A kind of cooking stable type cyclodextrin / slow digestion starch recombination rice particle and its directional rearrangement co-extrusion method

Abstract

The present application belongs to the technical field of grain deep processing, functional starch and low glycemic index food, and particularly relates to a steaming stable type cyclodextrin / slow digestion starch recombined rice particle and a directional rearrangement co-extrusion method thereof. The method comprises the following steps: starch from rice is gelatinized, and after being treated by pullulanase debranching and inactivation, alpha-cyclodextrin is added under a specified water content, so that the alpha-cyclodextrin and the debranched starch undergo directional rearrangement in a first stage at medium temperature and directional rearrangement in a second stage at low temperature to obtain an alpha-cyclodextrin-debranched starch co-rearrangement intermediate; the obtained intermediate is mixed with a rice flour base, and co-extruded into rice particle granules under controlled temperature and screw rotation speed; and the granules are subjected to low-temperature conditioning and low-temperature drying to obtain recombined rice particles. The obtained recombined rice particles contain a rice-derived continuous starch matrix and dispersed co-rearranged functional domains, which are beneficial to improving the cooking retention of alpha-cyclodextrin and slow digestion structure.

Description

Technical Field

[0001] This invention belongs to the technical fields of deep processing of grains, functional starches, and low glycemic index foods. Specifically, it relates to a cooking-stable recombinant rice granule with cyclodextrin / slow-digesting starch and its directional rearrangement co-extrusion method. In particular, it relates to a cooking-stable recombinant rice granule and its method, which is prepared by using rice starch as raw material through pullulanase debranching, two-stage directional rearrangement involving α-cyclodextrin, controlled co-extrusion, and low-temperature conditioning after extrusion. Background Technology

[0002] The starch in refined rice typically undergoes full gelatinization during cooking, forming a high proportion of rapidly digestible starch. Adding slow-digesting starch, resistant starch, or dietary fiber can reduce the rate of starch digestion, but the heat, shearing, and moisture effects during extrusion, cooking, and reheating can easily disrupt the original ordered structure, causing the slow-digesting or resistant starch to revert to easily digestible components.

[0003] US Patent Application Publication No. US20040161526A1 and its family of patents disclose methods for reducing the glycemic index of food by adding α-cyclodextrin, and list rice, noodles, cereal products, and combinations of α-cyclodextrin with low-digestibility carbohydrates such as resistant starch as examples. These methods primarily focus on the amount of α-cyclodextrin added and its food application, without proposing continuous process solutions for the internal fixation of α-cyclodextrin and the maintenance of the ordered structure of debranched starch during the extrusion and cooking of reconstituted rice.

[0004] Patent application WO2005025327A2 discloses the preparation of resistant starch with culinary properties using debranching enzymes such as pullulanase; patent applications WO2004066955A2 and EP1596843A2 disclose enzymatic preparation of slowly digestible starch. These technologies provide insights into starch debranching, the formation of slowly digestible starch, and crystal rearrangement, but do not disclose a continuous process involving the addition of α-cyclodextrin after enzyme inactivation and before the start of directional rearrangement, allowing the α-cyclodextrin and debranched starch to undergo two stages of rearrangement at medium and low temperatures, followed by controlled co-extrusion and post-extrusion low-temperature conditioning.

[0005] Patent application CN115299563A discloses a type of artificial rice with a lower glycemic index, which mainly relies on dietary fiber, gelling substances, organic chromium, and polyphenols to form its formulation system. This approach differs from the technical path of this invention, which involves α-cyclodextrin participating in the directional rearrangement of debranched starch, forming co-rearrangement functional domains, and improving the retention of slow-digesting structures after cooking.

[0006] However, existing technologies still need to address the following issues: First, α-cyclodextrin is prone to migration during soaking and cooking after final mixing or surface coating; second, the ordered structure formed by debranched starch is easily destroyed under high extrusion temperature and high shear conditions; third, increasing the proportion of functional components usually reduces the particle strength and cooking integrity of reconstituted rice; and fourth, simply stacking α-cyclodextrin and slow-digesting starch makes it difficult to form a stable internal structure that can be distinguished from existing technologies. Summary of the Invention

[0007] This invention aims to provide a cooking-stable recombinant rice grain and its preparation method, which allows α-cyclodextrin to undergo a controlled moisture-temperature history with debranched starch before co-extrusion, forming a co-rearrangement functional domain inside the grain. Controlled co-extrusion and low-temperature conditioning after extrusion reduce the migration of α-cyclodextrin and the loss of slow-digested structures during cooking.

[0008] Therefore, the present invention provides the following technical solution.

[0009] One aspect of the present invention provides a method for directional rearrangement co-extrusion of reconstituted rice grains containing cooking-stable cyclodextrin / slow-digesting starch, the method comprising the following steps: S1: Gelatinize rice starch in water to obtain gelatinized starch; S2: Pullulanase is added to the gelatinized starch for debranching treatment to obtain debranched starch material; S3: Add α-cyclodextrin to the debranched starch material to obtain a mixture, and then perform a first-stage directional rearrangement and a second-stage directional rearrangement on the obtained mixture to obtain a co-rearranged material; S4: The co-rearranged material is dried and pulverized to obtain an α-cyclodextrin / debranched starch co-rearrangement intermediate; S5: The α-cyclodextrin / debranched starch co-rearrangement intermediate is mixed with rice flour base material, and then the resulting mixture is co-extruded by twin screws and cut into rice-grain-shaped particles; S6: The rice-like particles are conditioned and then dried to obtain recombinant rice particles with cooking-stable cyclodextrin / slow-digesting starch.

[0010] In a preferred embodiment of the present invention, in step S1, the rice-derived starch is derived from japonica rice, indica rice, broken rice, or a combination thereof, and the amylose in the rice-derived starch accounts for 10-35% of the total starch content.

[0011] In a preferred embodiment of the present invention, in step S1, the mass fraction of the rice starch in water is 18-35%.

[0012] In a preferred embodiment of the present invention, in step S1, the gelatinization processing conditions are: temperature 80-98°C, time 10-40 min.

[0013] In a preferred embodiment of the present invention, in step S1, the gelatinization processing conditions are: temperature 85-95°C, time 15-30 min.

[0014] In a preferred embodiment of the present invention, in step S1, the degree of gelatinization of the gelatinized starch is 60-100%.

