Flaxseed / selenium-enriched soybean compound plant milk as well as preparation method and application thereof

Abstract

The invention relates to the technical field of food processing, in particular to flaxseed / selenium-rich soybean compound plant milk and a preparation method and application thereof, and the preparation method of the high-steady-state flaxseed / selenium-rich soybean compound plant milk comprises the following steps: preparing selenium-rich soybean milk; preparing linseed milk; the selenium-rich soybean milk and the flaxseed milk are mixed according to the volume ratio of 1: 9-5: 5, the flaxseed / selenium-rich soybean compound plant milk is obtained through ultrasonic treatment, the power of the ultrasonic treatment is 200-400 W, and the ultrasonic treatment time is 5-25 min. According to the invention, the linseed milk and the selenium-enriched soybean milk are scientifically compounded, and an ultrasonic synergistic treatment process is innovatively introduced. The problems that existing flaxseed milk is low in protein content, poor in stability, prone to oxidation and rough in taste are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of food processing, and more specifically, to a flaxseed / selenium-enriched soybean compound plant milk, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous growth of the global population, the increasing pressure on resources and the environment, and the significant improvement of consumers' health awareness, food safety and health have become the focus of global attention. Against this background, as an important alternative to traditional dairy products, plant milk has rapidly emerged with its core advantages of being natural, healthy, and sustainable, becoming a hot area for the innovative development of the food industry. Market data shows that the annual average growth rate of the global plant-based dairy product market exceeds 12%, and the Asia-Pacific region, especially the Chinese market, has the most significant growth. Plant milk is based on plant raw materials such as grains, beans, and nuts and is made through modern processing technologies. It has nutritional characteristics such as zero cholesterol, low saturated fat, and high dietary fiber, which can not only meet the rigid needs of lactose-intolerant people, vegetarians, and allergic people but also fit the pursuit of contemporary consumers for functional and environmentally friendly foods.

[0003] Current mainstream plant milk products include soy milk, walnut milk, coconut milk, etc., and their raw material characteristics and processing technologies have been relatively mature. However, single plant-based dairy products generally have problems such as unbalanced nutrition and single function. For example, although soy milk has a relatively high protein content, it has allergenicity; walnut milk has a relatively high fat content and is prone to oxidation; coconut milk has deficiencies in minerals and dietary fiber. To break through this limitation, the industry has begun to focus on new plant raw materials with both nutritional enhancement and functional characteristics. As a functional oil crop rich in ω-3 fatty acids, the processed product of flaxseed, flaxseed milk, shows significant nutritional advantages: Research shows that the bioavailability of α-linolenic acid (ALA) in flaxseed milk is increased by 40% - 60% compared with the whole seed form, and its active ingredients such as lignans and polysaccharides have unique effects of improving cognitive function, regulating blood lipid metabolism, and enhancing immunity. However, the industrialization of flaxseed milk still faces multiple technical obstacles: First, the raw material protein content is low (only about 18% - 25%), making it difficult to meet the market demand for high-protein beverages; second, the flaxseed gum and protein complex are prone to cause system stratification, and the shelf-life stability is insufficient; third, the product has a rough taste and a strong gelatinous texture, and the consumer acceptance is limited. Existing technologies mostly improve the product properties by adding stabilizers or high-pressure homogenization, but the introduction of chemical additives and high-energy-consuming processes significantly weaken the natural attributes and sustainable advantages of the product.

[0004] In view of the limitations of single plant-based milks, compounding technology is considered an effective way to improve the overall performance of the product. Studies have confirmed that nutritional complementarity and functional synergy can be achieved by scientifically combining different plant-based raw materials. For example, the combination of soy milk and almond milk can increase the protein content by 86.16%, while the combination of coconut milk and chickpea milk significantly improves the mineral content and system stability. Such results reveal the potential of compounding technology in optimizing the nutritional spectrum of plant-based milks and improving their physical properties. However, existing research has mostly focused on conventional raw material combinations, and the in-depth development of highly functional ingredients is still insufficient.

[0005] However, during the compounding process of plant-based milks, differences in the physical and chemical properties of different raw materials can easily lead to system instability. While traditional heat treatment and mechanical homogenization can improve stability, they can also cause the loss of heat-sensitive nutrients (such as ALA and lignans). Therefore, to address the issues of existing flaxseed milks, such as low protein content, poor stability, easy oxidation, and a rough taste, it is of great significance to develop a method for preparing a highly stable flaxseed / selenium-enriched soybean compounded plant-based milk. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a flaxseed / selenium-rich soybean compound plant milk and its preparation method and application, aiming to solve the problems raised in the technical background. Selenium-rich soybean milk is used as a supplementary raw material to flaxseed milk through scientific compounding and ultrasonic synergistic treatment, so as to solve the problems of low protein content, poor stability, easy oxidation and rough taste of existing flaxseed milk.

[0007] In order to solve the above technical problems, the present invention provides a method for preparing a flaxseed / selenium-enriched soybean compound plant milk, comprising the following steps: preparing selenium-enriched soybean milk; Prepare flaxseed milk; Selenium-enriched soybean milk and flaxseed milk were mixed in a volume ratio of 1:9 to 5:5, and the mixture was ultrasonically treated to obtain flaxseed / selenium-enriched soybean composite plant milk.

[0008] This invention optimizes the volume ratio of selenium-enriched soy milk and flaxseed milk, leveraging the ω-3 fatty acid benefits of flaxseed milk and the high protein and selenium nutritional properties of selenium-enriched soy milk to achieve amino acid complementarity and synergistic enhancement of functional ingredients. Furthermore, multi-band ultrasonic treatment technology is used to manipulate the structure of the protein-polysaccharide complex, enhancing system stability while maximizing the retention of heat-sensitive active ingredients.

[0009] Preferably, an ultrasonic cell disruptor is used for the ultrasonic treatment. The power of the ultrasonic cell disruptor is 200 W to 400 W, the ultrasonic treatment time of the ultrasonic cell disruptor is 5 min to 25 min, the diameter of the horn of the ultrasonic cell disruptor is 6 mm, and the immersion depth of the horn is 1 / 3 of the liquid level height.

