Preparation method of modified sweet potato residue dietary fiber

Abstract

The invention provides a preparation method of modified sweet potato residue dietary fibers. According to the method, the sweet potato residue dietary fibers are extracted, low-temperature plasma is adopted to modify the sweet potato residue dietary fibers, the surface energy of the sweet potato residues is increased through bombardment of high-energy active particles, etching and oxidation effects are formed, insoluble dietary fibers are converted into soluble dietary fibers, and therefore the content of the soluble dietary fibers in the sweet potato residues is increased; the preparation is made for the subsequent application in food. The method is simple to operate, short in acting time, energy-saving, environment-friendly and less in waste discharge. The content of soluble dietary fibers in the prepared modified sweet potato residue dietary fibers can reach 15.91 g / 100g dry basis, and the water-holding capacity, the water swelling capacity and the oil-holding capacity are 7.10 g / g, 4.32 mL / g and 4.67 g / g respectively and are increased by 4.90%, 17.29% and 5.88% compared with original dietary fiber values.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, and in particular to a method for preparing modified sweet potato residue dietary fiber. Background Art

[0002] Sweet potato residue is a byproduct of producing starch or silk. Every 1kg of starch extracted from fresh sweet potato produces about 0.43-0.56kg of sweet potato residue. At present, most of them are used as cheap feed or directly discarded. Sweet potato residue is rich in starch and dietary fiber, which has physiological activities such as improving intestinal flora, reducing obesity, diabetes and cardiovascular diseases. According to its solubility in water, dietary fiber can be divided into soluble dietary fiber (SDF) and insoluble dietary fiber (IDF). SDF content is an important indicator for evaluating the functional characteristics of dietary fiber. It is generally believed that dietary fiber with an SDF content higher than 10% has better physical and chemical properties and physiological activity. Natural sweet potato residue dietary fiber is mainly IDF, and its SDF content is only 5.93g / 100g dry basis, which greatly affects its physical and chemical properties and physiological activity such as water holding capacity and rheology, and also limits its wide application in the field of food processing.

[0003] At present, many commercial dietary fibers on the market are derived from by-products of the food industry. Although they have a high proportion of total dietary fiber, their soluble dietary fiber content is relatively low. Therefore, modifying dietary fiber to produce high-quality and efficient modified dietary fiber products has become a key research topic for practitioners at home and abroad. The modification methods of dietary fiber mainly include physical modification, chemical modification and biological modification. Physical modification mainly destroys the glycosidic bonds of dietary fiber by external high temperature, high pressure, instantaneous decompression, explosion, high-speed impact and shearing, so as to achieve the purpose of modification, such as ultrafine grinding, extrusion, steam explosion, microwave technology and dynamic high-pressure microfluidization. Chemical method uses chemical reactions to change the structure and functional properties of DF, such as alkaline hydrogen peroxide treatment, carboxymethylation and hydroxypropylation. Chemical modification is cheap and has good modification effect, but some chemical reagents used in the modification process and the by-products produced are easy to pollute the environment if they are not handled properly. The most studied biological modification is enzymatic modification, which is the method of using biological enzymes to hydrolyze macromolecules in dietary fiber into small molecule compounds. The more commonly used enzymes are green wood enzymes, xylanases, lignin oxidases, etc. Enzymatic modification is mild, has a short reaction time and high purity. It is a more effective modification method, but it has high requirements for reaction conditions and production conditions are difficult to effectively control.

[0004] Therefore, the present invention provides a method for preparing modified sweet potato residue dietary fiber. Summary of the invention

[0005] The invention provides a method for preparing modified sweet potato residue dietary fiber, and aims to solve the problem that sweet potato residue is often used as waste or has a low recycling rate in real life.

[0006] In order to achieve the above-mentioned object, the embodiment of the present invention provides a preparation method of modified sweet potato residue dietary fiber, the method extracts sweet potato residue dietary fiber, uses low-temperature plasma to modify the sweet potato residue dietary fiber, increases the surface energy of the sweet potato residue by high-energy active particle bombardment, forms etching and oxidation effects, and transforms insoluble dietary fiber into soluble dietary fiber, thereby increasing the soluble dietary fiber content of the sweet potato residue, and preparing for its subsequent application in food. The present invention is simple to operate, short in action time, energy-saving and environmentally friendly, and has less waste discharge. The content of soluble dietary fiber in the modified sweet potato residue dietary fiber prepared by the present invention can reach 15.91g / 100g dry basis, and the water holding capacity, water absorption expansion capacity and oil holding capacity are 7.10g / g, 4.32mL / g and 4.67g / g, respectively, which are 4.90%, 17.29% and 5.88% higher than the original dietary fiber value.

