Mango seed resistant starch and preparation method thereof

Abstract

The invention discloses mango seed resistant starch and a preparation method thereof, and belongs to the technical field of food processing, and the preparation method comprises the following steps: mixing mango seed starch with water, performing high-temperature and high-pressure treatment, performing aging treatment, drying, crushing, and repeating the steps to obtain the mango seed resistant starch. The obtained mango seed resistant starch has good digestion resistance, in addition, the mango seed resistant starch has excellent structural stability, has remarkable potential in the food industry, is especially suitable for development of functional food and intestinal health regulation, and has great application prospects in preparation of low-GI food, weight-losing food and prebiotic food.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, and in particular relates to mango kernel resistant starch and a preparation method thereof. Background Art

[0002] As one of the most common polysaccharides in nature, starch is widely found in the seeds, rhizomes, fruits and other parts of plants, and plays an important role in the food industry, medicine, chemical industry and other fields. According to its digestion characteristics, starch can be divided into ordinary starch and resistant starch. Ordinary starch is easily broken down into glucose by α-amylase in the human body during digestion, causing blood sugar levels to rise rapidly. In contrast, resistant starch (RS) is a special type of starch that is not easily degraded by digestive enzymes in the gastrointestinal tract. It can reach the large intestine and be fermented by intestinal microorganisms to produce short-chain fatty acids, thereby providing the human body with a variety of health benefits, such as regulating blood sugar, promoting intestinal health, reducing the risk of obesity and preventing certain cancers.

[0003] Mango (Mangifera indica) is a tropical and subtropical fruit that is loved by consumers for its unique flavor and rich nutrients. In my country, the annual output of mango has been growing steadily and has become an important part of the fruit industry. However, large-scale mango production is also accompanied by the production of a large number of by-products such as mango pits. These by-products are often treated as waste without effective utilization, which not only wastes resources but also causes a certain degree of pollution to the environment. According to statistics, mango pits account for about 20% to 60% of the total weight of mangoes, of which the kernel content accounts for 45% to 75% of the total weight of mango pits, and the shell accounts for 25% to 55%. If the potential value of mango pits can be deeply explored and developed, it will help to efficiently utilize resources and alleviate environmental problems.

[0004] At present, most of the research at home and abroad is on mango pulp starch, while the research on mango kernel starch is relatively lacking, mainly focusing on its composition, physical and chemical properties and potential functional development. The raw material sources and raw material properties of mango pulp starch and mango kernel starch are different. Since the starch content of mango pulp is relatively low, the starch molecules in the pulp usually have a low molecular weight and a simpler structure. In addition, mango pulp starch is more hygroscopic, easy to dissolve when heated, and can be quickly converted into sugar. Due to the high water content, the thermal stability of pulp starch is poor, it is not resistant to high temperatures, and it is easy to be quickly converted during heating or digestion. The chemical structure of mango kernel starch is usually more complex, the starch molecular weight is larger, and the molecular chain is longer, so its digestion rate is slower. And the kernel starch has good thermal stability and hydrolysis resistance, especially at high temperatures, it can still maintain good physical properties. Therefore, it is impossible to directly refer to the research method of mango pulp starch to treat mango kernel starch in the same way. Early studies have shown that the content of easily digestible starch (RDS) and slowly digestible starch (SDS) in mango kernel starch is lower than that of corn starch, while its resistant starch (RS) content is significantly higher than that of corn starch. In addition, the glycemic index (GI) of mango kernel starch is significantly lower than that of corn starch. Indu Bharti et al. studied the effects of heat and humidity treatment on the morphology, gelatinization, structure and physicochemical properties of mango kernel starch of Indian cultivars and found that it has a low reverse degradation rate and a high amylose content, making it suitable for the preparation of environmentally friendly materials such as biodegradable films. Gurvendra Pal Singh et al. further studied the potential of mango kernel starch in the development of films based on starch and starch nanoparticles (SNPs). David Ramírez-Brewer et al. used mango kernel starch to prepare water-in-oil emulsions and found that it has significant advantages in rheological properties, microstructure and stability, which provides possibilities for the development of new formulas in the food field.

[0005] Although the composition, physicochemical properties and potential applications of mango kernel starch have been studied to some extent, there is still a lack of systematic research on the preparation, structural characteristics and health function development of mango kernel resistant starch. With the increasing demand for healthy functional ingredients in the food industry, resistant starch has gradually attracted widespread attention due to its multiple functions such as promoting intestinal health, regulating blood sugar and improving lipid metabolism. Mango kernel, as a common agricultural waste, is rich in starch and has the potential to be a source of resistant starch.

[0006] Therefore, how to further develop and utilize mango kernel starch is a technical problem that those skilled in the art urgently need to solve. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a mango kernel resistant starch and a preparation method thereof.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A method for preparing mango kernel resistant starch comprises the following steps:

[0010] The mango kernel starch is mixed with water, treated at high temperature and high pressure, and then dried and crushed after aging. The above steps are repeated to obtain the mango kernel resistant starch.

[0011] Beneficial effects: In the preparation process of the present invention, mixing mango kernel starch with water is one of the key steps. The addition of water can promote the interaction between starch molecules, improve the swelling property of starch molecules, enhance the reactivity, effectively adjust the humidity and viscosity of the raw materials, and lay the foundation for subsequent physical and chemical changes.

[0012] In addition, the high temperature and high pressure treatment in the present invention can effectively destroy the structure of starch molecules, causing them to undergo "reversible expansion" and "irreversible gelation" reactions during the heat treatment process. During this process, part of the water-soluble part of the starch molecules is converted into difficult-to-digest resistant starch, thereby significantly improving its digestibility, acid resistance and safety.

