Green process for extracting natural components of pericarpium citri reticulatae with water and application of natural components of pericarpium citri reticulatae in beverage

Abstract

The invention relates to a green process for extracting natural components of pericarpium citri reticulatae with water and application of the natural components in a beverage. The process comprises the following steps: crushing and drying a dried orange peel raw material; extracting with water at 105-125 DEG C under 0.8-1.5 MPa under a low-oxygen condition to obtain a first extracting solution and first-stage residues; the residues are extracted at the temperature of 130-150 DEG C and the pressure of 1.5-2.2 MPa, and a second extracting solution is obtained; treating the second extracting solution at the temperature of 145-165 DEG C and the pressure of 1.8-2.5 MPa to obtain a low-ester pectin component containing bound flavone; mixing the first extracting solution with the low-methoxyl pectin component, and homogenizing, so that the volatile oil component is dispersed in the water phase containing the low-methoxyl pectin component; and concentrating and / or drying the obtained dispersion to obtain the pericarpium citri reticulatae extract. The extract can be used as a natural flavor additive for beverages.

Description

Technical Field

[0001] This invention belongs to the field of natural product extraction and application technology, specifically relating to a green process for water extraction of natural components from dried tangerine peel and its application in beverages. Background Technology

[0002] Dried tangerine peel (Citrus reticulata Blanco) is the dried, mature peel of the citrus fruit and its cultivated varieties, belonging to the Rutaceae family. It is a traditional Chinese medicine and a natural flavoring ingredient. The pharmacopoeia records that dried tangerine peel has dotted oil cells on its outer surface, and hesperidin, nobiletin, and tangeretin are used as quality control indicators. Modern research also shows that citrus peels are rich in volatile oils, flavonoids, pectin, and other functional components, possessing high value for food and health product development.

[0003] Traditional methods for extracting dried tangerine peel mainly include steam distillation, organic solvent extraction, and supercritical CO2 extraction. However, steam distillation has low yields and struggles to extract non-volatile components, organic solvent extraction carries the risk of solvent residue, and supercritical CO2 extraction requires large equipment investments and is difficult to efficiently extract polar components such as pectin. None of these methods can simultaneously achieve low-temperature protective extraction of volatile oils and high-temperature release and structural regulation of pectin-flavonoid components in a single process flow.

[0004] Subcritical water extraction technology utilizes the characteristic that the dielectric constant of water decreases with increasing temperature under high temperature and pressure. By adjusting the temperature and pressure, the solvent polarity can be changed, achieving selective extraction of components with different polarities. Furthermore, water is used as the solvent throughout the process, aligning with the trend of green chemistry. Existing technologies have reported the use of subcritical water for extracting citrus raw materials, such as CN102526295A, which discloses a method for the comprehensive utilization of dried tangerine peel. However, these methods generally suffer from the following shortcomings: lack of in-situ control over the degree of pectin esterification and molecular weight, making it impossible to simultaneously prepare low-ester pectin with emulsifying functions during extraction; lack of control over the oxygen content of the volatile oil extraction environment, resulting in a high risk of thermal oxidation and deterioration; and the separate collection of the extracted volatile oil and pectin as independent products, failing to achieve in-situ emulsification and encapsulation of the volatile oil, leading to insufficient dispersion stability of the extract in aqueous beverage systems.

[0005] Furthermore, in end-use applications such as beverages, the volatile oil of dried tangerine peel is highly susceptible to stratification in aqueous systems due to its water insolubility. Current technologies lack an integrated process suitable for acidic beverages, utilizing dried tangerine peel raw materials, a fully aqueous phase, and in-situ controlled emulsification of its own volatile oil with homologous pectin obtained via subcritical water, all in a single aqueous phase. Therefore, developing a green extraction process for dried tangerine peel that uses water as the solvent throughout the entire extraction process and simultaneously achieves pectin deesterification modification and in-situ emulsification and encapsulation of volatile oils is of great significance for preparing high-quality dried tangerine peel extracts that can be directly applied to the beverage industry. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, the first objective of this invention is to provide a green process for water extraction of natural components from dried tangerine peel. This process employs a strategy combining gradient temperature and pressure fractional extraction with in-situ emulsification, using only water as the solvent throughout the entire process. Simultaneously, it achieves low-oxygen protective extraction of volatile oils, subcritical hydrothermal deesterification modification of pectin, and in-situ emulsification and encapsulation of volatile oils. The resulting dried tangerine peel extract can be directly applied to aqueous beverage systems.

[0007] The second objective of this invention is to provide a dried tangerine peel extract obtained by the aforementioned green process.

[0008] A third objective of this invention is to provide the application of the above-mentioned tangerine peel extract in the preparation of natural flavor additives for beverages.

[0009] A fourth objective of this invention is to provide a beverage comprising the above-mentioned tangerine peel extract.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] This invention provides a green process for water extraction of natural components from dried tangerine peel, comprising the following steps:

[0012] S1. Grind the dried tangerine peel raw material to 30-80 mesh and dry it until the moisture content is no more than 10% to obtain pretreated dried tangerine peel. Controlling the particle size within the 30-80 mesh range ensures sufficient disruption of the tangerine peel cell walls, facilitating solvent penetration and mass transfer during subsequent extraction, while avoiding problems such as material caking and poor flowability caused by excessively fine particles. Drying to a moisture content of no more than 10% helps control the consistency of material moisture content during subsequent subcritical water extraction, ensuring the repeatability of extraction conditions.

