Preparation method of high-activity lemon dietary fiber

Abstract

The invention provides a preparation method of high-activity lemon dietary fiber, and relates to the technical field of food processing, and the preparation method comprises the key steps of raw material treatment, cold plasma surface functionalization treatment, enzymatic targeting surface modification and the like. The surface of the fiber is effectively activated through cold plasma treatment, active groups are introduced, then the surface structure is accurately regulated and controlled through targeted enzymatic reaction, and the activity of the fiber is remarkably improved. The obtained high-activity lemon dietary fiber has excellent functional characteristics, the water-holding capacity is greater than 15 g / g, the oil-holding capacity is greater than 8 g / g, the cation exchange capacity is greater than 0.8 meq / g, and generally, the high-activity lemon dietary fiber has relatively low bulk density. The method provides a new way for efficiently preparing the high-performance lemon dietary fiber, the product can be used as a novel functional ingredient to be applied to the fields of food, medicine and the like, and meanwhile resource utilization of lemon processing byproducts is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, in particular to a method for preparing highly active lemon dietary fiber. Background Art

[0002] According to a preparation method of highly active lemon dietary fiber disclosed in China Publication (Announcement) No. CN101961100A, fresh lemon peel residue is used as raw material, and the process steps are as follows: (1) enzyme inactivation treatment, the lemon peel residue is blanched in water at 95°C to 100°C for 4 to 6 minutes to destroy the pectinase activity in the lemon peel residue; (2) cooling and dehydration, the lemon peel residue after enzyme inactivation treatment is cooled to room temperature by rinsing with tap water, and then dehydrated; (3) ethanol extraction, the dehydrated lemon peel residue is soaked in ethanol with a volume concentration of 95% at normal pressure and 40°C to 50°C for at least 90 minutes, and then filtered to obtain the filter residue, which is the lemon dietary fiber; (4) drying and crushing, the obtained lemon dietary fiber is pre-frozen, then dried to constant weight using a vacuum freeze dryer, and then crushed to 10 mesh to 40 mesh to obtain the lemon dietary fiber product.

[0003] However, the above-mentioned preparation method presents the following problems: it primarily relies on relatively traditional methods such as heat treatment and ethanol extraction. This method has shortcomings in terms of cell wall disruption efficiency and precise control of dietary fiber structure. It is difficult to fully release and retain all the beneficial components in lemon peel residue, and it is also difficult to carry out targeted functional modification of the dietary fiber itself. Therefore, although dietary fiber products can be obtained, their potential for achieving "high activity" is limited, and they cannot maximize the comprehensive functions and health benefits of dietary fiber. Summary of the Invention

[0004] Technical problems solved

[0005] In view of the deficiencies in the prior art, the present invention provides a method for preparing highly active lemon dietary fiber, which solves the problems raised in the background art.

[0006] Technical Solution

[0007] To achieve the above object, the present invention is implemented by the following technical scheme: a preparation method of highly active lemon dietary fiber, comprising the following steps:

[0008] Sp1: Refined processing of raw materials: After washing, crushing and enzyme inactivation, the lemon raw materials are dried and ultrafinely crushed to obtain lemon powder;

[0009] Sp2: Cold plasma surface functionalization treatment: The lemon powder obtained in Sp1 is placed in a cold plasma reaction device. Under the conditions of atmospheric pressure, applied electric field frequency and input power density, a reaction gas containing oxygen or an oxygen-containing gas mixture is introduced to perform cold plasma treatment. The treatment is sufficient to introduce oxygen-containing active groups on the surface of the lemon powder particles and cause surface micro-etching;

[0010] Sp3: Enzymatic targeted surface modification: The lemon powder treated with Sp2 is dispersed in a buffer solution according to the solid-liquid ratio, and then an enzyme preparation selected from endoglucanase, specific pectinase, hemicellulase or a combination thereof is added. The enzymatic reaction conditions are precisely controlled by pH value, reaction temperature and reaction end point, aiming to selectively act on the plasma-activated surface sites to achieve fine adjustment of the fiber surface structure and release of specific oligosaccharide fragments;

[0011] Sp4: Product purification and typing:

[0012] Sp4.1: Inactivate the enzyme of the reaction product of Sp3.