[0013] Furthermore, during the aging process of the present invention, low-temperature cooling overnight can cause the starch molecules to undergo a physical aging reaction, making the starch molecular chain structure tighter, further enhancing the stability and digestibility of the resistant starch, and reducing the possibility of its enzymatic hydrolysis by the human body, thereby achieving the purpose of increasing its dietary fiber content and nutritional value.

[0014] Furthermore, the design of the cyclic high temperature and high pressure treatment and aging step of the present invention helps to further improve the content and quality of resistant starch in mango kernels. By repeating the treatment multiple times, soluble starch can be gradually removed to maximize the concentration of resistant starch.

[0015] Preferably, the method for preparing mango kernel starch comprises the following steps:

[0016] The outer skin of mango kernels is removed and then cut into pieces, water is repeatedly added to homogenize, and the supernatant is collected by filtration. The pH value of the obtained supernatant is adjusted and then centrifuged. The obtained precipitate is dried and then crushed and sieved to obtain the mango kernel starch.

[0017] Preferably, the solid-liquid ratio of the water-added homogenate is 1:3.

[0018] Beneficial effects: The above-mentioned appropriate solid-liquid ratio helps to fully swell and disperse the starch particles in the mango kernel, ensuring that the starch is evenly distributed during the homogenization process. Orthogonal and single factor experiments show that a solid-liquid ratio of 1:3 can effectively balance the dispersion of water and starch, optimize the subsequent filtration and centrifugation process, and ensure the maximum recovery rate of starch.

[0019] Preferably, the pH is adjusted to 8.

[0020] Beneficial effects: Under the above pH conditions, it helps to improve the precipitation performance of starch and optimize the starch recovery efficiency during centrifugal separation. Under this pH condition, the interaction between starch and other impurities (such as protein, sugar, etc.) is low, which helps to improve the purity of starch. In addition, pH 8 is also the optimal range for the stability of many starch substances, which is conducive to maintaining the natural physical and chemical properties of starch.

[0021] Preferably, the centrifugal speed is 3000 rpm and the time is 10 min.

[0022] Beneficial effects: The speed of 3000rpm is high enough to effectively separate starch from other impurities, ensuring efficient separation of starch and minimizing the residue of other water-soluble substances. The centrifugal time of 10 minutes ensures a sufficient precipitation process, avoiding starch decomposition caused by too long a time and incomplete precipitation caused by too short a time.

[0023] Preferably, the temperature of the high temperature and high pressure treatment is 121°C and the pressure is 100 MPa. ， The time is 20 to 60 minutes.

[0024] Preferably, the aging treatment is a low-temperature aging treatment at 4°C for 24 hours.

[0025] Beneficial effects: The temperature of the low-temperature aging treatment in the present invention can enhance the resistant starch content of mango kernel starch through slow hydration and molecular rearrangement processes, while maintaining the stability of its natural structure. Low-temperature treatment effectively reduces the damage of heat to the starch structure, allowing the starch to maintain a high dietary fiber content and good digestibility. The 24-hour treatment time ensures sufficient molecular rearrangement and hydration, while avoiding the negative effects of excessive aging. This aging treatment process not only improves the resistance of mango kernel starch, but also ensures its functionality and nutritional value, and has good prospects for industrial application.

[0026] Preferably, the number of cycles is 1-4 times.

[0027] Preferably, the material-liquid ratio of the mango kernel starch to water is 1:(3-6).

[0028] A mango kernel resistant starch prepared by the preparation method.

[0029] Compared with the prior art, the present invention has the following advantages and technical effects:

[0030] The present invention uses mango kernel starch as raw material, adopts autoclave method combined with single factor analysis and orthogonal test, explores the optimal process conditions for preparing mango kernel resistant starch, and studies its basic physicochemical properties. Finally, the mango kernel resistant starch obtained by the present invention has a small molecular weight and a compact molecular structure, and its water content is second only to potato starch; the water solubility is generally between corn starch and potato starch, which is significantly lower than mango kernel starch; the swelling degree does not change significantly with the increase of temperature, and is the lowest overall. Compared with other starches, the enzymatic hydrolysis characteristics of mango kernel resistant starch are weaker, showing better resistance to digestion. In addition, it has excellent structural stability and has significant potential in the food industry. It is particularly suitable for the development of functional foods and intestinal health regulation, and has great application prospects in the preparation of low GI foods, weight loss foods and prebiotic foods. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0032] Figure 1 This is a graph showing the yield of mango kernel resistant starch obtained in Examples 1-5;

[0033] Figure 2 This is a graph showing the yield of mango kernel resistant starch obtained in Example 1 and Examples 6-9;

[0034] Figure 3 This is a graph showing the yield of mango kernel resistant starch obtained in Example 1 and Examples 10-13;

[0035] Figure 4 This is the result of orthogonal test for resistant starch yield;

[0036] Figure 5 This is a comparison chart of the water content of the mango core resistant starch obtained in Example 1, the mango core starch obtained in Example 1, corn starch and potato starch;

[0037] Figure 6 This is a solubility comparison chart of the mango core resistant starch obtained in Example 1, the mango core starch obtained in Example 1, corn starch and potato starch;

[0038] Figure 7 This is a comparison chart of the swelling degrees of the mango core resistant starch obtained in Example 1, the mango core starch obtained in Example 1, corn starch and potato starch;

[0039] Figure 8 It is a comparison chart of the sedimentation volumes of the mango core resistant starch obtained in Example 1, the mango core starch obtained in Example 1, corn starch and potato starch;

[0040] Fig. 9 This is a comparison chart of the in vitro digestion results of the mango core resistant starch obtained in Example 1, the mango core starch obtained in Example 1, corn starch and potato starch;