[0013] S2. Under low-oxygen conditions, the pretreated tangerine peel is extracted with water as the extraction solvent at 105–125°C and 0.8–1.5 MPa for 5–15 min. The extract is then discharged and cooled to 20–35°C. Solid-liquid separation is performed to obtain the first extract and the first-stage residue. This stage is the protective extraction stage for volatile oil components. Within the temperature range of 105–125°C, the dielectric constant of subcritical water decreases to a level similar to that of low-polarity organic solvents, which can selectively dissolve volatile aroma components such as limonene and γ-terpinene, while more polar components such as flavonoids and pectin are retained in the tangerine peel residue. After extraction, the extract is rapidly cooled to 20–35°C, which allows the volatile components dissolved in subcritical water to condense and remain in the liquid phase in the form of fine oil droplets, avoiding the loss of aroma components due to slow cooling or flash evaporation.

[0014] S3. The residue from the first stage is extracted with water as the extraction solvent at 130–150℃ and 1.5–2.2 MPa for 8–20 min. The second extract is obtained after solid-liquid separation. This stage is for the extraction of pectin and bound flavonoids. When the temperature is increased to 130–150℃, the dielectric constant of subcritical water further decreases, while the ion product of water increases, enhancing acid-base catalytic activity and facilitating the dissolution and release of pectin from the cell walls of dried tangerine peel. Simultaneously, flavonoids bound to pectin dissolve along with the pectin, maintaining the bound structure of pectin-flavonoids. "Bound flavonoids" refer to flavonoids that are bound to pectin through non-covalent interactions (such as hydrogen bonds and hydrophobic interactions) and remain coexisting with pectin after being filtered by a specific molecular weight ultrafiltration membrane.

[0015] S4. The second extract is treated at 145–165°C and 1.8–2.5 MPa for 2–8 min, and then cooled to 40–60°C to obtain a low-ester pectin component containing bound flavonoids. This step is one of the key technical aspects of this invention, essentially utilizing the high temperature and high pressure conditions of subcritical water to perform in-situ deesterification modification of the pectin dissolved in S3. Under the conditions of 145–165°C, the enhanced ion product in subcritical water significantly accelerates the hydrolysis rate of water molecules on the methyl ester groups of the pectin galacturonic acid chain, thereby converting high-ester pectin into low-ester pectin. The treatment time is controlled at 2–8 min to ensure that the pectin is deesterified to the target esterification range while avoiding excessive breakage of the pectin backbone and excessive reduction of molecular weight due to excessively long high-temperature treatment.

[0016] S5. At 45–60°C, the first extract is mixed with the low-ester pectin component containing bound flavonoids and homogenized to obtain an oil / water dispersion in which the volatile oil component of the first extract is dispersed in the aqueous phase. The first extract containing volatile oil obtained in S2 and the low-ester pectin component containing bound flavonoids obtained in S4 are mixed and homogenized at a mild temperature. Under the action of homogenization shear force, the low-ester pectin migrates to the oil / water interface to form a stable adsorption film layer, encapsulating the volatile oil droplets in the continuous pectin phase. The mixing temperature is controlled at 45–60°C, which is beneficial for reducing the viscosity of the system to improve the homogenization efficiency, and also avoids the secondary volatilization loss of the volatile oil component due to excessively high temperature.

[0017] S6. The oil / water dispersion is concentrated and / or dried to obtain tangerine peel extract. Depending on the target product form, the oil / water dispersion can be concentrated under reduced pressure to obtain a concentrated solution, or obtained as a powder product through spray drying, freeze drying, or other methods. The dried tangerine peel extract can be reconstituted in water to form a stable oil / water dispersion with good reconstitution and dispersibility.

[0018] Furthermore, the tangerine peel is the dried, mature peel of the citrus fruit (Citrus reticulata) and its cultivated varieties, belonging to the Rutaceae family. The extraction solvent is deionized water or purified water to avoid the influence of metal ions and microorganisms in the water on the quality of the extract.

[0019] Furthermore, the drying in S1 is vacuum drying at 40–55°C. Using low-temperature vacuum drying can remove moisture while maximizing the retention of volatile aroma precursors in the dried tangerine peel, avoiding aroma loss and degradation of heat-sensitive active ingredients caused by high-temperature drying under normal pressure.

[0020] Furthermore, the low-oxygen condition in S2 is that the dissolved oxygen in the extraction water is not higher than 2 mg / L, and / or the top space of the extraction device is replaced with an inert gas. Specifically, the extraction water can be degassed (e.g., vacuum degassed, nitrogen bubbling degassed, etc.) to reduce its dissolved oxygen to below 2 mg / L, and / or the air in the top space of the extraction device can be replaced with nitrogen or other inert gases after the extraction device is loaded and sealed, and before heating for extraction, thereby creating a low-oxygen extraction environment.

