A yam powder suitable for people with abnormal glucose metabolism and its preparation method

Abstract

This invention discloses a method for preparing yam powder suitable for industrial production and applicable to people with abnormal glucose metabolism, comprising the following steps: Step 1: Raw yam powder is added to a twin-screw extruder equipped with an extrusion screw assembly for extrusion processing to obtain yam extrudate; during the extrusion process, the screw speed is maintained at 100~150 rpm, and the temperatures of extruder temperature zones II~VI are set to 60~65℃, 60~65℃, 90~105℃, 90~105℃, and 60~65℃ respectively, while controlling the moisture content of the material to be 35~45%; Step 2: The yam extrudate is refrigerated, and then the refrigerated yam extrudate is dried by hot air, pulverized, and sieved to obtain yam powder suitable for people with abnormal glucose metabolism. This invention also discloses yam powder suitable for people with abnormal glucose metabolism prepared by the above method.

Description

Technical Field

[0001] This invention belongs to the field of food processing, specifically relating to a yam powder suitable for people with abnormal sugar metabolism and its preparation method. Background Technology

[0002] Yam is a representative food and medicinal resource in my country; the annual output of yam in my country reaches 5 to 6 million tons, making it an important specialty economic crop in many regions. Yam is rich in bioactive components such as polysaccharides, saponins, allantoin, and polyphenols, and has abundant nutritional value. The Compendium of Materia Medica records that yam has the effects of "benefiting kidney qi and strengthening the spleen and stomach." Zhang Xichun, in his representative work *Medical Records of Integrating Chinese and Western Medicine*, specifically proposed that yam is effective in treating diabetes and created the famous traditional Chinese medicine formula "Yu Ye Tang" using yam as the "chief ingredient" to treat diabetes. Recent scientific studies have also continuously confirmed that the active components of yam, such as saponins and polysaccharides, have the effect of improving glucose metabolism. As a root vegetable rich in starch, the starch content of yam accounts for 50% to 80% of its dry weight, of which resistant starch accounts for about 50% to 72% of the total starch, far exceeding that of various grains with similar starch content. As is well known, dietary regulation is the foundation and key to effectively controlling blood sugar levels and delaying disease progression in people with abnormal glucose metabolism. Increasing the proportion of slow-digesting / resistant-digesting starches in dietary carbohydrates is the fundamental way to control postprandial blood sugar. Therefore, partially replacing rice and wheat-based staple foods in the daily diet with yam can help reduce the proportion of rapidly digestible starches in the diet and help people with abnormal glucose metabolism control their blood sugar levels.

[0003] However, yams are not suitable for long-term storage and are difficult to process, which hinders their widespread use in the diets of people with abnormal glucose metabolism. Therefore, processing yams into yam powder and using it as a carbohydrate ingredient in nutritional formula foods is an important way to promote the use of yams in people with abnormal glucose metabolism.

[0004] Extrusion puffing is a rapid and efficient processing technology for starch-based agricultural products such as grains, and it is widely used in the processing of grain flour. In conventional extrusion puffing processes, the moisture content of the material is typically controlled below 30%, and the extrusion temperature is generally 140-170℃ (see: Effects of Extrusion Puffing Treatment on the Structure and Function of Three Types of Millet Flour and Their Dough Quality, Grains and Oils, 2025, 38; Optimization of Extrusion Puffing Process of Brown Rice Flour and Study on the In Vitro Digestibility of Protein Bars Prepared from it, Food Industry Technology, 2025). The applicant also proposed using enzymatic hydrolysis-extrusion puffing to process yam powder in patent application CN119586712A. However, the inventors found through experiments that directly processing yam powder with an extrusion puffing processing condition of 20% moisture content and an extrusion temperature of 150℃ increased the proportion of rapidly digestible starch in the total starch from less than 10% to 93.4%. The aforementioned patent application discloses an increase in the resistant starch content in yam powder after enzymatic hydrolysis and extrusion puffing. The reason for these two different results lies in the fact that CN119586712A uses amylase hydrolysis during the extrusion puffing process. After amylase hydrolysis, the easily digestible starch in the yam is degraded into dextrin, reducing the total starch content. The unhydrolyzed starch is mainly slow-digesting and resistant starch. Therefore, the resistant starch content (the proportion of resistant starch to the total remaining starch) in the yam powder after enzymatic hydrolysis and extrusion puffing increases. In other words, CN119586712A does not increase the resistant starch content by converting rapidly digestible starch into resistant starch. Furthermore, although the proportion of resistant starch in the total starch content increases after the enzymatic hydrolysis and extrusion puffing processing described in patent application CN119586712A, it also produces a large amount of dextrin, which is more easily digested and absorbed than starch and thus raises blood sugar. Overall, the risk of this yam powder raising postprandial blood sugar may be further increased. Therefore, it is impossible to obtain yam powder suitable for people with abnormal sugar metabolism by directly using extrusion puffing processing technology.