[0041] Fig.10 These are optical microscope photos (×40) of the mango core resistant starch obtained in Example 1, the mango core starch obtained in Example 1, corn starch, and potato starch particles;

[0042] Among them, A is mango kernel starch; B is mango kernel resistant starch; C is potato starch; and D is corn starch. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources;

[0046] Among them, mango kernels, potato starch, and corn starch were purchased from supermarkets in Qingxiu District, Nanning, Guangxi;

[0047] α-Amylase (food grade) was purchased from Jiangsu Ruiyang Biotechnology Co., Ltd.;

[0048] Pepsin (biological reagent) was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0049] Potassium hydroxide (analytical grade) was purchased from Guangdong Chemical Reagent Engineering Technology Research and Development Center;

[0050] Hydrochloric acid (analytical grade) was purchased from Lianjiang Ailian Chemical Reagent Co., Ltd.;

[0051] Sodium hydroxide and iodine (analytical grade) were purchased from Xilong Chemical Co., Ltd.

[0052] Maleic acid, 3,5-dinitrosalicylic acid, and potassium iodide (analytical grade) were purchased from Tianjin Guangfu Fine Chemical Research Institute;

[0053] Glucoamylase (analytical grade) was purchased from Beijing Solebow Technology Co., Ltd.;

[0054] Glucose (analytical grade) was purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd.;

[0055] Phosphoric acid and sulfuric acid (analytical grade) were purchased from Chengdu Jinshan Chemical Reagent Co., Ltd.;

[0056] Glycerol (analytical grade) was purchased from Tianjin Fuyu Fine Chemical Co., Ltd.

[0057] Preparation method of DNS solution: Weigh 3.25g 3,5-dinitrosalicylic acid and dissolve it in a small amount of water. Transfer it into a 500ml volumetric flask, add 162.5ml 2mol / L sodium hydroxide solution, then add 22.5g propylene glycol, shake well, and make up to 500ml to obtain DNS solution. Store it in a brown bottle and place it in the refrigerator for use.

[0058] The detection instrument used in the embodiment of the present invention includes:

[0059] DHG-9140A electric constant temperature air drying oven: Shanghai Yunan Instrument Co., Ltd.;

[0060] YXQ-LS-Vertical Pressure Steam Sterilizer: Shanghai Boxun Industrial Co., Ltd. Medical Equipment Factory;

[0061] JP-300C high-speed multifunctional pulverizer: Yongkang Jiupin Industry and Trade Co., Ltd.;

[0062] 752N UV spectrophotometer: Shanghai Yidian Analytical Instrument Co., Ltd.;

[0063] 80-2 centrifugal precipitator: Jintan Medical Instrument Factory;

[0064] HH-4 digital constant temperature water bath: Guohua Electric Co., Ltd.;

[0065] JJ200 electronic balance: Changshu Shuangjie Testing Instrument Factory;

[0066] BSA224S analytical balance: Sartorius Scientific Ltd.;

[0067] pHS-3C pH meter: Shanghai Yidian Scientific Instrument Co., Ltd.;

[0068] Desktop low-speed centrifuge: Sichuan Shuke Instrument Co., Ltd.;

[0069] Optical microscope: Nanjing Jiangnan New Optics Co., Ltd.

[0070] Unless otherwise specified, the room temperature or normal temperature in the embodiments of the present invention refers to 25±3°C.

[0071] Example 1

[0072] A method for preparing mango kernel resistant starch comprises the following steps:

[0073] (1) Preparation of mango kernel starch: soak the mango kernel in distilled water for 18 hours, remove the shell and wash off the outer skin of the mango kernel, cut into small pieces of about 2 mm and homogenize with distilled water (solid-liquid ratio is 1:3), filter the supernatant and collect it, repeat 4 times to obtain a filtrate. Adjust the pH of the filtrate to 8.0 and centrifuge it at 3000 rpm / min for 10 minutes in a centrifuge, place the precipitate in a 60°C forced air drying oven for 2 hours and then dry it, crush it with a pulverizer and sieve it to obtain mango kernel starch.

[0074] (2) Preparation process of mango kernel resistant starch: weigh the mango kernel starch, add distilled water at a solid-liquid ratio of 1:5 to prepare a starch emulsion, treat it at a high temperature and high pressure of 121°C and 100 MPa for 40 min, take it out, place it in a 4°C refrigerator for aging treatment for 24 h, and then dry it in a drying oven at 80°C for 12 h. After crushing it with a grinder, pass it through a 100-mesh sieve, add distilled water, and finally dry it and pass it through a mesh sieve to obtain the mango kernel resistant starch.

[0075] Embodiment 2-5

[0076] A method for preparing mango kernel resistant starch, which is different from Example 1 in that the material-liquid ratio of mango kernel starch to water in step (2) is 1:2, 1:3, 1:4, and 1:6 respectively. The remaining process steps and parameters are the same as those in Example 1.

[0077] Embodiment 6-9

[0078] A method for preparing mango kernel resistant starch, which is different from Example 1 in that the time of treatment under high temperature and high pressure in step (2) is 20 minutes, 30 minutes, 50 minutes, and 60 minutes respectively. The remaining process steps and parameters are the same as those in Example 1.

[0079] Examples 10-13

[0080] A method for preparing mango kernel resistant starch is different from that in Example 1 in that the total number of cycles in the treatment process of the cyclic step (2) is 2, 3, and 4 respectively. The remaining process steps and parameters are the same as those in Example 1.