[0013] Sp4.2: The solid fibers are then collected by centrifugation or filtration separation;

[0014] Sp4.3: Wash the solid fiber with ethanol solution 2-4 times, then wash with water;

[0015] Sp4.4: Finally, the washed fiber is dried by a vacuum freeze-drying method to obtain a powdered high-activity lemon dietary fiber product.

[0016] Preferably, the lemon raw material in Sp1 is lemon pomace after juicing, and is subjected to a debittering pretreatment before ultrafine grinding.

[0017] Preferably, the cold plasma reaction device in Sp2 is a dielectric barrier discharge or radio frequency glow discharge device.

[0018] Preferably, the reaction gas introduced into Sp2 is air, pure oxygen, or a mixture of oxygen and an inert gas.

[0019] Preferably, the oxygen-containing active groups introduced in Sp2 are mainly carboxyl groups.

[0020] Preferably, the enzyme preparation in Sp3 is preferably an enzyme species with high selectivity for amorphous regions of cellulose or specific regions of pectin chains. The enzyme preparation is specifically a combination of endoglucanase from Trichoderma reesei and polygalacturonase from Aspergillus niger. The enzyme activity ratio is adjusted according to the target modification effect, thereby achieving fine adjustment of the structure and the release of specific oligosaccharide fragments, while avoiding significant damage to the main fiber skeleton.

[0021] Preferably, the pH and temperature of the enzymatic reaction in Sp3 are precisely controlled according to the selected enzyme preparation to facilitate surface modification rather than deep degradation.

[0022] Preferably, the bulk density of the product obtained by vacuum freeze drying in Sp4 is lower than 0.4 g / cm 3 .

[0023] Preferably, the highly active lemon dietary fiber has at least one of the following characteristics:

[0024] (1) Water holding capacity greater than 15 g water / g dry basis;

[0025] (2) Oil holding capacity greater than 8 g oil / g dry basis;

[0026] (3) cation exchange capacity greater than 0.8 meq / g dry basis;

[0027] (4) Swelling capacity greater than 25 mL / g dry basis.

[0028] Beneficial effects

[0029] The present invention has the following beneficial effects:

[0030] The inherent functionality of lemon dietary fiber was significantly improved through the synergistic effect of cold plasma surface functionalization and targeted enzymatic modification. Cold plasma treatment effectively activated the fiber surface and introduced active groups, while the subsequent precisely controlled enzymatic modification selectively optimized the surface structure. The combination of the two overcomes the shortcomings of traditional lemon fiber's insufficient functionality. The highly active lemon dietary fiber prepared in this way exhibits water holding capacity (>15g / g), oil holding capacity (>8g / g) and significantly enhanced cation exchange capacity (>0.8meq / g) far higher than conventional levels, giving the product better food application potential and potential health benefits. In addition, this method preferentially utilizes lemon pomace to achieve efficient resource utilization, and removes undesirable components through pretreatment to improve product quality; vacuum freeze-drying also ensures the excellent physical form of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a flow chart of the method for preparing highly active lemon dietary fiber. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Specific embodiment one;

[0034] A method for preparing highly active lemon dietary fiber comprises the following steps:

[0035] Sp1: Refined processing of raw materials: The lemon raw materials are washed, crushed, and enzyme-inactivated, and then dried and ultrafinely pulverized to obtain lemon powder with an average particle size D50 of 10-100 microns.

[0036] Sp2: Cold plasma surface functionalization treatment: The lemon powder obtained in Sp1 was placed in a cold plasma reaction device, and the pressure was 0.1kPa to normal pressure, the external electric field frequency was 1kHz to 13.56MHz, and the input power density was 0.1-10W / cm 2 Under the conditions of , a reaction gas containing oxygen or an oxygen-containing mixture is introduced, and a cold plasma treatment is performed for 1-30 minutes. The treatment is sufficient to introduce oxygen-containing active groups on the surface of the lemon powder particles and cause surface micro-etching, so that the oxygen-carbon atomic ratio of the powder surface after treatment increases by at least 10% compared to before treatment, and the water contact angle decreases by at least 20%.