[0005] Furthermore, patent application CN117918500A discloses a method for preparing yam powder with a low glycemic index (eGI). This method involves using pullulanase enzymatic hydrolysis combined with 1-4% bamboo leaf flavonoids for modification, resulting in yam powder with an estimated eGI <55. However, this technical solution involves a complex and cumbersome processing method, which is not conducive to industrial production. More importantly, it contains a high proportion of bamboo leaf flavonoids. When consumed as a staple food ingredient or carbohydrate base, this can lead to flavonoid intake exceeding normal levels, potentially increasing the metabolic burden on the liver. Therefore, it is necessary to invent a yam powder processing technology suitable for industrial production and applicable to individuals with abnormal glucose metabolism. Summary of the Invention

[0006] One objective of this invention is to provide a method for preparing yam powder suitable for industrial production and applicable to people with abnormal glucose metabolism. Another objective is to provide a yam powder suitable for people with abnormal glucose metabolism, which can effectively control postprandial blood glucose levels.

[0007] The objective of this invention can be achieved through the following technical solutions.

[0008] A method for preparing yam powder suitable for industrial production and applicable to people with abnormal glucose metabolism includes the following steps:

[0009] Step 1: Take raw yam powder and add it to a twin-screw extruder equipped with an extrusion screw assembly for extrusion processing to obtain yam extrudate. During the extrusion process, the screw speed is maintained at 100~150 rpm, and the temperatures of extruder temperature zones II~VI are set to 60~65℃, 60~65℃, 90~105℃, 90~105℃ and 60~65℃ respectively, while controlling the moisture content of the material to be 35~45%.

[0010] Step 2: Refrigerate the yam extrudate, then dry the refrigerated yam extrudate with hot air, pulverize and sieve it to obtain yam powder suitable for people with abnormal sugar metabolism.

[0011] This invention establishes a preparation method using raw yam powder as raw material through extrusion-refrigeration-drying processing, specifically:

[0012] Using an extrusion press for the processing of starch-based agricultural products offers advantages such as high production efficiency, making it suitable for large-scale production. By utilizing extrusion processing and adjusting conditions such as material moisture content, extrusion temperature, and screw speed during the extrusion process, the crystal structure of macromolecules such as starch in yam powder is reshaped, inducing interactions between starch and active ingredients such as polyphenols, saponins, and polysaccharides, promoting the formation of complexes. This alters the digestibility of starch on one hand, and the formation of these complexes facilitates the encapsulation of active ingredients by starch, reducing degradation losses during processing. Furthermore, this invention, through cold refrigeration of yam extrudate under high moisture content conditions, promotes the rearrangement of gelatinized starch molecular structures, forming an ordered structure and reducing its digestibility.

[0013] This invention controls the degree of starch gelatinization by adjusting the amount of water added, the temperature of each temperature zone, and the screw speed during the extrusion processing of yam powder. Furthermore, it compares the effects of different refrigeration times on the starch digestibility, and establishes an effective yam powder cooking processing technology to control starch digestibility. The resulting yam powder has a low eGI value, which can control postprandial blood glucose levels and is suitable for people with glucose metabolism disorders.