[0081] Technical effects:

[0082] 1. Detection method

[0083] 1. Determination of resistant starch content

[0084] (1) Preparation of glucose standard curve

[0085] Preparation of 1mg / mL glucose standard solution: accurately weigh 100mg glucose, add distilled water to dissolve, and dilute to 100mL. Accurately pipette 0, 0.20, 0.40, 0.60, 0.80, 1.00mL of glucose standard solution into 15mL stoppered test tubes, add distilled water to a total volume of 2mL, add 1.5mL DNS solution, shake each test tube and boil it in a water bath for 5min, take it out and quickly cool it in running water, dilute to 15mL with distilled water, adjust to zero with distilled water at 540nm, and test the absorbance of each tube. With absorbance as the horizontal coordinate and glucose content as the vertical coordinate, the linear regression equation Y=0.3604X+0.003, R2=0.9985 is obtained.

[0086] (2) Calculation of resistant starch yield (RS%) of mango kernel

[0087] The Goni method was used for determination: 300 mg of the sample of resistant starch to be tested was accurately weighed and placed in a 50 mL centrifuge tube, 10 mL of HCl-KCl buffer and 0.2 mL of pepsin solution were added, and the sample was shaken at a constant temperature of 40 ° C for 1 hour to remove the protein in the sample; the sample was taken out and naturally cooled to room temperature, 9 mL of 0.1 mol / L maleic acid buffer was added, and the pH was adjusted to 6.0-6.4 with 2 mol / L HCl and 0.5 mol / L NaOH, 1 mL of high temperature resistant α-amylase solution (2000 U / mL) was added, and the sample was shaken in a constant temperature water bath at 95 ° C for 30 minutes to hydrolyze the digestible starch therein; the sample was centrifuged at 3000 rpm for 15 minutes, the supernatant was poured out, distilled water was added for washing, the sample was centrifuged again, and the supernatant was combined; the remaining residue was moistened with 3 mL of distilled water, 3 mL of 4 mol / L KOH was added for mixing, 5.5 mL of 2 mol / L HCl and 3 mL 0.4 mol / L sodium acetate buffer solution, adjust pH to 4.75, add 100 μL glucose amylase solution, shake in a 60°C constant temperature water bath for 45 min; after cooling, centrifuge at 3000 rpm for 15 min, collect the supernatant into a 100 mL volumetric flask, wash once with 10 mL of distilled water, centrifuge for 15 min, collect the supernatant, combine into a 100 mL volumetric flask, and dilute to the mark.

[0088] Take 1 mL of supernatant in a 15 mL test tube, add 1 mL of distilled water and 1.5 mL of DNS, shake well and place in a boiling water bath for 5 min, take out and quickly cool in running water, dilute to 15 mL with distilled water, measure its absorbance at 540 nm, calculate the glucose content using the standard curve, and calculate the resistant starch content according to the following formula:

[0089]

[0090] Wherein: M represents the glucose content (obtained from the glucose standard curve), mg / mL; W represents the dry mass of the sample, g; V represents the volume of the test solution, mL.

[0091] 2. Orthogonal Experimental Design

[0092] On the basis of single factor test, according to the principle of orthogonal test design, the appropriate factor level range was determined, the extraction rate of resistant starch from mango kernel was used as the evaluation index, the solid-liquid ratio (A), sub-heat time (B), and the number of cycles (C) were selected as variables, and the orthogonal test was designed. After the range analysis of the test results, the influence of different extraction conditions on the extraction rate of resistant starch from mango kernel was determined, and the optimal extraction process was verified. The factor level design is shown in Table 1.

[0093] Table 1 Orthogonal experimental factor level table

[0094]

[0095] 3. Determination of the physicochemical properties of mango kernel resistant starch

[0096] (1) Determination of water content

[0097] The water contents of mango kernel resistant starch, mango kernel starch, corn starch and potato starch were determined by the direct drying method in GB 5009.3-2010.

[0098] (2) Water solubility and swelling degree

[0099] Take 1g of mango kernel resistant starch, mango kernel starch, corn starch and potato starch respectively to prepare 50mL of starch suspension with a mass fraction of 2%, and heat them at 50, 60, 70, 80 and 90℃ for 40min, and shake them once every 5min. Cool them to room temperature, centrifuge them at 4000r / min for 15min, separate the upper layer liquid and sediment of the samples with a pipette, and treat them in the following ways: the upper layer liquid is placed in an evaporating dish and dried and weighed in a constant temperature water bath, and the sediment is directly weighed and recorded, and the water solubility and swelling degree are calculated according to the following formula.

[0100]

[0101] Where: W represents the mass of starch in g; A represents the mass of the upper liquid after evaporation in g; P represents the mass of the precipitate after centrifugation in g.

[0102] (3) Enzymatic hydrolysis characteristics

[0103] Accurately weigh 1.0g of mango kernel resistant starch, mango kernel starch, corn starch, and potato starch samples, add 30mL of 0.2mol / L phosphate buffer solution, adjust the pH to 6.0 with 2mol / L sodium hydroxide solution, boil in water for 30min, wait until cooled to 50°C, add 5.0mL of 200g / L α-amylase solution, shake at 60°C for 4h, terminate the reaction with 30mL of 1.0% sulfuric acid solution, and centrifuge at 4000rpm for 15min. The supernatant of mango kernel resistant starch, mango kernel starch, potato starch, and corn starch is placed in a 200mL volumetric flask, fixed to volume, and set aside. Take 1 mL of supernatant in a 15 mL test tube, add 1 mL of distilled water and 1.5 mL of DNS, shake well and place in a boiling water bath for 5 min, take out and quickly cool in running water, dilute to 15 mL with distilled water, shake well, measure the absorbance at 540 nm, and draw a glucose standard curve according to the above method for making a glucose standard curve: Y = 0.3626X + 0.266, R 2 =0.9991. Substitute the result into the equation and multiply it by 0.9 to get the mass of starch after enzymatic hydrolysis of each starch, and calculate the enzymatic hydrolysis rate according to the following formula:

[0104]

[0105] (4) Transmittance analysis

[0106] Weigh 0.5 g of mango kernel resistant starch, mango kernel starch, corn starch, and potato starch samples, add water to make up to 50 mL, heat in a boiling water bath for 30 min while stirring, add water to keep the total volume constant, let stand for 24 h, discard the supernatant, use distilled water as a blank, and measure the transmittance of the coagulated starch paste at 620 nm using a spectrophotometer.