[0015] In a preferred embodiment of the present invention, in step S2, pullulanase is added at an amount of 2 to 15 ASPU per gram of dry starch.

[0016] In a preferred embodiment of the present invention, in step S2, pullulanase is added at an amount of 3-8 ASPU per gram of dry starch.

[0017] In a preferred embodiment of the present invention, in step S2, the debranching treatment conditions are: temperature of 48-62°C, pH of 5.2-6.5, and time of 1.5-6h.

[0018] In a preferred embodiment of the present invention, in step S2, the debranching treatment conditions are: temperature of 52-58°C, pH of 5.2-6.5, and time of 3-5 hours.

[0019] In a preferred embodiment of the present invention, step S2 further includes an enzyme inactivation step after the debranching treatment, wherein the enzyme inactivation conditions are: temperature of 85-100°C and time of 5-20 min.

[0020] In a preferred embodiment of the present invention, step S3 further includes, before adding α-cyclodextrin to the debranched starch material, adjusting the moisture content of the debranched starch material to 45-70%.

[0021] In a preferred embodiment of the present invention, in step S3, the α-cyclodextrin is added in an amount with a mass ratio of 0.15:1 to 0.40:1 to the dry matter of debranched starch.

[0022] In a preferred embodiment of the present invention, in step S3, the α-cyclodextrin is added in an amount with a mass ratio of 0.2:1 to 0.35:1 to the dry matter of debranched starch.

[0023] In a preferred embodiment of the present invention, in step S3, the first stage of directional rearrangement conditions are: a temperature of 50–65°C and a time of 2–10 hours. This allows the debranched linear or low-branched dextran segments to migrate, pair, and initially become ordered.

[0024] In a preferred embodiment of the present invention, in step S3, the first stage of directional rearrangement conditions are: temperature of 55-62°C and time of 4-8h.

[0025] In a preferred embodiment of the present invention, in step S3, the second-stage directional rearrangement conditions are: temperature 2–15°C, time 6–36 h. This further fixes the formed ordered structure, obtaining an α-cyclodextrin-debranched starch co-rearranged material.

[0026] In a preferred embodiment of the present invention, in step S3, the second stage directional rearrangement conditions are: temperature of 4-10°C and time of 8-24h.

[0027] In a preferred embodiment of the present invention, in step S4, the drying conditions are: temperature ≤ 60°C, moisture content ≤ 14%.

[0028] In a preferred embodiment of the present invention, in step S4, the median particle size D50 of the α-cyclodextrin / debranched starch co-rearrangement intermediate is 60-250 μm.

[0029] In a preferred embodiment of the present invention, in step S5, the rice flour base material is derived from japonica rice, indica rice, broken rice, or a combination thereof.

[0030] In a preferred embodiment of the present invention, in step S5, the α-cyclodextrin / debranched starch co-rearrangement intermediate is mixed with rice flour base material at a mass ratio of (20-45):(55-80).

[0031] In a preferred embodiment of the present invention, in step S5, the α-cyclodextrin / debranched starch co-rearrangement intermediate is mixed with rice flour base material at a mass ratio of (25-40):(60-75).

[0032] In a preferred embodiment of the present invention, step S5 further includes adjusting the total moisture content of the resulting mixture to 24-36% before performing twin-screw co-extrusion.

[0033] In a preferred embodiment of the present invention, in step S5, the twin-screw co-extrusion conditions are as follows: the temperatures of the feeding zone, compression zone, gelatinization mixing zone, and metering and shaping zone of the extruder along the material conveying direction are 45-80°C, 75-110°C, 95-140°C, and 80-120°C, respectively; the screw speed is 80-220 rpm; and the average residence time is 20-120 seconds.

[0034] In a preferred embodiment of the present invention, in step S5, the twin-screw co-extrusion conditions are as follows: the temperatures of the feeding zone, compression zone, gelatinization mixing zone, and metering and shaping zone of the extruder along the material conveying direction are 45-80°C, 75-110°C, 105-130°C, and 80-120°C, respectively, and the screw speed is 90-160 rpm.

[0035] In a preferred embodiment of the present invention, in step S6, the conditioning conditions are: temperature of 2-15°C and time of 4-24h.

[0036] In a preferred embodiment of the present invention, in step S6, the conditioning conditions are: temperature of 4-10°C and time of 6-16 hours.

[0037] In a preferred embodiment of the present invention, in step S6, the drying conditions are: temperature ≤ 60°C, moisture content ≤ 14%.

[0038] Another aspect of the present invention provides a cooking-stable cyclodextrin / slow-digesting starch recombinant rice grain obtained according to the method described above, wherein the cooking-stable cyclodextrin / slow-digesting starch recombinant rice grain has a length of 4-8 mm, a width of 1.5-3.5 mm, and a moisture content of not more than 14%. In a preferred embodiment of the present invention, the cookable stable cyclodextrin / slow-digesting starch recombinant rice grains comprise a rice-derived continuous starch matrix and co-rearrangement functional domains dispersed within the rice-derived continuous starch matrix. The co-rearrangement functional domains are formed from α-cyclodextrin / debranched starch co-rearrangement intermediates. The α-cyclodextrin / debranched starch co-rearrangement intermediates account for 20–45% of the dry matter of the recombinant rice grains, and α-cyclodextrin accounts for 4–11% of the dry matter of the recombinant rice grains. The dry matter derived from debranched starch accounts for 12–34% of the dry matter of the recombinant rice grains.

[0039] In a preferred embodiment of the present invention, the glycemic index of the cooked stable cyclodextrin / slow-digesting starch recombinant rice grains, as determined according to ISO 26642 or its equivalent standard, is not higher than 55.

[0040] Another aspect of the present invention provides a cooking method for cooking stable cyclodextrin / slow-digesting starch recombinant rice grains, the method comprising the following steps: taking 10.0 g of dry basis of the recombinant rice grains and adding 14.0 g of water to soak for 20 minutes, then heating in a normal pressure steam environment for 25 minutes and letting it sit for 10 minutes, wherein the sum of slow-digesting starch and resistant starch accounts for not less than 15% of the total starch mass.

