Preparation method of red date juice rich in xanthophyll

Abstract

The invention provides a lutein-loaded modified pea protein isolate-beet pectin nano-composite, which is prepared by the following steps: by taking lutein as a fat-soluble nutrient raw material, carrying out ultrasonic modification on pea protein isolate (PPI), carrying out ultrasonic pretreatment on PPI and carrying out grafting modification by combining xylose (Xyl), and preparing a single-layer nano-composite by taking the lutein as a raw material through a pH shift method, so as to obtain the lutein-loaded modified pea protein isolate-beet pectin nano-composite. The preparation method comprises the following steps: preparing red date juice, adding xanthophyll into the red date juice to form a xanthophyll-loaded single-layer nano-composite, carrying out electrostatic self-assembly compounding on the xanthophyll-loaded single-layer nano-composite and beet pectin under the condition that the pH value is 2-4 to form a double-layer xanthophyll-wrapped stable system, and adding the nano-composite into the red date juice so as to increase the content of fat-soluble nutrients in the red date juice. The xanthophyll double-layer nanocomposite has excellent storage stability and solubility, and can effectively prevent degradation of xanthophyll, so that the embedding rate and stability of xanthophyll are remarkably improved, and the utilization rate of xanthophyll is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of food engineering technology, specifically relating to a method for preparing a modified pea protein isolate-beet pectin nanocomposite loaded with lutein and its application in jujube juice. Background Technology

[0002] Lutein is a natural carotenoid, mainly found in fruits and vegetables, and can be used as a natural colorant in food. More importantly, lutein, as a nutritional supplement, has functions such as reducing macular degeneration, promoting brain development, and anti-inflammation. It can also reduce the formation of some chronic diseases, such as cataracts, coronary heart disease, and atherosclerosis. Despite its excellent functional properties, its poor solubility in aqueous solutions and low bioavailability limit its application in other foods. Therefore, encapsulating fat-soluble nutrients using nanodelivery systems has become a popular method in recent years.

[0003] In particular, using some food-derived proteins as carriers to construct nanocomposites has proven to be a promising approach. Pea protein isolate (PPI), as a natural protein, possesses certain emulsifying and foaming properties, and exhibits low allergenicity, making it relatively safe. However, pea globulin mainly exists in trimer form, with molecules bound together through hydrophobic interactions. Therefore, the relatively poor functional properties of pea protein limit its widespread use as a functional component in food systems. Appropriate modification of the pea protein structure is an effective means to improve its functional properties. Glycosylation has been recognized as a green, mild, and effective strategy for altering the functional properties of various proteins. Since carbohydrates can be covalently linked to available amino groups in proteins through spontaneous Maillard reactions, they can effectively regulate functional properties such as solubility, emulsifying properties, and antioxidant properties through interactions with proteins.

[0004] However, nanocomposites composed of single proteins are prone to aggregation and precipitation at the isoelectric point of the protein, thus disrupting the system. To further expand the application range of protein-based nanocomposites in different pH environments, various polysaccharides, such as carboxymethyl cellulose, gum arabic, hyaluronic acid, and chitosan, have been introduced to coat proteins on their surfaces through intermolecular interactions such as electrostatic interactions and hydrogen bonds. However, research on using modified pea protein isolate and beet pectin to form multilayer core-shell nanocomposites for loading lutein has not yet been reported.

[0005] Red dates (scientific name: Ziziphus jujuba Mill.As a traditional medicinal and edible resource, jujubes hold an important position in both the food and pharmaceutical fields due to their rich nutritional composition and medicinal properties. Nutritional analysis shows that jujubes contain 70%-85% carbohydrates, with a significant proportion of free sugars such as fructose and glucose, which can quickly provide energy to the body. They are also rich in vitamins (such as vitamin C, B vitamins B1, B2, and niacin) and minerals such as potassium, iron, calcium, and phosphorus. While the iron is mainly non-heme iron with a lower absorption rate, vitamin C can aid in its absorption. Furthermore, jujubes contain dietary fiber (approximately 6%-10%), cyclic adenosine monophosphate (cAMP), triterpenoids, and flavonoids, all of which contribute to their high nutritional value and physiological activity. Current research confirms that jujubes have potential positive effects in regulating blood lipids, enhancing immunity, and antioxidation. In particular, for patients with hyperlipidemia, daily intake of more than 30 g for more than 3 months can significantly improve serum triglyceride levels and other indicators. Red date juice, a core product of deep-processed red dates, is made from fresh or dried red dates through standardized processes including washing, pitting, crushing, extraction, filtration, and sterilization. This process effectively preserves the core nutrients and characteristic flavor of red dates. Compared to dried red dates, red date juice offers advantages such as improved convenience of consumption and higher bioavailability of nutrients due to the partial degradation of dietary fiber and the liquefaction of nutrients. It is particularly suitable for the elderly, children, and those seeking convenient health management, especially those with weaker digestive systems. In recent years, with the popularization of healthy consumption concepts, red date juice, positioned as "natural, nutritious, and healthy," has seen a continuous rise in attention in the beverage market. Currently, its application has expanded from daily beverages to functional beverages, and its development potential is widely recognized.

[0006] However, as a convenient dietary supplement, fruit and vegetable juices have significant shortcomings in their nutritional system, primarily manifested in their limited nutritional composition and the instability of active ingredients. Specifically, the nutritional composition exhibits an imbalance of "primarily water-soluble, with a lack of fat-soluble components": fat-soluble nutrients naturally present in fruit and vegetable raw materials, such as vitamins A, E, and lutein, are tightly bound to dietary fiber and have low solubility in aqueous systems, resulting in a loss rate exceeding 70% during juicing and clarification processes. This leads to over 90% of detectable nutrients in commercially available products being water-soluble components such as vitamin C and B vitamins, making long-term consumption of only these nutrients insufficient to meet balanced nutritional needs. Therefore, using encapsulation technologies (nanoemulsions, liposomes, cyclodextrin inclusion complexes, etc.) to load fat-soluble nutrients into jujube juice can fundamentally improve these nutritional deficiencies. Its core technological advantages are: firstly, improved stability and bioavailability of fat-soluble nutrients; secondly, a balanced upgrade of the nutritional system; and thirdly, ensuring the stability of the product's sensory quality, providing a systematic solution for fortifying fat-soluble nutrients.

[0007] Based on this, this application was developed. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a modified pea protein isolate-beet pectin bilayer nanocomposite loaded with lutein. This bilayer nanocomposite exhibits excellent storage stability, effectively protects lutein, thereby improving its utilization rate, and when applied to jujube juice, it significantly enriches the nutritional components of the jujube juice, making its internal nutrition more balanced.