[0014] By comparing and analyzing the starch digestibility of extruded materials under different combinations of moisture content, extrusion temperature, and screw speed during the extrusion process, it was found that when the moisture content of the material is in the range of 35-45%, the temperature of extruder zones IV-V is below 105℃ (zone I is located in the feeding zone, i.e., its temperature is room temperature), and the screw speed is in the range of 100-150 rpm, the proportion of rapidly digestible starch in yam powder can be significantly reduced compared with conventional extrusion puffing.

[0015] Preferably, in step two, the yam extrudate is placed in a cold storage at 2-6°C for more than 36 hours.

[0016] This invention compares the effects of direct drying and low-temperature refrigeration for different times on the starch digestibility of extrudates. It found that refrigeration for 24 hours significantly increases the content of slowly digestible starch, and this effect becomes more pronounced after 36 hours of refrigeration. However, further extending the refrigeration time does not significantly alter the effect on starch digestibility. Therefore, the preferred refrigeration time for the yam extrudates described in this invention is not less than 36 hours.

[0017] The raw yam powder of this invention is made from dried and pulverized yam and can be a commercially available product. Preferably, the preparation method of the raw yam powder is as follows: the yam is washed, peeled, sliced, and then dried in hot air at 45~65℃ for 24 hours, and then pulverized into raw yam powder.

[0018] Preferably, in step two, the refrigerated yam extrudate is dried by hot air at 45-65°C for 24 hours.

[0019] In this invention, the temperature is controlled below 65°C during the hot air drying process. This is based on the analysis results of the gelatinization characteristics of yam starch, which show that the starch gelatinization temperature is about 70°C. Within the temperature range of 45~65°C, the moisture content in the yam slices prepared from raw yam powder can be reduced to below 10% within 24 hours without causing starch gelatinization. Moreover, under this temperature condition, heat-sensitive active ingredients such as saponins and polyphenols in yam can also remain stable.

[0020] The present invention also provides yam powder suitable for people with abnormal glucose metabolism prepared by the above preparation method.

[0021] The present invention has the following beneficial effects:

[0022] (1) The present invention uses an extrusion puffing machine to directly extrude and cook yam powder, which has high production efficiency and can change the starch digestion characteristics of yam powder, increase the content of slow / resistant starch, and does not require the use of a large amount of enzyme preparations or repeated adjustment of reaction temperature for enzymatic hydrolysis, thus saving energy consumption and production costs.

[0023] (2) By adjusting parameters such as the moisture content and extrusion temperature of the material during the extrusion process, the digestibility of starch is controlled. The total content of slow-digestible starch and resistant-digestible starch in the yam powder increases from 6.6% in conventional extrusion puffing to 25.2%. Furthermore, after being refrigerated at low temperature for 36 hours, the total content of slow-digestible starch and resistant-digestible starch increases to 33.5%. The starch has obvious resistant-digestion characteristics and is suitable for people with abnormal sugar metabolism.

[0024] (3) After administering the yam powder prepared by this invention to 8-week-old male SD rats by gavage (the rats were fasted for 16 hours before gavage), the area under the blood glucose time curve and the peak blood glucose concentration of the rats were reduced by 27.7% and 18.7% respectively compared with the same amount of conventional extruded puffed yam powder, which has a significant effect on controlling the stability of postprandial blood glucose.

[0025] (4) The cooked yam powder rich in slow / resistant starch prepared by the present invention can be used as a carbohydrate base for nutritional formula food for people with abnormal sugar metabolism, replacing carbohydrate ingredients such as resistant starch and resistant dextrin, improving the flavor and quality of the product, and introducing active ingredients such as polysaccharides, polyphenols, allantoin and saponins contained in yam. Attached Figure Description

[0026] Figure 1 Blood glucose changes in SD rats after gavage administration of different yam powders (left) and area under the curve (AUC) (right). Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Unless otherwise specified, the reagents or materials used in the embodiments are all from commercial sources.

