Apple pomace water-soluble dietary fiber powder based on subcritical water extraction and preparation method thereof

Abstract

The application discloses apple residue water-soluble dietary fiber powder based on subcritical water extraction and a preparation method thereof, and belongs to the technical field of high-value utilization of agricultural product by-products and functional food ingredients. The water-soluble dietary fiber powder prepared by the application is mainly composed of pectin polysaccharide and fiber oligosaccharide, wherein the pectin polysaccharide is mainly composed of galacturonic acid, arabinose, galactose and rhamnose, the main peak molecular weight is distributed in 1.60*10 5 ~2.00*10 5 Da according to different extraction conditions; and the fiber oligosaccharide component is mainly composed of glucose. Experiments show that the dietary fiber powder has good prebiotic potential and is suitable for preparing food or beverage with potential prebiotic function.

Description

Technical Field

[0001] This invention belongs to the field of high-value utilization of agricultural by-products and functional food ingredients, specifically involving a water-soluble dietary fiber powder of apple pomace based on subcritical water extraction and its preparation method. Background Technology

[0002] As one of the world's most abundant fruits, apples generate a large amount of byproducts—apple pomace—during processing such as juice production and canning. This pomace accounts for approximately one-quarter to one-third of the total apple raw material and is rich in pectin, cellulose, hemicellulose, and polyphenols, representing a biomass resource with significant development potential. However, currently, the vast majority of apple pomace is not utilized efficiently, often being discarded directly or used only as low-value animal feed. This not only leads to resource waste but may also cause accumulated environmental pressure. Therefore, achieving high-value comprehensive utilization of apple pomace, especially transforming it into food ingredients with clearly defined health benefits, has become a key focus in the fields of agricultural product processing and food science.

[0003] Among the various components of apple pomace, water-soluble dietary fiber is highly valued due to its excellent solubility, prebiotic potential, and thickening and stabilizing properties in food systems. Traditional methods for extracting soluble fiber from apple pomace mainly include acid extraction, hot water extraction, alkaline extraction, and, in recent years, enzymatic extraction, microwave-assisted extraction, and ultrasound-assisted extraction. These methods generally aim to increase the yield of a single target component, and their processes often rely on empirical parameter settings, lacking systematic and targeted control of key conditions during the extraction process.

[0004] Among various novel extraction technologies, microwave and ultrasound-assisted extraction, while improving extraction efficiency, typically suffer from high equipment costs, high energy consumption, and difficulties in controlling uniformity during large-scale production. In contrast, subcritical water extraction technology, as a green and efficient method, is gradually gaining attention. This technology uses water as a solvent and extracts at temperatures and pressures above the boiling point but below the critical point. It is not only environmentally friendly, but also allows for significant changes in the polarity, dielectric constant, and ion product of water under subcritical conditions, simultaneously achieving catalytic degradation similar to acids or bases. This efficiently disrupts plant cell walls and promotes the dissolution of target components.

[0005] However, several technical challenges remain when using high-temperature, high-pressure water-based treatment to prepare water-soluble dietary fiber from apple pomace. Apple pomace has a complex composition, containing polysaccharides such as pectin, cellulose, and hemicellulose, as well as polyphenols, proteins, and other soluble impurities. During treatment, cell wall disruption, dissolution of target components, and polysaccharide chain degradation often occur simultaneously. If the treatment conditions are too harsh, excessive degradation of water-soluble dietary fiber such as pectin can occur, leading to a decrease in molecular weight, changes in structural composition, and even problems such as increased browning, increased impurity release, and difficulties in subsequent separation and purification. Conversely, if the treatment conditions are too weak, insufficient cell wall disruption, inadequate dissolution of target components, and low yield may result. Furthermore, apple pomace treatment is prone to problems such as large variations in system viscosity, difficulties in solid-liquid separation, and insufficient product composition stability, which in turn affect the consistency and application performance of the resulting water-soluble dietary fiber product.

[0006] Therefore, there is a need in the field for a method that can directionally prepare water-soluble dietary fiber components with specific molecular structures from apple pomace and match their prebiotic activity or food processing suitability by precisely controlling the extraction conditions. Summary of the Invention

[0007] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0008] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0009] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing apple pomace water-soluble dietary fiber powder based on subcritical water extraction.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing apple pomace water-soluble dietary fiber powder based on subcritical water extraction, characterized in that it includes: The apple pomace is dried, crushed, and sieved to obtain apple pomace powder; Apple pomace powder and water were mixed at a material-to-liquid ratio of 1:10 to 1:20 (g / mL), the pH of the system was adjusted to 3.5 to 4.5, and subcritical water extraction was carried out at 100 to 120℃ for 1 to 2 h to obtain the extract. The extract is subjected to solid-liquid separation, the filtrate or supernatant is collected, and concentrated to 1 / 4 to 1 / 5 of the original volume to obtain a concentrated solution; The concentrate was dried to obtain apple pomace water-soluble dietary fiber powder; The apple pomace water-soluble dietary fiber powder contains pectin polysaccharides and fiber oligosaccharides.

