Emulsion with high tea oil oxidation stability as well as preparation method and application of emulsion

Abstract

The invention discloses an emulsion with high tea oil oxidation stability as well as a preparation method and application of the emulsion. The emulsion is prepared by the method comprising the following steps: preparing a konjac glucomannan solution and a tea polyphenol solution; preparation of a konjac glucomannan-tea polyphenol compound; preparing a mixed protein dispersion liquid; and preparing the tea oil emulsion. The invention also discloses application of the emulsion in preparation of water-phase matrix food. Konjac glucomannan and tea polyphenol are prepared into a compound to be applied to the tea oil emulsion, so that the emulsification stability is improved, especially the oxidation stability is improved, and the combination amount of tea polyphenol on konjac glucomannan is increased by adopting a proper acidic condition and a two-step action method of combining normal temperature and low temperature; the tea oil is prepared into an oil-in-water emulsion form with high tea oil oxidation stability, the application field of the tea oil in the food industry is widened, the whey protein and the casein are used for replacing a chemically synthesized emulsifier to prepare the tea oil emulsion, the food safety risk of the chemically synthesized emulsifier is avoided, and the nutritional quality of the tea oil emulsion is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of camellia oil emulsions, and particularly relates to an emulsion with high oxidation stability of camellia oil, a preparation method thereof, and an application thereof. Background Art

[0002] Camellia oil is a unique woody edible vegetable oil in China, with excellent nutritional value and health care functions. The saturated fatty acid content of camellia oil is less than 11%, and the unsaturated fatty acid content is more than 85%. Among them, the oleic acid content is the highest, and it also contains rich essential fatty acids linoleic acid and linolenic acid for the human body. Its fatty acid composition is similar to that of olive oil, and it is known as the "Oriental olive oil". The unsaturated fatty acids in camellia oil have various physiological functions and health care effects such as regulating human lipid metabolism, preventing and treating cardiovascular and cerebrovascular diseases, anti-inflammatory, anti-cancer, anti-obesity, promoting the development of infants and young children, improving the body's immunity, preventing and improving Alzheimer's disease, etc. Long-term consumption of camellia oil is beneficial to maintaining human health.

[0003] Based on the hydrophobic characteristics of camellia oil, it is not conducive to its dispersion in water-phase matrix foods. Therefore, it needs to be prepared into an oil-in-water emulsion form and then applied to water-phase matrix foods to promote its uniform dispersion in water-phase matrix foods by improving hydrophilicity.

[0004] At the same time, because camellia oil has a high content of unsaturated fatty acids, the double bonds of unsaturated fatty acids are extremely easy to be oxidized and deteriorated and rancid under the conditions of oxygen, light, and high temperature, resulting in camellia oil losing its original flavor, taste, and physiological functions, and even generating substances harmful to human health. Therefore, improving the oxidation stability of camellia oil and reducing the oxidative loss of unsaturated fatty acids are the key technical problems that need to be solved to maintain the nutritional quality of camellia oil emulsions.

[0005] Tea polyphenols are the general term for various polyphenolic substances containing 2-phenylbenzopyran structures in tea leaves, mainly including: catechin compounds, flavonoid compounds, anthocyanins and leucoanthocyanin compounds, phenolic acids and condensed phenolic acids, etc. Among them, catechin compounds are the most common, accounting for more than 70% of the total amount of tea polyphenols. Since tea polyphenols are mostly polyhydric phenols containing more than 2 ortho-hydroxy groups and have strong hydrogen-donating ability, they are an ideal natural antioxidant, and their antioxidant ability is 4-6 times that of synthetic antioxidants dibutylhydroxytoluene and butylhydroxyanisole, 5-10 times that of vitamin C, and 6-7 times that of vitamin E. However, due to its high solubility in water and poor oil solubility, its antioxidant effect in oils is affected.

[0006] Konjac glucomannan is the main functional component of konjac tubers. Its main chain is composed of D-glucose and D-mannose connected by β-1,4-glycosidic bonds in a molar ratio of 1:1.4 or 1:1.6, and contains rich hydroxyl groups. It is a natural high-molecular heteropolysaccharide with excellent hydrophilicity, gelation, emulsification, film-forming, and thickening effects. [[ID=,21]]

[0007] The present invention intends to prepare a complex of konjac glucomannan and tea polyphenols for use in the preparation of tea oil emulsion and conduct research on its oxidative stability. Summary of the Invention

[0008] One of the objectives of the present invention is to provide an emulsion with high oxidative stability of tea oil and a method for its preparation.

[0009] Another objective of the present invention is to provide the application of the above-mentioned emulsion with high oxidative stability of tea oil in the preparation of aqueous matrix foods.

[0010] The above first objective of the present invention can be achieved through the following technical solution: An emulsion with high oxidative stability of tea oil is prepared by a method comprising the following steps:

[0011] (1) Preparation of konjac glucomannan solution and tea polyphenol solution:

[0012] Take konjac glucomannan and dissolve it in an acetic acid buffer solution with a pH of 4.5 - 5.5. After stirring, a konjac glucomannan solution is obtained.

[0013] Take tea polyphenols and dissolve them in an acetic acid buffer solution with a pH of 4.5 - 5.5. After stirring, a tea polyphenol solution is obtained.

[0014] (2) Preparation of konjac glucomannan - tea polyphenol complex:

[0015] At room temperature, add the tea polyphenol solution to the continuously stirred konjac glucomannan solution and continue stirring for 2 - 3 h to obtain a konjac glucomannan - tea polyphenol complex solution.

