Resistance dextrin as well as preparation method and application thereof

Abstract

The invention provides resistant dextrin as well as a preparation method and application thereof, and belongs to the technical field of preparation of resistant dextrin. The preparation method of the cassava starch resistant dextrin comprises the following steps: gelatinizing cassava starch, mixing the gelatinized cassava starch with pullulanase, carrying out debranching enzymolysis, mixing supernate with an ethanol water solution, washing precipitates with absolute ethyl alcohol, mixing the precipitates with water, recrystallizing at 45-55 DEG C, and collecting crystal substances, so as to obtain the cassava starch resistant dextrin. The cassava starch resistant dextrin with high purity and high resistant starch content can be prepared by taking cassava starch as a raw material and pullulanase as debranching enzyme and adopting a green preparation process of debranching, alcohol precipitation and recrystallization, and the resistant starch content in the prepared resistant dextrin is 50-70%. The preparation method is energy-saving and environment-friendly, and can be commercially applied. Theoretical guidance is provided for preparing the resistant dextrin based on a green process, and a basis is provided for improving the application of the resistant dextrin in the food industry.

Description

Technical Field

[0001] The present invention belongs to the technical field of resistant dextrin preparation, and particularly relates to a resistant dextrin, a preparation method thereof and an application thereof. Background Art

[0002] Resistant dextrin is a new type of low-calorie glucan and an important low-molecular-weight, non-viscous water-soluble dietary fiber. It uses starch as a raw material and forms soluble dietary fiber through highly controlled partial hydrolysis and repolymerization during the dextrinization process, through partial degradation and glycosyl transfer. Resistant dextrin contains parts that cannot be digested by in vivo digestive enzymes connected by α-1,6, α-1,2, α-1,3 glycosidic bonds, etc. Resistant dextrin is specifically a white powder slightly with a light yellow color, slightly sweet, easily soluble in cold water, insoluble in ethanol, and has a high solubility in aqueous solution. Since resistant dextrin is difficult to digest or digests slowly in the human digestive system, it is used as an expanding agent and fat substitute in foods. Research shows that when animals or humans ingest resistant dextrin, it can inhibit the increase in blood glucose concentration, reduce blood lipids, regulate probiotic populations, lose weight, and enhance the absorption of trace elements, etc. Resistant dextrin is widely used in food production and processing, and is commonly used in meat products, baked foods, health products, infant foods, and dairy products.

[0003] The main preparation methods of resistant dextrin at home and abroad mainly include acid-heat method, baking process method, microwave method, enzymatic hydrolysis method, three-step dry heat method, etc. Currently, the most widely used method is still the acid-heat method, and this preparation method has been maturely applied to industrial production. The advantages of the acid-heat method are that the prepared resistant dextrin has relatively good water solubility and anti-digestibility. The disadvantages are that the acid-heat preparation process of resistant dextrin is time-consuming and energy-consuming, and it causes environmental pollution and energy waste during the post-treatment process, and many impurities are generated during the process, and the color of the prepared dextrin is relatively deep. The enzymatic hydrolysis method has relatively mild production conditions, few side reactions, and is convenient for purification, but the resistant components of the prepared finished products are often relatively low. The research on the preparation of resistant dextrin by the microwave method is relatively less. Although the yield of the microwave method has been improved, the microwave time and temperature have a greater impact on the structure. Long-time microwave and high temperature will cause the sample structure to be damaged and the sample to undergo thermal degradation, and the control requirements for temperature and time are relatively high. Therefore, there is currently a lack of a preparation method in this field that is green and environmentally friendly, has mild preparation conditions, can be commercialized, and can prepare resistant dextrin with high purity and good anti-digestibility. Summary of the Invention

[0004] In view of this, one of the purposes of the present invention is to provide a preparation method of resistant dextrin that is green and environmentally friendly and has mild preparation conditions. The preparation method of the present invention can be commercially applied and can prepare resistant dextrin with high purity and good anti-digestibility.

[0005] The second purpose of the present invention is to provide the resistant dextrin prepared by using the said preparation method and its application.

[0006] To achieve the above-mentioned invention object, the present invention provides the following technical solutions:

[0007] The present invention provides a preparation method of cassava starch resistant dextrin, comprising the following steps: gelatinizing cassava starch to obtain a gelatinized solution; mixing the gelatinized solution with pullulanase for debranching enzymolysis, taking the supernatant and mixing it with an ethanol aqueous solution, taking the precipitate, washing it with absolute ethanol, then mixing it with water, and performing recrystallization at 45°C to 55°C, collecting the crystallized product to obtain cassava starch resistant dextrin; the volume fraction of the ethanol aqueous solution is 45% to 55%.