[0011] In a preferred embodiment of the preparation method described in this invention, the apple pomace is dried, pulverized, and sieved, wherein the drying temperature is 55–65°C, and the sieving is performed through a 70–90 mesh sieve.

[0012] In a preferred embodiment of the preparation method described in this invention, the pH of the system is 3.8 to 4.2.

[0013] In a preferred embodiment of the preparation method described in this invention, the subcritical water extraction temperature is 110–120°C.

[0014] In a preferred embodiment of the preparation method described in this invention, the solid-liquid separation is performed by filtration, centrifugation, or a combination of filtration and centrifugation.

[0015] As a preferred embodiment of the preparation method described in this invention, the concentrated liquid is dried, wherein the drying is freeze-drying; the pre-freezing temperature is not higher than -40°C, the cold trap temperature is not higher than -50°C, and the vacuum degree is not higher than 10 Pa.

[0016] Another objective of this invention is to overcome the shortcomings of the prior art and provide an apple pomace water-soluble dietary fiber powder, characterized in that: the apple pomace water-soluble dietary fiber powder is prepared by the above-described method and contains pectin polysaccharide components and fiber oligosaccharide components.

[0017] As a preferred embodiment of the apple pomace water-soluble dietary fiber powder of the present invention, wherein the uronic acid content of the dietary fiber powder is not less than 45%.

[0018] In a preferred embodiment of the apple pomace water-soluble dietary fiber powder of the present invention, the main peak molecular weight of the alcohol-precipitated pectin polysaccharide component obtained after ethanol fractionation of the dietary fiber powder is 1.60 × 10⁻⁶. 5 ~2.00×10 5 Da.

[0019] Another objective of this invention is to overcome the shortcomings of the prior art and provide an application of apple pomace water-soluble dietary fiber powder in the preparation of food, beverages, solid beverages, nutritional preparations, functional ingredients, or food ingredients used to promote the growth of Lactobacillus rhamnosus.

[0020] Beneficial effects of this invention: (1) The method for preparing dietary fiber powder of the present invention includes: drying and pulverizing apple pomace, extracting it with subcritical water under specific pH conditions, and then separating, concentrating and drying it to obtain water-soluble dietary fiber powder; further, the pectin polysaccharide and fiber oligosaccharide components can be separated and analyzed by alcohol precipitation fractionation.

[0021] Extraction conditions not only affect the total yield of water-soluble dietary fiber from apple pomace, but also significantly regulate the distribution between pectin polysaccharide components and fiber oligosaccharide components. Among them, milder or near-neutral conditions are more conducive to obtaining a higher total yield and retaining neutral sugars, while weakly acidic conditions are more conducive to the enrichment of pectin components.

[0022] (2) By synergistically optimizing the temperature and pH of the subcritical water extraction process, this invention achieves efficient extraction of natural water-soluble dietary fiber components from apple pomace while preserving its characteristic complex structure.

[0023] This method abandons the traditional approach of pursuing a single high-purity component and innovatively prepares a product with "total soluble dietary fiber powder" as its core in a one-step process. This product is a natural complex dietary fiber system composed of pectin polysaccharides and fiber oligosaccharides, with clear synergistic prebiotic potential. It not only has a high yield but also good structural integrity.

[0024] (3) The process of this invention is green and efficient, with a simple process. It does not rely on complex reagents or expensive equipment and is easy to scale up for industrial application. It provides an economical and feasible new way for the high-value utilization of apple pomace and the development of functional foods. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 The effects of each component in Example 1 and commercially available inulin on the proliferation of Lactobacillus rhamnosus are shown. Detailed Implementation

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0027] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0028] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0029] The apple pomace used in this embodiment of the invention is sourced from Yantai Xingnong Juice Food Co., Ltd.

