Method for improving oxidative stability of oil and fat and edible oil

Abstract

The application relates to the field of food processing and discloses a preparation method for improving the oxidation stability of oil and edible oil, which comprises the following steps: S1, peeling oilseed kernels to obtain seed coats and kernel seeds; S2, first roasting the seed coats; S3, mixing the roasted seed coats with the kernel seeds, sequentially performing second roasting and pressing to obtain cake meal; S4, homogenizing the cake meal with an alkaline substance and ethanol to obtain a homogenate; S5, mixing the homogenate with glucosidase to perform enzymolysis, thereby obtaining an enzymolysis liquid; and S6, mixing the enzymolysis liquid with vegetable oil to reserve an oil phase; wherein the temperature of the first roasting is 50-90 DEG C higher than that of the second roasting. The method disclosed by the application can significantly increase the content of phenolic substances in edible oil and further improve the oxidation stability of the edible oil.

Description

Technical Field

[0001] This invention relates to the field of food processing, and specifically to a method for improving the oxidative stability of oils and edible oils. Background Technology

[0002] Plant polyphenols are a collective term for polyhydroxyphenolic compounds found in plants, mainly including flavonoids, tannins, anthocyanins, and phenolic acids. Phenolic substances in plants exist primarily in free and bound states. Free phenols are phenolic compounds that do not interact physically or chemically with other macromolecules; bound phenols are polyphenols covalently bonded to food matrices (such as cell wall substances) and require chemical or enzymatic treatment to separate them from the cell wall. In recent years, phenolic compounds widely found in oil-bearing plants have been shown to contribute to their therapeutic properties, including anticancer, antiviral, antioxidant, hypoglycemic, lipid-lowering, and anti-inflammatory activities. Due to their diverse sensory and health-promoting properties, phenolic substances in oilseed plants are considered important secondary food components and are used as sources of food or food ingredients.

[0003] Rapeseed is rich in polyphenols, containing 10-30 times more than other oilseeds. The polyphenols in rapeseed mainly include free phenolic acids such as sinapic acid, caffeic acid, ferulic acid, and canolol, as well as bound polyphenols such as sine. These polyphenols can be called "rapeseed polyphenols" or "rapeseed phenols." In recent years, phenolic compounds widely found in oil-bearing plants have been shown to contribute to their therapeutic properties, including anticancer, antiviral, antioxidant, hypoglycemic, lipid-lowering, and anti-inflammatory activities, and have significant application value. Therefore, increasing the polyphenol content in rapeseed oil is of great importance.

[0004] The study, titled "The Effect of Dry Roasting on Rapeseed Polyphenols and Rapeseed Oil Quality; Wang Weijun, Journal of Chinese Cereals and Oils, 36(3)", investigated the effect of rapeseed roasting temperature on polyphenol content. The results showed that as the roasting temperature increased, the total phenol content in rapeseed oil increased, increasing by 27.4 times at 160℃.

[0005] The study investigated the effects of different steam explosion conditions on the polyphenol content of rapeseed oil. The results showed that steam explosion can be used as a heating pretreatment technology for rapeseed in the process of preparing rapeseed oil, which can effectively improve the polyphenol yield and antioxidant activity of rapeseed. The polyphenol content in rapeseed cake and oil reached its maximum when the steam pressure was 0.7 MPa and the pressure was maintained for 3 min.

[0006] Increasing the roasting temperature (above 160℃) can increase the polyphenol content, but it significantly impacts the quality of the oil. For example, high temperatures can lead to an excessively burnt flavor, higher peroxide values, or increased levels of harmful substances like benzo[a]pyrene, thus reducing the oil's quality. Therefore, the roasting temperature for flavored oils should not exceed 170℃. Steam explosion is effective in increasing polyphenol content, but it significantly increases the moisture content of the oilseeds, making them unsuitable for direct pressing and requiring pre-drying, which increases energy costs. Furthermore, the hydrolysis of oil into free fatty acids during steam explosion results in excessively high acid values ​​and poor quality. Low-temperature cold pressing improves the quality of both the oil and the oil cake, but cold-pressed rapeseed oil has a noticeable green, unpleasant flavor.