[0016] In a low - temperature constant - temperature reaction device at 4 - 6 °C, let the konjac glucomannan - tea polyphenol complex solution stand for 2 - 3 h to obtain a konjac glucomannan - tea polyphenol complex solution with a tea polyphenol binding amount > 900 mg / g.

[0017] (3) Preparation of mixed protein dispersion:

[0018] Take equal masses of whey protein and casein, mix them evenly, add them to water, stir, and then place them in the refrigerator to stand for sufficient hydration to obtain a mixed protein dispersion with a mass percentage content of 4 - 5%.

[0019] (4) Preparation of tea oil emulsion:

[0020] The konjac glucomannan-tea polyphenols composite solution prepared in step (2) is added to the mixed protein dispersion prepared in step (3), and after mixing, tea oil is added. A shear homogenizer is first used to shear the solution to prepare a primary emulsion, and then a micro-jet high-pressure homogenizer is used to homogenize the solution to prepare an O / W tea oil emulsion. After filling, the solution is sterilized at high temperature and cooled to obtain a finished emulsion with high oxidative stability of tea oil.

[0021] In the above tea oil emulsion with high oxidation stability:

[0022] Preferably, the concentration of the konjac glucomannan solution in step (1) is 2.0-2.5 mg / mL, and the concentration of the tea polyphenol solution is 20-25 mg / mL.

[0023] More preferably, a certain amount of konjac glucomannan is weighed in step (1), dissolved in an acetate buffer solution having a pH of 4.5 to 5.5, and stirred on a magnetic stirrer for 60 to 90 minutes to obtain a uniform and transparent konjac glucomannan solution having a concentration of 2.0 to 2.5 mg / mL.

[0024] More preferably, a certain amount of tea polyphenols is weighed in step (1), dissolved in an acetate buffer solution at pH 4.5 to 5.5, and stirred on a magnetic stirrer for 20 to 30 minutes until the tea polyphenols are fully dissolved, to obtain a clear and transparent tea polyphenol solution with a concentration of 20 to 25 mg / mL.

[0025] Since tea polyphenols have good structural stability in the pH range of 4.0-6.8, strong acid, neutral and alkaline conditions will cause partial dissociation of phenolic hydroxyl groups, greatly reducing the hydroxyl groups that can interact with konjac glucomannan to form hydrogen bonds. Therefore, in order to maintain the stability of the molecular structure of tea polyphenols and improve the hydrogen bonding efficiency with konjac glucomannan, acetate buffer solution with a pH of 4.5 to 5.5 was used to prepare konjac glucomannan and tea polyphenol solutions.

[0026] Since the hydrogen bonding force increases significantly with decreasing temperature, the hydrogen bonding force at low temperatures of 4 to 6°C is significantly stronger than that at room temperature. However, the increased viscosity of the konjac glucomannan solution at low temperatures will reduce the molecular movement speed, which is not conducive to the formation of hydrogen bonds between it and tea polyphenols. Therefore, in step (2) of the present invention, a two-step treatment method of room temperature bonding plus low temperature strengthening is adopted to prepare the konjac glucomannan-tea polyphenols complex.

[0027] Preferably, in step (2), the volume ratio of the tea polyphenol solution to the konjac glucomannan solution is 1:3-4.

[0028] More preferably, in step (2), the konjac glucomannan solution is placed on a magnetic stirrer at room temperature and continuously stirred, and the tea polyphenol solution is slowly added to the continuously stirred konjac glucomannan solution in a volume ratio of 1:3-4 between the tea polyphenol solution and the konjac glucomannan solution, and stirring is continued for 2-3 hours to allow the two to fully react and obtain a hydrogen bonded complex solution.

[0029] More preferably, in step (2), the composite solution is placed in a low-temperature constant-temperature reaction bath at 4-6° C. and maintained for 2-3 hours to further strengthen the hydrogen bonding force between the two and increase the binding amount of tea polyphenols and konjac glucomannan. After completion, a konjac glucomannan-tea polyphenol complex solution with a tea polyphenol binding amount of >900 mg / g can be obtained.

[0030] Preferably, the tea polyphenol binding amount is calculated according to the following formula: tea polyphenol binding amount = (total tea polyphenol amount - free tea polyphenol amount) / total konjac glucomannan amount × 100%, wherein the free tea polyphenol amount is determined by spectrophotometry. In the following experimental examples, the determination is repeated 3 times, and the binding amount results are calculated as the mean ± standard deviation.

[0031] In step (3) of the present invention, whey protein and casein with good emulsification properties are used to replace chemical synthetic emulsifiers to prepare tea oil emulsion.

[0032] Preferably, in step (3), the mixture is placed in a refrigerator at 4°C for 10 to 12 hours to allow it to be fully hydrated.

[0033] More preferably, in step (3), according to the ratio for preparing a protein dispersion with a mass fraction of 4.0-5.0% (m / m), equal masses of whey protein and casein are weighed respectively, mixed evenly and added to purified water, placed on a magnetic stirrer and stirred for 120-150 minutes, and placed in a refrigerator at 4°C for 10-12 hours to fully hydrate, to obtain a mixed protein dispersion with a mass fraction of 4.0-5.0% (m / m).

[0034] Preferably, the amount of the konjac glucomannan-tea polyphenols composite solution in step (4) is 1.2-1.6% of the total mass of the mixed protein dispersion.

[0035] Preferably, the amount of tea oil used in step (4) is 15-20% of the total mass of the tea oil emulsion.