[0037] Sp3: Enzymatic targeted surface modification: The lemon powder treated with Sp2 is dispersed in a buffer solution with a solid-liquid ratio of 1:(10-50) (w / v) in a pH 4.0-6.0 buffer solution, and then an enzyme preparation selected from endoglucanase, specific pectinase, hemicellulase or a combination thereof is added. The total amount of the enzyme preparation added is 0.01%-0.2% (w / w) based on the dry weight of the substrate. The reaction is carried out at 40-60°C for 15-90 minutes. The enzymatic reaction conditions are precisely controlled to selectively act on the plasma-activated surface sites to achieve fine adjustment of the fiber surface structure and release of specific oligosaccharide fragments, while ensuring that the average molecular weight M_w of the insoluble dietary fiber main part is reduced by no more than 15%, and the increase in total reducing sugars in the reaction system is less than 2% of the dry weight of the substrate. The fiber surface after cold plasma activation is used as a basis, and a highly specific enzyme preparation with an extremely low concentration (0.01%-0.2%) is used to carry out a targeted enzymatic reaction under precisely controlled pH (4.8±0.2) and temperature (50±2°C). This precise control is designed to selectively act on the plasma-induced active sites or specific regions of the cellulose and pectin chains (cellulose amorphous regions), rather than deeply degrading the fiber body. By strictly controlling the reaction time and monitoring the reaction extent (through the reduction in molecular weight or the increase in reducing sugars), it is ensured that the enzymatic modification occurs only on the surface, thereby optimizing the fiber surface structure and selectively releasing a small amount of specific oligosaccharide fragments.

[0038] Sp4: Product purification and finalization: The reaction product of step Sp3 is subjected to enzyme inactivation treatment, and then the solid fiber is collected by centrifugation or filtration separation; the solid fiber is washed 2-4 times with at least 70% (v / v) ethanol solution, and then washed with water; finally, the washed fiber is dried by vacuum freeze drying to obtain a powdered high-activity lemon dietary fiber product.

[0039] The lemon raw material in Sp1 is specifically the lemon pomace remaining after lemon juice extraction and subjected to squeezing and dehydration. Moreover, before ultrafine grinding, the pomace undergoes an enzymatic debittering treatment using naringinase or β-glucosidase at a pH of 3.5-5.0 and a temperature of 45-60° C. for 1-3 hours to reduce the limonin content to below 50 ppm. The ultrafine grinding controls the average particle size D50 of the lemon powder within the range of 20-50 microns.

[0040] The Sp2 medium-cold plasma reaction device is specifically a dielectric barrier discharge device, which includes a dielectric barrier layer composed of quartz glass or alumina ceramic, and the electrode spacing is 1-5mm; alternatively, the device is an inductively coupled plasma or radio frequency glow discharge device, operating under low pressure (0.1-10kPa).

[0041] The reaction gas introduced into Sp2 is medical grade air, or a mixed gas with a volume ratio of argon to oxygen of (80-95): (5-20); the total gas flow rate is controlled at 0.5-5 standard liters / minute; the plasma treatment time is preferably controlled at 5-15 minutes, and the input power density is preferably controlled at 0.5-5 W / cm 2 .

[0042] After Sp2 medium cold plasma treatment, the increase in fiber surface carboxyl content measured by sodium hydroxide titration reached 0.1-0.5 meq / g dry basis; and through X-ray photoelectron spectroscopy C1 s spectrum analysis, the proportion of the peak area corresponding to the OC=O group to the total carbon peak area increased by 5%-20% compared with before treatment.

[0043] The enzyme preparation in Sp3 is specifically a combination of endoglucanase from Trichoderma reesei and polygalacturonase from Aspergillus niger. The enzyme activity ratio (U / U) is adjusted between 1:0.5 and 1:2 according to the target modification effect; the enzyme preparation used is a purified product with a specific activity greater than 50U / mg protein, thereby achieving fine adjustment of the structure and the release of specific oligosaccharide fragments, while avoiding significant damage to the main fiber skeleton.

[0044] The pH value of the enzymatic reaction in Sp3 is precisely controlled within the range of 4.8±0.2 by adding a citric acid-sodium citrate buffer pair, and the reaction temperature is precisely controlled at 50±2°C using a water bath or jacket. The reaction endpoint is determined by monitoring the reaction solution viscosity change rate with an online viscometer below a preset threshold (<1% / 5min) or by sampling and testing specific oligosaccharides (cellobiose or galacturonic acid oligosaccharides) to reach the target range (0.1-0.5mg / mL), and the enzyme is immediately inactivated.