[0009] The present invention also provides a method for preparing the above-mentioned lutein-loaded modified pea protein isolate-beet pectin nanocomposite and its application in jujube juice.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a lutein-loaded modified pea protein isolate-beet pectin bilayer nanocomposite, comprising the following steps: (1) Pea protein isolate (PPI) was prepared into a protein suspension, ultrasonically treated with an ultrasonic cell disruptor, and then freeze-dried into powder; (2) The protein powder obtained in step (1) is reconstituted into a protein suspension (1-30 mg / mL), xylose is added to it, and the mixture is reacted at 60-100℃ for 60-160 min. Then, it is freeze-dried at -80℃~-60℃ for 36-48 h to obtain glycosylated protein powder. (3) The glycosylated protein powder obtained in step (2) is formulated into a protein suspension, and lutein is encapsulated using the pH shift method to form a monolayer nanocomposite. (4) Add beet pectin to the monolayer nanocomposite obtained in step (3), adjust the pH to 2-4, stir for 2-4 h, then evaporate the solvent by rotary evaporation, and replenish the evaporated solvent with an equal volume of distilled water. After centrifugation, freeze dry at -80℃ to -60℃ for 36-48 h to obtain the final product.

[0011] Specifically, in step (1), the processing power of the ultrasonic cell disruptor is 100-800 W, and the processing time is 5-30 min. The ultrasonic treatment is preferably 150-750 W, more preferably 200-600 W, and most preferably 300-500 W; the processing time is preferably 5-25 min, further preferably 10-25 min, and most preferably 15-25 min.

[0012] Specifically, the concentration of the protein suspension prepared in step (2) is 1-30 mg / mL; further selection is 5-25 mg / mL; preferably 5-20 mg / mL; more preferably 5-15 mg / mL; most preferably 8-12 mg / mL. Xylose is added to the protein suspension at a protein powder to sugar mass ratio of 5-1:1. Further selection is 4-1:1; preferably 3-1:1; most preferably 2-1:1.

[0013] Furthermore, in step (2), the reaction is carried out at 60-100℃ for 60-160 min; it can be carried out at 60-90℃ for 70-140 min; it can be carried out at 70-85℃ for 80-120 min; preferably at 75-85℃ for 85-105 min; and most preferably at 75-85℃ for 85-95 min.

[0014] Furthermore, the concentration of the protein suspension prepared in step (3) is 1-30 mg / mL; further selected is 5-25 mg / mL; preferably 5-20 mg / mL; more preferably 5-15 mg / mL; most preferably 8-12 mg / mL.

[0015] Specifically, the pH shifting method used in step (3) is as follows: First, adjust the pH to 11-13 with 1 mol / L NaOH solution and stir for 20-60 min. Then, adjust the pH to 7 with 1 mol / L HCl solution and stir for 20-60 min. Subsequently, add lutein solution dissolved in anhydrous ethanol, keeping the pH constant throughout the process, and equilibrate for 20-60 min to obtain a monolayer nanocomposite. The mass ratio of lutein to glycosylated protein is 1:1-40. Further selection of the mass ratio is 1:1-30, preferred mass ratio is 1:10-30, more preferred mass ratio is 1:15-30, and most preferred mass ratio is 1:15-25.

[0016] Specifically, in step (4), the mass ratio of glycosylated protein to beet pectin is 1:10-40:1, a further selected mass ratio is 1:5-20:1, a preferred mass ratio is 1:5-10:1, a more preferred mass ratio is 1:5-5:1, and the most preferred mass ratio is 1:2-2:1. The temperature during rotary evaporation is 40-45℃. The preferred additive is a beet pectin solution with a concentration of 0.5-5 mg / mL. The pH is adjusted to 2-4 using 1 mol / L HCl, and the mixture is stirred for 2-4 h. Then, the solution is placed in a rotary evaporator at 40-45℃ to evaporate the ethanol, and the same volume of distilled water is used to replenish the evaporated ethanol. The freshly prepared sample is centrifuged (centrifugation speed is 3000-4000 r / min, centrifugation time is 10-15 min) to remove unencapsulated lutein, and then freeze-dried to obtain the bilayer nanocomposite powder.

[0017] This invention provides a modified pea protein isolate-beet pectin nanocomposite prepared by the above method, which is a modified pea protein isolate-beet pectin-lutein composite nanocomposite delivery system. The modified pea protein isolate and lutein form a hydrophobic core, and the beet pectin is coated on the surface through electrostatic adsorption to form an outer shell layer.

[0018] The present invention also provides the application of the above-mentioned lutein-loaded modified pea protein isolate-beet pectin nanocomposite in jujube juice.

[0019] Another aspect of the present invention is to provide a method for preparing jujube juice rich in lutein, which involves mixing jujube juice with the lutein-loaded modified pea protein isolate-beet pectin nanocomposite until homogeneous.

[0020] Furthermore, the mass ratio of the jujube juice to the lutein-loaded modified pea protein isolate-beet pectin nanocomposite is 50-200:1 (preferably 50-150:1; more preferably 50-120:1; most preferably 80-120:1); the two are mixed uniformly by ultrasonication at a power of 150-400 W; more preferably 150-300 W; most preferably 200-250 W. The ultrasonication time is 1-8 min; more preferably 2-8 min; more preferably 3-6 min; most preferably 3-5 min.

[0021] Furthermore, the method for preparing the jujube juice includes: washing jujubes, adding water at a solid-liquid ratio of 1:5-8 g / L to form a pulp, enzymatically hydrolyzing, inactivating the enzyme, filtering, centrifuging, and adjusting to obtain jujube juice. The enzymatic hydrolysis uses a complex enzyme composed of pectinase and cellulase, with an addition amount of 2-4 g / L, and is performed at 40±5℃ for 2-4 h. After enzymatic hydrolysis, the mixture is immediately reacted at 80-90℃ for 15-30 min to inactivate the enzyme activity. After cooling to room temperature, the mixture is filtered using three layers of gauze. After filtration, the mixture was centrifuged (6000 r / min, 4℃, 8 min). The supernatant of the jujube juice was collected and mixed with 0.10% citric acid and 3.0% white sugar. A modified pea protein isolate-beet pectin nanocomposite loaded with lutein was added to the jujube juice supernatant at a mass ratio of 100:1. The different jujube juices were then treated separately in an ultrasonic cell disruptor at 225 W for 4 min to further mix the added solution with the jujube juice. Finally, after pasteurization (85℃, 15 min), the lutein-rich jujube juice beverage (JJB) was obtained and stored at -4℃.

