Preparation method and application of high-resistance starch RS3 mashed sweet potatoes

Abstract

The invention discloses a preparation method and application of high-resistance starch RS3 mashed sweet potatoes, and belongs to the technical field of resistant starch. The preparation method comprises the following steps: mixing mashed sweet potatoes with water to prepare a suspension, and carrying out autoclaving cooling treatment, pullulanase debranching treatment, enzyme deactivation and cooling on the suspension to prepare the high-resistance starch RS3 mashed sweet potatoes. According to the preparation method and application of the mashed sweet potatoes containing the high-resistance starch RS3, the content of the resistant starch can be remarkably increased and the thermal stability can be remarkably improved without multiple times of pressure heating and enzymolysis after pressure heating gelatinization under the appropriate enzymolysis condition, the safety is high, and the preparation cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of resistant starch, and in particular to a high-resistant starch RS 3 A preparation method and application of sweet potato puree. Background Art

[0002] Carbohydrates are the main source of energy in the human diet, mainly from starch in plant foods. Starch can be divided into rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS) according to its digestibility.

[0003] Rapidly digestible starch is the part of starch that causes a rapid increase in postprandial blood sugar levels after ingestion and is related to the glycemic index (GI). Slowly digestible starch is the part of starch that can be completely digested in the small intestine, and resistant starch is the part of starch that cannot be digested in the small intestine but can be fermented by microorganisms in the large intestine.

[0004] Among them, RS 3 Resistant starch has the characteristics of high thermal stability, low water holding capacity, white color, no odor, etc. It helps regulate intestinal health and lower the glycemic index. 3 Ingredients are a viable way to improve human health. Sweet potatoes are rich in RS 3 Ingredients: Most of the existing sweet potato products are processed by extracting starch and processing it. The production process is simple, but there are many by-products, high energy consumption, and a large amount of nutrient loss. There are few sweet potato products with complete nutrition, which makes it difficult to meet the health needs of consumers.

[0005] The preparation process of sweet potato puree is simple, involving washing, peeling, steaming and other steps, which effectively avoids the drying process, thereby retaining its nutritional value and having low energy consumption. It can be sold independently or used to enhance the flavor and nutritional value of other foods. However, the variety of sweet potato puree products is relatively limited, and the technology is backward, the quality is unstable, and the market share is not high, which restricts the healthy development of the entire industry.

[0006] As the pace of life accelerates, more and more people tend to eat pre-cooked sweet potato foods. Such foods are preserved at low temperatures and only need to be heated for a few minutes before consumption. However, the limitations of this cooking method in terms of nutrition and health cannot be ignored. Due to the large amount of starch gelatinization, cooked sweet potatoes are quickly digested and subsequently induce higher glucose production. Modification treatment has a positive effect on the glycemic index of sweet potatoes.

[0007] A resistant starch RS 3The preparation method (application number: 201310712644.9) uses corn, wheat, rice, sweet potato and potato starch as raw materials, prepares starch milk, adds acid α-amylase for autoclaving, adds pullulanase for debranching treatment after cooling, separates into heavy phase and light phase after centrifugation, crystallizes and washes sugar, and finally dries. Although the content of resistant starch RS3 is significantly increased, the operation is cumbersome and the process is complicated.

[0008] A preparation method and application of kudzu root resistant starch (application number: 202110490643.9), wherein kudzu root starch milk is subjected to pregelatinization, heat-pressing and debranching enzymatic hydrolysis in sequence, and then dried to obtain kudzu root resistant starch. Although this invention eliminates the steps of repeated enzymatic hydrolysis, multiple drying treatments are still required.

[0009] Preparation of high-resistant starch (RS) by autoclave treatment and enzymatic debranching 3 ) content and its preparation method (application number: 201510441229.3), the starch suspension is subjected to hydraulic heat treatment and then cooled, the pH is adjusted, the starch is subjected to enzymatic debranching treatment or aging treatment and then the pH is adjusted for debranching treatment, the sample is inactivated, aged, dried, ground and sieved to obtain a resistant starch product. This invention also eliminates the steps of repeated enzymatic hydrolysis, but still requires multiple drying treatments, and the preparation process of the resistant starch product is complicated.

[0010] At present, in the existing research, there is no modification of cooked sweet potato whole paste starch to prepare RS 3 Therefore, the development of high-content and high-efficiency resistant starch is of great significance to improving public health. Summary of the invention

[0011] The purpose of the present invention is to provide a high-resistant starch RS 3 The preparation method and application of sweet potato puree not only provide new ideas for the preparation of resistant starch raw materials, but also provide a theoretical basis for the research on modified cooked sweet potato starch, so as to further extend the sweet potato industry chain, which is of great significance for the development of healthy potato puree food.

[0012] To achieve the above object, the present invention provides a high-resistant starch RS 3 The method for preparing sweet potato puree comprises: mixing sweet potato puree with water to prepare a suspension, subjecting the suspension to autoclave cooling, pullulanase debranching, enzyme inactivation, and cooling to prepare high-resistant starch RS 3 Mashed sweet potatoes.