[0030] The testing methods used in the embodiments of this invention are as follows: (1) Determination of molecular weight of pectin The molecular weight of pectin polysaccharides was determined using a Waters 1525 series high performance liquid chromatography system equipped with a differential refractive index detector (2410, Waters) and an Ultrahydrogel™ Linear 250 column (7.8 mm × 300 mm, 6 µm particle size) (Waters, Milford, MA, USA).

[0031] 50 mg of pectin was dissolved in 10 mL of ultrapure water, filtered through a 0.22 μm aqueous membrane, and then injected. The chromatographic conditions were: mobile phase 0.1 mol / L NaNO3; flow rate 0.5 mL / min; column temperature 40℃; injection volume 10 μL; analysis time 30 min.

[0032] The relationship between retention time and molecular weight was established using dextran of different molecular weights (200,000 Da, 300,600 Da, 135,030 Da, 9,750 Da, and 2,700 Da) as standards. The apparent molecular weight of each separated peak in the sample was calculated based on the chromatogram. When multiple peaks appeared in the sample, the molecular weights of the main peak and peaks 1 to 3 were recorded respectively. All standards were purchased from the China National Institutes for Food and Drug Control (Beijing, China).

[0033] (2) Determination of monosaccharide composition of pectin The monosaccharide analysis of pectin was performed using a two-step hydrolysis combined with a high-performance anion exchange chromatography system (ICS-5000+SP-5, ThermoFisher, USA). The chromatographic column was a Dionex™ CarboPac PA20 (3 mm × 150 mm), and the detector was a pulsed amperometric detector (PAD).

[0034] Weigh out 3 lyophilized samples, 4.0 mg each, and place them in capped acid-resistant glass hydrolysis tubes; add 4.0 mL of 2 mol / L hydrochloric acid-methanol solution to each tube, seal and react at 100 °C for 5 h; after the reaction is complete, cool to room temperature and gently dry in a fume hood to remove methanol and acid.

[0035] Then add 4.0 mL of 2 mol / L trifluoroacetic acid solution to each tube, seal again, and react at 120℃ for 1 h. After the reaction is complete, cool and gently blow dry to remove trifluoroacetic acid. If necessary, add a small amount of methanol to blow dry 1-2 times to help remove residual acid.

[0036] After drying, add an appropriate amount of ultrapure water to fully dissolve the sample, transfer it to a 10 mL volumetric flask and make up to volume. After mixing, filter the solution through a 0.22 μm aqueous filter membrane. The resulting filtrate is used as the sample to be tested, and the final sample concentration is 0.4 mg / mL.

[0037] Chromatographic conditions were as follows: flow rate 0.5 mL / min; column temperature 30℃; injection volume 10 μL. External standards were commercially available monosaccharide standards (L-rhamnose, L-arabinose, L-galactose, galacturonic acid), all purchased from BBI Life Sciences (Shanghai, China).

[0038] (3) Determination of neutral sugar content Neutral sugar content was determined using the phenol-sulfuric acid method, and the specific steps are as follows: Prepare a glucose standard solution with a concentration of approximately 0.1 mg / mL. Take different volumes (0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.5 mL) of the standard solution into glass test tubes, add water to a final volume of 0.5 mL, and mix well.

[0039] 0.5 mL of 6% (w / v) phenol solution and 2.5 mL of concentrated sulfuric acid were added sequentially, and the mixture was vortexed immediately after each addition. The mixture was then allowed to stand at room temperature in the dark for 30 min. Subsequently, the absorbance of each reaction solution was measured at a wavelength of 490 nm using a UV spectrophotometer, and a glucose equivalent-absorbance standard curve was plotted.

[0040] The sample was prepared into a 0.1 mg / mL solution in the same manner, and its absorbance at 490 nm was measured in the same way. The glucose equivalent in the sample was calculated according to the standard curve. Finally, the neutral sugar content was calculated according to the formula "neutral sugar content (%) = glucose equivalent in sample (g) / sample mass (g) × 100%".

[0041] (4) Determination of uronic acid content The determination of uronic acid content uses the sulfuric acid-carbazole method, and the main steps are as follows: First, prepare sodium tetraborate-sulfuric acid solution and 0.15% carbazole ethanol solution, and prepare a galacturonic acid standard solution of approximately 0.1 mg / mL. Accurately pipette 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, and 0.5 mL of the galacturonic acid standard solution and add them to stoppered glass test tubes respectively. Add water to a final volume of 0.5 mL, add 2.5 mL of sodium tetraborate-sulfuric acid solution to an ice bath, mix well, and heat in a boiling water bath for 20 minutes. After cooling, add 0.1 mL of carbazole solution, heat in a boiling water bath again for 20 minutes, and after cooling, measure the absorbance at a wavelength of 523 nm to plot a standard curve. The samples were processed and measured using the same method. The sample concentration was 0.1 mg / mL. The galacturonic acid equivalent was calculated based on the standard curve, and the content was calculated using the formula "galacturonic acid content (%) = galacturonic acid equivalent in sample (g) / sample mass (g) × 100%".