[0041] After cooking under the above conditions, the sum of slow-digesting starch and resistant starch should account for no less than 18% of the total starch, with a slow-digesting structure retention rate of no less than 55%, an α-cyclodextrin retention rate of no less than 60%, and a cooking loss rate of no more than 10%. By employing the above technical solution, the present invention has at least the following advantages: ①Because α-cyclodextrin is added after debranching and before directional rearrangement begins, α-cyclodextrin and debranched starch undergo segment rearrangement under controlled hydration, which can reduce the migration caused by α-cyclodextrin being distributed only on the particle surface during soaking and cooking.

[0042] ② Through a continuous process of “medium-temperature first-stage rearrangement - low-temperature second-stage rearrangement - controlled co-extrusion - low-temperature conditioning after extrusion”, the functional phase is pre-formed before extrusion and fixed again after extrusion, which can improve the processing stability of slow-digesting or resistant structures.

[0043] ③ By controlling the ratio of co-rearranged intermediates to rice flour base, material moisture content, extrusion temperature and shear strength, a balance can be achieved between functional component content, particle forming strength, cooking integrity and taste.

[0044] ④ This method mainly uses food-grade rice as raw material, α-cyclodextrin and food-grade enzymes, and can be industrially scaled up using existing starch reaction equipment, twin-screw extrusion equipment and low-temperature drying equipment.

[0045] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below. Attached Figure Description

[0046] Figure 1 This is a schematic flowchart of the method for directional rearrangement co-extrusion of recombinant rice grains with cooking-stable cyclodextrin / slow-digesting starch according to the present invention; wherein, 101 is the starch slurry preparation and gelatinization step, 102 is the pullulanase debranching step, 103 is the enzyme inactivation and moisture content adjustment step, 104 is the α-cyclodextrin timed addition step, 105 is the two-stage directional rearrangement step, 106 is the drying and pulverizing step of the co-rearrangement intermediate, 107 is the controlled co-extrusion molding step, and 108 is the low-temperature conditioning and drying step after extrusion.

[0047] Figure 2 This is a schematic diagram of the cross-section of the recombinant rice grains of the cooking-stable cyclodextrin / slow-digesting starch of the present invention; wherein, 201 is the dense outer layer of the grain, 202 is the continuous starch matrix of rice source, 203 is the co-rearrangement functional domain, and 204 is the micropore or water migration channel. Detailed Implementation

[0048] To make the technical means, creative features, achieved objectives, and effects of this invention readily understandable, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0049] The following embodiments involve and refer to the following: 1. Materials, instruments, and their sources Rice-derived starch can be japonica rice starch, indica rice starch, or a mixture thereof; The rice flour base can be japonica rice flour, indica rice flour, broken rice flour or a mixture thereof, preferably sieved through an 80-100 mesh sieve.

[0050] The α-cyclodextrin used is a food-grade product with a purity preferably not less than 95%.

[0051] Pullulanase: Food-grade preparation, enzyme activity 5000U / ml (its enzyme activity is converted to ASPU according to the supplier's method), purchased from Longchuan (Nanjing) Biotechnology Co., Ltd.

[0052] Rice protein: JNSP-NSG801, purchased from Wuxi Jinong Biotechnology Co., Ltd.

[0053] Twin-screw extruder: DG20-Ⅱ, with a preferred length-to-diameter ratio of 36:1. The screw assembly is preferably composed mainly of conveying elements and low-shear mixing elements to reduce the damage to the co-rearrangement functional domain caused by prolonged high shear. Purchased from Jinan Degu Machinery Equipment Co., Ltd.

[0054] 2. Standard steaming / cooking procedure Take 10.0 g of dry-based reconstituted rice grains, add 14.0 g of water, and soak for 20 minutes; heat in a normal pressure steam environment for 25 minutes, and let it sit for 10 minutes after stopping heating. For implementation methods with different water absorption rates, the amount of water added can be adjusted for verification while maintaining a consistent dose of available carbohydrates in each sample.

[0055] 3. Detection Method ① Determination of slow-digesting starch and resistant starch After standard cooking, the samples were cooled to edible temperature and homogenized. Free glucose (FG), glucose release at 20 minutes (G20), and glucose release at 120 minutes (G120) were determined according to the Englyst time fractionation principle. Rapidly digestible starch RDS was calculated as (G20 - FG) × 0.9 / TS × 100%, slowly digestible starch SDS as (G120 - G20) × 0.9 / TS × 100%, and resistant starch RS as 100% - RDS - SDS, where TS is the total starch mass of the sample. Parallel validation can be performed using AOAC-approved methods.

[0056] ② α-Cyclodextrin retention rate The mass of α-cyclodextrin in the granules before cooking and in the solids after cooking were determined separately. The retention rate was calculated by dividing the mass of α-cyclodextrin in the solids after cooking by the mass of α-cyclodextrin in the granules before cooking and multiplying by 100%. HPLC-differential refractive index detection was used.

[0057] ③ Slow digestion structure retention rate The result is calculated by dividing the sum of the masses of SDS and RS in the solids after cooking by the sum of the masses of SDS and RS in the particles before cooking, and then multiplying by 100%.

[0058] ④ Cooking loss rate Collect the cooking liquor and dry it to constant weight. Calculate the weight by dividing the mass of solids in the cooking liquor by the mass of the dry sample before cooking and multiplying by 100%.

[0059] ⑤ In vitro digestion curve At the same available starch dose, the samples of the present invention, samples without added functional components, samples with only added α-cyclodextrin, samples with only added debranched rearranged starch, and samples with a simple mixture of α-cyclodextrin and debranched rearranged starch were compared; glucose release was recorded at 30 minutes, 60 minutes, 90 minutes, and 120 minutes.

[0060] ⑥ Glycemic index measurement In human glycemic index (GI) determination, the test food and the reference food provided the same amount of available carbohydrates. Blood glucose responses were recorded for each subject at fasting and at 30, 60, 90, and 120 minutes postprandial. The GI of the test food relative to the reference food was calculated based on the area under the postprandial glucose curve (IAUC) for each subject, and then the individual GIs were summarized. According to WS / T 652-2019, "Method for Determination of Glycemic Index of Foods," 12 subjects were included in the experiment. The reference food was anhydrous glucose. The determination period included at least three independent food trials, two with the reference food and one with the test food.