[0045] The specific process parameters for vacuum freeze-drying in Sp4 are: a pre-freezing temperature maintained below -40°C for more than 2 hours, a drying chamber vacuum of less than 10Pa, a plate temperature controlled between -20°C and 0°C during the sublimation drying phase, and a plate temperature slowly raised to 20-30°C during the desorption drying phase. The final product is a white or light yellow loose porous powder, whose scanning electron microscope image shows a rich honeycomb or reticular microporous structure with an average pore size in the range of 1-10 microns.

[0046] (1) Water holding capacity, determined according to AACC method 56-11.01, greater than 18 g water / g dry basis;

[0047] (2) oil holding capacity, measured using soybean oil, greater than 10 g oil / g dry basis;

[0048] (3) cation exchange capacity, measured by sodium ion binding at pH 7.0, greater than 1.0 meq / g dry basis;

[0049] (4) Swelling capacity, measured after standing in water for 18 hours, greater than 25 mL / g dry basis. Specific embodiment 2

[0051] The refinement and standardization of the starting raw materials are the basis for achieving subsequent efficient and uniform modification. It is preferred to use the by-product of lemon juice processing, namely lemon pomace, which not only complies with the principle of resource utilization, but also becomes an ideal base material because it is rich in dietary fiber. Fresh or frozen pomace must first be thoroughly washed to remove impurities, and the particle size must be initially reduced by crushing or pulping to increase the uniformity of subsequent processing. The key step is to inactivate the enzyme by blanching (90-100°C, 3-5 minutes), which aims to quickly inactivate endogenous enzymes such as pectin methylesterase inherent in lemons to prevent them from acting on pectin uncontrollably during subsequent processing, resulting in unpredictable changes in product viscosity, gel properties, etc. or the production of unpleasant flavors. Considering the unpleasant taste of limonoids (limonene and naringin) that may be present in lemon peel or pomace, debittering is selectively performed before pulverization. Using enzymes specific for bitter substances (naringinase and β-glucosidase) under appropriate conditions (pH 3.5-5.0, 45-60°C, 1-3 hours), the bittering content is reduced to an acceptable level (below 50 ppm), which is crucial for the palatability of the final product. The debittered (and enzyme-inactivated) material is then dried and subjected to ultrafine grinding, aiming to obtain a fine powder with an average particle size (D50) of 10-100 microns, preferably 20-50 microns. This fine particle size is essential because it significantly increases the specific surface area per unit mass of material, providing a maximum contact surface for the subsequent cold plasma treatment, ensuring uniform and efficient treatment.

[0052] Cold plasma treatment is designed to controllably activate and functionalize the surface of lemon fiber. Unlike high-temperature or strong chemical methods, cold plasma is carried out at near room temperature and atmospheric pressure or near atmospheric pressure, avoiding thermal damage to the main structure of the fiber. By ionizing gases (air, oxygen, argon, nitrogen or their mixtures) under the action of a high-frequency electric field (frequency ranges from kHz-level audio to MHz-level radio frequency, and even GHz-level microwaves), a plasma containing highly active substances such as electrons, ions, free radicals (O·, OH·, O2·-), metastable particles and ultraviolet photons is generated. These active substances undergo complex physical and chemical interactions with the exposed surface of lemon fiber powder. Physically, the bombardment of high-energy particles will produce a micro-etching effect on the surface, increasing the surface roughness and porosity, which will help to subsequently improve the water and oil holding capacity of the fiber. Chemically, if the reaction gas contains oxygen (using air, pure oxygen or Ar / O2 mixed gas, preferably with an oxygen volume fraction of 5%-100%), the active oxygen species in the plasma will react with the bonds on the fiber surface, introducing oxygen-containing functional groups, mainly polar carboxyl, carbonyl and hydroxyl groups. These newly introduced functional groups significantly change the chemical properties of the fiber surface: first, the polarity and hydrophilicity of the surface are greatly improved, which is manifested in a significant decrease in the water contact angle (at least 20% decrease), improving the dispersion and wettability of the fiber in water; second, the negative charge and ion exchange sites on the surface are increased, especially the introduction of carboxyl groups, which directly improves the cation exchange capacity of the fiber and enhances its ability to adsorb metal ions; third, these active sites also provide targets that are easier to approach and act on for subsequent enzymatic reactions. In order to achieve the ideal modification effect, it is necessary to precisely control the plasma treatment parameters: gas pressure (0.1kPa to normal pressure), electric field frequency (kHz to MHz), input power density (0.1-10W / cm 2 , preferably 0.5-5W / cm 2 to balance efficiency and mildness), reaction gas composition and flow rate (Ar / O2 mixture, total flow rate 0.5-5 SLM), and treatment time (1-30 minutes, preferably 5-15 minutes to fully modify the surface without damaging the interior). The treatment effect can be quantitatively characterized by surface elemental analysis (XPS determination of the O / C atomic ratio, requiring an increase of at least 10%) and surface chemical group analysis (titration determination of an increase of 0.1-0.5 meq / g in the carboxyl content, or XPSC1 s spectrum analysis of an increase in the peak area of ​​specific oxygen-containing groups). Commonly used equipment types include dielectric barrier discharge devices suitable for atmospheric pressure processing of large quantities of powders, whose structure usually includes a dielectric layer composed of quartz or ceramics, or radio frequency glow discharge or inductively coupled plasma devices for more precise control and low-pressure environments.