[0007] Flax lignans are a collective term for a large class of substances, representing the main polyphenols in flaxseed. They primarily exist as diglucoside dimethyl sulforaphane (SDG) and serosol phenol (SECO), which are mainly found in the secondary cell walls of the outer seed coat cells of flaxseed (approximately 92%), with a smaller amount found in the endosperm cell inclusions (approximately 8%). Flaxseed coat contains a large amount of flaxseed gum, which exhibits high viscosity, strong water-holding capacity, gelling properties, and emulsifying properties. Furthermore, the cross-linking of flaxseed gum forms a spatial network structure, which restricts the transfer of lignans during oil extraction.

[0008] A study by Deng Qianchun's team on flaxseed from different regions in China revealed significant differences in flax lignan content among oilseeds from different planting areas. Flaxseed varieties from Hebei and Inner Mongolia exhibited higher SDG content. Techniques to enhance flax lignan migration in the oil extraction process include: ① Germination: Studies show that compared to ungerminated flaxseed, 8-day germinated flaxseed showed a 6.3-fold increase in SDG and a 4.5-fold increase in SECO content, accompanied by an increase in the expression of genes encoding SDG biosynthesis. ② Supercritical: Studies indicate that supercritical CO2 extraction significantly increases the content of phenolic compounds in flaxseed oil, primarily manifested in the migration of flax lignans in the oil phase. ③ Physical fields: Physical field techniques such as ultrasound and microwave treatment can disrupt the spatial cross-linking structure of cell walls and flaxseed gum, thereby promoting the release and migration of lignans. Studies have shown that moderate microwave treatment effectively promotes the oil phase migration of flax lignan macromolecules and their depolymerized monomers SDG, free vanillin, vanillic acid, and ferulic acid. ④ Steam explosion has a good effect on increasing polyphenols, but it also causes a significant increase in basic physicochemical properties such as acid value and peroxide value of oils.

[0009] While the methods described above do increase polyphenol content to some extent, each method has its drawbacks. For example, physical field treatments (such as microwaves and ultrasound) can disrupt the cell walls and spatial cross-linking structure of flaxseed gum, thereby promoting the release and migration of lignans, but this is difficult to implement in industrial production. Steam explosion has a good effect on increasing polyphenol content, but because the moisture content of the oilseed increases significantly after steam explosion, it causes a significant increase in the basic physicochemical properties of the oil, such as acid value and peroxide value. It also makes the material unsuitable for direct oil pressing and requires drying, which greatly increases energy consumption. Germination also has a certain effect on increasing polyphenol content, but the germination process needs to be carried out at a suitable temperature. Too cold and germination will not occur, while too hot and the seed activity will be affected. The temperature of seed germination is usually close to the temperature of microbial reproduction, so the germination process inevitably produces contaminants, which may lead to increased acid value and foul flavor in the oil produced from the germinated oilseeds. Furthermore, the germination process consumes seed nutrients and may also cause a significant decrease in the oil yield after germination. Summary of the Invention

[0010] The purpose of this invention is to overcome the technical problems of existing edible oils having excessively high acid value, peroxide value, and low polyphenol content, resulting in low nutrient content and poor oxidative stability. This invention provides a method and edible oil for improving the oxidative stability of oils. This method significantly increases the content of polyphenolic antioxidant nutrients (especially flaxseed SECO and rapeseed Canolol) in edible oils, thereby improving the oxidative stability of edible oils.

[0011] To achieve the above objectives, a first aspect of the present invention provides a method for increasing the nutrient content in edible oils, the method comprising the following steps: S1. Remove the outer skin from the oilseeds to obtain the seed coat and kernel; S2. The seed coats are sequentially subjected to the first stir-frying process; S3. Mix the roasted seed coat with the seed kernel, and then perform a second roasting and pressing to obtain cake meal; S4. The cake is mixed with an alkaline substance and ethanol and homogenized to obtain a homogenate. S5. Mix the homogenate with glucosidase and perform enzymatic hydrolysis to obtain the enzymatic hydrolysate; S6. Mix the enzymatic hydrolysate with vegetable oil, retaining the oil phase; The temperature of the first stir-fry is 50-90℃ higher than that of the second stir-fry.

