Method for preparing starch-polyphenol RS5 type resistant starch

Abstract

The invention belongs to the field of starch modification processing, and provides a method for preparing starch-polyphenol RS5 type resistant starch. According to the method, through physical-polyphenol composite synergistic modification, a procyanidine polyphenol structure and sweet potato starch are utilized to form a hydrogen bond / hydrophobic effect, starch molecular chains are induced to be directionally rearranged, a resistant crystal structure is stabilized, and the preferable process conditions are as follows: the temperature is 85-90 DEG C, the time is 18-20 minutes, the addition amount of procyanidine is 3-7% of a starch dry basis, and the final resistant starch content reaches 36.39-46.86%. Compared with a traditional method, the raw material utilization rate and the product yield are remarkably improved. The whole process has the advantages of no chemical reagent, simple operation, low equipment cost, and stable resistant starch content of the product.

Description

Technical Field

[0001] This invention belongs to the field of starch modification and processing, and specifically relates to a method for preparing sweet potato starch-proanthocyanidin RS5 type resistant starch. Background Technology

[0002] RS5 resistant starch, due to its unique slow digestion characteristics and gut-benefiting function, has broad application prospects in functional foods, dietary supplements, and foods for special medical purposes. Currently, the conventional technical routes for preparing RS5 resistant starch mainly cover three categories: physical methods, chemical methods, and enzymatic methods, but each method has significant technical bottlenecks.

[0003] Physical methods are represented by hydrothermal treatment and extrusion. Hydrothermal treatment induces starch molecular chain rearrangement through the synergistic effect of temperature and moisture, forming a resistant structure; extrusion utilizes high shear force and thermal effect to promote cross-linking between starch molecules. Although these methods avoid chemical reagent residues, they have drawbacks such as high equipment energy consumption, narrow process parameter windows (e.g., temperature fluctuations can easily lead to excessive starch degradation or insufficient crystallinity), and unstable resistant starch content in the product. Furthermore, they are highly sensitive to the purity and amylose content of sweet potato starch raw materials, resulting in large batch-to-batch quality variations during large-scale production.

[0004] Chemical methods include acid treatment and esterification modification. Acid treatment selectively hydrolyzes the amorphous regions of starch in an acidic medium, exposing the crystalline regions to enhance resistance to enzymatic hydrolysis. Esterification modification, on the other hand, introduces ester groups to alter the polarity of starch molecules, inhibiting the action of digestive enzymes. However, chemical methods have two major problems: First, acid / ester reagents (such as hydrochloric acid and octenyl succinic anhydride) are prone to remain in the product, requiring repeated washing to remove them, leading to a surge in wastewater discharge (up to 5-8 tons of wastewater per ton of product) and increased production costs. Second, residual chemicals may violate safety standards for food-grade applications (such as the residue limits for acid-treated starch in GB 2760-2014, "National Food Safety Standard for the Use of Food Additives"), limiting their direct application in the food industry.

[0005] Enzymatic methods primarily utilize amylase-assisted treatment, constructing resistant structures through targeted hydrolysis and recrystallization by α-amylase, β-amylase, or pullulanase. While environmentally friendly, this method relies on high-cost enzyme preparations (e.g., pullulanase, with a market price of approximately 800,000-1,200,000 RMB / ton) and requires strict control of enzymatic hydrolysis temperature (typically 40-60℃), time (2-6 hours), and pH value (4.5-6.5), making the process highly sensitive to these parameters. In large-scale production, ensuring the uniformity of the enzymatic hydrolysis reaction is difficult, easily leading to localized over- or under-hydrolysis, resulting in fluctuations in the resistant starch content of the product (typically within the 40%-65% range). Furthermore, multiple steps such as enzyme inactivation and drying are required after enzymatic hydrolysis, further increasing production costs and process complexity.

[0006] It is worth noting that existing technologies do not incorporate proanthocyanidins as a key composite component in the preparation process of RS5-type resistant starch from sweet potato starch. Proanthocyanidins, as natural polyphenols, possess strong antioxidant properties and the ability to interact with starch molecules. They can form complex structures with starch molecules through non-covalent bonds (such as hydrogen bonds and hydrophobic interactions), theoretically enhancing the stability and functionality of resistant starch. However, existing methods for preparing RS5-type resistant starch focus on the physical / chemical / enzymatic modification of single starches, without exploring the composite preparation process of sweet potato starch and proanthocyanidins. This limits the application of such composite resistant starches in the development of functional foods.