[0053] The next enzymatic targeted surface modification step utilizes the favorable conditions created by plasma treatment to perform extremely gentle and precise "surface polishing" or "structural fine-tuning." The key concept in this step is to utilize highly specific enzyme preparations at extremely low concentrations (only 0.01%-0.2% w / w based on substrate dry weight) to selectively target plasma-activated, more accessible fiber surface regions or specific chemical bonds within a tightly controlled, short time (15-90 minutes). The choice of enzyme is crucial. For example, one can choose an endoglucanase (EC 3.2.1.4, from sources such as Trichoderma reesei) that has a preference for amorphous regions or accessible β-1,4-glycosidic bonds in cellulose chains, or a polygalacturonase (EC 3.2.1.15, from sources such as Aspergillus niger) that specifically targets specific regions of pectin chains (between unesterified galacturonic acid residues), or an enzyme that targets hemicellulose side chains or backbones. If necessary, a single enzyme or an optimized ratio of complex enzymes (endoglucanase and polygalacturonase in an enzyme activity ratio of 1:0.5 to 1:2) can be selected according to the desired modification effect (focusing on increasing solubility or optimizing pore structure). The use of high specific activity, purified enzyme preparations (>50U / mg protein) helps to achieve more precise control. The reaction conditions (pH 4.0-6.0, preferably 4.8±0.2; temperature 40-60°C, preferably 50±2°C) need to be precisely regulated according to the characteristics of the selected enzyme. Sometimes, even the suboptimal zone outside the optimal conditions of the enzyme is selected to further limit the activity of the enzyme and ensure its mild action and surface limitation. The most important thing is to strictly control the degree of reaction and avoid significant damage to the main skeleton of the fiber. Control indicators can be: ensuring that the weight-average molecular weight (Mw) of the insoluble dietary fiber fraction decreases by no more than 15% (determined by gel permeation chromatography (GPC)), and / or monitoring the increase in total reducing sugars in the reaction solution to be less than 2% relative to the dry weight of the substrate (determined by the DNS method). The reaction endpoint can be determined by real-time monitoring of the rate of change of the viscosity of the reaction system (stopping when the rate of change falls below a certain threshold) or detecting that the concentration of a specific oligosaccharide product (indicating that the enzyme has acted on the target site) reaches a preset trace level. Once this level is reached, the enzyme is completely inactivated by heating (90-100°C for 10-15 minutes) to terminate the reaction.

[0054] The final product purification and shaping steps are crucial for maintaining and reflecting the high activity of the fiber. After the enzyme is inactivated, the solid phase modified dietary fiber is separated from the liquid phase (containing buffer salts, inactivated enzymes, and trace amounts of released sugars) by centrifugation or filtration. In the subsequent washing step, it is first washed several times (2-4 times) with at least 70% (v / v) ethanol solution, which not only effectively removes residual buffer salts and small molecule sugars, but also removes some fat-soluble impurities and pigments, and helps dehydrate the fiber. It is then washed with pure water to remove residual ethanol. The choice of drying method has a huge impact on the microstructure and physical properties of the final product. The present invention preferably uses vacuum freeze drying (freeze drying) because at low temperature and high vacuum, water directly sublimates from the solid state (ice) to the gaseous state, avoiding the collapse of the fiber network structure and pore closure caused by the surface tension of liquid water during evaporation. Freeze-drying can maximize the preservation of the loose porous structure formed or optimized during plasma treatment and enzyme modification, thus giving the final product extremely high water holding capacity, oil holding capacity, rapid rehydration and low bulk density (less than 0.4 g / cm 3 , preferably 0.2-0.35g / cm 3 Scanning electron microscopy reveals the typical honeycomb or reticular microporous structure (average pore size 1-10 microns) preserved by freeze-drying, which is the important physical basis for its high activity. The final product is a highly active lemon dietary fiber product that is white or light yellow, extremely loose and light in powder form. Specific embodiment three

