Method for extracting and analyzing bamboo shoot skin dietary fibers by ultrasonic compound enzyme method

Abstract

The invention discloses an extraction and analysis method of bamboo shoot skin dietary fibers. The method comprises the following specific steps: washing fresh bamboo shoot skin, drying at 70 DEG C until the weight is constant, crushing, sieving with a 80-mesh sieve, adding a proper amount of distilled water, adding 3.6% of compound enzyme in a proper proportion at 40 DEG C, reacting for 25 minutes, and inactivating in a water bath at 100 DEG C for 10 minutes; stirring and centrifuging to take supernate and precipitate, concentrating the supernate, adding four times of absolute ethyl alcohol, precipitating and filtering at the temperature of 4 DEG C, centrifuging, drying the precipitate to obtain soluble dietary fiber powder, eluting the precipitate with absolute ethyl alcohol, and drying to obtain an insoluble dietary fiber product. The extraction rate of soluble dietary fibers in the bamboo shoot skin is 18.38%, and the extraction rate of insoluble dietary fibers in the bamboo shoot skin is 46.42%. Soluble and insoluble dietary fibers are subjected to scanning electron microscope analysis, Fourier transform infrared spectroscopic analysis, X-ray diffraction analysis and antioxidant ability analysis to obtain characterization structure results of the soluble and insoluble dietary fibers. The process is simple and rapid, the extraction rate is high, the product purity is high, and the functionality is good.

Description

Technical Field

[0001] This invention belongs to the technical field of agricultural product processing and high-value utilization of by-products. Specifically, it relates to a method for extracting soluble dietary fiber (SDF) and insoluble dietary fiber (IDF) from bamboo shoot sheaths, and characterizing them. This invention aims to provide an efficient, environmentally friendly extraction process that effectively maintains the structure and activity of dietary fiber, providing technical support for the comprehensive utilization of bamboo shoot by-product resources and the development and application of dietary fiber. Background Technology

[0002] Bamboo shoot sheaths, typically referring to the sheath-like structures that wrap around the bamboo shoot during its growth, are one of the main byproducts of bamboo shoot processing. Traditionally, some bamboo shoot sheaths have been used as roughage or discarded directly, resulting in resource waste and potential environmental pressure. Studies have shown that bamboo shoot sheaths are rich in dietary fiber, polyphenols, flavonoids, and other bioactive substances, and have high development and utilization value.

[0003] Dietary fiber (DF) refers to the collective term for polysaccharide carbohydrates and lignin in plants that cannot be broken down by human digestive enzymes. Based on its solubility in water, it can be divided into soluble dietary fiber (SDF) and insoluble dietary fiber (IDF). SDF has physiological functions such as lowering cholesterol, regulating blood sugar, and promoting the proliferation of beneficial bacteria; IDF can increase stool volume, promote intestinal peristalsis, and prevent constipation and colon cancer. Therefore, developing high-quality dietary fiber products has significant health implications and market potential.

[0004] Currently, dietary fiber extraction methods mainly include chemical methods (acid and alkali methods), physical methods (hot water extraction, ultrasound-assisted extraction, microwave-assisted extraction, and extrusion cooking), and biological methods (enzymatic and fermentation methods). While chemical methods offer high extraction efficiency, the harsh conditions can easily lead to structural damage and reduced functional activity of dietary fiber, and generate large amounts of waste liquid, which is environmentally unfriendly. Traditional hot water extraction is time-consuming, energy-intensive, and has a low extraction rate. Ultrasonic-assisted extraction, as a physical aid, can improve extraction efficiency at lower temperatures and reduce solvent usage; however, the selection of ultrasonic parameters (such as power, time, and temperature) is crucial to the yield and structural integrity of dietary fiber. Excessive power or time may damage the microstructure of dietary fiber, affecting its functional properties. Enzymatic extraction of dietary fiber has advantages such as mild conditions and high selectivity; however, the extraction effect of a single enzyme is often limited, and enzymes are relatively expensive.

[0005] Therefore, developing a method that is mild, easy to operate, environmentally friendly, and can effectively extract SDF and IDF from bamboo shoot skins while maintaining their good functional properties is of great significance for the high-value utilization of bamboo shoot skin resources. Summary of the Invention

[0006] Technical challenges: Among existing dietary fiber extraction methods, chemical methods cause significant damage to the dietary fiber structure and result in severe environmental pollution; traditional physical methods have low extraction efficiency and high energy consumption; single ultrasonic extraction, if parameters are not properly controlled, can easily damage the dietary fiber structure, affecting its application value; single enzymatic extraction has limited effectiveness and high cost. Furthermore, how to efficiently separate and obtain high-quality SDF and IDF is also a problem that needs to be solved.