[0042] (5) Determination of total phenol content The total phenol content was determined using the Folin-Ciocalteu method, and the main steps are as follows: Prepare a 0.1 mg / mL gallic acid standard solution. Pipette 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, and 0.4 mL of the standard solution into test tubes, and add water to a final volume of 3 mL. Add 0.25 mL of Folin-Ciocalteu reagent and 0.75 mL of 20% (w / v) sodium carbonate solution sequentially, completing the addition within 1-8 minutes. Finally, add 1 mL of deionized water and mix well.

[0043] The reaction system was heated in a water bath at 40°C for 2 hours in the dark, and then rapidly cooled to room temperature. The absorbance was measured at a wavelength of 760 nm using a UV spectrophotometer, and a standard curve of gallic acid concentration-absorbance was plotted.

[0044] The sample was prepared into a 1 mg / mL solution, and its absorbance at 760 nm was measured using the same method. The gallic acid equivalent in the sample was calculated according to the standard curve, and the content was calculated according to the formula "total phenol content (%) = gallic acid equivalent in sample (g) / sample mass (g) × 100%".

[0045] (6) Protein content determination Protein content was determined using the Coomassie Brilliant Blue G-250 method, and the main steps are as follows: Accurately weigh 1 g of the mixed sample, dilute to 100 mL with water, centrifuge a portion of the solution at 4000 r / min for 15 minutes, and use the supernatant as the test solution; accurately pipette 0.00 mL, 0.03 mL, 0.06 mL, 0.12 mL, 0.24 mL, 0.48 mL, 0.72 mL, 0.84 mL, and 0.96 mL of 0.1 mg / mL bovine serum albumin (BSA) standard solution, and add them to a set of 10 mL colorimetric tubes respectively, and add distilled water to make the total volume of liquid in each tube 1.0 mL.

[0046] Next, add 5.0 mL of Coomassie Brilliant Blue G-250 solution to each colorimetric tube, vortex to mix, let stand for 2 minutes, and then measure the absorbance at 595 nm using a 1 cm cuvette with the reagent blank as a reference. Finally, plot a standard curve of absorbance versus protein concentration.

[0047] The sample was then measured: 0.5 mL of the sample solution was pipetted into a colorimetric tube, 0.5 mL of distilled water and 5 mL of Coomassie Brilliant Blue G-250 solution were added, the mixture was mixed and allowed to stand for 2 minutes, and the absorbance was measured under the same conditions as when the standard curve was prepared. The corresponding protein concentration was then determined based on the standard curve.

[0048] Finally, the calculation is performed: the protein content (X, in g / 100 g) in the sample is calculated according to the formula X=[(c-c0)×V] / (m×1000)×100, where c is the protein concentration of the sample obtained from the standard curve (mg / mL), c0 is the blank concentration (mg / mL), V is the fixed volume of the sample (100 mL), and m is the mass of the sample (g).

[0049] (7) Determination of the growth curve of Lactobacillus rhamnosus The culture medium for Lactobacillus rhamnosus was: tryptone (0.5 g / 100 mL), beef extract (0.25 g / 100 mL), yeast extract (0.2 g / 100 mL), dipotassium hydrogen phosphate (0.2 g / 100 mL), triammonium citrate (0.2 g / 100 mL), sodium acetate (0.5 g / 100 mL), magnesium sulfate (0.02 g / 100 mL), manganese sulfate (0.005 g / 100 mL), Tween 80 (0.1 mL / 100 mL), and different samples (0.2 g / 100 mL).

[0050] Take 100 μL of Lactobacillus rhamnosus activated for three generations in commercial MRS medium, inoculate it into 5 mL of the above medium, take samples every 2 h, measure the absorbance at a wavelength of 600 nm, and plot the growth curve.

[0051] Example 1 This embodiment provides a method for preparing apple pomace water-soluble dietary fiber powder based on subcritical water extraction, including the following steps: (1) Raw material pretreatment: The apple pomace was dried in a 60°C forced-air drying oven until constant weight, then pulverized using a high-speed pulverizer and passed through an 80-mesh standard sieve to obtain dry apple pomace powder, which was then sealed for later use.