[0056] Comparison of traditional enzymatic hydrolysis and ultrasonic enzymatic hydrolysis, showing the effects of cold plasma surface functionalization and targeted enzymatic modification on the water-holding capacity, oil-holding capacity, cation exchange capacity, and swelling capacity of lemon dietary fiber;

[0057]

[0058] Comparison; Case 1: Highly active lemon fiber synbiotic powder supplement

[0059] The development of a powdered synbiotic dietary supplement that combines the prebiotic properties of highly active lemon dietary fiber, high cation exchange capacity, and carrier function, and is compounded with specific probiotic strains, aims to provide a solution for people who are concerned about their intestinal microbiome, desire regular bowel movements, and are concerned about heavy metal exposure. Highly active lemon dietary fiber plays multiple roles in this product: its high cation exchange capacity of over 1.0 meq / g, thanks to its abundant surface carboxyl groups, can chelate heavy metal ions (lead and cadmium) that may be present in the diet within the digestive tract, promoting their excretion. As a high-quality prebiotic, it provides nutrition to the probiotics in the formula, supporting their colonization and proliferation in the intestine. Furthermore, its loose porous structure and high specific surface area, achieved through freeze-drying, make it an ideal physical carrier for probiotic powders, facilitating uniform mixing and potentially providing some physical protection. Its high water-holding capacity and swelling capacity (SC>25 mL / g) contribute to the formation of a beneficial chyme state after reconstitution. A sample recipe for a single-serving bar (5g) might include: 4.0g of highly active lemon dietary fiber as the primary base, a blend of freeze-dried, high-potency probiotics (guaranteed total viable count ≥20 billion CFU / bar), 0.5g of FOS (for enhanced prebiotic effects), immune-supporting ingredients like vitamin C or zinc, and a trace amount of an anti-caking agent (<1% silicon dioxide). The production process is conducted under standard conditions in a GMP-compliant cleanroom. All powders (especially the probiotics, which must be handled in a low-humidity environment) are uniformly dry-blended using high-efficiency mixing equipment, then precisely packaged into moisture-proof, individual bar bags and sealed.

[0060] Comparison; Case 2: Highly active lemon fiber fortified prebiotic yogurt

[0061] Stirred yogurt containing highly active lemon dietary fiber is designed to significantly increase fiber content, improve texture, and provide prebiotic functionality. The key to achieving this goal lies in leveraging the unique properties of highly active lemon dietary fiber, obtained through innovative processing: its ultra-high water-holding capacity (>18g / g) effectively binds water, giving the yogurt a creamier texture and viscosity, while significantly reducing whey precipitation during storage and improving product stability. Its excellent dispersibility and fine particle size ensure its uniform distribution in the milk matrix, avoiding the potential for graininess in the finished product and ensuring a delicate and smooth taste. Furthermore, the fiber's inherent fermentability and the oligosaccharides that may be released during the surface modification process give it clear prebiotic potential, making it a nutrient source for intestinal probiotics (including starter cultures and additional strains). Because the raw materials are debittered and the modification process is gentle, the fiber itself has a neutral flavor and does not affect the overall flavor of the yogurt. A typical production recipe (based on 100kg) might include: 3kg of skim milk powder, 5kg of sugar or sweetener, and 2.0kg of high-activity lemon dietary fiber powder (ensuring a final fiber content of ≥2g / 100g) are slowly added to 85kg of standardized milk with thorough stirring. After thorough mixing, the liquid is preheated, homogenized under high pressure (15-20MPa), and pasteurized (90-95°C, 5-10 minutes). It is then cooled to an appropriate temperature (42-43°C) and inoculated with a standard yogurt starter culture. After fermentation at a constant temperature to a pH of 4.5-4.6, the milk is gently demulsified, rapidly cooled, aseptically filled, and refrigerated at 4°C for post-maturation.