[0010] Taking physical stability (TSI, average particle size, Zeta potential) as an index, if the ultrasonic power and time are too large or too small, the physical stability of the selenium-enriched soybean milk will decrease.

[0011] Preferably, the selenium-enriched soybean milk and the flaxseed milk are mixed at a mass ratio of 3:7, the power of the ultrasonic treatment is 297 W, and the ultrasonic treatment duration is 21 min.

[0012] Taking physical stability (TSI, average particle size, Zeta potential) as an index, at this ultrasonic power and ultrasonic duration, the selenium-enriched soybean milk and the flaxseed milk mixed at a mass ratio of 3:7 have the best stability.

[0013] Preferably, the method for preparing the selenium-enriched soybean milk comprises the following steps: Select selenium-enriched soybeans with plump grains and no mildew. After cleaning with clean water, soak them in clean water at room temperature. After peeling, grind the dried selenium-enriched soybeans and clean water at a mass ratio of 1:5 to 1:9, and obtain selenium-enriched soybean milk through filtration.

[0014] If the mass ratio of the dried selenium-enriched soybeans after peeling to the clean water is too small and less water is added, grinding cannot be carried out. If the mass ratio is large and more water is added, the contents of plant milk solids, protein, etc. obtained by grinding are not enough and do not meet the subsequent use conditions.

[0015] Preferably, after cleaning, the selenium-enriched soybeans are soaked at a mass ratio of 1:2 at room temperature for 12 hours. After peeling, the dried selenium-enriched soybeans and clean water are ground at a mass ratio of 1:6, and the soybean dregs are removed by filtration through a 200-mesh sieve to obtain selenium-enriched soybean milk. The mass ratio of 1:6 is selected by comparing indicators such as nutritional components, selenium content, and physical stability.

[0016] Preferably, the method for preparing the flaxseed milk comprises the following steps: Adjust the moisture content of the flaxseeds to 17%, and perform microwave treatment at 700 W for 10 min; Here, adjusting the moisture content of the flaxseeds is to achieve better detoxification effect and nutrient dissolution effect; microwave is to remove anti-nutritional factors such as cyanogenic glycosides; the moisture content value of the adjusted flaxseeds and the microwave treatment power conditions are obtained by screening and optimizing the preparation process conditions of flaxseed milk in the early stage of the laboratory.

[0017] The defatted flaxseeds after microwave treatment are repeatedly washed and degummed in warm water at 50°C. After drying, they are ground at a ratio of flaxseeds to water of 1:5 to 1:9, and then homogenized to obtain flaxseed milk.

[0018] Among them, the defatted flaxseeds after microwave treatment are repeatedly washed and degummed in warm water at 50°C. After drying, they are homogenized at a ratio of flaxseeds to water of 1:5 to 1:9 to obtain flaxseed milk. When the ratio of flaxseeds to water is 1:5 after drying, the nutritional components of the flaxseed milk obtained after homogenization are the best.

[0019] Preferably, according to the method for preparing flaxseed / selenium-enriched soybean compound plant milk described in claim 1, the average particle size of the compound plant milk is ≤ 320 nm, the absolute value of the Zeta potential is ≥ 30 mV, the selenium content is ≥ 0.26 mg / kg, the protein content of the flaxseed / selenium-enriched soybean compound plant milk is increased by 41.42%, the total phenol of the flaxseed / selenium-enriched soybean compound plant milk is increased by 16.36%, and the TSI value of the flaxseed / selenium-enriched soybean compound plant milk is < 0.4.

[0020] The present invention also provides a highly stable flaxseed / selenium-enriched soybean compound plant milk prepared by the method for preparing flaxseed / selenium-enriched soybean compound plant milk.

[0021] The present invention also provides the application of flaxseed / selenium-enriched soybean compound plant milk in health foods, functional foods and nutrient-enriched foods. The fat-soluble active ingredients are common carotenoids including lycopene or astaxanthin.

[0022] Preferably, the fat-soluble carotenoid active ingredients are embedded with flaxseed / selenium-enriched soybean compound plant milk as a carrier, and the embedding rate is greater than 85%.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention scientifically combines flaxseed milk and selenium-enriched soybean milk and innovatively introduces an ultrasonic synergistic treatment process, solving the problems of low protein content, poor stability, easy oxidation and rough taste existing in the existing flaxseed milk.

[0024] This is because the preparation method of the flaxseed / selenium-enriched soybean compound plant milk given by the present invention has a synergistic effect between the selenium in the selenium-enriched soybean milk and the polyphenols in the flaxseed milk, so that the stability of the flaxseed / selenium-enriched soybean compound plant milk is extended to more than twice that of the traditional flaxseed milk product, the lipid oxidation inhibition rate of the flaxseed milk exceeds 60%, and there are no chemical additives throughout the process. At the same time, by mixing the prepared selenium-enriched soybean milk and flaxseed milk according to a volume ratio of 1:9 to 5:5, a flaxseed-selenium-enriched soybean dual-raw material compound system is constructed. On the basis of the extended stability of the flaxseed / selenium-enriched soybean compound plant milk, the functional advantages of ω-3 fatty acids in the flaxseed milk and the high-protein-selenium nutritional characteristics of the selenium-enriched soybean milk are fully exerted, realizing amino acid complementarity and synergistic enhancement of functional components. Therefore, while achieving the physical and chemical stability of the flaxseed / selenium-enriched soybean compound plant milk, the nutritional limitations of a single plant milk are broken through.

[0025] At the same time, within the ultrasonic treatment time of 5 min to 25 min, the ultrasonic combined treatment technology with a power of 200 W to 400 W is adopted to replace the traditional chemical additives and high-shear homogenization process, and the structure of the protein-polysaccharide complex is directionally regulated. While improving the stability of the system, the problem that traditional heat treatment and machinery improve the stability of the compound plant milk but cause the loss of heat-sensitive nutrients (such as ALA and lignans) is solved, so as to maximize the retention of heat-sensitive active ingredients and increase the protein content; in addition, the taste of the flaxseed / selenium-enriched soybean compound plant milk is improved by ultrasonic waves. At the same time, the energy consumption of ultrasonic treatment is reduced by 40%, which is suitable for large-scale production.