[0052] (2) Subcritical water extraction: Accurately weigh 20.00 g of apple pomace powder and place it in a 500 mL Erlenmeyer flask. Add 300 mL of deionized water at a material-to-liquid ratio of 1:15 (g / mL).

[0053] After mixing thoroughly on a magnetic stirrer, adjust the pH of the system to 4.00 ± 0.05 dropwise with 1 M HCl solution. Transfer the mixed suspension to a 500 mL micro-mechanically stirred high-pressure reactor and seal it.

[0054] Set the reaction program as follows: heat to 110℃ at a rate of 5℃ / min, set the stirring speed to 100 rpm, and extract at a constant temperature for 1.5 h.

[0055] (3) Solid-liquid separation and concentration: After the reaction is complete, allow it to cool naturally to room temperature. Filter the reaction solution from step (2) to separate the residue and collect the extract.

[0056] The obtained extract was placed in a rotary evaporator at 55°C and concentrated under reduced pressure to 1 / 5 of its original volume to obtain a concentrated solution.

[0057] (4) Drying and grinding: The concentrate obtained in step (3) was pre-frozen in an ultra-low temperature freezer at -80℃ for 4 h, and then transferred to a freeze dryer and freeze-dried at -50℃ and <10 Pa for 48 h to obtain the product apple pomace total water-soluble dietary fiber powder.

[0058] (5) Alcohol precipitation fractionation: Transfer the concentrate from step (3) to a 250 mL beaker. Under magnetic stirring, slowly add 4 times the volume of pre-cooled anhydrous ethanol to make the ethanol concentration of the system ≥80%. Let the mixture stand in a 4℃ refrigerator for 12 h to allow complete precipitation.

[0059] After standing, centrifuge at 4℃ and 8000 r / min for 15 min, discard the supernatant and collect the precipitate.

[0060] The precipitate was transferred to a petri dish and pre-frozen in an ultra-low temperature freezer at -80℃ for 4 h. Then it was transferred to a freeze dryer and freeze-dried at -50℃ and <10 Pa for 48 h to obtain alcohol-precipitated pectin polysaccharide.

[0061] Example 2 The difference between this embodiment and embodiment 1 is that the extraction temperature in step (2) is adjusted to 100℃, 120℃ and 130℃ respectively, while the other parameters and conditions are the same as in embodiment 1.

[0062] Example 2-1: The extraction temperature was set to 100℃.

[0063] Example 2-2: The extraction temperature was set to 120℃.

[0064] Examples 2-3: The extraction temperature was set to 130℃.

[0065] Example 3 The difference between this embodiment and embodiment 1 is that the extraction pH value in step (2) is adjusted to 3.0, 5.0 and 6.0 respectively, the extraction temperature is fixed at 110℃, and the other parameters and conditions are the same as in embodiment 1.

[0066] Example 3-1: The extraction pH was set to 3.0.

[0067] Example 3-2: The extraction pH was set to 5.0.

[0068] Example 3-3: The extraction pH was set to 6.0.

[0069] Comparative Example 1 The only difference between this comparative example and Example 1 is that in step (2), the pH of the system was adjusted to 2.0 with 1 M HCl. All other parameters and conditions are the same as in Example 1.

[0070] Comparative Example 2 The only difference between this comparative example and Example 1 is that in step (2), the pH of the system was adjusted to 9.0 with 1 M NaOH. All other parameters and conditions are the same as in Example 1.

[0071] Comparative Example 3 The difference between this comparative example and Example 1 is that in step (1), uncrushed raw apple pomace was used for extraction, while the other parameters and conditions were the same as in Example 1.

[0072] Comparative Example 4 The difference between this comparative example and Example 1 is that the extraction conditions in step (2) are 90°C, while the other parameters and conditions are the same as in Example 1.

[0073] Comparative Example 5 The difference between this comparative example and Example 1 is that the extraction conditions in step (2) are room temperature (25°C) and natural pH, while the other parameters and conditions are the same as in Example 1.

[0074] Comparative Example 6 The difference between this comparative example and Example 1 is that step (2) uses the traditional hot water extraction method: apple pomace powder and water are mixed at a material-to-liquid ratio of 1:15 (g / mL), the pH is not adjusted, and the extraction is carried out under natural pH conditions in a 95°C water bath for 1.5 h. After extraction, solid-liquid separation is performed in the same way as in Example 1, the extract is collected, and further concentrated and dried to obtain the extracted product.

