A method for fractionating a hot water soluble dietary fibre from a potato processing by-product

Abstract

The application provides a grading preparation method of hot water soluble dietary fiber of potato processing by-products, and belongs to the technical field of resource utilization of potato processing by-products. The method comprises the following steps: mixing potato starch processing residues in a wet state with water to prepare slurry, introducing carbon dioxide under airtight conditions to perform medium-low pressure pressure maintaining treatment, then performing step-by-step pressure reduction and solid-liquid separation, collecting the obtained liquid phase and not using the liquid phase as a target fraction extraction liquid; performing hot water extraction on the obtained solid at 50-60 DEG C, 65-75 DEG C and 80-95 DEG C in sequence to obtain first, second and third extraction liquids respectively; and performing concentration, alcohol precipitation, separation and drying on the extraction liquids to obtain corresponding hot water soluble dietary fiber fractions. The method is different from the conventional one-time mixed extraction mode through the cooperation of carbon dioxide water phase pressure maintaining, step-by-step pressure reduction, sequential hot water extraction and grading alcohol precipitation, and can obtain soluble dietary fiber fractions corresponding to different hot water extraction stages, and is suitable for fine utilization of the potato starch processing residues in a wet state.

Description

Technical Field

[0001] This invention relates to the field of resource utilization of potato processing by-products and preparation of dietary fiber, and particularly to a method for graded preparation of hot water soluble dietary fiber from potato processing by-products, specifically a method for graded preparation of hot water soluble dietary fiber using wet potato starch processing residue as raw material. Background Technology

[0002] Potato starch processing generates a certain amount of wet potato residue. This residue typically contains residual starch, cell wall fragments, pectin, hemicellulose, protein, and dietary fiber, and has a high water content. Direct discharge or low-value utilization of this residue not only wastes resources but also increases the burden of subsequent processing. Fresh potato residue can have a water content as high as 70%–85%, and its dry matter contains approximately 18%–43% dietary fiber. Therefore, converting potato starch processing residue into dietary fiber-based food ingredients or functional raw materials is one of the important directions for the resource utilization of potato processing byproducts.

[0003] In existing technologies, the preparation of soluble dietary fiber from potato residue or other plant processing byproducts typically employs methods such as hot water extraction, acid-base treatment, compound enzymatic hydrolysis, extrusion puffing, ultrasonic-assisted extraction, microwave-assisted extraction, fermentation, or alcohol precipitation. These methods can, to some extent, improve the yield of soluble dietary fiber or reduce the content of impurities such as residual starch and protein. However, in actual preparation processes, these methods primarily aim to increase the total amount or overall purity of the target product, and usually do not sequentially recover and separately utilize the soluble components that enter the extract at different stages of hot water treatment.

[0004] In wet potato starch processing residue, residual starch, pectin, hemicellulose, and cell wall fragments easily form encapsulation, entanglement, or coexistence. When using conventional single-stage high-temperature hot water extraction, strong enzymatic hydrolysis, or strong acid-base treatment, soluble components with different binding states and varying degrees of release ease tend to enter the same extract, resulting in products that are mostly mixed-type soluble dietary fiber components. While these mixed products can be used as ordinary dietary fiber raw materials, their differences in water-holding capacity, viscosity, uronic acid content, glucose adsorption capacity, and bile salt adsorption capacity are difficult to distinguish, limiting their subsequent targeted application in food ingredients.

[0005] In addition, existing technologies also include methods for treating plant fibers or polysaccharide raw materials with carbon dioxide, such as promoting changes in plant tissue structure or polysaccharide release through carbon dioxide explosion, extrusion puffing, or high-pressure carbon dioxide aqueous phase treatment. However, these treatment methods usually aim to enhance release, modify structure, or improve extraction efficiency. Their process routes are often combined with explosion, puffing, fermentation, or direct extraction, and they do not address the segmented release characteristics of hot water-soluble dietary fiber in wet potato starch processing residue, nor do they establish a method for sequential hot water segmented extraction and separate recovery of solids after carbon dioxide aqueous phase treatment.