[0026] 2. The flaxseed / selenium-enriched soybean compound plant milk provided by the present invention is used as an embedding carrier for fat-soluble carotenoid active ingredients, with an embedding rate greater than 85%, and the retention rate of carotenoid components is greater than 90% after storage at 37°C for one month, having strong physical and chemical stability. Brief Description of the Drawings

[0027] Figure 1 Analysis diagrams of the average particle size, Zeta potential and TSI of flaxseed milk and flaxseed / selenium-enriched soybean compound plant milk, where A is the average particle size diagram, B is the Zeta potential diagram, and C is the TSI diagram.

[0028] Figure 2Appearance morphology analysis, CLSM analysis, and cryo-SEM analysis test diagrams of selenium-enriched soybean milk, flaxseed milk, and flaxseed / selenium-enriched soybean compound plant milk. Among them, a is the appearance morphology analysis diagram of selenium-enriched soybean milk, b is the appearance morphology analysis diagram of flaxseed milk, c is the appearance morphology analysis diagram of flaxseed / selenium-enriched soybean compound plant milk, B is the CLSM analysis diagram of flaxseed milk, C is the CLSM analysis diagram of flaxseed / selenium-enriched soybean compound plant milk, A1 is the cryo-SEM diagram of selenium-enriched soybean milk at 5 times magnification, A2 is the cryo-SEM diagram of selenium-enriched soybean milk at 20 times magnification, B1 is the cryo-SEM diagram of flaxseed milk at 5 times magnification, B2 is the cryo-SEM diagram of flaxseed milk at 20 times magnification, C1 is the cryo-SEM diagram of flaxseed / selenium-enriched soybean compound plant milk at 5 times magnification, and C2 is the cryo-SEM diagram of flaxseed / selenium-enriched soybean compound plant milk at 20 times magnification.

[0029] Figure 3 Hydroperoxide content and TBARS values of flaxseed milk and flaxseed / selenium-enriched soybean compound plant milk. Among them, A is the hydroperoxide content value of flaxseed milk and flaxseed / selenium-enriched soybean compound plant milk, and B is the TBARS value of flaxseed milk and flaxseed / selenium-enriched soybean compound plant milk.

[0030] Figure 4 Analysis diagrams of the emulsifying properties and foaming properties of common soy protein (SPI) and selenium-enriched soy protein (SSPI). Among them, A is the emulsifying property analysis diagram, and B is the foaming property analysis diagram.

[0031] Figure 5 Analysis diagram of the free sulfhydryl and disulfide bond contents of common soy protein (SPI) and selenium-enriched soy protein (SSPI).

[0032] Figure 6 Adsorption kinetics diagrams of common soy protein (SPI) and selenium-enriched soy protein (SSPI) at the interface. Among them, A is the diagram of the change in surface tension of common soy protein (SPI) and selenium-enriched soy protein (SSPI) over time, and B is the diagram of the change in surface tension of common soy protein (SPI) and selenium-enriched soy protein (SSPI) with the square root of time.

[0033] Figure 7Appearance and CLSM of flaxseed milk and flaxseed / selenium-enriched soybean compound plant milk stored in the dark at 55°C. Here, A represents storage for 0 days. Then, Aa1, Ab1, and Ac1 are the appearance diagrams of flaxseed milk with pH 5, pH 7, and pH 9 respectively after storage for 0 days. Ad1, Ae1, and Af1 are the appearance diagrams of flaxseed / selenium-enriched soybean compound plant milk with pH 5, pH 7, and pH 9 respectively after storage for 0 days. Aa2, Ab2, and Ac2 are the CLSM diagrams of flaxseed milk with pH 5, pH 7, and pH 9 respectively after storage for 0 days. Ad2, Ae2, and Af2 are the CLSM diagrams of flaxseed / selenium-enriched soybean compound plant milk with pH 5, pH 7, and pH 9 respectively after storage for 0 days. Figure 8 Appearance and CLSM of flaxseed milk and flaxseed / selenium-enriched soybean compound plant milk stored in the dark at 55°C. Here, B represents storage for 8 days. Ba1, Bb1, and Bc1 are the appearance diagrams of flaxseed milk with pH 5, pH 7, and pH 9 respectively after storage for 8 days. Bd1, Be1, and Bf1 are the appearance diagrams of flaxseed / selenium-enriched soybean compound plant milk with pH 5, pH 7, and pH 9 respectively after storage for 8 days. Ba2, Bb2, and Bc2 are the CLSM diagrams of flaxseed milk with pH 5, pH 7, and pH 9 respectively after storage for 8 days. Bd2, Be2, and Bf2 are the CLSM diagrams of flaxseed / selenium-enriched soybean compound plant milk with pH 5, pH 7, and pH 9 respectively after storage for 8 days. Figure 9 Average particle size, Zeta potential, hydroperoxide content, and TBARS value of flaxseed milk (FM) and flaxseed / selenium-enriched soybean compound plant milk (CM) at different pH values. Here, A is the diagram for average particle size measurement, B is the diagram for Zeta potential measurement, C is the diagram for hydroperoxide content measurement, and D is the diagram for TBARS value measurement. Detailed implementation mode

[0034] In order to make the above objects, features, and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0035] The inventor found that the raw material of single linseed milk has a low protein content (only about 18% - 25%), which is difficult to meet the market demand for high-protein beverages; and the linseed gum-protein complex is prone to cause system stratification and insufficient shelf-life stability; the product has a rough taste and a strong gelatinous texture, resulting in limited consumer acceptance. As a new type of functional raw material, selenium-enriched soybeans have a protein content as high as 35% - 45%, the biological availability of selenium is more than 90%, and the selenoprotein complex has strong antioxidant and immunomodulatory functions. The introduction of the selenium-enriched soybean milk into the compound system can not only make up for the protein deficiency of linseed milk, but also enhance the functional characteristics of the product through the synergistic effect of selenium-polyphenol, and improve the taste through compounding.