[0022] The present invention also provides jujube juice rich in lutein prepared by the above method.

[0023] Based on the background described in the prior art, this invention uses ultrasonic treatment and ultrasonic pretreatment combined with glycosylation modification of PPI to improve its functional properties, and then performs self-assembly with beet pectin to form a bilayer nanocomposite for loading lutein, thereby more stably encapsulating lutein and significantly improving lutein utilization. Subsequently, the prepared nanocomposite is added to jujube juice, and lutein-rich jujube juice is prepared using ultrasonic technology. Compared with the prior art, this invention has the following advantages and beneficial effects: 1) The ultrasonic treatment expands the structure of PPI to some extent, providing more sites for glycosylation and thus improving its grafting efficiency. This results in better stability and delivery efficiency of fat-soluble nutrients in the prepared nanocomposite. Furthermore, using beet pectin as the "shell" and the modified protein-lutein "core" for self-assembly via electrostatic interactions and intermolecular forces such as hydrogen bonds further enhances its stability and the encapsulation rate of fat-soluble nutrients. Simultaneously, the preparation method of this invention is simple, has low production costs, uses natural or low-toxicity raw materials, and the prepared nanocomposite exhibits high safety and good biocompatibility. 2) Compared with the traditional process of making jujube juice, the present invention is simple to operate. The antioxidant activity of jujube juice after adding nanocomplex is significantly improved, and the content of some nutrients is increased, thereby making up for the lack of fat-soluble nutrients in commercially available jujube juice. Attached Figure Description

[0024] The advantages of the present invention, as described above and / or in more detail with reference to the accompanying drawings and specific embodiments, will become clearer.

[0025] Figure 1 The measurements of particle size (Size, nm) and potential (Zeta-potential, mV) of the prepared nanocomposite were performed in Example 2.

[0026] Figure 2 The encapsulation efficiency (EE, %) and loading efficiency (LE, %) of the prepared nanocomposite were measured in Example 3.

[0027] Figure 3 The DPPH and hydroxyl radical scavenging capabilities of the prepared nanocomposite were measured in Example 4.

[0028] Figure 4The photostability of the prepared nanocomposite was measured in Example 5.

[0029] Figure 5 The thermal stability of the prepared nanocomposite was measured in Example 5 (A, 4°C; B, 25°C; C, 60°C).

[0030] Figure 6 The pH stability of the prepared nanocomposite was measured in Example 5, with average particle size (Size, nm, left) and zeta potential (Zeta-potential, mV, right).

[0031] Figure 7 The results are from the in vitro simulated digestion experiment performed on the prepared nanocomposite in Example 6.

[0032] Figure 8 The results of the storage stability (0-180 d) test of the lutein-rich jujube juice prepared in Example 11 are as follows: average particle size (A), zeta potential (B), and centrifugal sedimentation rate (CSR, C).

[0033] Figure 9 The images show the appearance of the lutein-rich jujube juice prepared in Example 12 (0 d, 45 d, 70 d, 180 d, samples from left to right are JJB-Pure, JJB-LUT, JJB-S40, JJB-LP, JJB-LPS, JJB-LUS, JJB-L-UX-S). Detailed Implementation

[0034] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0035] In the following examples, all raw materials used were commercially available products that could be directly purchased or prepared using conventional techniques in the art. For example, pea protein isolate (PPI) was purchased from Xi'an Binghe Biotechnology Co., Ltd.; beet pectin (SBP) was purchased from Nanjing Siji Qianshun Biotechnology Co., Ltd.; lutein (purity >75%), pepsin (enzyme activity: 30000 u / g), trypsin (enzyme activity: Trypsin 1:250), and bile salts were purchased from Shanghai Yuanye Biotechnology Co., Ltd.; 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH, reagent grade, purity ≥97.0%) and salicylic acid (reagent grade, purity: 99.5%) were purchased from Shanghai Maclean Biotechnology Co., Ltd.; fresh red dates were purchased from Henan Haoxiangni Health Food Co., Ltd.; ascorbic acid (Vc), gallic acid, rutin, and bovine serum albumin (BSA) were purchased from Shanghai Maclean Biotechnology Co., Ltd.; and Folin-Ciocalteu reagent was purchased from Beijing Solarbio Technology Co., Ltd.

[0036] Room temperature refers to 25±5℃. Example 1

[0037] A method for preparing a lutein-loaded modified pea protein-beet pectin nanocomposite, comprising the following steps: (1) Add PPI to deionized water and stir at 35°C for 30 min to fully dissolve the protein and prepare a protein suspension of 10 mg / mL. Cool to room temperature and use an ultrasonic cell disruptor to sonicate the protein suspension (360 W, 20 min). Freeze-dry the treated protein solution at -80°C for 48 h to obtain UPPI powder. (2) The UPPI powder obtained in step (1) was reconstituted into a protein suspension of 10 mg / mL using deionized water. Xylose was added to the protein suspension at a mass ratio of 2:1 between UPPI powder and sugar. The mixture was stirred to mix the protein and sugar. The mixture was reacted in a water bath at 80°C for 90 min. After the reaction was completed, the mixture was immediately placed in an ice-water bath to stop the reaction. Then, it was freeze-dried at -80°C for 48 h to obtain the UPPIX grafted product (i.e., glycosylated protein powder). (3) Prepare protein suspensions of 10 mg / mL using deionized water for PPI, UPPI, or UPPIX respectively, stir for 30 min, adjust the pH of the system to 12.0 using 1 mol / L NaOH aqueous solution, stir for 30 min, then adjust the pH of the system to 7.0 using 1 mol / L HCl, and stir for equilibration for 30 min. Then add lutein ethanol solution dissolved in anhydrous ethanol, keeping the pH constant during the process, and equilibrate for 30 min to obtain a monolayer nanocomposite. The mass ratio of lutein (LUT) to protein is 1:20. (4) Dissolve beet pectin in deionized water to a concentration of 5 mg / mL, then add it to the monolayer nanocomposite at a ratio of 1:1 with the modified protein. Adjust the pH of the solution to 4.0, stir for 3 h, and then evaporate the ethanol in a rotary evaporator at 42 °C. The evaporated ethanol is then replenished with the same volume of distilled water. The resulting solution is then centrifuged at 4000 r / min for 10 min, and finally freeze-dried at -80 °C for 48 h to obtain the bilayer nanocomposite powder product.