[0006] Therefore, it is necessary to propose a new method for preparing hot water soluble dietary fiber from potato processing byproducts. This method should not simply pursue the total extraction yield, but rather enable the pretreatment of wet potato starch processing residue under relatively mild conditions. Through subsequent segmented hot water extraction and graded recovery, hot water soluble dietary fiber fractions corresponding to different hot water extraction stages can be obtained, thereby improving the precision and applicability of resource utilization of potato starch processing residue. Summary of the Invention

[0007] In view of this, the present invention proposes a graded preparation method for hot-water soluble dietary fiber from potato processing byproducts. This method uses wet potato starch processing residue as the main processing target, and combines carbon dioxide aqueous phase pressure treatment, segmented pressure reduction treatment, sequential hot water extraction, and graded alcohol precipitation recovery. This allows the hot-water soluble dietary fiber in the wet potato starch processing residue to enter different extracts according to different hot water extraction stages, thereby obtaining multiple fractions of hot-water soluble dietary fiber.

[0008] In this invention, the hot water soluble dietary fiber refers to the soluble dietary fiber component obtained by extracting wet potato starch processing residue into an aqueous phase at 50–95°C, followed by concentration, ethanol precipitation, separation, and drying. The hot water soluble dietary fiber may contain small amounts of protein, ash, residual sugars, or other accompanying components that enter the product during aqueous phase extraction.

[0009] The technical solution of this invention is achieved as follows: This invention provides a method for graded preparation of hot water soluble dietary fiber, a byproduct of potato processing, comprising the following steps: Wet potato starch processing residue is mixed with water to obtain a by-product slurry. The by-product slurry is placed in a sealed container, and carbon dioxide is introduced into the container. The mixture is then pressurized at 0.4–1.0 MPa and 35–50°C for 20–40 minutes. After pressurization, the sealed container is depressurized in stages, followed by solid-liquid separation. The resulting liquid phase is collected separately and is not used as the first, second, or third extract. The solids are collected. The obtained solids are mixed with water and extracted at 50–60°C for 20–60 minutes. The first extract and the first residue were obtained by separation. The first residue was mixed with water and extracted at 65-75°C for 30-90 min, followed by solid-liquid separation to obtain the second extract and the second residue. The second residue was mixed with water and extracted at 80-95°C for 30-120 min, followed by solid-liquid separation to obtain the third extract. The first extract, the second extract, and the third extract were concentrated, precipitated with alcohol, separated, and dried to obtain the first hot water soluble dietary fiber fraction, the second hot water soluble dietary fiber fraction, and the third hot water soluble dietary fiber fraction.

[0010] In this invention, the carbon dioxide pressure treatment is performed before the hot water fractional extraction, and the resulting liquid phase is not used as the first, second, or third extract. In other words, this invention does not use the carbon dioxide aqueous phase treatment stage as the direct extraction stage for the target hot water soluble dietary fiber fraction. Instead, it connects the carbon dioxide aqueous phase treatment, fractional pressure reduction, solid-liquid separation, and subsequent three-stage hot water extraction, using the solids as the subsequent extraction target. This sequence of steps helps distinguish it from simple direct carbon dioxide extraction, carbon dioxide explosion modification, one-time high-temperature hot water extraction, or conventional acidification extraction.

[0011] In some embodiments, a pre-washing step is included before preparing the by-product slurry: the wet potato starch processing residue is mixed with water and washed with stirring at 20–40°C for 5–20 minutes, followed by solid-liquid separation; the pre-washing step is repeated 1–3 times. This pre-washing step is mainly used to remove free starch, silt, free sugars, and some low-molecular-weight soluble impurities, preventing these impurities from entering the first extract in large quantities during the subsequent low-temperature hot water extraction stage. The pre-washing step uses a lower temperature and a shorter time and is not considered a primary extraction step for hot water-soluble dietary fiber.

[0012] In some embodiments, the ratio of wet potato starch processing residue to water is 1:8 to 1:25 based on the dry weight of the residue; the solid content of the by-product slurry is 4% to 12%. Since the moisture content of wet potato starch processing residue varies significantly between different batches, using a dry weight to calculate the liquid-to-residue ratio helps reduce the impact of moisture content differences between batches on carbon dioxide treatment and subsequent hot water extraction. Controlling the solid content within the above range ensures the slurry has stirability and mass transferability, while avoiding an excessively thin system that would lead to an excessive burden on subsequent concentration.

[0013] In some embodiments, after carbon dioxide is introduced into the byproduct slurry, the pH of the slurry is 4.2–5.8. By creating a slightly acidic environment through the dissolution of carbon dioxide in the aqueous phase, the slurry state can be adjusted without the addition of strong acid. This pH range facilitates integration with subsequent hot water extraction conditions and helps prevent excessive degradation of polysaccharide components under strong acid conditions. This feature is used to define the extent of carbon dioxide aqueous phase treatment, rather than setting the carbon dioxide treatment stage as the direct extraction stage of the target fraction.