[0036] Based on the structural characteristics of tea polyphenols and konjac glucomannan, the present invention compounds tea polyphenols and konjac glucomannan through hydrogen bonds formed by their hydroxyl groups, thereby improving the adsorption capacity of tea polyphenols at the oil phase interface and significantly enhancing the antioxidant effect of tea polyphenols on tea oil.

[0037] The present invention prepares a complex of konjac glucomannan and tea polyphenols and applies it to the tea oil emulsion, achieving the synergistic effect of the emulsifying property of konjac glucomannan and the antioxidant property of tea polyphenols. It not only improves the emulsifying stability of the tea oil emulsion, but especially significantly improves the oxidation stability of the tea oil, and significantly reduces the oxidation loss of unsaturated fatty acids in the tea oil.

[0038] Preferably, in step (4), a primary emulsion is first prepared by shearing treatment with a shearing homogenizer at a rate of 7000 - 8000 r / min for 3 - 5 min, and then homogenized 2 - 3 times with a microfluidic high-pressure homogenizer at a pressure of 80 - 100 MPa to obtain the O / W tea oil emulsion.

[0039] Preferably, after filling in step (4), it is sterilized at 120 - 122 °C and 100 - 105 kPa under high temperature and high pressure for 15 - 20 min.

[0040] More preferably, after filling in step (4), it is sterilized at 121 °C and 103 kPa under high temperature and high pressure for 15 - 20 min.

[0041] In the emulsion product with high oxidation stability of tea oil obtained in step (4) of the present invention, the usage amount of tea polyphenols complies with the "National Food Safety Standard - Standard for the Use of Food Additives (GB2760—2024)".

[0042] Therefore, the present invention also provides an emulsion with high oxidation stability of tea oil, which is obtained by the above method.

[0043] The second technical problem of the present invention can be achieved by the following technical solution: Application of the above emulsion with high oxidation stability of tea oil in the preparation of aqueous matrix foods.

[0044] Compared with the prior art, the present invention has the following advantages:

[0045] (1) The present invention prepares a complex of konjac glucomannan and tea polyphenols and applies it to the tea oil emulsion, which not only improves the emulsifying stability of the tea oil emulsion, but especially significantly improves the oxidation stability of the tea oil emulsion. The reasons are:

[0046] Konjac glucomannan has excellent hydrophilicity, gelation, emulsification, film-forming and thickening effects. Tea polyphenols are an ideal natural antioxidant. However, due to their high solubility in water and poor oil solubility, their antioxidant effect in oils is affected. In this invention, konjac glucomannan and tea polyphenols are prepared into a complex and applied to camellia oil emulsion, realizing the synergistic effect of the emulsification of konjac glucomannan and the antioxidant property of tea polyphenols. It not only plays the role of konjac glucomannan forming a physical protection wall at the oil-water interface, i.e., on the surface of the emulsion camellia oil droplets, to block oxidants, but also increases the concentration of the antioxidant tea polyphenols on the surface of the emulsion camellia oil droplets, further improving the oxidation stability of the camellia oil emulsion and significantly reducing the loss of unsaturated fatty acids in camellia oil.

[0047] Applying the complex formed by konjac glucomannan and tea polyphenols through hydrogen bonds under weakly acidic conditions to camellia oil emulsion, based on the good emulsifying properties of konjac glucomannan, a physical protection wall is formed on the surface of the emulsion camellia oil droplets by the tea polyphenol-konjac glucomannan complex, inhibiting the entry and further diffusion of oxygen and other oxidants or pro-oxidants. At the same time, as a physical protection wall, it can also limit the movement and diffusion of free radicals and oxidizing substances inside the camellia oil droplets. Therefore, it can improve the oxidation stability of camellia oil and its emulsion and reduce the oxidation loss of unsaturated fatty acids in camellia oil. More importantly, through hydrogen bonding with konjac glucomannan, tea polyphenols can be adsorbed on the oil-water interface by virtue of the emulsification of konjac glucomannan. For the tea polyphenols not complexed with konjac glucomannan, due to their high solubility in water and poor oil solubility, they mainly remain free in the aqueous phase and have little contact with the oil phase. Since the concentration of tea polyphenols on the surface of the camellia oil droplets in the camellia oil emulsion added with the konjac glucomannan-tea polyphenol complex increases significantly, its antioxidant ability is significantly enhanced compared with free tea polyphenols, and it can further improve the oxidation stability of camellia oil and its emulsion and reduce the oxidation loss of unsaturated fatty acids in camellia oil.

[0048] (2) This invention uses an appropriate acidic condition and a two-step method combining normal temperature and low temperature to increase the binding amount of tea polyphenols on konjac glucomannan. The reasons are as follows:

[0049] During the preparation of the konjac glucomannan-tea polyphenol complex, aiming at the chemical property that tea polyphenols have a stable structure and phenolic hydroxyl groups are not easily dissociated under appropriate acidic conditions, an appropriate acidic condition is used to stabilize the phenolic hydroxyl group structure and improve the efficiency of hydrogen bonding with konjac glucomannan.

[0050] In addition, since the hydrogen bond force increases significantly as the temperature decreases, the hydrogen bond force at a low temperature of 4-6 °C is significantly stronger than that at room temperature. However, the increase in the viscosity of konjac glucomannan solution at low temperature will reduce the molecular movement speed, which is not conducive to the formation of hydrogen bonds with tea polyphenols. Therefore, the present invention adopts a two-step method combining room temperature and low temperature. First, at room temperature, taking advantage of the low viscosity of konjac glucomannan solution which is beneficial to molecular movement, it promotes the rapid formation of hydrogen bond bonding with tea polyphenols. Subsequently, low-temperature treatment is adopted to increase the hydrogen bond force and further strengthen the hydrogen bond bonding between the two, thereby increasing the binding amount of tea polyphenols on konjac glucomannan.