[0036] In view of this, the present invention provides a compound plant milk of linseed / selenium-enriched soybeans and its preparation method and application, aiming to solve the problems raised in the technical background, proposing to scientifically compound linseed milk and selenium-enriched soybean milk, and innovatively introducing an ultrasonic synergistic treatment process. Through the optimization of raw material ratios, the functional advantages of ω-3 fatty acids in linseed milk and the high-protein-selenium nutritional characteristics of selenium-enriched soybean milk are fully utilized to achieve amino acid complementarity and synergistic enhancement of functional components. At the same time, a multi-frequency ultrasonic combined treatment technology is used to directionally regulate the structure of protein-polysaccharide complexes, maximizing the retention of thermosensitive active ingredients while improving the system stability.

[0037] It should be noted that when the present invention involves numerical ranges, it should be understood that any value between the two endpoints of each numerical range and the two endpoints can be selected. Since the steps and methods adopted are the same as those in Examples 1 - 9, in order to avoid repetition, the present invention describes the preferred embodiments, but the present invention is not limited thereto, but can also be specifically implemented in other ways within the scope of the technical solutions defined in the appended claims.

[0038] The technical solution of the present invention will be further illustrated by specific examples below.

[0039] According to the key process parameters given in Table 1, the following examples are designed through single-factor experiments and the response surface method (Box-Behnken design).

[0040] Table 1 Key process parameters [[ID=1?]] Example 1 A preparation method of a compound plant milk of linseed / selenium-enriched soybeans, comprising the following steps: [[ID=2?]]Select selenium-enriched soybeans with plump and non-moldy grains, soak them at room temperature for 12 hours at a mass ratio of 1:2, and after peeling, grind the selenium-enriched soybean dry beans and water at a mass ratio of 1:6, and filter through a 200-mesh sieve to remove the bean dregs to obtain selenium-enriched soybean milk.

[0041] Adjust the moisture content of flaxseeds to 17%. After microwave treatment at 700 W for 10 min, wash the microwave-treated flaxseeds repeatedly with warm water at 50 °C to degum them. After drying, grind and homogenize them according to the mass ratio of flaxseeds to water of 1:5 to obtain flaxseed milk.

[0042] Mix selenium-enriched soybean milk and flaxseed milk in a volume ratio of 3:7, and perform ultrasonic treatment at an ultrasonic power of 297 W for 21 min to obtain flaxseed / selenium-enriched soybean compound plant milk.

[0043] Example 2 Compared with Example 1, only the mass ratio of peeled selenium-enriched soybean dry beans to clear water is different from that in Example 1, and the experimental steps of other preparation methods are the same as those in Example 1. Among them, the peeled selenium-enriched soybean dry beans and clear water are ground in a mass ratio of 1:5, and the bean dregs are removed by filtration through a 200-mesh sieve to obtain selenium-enriched soybean milk.

[0044] Example 3 Compared with Example 1, only the mass ratio of peeled selenium-enriched soybean dry beans to clear water is different from that in Example 1, and the experimental steps of other preparation methods are the same as those in Example 1. Among them, the peeled selenium-enriched soybean dry beans and clear water are ground in a mass ratio of 1:9, and the bean dregs are removed by filtration through a 200-mesh sieve to obtain selenium-enriched soybean milk Example 4 Compared with Example 1, only the mass ratio of flaxseeds to water after drying is different from that in Example 1, and the experimental steps of other preparation methods are the same as those in Example 1. Among them, the mass ratio of flaxseeds to water after drying is 1:8.

[0045] Example 5 Compared with Example 1, only the mass ratio of flaxseeds to water after drying is different from that in Example 1, and the experimental steps of other preparation methods are the same as those in Example 1. Among them, the mass ratio of flaxseeds to water after drying is 1:9.

[0046] Example 6 Compared with Example 1, only the volume ratio of selenium-enriched soybean milk to flaxseed milk is different from that in Example 1, and the experimental steps of other preparation methods are the same as those in Example 1. Among them, the volume ratio of selenium-enriched soybean milk to flaxseed milk is 1:9.

[0047] Example 7 Compared with Example 1, only the volume ratio of selenium-enriched soybean milk to flaxseed milk is different from that in Example 1, and the experimental steps of other preparation methods are the same as those in Example 1. Among them, the volume ratio of selenium-enriched soybean milk to flaxseed milk is 5:5.

[0048] Example 8 When Example 8 is compared with Example 1, only the ultrasonic treatment conditions are different from those in Example 1, and the experimental steps of other preparation methods are the same as those in Example 1. Among them, the power of ultrasonic treatment is 200 W, and the ultrasonic treatment time is 5 min.

[0049] Example 9 When Example 9 is compared with Example 1, only the ultrasonic treatment conditions are different from those in Example 1, and the experimental steps of other preparation methods are the same as those in Example 1. Among them, the power of ultrasonic treatment is 400 W, and the ultrasonic treatment time is 25 min.

[0050] The above Examples 1 to 9 can all prepare the flaxseed / selenium-enriched soybean compound plant milk. By optimizing the TSI value, average particle size and Zeta potential of the flaxseed / selenium-enriched soybean compound plant milk, the optimal process parameters are determined as follows: the mass ratio of selenium-enriched soybean milk to flaxseed milk in Example 1 is 3:7, the ultrasonic power is 297 W, and the ultrasonic duration is 21 min. Next, the flaxseed / selenium-enriched soybean compound plant milk prepared in Example 1 is selected for experiments.

[0051] Experiment 1: Determination experiment of basic nutritional indexes of flaxseed / selenium-enriched soybean compound plant milk The protein content of the prepared flaxseed / selenium-enriched soybean compound plant milk was determined with reference to GB5009.5-2016 Determination of Protein in Foods; the total solids content was determined with reference to GB5413.39-2010 Determination of Non-fat Milk Solids in Milk and Dairy Products; the fatty acid composition and content were determined with reference to GB5009.168-2016 Determination of Fatty Acids in Foods; the selenium content was determined by atomic fluorescence method; the total phenol content was determined by Folin-Ciocalteu colorimetric method; the polysaccharide content was determined by phenol-sulfuric acid method with glucose as the standard. The measured indexes are as follows:

[0052] The selenium content of the flaxseed / selenium-enriched soybean compound plant milk is (0.26±0.01) mg / kg. According to the local standard DB61 / T556-2018 "Selenium Content Standard for Selenium-enriched Foods and Related Products", the selenium content of liquid milk ≥ 0.075 mg / kg is defined as selenium-enriched milk. This indicates that the flaxseed / selenium-enriched soybean compound plant milk prepared this time meets the requirements of selenium-enriched plant milk. Compared with flaxseed milk, the flaxseed / selenium-enriched soybean compound plant milk has improved in terms of nutritional components such as protein content, total solids content, and total phenol content (see Table 2), indicating that the addition of selenium-enriched soybean milk realizes the complementarity of nutritional components and enhances the nutritional value of the flaxseed / selenium-enriched soybean compound plant milk. After ultrasonic compounding, the average particle size and Zeta potential of the flaxseed / selenium-enriched soybean compound plant milk are also significantly lower than those of flaxseed milk, indicating that the addition of selenium-enriched soybean milk significantly improves its physical stability through ultrasonic treatment, and the significant reduction in the average particle size also indicates an improvement in the taste of the flaxseed / selenium-enriched soybean compound plant milk. From the oxidation index, the acid value of flaxseed milk is (0.59±0.04) mgKOH / g, and the acid value of the flaxseed / selenium-enriched soybean compound plant milk is (0.19±0.00) mgKOH / g, both of which are far lower than the requirement of ≤3.0 mgKOH / g in the national standard GB5009.229-2016 "Determination of Acid Value in Foods". In contrast, the acid value of the flaxseed / selenium-enriched soybean compound plant milk is lower, indicating a longer shelf life. The peroxide value of flaxseed milk is (1.93±0.01) mmol / kg, and the peroxide value of the flaxseed / selenium-enriched soybean compound plant milk is (1.76±0.02) mmol / kg, indicating that the oxidation at the initial stage of preparing the flaxseed / selenium-enriched soybean compound plant milk is low, both are lower than the national standard, and meet the market requirements.

[0053] Table 2 Nutritional Components of Selenium-enriched Soybean / Flaxseed Compound Plant Milk Experiment 2: Determination Experiment on the Storage Stability of Flaxseed / Selenium-enriched Soybean Compound Plant Milk The prepared flaxseed / selenium-enriched soybean compound plant milk was dispensed into sample bottles and stored in the dark at 55°C. The specific results of the storage stability analysis are as Figure 1 shown, where the average particle size of flaxseed milk and flaxseed / selenium-enriched soybean compound plant milk during storage in the dark at 55°C is as Figure 1 shown in (A), and the change in Zeta potential of flaxseed milk and flaxseed / selenium-enriched soybean compound plant milk during storage in the dark at 55°C is as Figure 1 shown in (B). It can be found from Figure 1 (A) that the average particle size of flaxseed milk increases significantly with the increase of storage time, especially increasing significantly after the 6th day; in contrast, the average particle size of the flaxseed / selenium-enriched soybean compound plant milk has not changed significantly since the 2nd day, showing more excellent physical stability.

[0054] It was found that Figure 1 (B)the Zeta potential of flaxseed milk and the flaxseed / selenium-enriched soybean compound plant milk increased with the increase of storage time, but the increase amplitude of the Zeta potential of flaxseed milk was greater, and the Zeta potential value had risen to -16.65 mV at the 14th day of storage.

[0055] The TSI analysis of the physical stability of flaxseed milk and the flaxseed / selenium-enriched soybean compound plant milk during storage in the dark at 55 °C is as Figure 1 shown in Figure 1 (C). It was found from the TSI analysis of the physical stability of flaxseed milk and the flaxseed / selenium-enriched soybean compound plant milk during one-week storage that the TSI value of flaxseed milk gradually increased with time and reached 9.71 at the 7th day, indicating that its fat globules were prone to aggregation, resulting in an unstable system. After supplementation with selenium-enriched soybean milk, the TSI value of the flaxseed / selenium-enriched soybean compound plant milk was significantly lower than that of flaxseed milk and tended to be stable from the 4th day, indicating that ultrasound fragmented the fat globules and protein particles into smaller sizes and increased their interfacial electrical repulsion force, significantly improving the system stability.

[0056] Meanwhile, the interfacial morphology between emulsion droplets and the continuous phase was recorded using a laser confocal microscope, a cryo-scanning electron microscope, and an ordinary camera, and the results are as Figure 2 shown below: It can be seen from the cryo-scanning electron microscope images that the selenium-enriched soybean milk (A1, A2) had fewer droplets, a simple structure, and a loose morphological distribution. The flaxseed milk (B1, B2) had larger and more complex droplets. A large amount of flaxseed gum (polysaccharide) in it would interact with other components of the emulsion, causing "depletion flocculation", resulting in a decrease in the fluidity of the system and the appearance of solid characteristics, reducing the physical stability of the emulsion. However, it can be seen from Figures C1 and C2 that after the selenium-enriched soybean milk and flaxseed milk were compounded by ultrasound at a ratio of 3:7, it was found that the droplets were smaller and evenly distributed. This may be due to the emulsification of the plant milk during the ultrasound compounding process, resulting in the rearrangement and distribution of protein and fat molecules. In addition, the ultrasonic treatment promoted the interaction between soy selenium protein and flaxseed protein, making the compounded milk have a stable network-like structure, wrapping the droplets and improving the stability.

[0057] It can be observed from the external morphology diagram that there is no obvious stratification or aggregation in the selenium-enriched soy milk during the entire storage period. The possible reason is that it is rich in soy selenium protein, which has good emulsifying and stabilizing properties, effectively preventing the aggregation of fat globules and the sedimentation of particles. Obvious stratification occurs in the flaxseed milk on the 2nd day of storage, and slight sedimentation begins on the 8th day. This may be due to the disappearance of the small droplet interface and the formation of large droplets, resulting in aggregation and ultimately the complete separation of the oil phase and the water phase. In addition, the solid particles in the flaxseed milk are relatively large and are prone to sedimentation under the action of gravity. The compound plant milk gradually shows stratification and sedimentation from the 2nd day, but the stratification phenomenon is slightly milder than that of the flaxseed milk and is relatively stable, indicating that after adding the selenium-enriched soy milk, the soy selenium protein in the compound plant milk interacts with the flaxseed gum, partially improving the stability of the flaxseed milk.