[0013] Preferably, the preparation of the sweet potato mash comprises: washing, peeling and cutting the sweet potatoes into 10-20 mm sweet potato slices, soaking the sweet potato slices in 0.1% citric acid for 10 minutes to obtain original sweet potatoes; cooking the original sweet potatoes, naturally cooling them to room temperature and then beating them into sweet potato mash.

[0014] Preferably, the sweet potato mash content in the suspension is 20%-30%.

[0015] Preferably, the conditions of the autoclave treatment are: 25-35 min in a sterilizer at 115°C-126°C, naturally cooling to room temperature, and reversing in a refrigerator at 4°C for 20h-30h.

[0016] Preferably, the enzymatic debranching treatment conditions are: pH 4.5-5, temperature 55° C.-60° C., enzymatic hydrolysis 6-10 h, and pullulanase activity 50-100 ASPU / g.

[0017] Preferably, the enzyme inactivation and cooling conditions are: 95-100°C, 10-15 min enzyme inactivation, natural cooling to room temperature after enzyme inactivation, and regeneration in a 4°C refrigerator for 20h-30h.

[0018] A high-resistant starch RS prepared by the above-mentioned preparation method 3 Mashed sweet potatoes.

[0019] A high resistant starch RS as described above 3 Use of sweet potato puree in the preparation of foods with a low glycemic index.

[0020] Therefore, the present invention is a high-resistant starch RS 3 The preparation method and application of sweet potato puree have the following beneficial effects: (1) The pressure heat-enzyme hydrolysis (PE) treatment can significantly change the gelatinization and retrogradation properties of starch in whole sweet potato puree. After the pressure heat treatment, the sweet potato puree starch promotes the rearrangement and crystallization of the starch molecular chains, and forms a stable B-type crystal structure after cooling. Under high temperature, high pressure and cooling, the starch molecules are bound to each other through hydrogen bonds, forming obvious sunken holes and honeycomb structures. After debranching, pullulanase can hydrolyze the α-1,6 glycosidic bonds in the starch molecules, release straight chain fragments, and form highly resistant double helices and V-shaped complexes through hydrogen bonding. Under the synergistic effect of the two, the content of amylose is significantly increased, providing a sufficient structural basis for the production of resistant starch, making the content of resistant starch much higher than that of single treatment and other treatment combinations. (2) The synergistic effect of whole sweet potato puree ingredients makes RS 3 The structural composition of the sweet potato puree after PE treatment changed. From the perspective of crystal structure, the relative crystallinity of the sweet potato puree after PE treatment increased, and B-type and V-type crystal diffraction peaks appeared, and the crystal structure became more compact, which helped to improve the resistance of starch to enzymatic hydrolysis. In terms of short-range order, the proportion of double helix structure of the sweet potato puree after PE treatment increased, and the molecular chain arrangement became more compact, further enhancing RS 3 Stability and resistance to digestion; (3) Compared with the existing methods, the preparation process provided by the present invention is further simplified, more efficient, and the instruments and equipment are common, which can be put into large-scale production; the reagents and materials are all food grade, and the preparation cost is low; (4) Compared with the existing methods, the preparation method provided by the present invention directly prepares potato mash, eliminating all drying treatments in starch modification, which not only shortens the time, but also significantly increases the content of resistant starch, and has a wide range of applications; (5) In vitro tests showed that the hydrolysis rate of mashed potato starch after pressure heat treatment and debranching was significantly lower than that of raw sweet potato and cooked sweet potato, and the GI was significantly reduced, making it a medium GI blood sugar food; therefore, it can be used for dietary management of patients with diabetes and obesity and can be directly used to produce staple foods with low GI values.

[0021] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The scanning electron micrograph of the whole sweet potato puree starch in the different starch samples of the present invention; Figure 2 The DSC curve diagram of whole sweet potato puree starch in different starch samples of the present invention; Figure 3 It is the hydrolysis curve diagram of whole sweet potato puree starch in different starch samples of the present invention; Figure 4 Scanning electron microscopy images of starch, mash and whole sweet potato mash starch prepared for different sweet potato varieties; Figure 5 XRD patterns and relative crystallinity of starch, mashed potato and whole sweet potato mashed starch prepared from different sweet potato varieties; Figure 6 In vitro hydrolysis kinetics of starch, mash and whole sweet potato mash prepared for different sweet potato varieties; Figure 7 Fourier transform infrared spectra of starch, mashed potato and whole sweet potato mashed starch prepared from different sweet potato varieties, where A is transmittance and B is absorbance; Figure 8 DSC spectra of starch, mash and whole sweet potato mash starch prepared from different sweet potato varieties; Fig. 9 RVA gelatinization curves of starch, mash and whole sweet potato mash prepared from different sweet potato varieties. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0025] Embodiment 1 The method of preparing mashed potatoes by the autoclave cooling method comprises the following steps: (1) Original sweet potato sample (NS): The washed sweet potatoes were peeled, cut into 10-20 mm thin slices, and soaked in 0.1% citric acid for 10 min to obtain original sweet potatoes (NS).