[0012] A second aspect of the present invention provides an edible oil prepared by the method of the present invention.

[0013] The above technical solution achieves at least the following beneficial effects: (1) The method of the present invention can further increase the content of polyphenolic nutrients in edible oil. In the preferred embodiment, the polyphenol content in flaxseed oil is as high as 1560.2 mg / kg and the SECO content is as high as 1500.9 mg / kg; the polyphenol content in rapeseed is as high as 1500.6 mg / kg and the Canolol content is as high as 1511.2 mg / kg. (2) The method of the present invention can improve the oxidative stability of edible oil. In a preferred embodiment, flaxseed oil prepared by the method of the present invention can be stored at 90°C for 35.1 h, and rapeseed oil prepared by the method can be stored at 90°C for 44.6 h. Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] A first aspect of the present invention provides a method for increasing the nutrient content in edible oil, the method comprising the following steps: S1. Remove the outer skin from the oilseeds to obtain the seed coat and kernel; S2. The seed coats are sequentially subjected to the first stir-frying process; S3. Mix the roasted seed coat with the seed kernel, and then perform a second roasting and pressing to obtain cake meal; S4. The cake is mixed with an alkaline substance and ethanol and homogenized to obtain a homogenate. S5. After removing the ethanol from the homogenate, mix it with glucosidase for enzymatic hydrolysis to obtain the enzymatic hydrolysate. S6. Mix the enzymatic hydrolysate with vegetable oil, retaining the oil phase; The temperature of the first stir-fry is 50-90℃ higher than that of the second stir-fry.

[0016] According to some embodiments of the present invention, in S1, the peeling conditions are such that the kernel content of the seed coat is less than 5 wt%.

[0017] In this invention, there is no particular limitation on the peeling method. For example, peeling and sorting equipment can be used to separate the seed coat and kernel of oilseeds. The peeling equipment was purchased from Liaoning Qiaopai Machinery Co., Ltd., and the instrument model is TFYMZ-200.

[0018] In this invention, increasing the temperature of the first roasting process can further promote the migration of polyphenols in oilseeds during processing, thereby significantly increasing the polyphenol content in flaxseed oil.

[0019] To further promote the dissolution of polyphenols in oilseeds and increase the content of flavor compounds, preferably, the temperature of the first roasting is 50-80°C higher than that of the second roasting.

[0020] Preferably, in S2, the conditions for the first stir-frying include: a temperature of 150-190℃ and a time of 20-40 minutes.

[0021] More preferably, in S2, the conditions for the first stir-frying include: a temperature of 160-180°C and a time of 25-35 minutes.

[0022] Preferably, in S3, the conditions for the second stir-frying include: a temperature of 60-140℃ and a time of 20-60 minutes.

[0023] Preferably, in S3, the conditions for the second stir-frying include: a temperature of 100-120℃ and a time of 30-40 minutes.

[0024] According to some embodiments of the present invention, in S3, the mass ratio of the roasted seed coat to the seed kernel is 1:(1-6).

[0025] According to some embodiments of the present invention, in S3, the pressing method includes pressing the kernel and seed coat after the second roasting in a screw press.

[0026] Preferably, the pressing pressure is 60-200 MPa.

[0027] In this invention, there are no particular limitations on the pressing method; any method that achieves physical pressing is acceptable. For example, a screw press can be used for pressing. The screw press was purchased from Shibayoufang Co., Ltd., and the instrument model is FL-S2017.

[0028] According to some embodiments of the present invention, in S4, the mass ratio of the cake and ethanol is 1:(1-2).

[0029] Preferably, in S4, the ethanol is provided in the form of an aqueous ethanol solution.