[0007] The purpose of this invention is to address the aforementioned problems in existing methods for extracting dietary fiber from bamboo shoots. This invention aims to provide a method for extracting dietary fiber from bamboo shoots using a compound enzymatic method. This method is mild and can effectively extract both soluble and insoluble dietary fiber from bamboo shoots, resulting in high-quality products. Furthermore, the process is relatively simple and environmentally friendly.

[0008] Technical solution: A method for extracting dietary fiber from bamboo shoot skin, comprising the following steps:

[0009] (1) Raw material pretreatment: Wash the fresh bamboo shoot skins, dry them at 65-75℃ to constant weight, then pulverize them and pass the powder through a 70-90 mesh sieve to obtain bamboo shoot skin powder for later use. For example, the drying temperature can be set to 70℃, and the powder can be passed through an 80 mesh sieve to obtain bamboo shoot skin powder with uniform particle size, which is beneficial to the subsequent enzymatic hydrolysis reaction.

[0010] (2) Enzymatic extraction: Mix the bamboo shoot powder obtained in step (1) with distilled water, controlling the solid-liquid ratio at 1:15-1:25 (g / mL). Add 3.0-4.0% (w / w) of a complex enzyme at 35-45℃ and react for 20-30 min. Specifically, the complex enzyme can be a mixture of cellulase and xylanase, with a mass ratio of 0.6:1 to 1:1. For example, the enzymatic hydrolysis temperature can be set to 40℃, the amount of complex enzyme added to be 3.6%, and the reaction time to be 25 min.

[0011] (3) Enzyme inactivation and separation: Heat the reaction solution to 95-105℃, inactivate the enzyme for 8-12 min, stir and centrifuge at 6000-8000 rpm for 8-12 min to obtain the supernatant and precipitate. For example, the reaction solution can be heated to 100℃ and inactivated for 10 min to ensure complete enzyme inactivation.

[0012] (4) Extraction of soluble dietary fiber: Concentrate the supernatant to 1 / 3-1 / 5 of its original volume, add 3-5 times its volume of anhydrous ethanol, precipitate at 2-6℃ for 10-14 h, filter, centrifuge (6000-8000 rpm, 8-12 min), and dry the precipitate to obtain soluble dietary fiber powder. Specifically, concentration can be performed under vacuum at a temperature not exceeding 50℃ to avoid thermal degradation of SDF. For example, 4 times its volume of anhydrous ethanol can be added, and precipitation can be carried out at 4℃ for 12 h.

[0013] (5) Extraction of insoluble dietary fiber: The precipitate obtained in step (3) is eluted with anhydrous ethanol 2-4 times and dried to obtain the insoluble dietary fiber product. For example, it can be eluted with anhydrous ethanol 3 times to fully remove any impurities that may remain in the precipitate.

[0014] Furthermore, the present invention also includes a step of characterizing the obtained soluble dietary fiber powder and insoluble dietary fiber products, wherein the characterization methods include scanning electron microscopy analysis, Fourier transform infrared spectroscopy analysis, X-ray diffraction analysis and antioxidant capacity analysis.

[0015] Furthermore, the antioxidant capacity analysis includes the determination of DPPH free radical scavenging rate and ABTS free radical scavenging rate.

[0016] In a preferred embodiment of the present invention, the extraction rate of soluble dietary fiber is 15-22%, and the extraction rate of insoluble dietary fiber is 40-50%.

[0017] The beneficial effects of this invention are:

[0018] 1. Efficient utilization of resources: This invention uses bamboo shoot skin as raw material, transforming it from a low-value by-product into a high-value-added dietary fiber product, thus achieving efficient utilization of resources and value enhancement.

[0019] 2. Mild and efficient process: Utilizing a compound enzyme method, the reaction conditions are milder compared to traditional chemical methods, avoiding the damage to dietary fiber structure caused by high temperatures, strong acids, and strong alkalis. Compared to traditional water extraction, the extraction time is shortened and efficiency is improved. The use of compound enzymes can more effectively degrade the cell walls in bamboo shoot sheaths, releasing more dietary fiber.