[0007] Therefore, there is an urgent need in this field to develop a new method for preparing RS5-type resistant starch by combining sweet potato starch and proanthocyanidins, in order to overcome the shortcomings of existing technologies such as chemical residues, high cost of enzyme preparations, complex processes, and failure to utilize the functional synergistic effect of proanthocyanidins, and to meet the needs of large-scale, safe, and functional production of food-grade resistant starch. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention proposes a method for preparing sweet potato starch-proanthocyanidin RS5-type resistant starch. Through the composite modification of sweet potato starch and proanthocyanidins, this invention not only solves the core defects of existing technologies, such as low yield, poor safety, and complex processes, but also establishes a standardized and quantifiable process parameter system. This achieves a breakthrough in the safety, efficiency, and large-scale production of RS5-type resistant starch, demonstrating significant technological advancement and industrial application value.

[0009] The technical solution of this invention is: A method for preparing starch-polyphenol RS5 resistant starch includes the following steps: (1) Preparation of sweet potato starch suspension: Weigh sweet potato starch and suspend it in distilled water at a solid-liquid ratio of 1g:(8-12)mL. Stir until completely dispersed to form a uniform sweet potato starch suspension. (2) Preparation of proanthocyanidin ethanol solution: Weigh 0.3-0.7g of proanthocyanidin, dissolve it in 100mL of 10% ethanol solution, and stir until the proanthocyanidin is completely dissolved to form proanthocyanidin ethanol solution; (3) Composite reaction and hydrothermal treatment: The proanthocyanidin ethanol solution prepared in (2) is slowly poured into the sweet potato starch suspension prepared in (1) at a volume ratio of 1: (0.8-1.2). While pouring, the mixture is stirred until it is evenly mixed. The mixture is then subjected to hydrothermal treatment at 80-100℃ for 10-30 min. (4) Cooling and freeze-drying: After the wet heat treatment, the mixture is naturally cooled to room temperature, freeze-dried, and the moisture and ethanol are removed to obtain the dried sweet potato starch-proanthocyanidin RS5 type resistant starch product.

[0010] Preferably, in (2), 0.62g of proanthocyanidins is weighed and dissolved in 100mL of 10% ethanol solution.

[0011] Preferably, in (3), the volume ratio of the proanthocyanidin ethanol solution to the sweet potato starch suspension is 1:1.

[0012] Preferably, in (3), the conditions for the damp heat treatment are 85-90℃ and the treatment time is 18-20min; During the initial stage of wet heat treatment, continuous stirring is required.

[0013] Preferably, the conditions for the damp heat treatment are 88.4°C.

[0014] Preferably, in (4), the freeze-drying conditions are: freeze-drying for 60-70 hours at -50℃ to -40℃ and a vacuum of 12-18Pa.

[0015] The present invention has the following advantages and effects compared with the prior art: (1) The yield of RS5 resistant starch prepared by existing physical, chemical and enzymatic methods is generally limited by the characteristics of raw materials and process defects. This invention utilizes the synergistic effect of sweet potato starch and proanthocyanidins to form non-covalent complexes such as hydrogen bonds and hydrophobic interactions between the polyphenolic structure of proanthocyanidins and sweet potato starch molecules, thereby inducing the directional rearrangement of starch molecular chains and stabilizing the resistant crystal structure. Experimental verification shows that the sweet potato starch-based RS5 resistant starch prepared by the preferred process of this invention (such as temperature 85-90℃, time 18-20min, and proanthocyanidin addition amount of 3%-7% starch dry basis) can reach a resistant starch content of 36.39%-46.86%, which significantly improves the raw material utilization rate and product yield compared with traditional methods. (2) The present invention adopts the physical-polyphenol composite synergistic modification technology path, without the use of chemical reagents throughout the process, avoiding residual risks and wastewater treatment burden; at the same time, proanthocyanidins, as natural polyphenol compounds, save preparation costs, and the composite preparation process only needs to control three core parameters: temperature, time and polyphenol addition amount, the operation steps are simple, and the equipment investment cost is further reduced. (3) Through orthogonal experimental design and response surface methodology optimization, the key process parameters for preparing RS5 type resistant starch by sweet potato starch-proanthocyanidin composite were systematically determined. After continuous trial production verification, the resistant starch content of the product prepared by using this parameter system is stable, effectively solving the technical problems of unstable process and large batch differences in the existing technology. Attached Figure Description