[0030] More preferably, the volume concentration of ethanol in the ethanol-water solution is 60v / v%-90v / v, more preferably 70v / v%-80v / v.

[0031] In this invention, the ethanol solution can be obtained commercially or prepared in-house.

[0032] According to some embodiments of the present invention, in S4, the alkaline substance is selected from at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0033] Preferably, the amount of alkaline substance used is such that the pH of the ethanol is 10-13.

[0034] Preferably, in step S4, the homogenization conditions further include: a temperature of 40-60°C and a time of 2-4 hours. More preferably, in step S4, the homogenization conditions further include: a temperature of 45-55°C and a time of 2-3 hours.

[0035] In this invention, in order to improve the enzymatic hydrolysis activity of glucosidase, preferably, in S5, the pH of the enzymatic hydrolysis is 3-6, more preferably 4-5.

[0036] In this invention, in order to improve the enzymatic hydrolysis activity of glucosidase and thus improve the enzymatic hydrolysis effect, preferably, the method further includes removing ethanol from the homogenate before mixing the homogenate with glucosidase.

[0037] In this invention, there is no particular limitation on the method of removing ethanol from the homogenate, including but not limited to distilling the homogenate.

[0038] In this invention, there is no particular limitation on the method of pH adjustment for the enzymatic hydrolysis of homogenate and glucosidase. For example, a pH adjuster (such as sulfuric acid and hydrochloric acid) can be added to the homogenate to make the pH of the system 3-6, and then glucosidase can be added for enzymatic hydrolysis.

[0039] According to some embodiments of the present invention, in step S5, the conditions for enzymatic hydrolysis further include: a temperature of 60-75°C and a time of 1-6 hours.

[0040] Preferably, the enzymatic hydrolysis conditions further include: a temperature of 68-70℃ and a time of 2-4 hours.

[0041] According to some embodiments of the present invention, in S5, the amount of glucosidase used is 200-4000U, preferably 500-1000U, relative to 1g of the cake meal.

[0042] In this invention, the activity unit of glucosidase is defined as the amount of enzyme required to convert 1 micromolar of substrate (glucose) within 1 minute at 25°C.

[0043] According to some embodiments of the present invention, in S5, the glucosidase is selected from α-glucosidase and / or β-glucosidase.

[0044] In this invention, α-glucosidase and β-glucosidase are obtained commercially, and there is no particular limitation on the manufacturers. For example, α-glucosidase can be purchased from Shanghai Yuanye Biotechnology Co., Ltd., and β-glucosidase can be purchased from Weilan Bio-enzyme Preparation Co., Ltd.

[0045] In this invention, preferably, the glucosidase is a β-glucosidase.

[0046] According to some embodiments of the present invention, in S6, the mass ratio of the enzymatic hydrolysate to the edible oil is 1:(2-20), preferably 1:(8-12).

[0047] In this invention, there is no particular limitation on the oilseeds, including but not limited to at least one of rapeseed, peanut, flaxseed, soybean, safflower seed, cottonseed, sesame, walnut, camellia seed, evening primrose seed, borage seed, perilla seed, pumpkin seed, maple seed, chia seed, wheat germ, pine nut, almond, rice bran, hazelnut, tomato seed, pomegranate seed, avocado, grape seed, coconut, milk thistle seed, jojoba seed, shea butter, babassu seed, hemp seed, and sunflower seed. In the specific embodiments provided by this invention, rapeseed oil and flaxseed oil are prepared using rapeseed and flaxseed as oilseeds, respectively.