[0051] (3) The present invention prepares camellia oil into an oil-in-water emulsion form, which greatly broadens the application field of camellia oil in the food industry. The reasons are as follows:

[0052] Based on the hydrophobic characteristics of camellia oil, it is not conducive to its dispersion in water-phase matrix foods. After being prepared into an oil-in-water emulsion form, it can be applied to water-phase matrix foods such as protein beverages, milk teas, nutritional emulsions, and ice creams, and promotes its uniform dispersion in water-phase matrix foods by improving hydrophilicity.

[0053] (4) The present invention uses whey protein and casein with good emulsifying properties to replace chemically synthesized emulsifiers to prepare camellia oil emulsion, which not only avoids the food safety risks of chemically synthesized emulsifiers but also improves the nutritional quality of camellia oil emulsion. The reasons are as follows:

[0054] In view of the food safety risks that chemically synthesized emulsifiers may cause, such as increasing the gastrointestinal burden and causing atherosclerosis, the present invention uses whey protein and casein with good emulsifying properties to replace chemically synthesized emulsifiers to prepare camellia oil emulsion.

[0055] Whey protein and casein are excellent natural protein nutrients. After ingesting whey protein, it can be quickly digested and absorbed, and can meet the body's amino acid needs faster; after ingesting casein, the digestion and absorption kinetics are slower, and it can relatively continuously and gently meet the body's amino acid needs. Therefore, based on the fast digestion of whey protein and the slow digestion characteristics of casein, the present invention combines the two and applies them to camellia oil emulsion, which can not only meet the body's rapid amino acid needs but also meet the body's continuous amino acid needs for a long time, further improving the nutritional quality of camellia oil emulsion. Description of the Drawings

[0056] Figure 1 This is the effect after adding 15 times the volume of pure water to the emulsion prepared in Example 1 in Test Example 3 of the present invention. The left figure is the emulsion before dilution, and the right figure is the emulsion diluted with 15 times the volume of pure water. Detailed Embodiments

[0057] The application method of the present invention will be further described below in conjunction with specific embodiments. The following embodiments and accompanying drawings are only for illustrative purposes and should not be construed as limiting the present invention. Unless otherwise specified, the raw materials used in the following embodiments are conventional commercially available or obtained through commercial channels, and the experimental instruments used are all conventional laboratory instruments.

[0058] Example 1

[0059] The emulsion with high oxidation stability of tea oil provided in this example is prepared by a method including the following steps:

[0060] (1) Preparation of konjac glucomannan solution and tea polyphenol solution

[0061] Weigh konjac glucomannan and dissolve it in acetic acid buffer solution with pH 5.0, place it on a magnetic stirrer and stir thoroughly for 80 min to prepare a konjac glucomannan solution with a concentration of 2.2 mg / mL, which is uniform and transparent;

[0062] Weigh tea polyphenols and dissolve them in acetic acid buffer solution with pH 5.0, place it on a magnetic stirrer and stir thoroughly for 25 min until it is fully dissolved to prepare a tea polyphenol solution with a concentration of 23 mg / mL, which is clear and transparent.

[0063] (2) Preparation of konjac glucomannan - tea polyphenol complex:

[0064] A two - step treatment method of normal - temperature bonding plus low - temperature strengthening is adopted to prepare the konjac glucomannan - tea polyphenol complex:

[0065] First step, place the konjac glucomannan solution on a magnetic stirrer and stir continuously at normal temperature. According to the volume ratio of tea polyphenol solution∶konjac glucomannan solution of 1∶3, slowly add the tea polyphenol solution to the continuously stirred konjac glucomannan solution and continue stirring for 2.5 h to make them fully react with each other and obtain a complex solution formed by hydrogen - bond bonding;

[0066] Second step, place the above composite solution in a low - temperature constant - temperature reaction bath at 5℃ and let it stand for 3 h. After completion, a konjac glucomannan - tea polyphenol complex solution with a tea polyphenol binding amount of 932.20 ± 17.24 mg / g is obtained.

[0067] The tea polyphenol binding amount is calculated according to the following formula: Tea polyphenol binding amount = (total amount of tea polyphenols - free tea polyphenol amount) / total amount of konjac glucomannan × 100%. Among them, the free tea polyphenol amount is determined by spectrophotometry. The determination in the following experimental examples is repeated 3 times, and the binding amount results are expressed as mean ± standard deviation, the same below.

[0068] (3) Preparation of mixed protein dispersion:

[0069] According to the ratio for preparing a protein dispersion with a mass fraction of 4.5% (m / m), equal masses of whey protein and casein were weighed respectively, mixed evenly, and added to purified water. The mixture was stirred on a magnetic stirrer for 140 minutes and placed in a refrigerator at 4°C for 11 hours to fully hydrate, thereby obtaining a 4.5% (m / m) mixed protein dispersion.

[0070] (4) Preparation of tea oil emulsion:

[0071] Then, the prepared konjac glucomannan-tea polyphenols complex solution is added according to the dosage ratio reaching 1.4% (m / m) in the protein dispersion. After uniform mixing, tea oil is added according to the ratio that the oil content of the tea oil emulsion reaches 18% (m / m). Subsequently, the above mixture is sheared for 4 minutes at a rate of 7500r / min using a shear homogenizer to prepare a primary emulsion. Then, a microjet high-pressure homogenizer is used to homogenize twice at a pressure of 90MPa to prepare an O / W tea oil emulsion. After filling, it is sterilized at a high temperature and high pressure of 121°C and 103kPa for 18 minutes. After cooling, a finished emulsion with high oxidative stability of tea oil is obtained.