[0038] The single-layer nanocomposites prepared in step (3) above are named LUT-PPI (LP), LUT-UPPI (LU) and LUT-UPPIX (L-UX), respectively. The double-layer nanocomposites prepared in step (4) above are named LUT-PPI-SBP (LPS), LUT-UPPI-SBP (LUS) and LUT-UPPIX-SBP (L-UX-S), respectively. Example 2

[0039] Size (nm) and potential (Zeta-potential, mV) of lutein-loaded nanocomposites.

[0040] The average particle size and zeta potential of each sample in Example 1 were measured using a Malvern laser particle size analyzer. The results are shown in [Figure Number]. Figure 1 .

[0041] from Figure 1 As can be seen, the particle size of unmodified PPI (LP) is 1064.3 nm, the particle size of PPI (LU) modified by ultrasonic pretreatment is 240.67 nm, and the particle size of PPI (L-UX) modified by ultrasonic pretreatment combined with xylose glycosylation is 304.7 nm. After the addition of beet pectin, the particle sizes of the LPS, LUS, and L-UX-S bilayer nanocomposites are significantly larger than those of the monolayer nanocomposites, reaching 1209 nm, 357.67 nm, and 397.77 nm, respectively. Furthermore, compared to LP, the Zeta-potentials of LU and L-UX change from -18.06 mV to -21.00 mV and -23.05 mV, respectively. After the addition of beet pectin, the absolute values ​​of the Zeta-potentials of LPS, LUS, and L-UX-S continue to increase relative to the monolayer nanocomposites. Notably, L-UX-S exhibits the highest absolute potential value of -33.07 mV. The higher the degree of negative charge carried by the zeta potential, the stronger the electrostatic repulsion, which helps to enhance the stability of the L-UX-S system. Overall, the L-UX-S system exhibits greater stability. Example 3

[0042] Encapsulation efficiency (EE, %) and loading efficiency (LE, %) of lutein by nanocomposites.

[0043] 0.2 g of each sample from Example 1 was dispersed in 20 mL of deionized water to prepare a suspension of 10 mg / mL. 1 mL of each suspension was mixed with 3 mL of ethyl acetate. The mixture was then vortexed for 30 s and centrifuged at 4000 × g for 5 min. The upper organic layer was carefully separated, and the extraction was repeated three times under the same conditions. The resulting organic layers were combined and brought to a final volume of 10 mL with ethyl acetate. The absorbance was measured at 446 nm using a UV-Vis spectrophotometer. The concentration of lutein was calculated based on a pre-determined standard curve, and the encapsulation efficiency (EE) and loading efficiency (LE) were calculated using formulas (1) and (2).

[0044]

[0045] Where M0 represents the total amount of lutein added, M1 represents the mass of free lutein, and M2 represents the total mass of the nanocomposite.

[0046] The encapsulation efficiency (EE) and loading efficiency (LE) of each nanocomposite for lutein are as follows: Figure 2 As shown. Due to the limited encapsulation capacity of the monolayer complex, the EE and LE values ​​of LP, LU, and L-UX were only 50.41% and 5.04%, 56.55% and 5.65%, and 59.06% and 5.91%, respectively. After the addition of beet pectin, the EE and LE values ​​of LPS, LUS, and L-UX-S were 75.67% and 7.57%, 82.50% and 8.79%, and 92.67% and 9.28%, respectively. The encapsulation and loading capacities were significantly improved after the addition of beet pectin compared to the monolayer nanocomplex. This is attributed to the formation of a stable "core-shell" structure in the protein-polysaccharide bilayer nanocomplex, preventing nanocomplex aggregation and precipitation; simultaneously, the hydrophilic polysaccharide shell can shield the internal lutein, reducing its degradation due to exposure. Example 4

[0047] Determination of the scavenging ability of nanocomposites against DPPH and hydroxyl radicals.

[0048] (1) DPPH radical scavenging activity Take 0.2 g of each sample from Example 1 and add it to 20 mL of deionized water to prepare a suspension of 10 mg / mL. Then, take 2 mL of each suspension and mix it with an equal volume of 0.2 mmol / L DPPH solution. Place the mixture in the dark and let it stand at room temperature for 30 min. After the reaction is complete, measure the absorbance at 517 nm (A1). For the control group (A2), anhydrous ethanol was used instead of DPPH solution, while in the blank group (A0), deionized water was used instead of the sample. Calculate the final result according to formula (3).

[0049]

[0050] (2) Hydroxyl radical scavenging activity Take 0.2 g of each sample from Example 1 and add it to 20 mL of deionized water to prepare a sample suspension of 10 mg / mL. Then, take 2 mL of each sample suspension and add it to the hydroxyl radical working solution (the working solution consists of 6.0 mmol / L FeSO4, 6.0 mmol / L salicylic acid, and 6.0 mmol / L H2O2, 1 mL of each component). Next, let the mixture incubate at room temperature for 30 min. After incubation, measure the absorbance at a wavelength of 510 nm and label the measured value as C1. For the control group, salicylic acid was used instead of deionized water (C2), while in the blank group, deionized water was used instead of the sample suspension (C3). The results were calculated using the formula in formula (4).

[0051]

[0052] like Figure 3 As shown, compared with free lutein (21.16% and 16.33%), the scavenging abilities of LP, LU, and L-UX monolayer nanocomposites for DPPH and hydroxyl radicals were significantly enhanced, at 41.27% and 32.05%, 49.43% and 44.72%, and 55.86% and 49.51%, respectively. Notably, the addition of beet pectin further enhanced the free radical scavenging abilities of the bilayer nanocomposites LPS, LUS, and L-UX-S, with scavenging rates of 70.75% and 66.92%, 81.25% and 79.65%, and 89.56% and 86.57% for DPPH and hydroxyl radicals, respectively. This may be due to the superior performance of the bilayer nanocomposites, which can more effectively block a series of adverse factors such as light, heat, and oxygen, significantly slowing down the degradation rate of lutein before storage and measurement.

[0053] Therefore, more intact lutein molecules with antioxidant activity can be retained and function during the measurement. Example 5

[0054] The stability of the prepared nanocomposite was studied experimentally.

[0055] Photostability The stability of each sample prepared in Example 1 under ultraviolet light was evaluated. Each sample was placed under ultraviolet light for 2 hours every 5 days, and the retention of lutein in each sample was measured. The retention rate of lutein was calculated using formula (5), and the results are as follows: Figure 4 As shown.