[0028] Example 1: Wash and peel the yam, cut it into 3-5 mm thick slices, and dry it with hot air at 45℃ for 24 hours. Grind it into 80-mesh raw yam powder. Select an extrusion screw assembly and install an extruder. Add the raw yam powder to the twin-screw extruder for extrusion processing. The screw speed is maintained at 100 rpm. The temperatures of extruder temperature zones II to VI are set to 60℃, 60℃, 90℃, 90℃ and 60℃ respectively. During the extrusion process, the moisture content of the material is controlled at 40% by a water addition device. After placing the obtained yam extrudate in a 4℃ cold storage for 36 hours, dry it with hot air at 50℃ for 24 hours, and grind it through an 80-mesh sieve to obtain yam powder suitable for people with abnormal sugar metabolism, which is high-moisture extruded-cold yam powder.

[0029] Example 2: Wash and peel the yam, cut it into 3-5 mm thick slices, dry it with hot air at 45℃ for 24 hours, and then grind it into 80-mesh raw yam powder. Use an extrusion screw assembly to add the raw yam powder to a twin-screw extruder for extrusion processing. The screw speed is 100 rpm, and the temperatures of extruder zones II to VI are set to 60℃, 60℃, 90℃, 90℃ and 60℃ respectively. During the extrusion process, the moisture content of the material is controlled at 40% by a water addition device. After placing the obtained yam extrudate in a 4℃ cold storage for 48 hours, dry it with hot air at 50℃ for 24 hours, and then grind it through an 80-mesh sieve to obtain yam powder suitable for people with abnormal sugar metabolism.

[0030] Example 3: Yam was washed, peeled, and sliced ​​into 3-5mm thick slices. It was then hot-air dried at 50℃ for 24 hours and pulverized into 80-mesh raw yam powder. A twin-screw extruder was installed, and the raw yam powder was added for extrusion. The screw speed was maintained at 150rpm. The temperatures in extruder zones II-VI were set to 65℃, 50℃, 105℃, 105℃, and 65℃, respectively. During extrusion, the moisture content of the material was controlled at 45% using a water-adding device. The resulting yam extrudate was refrigerated at 4℃ for 36 hours, then hot-air dried at 60℃ for 24 hours. The powder was then pulverized through an 80-mesh sieve to obtain yam powder suitable for people with abnormal glucose metabolism.

[0031] Example 4: Wash and peel the yam, cut it into 3-5 mm thick slices, dry it with hot air at 45℃ for 24 hours, and grind it into 80-mesh raw yam powder. Select an extrusion screw assembly and install an extruder. Add the raw yam powder to the twin-screw extruder for extrusion processing. The screw speed is maintained at 100 rpm. The temperatures of extruder temperature zones II to VI are set to 60℃, 60℃, 90℃, 90℃ and 60℃ respectively. During the extrusion process, the moisture content of the material is controlled at 40% by a water addition device. After placing the obtained yam extrudate in a 4℃ cold storage for 24 hours, dry it with hot air at 50℃ for 24 hours, grind it through an 80-mesh sieve, and obtain yam powder suitable for people with abnormal sugar metabolism.

[0032] Comparative Example 1: Wash and peel the yam, cut it into 3-5 mm thick slices, dry it with hot air at 45℃ for 24 hours, and grind it into 80-mesh raw yam powder; select an extrusion screw assembly and install an extruder, add the raw yam powder to the twin-screw extruder for extrusion processing, maintain the screw speed at 100 rpm, and set the temperatures of extruder temperature zones II to VI to 60℃, 60℃, 90℃, 90℃ and 60℃ respectively. During the extrusion process, the moisture content of the material is controlled at 40% by a water addition device; transfer the obtained yam extrudate to a drying oven, dry it with hot air at 50℃ for 24 hours, grind it through an 80-mesh sieve to obtain high-moisture extruded yam powder.

[0033] Comparative Example 2: Wash and peel the yam, cut it into 3-5 mm thick slices, dry it with hot air at 45℃ for 24 hours, and grind it into 80-mesh raw yam powder; select an extrusion screw assembly and install an extruder, add the raw yam powder to the twin-screw extruder for extrusion processing, the screw speed is 100 rpm, and the temperatures of extruder temperature zones II to VI are set to 60℃, 60℃, 90℃, 90℃ and 60℃ respectively. During the extrusion process, the moisture content of the material is controlled at 30% by a water addition device; transfer the obtained yam extrudate to a drying oven, dry it with hot air at 50℃ for 24 hours, grind it through an 80-mesh sieve to obtain extruded yam powder.