[0008] Preferably, 1500U to 1700U of pullulanase is added per g of cassava starch.

[0009] Preferably, the temperature of the debranching enzymolysis is 55°C to 60°C, and the time of the debranching enzymolysis is 22h to 26h.

[0010] Preferably, the volume ratio of the supernatant to the ethanol aqueous solution is 1:3 to 5.

[0011] Preferably, the time of the recrystallization is 46h to 50h.

[0012] Preferably, the gelatinization comprises the following steps: mixing cassava starch with a sodium acetate buffer solution until the concentration of cassava starch is 0.2g / mL, and heating it in boiling water for 28min to 32min; the sodium acetate buffer solution contains 0.02% sodium azide.

[0013] Preferably, the concentration of the sodium acetate buffer solution is 0.01M, and the pH of the sodium acetate buffer solution is 5.2.

[0014] Preferably, the temperature for mixing the supernatant with the ethanol aqueous solution is 48°C to 52°C.

[0015] The present invention also provides a cassava starch resistant dextrin, which is prepared by the above preparation method.

[0016] The present invention also provides the application of the above preparation method or the above cassava starch resistant dextrin in the preparation of low-GI foods.

[0017] The beneficial effects of the present invention:

[0018] The present invention uses tapioca starch (TS) as the raw material and pullulanase as the debranching enzyme, and adopts a green preparation process of debranching - alcohol precipitation - recrystallization, which can prepare tapioca starch resistant dextrin (TRD) with high purity and high resistant starch content. The resistant starch content in the prepared resistant dextrin is 50% - 70%. The preparation method of the present invention is energy - saving and environment - friendly and can be commercially applied. The present invention provides theoretical guidance for the preparation of resistant dextrin based on a green process and provides a basis for improving the application of resistant dextrin in the food industry. Description of the Drawings

[0019] Figure 1 are the infrared spectra of tapioca starch resistant dextrin and tapioca starch in different groups;

[0020] Figure 2 are the SEM morphology results of tapioca starch resistant dextrin and tapioca starch under different preparation conditions;

[0021] Figure 3 are the X - ray diffraction patterns of tapioca starch resistant dextrin and tapioca starch in different groups;

[0022] Figure 4 are the digestibility measurement results of tapioca starch resistant dextrin and tapioca starch in different groups. Detailed Embodiments

[0023] The present invention provides a preparation method of tapioca starch resistant dextrin, which includes the following steps: gelatinizing tapioca starch to obtain a gelatinized solution; mixing the gelatinized solution with pullulanase for debranching enzymolysis, taking the supernatant and mixing it with an ethanol aqueous solution, taking the precipitate, washing it with absolute ethanol, then mixing it with water, and recrystallizing at 45°C - 55°C, collecting the crystallized product to obtain tapioca starch resistant dextrin; the volume fraction of the ethanol aqueous solution is 45% - 55%.

[0024] The present invention has no special limitation on the specific sources of all raw materials used in the preparation method, and conventional commercially available products in the art can be used. In the present invention, the gelatinization preferably includes the following steps: mixing tapioca starch with a sodium acetate buffer solution until the concentration of tapioca starch is 0.2 g / mL, and heating it in boiling water for 28 min - 32 min; the sodium acetate buffer solution contains 0.02% sodium azide, where 0.02% refers to the volume percentage. In the present invention, the concentration of the sodium acetate buffer solution is preferably 0.01 M, and the pH of the sodium acetate buffer solution is preferably 5.2. In the present invention, when heating for gelatinization in boiling water, stirring is preferably required, and the heating time in boiling water is preferably 29 min - 31 min, more preferably 30 min. After gelatinization, it is preferably cooled down before mixing with pullulanase.

[0025] In the present invention, 1500 U to 1700 U of pullulanase is added per gram of tapioca starch, more preferably 1600 U. In the present invention, the temperature of the debranching enzymolysis is preferably 55°C to 60°C, more preferably 56°C to 59°C, and further preferably 57°C to 58°C; the time of the debranching enzymolysis is preferably 22 h to 26 h, more preferably 23 h to 25 h, and further preferably 24 h. After the debranching enzymolysis is completed, it is preferably subjected to high-pressure sterilization treatment, and then the supernatant is taken by centrifugation. The temperature of the high-pressure sterilization treatment is preferably 131°C, the time of the high-pressure sterilization treatment is preferably 30 min, and the centrifugation conditions are preferably centrifugation at 10000 g for 15 min.