[0021] Furthermore, the extract obtained in step S2 is cooled to 25–30°C within 30 seconds to 3 minutes. Rapid cooling allows the volatile aroma components dissolved in high-temperature subcritical water to be cooled to a temperature range far below their boiling points in a short time, remaining in the liquid phase as fine oil droplets or in a dissolved state, effectively reducing aroma loss caused by continuous volatilization and flash evaporation during slow cooling. Cooling can be achieved using plate heat exchangers, shell-and-tube heat exchangers, or other high-efficiency heat exchange devices.

[0022] Further, in the low-ester pectin component containing bound flavonoids obtained in step S4, the pectin content is 40–90 wt% on a dry basis, the total flavonoid content is 0.5–15 wt%, the degree of esterification of the pectin is 18–45%, and the weight-average molecular weight is 30–150 kDa. These parameter ranges characterize the deesterification modification effect of step S4: a degree of esterification of 18–45% indicates that the pectin has been converted from high-ester pectin to low-ester pectin, exhibiting good interfacial emulsifying activity; a weight-average molecular weight of 30–150 kDa indicates that the pectin backbone has undergone moderate degradation within a controllable range, which is beneficial for improving its adsorption efficiency and molecular flexibility at the oil / water interface, while still maintaining sufficient molecular weight to form a stable interfacial film; and the retention of 0.5–15 wt% of total flavonoid content indicates that the bound structure of pectin-flavonoids is effectively maintained during the deesterification process.

[0023] Furthermore, step S4 further includes: separating the cooled low-ester pectin component containing bound flavonoids through an ultrafiltration membrane with a molecular weight cutoff of 3–50 kDa, and collecting the retentate as the low-ester pectin component containing bound flavonoids for step S5. Ultrafiltration membrane separation can remove impurities such as small-molecule free monosaccharides, oligosaccharides, free flavonoid aglycones, and inorganic salts from the product of step S4, enriching the low-ester pectin-bound flavonoid complex within the target molecular weight range, improving its purity and emulsifying activity, thereby further improving the particle size uniformity and storage stability of the oil / water dispersion obtained in step S5.

[0024] Further, in step S5, the mass ratio of the volatile oil component in the first extract to the pectin in the low-ester pectin component containing bound flavonoids is 1:(2-30). This mass ratio range ensures that there is sufficient low-ester pectin in the system to adequately coat the volatile oil droplets at the interface, while avoiding excessive pectin leading to excessively high viscosity of the continuous phase, which would affect the taste and flowability of the product. The homogenization process employs high-pressure homogenization or microjets, with a homogenization pressure of 10-80 MPa. High-pressure homogenization or microjets can generate strong shear forces, cavitation effects, and turbulence, dispersing the volatile oil in the aqueous phase into submicron-sized fine oil droplets and promoting the rapid adsorption and film formation of low-ester pectin on the surface of the oil droplets. The volume average particle size (D50) of the oil / water dispersion obtained in step S5 is 0.1-0.8 μm. Dispersions within this particle size range exhibit good physical stability and are less prone to Ostwald ripening, aggregation, or stratification during the beverage's shelf life.

[0025] This invention also provides a dried tangerine peel extract, prepared by the aforementioned green process. The extract is an aqueous dispersion, its concentrate, or its dried product, comprising volatile oil components from dried tangerine peel and a low-ester pectin component containing bound flavonoids. The volatile oil components are dispersed as oil droplets in a continuous aqueous phase containing the low-ester pectin component. The extract is characterized by a microstructure in which the low-ester pectin forms a continuous adsorption film at the oil / water interface, encapsulating the volatile oil droplets within the continuous aqueous phase, thus forming a stable oil-in-water dispersion system.

[0026] Furthermore, after reconstitution in water, the tangerine peel extract forms a dispersion with a volume average particle size (D50) of 0.1–0.8 μm and a polydispersity index (PDI) of no more than 0.35 under pH conditions of 2.8–4.2. These particle size and polydispersity index ranges indicate that the tangerine peel extract can still form a stable dispersion with uniform particle size and narrow distribution under typical pH conditions in acidic beverage systems, without significant aggregation or stratification. The flavonoids in the bound flavonoids are selected from one or more of hesperidin, nonosiderin, naringenin, and capsanthin.

[0027] This invention also provides the application of the above-mentioned tangerine peel extract in the preparation of natural flavor additives for beverages. The tangerine peel extract obtained by the process of this invention has the characteristics of fresh and natural aroma, pure taste, and no organic solvent residue. Its volatile oil components are uniformly dispersed in the aqueous phase after being encapsulated by low-ester pectin, which can achieve a sustained release of aroma when drinking, giving the beverage product a lasting tangerine peel flavor and good flavor fullness.

[0028] This invention also provides a beverage comprising the aforementioned dried tangerine peel extract, wherein the amount of the dried tangerine peel extract added to the beverage is 0.03–0.12 wt%, and the pH of the beverage is 2.8–4.2. This addition range allows the beverage to acquire a distinct and moderate dried tangerine peel flavor, enhancing the fullness and intensity of the product's flavor without interfering with the main flavor profile. The pH of the beverage is controlled within the range of 2.8–4.2, which is within the gel stability range of low-ester pectin, thus helping to maintain the long-term physical stability of the oil / water dispersion in the dried tangerine peel extract.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The present invention uses a two-stage gradient temperature and pressure graded extraction strategy. In the first stage, volatile oil is selectively extracted under lower temperature and pressure conditions, and in the second stage, pectin and bound flavonoids are extracted under higher temperature and pressure conditions. This achieves the directional and segmented extraction of components with different polarity and thermal stability, and avoids thermal damage to volatile oil components under high temperature conditions.