[0107] (5) Sedimentation stability

[0108] Weigh 0.5g of mango kernel resistant starch, mango kernel starch, corn starch, and potato starch samples respectively, add water to 50mL, and heat in a boiling water bath for 30min while stirring to make the starch gelatinize completely. After cooling to room temperature, transfer to a 50mL graduated cylinder and let stand, record the sedimentation volume after 24h, and express it as the percentage of the volume occupied by the sediment.

[0109] (6) In vitro artificial gastric juice digestion and artificial intestinal juice digestion

[0110] Accurately weigh 1.0000g of starch sample, add 50mL of artificial gastric juice or intestinal juice, keep warm in a 37℃ water bath for 4h, and stir from time to time. Centrifuge at 4000rpm for 15min, discard the supernatant, transfer the precipitate to an evaporating dish that has been dried to a constant weight, put them in an oven together, weigh them after drying, and subtract the weight of the evaporating dish to obtain the mass of undigested starch. The digestion characteristics of artificial gastric juice or artificial intestinal juice are characterized by the following formula:

[0111]

[0112] 4. Determination of structural properties

[0113] (1) Starch granule morphology

[0114] The starch granule morphology was observed under a microscope. Mango kernel resistant starch, mango kernel starch, corn starch, and potato starch were used to prepare 1% starch milk, which was dropped on a glass slide and placed on a microscope sample stage. Appropriate eyepieces and objective lenses were selected to observe and photograph the starch granule morphology at the required magnification.

[0115] (2) UV scanning and average degree of polymerization determination

[0116] Using the iodine absorption method, weigh 20 mg of mango kernel resistant starch, mango kernel starch, corn starch, and potato starch samples, add 0.5 mL of anhydrous ethanol to wet the sample, then add 1 mL of 2 mol / mL potassium hydroxide solution to fully dissolve the sample, then add 10 mL of deionized water, and adjust the pH value to 6.0-7.0 with 0.1 mol / mL HCL solution, and add water to make up to 50 mL. Take 10 mL in a 100 mL volumetric flask, add 80 mL of deionized water and 2 mL of iodine solution, make up to 100 mL, and mix immediately. Scan with an ultraviolet spectrophotometer at a wavelength of 450-800 nm. Since starch is a mixture of homologous series with different molecular weights, it is expressed as an average degree of polymerization (DP) and calculated according to the Banks formula, as follows:

[0117]

[0118] 5. Data Processing

[0119] The single factor and orthogonal experiments were repeated three times, and the experiments to determine the four starch properties were repeated twice. The data were analyzed and plotted using Microsoft Excel 2019, Origin 2021, and SPSS26.0, and the data were expressed as mean ± standard deviation.

[0120] 2. Results and Analysis

[0121] 1. Single factor experiment and orthogonal experiment

[0122] (1) Effect of different material-liquid ratios on the yield of resistant starch from mango kernels (Examples 1-5)

[0123] The results are as follows Figure 1 As shown in the figure, it can be seen that with the increase of the solid-liquid ratio, the RS yield shows a trend of first decreasing, then increasing, and then decreasing. Specifically, when the solid-liquid ratio increases from 1:2 to 1:3, the RS yield decreases slightly. This shows that although the water content increases relatively, it is not enough to significantly promote the full expansion of starch granules. At the same time, the increase in the dispersion between granules may reduce the probability of the amylose molecules approaching each other, thereby inhibiting the formation of double helical structures and crystalline regions. As the solid-liquid ratio increases from 1:3 to 1:5, the RS yield increases significantly and reaches the highest value (3.8%) at 1:5. This result may be due to the fact that the appropriate amount of water can effectively promote the complete expansion of starch granules, while enhancing the migration and rearrangement of amylose molecules, thereby forming a more stable double helical structure and resistant starch crystals. However, when the solid-liquid ratio is further increased to 1:6, the RS yield decreases. This may be because the excess water dilutes the starch concentration and increases the viscosity of the starch paste, hindering the effective interaction between molecules and the stabilization of the crystal structure. Therefore, the solid-liquid ratio has a significant effect on the formation of resistant starch. Too high or too low a solid-liquid ratio is not conducive to the formation of RS. In this experiment, the solid-liquid ratio of mango kernel resistant starch extraction was in the range of 1:4 to 1:6, and the yield was the highest when it was 1:5.

[0124] (2) Effect of different autoclave times on the yield of resistant starch from mango kernels (Examples 1 and 6-9)

[0125] like Figure 2 As shown in the figure, in the single-factor autoclave time experiment, the yield of resistant starch ranged from 2.7% to 3.9%. The yield was the highest at 30 min, reaching 3.9%. When the autoclave time was 20 min, the yield was lower, which may be because the amylose molecules had not been completely released, resulting in a lower probability of molecules approaching each other; as the time was extended to 30 min, the starch granules were fully expanded and conducive to the formation of resistant starch. However, after the autoclave time exceeded 30 min, the yield began to decline, which may be due to the occurrence of excessive degradation, which hindered the formation of resistant starch. In addition, longer autoclave time increased energy consumption, while the yield of resistant starch did not differ much in different time periods.