[0026] In the present invention, the volume ratio of the supernatant to the ethanol aqueous solution is preferably 1:3 to 5, more preferably 1:4; the volume fraction of the ethanol aqueous solution is preferably 47% to 52%, more preferably 48% to 50%; the temperature of mixing the supernatant and the ethanol aqueous solution is preferably 48°C to 52°C, more preferably 49°C to 51°C. In the present invention, when performing alcohol precipitation with the ethanol aqueous solution, stirring is preferably required, the time of the alcohol precipitation is preferably 8 min to 12 min, more preferably 9 min to 11 min, and further preferably 10 min. In the present invention, the number of times of washing the precipitate with absolute ethanol is preferably 2 times. After washing, it is preferably dried, and then mixed with water for recrystallization. The drying temperature is preferably 50°C.

[0027] In the present invention, when mixing the washed and dried precipitate with water for recrystallization, the water is preferably deionized water, the mass-volume fraction of the washed and dried precipitate and water is preferably 10%, and recrystallization is carried out after sterilization. The sterilization temperature is preferably 131°C, and the sterilization time is preferably 30 min. The recrystallization temperature is preferably 47°C to 53°C, more preferably 49°C to 51°C, and further preferably 50°C;

[0028] The recrystallization time is preferably 46 h to 50 h, more preferably 48 h to 49 h. In the present invention, during recrystallization, stirring or shaking is not required. After recrystallization is completed, the crystalline product is collected by centrifugation, washed with distilled water and then freeze-dried to obtain tapioca starch resistant dextrin. The centrifugation conditions are preferably centrifugation at 10000 g for 15 min; the number of times of washing is preferably 2 times, the freeze-drying temperature is preferably -80°C, and the freeze-drying time is preferably 2 days.

[0029] The present invention uses cassava starch (TS) as a raw material and pullulanase as a debranching enzyme. Pullulanase has substrate specificity for hydrolysis and can hydrolyze α-1,6 glycosidic bonds of pullulan (a polysaccharide formed by maltotriose through α-1,6 glycosidic bonds formed into a linear structure by microorganisms). Cassava starch generally contains 21.4% of straight-chain starch and 78.6% of amylopectin. After the amylopectin solution is gelatinized in a boiling water bath, water molecules enter the starch crystallization region, most of the hydrogen bonds are disconnected, and the double helix structure is opened. At this time, a debranching enzyme is added to disconnect most of the α-1,6 glycosidic bonds of the amylopectin to form a large number of short straight chains. After debranching treatment, the amylopectin with high straight chain content undergoes molecular rearrangement under low temperature conditions to form a new crystal structure. At this time, part of the α-1,6 glycosidic bonds in the starch are converted into 1-2, 1-3 or 1-4 α or β glycosidic bonds. Since these bonds cannot or are difficult to be degraded by α-amylase or saccharifying enzyme, the purpose of slow digestion can be achieved, and it can be used to control excessive blood sugar fluctuations.

[0030] In the preparation method of the present invention, the thermodynamic properties of cassava starch undergo certain changes after debranching-alcohol precipitation-recrystallization, wherein the three preparation conditions of enzyme addition, ethanol aqueous solution concentration and recrystallization temperature all have certain effects on the thermodynamic properties; when other conditions are the same, the enzyme addition has a greater effect on the overall thermodynamic properties of TRD, while the ethanol aqueous solution concentration and recrystallization temperature only have a greater effect on the TRD peak temperature. In addition, when the enzyme addition is the same, the change in the ethanol aqueous solution concentration when the recrystallization temperature is 4°C has a greater effect on ΔH; or when the ethanol aqueous solution concentration is 55%, the recrystallization temperature also has a significant effect on ΔH.

[0031] The morphology and structure of the cassava starch resistant dextrin (TRD) prepared by the preparation method of the present invention are greatly different from that of the original cassava starch (TS). TS is smooth spherical particles, while TRD forms fragmented particles of various shapes and sizes, and the surface is relatively rough and uneven. After different degrees of enzymatic hydrolysis and recrystallization at different temperatures, the relative crystallinity of TRD is generally lower than that of TS. At the same time, the crystal structure of TS has undergone a major change. After becoming TRD, it changes from the original A-type crystal form to B-type crystal form or B+V-type crystal form. Compared with TS, TRD has a lower content of fast-digestible starch and a significantly higher content of resistant starch. At present, the resistant component of the cassava starch resistant dextrin prepared by the preparation method of the present invention can basically reach more than 60%.