[0072] Example 2

[0073] The tea oil emulsion with high oxidative stability provided in this embodiment is prepared by a method comprising the following steps:

[0074] (1) Preparation of Konjac Glucomannan Solution and Tea Polyphenols Solution

[0075] Weigh konjac glucomannan and dissolve it in acetate buffer at pH 4.5, place it on a magnetic stirrer and stir it for 60 minutes to prepare a uniform and transparent konjac glucomannan solution with a concentration of 2.0 mg / mL;

[0076] Tea polyphenols were weighed and dissolved in acetate buffer at pH 4.5, and the mixture was stirred on a magnetic stirrer for 20 min until it was fully dissolved, to prepare a clear and transparent tea polyphenol solution with a concentration of 20 mg / mL.

[0077] (2) Preparation of Konjac Glucomannan-Tea Polyphenols Complex:

[0078] Konjac glucomannan-tea polyphenols complex was prepared by a two-step process of room temperature bonding and low temperature strengthening:

[0079] The first step is to place the konjac glucomannan solution on a magnetic stirrer at room temperature and continuously stir it. The tea polyphenol solution is slowly added to the continuously stirred konjac glucomannan solution in a volume ratio of 1:3.5 between the tea polyphenol solution and the konjac glucomannan solution, and the stirring is continued for 2 hours to allow the two to fully react and form a hydrogen bonded complex solution.

[0080] In the second step, the above composite solution is placed in a low-temperature constant-temperature reaction bath at 4°C and allowed to stand for 2.5 h. After completion, a konjac glucomannan-tea polyphenol complex solution with a tea polyphenol binding amount of 940.51 ± 18.33 mg / g is obtained.

[0081] (3) Preparation of the mixed protein dispersion:

[0082] According to the ratio for preparing a protein dispersion with a mass fraction of 4.0% (m / m), equal masses of whey protein and casein are weighed respectively, mixed evenly, added to pure water, and placed on a magnetic stirrer and stirred thoroughly for 120 min. Then it is placed in a refrigerator at 4°C for 10 h to allow it to hydrate fully, obtaining a 4.0% (m / m) mixed protein dispersion.

[0083] (4) Preparation of the tea oil emulsion:

[0084] Then, according to the dosage ratio of reaching 1.2% (m / m) in the protein dispersion, the above-prepared konjac glucomannan-tea polyphenol complex solution is added. After mixing evenly, according to the ratio of the tea oil emulsion having an oil content of 15% (m / m), tea oil is added. Subsequently, the above mixture is sheared at a rate of 7000 r / min for 4 min using a shear homogenizer to prepare a primary emulsion, and then homogenized 3 times at a pressure of 80 MPa using a microfluidic high-pressure homogenizer to prepare an O / W tea oil emulsion. After filling, it is sterilized at 121°C and 103 kPa under high temperature and high pressure for 15 min, and after cooling, a finished tea oil emulsion with high oxidation stability is obtained.

[0085] Example 3

[0086] The tea oil emulsion with high oxidation stability provided in this example is prepared by a method including the following steps:

[0087] (1) Preparation of the konjac glucomannan solution and the tea polyphenol solution

[0088] Weigh konjac glucomannan and dissolve it in an acetic acid buffer solution with a pH of 5.5, place it on a magnetic stirrer and stir thoroughly for 90 min to prepare a konjac glucomannan solution with a concentration of 2.5 mg / mL, which is uniform and transparent;

[0089] Weigh tea polyphenols and dissolve them in an acetic acid buffer solution with a pH of 5.5, place it on a magnetic stirrer and stir thoroughly for 30 min until it is fully dissolved to prepare a tea polyphenol solution with a concentration of 24 mg / mL, which is clear and transparent.

[0090] (2) Preparation of the konjac glucomannan-tea polyphenol complex:

[0091] A two-step treatment method of room-temperature bonding plus low-temperature strengthening is used to prepare the konjac glucomannan-tea polyphenol complex:

[0092] The first step is to place the konjac glucomannan solution on a magnetic stirrer at room temperature and continuously stir it. The tea polyphenol solution is slowly added to the continuously stirred konjac glucomannan solution in a volume ratio of 1:4 between the tea polyphenol solution and the konjac glucomannan solution, and the stirring is continued for 3 hours to allow the two to fully react and form a hydrogen bonded complex solution.

[0093] In the second step, the composite solution was placed in a 6°C low-temperature constant-temperature reaction bath and kept still for 3 hours. After completion, a konjac glucomannan-tea polyphenols complex solution with a tea polyphenol binding amount of 937.66±18.14 mg / g was obtained.

[0094] (3) Preparation of mixed protein dispersion:

[0095] According to the ratio for preparing a protein dispersion with a mass fraction of 5.0% (m / m), equal masses of whey protein and casein were weighed respectively, mixed evenly, and added to purified water. The mixture was stirred on a magnetic stirrer for 150 minutes and placed in a refrigerator at 4°C for 12 hours to fully hydrate, thereby obtaining a 5.0% (m / m) mixed protein dispersion.