[0020] 3. Produces both soluble and insoluble dietary fiber with good quality: This method can simultaneously obtain both soluble and insoluble dietary fiber, meeting different application needs. By controlling process parameters, the obtained dietary fiber product has high purity and good structural integrity.

[0021] 4. Green and environmentally friendly: It mainly uses water and ethanol as solvents. Ethanol can be recycled, which reduces the use of chemical reagents and waste emissions, making it environmentally friendly.

[0022] 5. Scientific and systematic approach: This invention not only provides an extraction method, but also includes a systematic characterization of the product, providing a scientific basis for the structural confirmation, property analysis and potential applications of bamboo shoot peel dietary fiber. Attached Figure Description

[0023] Figure 1 Microscopic images of different parts of bamboo shoot sheath (a) and scanning electron microscopy (SEM) images of four types of dietary fiber (b).

[0024] Depend on Figure 1 A comparison of the microstructures of bamboo shoot sheaths of different colors (A: brown, B: yellow, C: white) shows that the white bamboo shoot sheath has a tight and regular fiber structure, which facilitates the acquisition of high-purity dietary fiber. Its moderate fineness and uniform pores help to adsorb water and nutrients, enhancing functionality. The low impurity content simplifies the extraction process, and the lighter color improves the product's appearance and enhances its market competitiveness. Figure 1 As shown in b, scanning electron microscopy (SEM) analysis was used to observe the surface microstructure characteristics of dietary fiber samples obtained by different extraction methods. SDF exhibited an irregular blocky or granular structure with some porosity or roughness. IDF, on the other hand, showed a larger sheet-like or layered structure with a rougher and more irregular surface. IDF samples had larger particle sizes and more pronounced lamellar features compared to SDF samples, which is consistent with their differences in solubility. Overall, different extraction methods and fiber types (SDF vs. IDF) significantly affected the microstructure of dietary fiber.

[0025] Figure 2 Fourier transform infrared (FT-IR) spectra of four types of dietary fiber.

[0026] Depend on Figure 2 It can be seen that the infrared absorption spectra of the four dietary fiber samples are generally similar, all showing typical absorption peaks of polysaccharides in the 3300-3400 cm⁻¹ range. -1 A broad and strong absorption peak appears nearby, which is attributed to the stretching vibration of the hydroxyl group (-OH), a typical characteristic peak of carbohydrates. This peak is observed at 2900-3000 cm⁻¹. -1 Area, approximately 2930cm -1 The nearby absorption peaks are caused by the stretching vibrations of the CH groups in the polysaccharide. (1650-1740 cm⁻¹) -1 The region exhibits multiple absorption peaks, such as at 1650 cm⁻¹. -1 The nearby peaks may be related to C=O stretching vibrations in bound water or residual proteins. (1400-1430 cm⁻¹) -1 In the region, peaks of CH bending vibration or symmetric stretching vibration of carboxylate COO- were observed. (1200-1250 cm⁻¹) -1The absorption peak in the region may be related to CO stretching vibrations. In the fingerprint region (1200 cm⁻¹)... -1 (The following) shows multiple strong absorption peaks, such as at 1140 cm⁻¹. -1 1080cm -1 1020cm -1 These peaks are attributed to the stretching vibrations of the COC glycosidic bond, the C-OH side group, and the vibrational overlap of the pyranose ring, indicating that the samples all contain polysaccharide structures.

[0027] Figure 3 X-ray diffraction (XRD) patterns of four types of dietary fiber.

[0028] Depend on Figure 3 It can be seen that the X-ray diffraction patterns of the four dietary fiber samples did not show obvious sharp crystalline diffraction peaks, but instead exhibited a broad, diffuse peak (amorphous peak) around a 2θ angle of approximately 20-22°. This indicates that the dietary fiber samples extracted by these methods mainly exist in an amorphous structure with no obvious crystalline structure. There were no significant differences in crystal structure among different extraction methods and fiber types, which is consistent with the crystallization characteristics of most natural dietary fibers.

[0029] Figure 4 This is an analysis chart of the antioxidant capacity of four types of dietary fiber (A: DPPH free radical scavenging rate).