[0056]

[0057] Where C represents the initial level of lutein, while C0 represents the lutein content at a specific point in time.

[0058] like Figure 4 As shown, after intermittent direct exposure to ultraviolet light and storage at 4°C for 30 days, the retention rates of lutein in free lutein, LUT-PPI, LUT-UPPI, and LUT-UPPIX were 23.14%, 37.03%, 45.40%, and 48.01%, respectively. The addition of beet pectin significantly improved the lutein retention rate, with LUT-PPI-SBP, LUT-UPPI-SBP, and LUT-UPPIX-SBP retaining 57.88%, 61.99%, and 72.03%, respectively. This indicates that encapsulating lutein in nanocomposites can greatly improve its photostability, and that bilayer nanocomposites provide better protection for lutein than monolayer nanocomposites. Among these, the bilayer nanocomposite (L-UX-S) prepared using ultrasound pretreatment-assisted glycosylation of proteins exhibited the strongest protective ability for lutein.

[0059] Thermal stability The stability of lutein in the samples prepared in Example 1 at different temperatures (4°C, 25°C, 60°C) was evaluated. The retention rate of lutein was measured according to the method described in Example 5 (1).

[0060] This study investigated the retention rates of lutein after 30 days of storage under low temperature (4℃), room temperature (25℃), and high temperature (60℃) conditions. The results are as follows: Figure 5As shown in (A), (B), and (C), the results indicate that during storage at 4℃, the lutein retention rates of the nanocomposites, except for free lutein, remained above 60%. Compared to 4℃, the lutein retention rate decreased slightly at 25℃, while under high-temperature (60℃) conditions, the lutein retention rate in the nanocomposites was significantly lower than under low-temperature and room-temperature conditions.

[0061] Meanwhile, after storage at 4℃, 25℃, and 60℃ for 30 days, the retention rates of free lutein were only 64.79%, 55.32%, and 25.12%, respectively, significantly lower than the retention rates of lutein in the nanocomposite. Furthermore, at different temperatures, the lutein retention rates in the bilayer nanocomposite were higher than those in the monolayer nanocomposite. Among these, L-UX-S exhibited the highest lutein retention rates at all temperatures. Therefore, the L-UX-S bilayer nanocomposite system possesses the best thermal storage stability.

[0062] pH stability The stability of the nanocomposites prepared in Example 1 under different pH conditions (3-8) was evaluated. The pH of the samples was adjusted to the range of 3-8 using 1 mol / L HCl and NaOH solutions, and then their particle size and zeta potential were measured.

[0063] Figure 6 The average particle size and zeta potential of different nanocomposites are shown in the pH range of 3.0 to 8.0. Monolayer nanocomposites exhibit the largest particle size at pH 4.0, with LP, LU, and L-UX having particle sizes of 787.0 nm, 539.5 nm, and 487.0 nm, respectively. However, after the addition of beet pectin, the particle sizes of LPS, LUS, and L-UX-S decreased significantly to 223.0 nm, 203.0 nm, and 187.8 nm, respectively. Meanwhile, the bilayer nanocomposites (LPS, LUS, and L-UX-S) showed excellent stability in particle size across the pH range of 3.0–8.0. Furthermore, the zeta potential of monolayer nanocomposites approached zero at pH 4, indicating a rapid decrease in electrostatic repulsion between nanocomposites and promoting their aggregation. However, the absolute values ​​of the zeta potential of bilayer nanocomposites were negative throughout the pH range of 3.0–8.0. It is worth noting that L-UX-S has a uniform particle size distribution and can maintain a high absolute potential value in a pH range of 3-8, which comprehensively indicates that the L-UX-S system has the highest stability. Example 6

[0064] An in vitro simulated digestion experiment was conducted on the prepared nanocomposite.

[0065] Specifically, 0.25 g of each sample from Example 1 was dissolved in 25 mL of deionized water to form a sample suspension with a concentration of 10 mg / mL. This suspension was then mixed with 25 mL of simulated gastric juice (SGF), which contained pepsin (3.2 mg / mL) and NaCl (2 mg / mL). The pH of the mixture was adjusted to 2.0, and the mixture was stirred at 37°C and 120 r / min for 2 h. Afterward, the pH of the mixture was adjusted to 7.4, and it was mixed with 50 mL of simulated intestinal fluid (SIF) containing trypsin (2 mg / mL), bile salts (52 mg / mL), KH₂PO₄ (6.82 mg / mL), and NaCl (8.82 mg / mL), and incubated at 37°C for another 4 h. Samples were taken at predetermined time intervals (every 0.5 h for simulated gastric juice and every 1 h for simulated intestinal fluid), and after enzyme inactivation in a 90°C water bath for 5 min, the mixture was centrifuged at 6000 × g for 15 min. The concentration of lutein was determined using the encapsulation efficiency method described in Example 3. The bioavailability of lutein was calculated using the following formula (6).

[0066]

[0067] Among them, C t C0 represents the mass of lutein in the digestion residue, while C0 represents the initial mass of lutein in the sample of Example 1.

[0068] like Figure 7 As shown, during the simulated gastric digestion phase, all samples initially released lutein rapidly over 0.5 h, followed by a slow release. Two h after simulated gastric digestion, the simulated intestinal digestion phase commenced, during which lutein release significantly increased. After 6 h of digestion, the bioavailability of free lutein was lowest at 22.96%, while the bioavailability of lutein in LUT-PPI-SBP, LUT-UPPI-SBP, and LUT-UPPIX-SBP was higher than that in LUT-PPI, LUT-UPPI, and LUT-UPPIX. Notably, LUT-UPPIX-SBP exhibited the highest lutein bioavailability at 61.08%. The addition of beet pectin, through electrostatic interactions with proteins, shields the hydrophobic amino acids within the proteins, providing additional protection during pepsin-induced degradation. This mechanism enhances the stability of lutein, resulting in higher bioavailability after the simulated in vitro digestion process. Example 7

[0069] A method for preparing jujube juice rich in lutein, comprising the following steps: A certain amount of high-quality jujubes was weighed, and then the jujubes and deionized water were mixed at a solid-liquid ratio of 1:6 (g / mL) to form a pulp. Subsequently, a mixed enzyme (m(pectinase):m(cellulase) = 1:2, mass ratio, 2.4 g / L) was used for enzymatic hydrolysis at 40℃ for 3 h. After hydrolysis, the mixture was immediately reacted at 85℃ for 15 min to inactivate the enzyme activity. After cooling to room temperature, the mixture was filtered through three layers of gauze. After filtration, the mixture was centrifuged (6000 r / min, 4℃, 8 min), and the supernatant of the jujube juice was collected. Citric acid 0.10% and white sugar 3.0% were added for adjustment. Then, the lutein-containing nanocomplexes (LP, LPS, LUS, L-UX-S) prepared in Example 1 were added to the jujube juice supernatant. The mass ratio of the jujube juice to the lutein-loaded modified pea protein isolate-beet pectin nanocomplex was 100:1.