[0126] (3) Effect of cycle number on yield of resistant starch from mango kernels (Examples 1 and 10-13)

[0127] The results are as follows Figure 3As shown in the figure, it can be seen that the RS yield gradually increases from 3.2% to 4.2% in the range of 1 to 4 cycles, and the yield is the highest at 4 cycles. The reason is that as the number of cycles increases, the autoclave process promotes the water absorption, swelling, gelatinization and decomposition of starch granules, resulting in the gradual release of amylose molecules and further forming a more stable double helix structure and crystal region, thereby increasing the RS content. This is consistent with the promotion of the cyclic treatment on the rearrangement of starch molecules and the formation of crystal structure. However, when the number of cycles exceeds 2, the increase in RS yield is not large, indicating that although more cyclic treatments have a certain contribution to RS content, their marginal benefits are reduced. At the same time, more cycles will significantly increase energy consumption and production cycle, which is not conducive to cost control in actual production.

[0128] (4) Optimization of extraction process of resistant starch from mango kernel

[0129] Orthogonal test scheme and result analysis are shown in Table 2-3 and Figure 4 , other process parameters and steps are the same as those in Example 1, directly comparing Table 2 and Figure 4 It can be seen that among the 9 experimental results, the yield of resistant starch in the experiment No. 6 is the highest, which is 8.04%, and its horizontal combination is A2, B3, and C1. It can be seen that the optimal combination of the various factor combinations in this experiment is A2B3C1, that is, the yield of the material-liquid ratio is 1:5, the pressure heating time is 40min, and the number of cycles is 1 (Example 1) is the highest. By comparing the size of the extreme difference R value, it can be seen that there is a significant order in the experimental factors, and the primary and secondary relationship of each factor is A>B>C. That is, the most important factor affecting the yield of resistant starch is the material-liquid ratio, followed by the pressure heating time and the number of cycles. Finally, it can be seen from the variance analysis Table 3 that the material-liquid ratio has a significant effect on the experimental results, while the other two factors have no significant effect.

[0130] Table 2 Pressure and heat orthogonal table

[0131]

[0132]

[0133] Table 3 Analysis of variance table

[0134] Sources of variance Material-liquid ratio Pressing time Cycle times error Total deviation Sum of Squares of Deviations 5.69147 1.3176 0.661067 0.086663 QT=7.7568 Degrees of Freedom 2 2 2 2 8 Mean square deviation 2.845735 0.6588 0.330533 0.043332 F-number 65.67359 15.20372 7.628018 Critical value <![CDATA[F 0.05 (2,2)=19.0]]> Significance *

[0135] 2. Analysis of the physicochemical properties of mango kernel resistant starch

[0136] (1) Water content

[0137] Figure 5The relationship between four starches and their water content is described. The water contents of potato starch, corn starch, mango kernel resistant starch obtained in Example 1, and mango kernel starch are 17.65%, 8.15%, 11%, and 5.5%, respectively. Potato starch has the highest water content, and mango kernel starch has the lowest water content. The water content of mango kernel resistant starch is higher than that of mango kernel starch, indicating that mango kernel resistant starch has stronger water holding capacity, which helps to improve the texture, water retention and processing performance of food.

[0138] (2)Water solubility

[0139] Figure 6 The solubility changes of potato starch, corn starch, mango kernel resistant starch obtained in Example 1, and mango kernel starch at different temperatures are shown. The data show that the solubility of these four starches increases with increasing temperature, indicating that during the heating process, the starch granules gradually dissolve, their crystalline structure is destroyed, and water molecules bind to the hydroxyl groups on the starch molecules (linear and amylopectin) through hydrogen bonds, thereby causing the granules to swell and promote dissolution. Among them, the solubility of mango kernel starch at various temperatures is significantly higher than that of other starches. For example, at 90°C, its solubility is as high as 26.05%, far exceeding mango kernel resistant starch (15.74%), corn starch (13.83%), and potato starch (8.06%). This may be related to the higher content of amylopectin in mango kernel starch, because the structure of amylopectin is easier to be destroyed and dissolved, and the presence of linear starch reduces the solubility of starch molecules. In addition, the solubility of mango kernel starch and mango kernel resistant starch increased relatively slowly at 50-70℃, but increased rapidly at 80-90℃. This phenomenon may be due to the fact that high temperature promotes the massive outflow of starch molecules, especially amylopectin. The solubility of corn starch and potato starch increased relatively steadily in the range of 50-90℃, indicating that their internal structure is more stable at high temperature.

[0140] (3) Expansion

[0141] like Figure 7As shown, the swelling degree of the four starches increases with increasing temperature, which reflects the process of starch granules absorbing water and swelling and the gradual destruction of the crystal structure during heating. The swelling degrees of corn starch, mango kernel starch and mango kernel resistant starch obtained in Example 1 show a gentle upward trend in the range of 50°C to 90°C, while the swelling degree of mango kernel starch is always higher than that of corn starch and mango kernel resistant starch. This may be due to the high content of amylopectin in mango kernel starch, and amylopectin can more effectively bind to water molecules, thereby enhancing its swelling ability. In contrast, the swelling degree of potato starch increases sharply from 60°C and is much higher than other starches at 90°C. However, combined with the solubility experiment, it can be seen that the amylopectin content of potato starch is lower than that of mango kernel starch. The reason for this phenomenon may be that the surface of potato starch particles forms more hydrogen bonds with water molecules. This strong and dense hydrogen bond network promotes the rapid water absorption and swelling of starch at high temperatures. The expansion degree of mango kernel resistant starch is the lowest in the range of 50℃ to 80℃, showing extremely strong stability, while in the high temperature range of 80℃ to 90℃, its expansion degree increases significantly, even exceeding corn starch and mango kernel starch. This property shows that mango kernel resistant starch maintains a high structural stability at lower temperatures and has a certain expansion capacity at high temperatures.