[0048] In this invention, there is no particular limitation on the type of vegetable oil, including but not limited to at least one of rapeseed oil, peanut oil, flaxseed oil, soybean oil, corn oil, safflower seed oil, cottonseed oil, sesame oil, walnut oil, camellia oil, evening primrose oil, borage oil, perilla seed oil, pumpkin seed oil, maple seed oil, chia seed oil, wheat germ oil, pine nut oil, almond oil, rice bran oil, hazelnut oil, tomato seed oil, pomegranate seed oil, avocado oil, grape seed oil, coconut oil, milk thistle seed oil, jojoba oil, shea butter, babassu oil, hemp seed oil, and sunflower seed oil. However, to meet customers' demand for high-quality edible oil, the vegetable oil is preferably refined vegetable oil. There is no particular limitation on the type of refined vegetable oil, including but not limited to at least one of the following: refined rapeseed oil, refined peanut oil, refined flaxseed oil, refined soybean oil, refined corn oil, refined safflower seed oil, refined cottonseed oil, refined sesame oil, refined walnut oil, refined camellia oil, refined evening primrose oil, refined borage oil, refined perilla seed oil, refined pumpkin seed oil, refined maple seed oil, refined chia seed oil, refined wheat germ oil, refined pine nut oil, refined almond oil, refined rice bran oil, refined hazelnut oil, refined tomato seed oil, refined pomegranate seed oil, refined avocado oil, refined grape seed oil, refined coconut oil, refined milk thistle seed oil, refined jojoba oil, refined shea butter, refined babassu oil, refined hemp seed oil, and refined sunflower seed oil. In the specific embodiments provided by the present invention, refined rapeseed oil and refined flaxseed oil are used as vegetable oils, respectively.

[0049] In this invention, there is no particular limitation on the source of refined vegetable oil. For example, it can be obtained by purchasing from COFCO Fortune Food Marketing Co., Ltd. Alternatively, the seed coat and kernel after roasting in this invention can be mixed and then roasted and pressed in sequence. The crude oil obtained is then refined (including neutralization, decolorization, dewaxing, and deodorization). The refined vegetable oil obtained is then mixed with the enzymatic hydrolysate as vegetable oil.

[0050] In this invention, preferably, the method further includes mixing the enzymatic hydrolysate with edible oil, allowing it to stand, separating the oil and water phases, discarding the aqueous phase, and retaining the oil phase.

[0051] More preferably, the method further includes deodorizing the obtained oil phase to obtain edible oil with high polyphenol content.

[0052] In this invention, the edible oil prepared according to the method of this invention has a high polyphenol content and can be blended according to market demand and product needs. The blended edible oil obtained is still within the scope of protection of this invention.

[0053] According to a particularly preferred embodiment of the present invention, a method for preparing oils with improved oxidative stability is provided, the method comprising the following steps: S1. Flaxseeds are dehulled using a flaxseed dehulling and sorting device to obtain flaxseed hulls and flaxseed kernels; The kernel content of flaxseed hulls is 1-4 wt%. S2. Stir-fry flaxseed hulls at 175-180℃ for 31-35 minutes; S3. Mix the roasted flaxseed hulls with the flaxseed kernels and roast at 115-120℃ for 36-40 minutes. Press the roasted material in a screw press (pressure 180-200MPa) to obtain crude oil and cake. The mass ratio of the roasted flaxseed hulls to the flaxseed kernels is 1:(1-2). S4. The crude oil is subjected to conventional neutralization, decolorization, dewaxing, and deodorization to obtain refined flaxseed oil; S5. Mix the pressed cake with an ethanol solution with a pH of 12-13 (add sodium hydroxide solution to the ethanol solution to make the pH of the ethanol solution 12-13), and homogenize at 46-55℃ for 2.5-3 hours to obtain a homogenate. The volume concentration of the ethanol solution is 75-78 v / v%. The mass ratio of the cake meal to the ethanol solution is 1:(1.6-2). S6. Distill the homogenate to remove residual ethanol; adjust the pH of the homogenate after ethanol removal to 4.5-5 using hydrochloric acid solution (concentration of 10mol / L), then add β-glucosidase and incubate at 68-70℃ for 3-6h to obtain the enzymatic hydrolysate. The amount of β-glucosidase used is 800-1000U relative to 1g of the cake meal; S7. Mix the enzymatic hydrolysate with refined flaxseed oil, let it stand until the oil and water separate, remove the oil phase, and obtain edible oil with better oxidation stability. The mass ratio of the enzymatic hydrolysate to refined flaxseed oil is 1:(8-10).