[0014] In some embodiments, the carbon dioxide pressure holding treatment is carried out at a pressure of 0.4–1.0 MPa, a temperature of 35–50°C, and a time of 20–40 min. Compared to higher-pressure carbon dioxide explosion or puffing treatments, the above treatment conditions are medium-to-low pressure aqueous phase pressure holding treatments, and the treatment target is an aqueously dispersed by-product slurry. This condition setting is easy to implement in food processing equipment and also facilitates continuous connection with subsequent staged depressurization and hot water extraction steps.

[0015] In some embodiments, the staged depressurization includes at least two depressurization stages, each with a depressurization rate of 0.05–0.5 MPa / min, and a holding period of 1–5 minutes after each stage. Using staged depressurization instead of direct rapid venting allows the slurry to gradually transition to atmospheric pressure after pressure holding. This step, serving as a transition between carbon dioxide aqueous phase treatment and hot water extraction, facilitates the formation of repeatable process conditions and is easier to control in production or pilot-scale equipment.

[0016] In some embodiments, the pressure holding and segmented depressurization processes are repeated 2-3 times; after each segmented depressurization, solid-liquid separation is performed, and the solids are remixed with water before entering the next pressure holding process. After the repetition, the resulting solids are used for the first stage of hot water extraction. This cyclical approach increases the contact process of the carbon dioxide aqueous phase treatment without increasing the pressure of each treatment cycle. Solid-liquid separation after each cycle removes some free impurities and low-molecular-weight soluble substances, reducing their impact on the subsequent first extract. This cyclical treatment method is optional and can be selected based on the residual starch content, soluble solids content, and processing conditions of the raw material.

[0017] In some embodiments, the first stage of hot water extraction is performed at a temperature of 50–60°C for 20–60 minutes; the second stage at 65–75°C for 30–90 minutes; and the third stage at 80–95°C for 30–120 minutes. The three extraction stages are conducted in ascending order of temperature, and solid-liquid separation is performed after each stage, with the residue from the previous stage used as the raw material for the next stage. This sequential processing allows for the separate collection of extracts from different hot water treatment stages, avoiding the mixing of soluble components from different stages into the same extract due to a single high-temperature extraction.

[0018] In some embodiments, during the hot water extraction at each stage, the solid-liquid ratio of the residue to the water is 1:8 to 1:20 based on the dry weight of the potato residue. Using this ratio ensures sufficient dispersion of the material during extraction and facilitates subsequent concentration and alcohol precipitation.

[0019] In some embodiments, the pH of the first, second, and third hot water extraction stages is all 5.0–6.5. This pH range corresponds to the state of the slurry after the aforementioned carbon dioxide aqueous phase treatment, which is suitable for the aqueous phase extraction of hot water-soluble dietary fiber from potato residue in wet potato starch processing, and also facilitates subsequent concentration and alcohol precipitation operations. If necessary, the pH of the extraction system can be adjusted by degassing, water replacement, or using food-grade pH adjusters.

[0020] In some embodiments, the first, second, and third extracts are concentrated to a soluble solids content of 5%–20% before alcohol precipitation. Concentrating each extract beforehand reduces the amount of ethanol used during precipitation and improves precipitation recovery efficiency. Separate concentration and alcohol precipitation of each extract helps maintain the independence of the soluble components obtained at different hot water extraction stages.

[0021] In some embodiments, the first, second, and third extracts undergo alcohol precipitation with different final ethanol concentrations, all of which are volume fractions. Specifically, the final ethanol concentration of the first extract is 75%–85%, the second extract is 65%–80%, and the third extract is 55%–75%. The first extract originates from a lower-temperature hot water extraction stage, while the third extract originates from a higher-temperature hot water extraction stage. The proportions of soluble components and accompanying impurities may differ in the different extracts. Therefore, setting separate final ethanol concentrations facilitates precipitation and recovery of each extract under appropriate conditions. These differentiated alcohol precipitation conditions, combined with the aforementioned segmented hot water extraction, prevent the use of uniform alcohol precipitation conditions from causing the recovery processes in different extraction stages to converge.

[0022] In some embodiments, the precipitate obtained after alcohol precipitation is washed with ethanol, dried at 40–70°C, and pulverized to 60–120 mesh. The drying can be performed by hot air drying, vacuum drying, freeze drying, or spray drying. The drying and pulverizing steps are used to obtain a hot water-soluble dietary fiber fraction product that is easy to store, transport, and subsequently use.