[0070] In addition, free lutein (LUT) and lutein loaded with conventional emulsifier (Span 40, S40) were prepared as controls for jujube juice containing nanocomplexes. The free lutein group of jujube juice (JJB-LUT) involves dissolving lutein in anhydrous ethanol to a concentration of 10 mg / mL, then adding the lutein to the jujube juice, resulting in a final mass ratio (mg / mL) of jujube juice to lutein of 100:1. The Span 40 group of jujube juice (JJB-S40) involves preparing a 10 mg / mL suspension of Span 40 using deionized water, stirring for 30 min, adjusting the pH to 12.0 with 1 mol / L NaOH aqueous solution, stirring for 30 min, then adjusting the pH to 7.0 with 1 mol / L HCl, and stirring for 30 min. Next, a lutein-ethanol solution dissolved in anhydrous ethanol (lutein to Span 40 mass ratio of 1:20) is added, maintaining a constant pH throughout the process, and equilibrating for 30 min. Finally, the resulting lutein-loaded Span 40 solution is added to the jujube juice. Similarly, the mass ratio of jujube juice to Span 40 solution loaded with lutein was 100:1.

[0071] The different jujube juices prepared above were then treated in an ultrasonic cell disruptor at 225 W for 4 minutes to further mix the added solution with the jujube juice. Finally, after pasteurization (85℃, 15 min), the lutein-rich jujube juice beverage (JJB) was obtained and stored at -4℃ for subsequent index determination. The beverage without added lutein was pure jujube juice. The different jujube juice beverages were named JJB-Pure, JJB-LUT, JJB-S40, JJB-LP, JJB-LPS, JJB-LUS, and JJB-L-UX-S, respectively. Example 8

[0072] DPPH and ABTS in jujube juice rich in lutein + Determination of free radical scavenging capacity, total phenol content, and total flavonoid content.

[0073] Specifically, each sample (2 mL) from Example 7 was mixed with an equal volume of 0.2 mmol / L DPPH solution. The mixture was placed in the dark and reacted at room temperature for 30 min. After the reaction was complete, the absorbance (A1) was measured at 517 nm using a UV spectrophotometer. The control group (A2) used anhydrous ethanol instead of DPPH solution, and the blank group (A0) used deionized water instead of the sample. The final result was calculated using the following formula (7).

[0074] A 7.0 mmol / L ABTS solution (10 mL) was mixed with a 4.95 mmol / L potassium persulfate solution (20 mL). The mixture was placed at room temperature and reacted in the dark for 12 h. Then, 1 mL of the prepared working solution was diluted with 60 mL of ethanol, and its absorbance was measured at 734 nm. The absorbance value should be controlled within the range of 0.70 ± 0.02. Next, under dark conditions, 20 μL of each jujube juice sample from Example 7 was added to 2 mL of the diluted working solution, and the reaction was carried out for 1 minute. Finally, the absorbance was recorded at 734 nm (denoted as B1). In the control group (denoted as B2), anhydrous ethanol was used instead of ABTS solution; while in the blank group (denoted as B0), deionized water was used instead of the sample. The final result was calculated using the following formula (8).

[0075]

[0076] A gallic acid standard solution with a concentration of 100 μg / mL was prepared. 0.1, 0.2, 0.3, 0.4, and 0.5 mL of the standard solution were respectively pipetted into brown test tubes, and diluted to 1 mL with distilled water. After thorough mixing, 0.5 mL of Folin-Ciocalteu reagent and 1.5 mL of 15% Na₂CO₃ solution were added sequentially. After mixing, the volume was adjusted to 10 mL with distilled water. The tubes were then allowed to stand at room temperature in the dark for 60 min, and the absorbance at 765 nm was measured. A standard curve was plotted with the gallic acid standard solution concentration and absorbance values ​​on the x and y axes. The determination of each sample was performed in the same manner as described above, and the results were expressed as the mass (mg) of gallic acid per 100 mL of sample. The total phenol content was calculated according to formula (9).

[0077]

[0078] Where C is the concentration of gallic acid in the sample, mg / mL; V1 is the final volume of the sample, mL; N is the dilution factor of the sample; and V2 is the sample volume, mL.

[0079] Take 0.2, 0.4, 0.6, 0.8, and 1.0 mL of rutin standard solution (concentration of 100 μg / mL) and place them in 50 mL volumetric flasks for the preparation of standard curves. Dilute 1 mL of each jujube juice sample 20 times with distilled water, transfer 1 mL of the diluted solution to 1 mL of sodium nitrite solution with a concentration of 5 mg / mL, mix thoroughly, and let stand at room temperature for 6 min; then add 1 mL of aluminum nitrate solution with a concentration of 10 mg / mL, shake again, and let stand for 6 min; then add 10 mL of sodium hydroxide solution with a concentration of 5 mg / mL, mix well, dilute to volume with ethanol, shake well, and let stand for another 15 min. Measure the absorbance of each solution at a wavelength of 510 nm and plot the standard curve accordingly. The results are expressed as the mass (mg) of rutin contained in 100 mL of sample. The total flavonoid content is calculated using formula (10).

[0080]

[0081] Where C is the concentration of rutin in the sample, mg / mL; V1 is the final volume of the sample, mL; N is the dilution factor of the sample; and V2 is the sample volume, mL.

[0082] Jujube juice beverage (JJB) is a beverage rich in polyphenols and flavonoids, and therefore already exhibits high DPPH and ABTS even before the addition of lutein-loaded nanocomplexes. + Free radical scavenging activity. However, as shown in Table 1, the addition of lutein-loaded nanocomposites significantly increased DPPH radical or ABTS free radical scavenging activity. +The free radical scavenging ability indicates that the lutein-containing nanocomposite can further enhance the antioxidant properties of JJB after its addition. This may be because the lutein-loaded nanocomposite can bind with polyphenols and flavonoids in jujube juice, thereby promoting its antioxidant capacity. Specifically, JJB-L-UX-S contains DPPH and ABTS. + The highest free radical scavenging activities were observed, at 66.26±0.52% and 69.24±0.05%, respectively. This is likely due to the high solubility of L-UX-S in aqueous solution, which leads to more frequent contact between free radicals and lutein, resulting in the highest free radical scavenging rate.