[0058] It can be observed from the CLSM analysis diagrams of the microstructure of the flaxseed milk (B) and the compound plant milk (C) during storage that under the laser confocal microscope, obvious large oil droplets can be seen in the freshly prepared flaxseed milk, which may be due to the increase in the oil content of the emulsion leading to aggregation and the formation of large droplets; while the milk droplets in the freshly prepared compound plant milk are evenly distributed, the particle size is significantly reduced, and there are no obvious aggregation and flocculation phenomena. However, the droplet size of the flaxseed milk increases significantly and there is more obvious aggregation after the 8th day of storage, while the change in the droplet size of the compound plant milk is relatively slight and basically remains stable.

[0059] The physicochemical stability of the flaxseed milk and the flaxseed / selenium-enriched soy compound plant milk during storage was analyzed, and the results are shown by Figure 3 It can be seen that Figure 3 As shown in (A), the content of hydroperoxides in the flaxseed milk increased relatively slowly at the initial stage of storage. Compared with the 6th day, the content of hydroperoxides increased significantly on the 8th day and reached the peak ((0.24 ± 0.03) mmol / kg) on the 10th day. Subsequently, due to severe stratification, the measured value decreased significantly. As Figure 3 As shown in (B), with the increase of storage time, the TBARS value of the flaxseed milk showed a trend of first increasing and then decreasing, increased significantly on the 6th day, and reached the peak ((58.41 ± 0.25) μmol / L) on the 10th day. As the storage time prolongs, the lipid oxidation reaction gradually tends to be stable, the generation rate of secondary oxidation products slows down, and at the same time the decomposition rate accelerates, resulting in the decrease of the TBARS value.

[0060] However, as shown in Figure 3 (A) and Figure 3 (B), the content of hydroperoxides and the TBARS value of the flaxseed / selenium-enriched soy compound plant milk changed little during the entire storage period, showed a slow upward trend, and were significantly lower than those of the flaxseed milk, indicating that the selenium-enriched soy milk has better oxidative stability.

[0061] Experiment 3: Experiment on the stability maintenance mechanism of selenium-enriched soy protein ① Experiment on the stronger emulsifying properties of selenium-enriched soy protein compared with ordinary soy protein The emulsifying properties and foaming properties of selenium-enriched soy protein and ordinary soy protein were compared, and the results are as Figure 4 shown in Figure 4 (A) and Figure 4 (B). The emulsifying ability (EAI, +4.62%) and emulsifying stability (ESI, +0.13%) of selenium-enriched soy protein were higher than those of ordinary soy protein, indicating that selenium-enriched soy protein can better maintain the stability of the emulsion system and prevent oil-water separation.

[0062] The possible reason is that selenium enhances the stability of the protein structure through bonding with protein molecules. The presence of selenium may improve the surface activity and functional properties of SSPI; selenium-enriched soy protein may have undergone microscopic changes in its molecular structure, such as increasing hydrophobic regions and exposing more non-polar amino acid residues (such as leucine and phenylalanine), enhancing the interaction with oil, making SSPI perform better in forming and maintaining the emulsion system. The foaming ability (FA, +15.46%) and foam stability (FS, +9.94%) of selenium-enriched soy protein were also significantly improved compared with ordinary soy protein. The possible reason is that selenium can interact with reactive groups in the protein, improve the protein structure, thereby enhancing its surface activity, making it easier to form and maintain stable foam; SSPI has a better conformation, increasing the ability to interact with the air interface and making the foam structure more stable; at the same time, the redox activity of selenium may increase surface polar groups (such as carboxyl groups), improve solubility in the aqueous phase, and form a stable interfacial film.

[0063] ② Experiment on the determination of the content of free sulfhydryl groups and disulfide bonds in ordinary soy protein (SPI) and selenium-enriched soy protein (SSPI) The measurement results are as Figure 5 shown. Comparing the content of free sulfhydryl groups (Free-SH) and disulfide bonds (DS) in selenium-enriched soy protein and ordinary soy protein, it was found that the content of free sulfhydryl groups in selenium-enriched soy protein was lower than that in ordinary soy protein, but the content of disulfide bonds was higher (+50%). Free sulfhydryl groups are the precursors of disulfide bonds, and the increase in disulfide bonds means that some free sulfhydryl groups have undergone oxidation reactions to form stable disulfide bonds. Selenium (especially in the form of selenocysteine or selenate) can indirectly enhance the oxidative environment by participating in the sulfur metabolic pathway, promoting the oxidation of free sulfhydryl groups to form intramolecular or intermolecular disulfide bonds; selenium may also directly react with sulfhydryl groups to form selenosulfide bonds (-Se-S-), which are then converted into more stable disulfide bonds. The increase in the content of disulfide bonds may enhance the thermal stability and structural strength of the protein, improve the functional properties of the protein, that is, increase emulsifying ability and foaming ability, etc.; enhance antioxidant properties, that is, reduce free radical damage and inhibit lipid oxidation.

[0064] ③ Experiment on the determination of protein content and solubility of common soy protein (SPI) and selenium-enriched soy protein (SSPI) There was no significant difference in the protein content between common soy protein and selenium-enriched soy protein, but the solubility of selenium-enriched soy protein increased significantly (+23.54%). The possible reason is that selenium can interact with amino acid residues in proteins, which may change the folding pattern of proteins or reduce intermolecular aggregation, thus improving solubility. The measurement results are shown in Table 3.