[0142] (4) Enzymatic hydrolysis characteristics

[0143] After testing and calculation, the enzymatic hydrolysis rates of potato starch, corn starch, mango kernel resistant starch obtained in Example 1 and mango kernel starch were 50.68±0.10%, 38.17±0.05%, 37.45±0.23% and 30.60±0.01%, respectively. Among them, the enzymatic hydrolysis rate of potato starch is the highest, while the enzymatic hydrolysis rate of mango kernel starch is the lowest. The enzymatic hydrolysis rate of mango kernel resistant starch is higher than that of mango kernel starch, indicating that it is easier to digest, but has lower stability; at the same time, compared with potato starch and corn starch, the enzymatic hydrolysis rate of mango kernel resistant starch is relatively low. From the experimental mechanism, the α-amylase used in the enzymatic hydrolysis experiment mainly acts on α-1,4 glycosidic bonds, which can hydrolyze starch into disaccharides, oligosaccharides and dextrins, but only decomposes the linear part of amylose and amylopectin. Combined with the results of the solubility and swelling experiments, it is inferred that the amylopectin content of mango kernel starch is significantly higher than that of the other three starches, while the amylopectin content of potato starch is the lowest. The level of amylose content determines the enzymatic hydrolysis rate of starch to a certain extent. Starch with high amylose content is easily decomposed by α-amylase. Therefore, potato starch has the highest enzymatic hydrolysis rate, while mango kernel starch has the lowest enzymatic hydrolysis rate. Although the enzymatic hydrolysis rate of mango kernel resistant starch is lower than that of potato starch and corn starch, it still maintains good digestibility. This special enzymatic hydrolysis characteristic provides more possibilities for the development of low digestibility and slow-release energy foods, and has high application value.

[0144] (5) Light transmittance

[0145] After testing and calculation, the transmittances of potato starch, corn starch, mango kernel resistant starch obtained in Example 1 and mango kernel starch at a wavelength of 620nm were 9.02±0.31%, 0.087±0.002%, 0.025±0.004% and 0.056±0.0035%, respectively. Among them, the transmittance of potato starch was significantly higher than that of the other three starches, while the transmittance of mango kernel resistant starch was the lowest, indicating that its transparency was low. This may be closely related to its branched starch ratio and molecular characteristics. The higher the branched starch content and the shorter the molecular chain length, the transparency of the starch system will be significantly improved, thereby reducing the transmittance. In addition, the particle size, structural looseness and particle size distribution of the starch will also significantly affect its transparency. Compared with potato starch, the transmittance of mango kernel resistant starch is lower, indicating that its structure is denser and its light scattering ability is stronger. This property is conducive to the preparation of opaque or milky products in the food industry, such as sauces and dairy substitutes.

[0146] (6) Coagulation stability

[0147] Figure 8 The difference in the sedimentation stability of potato starch, corn starch, mango kernel resistant starch obtained in Example 1 and mango kernel starch is intuitively shown, and the sedimentation volumes are: 99mL / 100mL for potato starch, 23mL / 100mL for corn starch, 11mL / 100mL for mango kernel resistant starch obtained in Example 1, and 21.5mL / 100mL for mango kernel starch. It can be seen that the sedimentation volume of potato starch is the largest, close to 100mL / 100mL, indicating that its water binding force is weak and the particles are easy to aggregate and settle; while the sedimentation volume of mango kernel resistant starch is the smallest, indicating that its system has the best sedimentation stability. The superior stability of mango kernel resistant starch may be attributed to the high-density arrangement and low particle size of its granular structure, which enhances its dispersibility and suspension stability. In addition, the special molecular arrangement of resistant starch may limit the interaction between starch particles, making it form a more stable suspension state in water. In contrast, potato starch is more likely to form sedimentation due to its large particles and loose structure. This stability property makes mango kernel resistant starch have greater potential for use in emulsions, sauces and suspended foods.

[0148] (7) In vitro digestion characteristics

[0149] Fig. 9The performance of potato starch, corn starch, mango kernel resistant starch obtained in Example 1 and mango kernel starch in artificial gastric juice and artificial intestinal juice digestion is intuitively demonstrated. By comparison, it is found that mango kernel resistant starch shows certain advantages over the other three starches during digestion, especially in the process of digestion in artificial intestinal juice, showing its lower digestion loss rate. This shows that mango kernel resistant starch is more resistant to digestion and can retain more undigested starch components during the digestion process in the stomach. This property is of great significance for slowing down the digestion rate of food, enhancing satiety and controlling food intake.

[0150] More significantly, in terms of the performance of artificial intestinal fluid digestion, the weight loss rate of mango kernel resistant starch is much lower than that of potato starch and corn starch, and only higher than that of mango kernel starch. This means that mango kernel resistant starch can be digested and absorbed less in the intestine, and may play a greater prebiotic role after entering the large intestine, promoting intestinal health. In addition, resistant starch has been shown to improve the diversity of intestinal microbial communities, promote the growth of probiotics, help improve intestinal function and regulate blood sugar levels. This digestion characteristic of mango kernel resistant starch is closely related to its unique molecular structure. Studies have shown that resistant starch is difficult to be rapidly degraded by gastrointestinal enzymes due to its crystalline structure and slower hydration, thereby reducing its digestion rate in the gastrointestinal tract, which helps to improve its health function.