[0007] The embodiment of the present invention provides a method for preparing modified sweet potato residue dietary fiber, comprising the following steps:

[0008] S1. Weigh the sweet potato residue powder, dilute it with deionized water, adjust the pH, add α-amylase and stir evenly, place it in a constant temperature water bath for enzymolysis, inactivate it after enzymolysis, and cool it to room temperature; adjust the pH, add saccharifying enzyme and stir evenly, place it in a constant temperature water bath for enzymolysis, inactivate it after enzymolysis, and cool it; add ethanol, let it stand at room temperature, wash, filter it, and dry it to obtain sweet potato residue dietary fiber;

[0009] S2. Put the sweet potato residue dietary fiber into a ziplock bag, place it in a high-voltage electric field low-temperature plasma system, and set the discharge voltage, discharge distance, discharge time and discharge frequency for plasma modification to obtain modified sweet potato residue dietary fiber.

[0010] Furthermore, in step S1, the particle size of the sweet potato residue powder is 0.1 mm; and the powder is diluted at a solid-liquid ratio of 1:12 (g / mL).

[0011] Furthermore, in step S1, the pH value is adjusted to 6.5 for the first time; the amount of α-amylase added is 300 U / g; the first enzymolysis temperature is 55° C., and the time is 60 min.

[0012] Furthermore, the inactivation temperature is 100°C, the inactivation time is 8 min, and the inactivation needs to be transferred to another water bath.

[0013] Furthermore, in step S1, the pH value is adjusted to 4.0 for the second time; the amount of saccharifying enzyme added is 250 U / g; the first enzymatic hydrolysis temperature is 65° C., and the time is 30 min.

[0014] Furthermore, in step S1, the ethanol concentration is 95%, and the amount added is 4 times the volume of the cooled material; and the mixture is allowed to stand at room temperature for 12 hours.

[0015] Furthermore, in step S1, washing is performed using 78% and 95% ethanol respectively; and the drying temperature is 70°C.

[0016] Furthermore, the dietary fiber of the sweet potato residue in step S2 is 5g.

[0017] Furthermore, in step S2, the discharge voltage is 100-160 kV, the discharge distance is 20-35 mm, the discharge time is 5-30 min, and the discharge frequency is 50-200 Hz. Furthermore, the discharge voltage is 119 kV, the discharge distance is 25 mm, the discharge time is 26 min, and the discharge frequency is 151 Hz.

[0018] Furthermore, the soluble dietary fiber content of the modified sweet potato residue dietary fiber in step S2 reaches 15.91 g / 100 g dry basis, and the water holding capacity, water absorption expansion capacity and oil holding capacity are 7.10 g / g, 4.32 mL / g and 4.67 g / g, respectively.

[0019] Furthermore, in step S2, the modified sweet potato residue dietary fiber is laid flat in a discharge region between two electrode plates of a high-voltage electric field low-temperature plasma system.

[0020] Plasma is a quasi-neutral gas, known as the fourth state of matter. It contains different active particles such as electrons, ions, free radicals and metastable excited atoms, which have enough energy to break covalent bonds and trigger some reactions. Low-temperature plasma refers to a gas in which the temperature of electrons (Te) is much higher than the temperature of ions, neutral and overall gas (Tg) (Te>>Tg). In low-temperature plasma, electrons and other ions are in non-thermodynamic equilibrium, and the overall temperature is close to the ambient temperature, even at atmospheric pressure. Low-temperature plasma contains a variety of active particles such as free radicals and high-energy particles, such as reactive oxygen, reactive nitrogen, charged particles, free radicals, etc. They are generated by collisions between electrons, atoms and molecules during plasma discharge. These active particles generated by low-temperature plasma can interact with the surface of solid materials, transfer their own energy to the material, induce the molecules in the material to form new chemical bonds, or break the original chemical bonds, etc. Low-temperature plasma technology is a low-energy, easy-to-operate green modification technology. In recent years, research reports have mainly focused on the modification of food macromolecules such as proteins and starch.

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

[0022] (1) The present invention utilizes low-temperature plasma technology to modify the sweet potato residue dietary fiber. The plasma technology increases the surface energy of the sweet potato residue through high-energy active particle bombardment, forming an etching and oxidation effect, thereby converting the insoluble dietary fiber into soluble dietary fiber, thereby increasing the soluble dietary fiber content. The soluble dietary fiber in the sweet potato residue dietary fiber of the present invention can reach 14.39%.