[0065] Table 3 Protein content and solubility of common soy protein (SPI) and selenium-enriched soy protein (SSPI) ④ Experiment on the interfacial properties of common soy protein (SPI) and selenium-enriched soy protein (SSPI) Proteins stabilize emulsions mainly in two ways: reducing the interfacial tension and generating repulsive interactions (such as steric and electrostatic), and then forming an interfacial film. Figure 6 Reveal the adsorption kinetics of common soy protein and selenium-enriched soy protein at the interface. The dynamic interfacial pressure is a key factor determining emulsifying properties and stability. Figure A shows the trend of the surface tension of SPI and SSPI decreasing with time. The initial surface tensions of SPI and SSPI are both relatively high, but the decrease rate of SSPI is faster, indicating that it adsorbs rapidly to the interface, has a stronger adsorption ability than SPI, and the interfacial tension value is lower than that of SPI, and reaches a relatively constant value (9.76 mN / m) at 8000 s. As can be seen from Figure B, the surface tension increases with the square root of time, growing rapidly in the initial stage and then increasing slowly, which indicates that the adsorption process is affected by the diffusion mechanism. The surface tension of SSPI is always higher than that of SPI, further confirming that selenium-enriched soy protein adsorbs more effectively at the interface than common soy protein. The slope at the initial stage of diffusion reflects the migration ability of proteins to the interface. The steeper slope of SSPI indicates that its diffusion is faster and the adsorption rate at the interface is faster. The later flat curve may represent the molecular rearrangement stage, and the faster equilibrium of SSPI further confirms its better interfacial activity. It shows that the presence of selenium changes the molecular structure (such as enhanced hydrophobicity or optimized charge distribution), which promotes diffusion and interfacial adsorption.

[0066] Experiment 4: Environmental stability experiment of flaxseed / selenium-enriched soy compound plant milk ① Acid and base environmental stability experiments of flaxseed / selenium-enriched soy compound plant milk Adjust the pH of the flaxseed / selenium-enriched soybean compound plant milk prepared in Example 1 to 5, 7, and 9 respectively with 0.5 M or 0.1 M sodium hydroxide or 0.5 M or 0.1 M hydrochloric acid. Then, separately fill the flaxseed / selenium-enriched soybean compound plant milk with pH values of 5, 7, and 9 into sample bottles, store them in the dark at 55 °C for an accelerated storage experiment. Use flaxseed milk as a control, adjust the pH of flaxseed milk to 5, 7, and 9 respectively with 0.5 M or 0.1 M sodium hydroxide or 0.5 M or 0.1 M hydrochloric acid. Then, separately fill the flaxseed milk with pH values of 5, 7, and 9 into sample bottles, store them in the dark at 55 °C for an accelerated storage experiment.

[0067] The storage stability results of the prepared flaxseed milk and flaxseed / selenium-enriched soybean compound plant milk in acidic and alkaline environments are as Figure 7 shown, where through Figure 7 (A), it was found that at day 0, from the perspective of appearance, there was no obvious stratification or precipitation in flaxseed milk at different pH values, and the flaxseed / selenium-enriched soybean compound plant milk was also in a uniform state, and the emulsification system was relatively stable. At day 8, obvious stratification occurred in flaxseed milk, a part of the liquid was clear, and there was precipitation or agglomerates at the bottom, indicating that the emulsification system was affected. Compared with flaxseed milk, the flaxseed / selenium-enriched soybean compound plant milk had slightly better stability at each pH value, with less severe stratification and still maintaining a certain emulsified state.

[0068] This is because the prominent problem of protein-stabilized emulsions is the flocculation of emulsions, especially when the pH value is close to the isoelectric point of the protein. The emulsion has poor stability when close to the isoelectric point of the protein and will undergo flocculation.

[0069] From Figure 7 the confocal laser scanning microscopy images in (A), it can be seen that at day 0 under the condition of pH 5, compared with the flaxseed / selenium-enriched soybean compound plant milk, the droplet size of flaxseed milk increased significantly, and obvious droplet aggregation occurred, while it was relatively normal at pH values of 7 and 9.

[0070] And from Figure 8 the confocal laser scanning microscopy images in (B), it shows that at day 8, the droplet distribution of flaxseed milk was sparse and there was aggregation, especially under the condition of pH 5, indicating the destruction of the emulsification system, and the aggregation of fat or protein particles led to precipitation. The droplet distribution of the compound milk was relatively uniform, but there was slight aggregation, indicating that its emulsification system had higher stability by comparison. The possible reason is that the compound milk contains selenium-enriched soybean protein, making its heat resistance and antioxidant ability stronger, so it can still maintain a certain degree of uniformity after 8 days of storage. Flaxseed milk has a relatively simple protein structure and lacks strong stability, and is prone to aggregation and precipitation during storage. It also shows that compared with natural proteins, selenium-enriched protein complexes have good acid resistance.

[0071] ② Experimental on the average particle size, Zeta potential, hydroperoxide content and TBARS value of flaxseed / selenium-enriched soybean compound plant milk at different pH values As Figure 9 shown in A, on the 0th day, the average particle sizes of flaxseed milk and flaxseed / selenium-enriched soybean compound plant milk were at relatively low levels at all pH values, indicating that the initial state of the emulsion was relatively uniform and the emulsification effect was good. However, when the pH value was 5, the average particle size was larger than that at pH values of 7 and 9. On the 8th day, the average particle size of flaxseed milk increased significantly with the extension of storage time, especially under acidic conditions, where the particle growth rate was faster and reached (23.78±0.83) μm, making it extremely prone to aggregation and stratification, indicating an increase in emulsion instability and possible precipitation or emulsification breakdown. During the entire storage process of flaxseed / selenium-enriched soybean compound plant milk, the increase in average particle size was relatively slow, especially under neutral and weakly alkaline conditions, showing better stability and smaller changes in particle size. The possible reason is that the flaxseed / selenium-enriched soybean compound plant milk contains selenium-enriched soybean protein, which may form a stronger adsorption layer at the emulsification interface, preventing the aggregation of fat or protein and keeping it in a better dispersed state after long-term storage; and the selenium-enriched soybean protein may enhance the emulsion stability by forming a more stable protein network and improving the emulsification ability, thus reducing particle aggregation.

[0072] The Zeta potential reflects the stability of the system. The more negative the value, the stronger the charge repulsion force of the emulsion and the better the stability. As Figure 9 shown in B, the longer the storage time of flaxseed milk, the lower the absolute value of the Zeta potential, indicating that the stability of the emulsion decreases with time. Under the condition of pH value of 5, the change in Zeta potential was relatively large and approached zero, reaching (-6.29±0.45) mV on the 8th day, and the emulsion stability decreased significantly. The Zeta potential value of the compound milk was always lower than that of flaxseed milk, and the decrease amplitude was smaller, indicating that the flaxseed / selenium-enriched soybean compound plant milk had better stability. Under the condition of pH value of 7, the potential of the flaxseed / selenium-enriched soybean compound plant milk was maintained relatively stable, indicating that the emulsification effect was better at this pH. The decrease in the potential of flaxseed milk may be related to the oxidation of unsaturated fatty acids (such as α-linolenic acid) in flaxseed milk. The oxidation products (such as aldehydes and ketones) may adsorb on the particle surface, increasing the negative charge density. The better stability of the flaxseed / selenium-enriched soybean compound plant milk may be due to the antioxidant effect of selenium (such as selenoprotein) in selenium-enriched soybeans, which delays the oxidation reaction and thus maintains the charge stability on the particle surface.