[0096] (4) Preparation of tea oil emulsion:

[0097] Then, the prepared konjac glucomannan-tea polyphenols complex solution is added according to the dosage ratio reaching 1.5% (m / m) in the protein dispersion, and after uniform mixing, tea oil is added according to the ratio that the oil content of the tea oil emulsion reaches 20% (m / m). Subsequently, the above mixture is sheared for 4 minutes at a rate of 8000r / min using a shear homogenizer to prepare a primary emulsion, and then a microjet high-pressure homogenizer is used to homogenize twice at a pressure of 100MPa to prepare an O / W tea oil emulsion. After filling, it is sterilized at a high temperature and high pressure of 121°C and 103kPa for 20 minutes, and after cooling, a finished emulsion with high oxidative stability of tea oil is obtained.

[0098] Test Example 1

[0099] In order to investigate the effectiveness of the method for improving the oxidative stability of tea oil adopted in the present invention, the following control groups were set up during the study to prepare tea oil emulsions. Other operations were consistent with Example 1 of the present invention:

[0100] Control group ①: Konjac glucomannan and tea polyphenols were not added, and the konjac glucomannan-tea polyphenols complex solution in the preparation of tea oil emulsion was replaced by acetate buffer with the same pH value and the same amount.

[0101] Control group ②: only Konjac Glucomannan was added without tea polyphenols. In the preparation of Konjac Glucomannan-Tea Polyphenols complex, the tea polyphenols solution was replaced by acetate buffer with the same pH value and the same amount.

[0102] Control group ③: Only tea polyphenols were added, without konjac glucomannan. In the preparation of the konjac glucomannan-tea polyphenol complex, the konjac glucomannan solution was replaced with an acetic acid buffer solution of the same pH value and the same dosage.

[0103] Control group ④: Konjac glucomannan and tea polyphenol solution were added, but there was no complex preparation process: According to the same ratio and the same dosage in the preparation of the konjac glucomannan-tea polyphenol complex, the konjac glucomannan solution and the tea polyphenol solution were respectively added to the protein dispersion to prepare the camellia oil emulsion.

[0104] The finished product of the camellia oil emulsion obtained in Example 1 of the present invention and the finished product of the camellia oil emulsion prepared in the above control group were simultaneously placed in a biochemical incubator, and the high-temperature storage oxidation stability was investigated under the constant temperature condition of 50°C. The peroxide value (POV), 2-thiobarbituric acid value (TBA), and the contents of unsaturated fatty acids in camellia oil such as oleic acid, linoleic acid, and linolenic acid were measured before and after 30 days of storage respectively. The determination of POV was carried out by the indicator titration method in GB 5009.227-2023 "National Food Safety Standard - Determination of Peroxide Value in Foods", the determination of TBA value was carried out by the direct method in GB / T 35252-2017 "Animal and Vegetable Oils - Determination of 2-Thiobarbituric Acid Value", and the determination of the contents of unsaturated fatty acids in camellia oil such as oleic acid, linoleic acid, and linolenic acid was carried out by the internal standard method in GB 5009.168-2016 "National Food Safety Standard - Determination of Fatty Acids in Foods". All determinations were repeated 3 times, and the results were expressed as mean ± standard deviation.

[0105] Table 1 Effects of high-temperature storage on POV and TBA values of camellia oil in the emulsion

[0106]

[0107] POV is an index characterizing the content of hydroperoxides formed in the initial stage of oil oxidation, which can indicate the oxidation degree in the initial stage of oil oxidation; the TBA value is an index characterizing the content of secondary oxidation products of oil represented by malondialdehyde, which can indicate the degree of deep oxidation of oil.

[0108] As can be seen from Table 1, before high-temperature storage, the POV of the camellia oil in Example 1 of the present invention was only 6.23±0.21 mg / 100 g, and the TBA was only 0.42±0.02 mg / kg. The POV of the control group samples all exceeded 20 mg / 100 g, and the TBA values all exceeded 1.1 mg / kg, which was significantly higher than that of Example 1 of the present invention. This was related to the fact that the emulsion samples were sterilized at 121°C and 103 kPa under high temperature and high pressure, indicating that after sterilization at 121°C, the initial and deep oxidation degrees of the camellia oil in the control group were significantly higher than those in Example 1. After 30 days of high-temperature storage at 50°C, the POV of the camellia oil in Example 1 of the present invention only increased to 14.32±0.55% mg / 100 g, and the TBA only increased to 0.63±0.03 mg / kg. However, the POV of the camellia oil in the control group samples all exceeded 170 mg / 100 g, and the TBA values all exceeded 7 mg / kg. In particular, the POV of control group ① reached 351.86±10.47 mg / 100 g, and the TBA reached 15.76±0.46 mg / kg. The above experimental result data were analyzed for significant differences using SPSS Statistics 22 software. The differences in the POV and TBA values before and after storage in Example 1 of the present invention and the 4 control groups all reached the significant level (P<0.05), and were all significantly lower than the 4 control groups (P<0.05), especially extremely significantly lower than control group ① (P<0.01). The results in Table 1 show that the antioxidant method adopted in the present invention can effectively improve the oxidation stability of camellia oil both during high-temperature sterilization and high-temperature storage.

[0109] It should be noted that control group ① did not take any antioxidant measures. Control group ② added konjac glucomannan, which could form a physical protection wall on the surface of the emulsion camellia oil droplets to block oxidants. Control group ③ added the natural antioxidant tea polyphenols. Control group ④ added konjac glucomannan and tea polyphenols. The results in Table 1 show that control groups ②, ③, and ④ all showed a certain effect of improving the oxidation stability of camellia oil, and the effect of control group ④ was significantly better than that of control groups ② and ③. However, due to the good water solubility and poor lipophilicity of tea polyphenols, in control group ④, konjac glucomannan and tea polyphenols were simply used in combination, and most of the tea polyphenols still remained free in the aqueous solution and could not fully play their antioxidant role. In the present invention, konjac glucomannan and tea polyphenols were prepared into a complex. Through hydrogen bonding with konjac glucomannan, tea polyphenols could be adsorbed on the oil-water interface with the help of the emulsifying property of konjac glucomannan, making full use of the structural characteristics and antioxidant advantages of konjac glucomannan and tea polyphenols, thus greatly improving the oxidation stability of camellia oil in the emulsion.