[0032] The invention also provides a cassava starch resistant dextrin, which is prepared by the above-mentioned preparation method.

[0033] The present invention also provides the preparation method or the use of the cassava starch resistant dextrin in the preparation of low GI food.

[0034] The technical solution provided by the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0035] In the following embodiments, unless otherwise specified, all are conventional methods.

[0036] In the following embodiments, the materials, reagents, etc. used, unless otherwise specified, can be obtained from commercial channels.

[0037] The tapioca starch in the following embodiments was purchased from Dongguan Dongyue Glucose Factory Co., Ltd.; pullulanase and amyloglucosidase were purchased from Shanghai Macklin Biochemical Co., Ltd.; GOPOD reagent (glucose oxidase - peroxidase - buffer mixture) was purchased from Megazyme Company, Ireland.

[0038] Example 1

[0039] A preparation method of tapioca starch resistant dextrin comprises the following steps:

[0040] Weigh 10 g of tapioca starch (TS), add sodium acetate buffer solution containing 0.02% (volume percentage) sodium azide (the concentration of the sodium acetate buffer solution is 0.01 M and pH is 5.2) until the concentration of tapioca starch is 0.2 g / mL, heat and stir under boiling water, gelatinize for 30 min to obtain a gelatinized solution; cool down to 37 °C, add pullulanase to the gelatinized solution according to the amount of 1600 U of pullulanase added per g of tapioca starch, and continuously stir magnetically in a water bath at 58 °C for 24 h for debranching enzymolysis. Put the enzymolyzed sample into an autoclave and carry out autoclaving at 131 °C for 30 min, then centrifuge at 10000 g for 15 min. In a 50 °C warm water bath, add the supernatant to an ethanol aqueous solution with a volume fraction of 50% at a ratio of 1:4 (v / v), gently stir at 50 °C for 10 min, centrifuge at 10000 g for 15 min, collect the precipitate, wash it twice with absolute ethanol, and then place it in a convection oven at 50 °C to dry until the water content is below 10%.

[0041] Disperse the dried substance in deionized water at a mass - volume ratio of 10%, carry out autoclaving at 131 °C for 30 min, then recrystallize at 50 °C for 2 days without any stirring or shaking. Centrifuge at 10000 g for 15 min to collect the crystals, wash them twice with distilled water, pour them into a flat plate, and freeze - dry at - 80 °C for 2 days to obtain tapioca starch resistant dextrin (TRD).

[0042] Example 2

[0043] A preparation method of tapioca starch resistant dextrin comprises the following steps:

[0044] Weigh 10 g of tapioca starch (TS), add sodium acetate buffer solution containing 0.02% (volume percentage) sodium azide (the concentration of the sodium acetate buffer solution is 0.01 M and pH is 5.2) until the concentration of tapioca starch reaches 0.2 g / mL. Heat and stir under boiling water, gelatinize for 28 min to obtain a gelatinized solution. Cool down to 37 °C, add pullulanase to the gelatinized solution according to the amount of 1500 U pullulanase per g of tapioca starch, and continuously stir magnetically in a 55 °C water bath for 26 h for debranching enzymolysis. Put the enzymolyzed sample into an autoclave and perform autoclaving at 131 °C for 30 min, then centrifuge at 10000 g for 15 min. In a 48 °C warm water bath, add the supernatant to an ethanol aqueous solution with a volume fraction of 45% at a ratio of 1:3 (v / v), gently stir at 48 °C for 12 min, centrifuge at 10000 g for 15 min, collect the precipitate, wash it twice with absolute ethanol, and then place it in a convection oven at 50 °C to dry until the moisture content is below 10%.

[0045] Disperse the dried substance in deionized water at a mass-to-volume ratio of 10%, perform autoclaving at 131 °C for 30 min, and then recrystallize at 45 °C for 2 days without any stirring or shaking. Centrifuge at 10000 g for 15 min to collect the crystals, wash them twice with distilled water, pour them into a plate, and freeze-dry at -80 °C for 2 days to obtain tapioca starch resistant dextrin (TRD).