[0030] Figure 4 The in vitro scavenging abilities of four dietary fiber samples against ABTS and DPPH free radicals were demonstrated and compared with the positive control BHT. Figure 4 (DPPH clearance rate curve) and Figure 5 The ABTS scavenging rate curves show that the scavenging ability of all dietary fiber samples for DPPH and ABTS free radicals is concentration-dependent; that is, the free radical scavenging rate increases with increasing sample concentration. Regarding DPPH free radical scavenging, within the detection concentration range, the positive control BHT showed the highest scavenging rate, followed by SDF, while IDF showed relatively lower DPPH scavenging ability. For ABTS free radical scavenging, the positive control BHT also showed the highest activity. Among the dietary fiber samples, SDF exhibited the best ABTS free radical scavenging ability, exceeding that of IDF. Figure 5 The bar chart further visually compared the ABTS free radical scavenging rates of the four dietary fiber samples at 5 mg / mL, showing that SDF exhibited the highest ABTS scavenging activity, followed by IDF. These results indicate that dietary fiber extracted using different methods and of different types possesses varying levels of antioxidant activity.

[0031] Figure 5The graph shows the antioxidant capacity analysis of four types of dietary fiber (B: ABTS scavenging rate). Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments, but these embodiments do not limit the scope of the present invention in any way. All equivalent substitutions or modifications made according to the content of the present invention are within the protection scope of the present invention.

[0033] Example 1

[0034] (1) Raw material pretreatment: Take 1 kg of fresh bamboo shoot skin, wash it, and dry it in a 70℃ forced-air drying oven until constant weight to obtain dried bamboo shoot skin. Crush the dried bamboo shoot skin with a universal pulverizer, pass it through an 80-mesh sieve, collect the sieve material, and obtain bamboo shoot skin powder.

[0035] (2) Ultrasonic water extraction: Weigh 100g of bamboo shoot powder, add water at a solid-liquid ratio of 1:20 (g / mL), and react at 40℃ for 25min.

[0036] (3) Separation: Heat the reaction solution to 100℃ and inactivate the enzyme for 10 min. Centrifuge the ultrasonically treated mixture at 7000 rpm for 10 min and collect the supernatant and precipitate.

[0037] (4) Extraction of soluble dietary fiber: The supernatant obtained in step (3) was concentrated to 1 / 4 of its original volume under vacuum at 50°C using a rotary evaporator. Four times the volume of anhydrous ethanol was slowly added to the concentrate while stirring, and then the mixture was allowed to stand for 12 hours at 4°C to precipitate. The precipitate was collected by filtration and centrifuged at 7000 rpm for 10 minutes, and the supernatant was discarded. The precipitate was dried to constant weight in a vacuum drying oven at 50°C and then pulverized to obtain bamboo shoot skin soluble dietary fiber (UAE-SDF) powder.

[0038] (5) Extraction of insoluble dietary fiber: The precipitate obtained in step (3) was washed three times with anhydrous ethanol. Each time, about 5 times the volume of the precipitate was added to the precipitate. After stirring evenly, the precipitate was centrifuged (6000 rpm, 8 min) and the supernatant was discarded. The washed precipitate was dried to constant weight in a 60℃ forced-air drying oven and then pulverized to obtain bamboo shoot skin insoluble dietary fiber (UAE-IDF) product.

[0039] (6) Product characterization: The obtained SDF powder and IDF products were analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The DPPH radical scavenging rate and ABTS radical scavenging rate of SDF powder were determined. The results showed that both SDF and IDF have the typical microstructure and chemical group characteristics of dietary fiber, and SDF exhibits certain antioxidant activity.

[0040] Example 2

[0041] (1) Raw material pretreatment: Same as in Example 1, take 1 kg of fresh bamboo shoot skin, wash it, dry it at 65℃ to constant weight, crush it and pass it through a 70-mesh sieve to obtain bamboo shoot skin powder.

[0042] (2) Enzymatic extraction: Weigh 100g of bamboo shoot skin powder and add water at a solid-liquid ratio of 1:20 (g / mL). Add a compound enzyme, which is a mixture of cellulase and xylanase, with a mass ratio of cellulase to xylanase of 0.8:1. The amount of compound enzyme added is 3.6% of the mass of the bamboo shoot skin powder. Place the mixture in a constant temperature water bath shaker and react at 55℃ for 30 min.

[0043] (3) Enzyme inactivation and separation: Heat the reaction solution to 95°C and inactivate the enzyme for 12 min. Centrifuge the ultrasonically treated mixture at 7000 rpm for 12 min and collect the supernatant and precipitate.