[0023] In some embodiments, the obtained first, second, and third hot water soluble dietary fiber fractions can be tested for soluble dietary fiber content, residual starch content, reducing sugar content, uronic acid content, apparent viscosity, water-holding capacity, glucose adsorption capacity, or bile salt adsorption capacity, respectively. These tests are not essential preparation steps in this method, but can be used to evaluate the compositional and functional differences between the different fractions and to provide a basis for subsequent food ingredient applications or process optimization.

[0024] The present invention has the following advantages over the prior art: This invention uses wet potato starch processing residue as raw material. Before hot water extraction, it incorporates carbon dioxide aqueous phase pressure treatment and segmented pressure reduction treatment. Furthermore, it employs a three-stage hot water extraction process from low to high pressure, followed by separate alcohol precipitation for recovery. This transforms the preparation of hot-water soluble dietary fiber from a conventional one-time mixed extraction to a sequential, fractional preparation. This method avoids strong acid / alkali treatment, extrusion puffing, or complex column separation equipment. The process steps are well-integrated with conventional production conditions such as wet potato residue processing, solid-liquid separation, concentration, alcohol precipitation, and drying. Through the combination of pre-washing, carbon dioxide pressure treatment, segmented pressure reduction, three-stage hot water extraction, and differentiated alcohol precipitation, this invention can obtain soluble dietary fiber fractions corresponding to different stages of hot water extraction. This improves the precision of resource utilization of wet potato starch processing residue and provides a foundation for subsequent food ingredient development based on the composition and functional characteristics of different fractions. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. Unless otherwise stated, the percentage content mentioned in the following embodiments are all mass percentages; the final ethanol concentrations are all volume fractions; and the material-liquid ratios are all calculated based on the dry basis mass of potato residue from wet potato starch processing.

[0026] In the following embodiments, the raw material is wet potato residue produced during potato starch processing. Its moisture content is measured before use, and the feed amount is calculated based on dry weight. The water is food processing water; the carbon dioxide is food-grade carbon dioxide; and the ethanol is ethanol used for food processing or testing. Solid-liquid separation can be carried out by filtration, centrifugation, or sedimentation, and the specific method can be selected according to the particle size of the raw material and equipment conditions.

[0027] I. Detection Methods To facilitate the evaluation of the preparation effects of products obtained from different implementation methods, the following tests can be performed using the following methods. Unless otherwise specified, each test item is measured in triplicate, and the results are expressed as mean ± standard deviation.

[0028] 1. Yield determination After drying each fraction to constant weight, weigh them and calculate the yield using the following formula: Yield (%) = Dry weight of each grade / Dry weight of potato residue from wet potato starch processing × 100%.

[0029] The first hot water soluble dietary fiber grade is denoted as F1-SDF, the second hot water soluble dietary fiber grade is denoted as F2-SDF, and the third hot water soluble dietary fiber grade is denoted as F3-SDF.

[0030] 2. Determination of soluble dietary fiber content Take the sample to be tested and perform the detection according to the enzymatic gravimetric method for the determination of dietary fiber in food. During the detection process, the sample is treated with heat-resistant α-amylase, protease, and saccharifying enzyme to remove digestible starch and protein. The soluble dietary fiber in the resulting enzymatic hydrolysate is precipitated with ethanol, filtered, washed, dried, and weighed. The soluble dietary fiber content is calculated after deducting protein and ash. A blank control is set up for the same batch of tests.

[0031] 3. Determination of residual starch content The samples to be tested were subjected to starch hydrolysis treatment, and the glucose content released was determined. The residual starch content was then calculated. All examples and comparative examples were compared using the same detection method.

[0032] 4. Determination of reducing sugar content Take the aqueous solution of the sample to be tested and determine the reducing sugar content using the 3,5-dinitrosalicylic acid colorimetric method. Establish a standard curve using glucose as the standard. The results are expressed as the dry weight of the sample.

[0033] 5. Determination of uronic acid content Take the aqueous solution of the sample to be tested and determine the uronic acid content using the carbazole-sulfuric acid colorimetric method. Establish a standard curve using galacturonic acid as the standard. The results are expressed as the dry weight of the sample.

[0034] 6. Apparent viscosity determination The analyte was prepared into a 2.0% (w / w) aqueous solution and fully hydrated at 25°C for 12 hours. The apparent viscosity was then measured using a rotational viscometer at 25°C and 60 r / min, and the readings were recorded after stabilization. All samples were measured using the same rotor, rotational speed, and hydration time.