[0034] Comparative Example 3: Wash and peel the yam, cut it into 3-5 mm thick slices, dry it with hot air at 45℃ for 24 hours, and grind it into 80-mesh raw yam powder; select an extrusion puffing screw assembly and install an extruder, add the raw yam powder to the twin-screw extruder for extrusion processing, maintain the screw speed at 100 rpm, and set the temperatures of extruder temperature zones II to VI to 60℃, 100℃, 130℃, 140℃, and 150℃ respectively. During the extrusion puffing process, the moisture content of the material is controlled to 20% by a water addition device; transfer the yam extrudate to a drying oven, dry it with hot air at 50℃ for 24 hours, grind it through an 80-mesh sieve to obtain extruded puffed yam powder.

[0035] The yam powders obtained in Examples 1-4 and Comparative Examples 1-3 were analyzed for their fast, slow, and resistant starch content and eGI, and their total saponin, allantoin, and total polyphenol content were also analyzed. The results are shown in Table 1.

[0036] Table 1. Starch digestibility and active ingredient content of yam powder obtained under different processing conditions

[0037] Example 1 66.5±3.8e 14.9±1.7a 18.6±2.9a 66.5±3.0d 1020.9±20.1a 368.2±13.7a 37.1±1.56a Example 2 68.9±4.2de 13.2±2.1ab 17.9±2.8a 68.0±2.4d 1002.0±19.3a 357.4±12.4a 38.3±2.31a Example 3 68.3±3.5de 14.2±2.3a 17.5±1.8a 67.9±5.1d 997.8±15.9a 361.7±10.9a 37.6±2.49a Example 4 70.2±3.5d 14.6±1.5a 15.2±2.1ab 69.7±2.4d 1008.0±22.9a 366.4±11.3a 35.7±2.22a Comparative Example 1 74.8±3.9c 12.7±2.4b 12.5±3.2bc 76.9±3.3c 1016.0±25.0a 360.8±13.1a 38.9±2.86a Comparative Example 2 81.9±4.8b 9.5±1.2c 8.6±1.3c 80.4±7.2b 981.9±16.6a 349.7±11.6b 37.5±3.29a Comparative Example 3 93.4±5.8a 2.9±0.2d 3.7±0.3d 94.8±6.3a 834.1±12.8b 257.8±11.2c 24.0±1.26b

[0038] Note: When the letters next to the numbers in the same column are completely different, it indicates that the difference is statistically significant (p < 0.05).

[0039] The results in Table 1 above indicate that, under the same high-moisture extrusion processing conditions, refrigeration for 24 hours (Example 4) significantly increased the proportion of slow-digesting and resistant-digesting starch and decreased the proportion of fast-digesting starch compared to no refrigeration under the same processing conditions (Comparative Example 1), thereby reducing the eGI level of the yam powder. However, compared to Examples 1-3 under the same high-moisture extrusion processing conditions, the effect of refrigeration for 24 hours in Example 4 on increasing the total content of slow-digesting and resistant-digesting starch was not as significant as that of refrigeration for 36 hours and 48 hours. Under the same extrusion temperature conditions, when the material moisture content decreased to 30% (Comparative Example 2), the fast-digesting starch content of the yam powder significantly increased, and its eGI level was also significantly higher than that at a moisture content of 40%, suggesting that the material moisture content has a significant impact on the digestibility of extruded yam powder. In Comparative Example 3, conventional extrusion puffing processing conditions were used, namely, the extruder temperature reached 150℃, the material moisture content was less than 30%, and the screw assembly of the equipment was selected accordingly for extrusion puffing. Under these conditions, the proportion of rapidly digestible starch and the eGI value of the yam powder were the highest. This further indicates that under the extrusion puffing processing conditions, the anti-digestive properties of starch in raw yam are significantly destroyed, which is not conducive to maintaining stable postprandial blood glucose.