[0046] Example 3

[0047] A preparation method of tapioca starch resistant dextrin, which consists of the following steps:

[0048] Weigh 10 g of tapioca starch (TS), add sodium acetate buffer solution containing 0.02% (volume percentage) sodium azide (the concentration of the sodium acetate buffer solution is 0.01 M and pH is 5.2) until the concentration of tapioca starch reaches 0.2 g / mL. Heat and stir under boiling water, gelatinize for 32 min to obtain a gelatinized solution. Cool down to 37 °C, add pullulanase to the gelatinized solution according to the amount of 1800 U pullulanase per g of tapioca starch, and continuously stir magnetically in a 60 °C water bath for 22 h for debranching enzymolysis. Put the enzymolyzed sample into an autoclave and perform autoclaving at 131 °C for 30 min, then centrifuge at 10000 g for 15 min. In a 52 °C warm water bath, add the supernatant to an ethanol aqueous solution with a volume fraction of 55% at a ratio of 1:5 (v / v), gently stir at 52 °C for 8 min, centrifuge at 10000 g for 15 min, collect the precipitate, wash it twice with absolute ethanol, and then place it in a convection oven at 50 °C to dry until the moisture content is below 10%.

[0049] The dried substance was dispersed in deionized water at a mass-to-volume ratio of 10%, autoclaved at 131 °C for 30 min, then recrystallized at 55 °C for 2 days without any stirring or shaking. The crystals were collected by centrifugation at 10000 g for 15 min, washed twice with distilled water, poured into a plate, and freeze-dried at -80 °C for 2 days to obtain tapioca starch resistant dextrin (TRD).

[0050] Example 4

[0051] The differences from Example 1 were that the enzyme addition amount, ethanol solution concentration, and recrystallization temperature were as shown in Table 1 respectively (TRD-3 in Table 1 represents Example 1), and the rest were the same as in Example 1. The tapioca starch resistant dextrins obtained under different preparation conditions were denoted as TRD-1, TRD-2, TRD-4, and TRD-5 respectively. Tapioca starch (TS) was used as the control group for the following analysis:

[0052] Table 1 Tapioca starch resistant dextrin obtained under different preparation conditions

[0053]

[0054] (1) Microscopic infrared spectroscopy analysis:

[0055] It was measured using a microscopic infrared spectrometer. The Fourier transform infrared spectrometer can characterize the relevant information of the chemical bonds and functional groups of TRD. Specifically, a small amount of resistant dextrin and tapioca starch samples (TS) from different groups were placed flat on a microscopic slide and then put under an infrared microscope. Infrared spectrum scanning was carried out in the range of 4000 - 600 cm -1 The best aperture was adjusted, the appropriate sample characteristics were found, and the spectral diagram was selected.

[0056] The infrared spectra of TS and TRD prepared under different conditions are as Figure 1 shown. As can be seen from Figure 1 , the absorption peak at 3100 cm -1 - 3600 cm -1 is mainly the vibration absorption peak of the hydroxyl group in the a-glucan molecule, and the absorption peak at 1600 cm -1 - 1700 cm -1 is the absorption peak of the tightly bound water in the starch. The vibration absorption peak of the -CH- group is around 2921 cm -1 , and a blue shift occurs for TRD compared to TS. The absorption peak with a relatively large intensity appears around 1640 cm -1 due to the vibration of the C=O group, and the peak intensity of TRD here is generally increased compared to TS, indicating an increase in the number of C=O groups in the TRD structure. The absorption peak around 1070 cm -1 may be the C-O-C stretching vibration in the structure of amylose or amylopectin. At the wavenumber of 1000 - 800 cm-1 The absorption peak at -1 is representative of the α- and β-glycosidic bonds unique to starch and resistant dextrin. Both TRD and TS exhibit stretching vibrations of a certain intensity. The absorption peak of TRD at around 2120.94 - 2100 cm