[0031] (2) The present invention adopts low oxygen conditions and rapid cooling measures in the volatile oil extraction stage, which effectively inhibits the thermal oxidation and deterioration and volatilization loss of terpene volatile components, so that the obtained volatile oil components maintain a fresh and natural aroma.

[0032] (3) The present invention utilizes the high temperature and high pressure conditions of subcritical water to perform in-situ deesterification modification of the extracted pectin. Without the addition of alkali or enzyme preparations, high-ester pectin can be converted into low-ester pectin with good emulsifying activity. At the same time, the combined structure of pectin and flavonoids is preserved, realizing the integration of functional modification and extraction of pectin.

[0033] (4) This invention utilizes in-situ prepared low-ester pectin containing bound flavonoids as a natural emulsifier to homogenize and encapsulate volatile oils, realizing an integrated process of "extraction and emulsification". The volatile oils in the obtained tangerine peel extract are uniformly dispersed in the pectin aqueous phase in the form of submicron-sized oil droplets. It has excellent dispersion stability in acidic beverage systems, and all components are derived from the tangerine peel raw material itself, without the need to introduce exogenous emulsifiers, which meets the requirements of clean label.

[0034] (5) The present invention uses only water as a solvent throughout the process, without the need for any organic solvents. The resulting extract has no solvent residue and can be directly used in the food and beverage industry, which is in line with the development trend of green chemistry and clean production. Attached Figure Description

[0035] Figure 1 The gas chromatographic (GC) chromatogram of the tangerine peel extract prepared in Example 1. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements, and equivalents included within the scope of the claims.

[0037] Raw materials and equipment

[0038] 1. Raw materials

[0039] Dried tangerine peel: The dried tangerine peel used in this invention is the dried, mature peel of Citrus reticulata Blanco and its cultivated varieties, belonging to the Rutaceae family. Preferably, it is Xinhui tangerine peel from the Xinhui production area of ​​Guangdong Province, which has a rich aroma and high content of active ingredients.

[0040] 2. Equipment

[0041] Subcritical water extraction unit: 5 L stainless steel high-pressure extraction vessel, equipped with a temperature control system (accuracy ±1℃), a pressure control system (accuracy ±0.05 MPa), a high-pressure water inlet pump, a plate heat exchanger, and a solid-liquid separation device. The extraction vessel is designed for a pressure ≥5 MPa and a temperature ≥250℃. An inert gas inlet valve is installed at the top of the extraction vessel for nitrogen purging.

[0042] High pressure homogenizer: working pressure range 0~120 MPa.

[0043] Ultrafiltration membrane separation device: equipped with hollow fiber ultrafiltration membrane modules with a molecular weight cutoff of 3 to 50 kDa.

[0044] Auxiliary equipment: pulverizer, vacuum drying oven, rotary evaporator, laser particle size analyzer, gel permeation chromatography (GPC), high performance liquid chromatography (HPLC), dissolved oxygen analyzer, analytical balance, etc.

[0045] Example 1

[0046] Take 500 g of dried tangerine peel from Xinhui, Guangdong, pulverize it to 50 mesh, and vacuum dry it at 50℃ until the moisture content is 8.2% to obtain pretreated tangerine peel, which is then placed into a 5 L subcritical water extraction vessel.

[0047] S2. First-stage extraction (protective extraction of volatile oils): Deionized water (dissolved oxygen 1.5 mg / L) treated with nitrogen bubbling degassing is introduced into the extraction vessel, while the top space of the extraction vessel is displaced with nitrogen. The temperature and pressure are increased to 115℃ and 1.2MPa, and extraction is performed for 10 min. After extraction, the first extract is rapidly cooled to 28℃ in about 1 min using a plate heat exchanger for solid-liquid separation. The first extract is collected, and the first-stage residue is retained in the vessel.

[0048] S3. Second-stage extraction (pectin-bound flavonoid extraction): Continue to purge the residue from the first stage with deionized water, raise the temperature and pressure to 140℃ and 1.8 MPa, and extract for 15 min. After extraction, perform solid-liquid separation and collect the second extract.

[0049] S4. Subcritical hydrothermal deesterification treatment: The obtained second extract was transferred to a high-pressure treatment vessel and treated at 155℃ and 2.2MPa for 5 min, and then cooled to 50℃ to obtain a low-ester pectin component containing bound flavonoids.

[0050] S5. In-situ emulsification: At 50°C, the first extract is mixed with a low-ester pectin component containing bound flavonoids (the mass ratio of volatile oil component to pectin is 1:15), and homogenized three times at 40 MPa using a high-pressure homogenizer to obtain an oil / water dispersion.

[0051] S6. Concentration and Drying: The oil / water dispersion is concentrated under reduced pressure at 45°C using a rotary evaporator to a solid content of about 15%, and then spray-dried (inlet air temperature 160°C, outlet air temperature 75°C) to obtain powdered tangerine peel extract.

[0052] Example 2

[0053] Take 500 g of dried tangerine peel from Xinhui, Guangdong, grind it to 40 mesh, and vacuum dry it at 45℃ until the moisture content is 7.5%.