[0035] 7. Water-holding capacity measurement Weigh 0.50 g of the dried sample, add 25 mL of water, and allow it to hydrate at 25 °C for 2 h. Then centrifuge at 4000 r / min for 10 min, discard the supernatant, weigh the mass of the precipitate after centrifugation, and calculate the water-holding capacity using the following formula: Water holding capacity (g / g) = mass of precipitate after centrifugation / mass of dried sample.

[0036] 8. Glucose adsorption capacity determination Weigh 0.50 g of the sample to be tested and add it to 25 mL of glucose solution with a concentration of 50 mmol / L. Incubate at 37 °C with shaking for 2 h, then centrifuge at 4000 r / min for 10 min and measure the glucose concentration in the supernatant. Calculate the glucose adsorption capacity of the sample based on the difference in glucose concentration before and after incubation.

[0037] 9. Determination of bile salt adsorption capacity Weigh 0.50 g of the sample to be tested and add it to 25 mL of sodium cholate solution with a concentration of 2.0 mg / mL. Adjust the pH of the system to 7.0 and incubate it with shaking at 37 °C for 2 h. Then, centrifuge it at 4000 r / min for 10 min and measure the sodium cholate concentration in the supernatant. Calculate the cholate adsorption capacity of the sample based on the difference in sodium cholate concentration before and after incubation.

[0038] 10. Evaluation of graded differences To evaluate the differences between F1-SDF, F2-SDF, and F3-SDF obtained under different treatment methods, at least three of the following indicators can be compared: soluble dietary fiber content, uronic acid content, apparent viscosity, glucose adsorption capacity, and bile salt adsorption capacity. This evaluation is not a necessary condition for the preparation steps, but only to illustrate the degree of difference between fractions obtained under different process conditions.

[0039] II. Example 1 This embodiment provides a method for graded preparation of hot water soluble dietary fiber, a byproduct of potato processing, comprising the following steps.

[0040] (1) Take wet potato starch residue, determine the moisture content and measure it in 100 parts by dry weight. Add water to the residue, stir and wash at 30°C for 10 min, and separate the solid and liquid. Repeat the washing once and collect the solids after washing.

[0041] (2) The washed solids were mixed with water, and the material-to-liquid ratio was controlled at 1:15 based on the dry weight of potato residue to obtain a by-product slurry. The solids content of the by-product slurry was 6.7%. The by-product slurry was placed in a sealed pressure-resistant container, and food-grade carbon dioxide was introduced to raise the pressure inside the container to 0.6 MPa. The pressure was maintained at 45°C for 30 minutes. At the end of the pressure maintenance, the pH of the slurry was measured, and the result was 5.2.

[0042] (3) After the pressure holding period, the pressure is reduced in stages: from 0.6 MPa to 0.4 MPa at a rate of 0.1 MPa / min and held for 3 min; then reduced to 0.2 MPa at a rate of 0.1 MPa / min and held for 3 min; finally reduced to atmospheric pressure at a rate of 0.1 MPa / min. After the pressure reduction is completed, solid-liquid separation is performed. The resulting liquid phase is collected separately and is not used as the first, second, or third extract. The solids are collected.

[0043] (4) Mix the solids obtained in step (3) with water, with a material-to-liquid ratio of 1:12 based on the dry weight of potato residue, extract at 55°C for 40 min, and separate the solids and liquids to obtain the first extract and the first residue.

[0044] (5) Mix the first residue with water, with a material-to-liquid ratio of 1:12 based on the dry weight of potato residue, extract at 70°C for 60 min, and separate the solid and liquid to obtain the second extract and the second residue.

[0045] (6) Mix the second residue with water, with a material-to-liquid ratio of 1:12 based on the dry weight of potato residue, extract at 90°C for 60 min, and separate the solid and liquid to obtain the third extract.

[0046] (7) Concentrate the first, second, and third extracts to a soluble solids content of 10%–15%, respectively. Add ethanol to the first extract concentrate to a final ethanol concentration of 80%; add ethanol to the second extract concentrate to a final ethanol concentration of 75%; add ethanol to the third extract concentrate to a final ethanol concentration of 65%. After alcohol precipitation, centrifuge each concentrate and collect the precipitate.

[0047] (8) Each precipitate was washed with ethanol, then dried at 55°C to constant weight, and pulverized through an 80-mesh sieve to obtain F1-SDF, F2-SDF and F3-SDF.

[0048] III. Example 2 The difference between this embodiment and Embodiment 1 is that in step (2), the carbon dioxide holding pressure is 0.4 MPa, the holding temperature is 40°C, and the holding time is 30 min; in step (3), the pressure is reduced from 0.4 MPa to 0.2 MPa at a rate of 0.1 MPa / min and held for 3 min, and then reduced to atmospheric pressure at a rate of 0.1 MPa / min. The remaining steps are the same as in Embodiment 1.