[0026] (2) Preparation of whole sweet potato puree (CT): After cooking NS, the NS was naturally cooled to room temperature, and the sweet potatoes were pureed using a blender to obtain whole sweet potato puree (CT).

[0027] (3) Preparation of resistant starch (P) by autoclave cooling method: Weigh 50 g of potato puree CT and mix it with water to form a potato puree suspension (25%, w / v, potato puree). Heat it in a 95°C water bath for 10 min, then heat it at 121°C for 30 min, cool it to room temperature, refrigerate it at 4°C for 24 h, take it out and cool it to room temperature to obtain potato puree (P) treated with autoclave cooling.

[0028] Embodiment 2 The pullulanase debranching method is used to prepare potato mash, comprising the following steps: Weigh 50g of potato puree CT, mix with water to make a potato puree suspension (25%, w / v, potato puree), heat in a 95℃ water bath for 10min, adjust the pH to 4.5 with 0.1% citric acid or 0.1% sodium bicarbonate, add pullulanase (100 ASPU / g), and shake at 60℃ for 6h. Quickly place the sample at 95℃ to inactivate the enzyme for 15min, and refrigerate at 4℃ for 24h. Pullulanase debranching treated potato puree (E) is obtained.

[0029] Embodiment 3 Preparation of RS containing high resistant starch by autoclave cooling-pullulanase debranching method 3 Sweet potato mash, comprising the following steps: Weigh 50g of mashed potato CT, vortex and oscillate the mashed potato suspension (25%, w / v, mashed potato) in a 95℃ water bath for 10min, then heat at 121℃ for 30min, cool to room temperature, refrigerate at 4℃ for 24h, and cool to room temperature. Use 0.1% citric acid or 0.1% sodium bicarbonate to adjust the pH to 4.5, then add pullulanase (100 ASPU / g), and oscillate at 60℃ for 6h. Quickly place the sample at 95℃ to inactivate the enzyme for 15min, and refrigerate at 4℃ for 24h. Obtain the mashed potato (PE) treated with autoclave cooling-pullulanase debranching.

[0030] Test Example 1 Scanning electron microscopy (SEM) determination The samples were placed in a -80°C ultra-low temperature freezer overnight and then freeze-dried. An appropriate amount of the samples were adhered to the conductive adhesive and sprayed with gold. The sample morphology was photographed using a scanning electron microscope at an accelerating voltage of 3 kV and magnified 100 times, 1000 times, and 5000 times, respectively.

[0031] The surface morphology of the sample is shown in Figure 2. Figure 1 shown.

[0032] Under 100x magnification, NS is mostly spherical, elliptical and polygonal, and some particles have concave surfaces. After cooking, the particle structure of CT is destroyed, showing irregular fragments with a rough surface. The particle structure of the modified samples is destroyed, arranged more closely, forming irregular blocks or superimposed clumps. These huge morphological changes may be due to debranching and degradation during high temperature and pressure, enzymatic hydrolysis and aging. The degradation of the amylose chain causes the starch structure to form a helical complex, which increases the density of the crystal structure and thus improves its resistance to enzyme digestion.

[0033] Under 1000 and 5000 times magnification, it can be clearly seen that the structure of P starch granules disappears after autoclave cooling, forming a continuous network with irregular shapes. There are multi-layered stripes on the surface of the granules, which may be due to the leaching of amylose in the starch, the loss of the crystalline area of ​​amylopectin during heating, and the re-binding of starch chains in the granules. E has a large number of pores on the surface of starch after pullulanase debranching, which may be due to the debranching of starch and the dissolution of some short-chain small molecules.

[0034] After PE is cooled by autoclave, the granular structure of starch may have been partially destroyed, and then after pullulanase debranching, the granules are further broken down into smaller fragments. Many loose and concentric layers can be seen on the outer surface of PE starch, which correspond to ordered and disordered sequences of substances, usually referred to as crystalline and non-crystalline regions. These concentric layers are attributed to the high temperature and high pressure and the debranching effect of pullulanase.

[0035] Test Example 2 In vitro digestion test The sample was placed in a -80°C ultra-low temperature freezer overnight and then freeze-dried. 500 mg of sweet potato puree was mixed with 5 mL of sodium acetate buffer (0.5 mol / L, pH 5.2) and vortexed at 3000 rpm for 2 min. The suspension was heated in a boiling water bath for 20 min, cooled to 37 ± 1°C, and 50 mg of pepsin was added to 10 mL of HCl (0.05 mol / L) in advance.

[0036] Add pepsin-hydrochloric acid solution to the sample centrifuge tube, mix well and place in a 37°C water bath with an oscillation rate of 180 r / min for 30 min. After pepsin hydrolysis, add 5 glass beads with a diameter of 6-8 mm and 5 mL of sodium acetate buffer (0.5 mol / L, pH 5.2).