[0054] The present invention will be described in detail below through embodiments.

[0055] The flaxseed and rapeseed dehulling and sorting equipment in the following examples was purchased from Liaoning Qiaopai Machinery Co., Ltd., and the instrument model is TFYMZ-200.

[0056] β-glucosidase was purchased from Weilan Bio-Enzyme Preparation Co., Ltd.

[0057] The screw press was purchased from Shibayoufang Co., Ltd., and the instrument model is FL-S2017.

[0058] Example 1 S1. Flaxseeds are dehulled using a flaxseed dehulling and sorting device to obtain flaxseed hulls and flaxseed kernels; The kernel content of flaxseed hulls is 1 wt%. S2. Stir-fry flaxseed hulls at 180℃ for 35 minutes; S3. Mix the roasted flaxseed hulls with the flaxseed kernels and roast at 120°C for 40 minutes. Press the roasted material in a screw press (pressure 180MPa) to obtain crude oil and cake. The mass ratio of the roasted flaxseed hulls to the flaxseed kernels is 1:1. S4. The crude oil is subjected to conventional neutralization, decolorization, dewaxing, and deodorization to obtain refined flaxseed oil; S5. Mix the pressed cake with an ethanol solution with a pH of 13 (add sodium hydroxide solution to the ethanol solution to make the pH of the ethanol solution 13), and homogenize at 55°C for 3 hours to obtain a homogenate. The volume concentration of the ethanol solution is 75 v / v%. The mass ratio of the cake meal to the ethanol solution is 1:2; S6. Distill the homogenate to remove residual ethanol; adjust the pH of the homogenate after ethanol removal to 4.5 using hydrochloric acid solution (concentration of 10 mol / L), then add β-glucosidase and incubate at 70℃ for 6 h to obtain the enzymatic hydrolysate. The amount of β-glucosidase used is 1000U relative to 1g of the cake meal; S7. Mix the enzymatic hydrolysate with refined flaxseed oil, let it stand until the oil and water separate, remove the oil phase to obtain flaxseed oil; The mass ratio of the enzymatic hydrolysate to refined flaxseed oil is 1:8.

[0059] Example 2 S1. Flaxseeds are dehulled using a flaxseed dehulling and sorting device to obtain flaxseed hulls and flaxseed kernels; The kernel content of flaxseed hulls is 5 wt%. S2. Stir-fry flaxseed hulls at 160℃ for 25 minutes; S3. Mix the roasted flaxseed hulls with the flaxseed kernels and roast at 100℃ for 30 minutes. Press the roasted material in a screw press (pressure 60MPa) to obtain crude oil and cake. The mass ratio of the roasted flaxseed hulls to the flaxseed kernels is 1:6. S4. The crude oil is subjected to conventional neutralization, decolorization, dewaxing, and deodorization to obtain refined flaxseed oil; S5. Mix the pressed cake with an ethanol solution with a pH of 10 (add sodium hydroxide solution to the ethanol solution to make the pH of the ethanol solution 10), and homogenize at 45°C for 2 hours to obtain a homogenate. The volume concentration of the ethanol solution is 70% v / v%. The mass ratio of the cake meal to the ethanol solution is 1:1. S6. Distill the homogenate to remove residual ethanol; adjust the pH of the homogenate after ethanol removal to 4 using hydrochloric acid solution (concentration of 10 mol / L), then add β-glucosidase and incubate at 68℃ for 1 h to obtain the enzymatic hydrolysate. The amount of β-glucosidase used is 500U relative to 1g of the cake meal; S7. Mix the enzymatic hydrolysate with refined flaxseed oil, let it stand until the oil and water separate, remove the oil phase to obtain flaxseed oil; The mass ratio of the enzymatic hydrolysate to refined flaxseed oil is 1:12.