[0057] (2) Scanning electron microscopy analysis

[0058] The SEM morphological characteristics of TS and TRD prepared under different conditions are shown respectively as Figure 2 follows. As Figure 2 can be seen, TS presents as relatively smooth spherical or ellipsoidal particles, and the spherical (ellipsoidal) particle agglomeration phenomenon is obvious, with relatively uniform dispersion. There are microporous structures on the particle surface, showing the morphological characteristics of A-type starch. After the gelatinization - debranching - alcohol precipitation - recrystallization treatment of TS, the morphological structure has changed greatly. TRD-1 forms irregular fragmented shapes, with a relatively smooth surface, and some fragmented particles are agglomerated, showing relatively uneven dispersion; TRD-2 is in the shape of irregular rocks and the particles are relatively dispersed; TRD-3 is in the form of dispersed granular particles with a rough surface; TRD-4 is in irregular shapes, and some spherical particle surfaces are attached with some laminated fragments, showing some undulations, and at the same time, a small part is in the form of smooth lamellar; TRD-5 also forms irregular granular particles of different sizes, and the surface of the large particles becomes uneven due to the adsorption of irregular small particles. This is because the granular structure of cassava starch is destroyed after gelatinization, and amylose dissolves and forms amylose crystals during the aging process, which presents as an irregular fragmented structure under the scanning electron microscope micrograph.

[0059] (3) Use a differential scanning calorimeter (DSC) to conduct thermal analysis on the samples to study their crystallization properties. Accurately weigh 3 mg ± 0.0003 g of resistant dextrin of different groups of cassava starch into an aluminum crucible using a ten-thousandth balance, add 7 μL of deionized water to prepare a starch milk, seal it with a press cover and transfer it to the instrument and let it stand for 24 h. The scanning program is: heat to 200 °C at a rate of 10 °C / min, with a carrier gas nitrogen flow rate of 20 mL / min, and use an empty crucible as a reference for each experiment. Record the thermal change signals during the heating process. Record the changes in T o (initial temperature), T p (peak temperature), T c (end temperature) and enthalpy value (ΔH). The results are shown in Table 2.

[0060] Table 2 Thermodynamic properties and significance analysis of resistant dextrin of cassava starch and cassava starch

[0061]

[0062] Note: Different letters in the same column indicate significant differences between data (P < 0.05).

[0063] It can be seen from the table that there are obvious differences in the thermodynamic properties of the whole TRD and TS. The endothermic peak appears at 86.89 °C - 98.53 °C, and ΔH is 9.85 J / g - 14.32 J / g. Compared with TS, the gelatinization temperature of the whole TRD increases, the stability increases, and the enthalpy value decreases. There are significant differences in T o , T p , T c and ΔH of TRD-1 and TRD-3. Thus, it can be known that when other conditions are the same, the addition amount of enzyme has a greater impact on the thermodynamic properties of the whole TRD. By comparing the two groups of samples of TRD-2, TRD-4 and TRD-3, TRD-5, there is no obvious difference in their T o , there is a significant difference in T p , and although there is a difference in T c , it is not obvious. Thus, it can be known that when the addition amount of enzyme and the concentration of ethanol solution are the same, the recrystallization temperature has little effect on T o , has little effect on T c , but has an obvious effect on T p . There is a significant difference in ΔH between TRD-2 and TRD-4, but there is no obvious difference in ΔH between TRD-3 and TRD-5. It can be known that when the concentration of ethanol solution is 55%, the recrystallization temperature has a greater impact on ΔH. By comparing the two groups of samples of TRD-2, TRD-5 and TRD-3, TRD-4, it can be known that there is also no obvious difference in their T o , there is a significant difference in T p , and there is also a small difference in T c . Thus, it can be known that when the addition amount of enzyme and the recrystallization temperature are the same, the influence of the concentration of ethanol solution on T o , T c and T p is similar to that of the recrystallization temperature. There is a significant difference in ΔH between TRD-2 and TRD-5, but there is no obvious difference in ΔH between TRD-3 and TRD-4. It can be known that when the recrystallization temperature is 4 °C, the concentration of ethanol solution has a greater impact on ΔH.

[0064] (4) X-ray diffraction

[0065] An X-ray diffractometer of the D8-ADVANCE type from BRUKER-AXS was used; the diffraction condition was a copper target; it worked under the conditions of 40 kV and 30 mA, the scanning region was 5° to 35° (2θ), the radiation line was CuKa; the scanning speed was 2° / min, and the step interval was 0.02. The crystallization region and the total area interval were respectively integrated and calculated through Jade software; the obtained ratio was the relative crystallinity (RC); as shown in the following formula.

[0066] RC(%) = Ac / (Ac + Aa) × 100

[0067] Where, Ac - the partial area of the crystalline region; Aa - the partial area of the amorphous region.