[0040] Furthermore, as shown in Table 1, the extrusion processing using the material moisture content and extruder temperature described in this invention can better ensure the retention of active ingredients such as allantoin, saponins, and polyphenols in yam.

[0041] Experimental Example: To confirm the effect of the yam powder prepared in this invention on maintaining stable postprandial blood glucose, the changes in blood glucose in rats after being administered yam powder with different processing methods by gavage were compared, referring to the oral glucose tolerance test (OGTT).

[0042] Twenty-four 8-week-old SPF-grade male SD rats were randomly divided into three groups of eight each. After one week of acclimatization feeding, all animals were fasted for 12 hours. Extruded puffed yam powder (Comparative Example 3), high-moisture extruded yam powder (Comparative Example 1), and high-moisture extruded-refrigerated yam powder (Example 1) were prepared into suspensions at a ratio of yam powder to water of 1:4. The three groups of rats were administered the suspensions prepared from the different yam powders by gavage at a dose of 1.2 mL / 100g body weight. Blood glucose levels were measured by tail clipping at 0 min before gavage and at 30 min, 60 min, 90 min, and 120 min after gavage.

[0043] from Figure 1It can be seen that the blood glucose levels of the three groups of rats were similar before gavage administration of yam powder (0 min), with no significant difference between groups. 30 min after gavage, blood glucose levels in all groups increased significantly, with the highest increase in the group administered Comparative Example 3 (extruded puffed yam powder), followed by the group administered Comparative Example 1 (high-moisture extruded yam powder), and the lowest in the group administered Example 1 (high-moisture extruded-refrigerated yam powder). By 60 min after gavage, although the difference between the latter two groups was no longer significant, both were significantly lower than those in the extruded puffed yam powder group. The area under the blood glucose time curve (AUC) results for each group also show that the AUC of the Example 1 (high-moisture extruded-refrigerated yam powder) group was significantly lower than that of the Comparative Example 3 (extruded puffed yam powder) group. The AUC and peak blood glucose concentration were reduced by 27.7% and 18.7% respectively compared to the same amount of extruded puffed yam powder administered; and compared to the Comparative Example 1 (high-moisture extruded yam powder) group, its AUC was also significantly reduced by 9.4% (P<0.05). It can be seen that, compared with conventional extrusion puffing processing, the high-moisture extruded-cold yam powder prepared by the present invention has a better effect on reducing the peak level of postprandial blood glucose and maintaining the stability of postprandial blood glucose.

Claims

1. A preparation method of yam powder suitable for industrial production and for people with abnormal sugar metabolism, characterized in that, Comprising the following steps: ​ Step one: take raw yam powder and add it to a double-screw extruder equipped with an extrusion screw group to perform extrusion processing, obtaining yam extrudate; during the extrusion processing, the screw rotation speed is maintained at 100-150 rpm, the temperatures of extruder temperature zones II-VI are set at 60-65℃, 60-65℃, 90-105℃, 90-105℃, and 60-65℃ respectively, and the moisture content of the material is controlled at 35-45%; Step two: the yam extrudate is refrigerated, then the refrigerated yam extrudate is hot-air dried, pulverized, and sieved, obtaining yam powder suitable for people with abnormal sugar metabolism.

2. The method of claim 1, wherein the Dioscorea root powder is prepared by the steps of: In step two, the yam extrudate is refrigerated in a 2-6℃ refrigerator for 36h or more. ​ 3. The method of claim 2, wherein the Dioscorea japonica powder is prepared by the steps of: The preparation method of the raw yam powder is: washing and peeling the yam, slicing, then hot-air drying at 45-65℃ for 24h, and pulverizing into raw yam powder. ​ 4. The method of claim 3, wherein the Dioscorea root powder is prepared by the steps of: In step two, the refrigerated yam extrudate is hot-air dried at 45-65℃ for 24h. ​ 5. Yam powder suitable for people with abnormal sugar metabolism prepared by the preparation method of the yam powder of claim 1.

Images