[0023] (2) The low-temperature plasma technology of the present invention is easy to operate, consumes little energy during the process, is safe, and does not use chemical reagents during the modification process, and does not generate secondary waste. It is a green modification technology. The dietary fiber extracted from the industrial by-product, sweet potato residue, is modified by low-temperature plasma, and the dietary fiber resources of sweet potato residue are effectively developed and utilized, solving the problems of low utilization rate of sweet potato residue and environmental pollution, and achieving the effect of saving resources and economical production.

[0024] (3) The content of soluble dietary fiber in the modified sweet potato residue dietary fiber prepared by the present invention can reach 15.91 g / 100 g dry basis; the water holding capacity, water absorption expansion capacity and oil holding capacity of the modified dietary fiber prepared by the present invention are 7.10 g / g, 4.32 mL / g and 4.67 g / g, respectively, which are increased by 4.90%, 17.29% and 5.88% compared with the original dietary fiber values. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 The effect of the discharge voltage of the present invention on the dietary fiber content of sweet potato residue;

[0027] Figure 2 The effect of the discharge distance of the present invention on the dietary fiber content of sweet potato residue;

[0028] Figure 3 The effect of the discharge frequency of the present invention on the dietary fiber content of sweet potato residue;

[0029] Figure 4 The effect of the discharge time of the present invention on the dietary fiber content of sweet potato residue;

[0030] Figure 5 The present invention is a response surface model for the effect of discharge voltage and discharge time on the soluble dietary fiber content in the sweet potato residue dietary fiber;

[0031] Figure 6 The present invention is a response surface model for the effect of discharge time and discharge frequency on the soluble dietary fiber content in sweet potato residue dietary fiber;

[0032] Figure 7 The invention discloses a response surface model for the effect of discharge frequency and discharge voltage on the soluble dietary fiber content in the sweet potato residue dietary fiber;

[0033] Figure 8 It is a scanning electron microscope image of the sweet potato residue, dietary fiber extracted from sweet potato residue and modified dietary fiber from sweet potato residue of the present invention; wherein, Figure 8 (A, B) are scanning electron microscope images of sweet potato residue. Figure 8 (C, D) are scanning electron micrographs of dietary fiber extracted from sweet potato residue. Figure 8 (E, F) are scanning electron micrographs of modified sweet potato residue dietary fiber. DETAILED DESCRIPTION

[0034] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0035] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0036] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0037] The present invention aims at the above-mentioned problems existing in the background technology, and provides a preparation method of modified sweet potato residue dietary fiber, which extracts sweet potato residue dietary fiber, uses low-temperature plasma to modify the sweet potato residue dietary fiber, increases the surface energy of the sweet potato residue by high-energy active particle bombardment, forms etching and oxidation effects, and transforms insoluble dietary fiber into soluble dietary fiber, thereby increasing the soluble dietary fiber content of the sweet potato residue, and preparing for its subsequent application in food. The present invention is simple to operate, short in action time, energy-saving and environmentally friendly, and has less waste discharge. The content of soluble dietary fiber in the modified sweet potato residue dietary fiber prepared by the present invention can reach 15.91g / 100g dry basis, and the water holding capacity, water absorption expansion capacity and oil holding capacity are 7.10g / g, 4.32mL / g and 4.67g / g, respectively, which are increased by 4.90%, 17.29% and 5.88% compared with the original dietary fiber value.

[0038] The following will describe in detail with reference to specific embodiments.

[0039] Example

[0040] This embodiment provides a method for preparing modified sweet potato residue dietary fiber.

[0041] The preparation method of this embodiment comprises the following steps:

[0042] 1. Extraction of dietary fiber from sweet potato residue

[0043] ① Crush the sweet potato residue and pass it through 60-mesh, 100-mesh, 150-mesh and 200-mesh sieves respectively. Collect the obtained sweet potato residue powders and place them in a dryer for later use.

[0044] ② Weigh a certain amount of sweet potato residue powder with different crushing particle sizes, dilute it with deionized water at a solid-liquid ratio of 1:12 (g / mL), and adjust the pH to 6.5; shake the mixture with α-amylase (300U / g) in a water bath at 55°C for 1h, and then in a water bath at 100°C for 10min to inactivate α-amylase; after cooling, adjust the pH of the mixture to 4.0, and add glucosidase (250U / g); after incubation at 65°C for 30min, inactivate glucosidase at 100°C for 10min; add 95% ethanol to the cooled mixture at a ratio of 1:4 (v / v) and place it at room temperature for 12h; after filtration, the residue is washed with 78% ethanol, 95% ethanol and acetone solvents in turn, and dried in an oven at 70°C to obtain sweet potato residue dietary fiber, thus obtaining sweet potato residue dietary fiber (SPR-DF).