[0075] Comparative Example 7 The difference between this comparative example and Example 1 is that step (2) uses the traditional acid extraction method: apple pomace powder and water are mixed at a material-to-liquid ratio of 1:15 (g / mL), the pH of the system is adjusted to 2.0 with 1 M HCl, and the mixture is extracted for 1.5 h in a water bath at 85°C. After extraction, solid-liquid separation is performed in the same manner as in Example 1, the extract is collected, and further concentrated and dried to obtain the extracted product.

[0076] Example 4 This embodiment analyzes the yield and basic chemical composition of dietary fiber powder prepared under different extraction conditions in the examples and comparative examples. Specifically: To systematically screen the optimal extraction process, a full factorial experiment was conducted on temperature (90-130℃) and pH (3-6) under the conditions of material-liquid ratio of 1:15 and time of 1.5 h. The yield of total water-soluble dietary fiber extract (total yield), pectin polysaccharide yield and basic chemical composition were determined, and the results are shown in the table below.

[0077] Table 1. Total yield, pectin polysaccharide yield, and fiber oligosaccharide yield under different extraction conditions.

[0078] Table 2. Basic chemical composition of pectin polysaccharides under different extraction conditions

[0079] As shown in Tables 1 and 2, the pectin polysaccharide yield of Example 1 was the highest at 24.87%, the uronic acid content reached 47.95%, and the total yield was 61.39%, all of which were at a high level. This indicates that the dissolution efficiency of water-soluble dietary fiber was high under these conditions, and the characteristic structure of pectin was well preserved.

[0080] This is mainly attributed to the fact that the weakly acidic environment of pH 4.0 is conducive to maintaining the stability of pectin chains, while the subcritical water conditions at 110℃ can effectively disrupt cell walls while avoiding excessive degradation, thus achieving an optimal balance between extraction efficiency and structural preservation. In contrast, other comparative processes all have significant shortcomings.

[0081] In Comparative Example 1, the excessive hydrolysis of glycosidic bonds under strong acid conditions significantly reduced the pectin polysaccharide yield to 15.26%. In Comparative Example 2, the β-elimination reaction was easily triggered under alkaline high temperature, resulting in a pectin polysaccharide yield of only 18.44%, with compromised structural integrity. In Comparative Example 3, the small specific surface area of ​​the raw material limited mass transfer, leading to a sharp drop in pectin polysaccharide yield to 8.51%, indicating that raw material pretreatment is crucial for extraction efficiency. In Comparative Example 4, the lack of a "catalytic" effect from subcritical water resulted in insufficient cell wall disruption, resulting in a pectin polysaccharide yield of only 17.21%. In Comparative Example 5, the total water-soluble dietary fiber yield was 45.93%, while the pectin polysaccharide yield was only 5.98%, demonstrating that room temperature extraction cannot effectively obtain structural polysaccharides, further confirming the advantages of subcritical water extraction technology.

[0082] It is noteworthy that the total extraction rate remained high even under weakly acidic conditions (pH 6), indicating that subcritical water treatment significantly affects the disruption of apple pomace cell walls and the release of soluble components, rather than solely relying on a strongly acidic environment. However, this condition retained a significant amount of neutral sugars and cellulose oligosaccharides, suggesting a preference for obtaining total water-soluble dietary fiber rather than high-purity pectin components.

[0083] To further compare the differences between the method of the present invention and the traditional extraction method in the preparation of water-soluble dietary fiber from apple pomace, samples were prepared using the methods of Example 1, Comparative Example 6, and Comparative Example 7, respectively. The yield, uronic acid content, and main peak molecular weight of the obtained samples were compared and analyzed. The results are shown in Table 3.

[0084] Table 3 Comparison of the method of the present invention with traditional extraction methods

[0085] As shown in Table 3, compared with the traditional hot water extraction method, the total yield and pectin polysaccharide yield of the method of the present invention are both higher, indicating that it is more conducive to the release of target components in apple pomace. Compared with traditional acid extraction methods, the samples obtained by the method of this invention have higher uronic acid content and a more suitable main peak molecular weight, indicating that it is more conducive to maintaining the structural characteristics of pectin polysaccharides while improving the dissolution of the target components. Therefore, the method of this invention achieves a better balance between extraction efficiency and structure preservation.

[0086] Example 5 This embodiment describes the structural characterization of the dietary fiber powders prepared in Examples 1-3, specifically as follows: (1) Molecular weight analysis of pectin polysaccharides Table 4 Effect of pH on the molecular weight of the main peak

[0087] Table 5. Effect of temperature on the molecular weight of the main peak

[0088] Molecular weight analysis results showed that extraction temperature and pH significantly affected the main peak molecular weight of alcohol-precipitated pectin polysaccharides.

