, characterized in that, The slowly digestible food has a rapidly digestible starch content of <51%.

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