[0110] Table 2 Effect of High-Temperature Storage on the Content of Unsaturated Fatty Acids in Camellia Oil in Emulsion

[0111]

[0112]

[0113] The results in Table 2 show that after high-temperature and high-pressure sterilization at 121 °C and 103 kPa, the contents of unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid in the emulsion sample of camellia oil in Example 1 of the present invention are significantly higher than those of each control group. After high-temperature storage at 50 °C for 30 days, the contents of the above three unsaturated fatty acids are not only significantly higher than those of the control group, but also their retention rates can reach more than 90% of that before storage, significantly improving the oxidation stability of unsaturated fatty acids in camellia oil. For the four control groups, not only the contents of the three unsaturated fatty acids before storage are significantly lower than those in Experiment Example 1, but also after high-temperature storage at 50 °C for 30 days, the retention rate of oleic acid can only reach 25.88 - 36.95% of that before storage, the retention rate of linoleic acid can only reach 23.20 - 31.52% of that before storage, linolenic acid was not detected in Control Groups ①, ②, and ③, and the retention rate of linolenic acid in Control Group ④ can only reach 37.50% of that before storage. The above experimental result data were analyzed for significant differences using SPSS Statistics 22 software. The differences in the contents of unsaturated fatty acids oleic acid, linoleic acid, and linolenic acid before and after storage in Example 1 of the present invention and the four control groups all reached a significant level (P < 0.05), and the contents were all significantly higher than those of the four control groups (P < 0.05).

[0114] The change in the content of unsaturated fatty acids in the camellia oil in Table 2 is consistent with the oxidation stability results presented by the POV and TBA values of the camellia oil in Table 1, that is, the lower the POV and TBA values, the better the oxidation stability of the camellia oil, and the higher its unsaturated fatty acid content and retention rate. Table 2 further illustrates the effectiveness of the present invention in improving the oxidation stability of camellia oil from the retention of unsaturated fatty acids in camellia oil.

[0115] Test Example 2

[0116] In order to investigate the effectiveness of the method adopted in the present invention to increase the binding amount of tea polyphenols on konjac glucomannan, the following control groups were set up respectively during the research process to prepare konjac glucomannan - tea polyphenol complexes, and other operations were the same as those in Example 1 of the present invention. After preparation, the binding amount of tea polyphenols was measured.

[0117] The calculation and measurement are the same as those in the foregoing invention content. The binding amount of tea polyphenols is calculated according to the following formula:

[0118] Binding amount of tea polyphenols = (total amount of tea polyphenols - amount of free tea polyphenols) / total amount of konjac glucomannan × 100%. Among them, the amount of free tea polyphenols was measured by spectrophotometry, and the measurement tests were repeated 3 times. The binding amount results are expressed as mean ± standard deviation.

[0119] Control Group ⑤: Konjac glucomannan solution and tea polyphenol solution were respectively prepared using pure water to replace the acetate buffer solution.

[0120] Control group ⑥: Cancel the low-temperature strengthening treatment and replace it with room-temperature bonding treatment for the same period of time.

[0121] Control group ⑦: Cancel the room-temperature bonding treatment and replace it with low-temperature treatment for the same period of time.

[0122] Table 3 Effects of different treatments on the tea polyphenol binding amount of the complex

[0123] Control group ⑤ Control group ⑥ Control group ⑦ Example 1 of the present invention Binding amount of tea polyphenols (mg / g) 616.59±12.18 382.47±7.61 512.83±10.29 932.20±17.24

[0124] The results in Table 3 show that for Control group ⑤, without adjusting the solution pH and directly preparing konjac glucomannan solution and tea polyphenol solution with pure water, and forming a complex by hydrogen bonding between the two in a solution system close to neutral, the tea polyphenol binding amount can only reach 66.14% of that in Example 1 of the present invention. The tea polyphenol binding amount of Control group ⑥, which cancels the low-temperature strengthening treatment, is the lowest, only reaching 41.03% of that in Example 1 of the present invention. The tea polyphenol binding amount of Control group ⑦, which cancels the room-temperature bonding treatment, only reaches 55.01% of that in Example 1 of the present invention. The above experimental result data were analyzed for significant differences using SPSS Statistics 22 software. The differences between the tea polyphenol binding amount in Example 1 of the present invention and the three control groups all reached the significant level (P < 0.05), and were all significantly higher than the three control groups (P < 0.05).

[0125] Thus, the present invention uses appropriate acidic conditions to stabilize the hydroxyl structure of tea polyphenols, and the two-step treatment of room temperature combined with low temperature combines the advantages of low viscosity of konjac glucomannan solution at room temperature, which is beneficial to molecular movement, and low-temperature treatment to increase the hydrogen bond force. It improves the tea polyphenol binding amount on konjac glucomannan in multiple dimensions, and then is applied to tea oil emulsion to achieve a substantial improvement in the oxidation stability of tea oil.