[0054] S2: Extraction water with dissolved oxygen 1.8 mg / L, headspace purged with nitrogen. Extraction at 105℃ and 0.8 MPa for 5 min. The extract was cooled to 25℃ within 2 min for solid-liquid separation.

[0055] S3: Extract at 130℃ and 1.5 MPa for 8 min, and collect the second extract by solid-liquid separation.

[0056] S4: Treat at 145℃ and 1.8 MPa for 8 min, then cool to 45℃.

[0057] S5: Homogenize at 45℃, with a volatile oil to pectin mass ratio of 1:5, and perform high-pressure homogenization at 20 MPa, for 4 homogenization cycles.

[0058] S6: After concentration under reduced pressure, freeze-dry to obtain powdered tangerine peel extract.

[0059] Example 3

[0060] Take 500 g of dried tangerine peel from Xinhui, Guangdong, grind it to 60 mesh, and vacuum dry it at 55℃ until the moisture content is 6.8%.

[0061] S2: Extraction water with dissolved oxygen 1.2 mg / L, headspace purged with nitrogen. Extraction at 125℃ and 1.5 MPa for 15 min. The extract was cooled to 30℃ within 30 s for solid-liquid separation.

[0062] S3: Extract at 150℃ and 2.2 MPa for 20 min, then collect the second extract by solid-liquid separation.

[0063] S4: Treat at 165℃ and 2.5 MPa for 2 min, then cool to 55℃.

[0064] S5: Homogenize at 55℃, with a volatile oil to pectin mass ratio of 1:25, and use micro-jet homogenization pressure of 80 MPa, homogenizing twice.

[0065] S6: After vacuum concentration, spray drying is performed to obtain powdered tangerine peel extract.

[0066] Example 4

[0067] Take 500 g of dried tangerine peel from Xinhui, Guangdong, grind it to 50 mesh, and vacuum dry it at 50℃ until the moisture content is 7.8%.

[0068] S2~S3: Process parameters are the same as in Example 1.

[0069] S4: The second extract was treated at 155℃ and 2.2 MPa for 5 min, cooled to 50℃, and then separated by a hollow fiber ultrafiltration membrane with a molecular weight cutoff of 10 kDa. The retentate was collected as the low-ester pectin component containing bound flavonoids.

[0070] S5~S6: Process parameters are the same as in Example 1.

[0071] Example 5

[0072] Take 500 g of dried tangerine peel from Xinhui, Guangdong, grind it to 50 mesh, and vacuum dry it at 50℃ until the moisture content is 8.0%.

[0073] S2~S3: Process parameters are the same as in Example 1.

[0074] S4: The second extract was treated at 155℃ and 2.2 MPa for 5 min, cooled to 50℃, and then separated by an ultrafiltration membrane with a molecular weight cutoff of 30 kDa. The retentate was collected.

[0075] S5~S6: Process parameters are the same as in Example 1.

[0076] Comparative Example 1

[0077] The process parameters are the same as in Example 1, but step S2 does not involve degassing or nitrogen purging; instead, undegassed deionized water (dissolved oxygen approximately 7.5 mg / L) is used directly, and the top space of the extraction vessel is not purged with inert gas. The parameters for the remaining steps remain unchanged.

[0078] Comparative Example 2

[0079] The process parameters for S2 to S3 are the same as in Example 1. The second extract obtained in S3 is not subjected to the high-temperature and high-pressure deesterification treatment in S4. Instead, it is directly cooled to 50°C and mixed with the first extract, and then homogenized under the same homogenization conditions as in Example 1. The parameters for the remaining steps remain unchanged.

[0080] Comparative Example 3

[0081] Take 500 g of dried tangerine peel from Xinhui, Guangdong, pulverize it to 50 mesh, add 1600 mL of 95% ethanol (solid-to-liquid ratio 1:8 g / mL), place in a three-necked flask and heat under reflux (approximately 78°C) for 3 h. Stop heating, cool to room temperature, filter, and remove the solvent from the filtrate using a rotary evaporator at 45°C under reduced pressure to obtain a viscous extract of dried tangerine peel.

[0082] Test methods

[0083] 1. Pectin content determination: The pectin content (on a dry basis) in the low-ester pectin component containing bound flavonoids was determined by the carbazole-sulfuric acid colorimetric method, using galacturonic acid as the standard.

[0084] 2. Determination of total flavonoid content: The total flavonoid content (on a dry basis) in the low-ester pectin component was determined by the AlCl3 colorimetric method with hesperidin as the standard.

[0085] 3. Determination of esterification degree: The degree of esterification (DE) of pectin was determined by titration (FAO / JECFA standard method).

[0086] 4. Determination of weight-average molecular weight: The weight-average molecular weight (Mw) of pectin was determined by gel permeation chromatography (GPC) with dextran series standards as calibration standards.

[0087] 5. Particle size and PDI determination: The volume average particle size D50 and polydispersity index (PDI) of the oil / water dispersion were determined using a laser particle size analyzer (dynamic light scattering method).

[0088] 6. Identification of flavonoids: High performance liquid chromatography (HPLC) was used to detect the content of flavonoids such as hesperidin, nonotrimonin, hesperidin and naringerin.