[0061] ⑦ Sensory evaluation Following GB / T 15682-2025, "Evaluation Method for Cooked and Edible Quality of Rice and Grain in Grain and Oil Inspection," the samples from the examples and comparative examples were evaluated for appearance, odor, hardness, stickiness, and overall acceptability. Sensory evaluation was also conducted on the samples from the examples and comparative examples, following GB / T 15682-2025. A scoring system was used, with color scored out of 10 points, integrity out of 5 points, stickiness out of 10 points, elasticity out of 20 points, taste out of 25 points, and texture of cold rice out of 5 points. The overall score was the sum of the scores for each sub-item. Ten volunteers were recruited to participate in the evaluation.

[0062] The present invention will be further described in detail below through specific embodiments and experimental examples, but the scope of protection of the present invention is not limited thereto.

[0063] Example 1: Japonica rice-based recombinant rice grains and their preparation The raw material composition of the japonica rice-based recombinant rice grains in this embodiment is as follows: on a dry matter basis, accurately weigh 100 parts by weight of japonica rice starch, 160 parts by weight of japonica rice flour, 22 parts by weight of α-cyclodextrin, 4 parts by weight of rice protein, and 0.8 parts by weight of mono- and diglyceride fatty acid esters; pullulanase is added at 8 ASPU per gram of japonica rice starch.

[0064] The preparation method of the japonica rice-based recombinant rice grains in this embodiment includes the following steps: 100 parts by weight of japonica rice starch are mixed with water to make a starch slurry with a dry matter mass fraction of 25%. The slurry is kept at 95°C for 15 minutes to allow the starch to fully gelatinize, resulting in gelatinized starch. The gelatinized starch is then cooled to 58°C, the pH is adjusted to 5.8, pullulanase is added, and the mixture is debranched at 58°C for 4 hours. After debranching, the system is heated to 90°C and held for 10 minutes to inactivate the enzyme, resulting in debranched starch material. The moisture content of the debranched starch material after enzyme inactivation is adjusted to 45%, then cooled to 65°C, and 22 parts by weight of α-cyclodextrin are added. The mixture is stirred at 100 r / min for 20 minutes at 65°C to ensure that the α-cyclodextrin is evenly distributed in the debranched starch system, resulting in a mixture. The resulting mixture was subjected to a first-stage directional rearrangement at 65°C for 4 hours; subsequently, it was cooled to 4°C at a rate not exceeding 1.5°C / min and held at this temperature for 12 hours for a second-stage directional rearrangement, yielding a co-rearranged material. The co-rearranged material was centrifuged or filtered to dehydrate it, reducing the moisture content to 40%; then dried at 55°C to a moisture content not exceeding 12%, pulverized, and passed through a 60-mesh sieve to obtain an α-cyclodextrin / debranched starch co-rearrangement intermediate. All of the α-cyclodextrin / debranched starch co-rearrangement intermediate was mixed with 160 parts by weight of japonica rice flour, 4 parts by weight of rice protein, and 0.8 parts by weight of mono- and diglycerides of fatty acids. The total moisture content of the resulting mixture was adjusted to 30%, and the mixture was allowed to stand for 60 minutes to condition. The resulting mixture was then extruded using a twin-screw extruder. The temperature zones were sequentially set to 45–55°C, 65–75°C, 80–90°C, and 90–100°C, with a die temperature of 80–90°C. The screw speed was 150 rpm, and the average residence time was 90 seconds. The extrudate was cut into rice-like granules with a length of 5 mm and a width of 2.0 mm. These granules were conditioned at 4°C and 70% relative humidity for 10 hours, then dried at 45°C until the moisture content did not exceed 14%. The granules were then sealed and equilibrated for at least 12 hours to obtain reconstituted japonica rice-based rice granules with a length of 6 mm and a width of 2 mm.

[0065] Example 2: Japonica rice-based recombinant rice grains and their preparation The raw material composition of the japonica rice-based recombinant rice grains in this embodiment is as follows: on a dry matter basis, accurately weigh 100 parts by weight of japonica rice starch, 150 parts by weight of japonica rice flour, 15 parts by weight of α-cyclodextrin, 3 parts by weight of rice protein, and 0.6 parts by weight of mono- and diglyceride fatty acid esters; pullulanase is added at 6 ASPU per gram of japonica rice starch.

[0066] The preparation method of the japonica rice-based recombinant rice grains in this embodiment includes the following steps: 100 parts by weight of japonica rice starch are mixed with water to make a starch slurry with a dry matter mass fraction of 20%. The slurry is kept at 95°C for 15 minutes to allow the starch to fully gelatinize, resulting in gelatinized starch. The gelatinized starch is then cooled to 60°C, the pH is adjusted to 5.8, pullulanase is added, and the mixture is debranched at 60°C for 4 hours. After debranching, the system is heated to 90°C and kept at 90°C for 10 minutes to inactivate the enzyme, resulting in debranched starch material. The moisture content of the debranched starch material after enzyme inactivation is adjusted to 55%. The resulting debranched starch material is then cooled to 65°C, 15 parts by weight of α-cyclodextrin are added, and the mixture is stirred at 100 r / min for 25 minutes at 65°C to ensure that the α-cyclodextrin is evenly distributed in the debranched starch system, resulting in a mixture. The resulting mixture was subjected to a first-stage directional rearrangement at 65°C for 4 hours; subsequently, it was cooled to 4°C at a rate not exceeding 1.5°C / min and held at this temperature for 14 hours for a second-stage directional rearrangement, yielding a co-rearranged material. The co-rearranged material was centrifuged or filtered to dehydrate it, reducing the moisture content to 35%; then dried at 55°C to a moisture content not exceeding 10%, pulverized, and passed through a 60-mesh sieve to obtain an α-cyclodextrin / debranched starch co-rearrangement intermediate. All of the α-cyclodextrin / debranched starch co-rearrangement intermediate was mixed with 150 parts by weight of japonica rice flour, 3 parts by weight of rice protein, and 0.6 parts by weight of mono- and diglycerides of fatty acids. The total moisture content of the resulting mixture was adjusted to 32%, and the mixture was allowed to stand for 60 minutes for conditioning. The extrusion was then performed using a twin-screw extruder, with the temperature zones set sequentially as follows: 45–55°C, 60–70°C, 75–85°C, and 90–100°C; the die temperature was 80–90°C; the screw speed was 120 rpm; and the average residence time was 90 seconds. The resulting extrudate was cut into rice-like granules with a length of 5 mm and a width of 2.0 mm. The rice-like granules were then conditioned at 4°C and 70% relative humidity for 12 hours, followed by drying at 45°C until the moisture content did not exceed 12%. The granules were then sealed and equilibrated for at least 14 hours to obtain reconstituted rice-based gluten pellets with a length of 6 mm and a width of 2 mm.