[0126] Test example 3

[0127] In order to investigate the effectiveness of preparing tea oil into an oil-in-water emulsion in the present invention, the dilution method was used to verify that the emulsion is of the oil-in-water type. An appropriate amount of the sample in Example 1 above was measured and added to a container containing more than 15 times its volume of pure water. After stirring, a homogeneous and stable liquid system was formed, without stratification or phase separation phenomenon (as Figure 1 shown), indicating that water is the continuous phase in the liquid system, and it is determined that the tea oil emulsion prepared in the present invention is of the oil-in-water type.

[0128] In addition, the tea oil emulsion prepared in Example 1 above was applied to the production of fruit and vegetable milk tea, which verified both the effectiveness of the oil-in-water tea oil emulsion and its application suitability.

[0129] The cucumber tea oil milk tea is prepared with the following formula ratios: 60 mL of cucumber juice, 40 mL of black tea soup, 100 mL of milk, and 12 mL of tea oil emulsion. Among them, the preparation method of cucumber juice is as follows: Select fresh cucumbers, wash, peel, cut into small pieces, and make a pulp with pure water in a mass ratio of 1:10, and obtain cucumber juice through filtration with a gauze. The preparation method of black tea soup is as follows: Weigh 5 g of dry black tea without mildew and odor, put it into a pot, mix it with an equal amount of white sugar, slowly stir-fry over low heat until caramel color, pour 1 L of boiling water, boil over low heat for 5 minutes, and obtain black tea soup through filtration with a gauze. Subsequently, according to the aforementioned formula ratios, the cucumber juice, black tea soup, milk, and tea oil emulsion are evenly blended. After being sealed in a cup and pasteurized, the finished product of cucumber tea oil milk tea with a uniform liquid tissue and a fresh and unique flavor is obtained.

[0130] The preparation of this cucumber tea oil milk tea is only an application example, and the formula and process can be adjusted according to the specific requirements of the aqueous matrix food product in actual applications.

[0131] The above are only non-limiting embodiments of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, several improvements can be made without departing from the principle of the present invention, and these are all regarded as the protection scope of the present invention.

Claims

1. An emulsion with high oxidation stability of tea oil, characterized in that, Obtained by a method comprising the following steps: (1) Preparation of konjac glucomannan solution and tea polyphenol solution: Take konjac glucomannan, dissolve it in acetic acid buffer solution with pH 4.5 - 5.5, and after stirring treatment, obtain konjac glucomannan solution; Take tea polyphenols, dissolve them in acetic acid buffer solution with pH 4.5 - 5.5, and after stirring treatment, obtain tea polyphenol solution; (2) Preparation of konjac glucomannan - tea polyphenol complex: At room temperature, add the tea polyphenol solution to the continuously stirred konjac glucomannan solution, and continue stirring for 2 - 3 h to obtain konjac glucomannan - tea polyphenol composite solution; In a low - temperature constant - temperature reaction device at 4 - 6 °C, let the konjac glucomannan - tea polyphenol composite solution stand for 2 - 3 h to obtain a konjac glucomannan - tea polyphenol composite solution with a tea polyphenol binding amount > 900 mg / g; (3) Preparation of mixed protein dispersion: Take equal masses of whey protein and casein, mix them evenly, add them to water, and after stirring, place them in the refrigerator and let them stand to fully hydrate to obtain a mixed protein dispersion with a mass percentage content of 4 - 5%; (4) Preparation of camellia oil emulsion: Add the konjac glucomannan - tea polyphenol composite solution prepared in step (2) to the mixed protein dispersion prepared in step (3), mix evenly, then add camellia oil. First, use a shear homogenizer to shear - process to make a primary emulsion, and then use a micro - fluidic high - pressure homogenizer for homogenization treatment to prepare an O / W camellia oil emulsion. After filling, it is subjected to high - temperature sterilization and cooling treatment to obtain a finished emulsion with high camellia oil oxidation stability.

2. The emulsion with high oxidation stability of tea oil according to claim 1, wherein, In step (1), the concentration of the konjac glucomannan solution is 2.0 - 2.5 mg / mL, and the concentration of the tea polyphenol solution is 20 - 25 mg / mL.

3. The emulsion with high oxidation stability of tea oil according to claim 1, characterized in that, In step (2), the volume ratio of the tea polyphenol solution to the konjac glucomannan solution is 1:3 - 4.

4. The emulsion with high oxidation stability of tea oil according to claim 1, characterized in that, In step (3), place it in a 4 °C refrigerator and let it stand for 10 - 12 h to fully hydrate.

5. The emulsion with high oxidation stability of tea oil according to claim 1, characterized in that, In step (4), the dosage of the konjac glucomannan - tea polyphenol composite solution is 1.2 - 1.6% of the total mass of the mixed protein dispersion.

6. The emulsion with high oxidation stability of tea oil according to claim 1, wherein In step (4), the dosage of the camellia oil is 15 - 20% of the total mass of the camellia oil emulsion.

7. The emulsion with high oxidation stability of tea oil according to claim 1, wherein In step (4), first use a shear homogenizer to shear - process at a rate of 7000 - 8000 r / min for 3 - 5 min to prepare a primary emulsion, and then use a micro - fluidic high - pressure homogenizer for homogenization treatment at a pressure of 80 - 100 MPa for 2 - 3 times to prepare an O / W camellia oil emulsion.

8. The emulsion with high oxidation stability of tea oil according to claim 1, wherein, In step (4), after filling, perform high - temperature high - pressure sterilization at 121 °C and 103 kPa for 15 - 20 min.

9. An emulsion with high oxidation stability of tea oil, characterized in that, Obtained by using the method described in any one of claims 1 - 8.

10. Use of the emulsion with high camellia oil oxidation stability described in claim 9 in the preparation of water - phase matrix foods.

Images