[0037] After 30 minutes of vibration, 10 mL of enzyme solution containing pancreatin and glucoamylase was added. After enzymatic hydrolysis, 0.5 mL of enzymatic hydrolysis solution was taken from each tube, and 4 mL of 80% ethanol solution was added to terminate the reaction. The collection time nodes were 0, 2, 5, 10, 15, 20, 30, 45, 60, 90, 120, 150 and 180 minutes.

[0038] The glucose content in the supernatant was determined by DNS method. The total starch mass (TS) was determined by the sample after the enzymatic hydrolysis reaction.

[0039] Heat in boiling water for 30 minutes, quickly put in an ice water bath for 10 minutes, and then add 10mL of 7mol / L KOH solution. After standing at 4℃ for 30 minutes, take 0.5mL of sample and mix it with 5mL of 0.5mol / L acetic acid solution. Then add 50μL of amyloglucosidase, shake in a 70℃ water bath for 30 minutes, take 0.25mL of aliquoted sample and mix it with 4.75mL of anhydrous ethanol to stop the enzymatic reaction. After centrifugation at 10000×g for 5 minutes, collect the supernatant and determine the glucose content. The calculation formulas for RDS, SDS, and RS are as follows.

[0040] ; ; ; Among them, G 20 and G 120 It is the glucose release at 20min and 120min, TS is the total glucose content of starch, and the conversion coefficient is generally 0.9, which is calculated by the starch monomer molecular weight / glucose molecular weight (162 / 180=0.9).

[0041] The starch hydrolysis was determined using the following formula: ; Among them, SH is the current starch hydrolysis amount (%); TS is the initial amount of starch (g); G x is the amount of glucose produced (g).

[0042] The kinetic parameters in the simulated digestion process were calculated using the nonlinear fitting method of the first-order equation model: ; Among them, C tCorresponding to the percentage of hydrolyzed starch at time t, C ∞ is the equilibrium concentration of hydrolyzed starch in the simulated gastrointestinal digestion process, k is the kinetic constant, and t is the time.

[0043] The area under the hydrolysis curve (AUC) and predicted glycemic index (GI) were calculated according to the formula: ; Where t is time (min), t f is the final time (180 min), t 0 is the initial time (0min).

[0044] ; The hydrolysis index (HI) is obtained by dividing the area under the hydrolysis curve of the starch sample by the hydrolysis area of ​​white bread.

[0045] The resistant starch content in different sweet potato puree samples is shown in Table 1: Table 1 Resistant starch content in sweet potato puree samples with different treatments ; Note: Different letters in the same column indicate statistically significant differences ( P <0.05).

[0046] As shown in Table 1, the resistant starch content in the sweet potato puree treated with autoclave, pullulanase debranching, and autoclave-pullulanase debranching was significantly increased compared with the original sweet potato starch and cooked sweet potato.

[0047] After autoclaving and cooling, the RDS content decreased significantly, while the RS content increased significantly. Autoclave treatment can promote the rearrangement and crystallization of starch molecular chains, forming a more stable crystal structure after cooling. Under high temperature, high pressure and cooling, starch molecules are associated with each other through hydrogen bonds to form obvious sunken holes and honeycomb structures, and the content of amylose increases, thereby increasing the formation of resistant starch. After debranching, pullulanase can hydrolyze the α-1,6 glycosidic bonds in starch molecules, increase the content of amylose molecules, promote the formation of a double helix structure of amylose, and then form a highly resistant crystal structure.

[0048] The starch digestion kinetics were tested within 20-120 min. The starch hydrolysis curve of sweet potato mash sample was as follows: Figure 2 The digestion characteristics during in vitro gastrointestinal digestion are shown in Table 2: Table 2 Digestion characteristics of different sweet potato puree samples during in vitro gastrointestinal digestion ; Note: Different letters in the same column indicate statistically significant differences ( P<0.05).

[0049] Depend on Figure 2 It can be seen that the hydrolysis rate of NS, P and E was faster in the first 20 minutes of digestion, the hydrolysis degree slowly increased after 20 minutes, the hydrolysis rate decreased significantly, the starch hydrolysis was completely completed after 60 minutes, and the total hydrolysis rate remained stable.

[0050] On the other hand, the hydrolysis rate of PE before 20 minutes was significantly lower than that of other samples; the hydrolysis rate within 20-60 minutes was significantly higher than that of other samples, indicating that its SDS and RS content was high. The digestible hydrolysis rates of P, E and PE were significantly lower than those of NS, and the digestible hydrolysis rates of other samples were all above 80%. Among them, the digestible hydrolysis rate of PE was the lowest, indicating that it had the strongest resistance to digestion.

[0051] GI value is used to comprehensively evaluate the postprandial blood sugar level of starchy foods. As shown in Table 2, after autoclaving, pullulanase debranching and autoclaving-pululanase debranching combined treatment, the GI value of starch was significantly reduced, which was mainly due to the reduction in digestible starch content. PE is a medium GI blood sugar food. Therefore, the sweet potato puree prepared by PE has the characteristics of low digestible starch content, which is particularly suitable for making low glycemic index foods for diabetic patients and may be directly used to produce staple foods with low GI values.