[0067] Example 3: Indica rice-based recombinant rice grains and their preparation The raw material composition of the indica rice-based recombinant rice grains in this embodiment is as follows: on a dry matter basis, accurately weigh 100 parts by weight of indica rice starch, 150 parts by weight of indica rice flour, 18 parts by weight of α-cyclodextrin, 4 parts by weight of rice protein, and 0.8 parts by weight of mono- and diglyceride fatty acid esters; pullulanase is added at 8 ASPU per gram of japonica rice starch.

[0068] The preparation method of the indica-based recombinant rice grains in this embodiment includes the following steps: 100 parts by weight of indica starch are mixed with water to make a starch slurry with a dry matter mass fraction of 25%. The slurry is kept at 95°C for 15 minutes to allow the starch to fully gelatinize, resulting in gelatinized starch. The gelatinized starch is then cooled to 58°C, the pH is adjusted to 5.8, pullulanase is added, and the mixture is debranched at 58°C for 4 hours. After debranching, the system is heated to 90°C and kept at 90°C for 10 minutes to inactivate the enzyme, resulting in debranched starch material. The moisture content of the debranched starch material after enzyme inactivation is adjusted to 55%. The resulting debranched starch material is then cooled to 65°C, 18 parts by weight of α-cyclodextrin is added, and the mixture is stirred at 100 r / min for 20 minutes at 65°C to ensure that the α-cyclodextrin is evenly distributed in the debranched starch system, resulting in a mixture. The resulting mixture was subjected to a first-stage directional rearrangement at 60°C for 4 hours; subsequently, it was cooled to 4°C at a rate not exceeding 1.5°C / min and held at this temperature for 12 hours for a second-stage directional rearrangement, yielding a co-rearranged material. The co-rearranged material was centrifuged or filtered to dehydrate it, reducing the moisture content to 40%; then dried at 55°C to a moisture content not exceeding 12%, pulverized, and passed through a 60-mesh sieve to obtain an α-cyclodextrin / debranched starch co-rearrangement intermediate. All of the α-cyclodextrin / debranched starch co-rearrangement intermediate was mixed with 150 parts by weight of indica rice flour, 4 parts by weight of rice protein, and 0.8 parts by weight of mono- and diglycerides of fatty acids. The total moisture content of the resulting mixture was adjusted to 30%, and the mixture was allowed to stand for 60 minutes for conditioning. The resulting mixture was then extruded using a twin-screw extruder. The temperature zones were sequentially set to 45–55°C, 65–75°C, 105–120°C, and 90–100°C, with a die temperature of 85–95°C. The screw speed was 150 rpm, and the average residence time was 90 seconds. The extrudate was cut into rice-like granules with a length of 5 mm and a width of 2.0 mm. These granules were conditioned at 4°C and 70% relative humidity for 10 hours, then dried at 45°C until the moisture content did not exceed 14%. The granules were then sealed and equilibrated for at least 12 hours to obtain indica rice-based reconstituted rice granules with a length of 5.5 mm and a width of 3 mm.

[0069] Example 4: Indica-based recombinant rice grains and their preparation The raw material composition of the indica rice-based recombinant rice grains in this embodiment is as follows: on a dry matter basis, accurately weigh 100 parts by weight of indica rice starch, 180 parts by weight of indica rice flour, 28 parts by weight of α-cyclodextrin, 4 parts by weight of rice protein, and 0.8 parts by weight of mono- and diglyceride fatty acid esters; pullulanase is added at 8 ASPU per gram of japonica rice starch.

[0070] The preparation method of the indica-based recombinant rice grains in this embodiment includes the following steps: 100 parts by weight of indica starch are mixed with water to make a starch slurry with a dry matter mass fraction of 25%. The slurry is kept at 95°C for 15 minutes to allow the starch to fully gelatinize, resulting in gelatinized starch. The gelatinized starch is then cooled to 58°C, the pH is adjusted to 5.8, pullulanase is added, and the mixture is debranched at 58°C for 4 hours. After debranching, the system is heated to 90°C and kept at 90°C for 10 minutes to inactivate the enzyme, resulting in debranched starch material. The moisture content of the debranched starch material after enzyme inactivation is adjusted to 50%. The resulting debranched starch material is then cooled to 65°C, 28 parts by weight of α-cyclodextrin are added, and the mixture is stirred at 100 r / min for 20 minutes at 65°C to ensure that the α-cyclodextrin is evenly distributed in the debranched starch system, resulting in a mixture. The resulting mixture was subjected to a first-stage directional rearrangement at 55°C for 8 hours; subsequently, it was cooled to 10°C at a rate not exceeding 1.5°C / min and held at this temperature for 24 hours for a second-stage directional rearrangement, yielding a co-rearranged material. The co-rearranged material was centrifuged or filtered to dehydrate it, reducing the moisture content to 40%; then dried at 55°C to a moisture content not exceeding 12%, pulverized, and passed through a 60-mesh sieve to obtain an α-cyclodextrin / debranched starch co-rearrangement intermediate. All of the α-cyclodextrin / debranched starch co-rearrangement intermediate was mixed with 180 parts by weight of indica rice flour, 4 parts by weight of rice protein, and 0.8 parts by weight of mono- and diglycerides of fatty acids. The total moisture content of the resulting mixture was adjusted to 30%, and the mixture was allowed to stand for 60 minutes for conditioning. The resulting mixture was then extruded using a twin-screw extruder. The temperature zones were sequentially set to 55–65°C, 85–95°C, 100–110°C, and 85–95°C, with a die temperature of 80–90°C. The screw speed was 100 rpm, and the average residence time was 90 seconds. The extrudate was cut into rice-like granules with a length of 5 mm and a width of 2.0 mm. These granules were conditioned at 8°C and 70% relative humidity for 16 hours, then dried at 45°C until the moisture content did not exceed 14%. The granules were then sealed and equilibrated for at least 12 hours to obtain indica rice-based reconstituted rice granules with a length of 6 mm and a width of 2.5 mm.