[0045] 2. Modification of low temperature plasma

[0046] Using a high-voltage electric field low-temperature plasma system, 5 g of the extracted sweet potato residue dietary fiber sample was placed in a ziplock bag and laid flat in the discharge area between the two electrode plates of the instrument.

[0047] The discharge voltages were 130kV, 140kV, 150kV, and 160kV, the discharge distances were 20mm, 25mm, 30mm, and 35mm, the discharge time was 5min, 10min, 15min, and 20min, and the discharge frequency was 50Hz, 100Hz, 150Hz, and 200Hz. After the discharge, the instrument door was opened, the sample was taken out, the instrument door was closed, and the instrument was turned off. The samples were collected and placed in a dryer for later use. A single-factor experiment was designed to determine the optimal process parameters for the plasma modification experiment by measuring the changes in the dietary fiber content of sweet potato residue under different process parameters.

[0048] Determination of dietary fiber: Refer to GB 5009.88-2014 to determine the dietary fiber samples of sweet potato residue.

[0049] 3. Optimization results of extraction and modification methods

[0050] (1) Effect of different crushing particle sizes on dietary fiber content of sweet potato residue

[0051] Table 1 Effect of different crushing particle sizes on dietary fiber content of sweet potato residue

[0052]

[0053] As can be seen from Table 1, as the particle size of the crushed particles becomes smaller, the total dietary fiber (TDF) content increases significantly, and the maximum value can be reached when the particle size is 150 mesh (pore size 106 μm); as the particle size continues to decrease, the TDF content gradually stabilizes. This may be because as the particle size decreases, the sweet potato residue particles are more in contact with the enzyme, the enzymatic hydrolysis efficiency is improved, and the total dietary fiber content obtained by enzyme extraction increases. In addition, during the crushing process, the agglomeration structure between dietary fiber molecules and starch will be destroyed, the specific surface area will be increased, and the contact area between the enzyme and the sample will increase, which is more conducive to enzymatic hydrolysis. Therefore, the sweet potato residue that was crushed through a 150-mesh sieve was selected for subsequent enzyme extraction experiments.

[0054] (2) Single factor experimental results of low temperature plasma modified sweet potato residue dietary fiber

[0055] The effect of discharge voltage on the content of SDF and IDF in SPR-DF is as follows: Figures 1 to 4 As shown. As the voltage increases, the SDF content increases. The discharge voltage will affect the generation of active particles such as active oxygen during the low-temperature plasma technology treatment, affecting the modification effect. The change in discharge distance (20-35mm) will not significantly affect the SDF content in SPR-DF after low-temperature plasma technology modification. When the discharge frequency increases from 50Hz to 100Hz, the SDF content increases significantly; there is no obvious change after exceeding 100Hz. High-frequency discharge can produce stable and large-volume plasma active particles. These active particles affect the modification effect by degrading molecules, corroding particles, and introducing functional groups; the increase in the number of active particles and the increase in energy can increase the damage of low-temperature plasma to the SPR-DF surface, thereby enhancing the modification effect. As the discharge time increases, the SDF content increases significantly. When the discharge time reaches 20min, the SDF content gradually stabilizes. As the discharge time increases, the damage to the SPR-DF structure by modification intensifies, cracks form in the outer layer of the fiber, the pores become larger, and a large number of water-soluble components and hydrophilic groups, such as pectin and hydroxyl groups, are exposed, thereby increasing the SDF content.

[0056] (3) Experimental results of optimizing low-temperature plasma technology to modify sweet potato residue dietary fiber using the Box-Behnken method

[0057] The three parameters of discharge voltage, discharge frequency and discharge time are selected according to the single factor experimental data (such as Figures 5 to 7) conducted a three-factor three-level response surface optimization experiment, and the results showed that the order of factors affecting the SDF content in SPR-DF was: discharge voltage> discharge frequency> discharge time. Combined with the actual experimental operation, the optimal process conditions for low-temperature plasma modified SPR-DF were finally determined to be: discharge distance 25mm, discharge voltage 119kV, discharge frequency 151Hz, and discharge time 26min. SPR-MDF was modified under this condition, and the SDF content was 15.91g / 100g dry basis, which was basically consistent with the theoretical prediction value, confirming that the response surface model is reliable, and the optimal process parameters obtained using this model are true and reliable.

[0058] like Figure 8 As shown in the figure, there are many smooth round starch particles in the microstructure of sweet potato residue, and the original sweet potato residue contains a lot of starch. Figure 8 C and 8D) have irregular flake structures, dense surfaces and clear fiber structures. After being treated with low-temperature plasma technology, the modified sweet potato residue dietary fiber ( Figure 8 E and 8F) showed a flaky structure with more cracks and surface wrinkles, presenting a more broken and loose structure.