[0151] 3. Structural characteristics of mango kernel resistant starch

[0152] (1) Starch granule morphology

[0153] Fig.10 Optical microscope photos (×40) of the starch granule morphology of potato starch, corn starch, mango kernel resistant starch obtained in Example 1, and mango kernel starch. It can be seen that the granules of mango kernel starch, potato starch, and corn starch in water are mostly oval, with relatively complete granules and relatively smooth edges, while the resistant starch granules obtained after treatment are irregular blocks and easily aggregated into agglomerates. The sizes of the four starches are potato starch>corn starch>mango kernel starch>mango kernel resistant starch, which is consistent with the above-mentioned precipitation stability test results.

[0154] (2) UV scanning and average degree of polymerization analysis

[0155] The calculation results of the maximum absorption wavelength and average degree of polymerization of potato starch, corn starch, mango kernel resistant starch obtained in Example 1 and mango kernel starch are shown in Table 4:

[0156] Table 4 Transmittance of four starches

[0157]

[0158] Amylose forms a colored complex when it meets iodine, which can be used to study the chain length and average molecular polymerization degree of amylose in starch. The maximum absorption peak (λmax) of amylose-iodine complex in the range of 620-680nm can reflect the molecular weight and structural characteristics of amylose. This peak varies according to the molecular size of amylose. Larger amylose molecules usually lead to a shift to the high end of this wavelength range. According to the data analysis in Table 4, the molecules of amylose in mango kernel resistant starch may be smaller than potato starch and corn starch, and slightly larger than mango kernel starch, which is basically consistent with the results of the above physical and chemical properties. At the same time, the degree of polymerization of mango kernel resistant starch is between mango kernel starch and corn starch, showing a smaller molecular weight characteristic. The degree of polymerization is closely related to the molecular structure and molecular weight of starch. A lower degree of polymerization usually means a smaller molecular weight. A smaller molecular weight helps to improve digestibility because its digestion rate in the gastrointestinal tract is slower, especially for resistant starch. Low molecular weight usually means slower digestion, which reduces the rapid release of energy and helps stabilize blood sugar. In addition, the lower absorption peak of mango seed resistant starch may be related to the compactness of its molecular structure, which further enhances its anti-digestive properties in the intestine. Therefore, although the degree of polymerization of mango seed resistant starch is low, its unique molecular characteristics give it significant advantages in digestibility and health promotion. Compared with traditional starch, mango seed resistant starch shows more potential in delaying food digestion, controlling blood sugar and intestinal health, indicating that it has broad application prospects in the field of functional foods.

[0159] In summary, the mango kernel resistant starch prepared by the autoclave method of the present invention has an optimal extraction process of a material-liquid ratio of 1:5, autoclave at 121°C for 40 minutes, and one cycle (ie, Example 1), with a yield of 8.04%. The mango kernel resistant starch is in the form of irregular fragments under a microscope, easily aggregated into agglomerates, and has a small molecular weight and a compact molecular structure. Its water content is 11%, second only to potato starch; its water solubility is generally between corn starch and potato starch, and significantly lower than mango kernel starch; its swelling degree does not change significantly with increasing temperature, and is generally the lowest. Compared with other starches, the enzymatic hydrolysis characteristics of mango kernel resistant starch are weaker, showing better resistance to digestion, the weight loss rate of artificial gastric juice digestion is lower than that of corn starch, and the weight loss rate of artificial intestinal juice digestion is only higher than that of mango kernel starch. In addition, its light transmittance is the lowest and its precipitation stability is the strongest, indicating that it has excellent structural stability. Taking into account its digestion resistance, low water solubility and high stability, mango kernel resistant starch has significant potential in the food industry, and also has unique advantages in slowing down carbohydrate digestion, controlling blood sugar and improving food structure stability, and is particularly suitable for the development of functional foods and intestinal health regulation. Therefore, the mango kernel resistant starch provided by the present invention can be used as a promising raw material for the preparation of low GI foods, weight loss foods and prebiotic foods.

[0160] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for preparing mango kernel resistant starch, characterized in that: The following steps are involved: The mango kernel starch is mixed with water, treated at high temperature and high pressure, and then dried and crushed after aging. The above steps are repeated to obtain the mango kernel resistant starch.

2. The method for preparing mango kernel resistant starch according to claim 1, characterized in that: The preparation method of mango kernel starch comprises the following steps: The outer skin of mango kernels is removed and then cut into pieces, water is repeatedly added to homogenize, and the supernatant is collected by filtration. The pH value of the obtained supernatant is adjusted and then centrifuged. The obtained precipitate is dried and then crushed and sieved to obtain the mango kernel starch.

3. The method for preparing mango kernel resistant starch according to claim 2, characterized in that: The solid-liquid ratio of the water-added homogenate is 1:

3.

4. The method for preparing mango kernel resistant starch according to claim 2, characterized in that: The pH is adjusted to 8.

5. The method for preparing mango kernel resistant starch according to claim 2, characterized in that: The centrifugal speed is 3000 rpm and the time is 10 min.

6. The method for preparing mango kernel resistant starch according to claim 1, characterized in that: The material-liquid ratio of the mango kernel starch to water is 1:(3-6).

7. The method for preparing mango kernel resistant starch according to claim 1, characterized in that: The temperature of the high temperature and high pressure treatment is 121°C and the pressure is 100KPa ， The time is 20 to 60 minutes.

8. The method for preparing mango kernel resistant starch according to claim 1, characterized in that: The aging treatment is: low-temperature aging treatment at 4° C. for 24 hours.

9. The method for preparing mango kernel resistant starch according to claim 1, characterized in that: The number of cycles is 1-4 times.

10. Mango kernel resistant starch prepared by the preparation method according to any one of claims 1 to 9.

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