[0049] The pH of the slurry was measured at the end of the pressure holding period, and the result was 5.5.

[0050] IV. Example 3 The difference between this embodiment and Embodiment 1 is that in step (2), the carbon dioxide holding pressure is 1.0 MPa, the holding temperature is 45°C, and the holding time is 30 min; in step (3), the pressure is successively reduced from 1.0 MPa to 0.7 MPa, 0.4 MPa, and 0.2 MPa at a rate of 0.1 MPa / min, each pressure stage is maintained for 3 min, and finally reduced to atmospheric pressure at a rate of 0.1 MPa / min. The remaining steps are the same as in Embodiment 1.

[0051] The pH of the slurry was measured at the end of the pressure holding period, and the result was 4.5.

[0052] V. Example 4 The difference between this embodiment and Embodiment 1 is that the carbon dioxide pressure treatment and the segmented depressurization treatment are performed in two cycles. After the first cycle, solid-liquid separation is performed, and the resulting liquid phase is collected separately and is not used as the first, second, or third extract. Water is added to the solids to make the material-to-liquid ratio 1:15 based on the dry weight of potato residue, and the second cycle is performed. In each cycle, the carbon dioxide pressure is 0.6 MPa, the pressure holding temperature is 45°C, and the pressure holding time is 20 min. The segmented depressurization method is the same as in Embodiment 1. After the second cycle, the solids obtained are used for the first stage of hot water extraction. The remaining steps are the same as in Embodiment 1.

[0053] The slurry pH was 5.3 at the end of the first cycle of pressure holding; the slurry pH was 5.1 at the end of the second cycle of pressure holding.

[0054] VI. Example 5 The difference between this embodiment and Embodiment 1 is that in step (4), the first stage of hot water extraction temperature is 50℃ and the extraction time is 60min; in step (5), the second stage of hot water extraction temperature is 65℃ and the extraction time is 90min; and in step (6), the third stage of hot water extraction temperature is 80℃ and the extraction time is 120min. The remaining steps are the same as in Embodiment 1.

[0055] VII. Example 6 The difference between this embodiment and Embodiment 1 is that in step (4), the first stage of hot water extraction temperature is 60℃ and the extraction time is 20min; in step (5), the second stage of hot water extraction temperature is 75℃ and the extraction time is 30min; and in step (6), the third stage of hot water extraction temperature is 95℃ and the extraction time is 30min. The remaining steps are the same as in Embodiment 1.

[0056] VIII. Example 7 The difference between this embodiment and Embodiment 1 is that in step (7), the final ethanol concentration of the first extract is 85%, the final ethanol concentration of the second extract is 80%, and the final ethanol concentration of the third extract is 75%. The remaining steps are the same as in Embodiment 1.

[0057] IX. Example 8 The difference between this embodiment and Embodiment 1 is that in step (7), the final ethanol concentration of the first extract is 75%, the final ethanol concentration of the second extract is 65%, and the final ethanol concentration of the third extract is 55%. The remaining steps are the same as in Embodiment 1.

[0058] 10. Comparative Example 1 This comparative example demonstrates a three-stage extraction method for ordinary hot water.

[0059] Take wet potato starch processing residue from the same batch as in Example 1 and pre-wash it according to step (1) of Example 1. After pre-washing, do not perform carbon dioxide pressure treatment or segmented pressure reduction treatment, but directly perform three-stage hot water extraction, differentiated alcohol precipitation, drying and pulverization according to steps (4) to (8) of Example 1 to obtain the corresponding F1-SDF, F2-SDF and F3-SDF.

[0060] XI. Comparative Example 2 This comparative example uses the same pH acidification treatment method.

[0061] Take wet potato starch processing residue from the same batch as in Example 1 and pre-wash it according to step (1) of Example 1. Mix the washed solids with water, control the material-to-liquid ratio to be 1:15 based on the dry weight of the potato residue, and adjust the pH of the slurry to be the same as the pH of the slurry at the end of the carbon dioxide pressure treatment in Example 1, i.e., pH 5.2, using citric acid. Stir at 45°C for 30 minutes. After the treatment, perform solid-liquid separation. Collect the obtained liquid phase separately and do not use it as the first, second, or third extract. Collect the solids and then perform three-stage hot water extraction, differentiated alcohol precipitation, drying, and pulverization according to steps (4) to (8) of Example 1.

[0062] 12. Comparative Example 3 This comparative example demonstrates a rapid venting method after carbon dioxide pressure is maintained.