[0016] Figure 1 X-ray diffraction patterns of sweet potato starch-proanthocyanidin RS5 type resistant starch and sweet potato starch in Example 1 of the present invention; Figure 2 Fourier transform infrared spectra of sweet potato starch-proanthocyanidin RS5 type resistant starch and sweet potato starch in Example 1 of the present invention; Figure 3 The nuclear magnetic resonance spectra of sweet potato starch-proanthocyanidin RS5 type resistant starch and sweet potato starch in Example 1 of the present invention are shown. Figure 4 The graph shows the effect of the amount of proanthocyanidins added on the content of RS5 resistant starch in Example 2 of the present invention. Figure 5 This is a graph showing the effect of the temperature of the wet heat treatment on the content of RS5 resistant starch in Example 2 of the present invention; Figure 6 This is a graph showing the effect of the wet heat treatment time on the content of RS5 resistant starch in Example 2 of the present invention; Figure 7 This is the response surface optimization diagram in Embodiment 2 of the present invention; Figure 8 These are electron microscope images of the present invention, wherein (A) is an electron microscope image of gelatinized sweet potato starch, and (B) is an electron microscope image of sweet potato starch-polyphenol complex. Detailed Implementation

[0017] To enable those skilled in the art to better understand the present invention, the present invention will now be further described in conjunction with specific embodiments.

[0018] Example 1 1.1 A method for preparing sweet potato starch-proanthocyanidin RS5 resistant starch, comprising the following steps: (1) Preparation of sweet potato starch suspension: Weigh 10g of sweet potato starch, suspend it in 100mL of distilled water, place it in a beaker, and stir with a glass rod until the starch is completely dispersed to form a uniform sweet potato starch suspension (solid-liquid ratio 1:10). Controlling the solid-liquid ratio to 1:10 is to ensure that the starch is fully gelatinized while avoiding an overly thin system that would increase energy consumption or an overly thick system that would result in uneven mixing. (2) Preparation of proanthocyanidin ethanol solution: Weigh 0.62 g of proanthocyanidin standard, dissolve it in 100 mL of 10% ethanol solution, place it in an SPS beaker, and stir until the proanthocyanidin standard is completely dissolved to form a proanthocyanidin ethanol solution (to ensure the solubility of proanthocyanidins and avoid precipitation that may affect the compounding effect). The reason for choosing 10% ethanol as the solvent for proanthocyanidins is that proanthocyanidins have low solubility in water, and 10% ethanol can significantly improve their solubility. In addition, ethanol is easy to remove by freeze-drying, with no risk of residue. (3) Composite reaction and hydrothermal treatment: The proanthocyanidin ethanol solution prepared in (2) was slowly poured into the sweet potato starch suspension prepared in (1) while stirring. After stirring for 10 minutes, the mixture was evenly mixed (to ensure that the proanthocyanidin and starch were evenly mixed before heating, laying the foundation for the subsequent composite reaction). The mixture was placed in a constant temperature water bath for wet heat treatment. In the initial stage of wet heat treatment, the stirrer was kept stirring continuously to ensure that the mixture was heated evenly and to avoid local overheating or uneven distribution of proanthocyanidins. The conditions for wet heat treatment were 88.4℃ and the time was 19.34 minutes. (4) Cooling and freeze-drying: After the wet heat treatment, the mixture was removed from the water bath and allowed to cool naturally to room temperature (25±2℃). The cooled sample was then placed in a freeze dryer and freeze-dried at -45℃ and 15Pa vacuum for 64 hours to remove moisture and ethanol from the system, resulting in dried sweet potato starch-proanthocyanidin RS5 type resistant starch product (freeze-drying can avoid proanthocyanidin degradation and starch structure damage caused by high-temperature drying, thus ensuring product quality).

[0019] 1.2 Structural Inspection The structure of the sweet potato starch-proanthocyanidin RS5 resistant starch prepared in section 1.1 was analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR). The results are as follows: Figures 1-3 , Figure 8 As shown.