[0083] Similarly, JJB-L-UX-S also achieved the highest level in terms of active ingredient content, with total phenols and total flavonoids of 76.67 mg GAE / 100 mL and 144.31 mg RE / 100 mL, respectively. It is worth noting that the total flavonoid content of JJB-LUT (138.81 mg RE / 100 mL) was slightly lower than that of the control group JJB-Pure. This may be due to the physical interaction between lutein and the juice matrix leading to the masking or precipitation of some flavonoids. However, jujube juice containing nanocomplexes (especially JJB-L-UX-S) not only overcame this decreasing trend but also significantly improved the retention rate of active substances, thereby significantly enhancing the functional properties of jujube juice.

[0084] Table 1. DPPH and ABTS of lutein-rich jujube juice + Free radical scavenging capacity, total phenol content and total flavonoid content Example 9

[0085] Determination of color difference in jujube juice rich in lutein.

[0086] Specifically, the color of each sample in Example 7 was measured using an automatic colorimeter. The luminance value (L*), red-green value (a*), and yellow-blue value (b*) were measured, and the color difference (ΔE) was calculated according to formula (11).

[0087]

[0088] Table 2 shows the chromaticity of different jujube juices, where L* represents brightness, a* represents the depth of color from green to red, and b* represents the depth of color from blue to yellow. For JJB-Pure, the L*, a*, and b* values ​​are 36.43±0.13, 6.95±0.07, and 25.44±0.34, respectively. Compared to JJB-Pure, the total color change (ΔE) of the other jujube juices ranges from 0.75 to 5.32. JJB-LUT and JJB-S40 show the largest ΔE changes, at 5.32±0.47 and 4.78±0.29, respectively, indicating that JJB-LUT and JJB-S40 exhibit more significant color changes compared to JJB-Pure. In addition, the color values ​​of jujube juice increased after the addition of lutein-loaded nanocomplexes, and the jujube juice had a higher brightness value and a deeper orange-yellow color, indicating that the jujube juice had a more vibrant color after the addition of lutein-loaded nanocomplexes.

[0089] Table 2. Color difference measurement results of lutein-rich jujube juice Example 10

[0090] Determination of soluble protein, soluble solids, titratable acid and pH value of jujube juice rich in lutein.

[0091] Specifically, in Example 7, the soluble protein content in each jujube juice was determined using the Coomassie Brilliant Blue method, and the concentration of soluble protein was then determined based on a standard curve; total soluble solids (TSS) were measured and separated using a handheld refractometer. Titratable acid content was determined using acid-base titration, and the titratable acid content was calculated using the conversion factor for malic acid according to the following formula (12):

[0092] Where C represents the concentration of sodium hydroxide solution (0.1 mol / L); V1 is the volume of sodium hydroxide solution used in the sample, mL; V2 is the volume of sodium hydroxide solution used in the blank test, mL; the conversion factor for malic acid is 0.067; and V represents the volume of the sample (5 mL).

[0093] Besides color, nutritional components are also crucial to the quality of fruit and vegetable juice beverages. Especially after adding exogenous substances, the original quality of the juice may be altered to some extent. Therefore, the changes in soluble protein, titratable acid, and soluble solids content in various jujube juices were measured. As shown in Table 3, with the addition of lutein-loaded nanocomposites to jujube juice, the soluble protein content increased significantly compared to JJB-Pure (0.084±0.006), and JJB-L-UX-S had the highest protein content, reaching 0.301±0.002. The results indicate that the lutein-loaded nanocomposites with a protein matrix can dissolve well in jujube juice, thus significantly increasing the protein content. Since L-UX-S has the best water solubility, JJB-L-UX-S has a higher soluble protein content. However, jujube juice containing both free lutein and lutein-loaded Span 40 showed almost no increase in soluble protein. Similarly, after the addition of the lutein-loaded nanocomposite, the soluble solids (TSS) in jujube juice increased slightly compared to JJB-Pure due to the presence of beet pectin, but the overall difference was not significant. Likewise, no significant differences were observed in the pH and titratable acid content of the different jujube juices. This may be because the addition of free lutein, lutein-loaded Span 40, and the lutein-loaded nanocomposite does not have a significant impact on the pH and titratable acid content of jujube juice.

[0094] Table 3. Results of soluble protein, soluble solids, pH and titratable acid content of lutein-rich jujube juice. Example 11

[0095] Storage stability of lutein-rich jujube juice (0-180 days).

[0096] The average particle size and zeta potential of each sample in Example 7 were measured every 7 days using a Malvern laser particle size analyzer. The centrifugal sedimentation rate (CSR) was determined by centrifuging each sample of Example 7 with a known mass (m1) at 4000 × g for 10 min, collecting the precipitate and measuring its mass (m2). The mass of the clean centrifuge tube was recorded as m0. Subsequently, the CSR was calculated using formula (13).

[0097]

[0098] like Figure 8As shown in Figure A, the particle size of all jujube juice samples showed a gradual increasing trend over time. However, the particle sizes of jujube juice containing free lutein, lutein-loaded Span 40, or lutein-loaded nanocomposites were all larger than those of JJB-Pure. After 180 days of storage, the particle size of JJB-Pure increased from 1867.67 ± 2.05 nm to 2936.67 ± 5.91 nm, an increase of 1069 nm. In contrast, JJB-L-UX-S showed the smallest increase in particle size, increasing only from 2002.00 ± 12.68 nm to 2729.67 ± 11.15 nm, an increase of only 727.67 nm. Meanwhile, the particle size of the group with added free lutein, JJB-LUT, increased from 1826.00 ± 8.29 nm to 3025.00 ± 0.82 nm, an increase of 1199.00 nm. Therefore, the sample appeared more turbid, and visible floating particles were observed.

[0099] like Figure 8 As shown in Figure B, after a 180-day storage period, the absolute values ​​of the zeta potential of all jujube juice samples showed a slow decreasing trend. The zeta potential of JJB-Pure decreased from -21.40 ± 0.37 mV to -13.60 ± 0.05 mV, a decrease of 7.77 mV. In contrast, the zeta potential of the group with added free lutein, JJB-LUT, decreased from -21.00 ± 0.10 mV to -12.80 ± 0.00 mV, a decrease of 8.19 mV. The decrease was the smallest for JJB-L-UX-S, decreasing from -25.50 ± 0.16 mV to -17.70 ± 0.05 mV, a decrease of only 7.77 mV, thus maintaining excellent physical stability.