[0071] Comparative Example 1: Recombinant rice grains were prepared by simply mixing α-cyclodextrin with debranched and rearranged starch. The raw material ratios in this comparative example are the same as those in Example 1, except that α-cyclodextrin does not participate in the two-stage rearrangement of debranched starch, but is instead used in a dry post-mixing process after the rearrangement, drying, and pulverization are completed. Specifically, this includes: 100 parts by weight of japonica rice starch were mixed with water to prepare a starch slurry with a dry matter content of 25%. The slurry was kept at 95°C for 15 minutes, cooled to 58°C, and the pH was adjusted to 5.8. Pullulanase was added at 8 ASPU per gram of japonica rice starch, and the starch was debranched at 58°C for 4 hours. The enzyme was then inactivated by keeping the slurry at 90°C for 10 minutes. The moisture content of the debranched starch material was adjusted to 45%, the same level as in Example 1. Without adding α-cyclodextrin, the starch was first rearranged at 65°C for 4 hours, and then cooled to 4°C at a rate not exceeding 1.5°C / min and kept at 4°C for 12 hours for the second stage of rearrangement. The rearranged material was centrifuged or filtered to dehydrate to a wet material moisture content of 40%, and then dried at 55°C to a moisture content not exceeding 12%. The starch was then pulverized and passed through a 60-mesh sieve to obtain debranched and rearranged starch. 22 parts by weight of α-cyclodextrin were dry-mixed with the obtained debranched rearranged starch, and then mixed with 160 parts by weight of japonica rice flour, 4 parts by weight of rice protein and 0.8 parts by weight of mono- and diglyceride fatty acid esters. The total moisture content of the resulting mixture was adjusted to 30%, and the mixture was allowed to stand for 60 minutes for conditioning. Subsequently, the mixture was co-extruded, pelletized, conditioned at 4°C for 10 hours and dried at 45°C under the same conditions as in Example 1 to obtain recombinant rice pellets with a length of 6 mm and a width of 2 mm.

[0072] Comparative Example 2: Preparation of Recombinant Rice Particles by Omitting the Second Stage of Low-Temperature Rearrangement This comparative example uses the same raw material ratios and other process conditions as Example 1, except that the second-stage low-temperature rearrangement is omitted. Specifically, it includes: Following the method in Example 1, the japonica rice starch was gelatinized, debranched with pullulanase, and inactivated at 90°C. The moisture content of the debranched starch material after enzyme inactivation was adjusted to the same level as in Example 1, 45%, and then cooled to 65°C. 22 parts by weight of α-cyclodextrin were added, and the mixture was stirred at 100 r / min for 20 minutes at 65°C to ensure that the α-cyclodextrin was evenly distributed in the debranched starch system, resulting in a mixture. The resulting mixture was kept at 65°C for 4 hours for the first stage of directional rearrangement, without proceeding to the second stage of low-temperature rearrangement at 4°C. After the first stage of directional rearrangement, the rearranged material was directly centrifuged or filtered to dehydrate to a wet material moisture content of 40%, and then dried at 55°C to a moisture content of no more than 12%. The material was then pulverized and passed through a 60-mesh sieve to obtain the α-cyclodextrin / debranched starch co-rearrangement intermediate. The obtained intermediate was mixed with 160 parts by weight of japonica rice flour, 4 parts by weight of rice protein and 0.8 parts by weight of mono- and diglycerides of fatty acids. The total moisture content of the mixture was adjusted to 30%, and the mixture was allowed to stand for 60 minutes for conditioning. The mixture was then co-extruded, pelletized, conditioned at 4°C for 10 hours and dried at 45°C under the same conditions as in Example 1 to obtain recombinant rice pellets with a length of 6 mm and a width of 2 mm.

[0073] Comparative Example 3: Preparation of recombinant rice grains by high-temperature high-shear extrusion without post-extrusion conditioning This comparative example uses the same raw material ratio and pre-extrusion process as Example 1, the difference being that high-temperature, high-shear extrusion is used and no low-temperature conditioning is performed after extrusion. Specifically, it includes: Following the method described in Example 1, the following processes were performed: gelatinization of japonica rice starch, pullulanase debranching, enzyme inactivation, addition of α-cyclodextrin, two-stage directional rearrangement, dehydration, low-temperature drying, and pulverization to obtain an α-cyclodextrin / debranched starch co-rearrangement intermediate. This intermediate was mixed with 160 parts by weight of japonica rice flour, 4 parts by weight of rice protein, and 0.8 parts by weight of mono- and diglycerides of fatty acids. The total moisture content of the mixture was adjusted to 30%, and the mixture was allowed to stand for 60 minutes. Extrusion was then performed using a twin-screw extruder, with the temperature zones set sequentially as 45–55°C, 65–75°C, 160–175°C, and 90–100°C, and the die temperature set at 80–90°C. The screw speed was 150 rpm, and the average residence time was 90 seconds. The extrudate was cut into rice-like granules with a length of 5 mm and a width of 2.0 mm. The obtained rice-like granules were dried directly at 70℃ until the moisture content was no more than 14% to obtain recombinant rice granules with a length of 6mm and a width of 2mm.

[0074] Comparative Example 4: Preparation of Recombinant Rice Particles with Only the Addition of α-Cyclodextrin 100 parts by weight of japonica rice starch, 160 parts by weight of japonica rice flour, 22 parts by weight of α-cyclodextrin, 4 parts by weight of rice protein, and 0.8 parts by weight of mono- and diglyceride fatty acid esters were weighed and directly dry-mixed. The total moisture content of the resulting mixture was adjusted to 30%, and the mixture was allowed to stand for 60 minutes for conditioning. Subsequently, rice-like granules were obtained under the same twin-screw co-extrusion and pelletizing conditions as in Example 1. The granules were then conditioned at 4°C and 70% relative humidity for 10 hours, and dried at 45°C until the moisture content was no higher than 14%, resulting in recombinant rice granules with a length of 6 mm and a width of 2 mm.