[0073] As Figure 9As can be seen from C, on the 0th day, the hydroperoxide contents of flaxseed milk and flaxseed / selenium-enriched soybean compound plant milk were both relatively low, indicating that at the beginning of storage, the oxidation degree of the system was relatively light. During storage, the hydroperoxide content of flaxseed milk increased significantly with the increase of storage time. Especially under the condition of pH 5, the oxidation level was higher and reached the peak on the 6th day ((3.81±0.42) mmol / kg).

[0074] As can be seen from Figure 9 D, the TBARS value of flaxseed milk also showed the same trend and reached the peak on the 6th day ((58.77±0.08) μmol / L). After the 6th day, the hydroperoxide content of flaxseed milk at three pH values decreased significantly. The possible reason is that the emulsion aggregation and stratification were more significant, resulting in demulsification, and the uneven sampling led to the decrease of the content. The oxidation degree (hydroperoxide content and TBARS value) of flaxseed / selenium-enriched soybean compound plant milk was generally lower than that of flaxseed milk. Especially under neutral and weakly alkaline conditions, the content change range was small, showing better antioxidant performance.

[0075] Experiment 4: Application experiment of flaxseed / selenium-enriched soybean compound plant milk Prepare flaxseed / selenium-enriched soybean compound plant milk according to the preparation method of flaxseed / selenium-enriched soybean compound plant milk given in Example 1, and then load fat-soluble bioactive components such as lycopene or astaxanthin in this system.

[0076] The specific implementation method is as follows: Dissolve carotenoids such as lycopene or astaxanthin with ethanol at 5 mg / mL, and add it to flaxseed / selenium-enriched soybean compound plant milk according to a volume ratio of 5% to obtain flaxseed / selenium-enriched soybean compound plant milk loaded with lycopene or astaxanthin.

[0077] It was measured that the encapsulation rates of carotenoids such as lycopene or astaxanthin were both greater than 85%, and they had good oxidation stability. After storing at room temperature for 1 month, the hydroperoxide values of the compound plant milk were all lower than 6 mmol / kgoil (lower than the national standard), and the carotenoid retention rates were all greater than 90%. In addition, compared with the ordinary method (stirring and loading of flaxseed plant milk), the oxidation stability (hydroperoxide value) decreased by 120%, and no instability phenomena such as cream separation and demulsification occurred.

[0078] Obviously, those skilled in the art can make various changes and deformations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and deformations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and deformations.

Claims

1. A preparation method of flaxseed / selenium-enriched soybean compound plant milk, characterized in that, It includes the following steps: Prepare selenium-rich soy milk; Prepare flaxseed milk; Mix the selenium-rich soy milk and flaxseed milk according to a volume ratio of 1:9 to 5:5, and obtain a flaxseed / selenium-rich soy milk compound plant milk through ultrasonic treatment. The power of the ultrasonic treatment is 200W to 400W, and the ultrasonic treatment time is 5min to 25min.

2. The preparation method of the flaxseed / selenium-enriched soybean compound plant milk according to claim 1, characterized in that, The selenium-rich soy milk and flaxseed milk are mixed according to a volume ratio of 3:

7. The power of the ultrasonic treatment is 297W, and the ultrasonic treatment duration is 21min.

3. The preparation method of the flaxseed / selenium-enriched soybean compound plant milk according to claim 1, characterized in that, The preparation method of the selenium-rich soy milk includes the following steps: Select selenium-rich soybeans with plump grains and no mildew. After cleaning with clean water, soak them in clean water at room temperature. After peeling, grind the selenium-rich soybeans dry beans and clean water according to a mass ratio of 1:5 to 1:9, and obtain selenium-rich soy milk through filtration.

4. The preparation method of the flaxseed / selenium-enriched soybean compound plant milk according to claim 3, characterized in that, After the selenium-rich soybeans are cleaned, soak them in clean water at a mass ratio of 1:2 at room temperature for 12h. After peeling, grind the selenium-rich soybeans dry beans and clean water according to a mass ratio of 1:6, and filter through 200 meshes to remove soybean dregs to obtain selenium-rich soy milk.

5. The preparation method of the flaxseed / selenium-rich soybean compound plant milk according to claim 1, characterized in that, The preparation method of the flaxseed milk includes the following steps: Adjust the moisture content of flaxseeds to 17%, and perform microwave treatment for 10min under 700W of microwave; Repeatedly wash and degum the microwave-treated flaxseeds in warm water. After drying, grind them according to the mass ratio of flaxseed dry weight to water of 1:5 to 1:9, and obtain flaxseed milk after homogenization treatment.

6. The preparation method of the flaxseed / selenium-rich soybean compound plant milk according to claim 1, wherein The average particle size of the compound plant milk is ≤320nm, the absolute value of Zeta potential is ≥30mV, and the selenium content is ≥0.26mg / kg.

7. The high-steady-state flaxseed / selenium-rich soy milk compound plant milk prepared by the preparation method of the flaxseed / selenium-rich soy milk compound plant milk according to any one of claims 1 to 6.

8. The application of the flaxseed / selenium-rich soy milk compound plant milk according to claim 7 in fat-soluble carotenoid health foods, functional foods, and nutritional fortified foods.

9. Use of the flaxseed / selenium-enriched soybean compound plant milk according to claim 8 in lipid-soluble carotenoid health foods, functional foods, and nutrient fortified foods, characterized in that, Encapsulate the active ingredient of fat-soluble carotenoid with the flaxseed / selenium-rich soy milk compound plant milk as the carrier, and the encapsulation rate is greater than 85%.

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