[0068] The X-ray diffraction patterns of TS and TRD prepared under different process conditions are as Figure 3 shown, and the corresponding crystal forms and relative crystallinity (RC) are shown in Table 3. According to different plant sources, starch can be divided into four types: A, B, C, and V. Type A starch only contains type A crystals, and has obvious single peaks at 15° and 23°, and connected double peaks at 17° and 18°. Type B starch only contains type B crystals. Type B crystals have an obvious characteristic peak at 5.6°, and weak diffraction peaks at 15°, 20°, 22°, and 24°; the C-type crystals contained in type C starch can be further divided into C A type and C B type, and have characteristic peaks at 5.6°, 15°, 17°, 19°, 23°, and 26°. The characteristic peaks of type V starch are at 7°, 13°, and 19.9°.

[0069] It can be seen from Figure 3 that: TS has obvious peaks at both 15° and 23°, and connected double peaks at 17° and 18°, so the crystal structure of TS is a typical type A crystal. Compared with TS, the crystal structure and relative crystallinity of TRD have changed greatly, and the relative crystallinity of TRD samples under different preparation conditions varies significantly. TRD as a whole shows an obvious diffraction peak at 17°, while TRD-2, TRD-4, and TRD-5 have obvious connected double peaks at 22° and 24°, and the peaks of TRD-1 and TRD-3 are relatively weak. TRD-1, TRD-3, and TRD-4 are more in line with type B crystals. While TRD-2 and TRD-5 have weak diffraction peaks at 15° and 19.9°, and their crystal form is B + V type. It can be seen from Table 3 that after starch is debranched and recrystallized, the relative crystallinity generally decreases compared with the original starch. TRD-2 may have a relatively high degree of crystallinity of 25.79% because of the relatively large number of double helix structures formed by the recrystallization of amylose.

[0070] Table 3 Crystal forms and relative crystallinity of resistant dextrin and native starch

[0071] Crystal type Relative crystallinity TS A 22.05％ TRD-1 B 17.59％ TRD-2 B+V 25.79％ TRD-3 B 13.30％ TRD-4 B 20.29％ TRD-5 B+V 18.85％

[0072] (5) Determination of in vitro digestion characteristics

[0073] 5.1 Preparation of enzyme digestion solution

[0074] Accurately weigh 3.15 mL of amyloglucosidase, add 3.6 mL of deionized water and mix well. Accurately weigh 3.0 g of porcine pancreatin into four 50 mL centrifuge tubes respectively, add 20 mL of deionized water to each, stir magnetically for 10 min. Place in a centrifuge and centrifuge at 2600×g for 10 min. Take 13.5 mL of the supernatant (a total of 54 mL) respectively, add 6 mL of the diluted amyloglucosidase solution and mix, then add 4 mL of deionized water.

[0075] 5.2 Preparation of buffer solution

[0076] Dissolve 13.6 g of CH3COONa·2H2O in 250 mL of saturated sodium benzoate, add deionized water to make up to 1 L. Adjust the pH to 5.2 with 0.1 mol / L acetic acid and add 4 mL of 1 M CaCl2 to each liter of buffer solution.

[0077] 5.3 Sample preparation and content determination

[0078] Accurately weigh 0.6 g of five kinds of cassava starch resistant dextrin and their cassava starch samples into 50 mL centrifuge tubes respectively, add 20 mL of sodium acetate buffer solution (pH 5.2, 0.1 mol / L), vortex thoroughly and mix evenly, place in a boiling water bath for 30 min, and keep shaking and mixing during the water bath process. Then cool and place in a 37℃ water bath for 30 min, stir magnetically; add 5 mL of the mixed enzyme digestion solution of porcine pancreatin and amyloglucosidase to the centrifuge tubes containing the samples respectively, shake and mix well, take out 0.25 mL of the enzyme digestion solution from each centrifuge tube at intervals of 1 min, and inactivate the enzyme in 10 mL of 66% ethanol at 20 min and 120 min respectively, then vortex and mix well. Centrifuge the enzyme digestion solution at 3500 rpm for 10 min, and determine the glucose content by using the Irish Megazyme D-glucose detection kit (GOPOD) method.

[0079] 5.4 Determination of glucose content

[0080] Prepare the GOPOD solution according to the method of Megazyme D-GLUCOSE ASSAY PROCEDURE. Transfer 3.0 mL of the GOPOD solution into 5 mL centrifuge tubes respectively. Add 0.1 mL of reagent blank, sample and glucose solution standard solution respectively, and vortex to mix evenly. Place it in a 50 °C water bath for color reaction for 20 min (protected from light), and measure its absorbance at 510 nm.