[0062] In summary, the present invention successfully improved the surface chemical properties (introduction of oxygen-containing groups, increased polarity) and physical structure (increased porosity and specific surface area) of dietary fiber by the synergistic effect of cold plasma surface functionalization and enzymatic targeted surface modification while maintaining the integrity of the main structure of dietary fiber, ultimately obtaining a highly active product with excellent comprehensive performance. Its activity is reflected in many aspects, such as extremely high water holding capacity (>18g / g), oil holding capacity (>10g / g), cation exchange capacity (1.0meq / g) and swelling capacity (>25mL / g), all of which are significantly better than lemon dietary fiber prepared by traditional methods.

[0063] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing highly active lemon dietary fiber, characterized in that: The following steps are included: Sp1: Refined processing of raw materials: After washing, crushing and enzyme inactivation, the lemon raw materials are dried and ultrafinely crushed to obtain lemon powder; Sp2: Cold plasma surface functionalization treatment: The lemon powder obtained in Sp1 is placed in a cold plasma reaction device. Under the conditions of atmospheric pressure, applied electric field frequency and input power density, a reaction gas containing oxygen or an oxygen-containing gas mixture is introduced to perform cold plasma treatment. The treatment is sufficient to introduce oxygen-containing active groups on the surface of the lemon powder particles and cause surface micro-etching; Sp3: Enzymatic targeted surface modification: The lemon powder treated with Sp2 is dispersed in a buffer solution according to a solid-liquid ratio, and then an enzyme preparation selected from endoglucanase, specific pectinase, hemicellulase, or a combination thereof is added. The enzymatic reaction conditions are precisely controlled by pH value, reaction temperature, and reaction endpoint, aiming to selectively act on plasma-activated surface sites to achieve fine adjustment of the fiber surface structure and release of specific oligosaccharide fragments. Sp4: Product purification and typing: Sp4.1: Inactivate the enzyme of the reaction product of Sp3. Sp4.2: The solid fibers are then collected by centrifugation or filtration separation; Sp4.3: Wash the solid fiber with ethanol solution 2-4 times, then wash with water; Sp4.4: Finally, the washed fiber is dried by a vacuum freeze-drying method to obtain a powdered high-activity lemon dietary fiber product.

2. The method for preparing a highly active lemon dietary fiber according to claim 1, wherein: The lemon raw material in Sp1 is lemon pomace after juicing, and is subjected to a debittering pretreatment before ultrafine grinding.

3. The method for preparing a highly active lemon dietary fiber according to claim 1, wherein: The cold plasma reaction device in Sp2 is a dielectric barrier discharge or radio frequency glow discharge device.

4. The method for preparing a highly active lemon dietary fiber according to claim 1 or 3, wherein: The reaction gas introduced into Sp2 is air, pure oxygen, or a mixture of oxygen and inert gas.

5. The method for preparing a highly active lemon dietary fiber according to claim 3, wherein: The oxygen-containing active groups introduced in Sp2 are mainly carboxyl groups.

6. The method for preparing a highly active lemon dietary fiber according to claim 1, wherein: The enzyme preparation described in Sp3 preferably uses enzymes with high selectivity for amorphous regions of cellulose or specific regions of pectin chains. The enzyme preparation is specifically a combination of endoglucanase derived from Trichoderma reesei and polygalacturonase derived from Aspergillus niger. The enzyme activity ratio is adjusted according to the target modification effect, thereby achieving fine adjustment of the structure and the release of specific oligosaccharide fragments, while avoiding significant damage to the main fiber skeleton.

7. The method for preparing a highly active lemon dietary fiber according to claim 1 or 6, wherein: The pH and temperature of the enzymatic reaction in Sp3 are precisely controlled according to the selected enzyme preparation to favor surface modification rather than deep degradation.

8. The method for preparing a highly active lemon dietary fiber according to claim 1, wherein: The bulk density of the product obtained by vacuum freeze drying in Sp4 is less than 0.4 g / cm 3 .

9. The method for preparing a highly active lemon dietary fiber according to claim 1, wherein: The highly active lemon dietary fiber has at least one of the following characteristics: (1) Water holding capacity greater than 15 g water / g dry basis; (2) Oil holding capacity greater than 8 g oil / g dry basis; (3) cation exchange capacity greater than 0.8 meq / g dry basis; (4) Swelling capacity greater than 25 mL / g dry basis.

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