[0089] 7. Evaluation of the aroma quality of volatile oils: The relative contents of major terpenoid compounds and their oxidative degradation products in volatile oils were analyzed by gas chromatography-mass spectrometry (GC-MS). Combined with a double-blind sensory evaluation by a 7-person sensory evaluation panel, the aroma quality of volatile oils was comprehensively evaluated (1 point = very poor, 9 points = very good).

[0090] 8. Dispersion stability test: The tangerine peel extract was added to the beverage base (pH 2.8–4.2) at the target dosage, mixed thoroughly, sealed, and subjected to accelerated stability testing in a 40℃ constant temperature incubator. The appearance and particle size changes were observed periodically.

[0091] Test Results

[0092] Table 1 Comparison of extraction rates of different extraction methods

[0093] project Example 1 Example 2 Example 3 Pectin content (wt%, dry basis) 68.5 55.2 72.3 Total flavonoid content (wt%, dry basis) 5.8 8.3 3.2 Degree of esterification DE (%) 32 38 22 Weight-average molecular weight Mw (kDa) 85 120 48

[0094] As shown in Table 1, under different S4 treatment conditions, the degree of esterification of the low-ester pectin components obtained in Examples 1-3 were all in the range of 18-45%, the pectin content was in the range of 40-90 wt%, the total flavonoid content was in the range of 0.5-15 wt%, and the weight-average molecular weight was in the range of 30-150 kDa. This indicates that subcritical hydrothermal treatment can effectively convert high-ester pectin from tangerine peel into low-ester pectin, and the bound flavonoids are effectively retained during the deesterification process. Among them, the pectin obtained in Example 1 (155°C / 5 min) had a moderate degree of esterification (32%) and molecular weight (85 kDa), possessing both good interfacial emulsification activity and sufficient molecular weight to form a stable interfacial film. The deesterification in Example 2 (145°C / 8 min) was relatively mild, with a higher degree of esterification (38%) and a better retention of molecular weight (120 kDa), but the interfacial activity was relatively insufficient. The deesterification in Example 3 (165°C / 2 min) was the most complete (DE22%), but the molecular weight was significantly degraded (48 kDa), and the stability of the interfacial film decreased.

[0095] Table 2 Particle size characteristics of oil / water dispersions in each group

[0096] Group D50 (μm) PDI Appearance description Example 1 0.22 0.16 Milky white homogeneous dispersion, with no visible oil droplets. Example 2 0.62 0.30 Milky white dispersion, uniform Example 3 0.28 0.20 A translucent, uniform emulsion dispersion. Example 4 0.18 0.13 Milky white, uniform dispersion, extremely homogeneous, with no visible oil droplets. Example 5 0.20 0.15 Milky white, uniform dispersion, extremely homogeneous, with no visible oil droplets. Comparative Example 1 0.25 0.19 Milky white dispersion, uniform Comparative Example 2 2.85 0.68 The surface is cloudy and uneven, with visible oil droplets.

[0097] Table 2 shows that the D50 of the dispersions obtained in Examples 1-5 were all in the range of 0.1-0.8 μm, and the PDI was no greater than 0.35, indicating that the in-situ prepared low-ester pectin containing bound flavonoids as an emulsifier can effectively disperse volatile oil into uniform submicron-sized oil droplets. In Example 1, because the degree of esterification (32%) and molecular weight (85 kDa) of the pectin were in the optimal equilibrium range, excellent dispersion was achieved under homogenization conditions of 40 MPa (D50=0.22 μm, PDI=0.16). In Example 2, due to the low S4 treatment temperature (145°C), the pectin deesterification was insufficient (DE 38%), resulting in relatively weak interfacial activity and a larger D50 (0.62 μm). Although Example 3 used 80 MPa microfluidic homogenization, the highest treatment temperature (165°C) in Example 4 resulted in excessive degradation of the pectin backbone (Mw 48 kDa), decreased interfacial membrane stability, and lower particle size (0.28 μm) and PDI (0.20) compared to Example 1. In Examples 4 and 5, the purity of the low-ester pectin was improved after ultrafiltration purification, and D50 and PDI were further optimized compared to Example 1.

[0098] Compared to Example 1, Comparative Example 1 (without hypoxia protection) showed little difference in particle size and PDI, indicating that hypoxia conditions primarily affected the aroma quality of the volatile oil rather than its emulsifying and dispersing properties (see Table 3 for details). Comparative Example 2 (without S4 deesterification treatment) exhibited a high D50 of 2.85 μm and a PDI of 0.68, with visible oil droplet aggregation on the surface, confirming the necessity of the S4 deesterification step for achieving in-situ emulsification.

[0099] Table 3. Effects of hypoxia on the aroma quality of volatile oils (GC-MS analysis and sensory evaluation)

[0100] Group Relative limonene content (%) Relative content of γ-terpinene (%) Relative content of linalool oxide (%) Relative content of cymene (%) Sensory aroma evaluation Example 1 (Hypoxia) 58.3 12.5 0.8 1.2 It has a fresh and natural citrus aroma, bright and with a prominent freshness. Comparative Example 1 (without hypoxia) 42.1 8.3 5.6 6.8 The aroma is rather dull and somber, with a noticeable oxidized smell, and the freshness is diminished.