[0052] Test Example 3 Differential Scanning Calorimetry (DSC) The sample was placed in a -80°C ultra-low temperature freezer overnight and then freeze-dried. The thermodynamic properties of the sample were determined using a differential scanning calorimeter. Weigh 3 mg of the sample into an aluminum crucible and add 6 µL of deionized water. After sealing, equilibrate at room temperature for 24 hours. Use a blank crucible as a control and heat the sample from 30°C to 200°C at a heating rate of 10°C / min. Calculate the initial (To), peak (Tp) and final (Tc) gelatinization temperatures and enthalpy change (ΔH) respectively. The DSC thermal properties of starch are as follows: Figure 3 As shown in Table 3: Table 3 Thermodynamic properties of different sweet potato mash samples ; Note: Different letters in the same column indicate statistically significant differences ( P <0.05).

[0053] like Figure 3 As shown in Table 3, autoclaving and enzymatic hydrolysis significantly increased the starch transition temperature (T o , T p and T c), indicating that thermal stability is improved, especially for PE. Compared with P and E, the gelatinization transition temperature of PE is further improved, indicating that the combined treatment has a synergistic effect. The pressure heat treatment can improve the stability of starch, and the pullulanase treatment further enhances the effect of this heat treatment. After the combined treatment, the starch transition temperature is increased. The gelatinization enthalpy of P is lower than that of NS and CT, while that of E and PE is significantly increased, indicating that the pullulanase-treated samples present significantly higher enthalpy values, indicating that the debranching of amylopectin is conducive to degradation.

[0054] Test Example 4 Select different varieties of fresh sweet potatoes to prepare sweet potato starch: wash and peel fresh sweet potatoes, crush them with a wall-breaking machine, soak them in a suitable amount of water for 12 hours, mix the sweet potato pulp with water and stir, filter after precipitation, repeat twice, and finally air-dry the wet starch. Hereinafter referred to as Xinxiang starch, Ji 25 starch, and Ji 26 starch.

[0055] The method of Example 1 was used to prepare whole sweet potato starch of different varieties of sweet potatoes, which are hereinafter referred to as Xinxiang potato puree, Ji 25 potato puree, and Ji 26 potato puree.

[0056] The method of Example 3 was used to prepare RS containing high resistant starch of different varieties of sweet potatoes 3 Sweet potato mash, PE-Xinxiang potato mash, PE-Ji 25 potato mash, PE-Ji 26 potato mash.

[0057] ①Determination of microstructure.

[0058] The sample was placed in an ultra-low temperature freezer (-80°C) overnight, freeze-dried and ground, passed through a 100-mesh sieve, and an appropriate amount of the sample was adhered to the conductive glue and sprayed with gold. The sample morphology was photographed using a Gemini field emission scanning electron microscope (SEM) at an accelerating voltage of 3.0 kV, and magnified 100 times, 1000 times, and 5000 times, respectively.

[0059] like Figure 4 As shown in the figure, at 1000 times, the sweet potato starch particles are mostly spherical, elliptical and irregular. After cooking, the particle size of the three kinds of mashed potatoes becomes larger, and the particles are gelatinized into flakes or irregular shapes. Cracks and holes appear on the surface, which may be caused by water absorption, expansion and rupture, and the linear and branched starch migrate and rearrange to form a smooth film. Small fragments (V-type complexes) are attached to the surface of the autoclave-enzymatic modified mashed potatoes, arranged in layered crystals, with holes, and PE-Xinxiang has the largest holes. PE-Ji 25 and PE-Ji 26 have rough surfaces with honeycomb or network structures, and PE-Ji 26 has more obvious changes. The combination of autoclave and enzymatic hydrolysis significantly affects the structure of starch granules, which is closely related to the physical and chemical properties.

[0060] ②Determination of crystal structure.

[0061] Spread the powder sample evenly on the sample plate, compact and flatten it with a glass slide. Then put the plate on the sample stage and test it in an X-ray diffractometer (XRD). Test conditions: Use a Cu-Ka radiation light source (wavelength 1.5406Å), set the voltage to 30kV, the current to 10mA, the scanning range to 5°-50° (2θ), and the scanning rate to 5° / min. Calculate the relative crystallinity (X) of the sample using MDI Jade 9.0 software, and the calculation formula is as follows: ; in, is the area of ​​the crystalline region, is the area of ​​the non-crystalline region.

[0062] The results are shown in Table 4 and Figure 5 As shown: Table 4 Crystal structure parameters of different samples ; Note: ND means not detected in the sample.