[0044] (4) Extraction of soluble dietary fiber: The supernatant was concentrated to 1 / 3 of its original volume, and 3 times the volume of anhydrous ethanol was added. The mixture was precipitated at 6°C for 10 h. Subsequent filtration, centrifugation (7000 rpm, 12 min), and drying were performed as in Example 1 to obtain UAEE-SDF powder.

[0045] (5) Extraction of insoluble dietary fiber: The precipitate obtained in step (3) was eluted twice with anhydrous ethanol and dried to obtain UAEE-IDF product.

[0046] Experimental data

[0047] The table below lists the extraction rates of soluble and insoluble dietary fiber in Examples 1 and 2: Example Soluble dietary fiber extraction rate (%) Insoluble dietary fiber extraction rate (%) 1 18.5 46.2 2 17.8 45.5

[0048] As can be seen from the table above, the method for extracting dietary fiber from bamboo shoot skin provided by this invention has a high extraction rate.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that those skilled in the art can make several improvements based on the technical solution and the description of the preferred embodiment of the present invention without departing from the principle of the present invention, and these improvements should also fall within the protection scope of the present invention.

Claims

1. A method for extracting dietary fiber from bamboo shoot skin, characterized in that, Includes the following steps: (1) Raw material pretreatment: Wash the fresh bamboo shoot skin, divide and observe according to the parts, dry at 65-75℃ to constant weight, crush and pass through a 70-90 mesh sieve to obtain bamboo shoot skin powder; (2) Enzymatic extraction: Mix bamboo shoot powder with distilled water at a solid-liquid ratio of 1:15-1:25 (g / mL), add 3.0-4.0% (w / w) of compound enzyme at 35-45℃, and react for 20-30 min. (3) Enzyme inactivation and separation: Heat the reaction solution to 95-105℃, inactivate the enzyme for 8-12 min, stir and centrifuge at 6000-8000 rpm for 8-12 min to obtain supernatant and precipitate; (4) Extraction of soluble dietary fiber: Concentrate the supernatant to 1 / 3-1 / 5 of the original volume, add 3-5 times the volume of anhydrous ethanol, precipitate at 2-6℃ for 10-14h, filter, centrifuge (6000-8000rpm, 8-12min) and dry the precipitate to obtain soluble dietary fiber powder. (5) Extraction of insoluble dietary fiber: The precipitate obtained in step (3) is washed with anhydrous ethanol 2-4 times and dried to obtain insoluble dietary fiber products.

2. The method for extracting dietary fiber from bamboo shoot sheaths according to claim 1, characterized in that, In step (1), the selection of bamboo shoot sheaths includes distinguishing bamboo shoot sheaths from different parts before extraction.

3. The method for extracting dietary fiber from bamboo shoot sheaths according to claim 1, characterized in that, In step (1), the drying temperature is 70°C, and the powder is passed through an 80-mesh sieve.

4. The method for extracting dietary fiber from bamboo shoot sheaths according to claim 1, characterized in that, The complex enzyme is a mixture of cellulase and xylanase in a mass ratio of 0.6:1 to 1:

1.

5. The method for extracting dietary fiber from bamboo shoot sheaths according to claim 1, characterized in that, In step (2), the enzymatic hydrolysis temperature is 40℃, the amount of compound enzyme added is 3.6%, and the reaction time is 25min.

6. The method for extracting dietary fiber from bamboo shoot sheaths according to claim 1, characterized in that, In step (4), the concentration is carried out under vacuum, with the temperature not exceeding 45°C. Four times the volume of anhydrous ethanol is added, and precipitation is carried out at 4°C for 12 hours.

7. The method for extracting dietary fiber from bamboo shoot sheaths according to any one of claims 1-5, characterized in that, It also includes a step of characterizing the obtained soluble dietary fiber powder and insoluble dietary fiber products, wherein the characterization methods include scanning electron microscopy analysis, Fourier transform infrared spectroscopy analysis, X-ray diffraction analysis and antioxidant capacity analysis.

8. The method for extracting dietary fiber from bamboo shoot sheaths according to claim 6, characterized in that, The antioxidant capacity analysis included the determination of DPPH free radical scavenging rate and ABTS free radical scavenging rate.

9. The method according to claim 1, wherein the extraction rate of soluble dietary fiber is 15-22% and the extraction rate of insoluble dietary fiber is 40-50%.

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