[0101] As shown in Table 3, the relative contents of the main aroma components, such as limonene and γ-terpinene, in the volatile oil extracted under hypoxic conditions in Example 1 were significantly higher than those in Comparative Example 1, while the relative contents of oxidative degradation products, such as linalool oxide and p-cymene, were significantly lower than those in Comparative Example 1. These results indicate that hypoxic conditions can effectively inhibit the thermal oxidative deterioration of volatile oils during high-temperature extraction, maintaining their fresh and natural aroma characteristics.

[0102] Table 4. Reconstitution and dispersion characteristics of tangerine peel extract under acidic conditions

[0103] Group Reconstitute pH D50 (μm) PDI Appearance after 24 hours Example 1 2.8 0.26 0.19 Uniform, without layering Example 1 3.5 0.23 0.17 Uniform, without layering Example 1 4.2 0.25 0.20 Uniform, without layering Example 4 3.5 0.20 0.14 Uniform, without layering Comparative Example 2 3.5 5.20 0.78 There is obvious stratification, and an oil film is visible on the surface.

[0104] Table 4 shows that the tangerine peel extract (powder) obtained in Example 1, after reconstitution in water, formed a stable dispersion with a D50 of 0.1–0.8 μm and a PDI of no more than 0.35 within a pH range of 2.8–4.2. After standing for 24 h, the dispersion exhibited a uniform appearance and no stratification, indicating that the low-ester pectin maintained good structural integrity in encapsulating the volatile oil droplets during drying and reconstitution. In Example 4, after ultrafiltration purification, the particle size and PDI of the reconstituted dispersion were further optimized. In Comparative Example 2, due to the insufficient emulsifying ability of the unmodified pectin, the particle size increased sharply and stratified rapidly after reconstitution.

[0105] Table 5. Application effects of tangerine peel extract in different beverages (dispersion stability and sensory evaluation)

[0106] Application System Extract source Amount added (wt%) pH Initial D50 (μm) 90-day D50 (μm)* 90-day appearance Sensory evaluation Sugar-free sparkling water Example 1 0.08 3.2 0.23 0.28 Clear, without sediment It has a fresh and natural aroma of dried tangerine peel and citrus, a refreshing taste with no bitterness, and blends well with the base. Sour Plum Drink Example 1 0.10 3.0 0.24 0.30 Uniform, without layering The tangerine peel has a distinct and fresh aroma that blends harmoniously with the flavor of the sour plum drink, resulting in a pure taste and a powerful burst of flavor. Sugar-free sparkling water Example 2 0.08 3.2 0.63 0.88 Slightly cloudy with a small amount of sediment at the bottom. The aroma of dried tangerine peel is rather weak, the texture is thin, and the flavor intensity is insufficient. Lemon tea Example 3 0.05 3.5 0.35 0.40 Uniform, without layering The complex aroma of dried tangerine peel and citrus blends naturally and harmoniously with the tea base. Fruit-flavored sparkling water Example 4 0.03 4.0 0.37 0.43 Clear, without sediment The delicate aroma of dried tangerine peel, the refreshing and delicate taste, and the excellent harmony with the fruity base flavor. Sugar-free sparkling water Example 1 0.12 3.2 0.23 0.29 Clear, without sediment The tangerine peel has a rich and full-bodied flavor, a pure taste, no bitterness, and a long-lasting flavor. Sour Plum Drink Comparative Example 3 0.10 3.0 — — — The tangerine peel flavor is strong, and the astringent taste at the end, combined with the sourness and astringency of the plum juice, makes it overall quite astringent. Sugar-free sparkling water Comparative Example 3 0.08 3.2 — — — The aroma of dried tangerine peel is strong but slightly dull, with a slightly astringent finish and a less refreshing taste.

[0107] *Note: Accelerated storage conditions at 40℃.

[0108] Table 5 shows that the tangerine peel extracts obtained in Examples 1, 3, and 4 exhibited minimal particle size increase (less than 0.1 μm) after 90 days of accelerated storage at 40°C in different acidic beverage bases. The appearance remained uniform and clear, with no precipitation or oil film formation, indicating excellent long-term dispersion stability in acidic beverage systems. Example 2, due to the mild deesterification conditions in S4 (145°C / 8 minutes), resulted in a high degree of pectin esterification (DE 38%) and insufficient emulsification and encapsulation ability. After 90 days of accelerated storage, the D50 increased to 0.88 μm, with slight turbidity and a small amount of precipitation. Sensory characteristics included a weak aroma and insufficient flavor intensity, further confirming the importance of moderate deesterification modification in the S4 step for final beverage applications. Example 1 exhibited a fresh and natural citrus aroma in both sugar-free sparkling water and plum juice, with a pure taste and no bitterness, and high integration with the beverage base. Compared with traditional ethanol reflux extraction (Comparative Example 3), the extract of this invention has a brighter and fresher aroma, no obvious astringency at the end, and a more rounded overall taste. This is mainly due to the effective inhibition of thermal oxidation and deterioration of volatile oils under low oxygen conditions and the protective effect of low-ester pectin on the micro-droplets of volatile oils.