[0020] Depend on Figure 1 It can be seen that the diffraction patterns of sweet potato starch-proanthocyanidin RS5 type resistant starch are significantly different from those of sweet potato starch, indicating that the interaction between polyphenols (proanthocyanidins) and sweet potato starch alters the original crystalline structure of sweet potato starch.

[0021] Depend on Figure 2 It can be seen that no new absorption peaks were found in the sweet potato starch-proanthocyanidin RS5 resistant starch in the Fourier transform infrared spectrum. This indicates that sweet potato starch and polyphenols (proanthocyanidins) can be bound through non-covalent interactions, and the complex reaches a peak at 3000 cm⁻¹. -1 Up to 3500 cm -1 The shift within the range reflects an increase in hydrogen bond density and strength.

[0022] Depend on Figure 3As can be seen, each curve in the nuclear magnetic resonance spectrum has four peaks, namely C1, C4, C2, 3, 5 and C6 of the starch dehydrated glucose unit. No new peaks were observed in the figure, which indicates that starch and polyphenols interact through non-covalent bonds.

[0023] like Figure 8 As shown, gelatinized sweet potato starch is in the form of irregular fragments, mostly flakes and blocks. The sweet potato starch-polyphenol complex is in the form of agglomerated blocks or spherical shapes with a rough surface. The particles aggregate due to hydrogen bonds and hydrophobic interactions between starch and polyphenols, which reflects the changes in the microstructure of starch caused by polyphenols.

[0024] Example 2 Parameter Optimization The content of RS5 resistant starch in the product was detected, and key parameters of the preparation method in Example 1 were screened and optimized.

[0025] Table 1. Factors and levels in response surface methodology experiments

[0026] Table 2. Response Surface Experiment Design and Results

[0027] The detection method for RS5 resistant starch content in the product is as follows: The digestibility of starch-polyphenol inclusion complexes was determined using an in vitro simulated digestion method. Pancreatic α-amylase (0.03 g, 16 U / mg) was added to 10.0 mL of acetate-sodium acetate buffer (0.02 M, pH 5.5), stirred for 10 min, and then centrifuged at 15000 × g for 5 min. 200 μL of amylase (260 U / mL) was added to the supernatant, and the mixture was vortexed to obtain a mixed enzyme solution of α-amylase and amylase. 20.0 mL of acetate-sodium acetate buffer (0.02 M, pH 5.5) was added to each sample (200 mg, dry basis), and the mixture was incubated at 37 °C for 10 min, followed by the addition of 1.0 mL of the mixed enzyme solution. At digestion times of 0, 20, and 120 min, 0.2 mL of the reaction solution was mixed with 0.8 mL of anhydrous ethanol to inactivate the enzymes, and then centrifuged at 8000 × g for 5 min to obtain the supernatant. The absorbance was measured at 510 nm using the GOPOD kit, and the glucose content was calculated.

[0028] Calculate the values ​​of RDS, SDS, and RS according to the formulas respectively.

[0029] RDS(%)=(G 20 -G0)0.9 / TS×100%; SDS(%)=(G 120 -G 20 0.9 / TS×100%; RS(%) = (1 - RDS - SDS) × 100%.

[0030] 2.1 Only the amount of proanthocyanidins added in step (3) of Example 1 was changed, and the remaining steps and parameters were the same as in Example 1.

[0031] The concentration of the sweet potato starch suspension is known to be 10 g / 100 mL.

[0032] Table 3. Effect of proanthocyanidin addition on RS5 resistant starch content.

[0033] From Table 3 and Figure 4 The data shows that when the amount of polyphenols (proanthocyanidin ethanol solution) added is too low (only 1%), it cannot fully occupy the binding sites after the sweet potato starch is gelatinized, the degree of complex reaction is low, and the starch resistance to digestion cannot be improved through the "cross-linking effect" of proanthocyanidins. Therefore, the RS content is reduced to only 40.83%. Too high a content will cause proanthocyanidin waste and may affect the purity of the product due to excessive unbound proanthocyanidins.

[0034] 2.2 Change the temperature of the damp heat treatment in step (3) of Example 1, and keep the other steps and parameters the same as in Example 1.