[0063] Wet potato starch processing residue from the same batch as in Example 1 was taken and pre-washed and subjected to carbon dioxide pressure treatment according to steps (1) and (2) of Example 1. After the pressure treatment was completed, instead of staged depressurization, the pressure was directly vented to atmospheric pressure within 3 minutes. Subsequently, solid-liquid separation was performed, and the resulting liquid phase was collected separately and not used as the first, second, or third extract. The solids were collected and then subjected to three-stage hot water extraction, differentiated alcohol precipitation, drying, and pulverization according to steps (4) to (8) of Example 1.

[0064] Thirteen, Comparative Example 4 This comparative example demonstrates a one-time high-temperature hot water extraction method.

[0065] Wet potato starch processing residue from the same batch as in Example 1 was pre-washed, subjected to carbon dioxide pressure treatment, and subjected to segmented depressurization treatment according to steps (1) to (3) of Example 1. Subsequently, instead of performing three-stage hot water extraction, the solids obtained in step (3) were mixed with water and extracted at 90°C for 120 min, followed by solid-liquid separation to obtain a one-time high-temperature extract. The one-time high-temperature extract was concentrated to a soluble solids content of 10%–15%, and ethanol was added until the final ethanol concentration was 75%. After alcohol precipitation, separation, drying, and pulverization, mixed hot water soluble dietary fiber was obtained.

[0066] XIV. Comparative Example 5 This comparative example uses a unified alcohol precipitation method.

[0067] Wet potato starch processing residue from the same batch as in Example 1 was taken and pre-washed, subjected to carbon dioxide pressure treatment, staged depressurization, and three-stage hot water extraction according to steps (1) to (6) of Example 1. Subsequently, the first extract, the second extract, and the third extract were concentrated to a soluble solids content of 10% to 15%, but all three were precipitated with 75% ethanol to a final concentration. The remaining drying and pulverizing steps were the same as in Example 1.

[0068] XV. Results Recording The fractions obtained from each embodiment and comparative example were tested according to the aforementioned detection method, and the results are recorded below. The data in the table are the average value and standard deviation of at least three parallel tests.

[0069] Table 1. Scoring rates at each level under different processing methods

[0070] Table 2. Composition indicators of each grade obtained in Example 1

[0071] Table 3 Functional indicators of each level obtained in Example 1

[0072] Table 4A Original index data of each level in Example 1 and the main comparative examples

[0073] Table 4 Comparison of grading effects between Example 1 and the main comparative example

[0074] Table 5 Comparison of Differentiated Alcohol Precipitation and Uniform Alcohol Precipitation

[0075] As shown in Table 1, the total yield of Example 1 was 17.21%, which was higher than that of Comparative Example 1 (13.82%), Comparative Example 2 (14.31%), and Comparative Example 3 (15.47%). This indicates that the combination of carbon dioxide aqueous phase pressure holding treatment, segmented pressure reduction treatment, and subsequent three-stage hot water extraction is beneficial to improving the recovery effect of hot water soluble dietary fiber fractions from wet potato starch processing residue. The total yields of Examples 3 and 4 were 18.28% and 18.81%, respectively, indicating that within the scope of this invention, increasing the carbon dioxide pressure or using a recycling process can still yield the corresponding hot water soluble dietary fiber fractions.

[0076] As shown in Tables 2 and 3, the F1-SDF, F2-SDF, and F3-SDF obtained in Example 1 differed in terms of soluble dietary fiber content, residual starch content, reducing sugar content, uronic acid content, apparent viscosity, water-holding capacity, glucose adsorption capacity, and bile salt adsorption capacity. Specifically, the soluble dietary fiber content and uronic acid content of F1-SDF, F2-SDF, and F3-SDF increased sequentially, while the residual starch content and reducing sugar content decreased sequentially, indicating that the fractions obtained from different hot water extraction stages were distinguishable in composition. Furthermore, the three fractions also exhibited different levels of apparent viscosity, water-holding capacity, glucose adsorption capacity, and bile salt adsorption capacity.