[0089] At 110℃, the main peak molecular weights of samples at pH 3, 4 and 5 were 182.85, 179.68 and 173.35 kDa, respectively, which were all in the same order of magnitude. However, when the pH was raised to 6.0, the molecular weight dropped sharply to 51.97 kDa, indicating that weakly acidic conditions are more conducive to maintaining the integrity of pectin segments, while near-neutral conditions are more likely to obtain components with lower molecular weights.

[0090] Under pH 4.0 conditions, as the extraction temperature increased from 100℃ to 130℃, the molecular weight of the main peak decreased significantly from 422.47 kDa to 179.68, 19.65 and 25.66 kDa, respectively, indicating that increasing the temperature significantly enhances the scission of pectin chains, especially at temperatures above 120℃.

[0091] Considering the combined yield, uronic acid content, and molecular weight results, Example 1 maintains a product yield of approximately 1.80 × 10⁻⁶ while ensuring a high pectin yield. 5 The main peak molecular weight of Da indicates that the conditions can achieve a good balance between cell wall disruption, pectin dissolution, and moderate degradation.

[0092] (2) Monosaccharide composition analysis of pectin polysaccharides Compare the differences in monosaccharide composition between Example 1 and its neighboring pH conditions and at different temperatures.

[0093] Table 6. Monosaccharide composition and main structural domain parameters (%)

[0094] Note: Rha: rhamnose; Ara: arabinose; Gal: galactose; GalA: galacturonic acid; HG / RG-I is the relative ratio of the homogalacturonic acid region to the rhamnose-galacturonic acid-I region calculated by molar percentage.

[0095] The monosaccharide composition and domain analysis results showed that, at 110℃, the contents of Rha, Ara, Gal, and GalA in Example 1 were 9.30%, 35.52%, 20.38%, and 34.80%, respectively, and the HG / RG-I ratio was 22.06 / 77.94, indicating that the sample has both a certain HG main chain and relatively abundant RG-I side chain characteristics.

[0096] Compared with the sample at pH 3 and 110℃, the GalA content of Example 1 decreased and the Ara content increased significantly, indicating that stronger acid conditions tend to retain or enrich HG-related components, while accompanied by the weakening of neutral sugar side chains. Compared with the sample at pH 5 and 110℃, Example 1 maintained a higher level of Ara and Gal while having a slightly higher GalA content, indicating that pH 4 is more conducive to the synergistic retention of the main chain and side chains.

[0097] In the pH 4 system, the Ara content in the 100℃ sample was higher than that in the GalA content, indicating that the extraction was relatively mild and the pectin backbone was not released sufficiently. The GalA content of the 120℃ sample increased to 46.83% and the HG content increased to 33.35%, but the molecular weight of the main peak decreased significantly, indicating that while high temperature promoted the enrichment of the main chain, it also triggered significant degradation.

[0098] Therefore, Example 1 exhibits a better balance between monosaccharide composition, domain distribution, and molecular weight control.

[0099] Example 6 This embodiment verifies the structure of the mixed dietary fiber prepared in Example 1, specifically as follows: (1) Dialysis separation The total water-soluble dietary fiber sample obtained in Example 1 was prepared into a 10 mg / mL solution. This solution was placed in a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed against ultrapure water at 4°C for 48 h, with the permeate being replaced every 8 h.

[0100] After dialysis, the fluids inside and outside the dialysis bag were collected separately, concentrated by rotary evaporation and freeze-dried to obtain the cut-off fraction (molecular weight ≥3500 Da) and the permeated fraction (molecular weight <3500 Da).

[0101] (2) Monosaccharide composition analysis of dialysis fraction The monosaccharide composition of the dialysis fraction of the total water-soluble dietary fiber obtained under the conditions of Example 1 was analyzed, and the results are shown in Table 7.

[0102] Table 7 Monosaccharide composition of dialysis components (%)

[0103] As shown in Table 7, the galacturonic acid content in the retained fraction is as high as 45.00%, and it also contains a high proportion of arabinose, galactose and rhamnose. This monosaccharide composition is consistent with the structural characteristics of pectin polysaccharides.

[0104] The relative content of glucose in the component is as high as 94%, while the content of other monosaccharides is extremely low. This indicates that its main components are free glucose and cellulose oligosaccharides.