[0075] Experimental Example 1: Cooking stability, glycemic index and sensory evaluation of recombinant rice grains First, the reconstituted rice grains of Examples 1-4 and Comparative Examples 1-4 were cooked according to the standard cooking procedure specified in the instructions. The blank controls were untreated indica rice and japonica rice. The specific steps included: Take 10.0 g of dry sample, add 14.0 g of water and soak for 20 min, heat in a normal pressure steam environment for 25 min, and let it sit for 10 min after stopping heating. Cool the cooked sample to an edible temperature and homogenize it.

[0076] The obtained cooked samples were then subjected to the following tests: ① SDS and RS were determined according to the Englyst time grading principle; the slow digestion structure retention rate was calculated by dividing the sum of the mass of SDS and RS in the solids after cooking by the sum of the mass of SDS and RS in the particles before cooking; the results are shown in Table 1.

[0077] ②The α-cyclodextrin retention rate was calculated as the ratio of the mass of solids after cooking to the mass of α-cyclodextrin in the particles before cooking; the results are shown in Table 2.

[0078] ③GI was calculated based on the area under the curve of individual postprandial blood glucose increment under conditions of equal amounts of available carbohydrates; the results are shown in Table 3.

[0079] ④ Sensory evaluation was conducted according to the indicators listed in the instruction manual; the results are shown in Table 4.

[0080] Table 1. SDS / RS and slow-digesting structure retention rates before and after cooking ; As shown in Table 1, the sum of SDS and RS of the recombinant rice grains in Examples 1-4 after cooking ranged from 24.0% to 32.1%, and the retention rate of slow-digesting structures ranged from 66.12% to 70.55%. All recombinant rice grains in Examples 1-4 met the preferred criteria of a sum of SDS and RS of not less than 18% and a retention rate of slow-digesting structures of not less than 55% after cooking. The average sum of SDS and RS of the recombinant rice grains in Examples 1-4 after cooking was 27.75%, higher than the average of 14.90% for the recombinant rice grains in Comparative Examples 1-4; the average retention rate of slow-digesting structures of the recombinant rice grains in Examples 1-4 after cooking was 68.14%, higher than the average of 55.39% for the recombinant rice grains in Comparative Examples 1-4 after cooking.

[0081] Table 2. Retention rate of α-cyclodextrin ; As shown in Table 2, the α-cyclodextrin retention rates of the recombinant rice grains in Examples 1-4 ranged from 71.97% to 78.99%, all exceeding 60%; while the α-cyclodextrin retention rates of the recombinant rice grains in Comparative Examples 1-4 ranged from 43.94% to 58.93%, all below 60%. This result indicates that adding α-cyclodextrin after enzyme inactivation and before the start of the first stage of directional rearrangement, and allowing it to undergo two stages of rearrangement at medium and low temperatures together with debranched starch, is beneficial in reducing the migration loss of α-cyclodextrin during soaking and cooking. No α-cyclodextrin was added to the blank japonica rice and blank indica rice, and their α-cyclodextrin retention rates were not statistically significant and were marked as "not applicable".

[0082] Table 3. Glycemic index and postprandial blood glucose curve ; As shown in Table 3, the GI of the recombinant rice grains in Examples 1-4 ranged from 40 to 52, none exceeding 55; the GI of the recombinant rice grains in Comparative Examples 1-4 ranged from 57 to 69. The GIs of ordinary japonica rice and ordinary indica rice were 84 and 75, respectively. The average GI of the recombinant rice grains in Examples 1 and 2 (based on japonica rice) was 50, a decrease of 34 points compared to ordinary japonica rice, representing a decrease of 40.48%; the average GI of the recombinant rice grains in Examples 3 and 4 (based on indica rice) was 42, a decrease of 33 points compared to ordinary indica rice, representing a decrease of 44.00%. The average GI of the recombinant rice grains in Examples 1-4 was 46, a decrease of 17 points compared to the average of 63 in Comparative Examples 1-4.

[0083] Table 4 Sensory Evaluation and Function—Mouth Balance ; As shown in Table 4, the sensory composite scores of the recombinant rice grains in Examples 1-4 ranged from 60.2 to 67.3, with an average of 64.4, which was higher than the average of 58.0 for the comparative examples. Among them, Example 2 had the highest composite score of 67.3. Table 3 also shows that its GI was 52, meeting all functional indicators, making it a formula with a relatively balanced functionality and edible quality. Furthermore, as shown in Tables 1-4, Example 4 exhibited the best functional indicators after cooking, with an SDS+RS of 32.1%, a slow-digesting structure retention rate of 70.55%, an α-cyclodextrin retention rate of 78.99%, and a GI of 40. However, its sensory composite score of 60.2 was lower than that of Examples 1-3, indicating that increasing the proportion of functional components and improving structural order may reduce viscosity, elasticity, or taste acceptability. A balance needs to be struck between the content of functional components, grain strength, and mouthfeel.

[0084] The results summarized in Tables 1-4 show that the average SDS+RS of the recombinant rice grains based on japonica rice in Examples 1-2 after cooking was 25.90%, the average retention rate of slow-digesting structures was 66.96%, the average retention rate of α-cyclodextrin was 73.20%, the average GI was 50, and the average comprehensive sensory score was 66.85. The corresponding values ​​for the recombinant rice grains based on indica rice in Examples 3-4 were 29.60%, 69.32%, 75.48%, 42, and 61.95, respectively. The indica rice system exhibited a higher content of slow-digesting structures and a lower GI after cooking, while the japonica rice system had a higher sensory score. These results indicate that the rice variety affects the formation of functional structures and eating quality, but the complete process can control the GI below 55 in both common rice varieties. Comparative Example 1 involved mixing α-cyclodextrin with debranched rearranged starch. The resulting recombinant rice grains had an SDS+RS of 19.3% after cooking, but the slow-digestible structure retention rate was only 51.47%, the α-cyclodextrin retention rate was 50.07%, and the GI was 60. This indicates that simple mixing cannot replace the internal functional domains formed by the joint rearrangement. Comparative Example 2 omitted the second-stage low-temperature rearrangement. The resulting recombinant rice grains had a slow-digestible structure retention rate of 57.14% after cooking, but the SDS+RS was only 17.6%, the α-cyclodextrin retention rate was 58.93%, and the GI was 57. This indicates that the low-temperature second-stage rearrangement plays a necessary role in fixing the ordered structure and retaining α-cyclodextrin. Comparative Example 3, which employed high-temperature, high-shear extrusion without post-extrusion low-temperature conditioning, resulted in recombinant rice grains with an SDS+RS of only 12.5%, a slow-digesting structure retention rate of 53.65%, a GI of 69, and a sensory composite score of 52.8 after cooking. These were among the worst results, indicating that excessively high temperatures and shear can damage the co-rearrangement functional domains, and the lack of post-extrusion conditioning hinders structural re-fixation. Comparative Example 4, which only added α-cyclodextrin, produced recombinant rice grains with an SDS+RS of 10.2%, an α-cyclodextrin retention rate of 43.94%, and a GI of 66 after cooking. This demonstrates that adding α-cyclodextrin alone cannot form a cooking-stable slow-digesting structure comparable to the co-rearrangement of debranched starch. None of the comparative examples above simultaneously met the four conditions of SDS+RS not less than 18% after cooking, slow digestion structure retention rate not less than 55%, α-cyclodextrin retention rate not less than 60%, and GI not higher than 55%. However, Examples 1 to 4 all met the above conditions simultaneously, indicating that the process steps are not simply parallel, but a continuous combination of technologies that work together to maintain the cooking stability of functional components.