[0035] Table 4. Effect of wet heat treatment temperature on RS5 resistant starch content

[0036] From Table 4 and Figure 5 According to the data, the reasons are as follows: 80℃ is not the gelatinization temperature of sweet potato starch. The starch granules absorb water and swell, and the molecular chain breaks to a limited extent, resulting in insufficient gelatinization. Furthermore, due to the insufficient expansion of the starch molecular chain, there are few binding sites with the hydroxyl and carbonyl groups of proanthocyanidins, which cannot form a stable complex structure. Therefore, the content of RS5 resistant starch decreases significantly. Excessive temperature leads to thermal degradation of proanthocyanidins, reducing their functional properties and compounding efficiency.

[0037] 2.3 Change the duration of the damp heat treatment in step (3) of Example 1. Table 5. Effect of wet heat treatment time on RS5 resistant starch content.

[0038] From Table 5 and Figure 6The data shows that excessively long wet heat treatment time (30 min) leads to thermal degradation of proanthocyanidins at high temperatures (such as oxidation of phenolic hydroxyl groups and breakage of glycosidic bonds), which not only reduces the amount of proanthocyanidins participating in the complex reaction, but also destroys some of the already formed starch-proanthocyanidin complex structures; excessively short wet heat treatment time leads to incomplete complex reaction between starch and proanthocyanidins.

[0039] 2.5 Response Surface Construction Table 6 Results of response surface variance analysis

[0040] As shown in Table 6, the model's F=36.01 and P<0.0001, indicating that the model is highly significant and can be used to analyze and predict the experimental results of preparing sweet potato starch-polyphenol complexes. The order of factors affecting the resistant starch content of the complex is: temperature > amount added > time.

[0041] The results obtained from the above response surface methodology experiments, such as Figure 7 As shown, the parameter range for optimal results is as follows: The optimal parameters were: water bath temperature 85-90℃, treatment time 18-20 min, and proanthocyanidin addition 3%-7%; the optimal parameters were: 10 g sweet potato starch, 100 mL distilled water, 0.62 g proanthocyanidins (corresponding to an addition of 6.2%), 100 mL 10% ethanol, water bath incubation at 88.4℃ for 19.34 min, initial stirring for 10 min, cooling to room temperature and then freeze-drying. Under these parameters, the product had the highest content of RS5 resistant starch, at 47.7%.

[0042] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the patent. All equivalent changes and modifications made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A method for preparing starch-polyphenol RS5 resistant starch, comprising the following steps: (1) Preparation of sweet potato starch suspension: Weigh sweet potato starch and suspend it in distilled water at a solid-liquid ratio of 1g:(8-12)mL. Stir until completely dispersed to form a uniform sweet potato starch suspension. (2) Preparation of proanthocyanidin ethanol solution: Weigh 0.3-0.7g of proanthocyanidin, dissolve it in 100mL of 10% ethanol solution, and stir until the proanthocyanidin is completely dissolved to form proanthocyanidin ethanol solution; (3) Composite reaction and hydrothermal treatment: The proanthocyanidin ethanol solution prepared in (2) is slowly poured into the sweet potato starch suspension prepared in (1) at a volume ratio of 1: (0.8-1.2). While pouring, the mixture is stirred until it is evenly mixed. The mixture is then subjected to hydrothermal treatment at 80-100℃ for 10-30 min. (4) Cooling and freeze-drying: After the wet heat treatment, the mixture is naturally cooled to room temperature, freeze-dried, and the moisture and ethanol are removed to obtain the dried sweet potato starch-proanthocyanidin RS5 type resistant starch product.

2. The method as described in claim 1, characterized in that, (2) Weigh 0.62g of proanthocyanidins and dissolve them in 100mL of 10% ethanol solution.

3. The method as described in claim 1, characterized in that, In (3), the volume ratio of the proanthocyanidin ethanol solution to the sweet potato starch suspension is 1:

1.

4. The method as described in claim 1, characterized in that, (3) The conditions for the damp heat treatment are 85-90℃ and the treatment time is 18-20min; During the initial stage of wet heat treatment, continuous stirring is required.

5. The method as described in claim 4, characterized in that, The conditions for the damp heat treatment were 88.4℃.

6. The method as described in claim 1, characterized in that, (4) The freeze-drying conditions are freeze-drying at -50~-40℃ and vacuum degree of 12-18Pa for 60-70h.

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