[0059] Table 2 Test results of water holding capacity, oil holding capacity and swelling capacity of sweet potato residue and sweet potato residue dietary fiber before and after modification

[0060]

[0061]

[0062] Among them, a, b, c: different letter superscripts indicate that the data are significantly different (p<0.05)

[0063] The improvement in water holding capacity may be due to the increase in the SDF content of sweet potato residue dietary fiber after low-temperature plasma treatment, the cleavage of macromolecules to form smaller molecular structures, more surface voids and wrinkles, increased specific surface area, and more hydrophilic groups exposed. Dietary fibers with high water holding capacity can lock more water in food, reduce the shrinkage of baked foods caused by dehydration, and thus improve product quality. In addition, they can promote defecation and accelerate the excretion of toxins.

[0064] The improved oil holding capacity may be due to the increase in the pore structure of the modified sweet potato residue dietary fiber. Dietary fiber with high oil holding capacity can significantly improve the sensory properties of food and make high-fat foods more stable, thus helping to extend the shelf life.

[0065] The improvement in swelling capacity may be due to the cleavage of the molecular surface, the exposure of more hydrophilic groups, and the increase in porous network structure. Good swelling capacity can make dietary fiber absorb water and swell in the intestine, increase the body's sense of fullness, and then affect appetite, achieving the purpose of weight loss.

[0066] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing modified sweet potato residue dietary fiber, characterized in that: The steps include: S1. Weigh the sweet potato residue powder, dilute it with deionized water, adjust the pH, add α-amylase and stir evenly, place it in a constant temperature water bath for enzymolysis, inactivate it after enzymolysis, and cool it to room temperature; adjust the pH, add saccharifying enzyme and stir evenly, place it in a constant temperature water bath for enzymolysis, inactivate it after enzymolysis, and cool it; add ethanol, let it stand at room temperature, wash, filter it, and dry it to obtain sweet potato residue dietary fiber; S2. Put the sweet potato residue dietary fiber into a ziplock bag, place it in a high-voltage electric field low-temperature plasma system, and set the discharge voltage, discharge distance, discharge time and discharge frequency for plasma modification to obtain modified sweet potato residue dietary fiber.

2. The method for preparing modified sweet potato residue dietary fiber according to claim 1, characterized in that: The particle size of the sweet potato residue powder in step S1 is 0.1 mm; the powder is diluted at a solid-liquid ratio of 1:12 (g / mL).

3. The method for preparing modified sweet potato residue dietary fiber according to claim 1, characterized in that: In step S1, the pH value is adjusted to 6.5 for the first time; the amount of α-amylase added is 300 U / g; the first enzymolysis temperature is 55° C. and the time is 60 min.

4. The method for preparing modified sweet potato residue dietary fiber according to claim 1, characterized in that: The inactivation temperature is 100℃, the inactivation time is 8min, and the inactivation needs to be transferred to another water bath.

5. The method for preparing modified sweet potato residue dietary fiber according to claim 1, characterized in that: In step S1, the pH value is adjusted to 4.0 for the second time; the amount of saccharifying enzyme added is 250 U / g; the first enzymatic hydrolysis temperature is 65° C. and the time is 30 min.

6. The method for preparing modified sweet potato residue dietary fiber according to claim 1, characterized in that: In step S1, the ethanol concentration is 95%, and the amount added is 4 times the volume of the cooled material; the mixture is allowed to stand at room temperature for 12 hours.

7. The method for preparing modified sweet potato residue dietary fiber according to claim 1, characterized in that: In step S1, washing is performed with 78% and 95% ethanol respectively; the drying temperature is 70°C.

8. The method for preparing modified sweet potato residue dietary fiber according to claim 1, characterized in that: The dietary fiber of the sweet potato residue in step S2 is 5g.

9. The method for preparing modified sweet potato residue dietary fiber according to claim 1, characterized in that: In step S2, the discharge voltage is 100-160 kV, the discharge distance is 20-35 mm, the discharge time is 5-30 min, and the discharge frequency is 50-200 Hz.

10. The method for preparing modified sweet potato residue dietary fiber according to claim 1, characterized in that: The soluble dietary fiber content of the modified sweet potato residue dietary fiber in step S2 reaches 15.91 g / 100 g dry basis, and the water holding capacity, water absorption expansion capacity and oil holding capacity are 7.10 g / g, 4.32 mL / g and 4.67 g / g, respectively.

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