[0077] As shown in Tables 4A and 4, compared with ordinary hot water three-stage extraction (Comparative Example 1), pH acidification treatment (Comparative Example 2), rapid venting treatment after carbon dioxide pressure holding (Comparative Example 3), and uniform alcohol precipitation treatment (Comparative Example 5), the F1-SDF, F2-SDF, and F3-SDF obtained in Example 1 exhibited clearer fractional differences in soluble dietary fiber content, uronic acid content, apparent viscosity, glucose adsorption capacity, and bile salt adsorption capacity (ranges of 8.4%, 7.5%, 127 mPa·s, 6.1 mg / g, and 8.1 mg / g, respectively), all significantly better than the comparative examples. These results indicate that the carbon dioxide aqueous phase pressure holding, segmented pressure reduction, sequential hot water extraction, and differentiated alcohol precipitation described in this invention have a process synergy, and are not simply a parallel superposition of carbon dioxide treatment, hot water extraction, and alcohol precipitation.

[0078] Table 5 shows that the purity of F1-SDF, F2-SDF, and F3-SDF obtained by differentiated alcohol precipitation treatment is higher than that of the corresponding fractions obtained by uniform alcohol precipitation treatment, and the reducing sugar content is lower than that of the corresponding fractions obtained by uniform alcohol precipitation treatment. This result indicates that using different final ethanol concentrations for alcohol precipitation of extracts from different hot water extraction stages helps reduce the entrainment of impurities such as low-molecular-weight sugars and maintains the differences between the fractions obtained from different extraction stages.

Claims

1. A method for graded preparation of hot water-soluble dietary fiber, a byproduct of potato processing, characterized in that, Includes the following steps: (1) Mix wet potato starch processing residue with water to obtain by-product slurry; (2) Place the by-product slurry in a sealed container, introduce carbon dioxide into the sealed container, and maintain pressure for 20 to 40 minutes at 0.4 to 1.0 MPa and 35 to 50°C. (3) After the pressure holding process is completed, the sealed container is depressurized in stages, and solid-liquid separation is performed after depressurization. The resulting liquid phase is collected separately and is not used as the first extract, second extract or third extract. The solids are collected. (4) Mix the solid obtained in step (3) with water and extract at 50-60°C for 20-60 min. Separate the solid and liquid to obtain the first extract and the first residue. (5) Mix the first residue with water and extract at 65-75°C for 30-90 min. Separate the solid and liquid to obtain the second extract and the second residue. (6) Mix the second residue with water and extract at 80-95℃ for 30-120 min, then separate the solid and liquid to obtain the third extract; (7) The first extract, the second extract and the third extract are concentrated, precipitated with alcohol, separated and dried respectively to obtain the first hot water soluble dietary fiber fraction, the second hot water soluble dietary fiber fraction and the third hot water soluble dietary fiber fraction.

2. The graded preparation method according to claim 1, characterized in that, Before step (1), a pre-washing step is also included: the wet potato starch processing residue is mixed with water and stirred and washed at 20-40°C for 5-20 minutes, followed by solid-liquid separation; the pre-washing step is repeated 1-3 times.

3. The graded preparation method according to claim 1, characterized in that, In step (1), the ratio of wet potato starch processing residue to water is 1:8 to 1:25 based on the dry weight of the potato residue; the solid content of the by-product slurry is 4% to 12%.

4. The graded preparation method according to claim 1, characterized in that, In step (2), the pH of the byproduct slurry after carbon dioxide is introduced is 4.2 to 5.

8.

5. The graded preparation method according to claim 1, characterized in that, In step (3), the segmented pressure reduction includes at least two pressure reduction stages, with a pressure reduction rate of 0.05 to 0.5 MPa / min for each stage, and a holding period of 1 to 5 minutes after each pressure reduction stage.

6. The graded preparation method according to claim 1, characterized in that, Steps (2) and (3) are repeated 2 to 3 times; after each segmented depressurization, solid-liquid separation is performed, and the solid is taken and mixed with water again before entering the next pressure holding process. After the repetition is completed, the obtained solid is used in step (4).

7. The graded preparation method according to claim 1, characterized in that, In steps (4), (5) and (6), the ratio of solids or residue to water is 1:8 to 1:20 based on the dry weight of potato residue.

8. The graded preparation method according to claim 1, characterized in that, In step (7), the alcohol precipitation is carried out using ethanol, and the final concentration of ethanol is a volume fraction; wherein, the final concentration of ethanol in the first extract is 75% to 85%, the final concentration of ethanol in the second extract is 65% to 80%, and the final concentration of ethanol in the third extract is 55% to 75%.

9. The graded preparation method according to claim 1, characterized in that, In step (7), before alcohol precipitation, the first extract, the second extract and the third extract are concentrated to a soluble solids content of 5% to 20%.

10. The graded preparation method according to claim 1, characterized in that, In step (7), the precipitate obtained after alcohol precipitation is washed with ethanol, dried at 40-70°C, and pulverized to 60-120 mesh.

Images