[0085] In summary, the recombinant rice grains of Examples 1-4 of this invention exhibit good cooking stability and low GI characteristics in both ordinary japonica and indica rice substrates. After cooking, the recombinant rice grains of Examples 1-4 showed a SDS-RS sum of 24.0-32.1%, a slow-digesting structure retention rate of 66.12-70.55%, an α-cyclodextrin retention rate of 71.97-78.99%, and a GI of 40-52, all meeting the corresponding preferred indices. Compared with comparative examples involving α-cyclodextrin post-mixing, omitting the low-temperature second-stage rearrangement, high-temperature high-shear treatment without extrusion conditioning, and only adding α-cyclodextrin, the recombinant rice grains of this invention demonstrate consistent advantages in slow-digesting structure content, α-cyclodextrin retention, and GI control after cooking. The results show that adding α-cyclodextrin before the first-stage rearrangement and undergoing two-stage directional rearrangement with debranched starch, followed by controlled co-extrusion and post-extrusion low-temperature conditioning to fix the structure, can form a co-rearrangement functional domain with high cooking stability inside the reconstituted rice grains.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the methods and techniques disclosed above without departing from the scope of the present invention to create equivalent embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for directional rearrangement co-extrusion of cooking-stable cyclodextrin / slow-digesting starch recombinant rice particles, characterized in that, The method includes the following steps: S1: Gelatinize rice starch in water to obtain gelatinized starch; S2: Pullulanase is added to the gelatinized starch for debranching treatment to obtain debranched starch material; S3: Add α-cyclodextrin to the debranched starch material to obtain a mixture, and then perform a first-stage directional rearrangement and a second-stage directional rearrangement on the obtained mixture to obtain a co-rearranged material; S4: The co-rearranged material is dried and pulverized to obtain an α-cyclodextrin / debranched starch co-rearrangement intermediate; S5: The α-cyclodextrin / debranched starch co-rearrangement intermediate is mixed with rice flour base material, and then the resulting mixture is co-extruded by twin screws and cut into rice-grain-shaped particles; S6: The rice-like particles are conditioned and then dried to obtain recombinant rice particles with cooking-stable cyclodextrin / slow-digesting starch.

2. The method according to claim 1, characterized in that, In step S1, the rice-derived starch is derived from japonica rice, indica rice, broken rice, or a combination thereof, and the amylose in the rice-derived starch accounts for 10-35% of the total starch content; The rice starch has a mass fraction of 18-35% in water; The gelatinization process conditions are: temperature 80–98℃, time 10–40 min; The degree of gelatinization of the gelatinized starch is 60-100%.

3. The method according to claim 1, characterized in that, In step S2, pullulanase is added at a rate of 2-15 ASPU per gram of dry starch; The debranching treatment conditions are: temperature 48–62℃, pH 5.2–6.5, and time 1.5–6h.

4. The method according to claim 1, characterized in that, In step S2, after the debranching treatment, there is also an enzyme inactivation step, wherein the enzyme inactivation conditions are: temperature of 85℃~100℃ and time of 5~20min.

5. The method according to claim 1, characterized in that, In step S3, before adding α-cyclodextrin to the debranched starch material, the step of adjusting the moisture content of the debranched starch material to 45-70% is further included.

6. The method according to claim 1, characterized in that, In step S3, the α-cyclodextrin is added at a mass ratio of 0.15:1 to 0.40:1 with the dry matter of debranched starch; The conditions for the first stage of directional rearrangement are: temperature 50-65℃, time 2-10h; The conditions for the second stage of directional rearrangement are: temperature of 2-15℃ and time of 6-36h.

7. The method according to claim 1, characterized in that, In step S4, the drying conditions are: temperature ≤ 60℃, moisture content ≤ 14%.

8. The method according to claim 1, characterized in that, In step S4, the median particle size D50 of the α-cyclodextrin / debranched starch co-rearrangement intermediate is 60–250 μm.

9. The method according to claim 1, characterized in that, In step S5, the rice flour base material is derived from japonica rice, indica rice, broken rice, or a combination thereof.

10. The method according to claim 1, characterized in that, In step S5, the α-cyclodextrin / debranched starch co-rearrangement intermediate is mixed with rice flour base material at a mass ratio of (20-45):(55-80); Prior to twin-screw co-extrusion, the process also includes adjusting the total moisture content of the resulting mixture to 24–36%. The twin-screw co-extrusion conditions are as follows: the temperatures of the feeding zone, compression zone, gelatinization mixing zone, and metering and shaping zone of the extruder along the material conveying direction are 45-80℃, 75-110℃, 95-140℃, and 80-120℃, respectively, and the screw speed is 80-220 rpm.

11. The method according to claim 1, characterized in that, In step S6, the conditioning conditions are: temperature of 2-15℃ and time of 4-24h. The drying conditions are: temperature ≤ 60℃, moisture content ≤ 14%.

12. The cooking-stable cyclodextrin / slow-digesting starch recombinant rice grains obtained by the method according to any one of claims 1 to 11, characterized in that, In step S6, the length of the cooked stable cyclodextrin / slow-digesting starch recombinant rice grains is 4-8 mm, the width is 1.5-3.5 mm, and the moisture content is not higher than 14%.

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