[0081] Calculate the glucose content in the corresponding sample through the following formula:

[0082]

[0083] A t = Absorbance of the test solution; V t = Total volume of the test solution; C = Concentration of standard glucose (mg / mL); A s = Absorbance of standard glucose; W t = Weight of the sample; D = Dilution factor.

[0084] The contents of rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS) are calculated according to the following formula:

[0085] RDS% = (G20 - FG) × 0.9

[0086] SDS% = (G120 - G20) × 0.9

[0087] RS% = [TS - (RDS + SDS)] = [TS - (G120 × 0.9)]

[0088] G20 = Glucose content (mg) in the enzymatic hydrolysate of starch hydrolyzed for 20 min; FG = Initial glucose content; G120 = Glucose content (mg) in the enzymatic hydrolysate of starch hydrolyzed for 120 min; TS = Total starch content (mg) of the sample.

[0089] The digestibility determination results of TS (native starch) and TRD (resistant dextrin) prepared under different process conditions are as Figure 4 shown. From Figure 4It can be seen that the content of rapidly digestible starch in the native starch is as high as 82.62%, and the content of resistant starch is only 2.24%. In contrast, the content of resistant starch in resistant dextrin is above 55%, which is significantly higher than that of native starch. Among the prepared resistant dextrins, the anti-digestibility of TRD-1 is relatively low, and its rapidly digestible starch content is as high as 41.55%, which is significantly higher than that of other resistant dextrins. Moreover, its resistant starch content is 55.28%, which is lower than that of other prepared samples. By comparing the two groups of samples of TRD-3 and TRD-1, the resistance of TRD-3 is higher than that of TRD-1. Thus, it can be known that when the concentration of ethanol solution and the recrystallization temperature are the same, the higher the enzyme addition amount, the higher the resistant starch content of the sample. By comparing the two groups of samples of TRD-2 and TRD-4, and TRD-3 and TRD-5, it can be known that when the ethanol solution of the same concentration is used and the enzyme addition amount is the same, the resistant starch content of the sample crystallized at 50 °C is higher than that crystallized at 4 °C. By comparing the resistant starch content of the two groups of resistant dextrins of TRD-2 and TRD-5, and TRD-3 and TRD-4, it can be known that when the crystallization temperature and the enzyme addition amount are the same, the content of resistant components in the sample obtained by alcohol precipitation with 50% (v / v) ethanol aqueous solution is higher.

[0090] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of cassava starch resistant dextrin, characterized in that, It includes the following steps: gelatinize tapioca starch to obtain a gelatinized solution; mix the gelatinized solution with pullulanase for debranching enzymolysis, take the supernatant and mix it with an ethanol aqueous solution, take the precipitate, wash it with absolute ethanol, then mix it with water, and recrystallize at 45°C to 55°C, collect the crystals to obtain tapioca starch resistant dextrin; the volume fraction of the ethanol aqueous solution is 45% to 55%.

2. The preparation method according to claim 1, characterized in that, Add 1500U to 1700U of pullulanase per g of tapioca starch.

3. The preparation method according to claim 1, characterized in that, The temperature of the debranching enzymolysis is 55°C to 60°C, and the time of the debranching enzymolysis is 22h to 26h.

4. The preparation method according to claim 1, wherein, The volume ratio of the supernatant to the ethanol aqueous solution is 1:3 to 5.

5. The preparation method according to claim 1, characterized in that, The time of the recrystallization is 46h to 50h.

6. The preparation method according to claim 1, wherein The gelatinization includes the following steps: mix tapioca starch with sodium acetate buffer solution until the concentration of tapioca starch is 0.2g / mL, and heat it in boiling water for 28min to 32min; the sodium acetate buffer solution contains 0.02% sodium azide.

7. The preparation method according to claim 6, characterized in that, The concentration of the sodium acetate buffer solution is 0.01M, and the pH of the sodium acetate buffer solution is 5.

2.

8. The preparation method according to claim 1, characterized in that, The temperature for mixing the supernatant with the ethanol aqueous solution is 48°C to 52°C.

9. A cassava starch resistant dextrin, characterized in that, The tapioca starch resistant dextrin is prepared by the preparation method described in any one of claims 1 to 8.

10. The application of the preparation method described in any one of claims 1 to 8 or the tapioca starch resistant dextrin described in claim 9 in the preparation of low-GI foods.

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