[0063] The results showed that the relative crystallinity of the three sweet potato varieties increased after autoclave-enzyme hydrolysis. The characteristic diffraction angles of the original starch were around 15°, 17°, 18° and 23°, which were CA-type crystals with a relative crystallinity of 23.51%-27.70%. After cooking, the CA-type crystal diffraction peaks of mashed potatoes disappeared, showing an amorphous structure, and the relative crystallinity decreased significantly, because the starch granules absorbed water and expanded, hydrogen bonds broke, and the crystal structure was destroyed. After autoclave-enzyme hydrolysis, mashed potatoes showed B-type crystal diffraction peaks at 17°, 22°, and 24°, and V-type crystal diffraction peaks at 14° and 20°, and the crystal structure changed. Among them, the characteristic diffraction angle of Ji 26 mashed potatoes changed the most, and the relative crystallinity reached 32.47%, which was significantly higher than the 12.70% of Ji 26 mashed potatoes. The relative crystallinity order is PE-Ji 26 mashed potatoes > PE-Xinxiang mashed potatoes > PE-Ji 25 mashed potatoes > Ji 26 starch > Xinxiang starch > Ji 25 starch > Ji 26 mashed potatoes > Xinxiang mashed potatoes > Ji 25 mashed potatoes. Autoclave-enzymatic hydrolysis can effectively change the crystallization characteristics of mashed potatoes and improve their digestibility.

[0064] ③Determination of in vitro digestibility and starch hydrolysis kinetics.

[0065] An in vitro digestion model was used. 500 mg of sweet potato puree sample was mixed with 5 mL of sodium acetate buffer (0.5 mol / L, pH 5.2) and vortexed at 3000 rpm for 2 min. The suspension was heated in a boiling water bath for 20 min, cooled to 37 ± 1 °C, and 50 mg of pepsin was added to 10 mL of HCl solution (0.05 mol / L) in advance. The pepsin-hydrochloric acid solution was added to the sample centrifuge tube, mixed and placed in a 37 °C water bath with an oscillation rate of 180 r / min for 30 min. After pepsin hydrolysis, 5 glass beads with a diameter of 6-8 mm and 5 mL of sodium acetate buffer (0.5 mol / L, pH 5.2) were added. After 30 min of shaking, 10 mL of enzyme solution containing pancreatin and glucoamylase was added.

[0066] After enzymatic hydrolysis, 0.5 mL of enzymatic hydrolyzate was taken from each tube, and 4 mL of ethanol solution (80%) was added to terminate the reaction. The collection time nodes were 0, 2, 5, 10, 15, 20, 30, 45, 60, 90, 120, 150 and 180 min. The glucose content in the supernatant was determined by DNS method.

[0067] The total starch mass (TS) was determined using samples after the enzymatic hydrolysis reaction. Heat in boiling water for 30 minutes, quickly place in an ice water bath for 10 minutes, and then add 10mL of 7mol / L KOH solution. After standing at 4°C for 30 minutes, take 0.5mL of sample and mix it with 5mL of 0.5mol / L acetic acid solution. Then add 50μL of amyloglucosidase, shake in a 70°C water bath for 30 minutes, take 0.25mL of sample and mix it with 4.75mL of anhydrous ethanol to stop the enzymatic hydrolysis reaction. After centrifugation at 10000×g for 5 minutes, collect the supernatant to determine the glucose content. The calculation formulas for RDS, SDS and RS are as follows: ; ; ; in, is the free glucose content in mashed potatoes (mg), and is the glucose release at 20min and 120min (mg), TS is the total glucose content in mashed potatoes (mg), and the conversion factor is 0.9, which is calculated by the starch monomer molecular weight / glucose molecular weight (162 / 180=0.9).

[0068] The calculation formula of starch hydrolysis rate (SH) is as follows: ; in, is the current amount of starch hydrolysis (%), TS is the initial amount of starch (g), and GX is the amount of glucose produced (g).

[0069] The kinetic parameters in the simulated digestion process were calculated using the nonlinear fitting method of the first-order equation model: ; in, Corresponding to the percentage of hydrolyzed starch at time t (%), is the equilibrium concentration of hydrolyzed starch in the simulated gastrointestinal digestion process (%), k is the kinetic constant (min -1 ), t is time (min).

[0070] The area under the hydrolysis curve (AUC) and predicted glycemic index (pGI) were calculated according to the following formula: ; Where t is time (min), is the final time (min), is the initial time (min).

[0071] ; The hydrolysis index (HI) is the ratio of the area under the hydrolysis curve of the starch sample to the hydrolysis area of ​​white bread.

[0072] The results are shown in Tables 5, 6 and Figure 6 As shown: Table 5 Digestion performance of different samples ; Note: Different letters in the same column indicate statistically significant differences ( P <0.05).

[0073] Table 6 Characteristic parameters of starch hydrolysis kinetic equations of different samples ; Note: Different letters in the same column indicate statistically significant differences ( P <0.05).

[0074] As shown in Table 5, the original starch RS content of Ji 26 was the highest (6.50%). After cooking, the RDS of the three mashed potatoes increased, while the SDS and RS decreased, because the starch granules were broken and the enzymes were easy to contact the starch molecules to promote hydrolysis. After modification, the RS content of Ji 26 was still the highest (33.49%), because its original RS and relative crystallinity were high. Autoclave-enzyme hydrolysis increased the SDS and RS contents, because high temperature, high pressure and enzyme hydrolysis caused the starch molecular chains to rearrange and recrystallize on cooling, which synergistically stabilized the structure of the mashed potatoes and increased the SDS and RS contents.