[0100] The more precipitate produced after centrifugation, the worse the colloid's stability. For example... Figure 8 As shown in Figure C, after 180 days of storage, the CSR value of the JJB-Pure sample increased by 2.69%, while the increase of JJB-LUT was the largest, reaching 2.80%. In contrast, the increase of JJB-L-UX-S was the smallest, at only 2.41%, thus demonstrating better stability. This phenomenon is consistent with the trend of particle size changes during storage. Example 12

[0101] Image showing the storage appearance of jujube juice rich in lutein.

[0102] like Figure 9As shown, after 45 days of storage, jujube juice containing free lutein (JJB-LUT) showed visible precipitation at the bottom, while the other samples did not produce any precipitation. After 70 days, jujube juice loaded with lutein using Span 40 (JJB-S40) also showed precipitation, while the other jujube juices did not produce any precipitation. The situation was similar when stored for 180 days. Similarly, jujube juices using single / composite nanocomposites (JJB-LP, JJB-LPS, JJB-LUS, JJB-L-UX-S) still maintained a relatively uniform appearance and texture. Because free lutein is sensitive to light, heat, and oxygen, when directly added to jujube juice, it exists in a molecular state without protection, making it prone to precipitation. Unstable lutein molecules aggregate to form precipitates. Lutein may also gel with polysaccharides, becoming encapsulated and co-precipitated, or interact hydrophobically with polyphenols to form insoluble compounds. While Span 40, loaded with lutein, is an encapsulation system, its large droplets (micrometer-scale) weaken the physical barrier, leading to demulsification during long-term storage. This releases lutein, which then binds to other components of the jujube juice, causing aggregation and precipitation. In contrast, jujube juice containing lutein-loaded nanocomposites, with its nano-sized particles, effectively resists environmental influences, maintaining a homogeneous state with almost no precipitation after 180 days of storage.

[0103] In summary, this invention uses lutein as a fat-soluble nutrient raw material. Pea protein isolate (PPI) is modified by ultrasound, and PPI is pretreated by ultrasound and grafted with xylose (Xyl). Using this as a raw material, a monolayer nanocomposite is first prepared via a pH shift method. Lutein is then added to this nanocomposite to form a lutein-loaded monolayer nanocomposite. Subsequently, it is combined with a beet pectin (SBP) aqueous solution at pH 4 through electrostatic self-assembly to form a stable bilayer nanoparticle system encapsulating lutein, thereby improving the retention rate and bioavailability of lutein. The nanocomposite is then added to jujube juice to increase the fat-soluble nutrient content. Compared to nanocomposites formed from a single protein, the lutein bilayer nanocomposite of this invention exhibits superior storage stability and solubility, and effectively prevents lutein degradation, significantly improving the encapsulation rate and stability of lutein, thus effectively increasing its utilization rate. Adding it to jujube juice can also compensate for the lack of fat-soluble nutrients in water-soluble beverage systems, meeting the needs of nutritional balance.

[0104] In summary, the above description represents only a relatively ideal specific embodiment of the present invention. However, the scope of protection of the present invention is not limited thereto. Within the technical field disclosed in this invention, any person skilled in the art who makes equivalent substitutions or corresponding changes based on the technical solution and inventive concept of this invention should also be included within the scope of protection of this invention.

Claims

1. A method for preparing a lutein-loaded modified pea protein isolate-beet pectin nanocomposite, characterized in that, Includes the following steps: (1) Prepare a protein suspension from pea protein isolate, sonicate it, and then freeze-dry it into powder; (2) The protein powder obtained in step (1) is reconstituted into a protein suspension, xylose is added, and the mixture is reacted at 60-100℃ for 60-160 min. Then it is freeze-dried to obtain glycosylated protein powder. (3) The glycosylated protein powder obtained in step (2) is formulated into a protein suspension, and lutein is encapsulated using the pH shift method to form a monolayer nanocomposite. (4) Add beet pectin to the monolayer nanocomposite obtained in step (3), adjust the pH to 2-4, stir, then evaporate the solvent by rotary evaporation, and replenish the evaporated solvent with an equal volume of distilled water. After centrifugation and freeze drying, the product is obtained.

2. The method for preparing the lutein-loaded modified pea protein isolate-beet pectin nanocomposite as described in claim 1, characterized in that, In step (1), the processing power of the ultrasonic cell disruptor is 100-800 W and the processing time is 5-30 min.

3. The method for preparing the lutein-loaded modified pea protein isolate-beet pectin nanocomposite as described in claim 1, characterized in that, The concentration of the protein suspension prepared in step (2) is 1-30 mg / mL; xylose is added to the protein suspension according to the mass ratio of protein powder to sugar of 5-1:

1.

4. The method for preparing the lutein-loaded modified pea protein isolate-beet pectin nanocomposite as described in claim 1, characterized in that, The pH shift method used in step (3) is as follows: first, adjust the pH to 11-13 with NaOH solution, stir for 20-60 min, then adjust the pH to 7 with HCl solution, stir for 20-60 min, then add lutein solution dissolved in anhydrous ethanol, and balance for 20-60 min to obtain the final product; the mass ratio of lutein to glycosylated protein is 1:1-40.

5. The method for preparing the lutein-loaded modified pea protein isolate-beet pectin nanocomposite as described in claim 1, characterized in that, In step (4), the mass ratio of glycosylated protein to beet pectin is 1:10-40:1, and the temperature during rotary evaporation is 40-45℃.

6. A modified pea protein isolate-beet pectin nanocomposite loaded with lutein prepared by any one of the methods described in claims 1 to 5.

7. The application of the lutein-loaded modified pea protein isolate-beet pectin nanocomposite according to claim 6 in jujube juice.

8. A method for preparing jujube juice rich in lutein, characterized in that, The jujube juice is mixed evenly with the lutein-loaded modified pea protein isolate-beet pectin nanocomposite described in claim 6 to obtain the final product.

9. The method for preparing jujube juice rich in lutein as described in claim 8, characterized in that, The mass ratio of the jujube juice to the lutein-loaded modified pea protein isolate-beet pectin nanocomposite is 50-200:1; the two are mixed uniformly by ultrasonication at a power of 150-400 MPa for 1-8 min.

10. Jujube juice rich in lutein prepared by the method of claim 8 or 9.

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