[0105] (3) Mixed dietary fiber composition model Based on the above research, the water-soluble dietary fiber powder of this invention, produced from apple pomace using a specific subcritical water process, is a naturally compounded dietary fiber system. This system mainly consists of pectin polysaccharides and cellulose oligosaccharides. These two components complement and synergistically enhance each other in terms of molecular weight, charge properties, glycosidic bond type, and prebiotic metabolic pathways, collectively forming the unique multidimensional health function basis of the product of this invention.

[0106] Example 7 This embodiment investigates the effects of each component in Example 1 and commercially available inulin on the growth characteristics of Lactobacillus rhamnosus. The results are shown in Table 8. Table 8 Effects of different carbon sources on the growth characteristics of Lactobacillus rhamnosus

[0107] As shown in Table 8, *Lactobacillus rhamnosus* exhibited the best growth kinetics when total water-soluble dietary fiber was used as the carbon source. Its lag phase was shorter than 4 hours, significantly shorter than that of the pectin polysaccharide component, indicating that this system effectively reduced the difficulty of bacterial adaptation to complex carbon sources and accelerated growth initiation.

[0108] After entering the logarithmic growth phase, the total water-soluble dietary fiber group exhibited strong and stable proliferation capacity, with the growth phase lasting up to 18 hours and reaching its maximum OD value at 18 hours. This peak value was higher than that of other single components and the commercially available inulin control. After entering the stationary phase, the compound group maintained the highest cell density, demonstrating good fermentation continuity.

[0109] The results showed that single pectin polysaccharides, due to their complex molecular structure, resulted in low utilization efficiency by microorganisms; while single cellulose oligosaccharides were easily and rapidly utilized, their supporting effect was not long-lasting. The natural compound system obtained by subcritical water extraction in this invention combines the structural support of pectin polysaccharides with the rapid energy supply characteristics of cellulose oligosaccharides. Compared to inulin, this product achieves higher biomass while exhibiting superior growth sustainability, suggesting a potentially longer-lasting regulatory effect in the intestinal environment.

[0110] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing apple pomace water-soluble dietary fiber powder based on subcritical water extraction, characterized in that: include, The apple pomace is dried, crushed, and sieved to obtain apple pomace powder; Apple pomace powder and water were mixed at a material-to-liquid ratio of 1:10 to 1:20 g / mL. The pH of the system was adjusted to acidic, and subcritical water extraction was carried out at 100 to 120°C for 1 to 2 hours to obtain the extract. The extract is subjected to solid-liquid separation, the filtrate or supernatant is collected, and concentrated to 1 / 4 to 1 / 5 of the original volume to obtain a concentrated solution; The concentrate was dried to obtain apple pomace water-soluble dietary fiber powder; The apple pomace water-soluble dietary fiber powder contains pectin polysaccharides and fiber oligosaccharides.

2. The preparation method according to claim 1, characterized in that: The process of drying, crushing, and sieving apple pomace involves drying at a temperature of 55–65°C and sieving through a 70–90 mesh sieve.

3. The preparation method according to claim 1, characterized in that: The pH of the system is 3.8 to 4.

2.

4. The preparation method according to claim 1, characterized in that: The extraction temperature of the subcritical water is 110–120°C.

5. The preparation method according to claim 1, characterized in that: The solid-liquid separation is performed by filtration, centrifugation, or a combination of filtration and centrifugation.

6. The preparation method according to claim 1, characterized in that: The concentrated liquid is dried, wherein the drying is freeze-drying; the pre-freezing temperature is not higher than -40°C, the cold trap temperature is not higher than -50°C, and the vacuum degree is not higher than 10 Pa.

7. A water-soluble dietary fiber powder made from apple pomace, characterized in that: The apple pomace water-soluble dietary fiber powder is prepared by the method described in any one of claims 1 to 6, and contains pectin polysaccharide components and fiber oligosaccharide components.

8. The apple pomace water-soluble dietary fiber powder as described in claim 7, characterized in that: The dietary fiber powder has a uronic acid content of not less than 45%.

9. The apple pomace water-soluble dietary fiber powder as described in claim 7, characterized in that: The main peak molecular weight of the pectin polysaccharide component obtained after ethanol fractionation of the dietary fiber powder was 1.60 × 10⁻⁶. 5 ~2.00×10 5 Da.

10. The use of the apple pomace water-soluble dietary fiber powder as described in any one of claims 7 to 9 in the preparation of food, beverages, solid beverages, nutritional preparations, functional ingredients, or food ingredients for promoting the growth of Lactobacillus rhamnosus.

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