[0075] like Figure 6 As shown in Table 6, the three mashed potatoes reached the hydrolysis plateau in 20 minutes, while starch and heat-pressed enzymatic mashed potatoes required 30 minutes. ∞ The order is Ji 25 mashed potatoes > Xinxiang mashed potatoes > Ji 26 mashed potatoes > Ji 25 starch > Xinxiang starch > Ji 26 starch > PE-Ji 25 mashed potatoes > PE-Xinxiang mashed potatoes > PE-Ji 26 mashed potatoes, PE-Ji 26 mashed potatoes C ∞ The lowest (48.98%) was 35.7% lower than that of Ji 26 mashed potatoes. The k values ​​of the three starches and mashed potatoes were similar, because gelatinization made the starch easy to be enzymatically hydrolyzed, but the structure of the mashed potatoes did not change significantly. The k value of the autoclaved-enzymatic mashed potatoes was significantly reduced, because the reduction of water content and the enzymatic treatment reduced the enzymatic efficiency.

[0076] In summary, PE-Ji 26 mashed potatoes had the slowest enzymatic hydrolysis and the lowest final hydrolysis degree. The hydrolysis index (HI) of mashed potato samples was 87.48-91.22, and the corresponding predicted in vitro glycemic index (pGI) was 87.74-89.79. The HI and pGI of sweet potato mash increased significantly after cooking. This is because the starch granules absorbed water, expanded and ruptured during cooking, exposing the molecular chains, and gelatinization made the molecular chains disordered, which increased the accessibility of the enzyme and promoted the rapid hydrolysis of starch.

[0077] The HI and pGI of PE-Ji 26 potato puree in Table 6 are significantly lower than those of the other two varieties, which are 51.87 and 67.98 respectively, indicating that its saccharification degree is moderate under simulated human digestion conditions. It is a medium GI food that can avoid rapid increase in blood sugar and supply energy in time. It is an ideal choice for people who need to control blood sugar.

[0078] ④Determination of Fourier exchange infrared spectroscopy.

[0079] Prepare dried potassium bromide and sample in advance, mix them in a ratio of 100:1, put them into a vacuum compressor and press them into thin sheets. -1 Within 4cm -1 The spectra were detected with a Fourier transform infrared spectrometer (FT-IR) and baseline corrected, and the FT-IR spectra were deconvoluted using OMNIC software.

[0080] The results are shown in Table 7 and Figure 7 As shown: Table 7 Ratios of DO and DD of different samples ; Note: Different letters in the same column indicate statistically significant differences (P<0.05).

[0081] The results showed that the FT-IR spectra of starch, mashed potatoes and autoclaved-enzymatic mashed potatoes of the three sweet potato varieties were similar, the positions of characteristic absorption peaks remained basically unchanged, and no new groups and chemical bonds were generated. The reactions of Xinxiang and Ji 26 sweet potatoes were significantly stronger than those of Ji 25, which may be related to factors such as varieties and starch structure. The infrared spectra of Ji 25 and Ji 26 were highly similar, perhaps due to their close relationship and similar growth environment, but the reaction of Ji 26 mashed potatoes after autoclave-enzymatic hydrolysis was stronger, and the absorption peak intensity exceeded that of Ji 25 mashed potatoes. 3100-3400cm -1 The absorption peak at 1750cm moves to a higher wavelength, indicating that the amylose overflows and the hydrogen bonds between molecules weaken. -1 There was no change in the absorption intensity at the position, indicating no chain breakage. The ratio of the fingerprint area of ​​potato puree decreased after heat treatment, confirming the change of starch granules. The DO value and DD value of the heat-enzyme-hydrolyzed potato puree increased significantly, and the ratio of PE-Ji 26 potato puree was the highest, indicating that its structural change was the most significant.

[0082] ⑤Determination of thermodynamic properties The thermodynamic properties of the samples were determined by differential scanning calorimetry (DSC). 3 mg of the sample was weighed and placed in an aluminum crucible and 6 µL of deionized water was added. After sealing, the sample was equilibrated at room temperature for 24 h. A blank crucible was used as a control and the sample was heated from 30°C to 180°C at a heating rate of 10°C / min. The onset (To), peak (Tp) and end (Tc) gelatinization temperatures and gelatinization enthalpy (ΔH) were calculated using TA Universal Analysis software.

[0083] The results are shown in Table 8 and Figure 8 As shown: Table 8 DSC parameters of different samples ; Note: Different letters in the same column indicate statistically significant differences ( P <0.05).