[0109] Table 6. Composition of bound flavonoids in the extracts of each example (HPLC analysis)

[0110] Group Hesperidin (mg / g dry basis) Noriheptacorlin (mg / g dry basis) Hesperidin (mg / g dry basis) Naringenin (mg / g dry basis) Example 1 18.5 6.2 2.8 1.5 Example 2 22.3 7.8 3.5 2.0 Example 3 12.6 4.5 1.8 0.9 Example 4 20.2 6.8 3.0 1.6

[0111] Table 6 shows that hesperidin, nonotrimonin, hesperidin, and naringerin were detected in the tangerine peel extracts obtained in all examples, with hesperidin having the highest content and being a characteristic flavonoid of tangerine peel. In Example 2, due to the lower S4 treatment temperature (145℃) and longer treatment time (8 min), pectin deesterification was gentler, resulting in the highest retention rate of bound flavonoids. In Example 3, due to the highest S4 treatment temperature (165℃), some bound flavonoids underwent hydrolysis and release, resulting in a relatively lower total flavonoid content.

[0112] Based on the data in Tables 1 to 6, the S4 treatment conditions (155°C, 2.2 MPa, 5 min) in Example 1 achieved the best balance between pectin deesterification, molecular weight retention, emulsification effect, and flavonoid retention: the emulsification and dispersion effect was optimal (D50 = 0.22 μm), and the retention of bound flavonoids was at a high level (hesperidin 18.5 mg / g), representing the optimal implementation method of the present invention.

[0113] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A green process for water extraction of natural components from dried tangerine peel, characterized in that, Includes the following steps: S1. Grind the dried tangerine peel raw material to 30-80 mesh and dry it until the moisture content is no more than 10% to obtain pretreated dried tangerine peel; S2. Under low oxygen conditions, the pretreated tangerine peel is extracted with water as the extraction solvent at 105-125℃ and 0.8-1.5 MPa for 5-15 min. The extract is exported and cooled to 20-35℃. The first extract and the first stage residue are obtained by solid-liquid separation. S3. The residue from the first stage is extracted with water as the extraction solvent at 130–150°C and 1.5–2.2 MPa for 8–20 min, and the second extract is obtained by solid-liquid separation. S4. The second extract is treated at 145-165℃ and 1.8-2.5 MPa for 2-8 min and then cooled to 40-60℃ to obtain a low-ester pectin component containing bound flavonoids. S5. At 45-60°C, the first extract is mixed with the low-ester pectin component containing bound flavonoids and homogenized to obtain an oil / water dispersion in which the volatile oil component in the first extract is dispersed in the aqueous phase. S6. Concentrate and / or dry the oil / water dispersion to obtain tangerine peel extract.

2. The green process according to claim 1, characterized in that, The dried tangerine peel is the dried, mature peel of the citrus fruit and its cultivated varieties, belonging to the Rutaceae family; the extraction solvent is deionized water or purified water.

3. The green process according to claim 1, characterized in that, The drying in S1 is vacuum drying at 40–55°C; the low-oxygen conditions in S2 are that the dissolved oxygen in the extraction water is not higher than 2 mg / L, and / or the top space of the extraction device is replaced with an inert gas; the extract exported in S2 is cooled to 25–30°C within 30 s to 3 min.

4. The green process according to claim 1, characterized in that, The low-ester pectin component containing bound flavonoids obtained in S4 has a pectin content of 40–90 wt% and a total flavonoid content of 0.5–15 wt% on a dry basis. The degree of esterification of the pectin is 18–45%, and the weight-average molecular weight is 30–150 kDa.

5. The green process according to claim 1, characterized in that, S4 further includes: separating the low-ester pectin component containing bound flavonoids obtained after cooling through an ultrafiltration membrane with a molecular weight cutoff of 3 to 50 kDa, and collecting the retentate as the low-ester pectin component containing bound flavonoids for use in S5.

6. The green process according to claim 1, characterized in that, The mass ratio of the volatile oil component in the first extract of S5 to the pectin in the low-ester pectin component containing bound flavonoids is 1:(2-30); the homogenization process is carried out by high-pressure homogenization or microfluidic homogenization, and the homogenization pressure is 10-80 MPa; the volume average particle size D50 of the oil / water dispersion obtained in S5 is 0.1-0.8 μm.

7. A tangerine peel extract, characterized in that, It is prepared by the green process described in any one of claims 1 to 6, wherein the tangerine peel extract is an aqueous dispersion, its concentrate or its dried product, comprising tangerine peel volatile oil component and low-ester pectin component containing bound flavonoids; wherein the tangerine peel volatile oil component is dispersed in the form of oil droplets in an aqueous continuous phase containing the low-ester pectin component.

8. The tangerine peel extract according to claim 7, characterized in that, The tangerine peel extract, after being reconstituted in water, forms a dispersion with a volume average particle size (D50) of 0.1–0.8 μm and a polydispersity index (PDI) of no more than 0.35 under pH conditions of 2.8–4.2; the flavonoids in the bound flavonoids are selected from one or more of hesperidin, nonosiderin, hesperidin and naringerin.

9. The use of the tangerine peel extract according to claim 7 or 8 in the preparation of natural flavor additives for beverages.

10. A beverage, characterized in that, The beverage includes the tangerine peel extract as described in claim 7 or 8, wherein the amount of the tangerine peel extract added to the beverage is 0.03 to 0.12 wt%, and the pH of the beverage is 2.8 to 4.2.

Images