[0084] The results showed that the DSC curves of the three sweet potato starches were similar, with endothermic peaks at 53.43-98.76℃ and ΔH of 9.06-12.77J / g. After cooking, the gelatinization temperature did not decrease significantly because the ratio of straight chain and branched starch remained basically unchanged, but ΔE decreased significantly because the starch granules were broken and the integrity was reduced. After autoclaving-enzymatic hydrolysis, the mash To, Tp, Tc and ΔH were significantly increased. The PE-Xinxiang mash had the highest Tp (140.61℃) and the PE-Ji 26 had the highest ΔH (15.54J / g) because the non-starch components in the mash formed a composite structure with the starch granules, which limited the expansion and gelatinization. The combined autoclaving and enzymatic hydrolysis can form a heat-resistant crystalline structure, which has the potential to produce heat-resistant resistant starch.

[0085] ⑥ Determination of RVA gelatinization characteristics The viscosity characteristics of the sample starch were measured by a rapid starch viscometer (RVA) and analyzed by the TCW supporting software. Weigh 3g of starch and add 25g of water. The temperature changes in the tank are as follows: keep at 50℃ for 1min, and increase the temperature to 95℃ at a rate of 15℃ / min. Keep at 95℃ for 2min and then decrease to 50℃ at a rate of 1℃ / min. The agitator starts with a speed of 960r / min for 10s and then maintains at 160r / min. The RVA gelatinization curve of the sample and the gelatinization characteristic parameters including peak viscosity, valley viscosity, final viscosity, disintegration value and recovery value are analyzed by the software provided by the equipment.

[0086] The results are shown in Table 9 and Fig. 9 As shown: Table 9 Gelatinization characteristic parameters of different samples ; Note: Different letters in the same column indicate statistically significant differences ( P <0.05).

[0087] The results showed that the RVA curve of natural sweet potato starch had a typical viscosity peak, which was almost a straight line after autoclave-enzymatic hydrolysis, and the viscosity response ability decreased significantly. Pullulanase debranching reduced the branched starch, shortened the molecular chain, and reduced the swelling and gelling ability. The increase of irregular network structure and crystalline area limited the swelling of particles and inhibited the viscosity change. Unlike the traditional wet method, all viscosity parameters of potato mash decreased after autoclave-enzymatic hydrolysis. Heat treatment caused mechanical and thermal damage to starch granules, accelerated water absorption expansion and rupture, increased the degree of molecular disorder, and reduced viscosity. The gelatinization time increased significantly after autoclave-enzymatic hydrolysis because the increase in crystallinity and double helix structure made the starch granules more stable and gelatinization took longer.

[0088] Therefore, the present invention is a high-resistant starch RS 3 The preparation method and application of sweet potato puree can significantly increase the content of resistant starch and significantly improve thermal stability under suitable enzymolysis conditions after autoclave gelatinization without multiple autoclaves and enzymolysis, and the reagents and materials are all food grade, with low preparation cost. Compared with the existing method, the preparation process provided by the present invention is further simplified, more efficient, and the instruments and equipment are common, which can be put into large-scale production. The preparation method provided by the present invention directly prepares sweet potato puree, omitting all drying treatments in starch modification, which not only shortens the time, but also significantly increases the content of resistant starch, and has a wide range of applications.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing high-resistant starch RS3 sweet potato puree, characterized in that: include: The sweet potato puree is mixed with water to prepare a suspension, and the suspension is subjected to autoclave cooling treatment, pullulanase debranching treatment, enzyme inactivation, and cooling to prepare high-resistant starch RS3 sweet potato puree.

2. The method for preparing the high-resistant starch RS3 sweet potato puree according to claim 1, characterized in that: The preparation of the sweet potato mash comprises: The sweet potatoes are washed, peeled, and cut into 10-20 mm sweet potato slices, and the sweet potato slices are soaked in 0.1% citric acid for 10 minutes to obtain raw sweet potatoes; the raw sweet potatoes are cooked, naturally cooled to room temperature, and then whipped into sweet potato puree.

3. The method for preparing the high-resistant starch RS3 sweet potato puree according to claim 1, characterized in that: The sweet potato mash content in the suspension is 20%-30%.

4. The method for preparing the high-resistant starch RS3 sweet potato puree according to claim 1, characterized in that: The conditions of the autoclave cooling treatment are: Place in a sterilizer at 115℃-126℃ for 25-35min, cool naturally to room temperature, and rehydrate in a refrigerator at 4℃ for 20h-30h.

5. The method for preparing the high-resistant starch RS3 sweet potato puree according to claim 1, characterized in that: The pullulanase debranching treatment conditions are: The pH is 4.5-5, the temperature is 55℃-60℃, the enzymatic hydrolysis is 6-10h, and the pullulanase activity is 50-100 ASPU / g.

6. The method for preparing the high-resistant starch RS3 sweet potato puree according to claim 1, characterized in that: The enzyme inactivation and cooling conditions are: Inactivate the enzyme at 95-100℃ for 10-15min, cool naturally to room temperature, and revive in a 4℃ refrigerator for 20h-30h.

7. A high-resistant starch RS3 sweet potato puree prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the high-resistant starch RS3 sweet potato puree as claimed in claim 7 in preparing food with a low glycemic index.

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