[0060] Example 3 S1. Flaxseeds are dehulled using a flaxseed dehulling and sorting device to obtain flaxseed hulls and flaxseed kernels; The kernel content of flaxseed hulls is 3 wt%. S2. Stir-fry flaxseed hulls at 170℃ for 30 minutes; S3. Mix the roasted flaxseed hulls with the flaxseed kernels and roast at 110°C for 35 minutes. Press the roasted material in a screw press (pressure 100MPa) to obtain crude oil and cake. The mass ratio of the roasted flaxseed hulls to the flaxseed kernels is 1:3. S4. The crude oil is subjected to conventional neutralization, decolorization, dewaxing, and deodorization to obtain refined flaxseed oil; S5. Mix the pressed cake with an ethanol solution with a pH of 11 (add sodium hydroxide solution to the ethanol solution to make the pH of the ethanol solution 11), and homogenize at 50°C for 3 hours to obtain a homogenate. The volume concentration of the ethanol solution is 80 v / v%. The mass ratio of the cake meal to the ethanol solution is 1:1.5. S6. Distill the homogenate to remove residual ethanol; adjust the pH of the homogenate after ethanol removal to 6 using hydrochloric acid solution (concentration of 10 mol / L), then add β-glucosidase and incubate at 69℃ for 3 h to obtain the enzymatic hydrolysate. The amount of β-glucosidase used is 750 U relative to 1 g of the cake meal; S7. Mix the enzymatic hydrolysate with refined flaxseed oil, let it stand until the oil and water separate, remove the oil phase to obtain flaxseed oil; The mass ratio of the enzymatic hydrolysate to refined flaxseed oil is 1:10.

[0061] Example 4 S1. Flaxseeds are dehulled using a flaxseed dehulling and sorting device to obtain flaxseed hulls and flaxseed kernels; Of these, the kernel content of flaxseed hulls is 5%; S2. Stir-fry flaxseed hulls at 150℃ for 20 minutes; S3. Mix the roasted flaxseed hulls with the flaxseed kernels and roast at 80°C for 20 minutes. Press the roasted material in a screw press (pressure 60MPa) to obtain crude oil and cake. The mass ratio of the roasted flaxseed hulls to the flaxseed kernels is 1:6. S4. The crude oil is subjected to conventional neutralization, decolorization, dewaxing, and deodorization to obtain refined flaxseed oil; S5. Mix the pressed cake with an ethanol solution with a pH of 10 (add sodium hydroxide solution to the ethanol solution to make the pH of the ethanol solution 10), and homogenize at 40°C for 2 hours to obtain a homogenate. The volume concentration of the ethanol solution is 60 v / v%. The mass ratio of the cake meal to the ethanol solution is 1:1. S6. Distill the homogenate to remove residual ethanol; adjust the pH of the homogenate after ethanol removal to 3 using hydrochloric acid solution (concentration of 10 mol / L), then add β-glucosidase and incubate at 60℃ for 1 h to obtain the enzymatic hydrolysate. The amount of β-glucosidase used is 200U relative to 1g of the cake meal; S7. Mix the enzymatic hydrolysate with refined flaxseed oil, let it stand until the oil and water separate, remove the oil phase to obtain flaxseed oil; The mass ratio of the enzymatic hydrolysate to refined flaxseed oil is 1:12.

[0062] Example 5 S1. Flaxseeds are dehulled using a flaxseed dehulling and sorting device to obtain flaxseed hulls and flaxseed kernels; Of these, the kernel content of flaxseed hulls is 3%; S2. Stir-fry flaxseed hulls at 190℃ for 30 minutes; S3. Mix the roasted flaxseed hulls with the flaxseed kernels and roast at 140℃ for 60 minutes. Press the roasted material in a screw press (pressure 200MPa) to obtain cake. The mass ratio of the roasted flaxseed hulls to the flaxseed kernels is 1:3. S4. The crude oil is subjected to conventional neutralization, decolorization, dewaxing, and deodorization to obtain refined flaxseed oil; S5. Mix the pressed cake with an ethanol solution with a pH of 13 (add sodium hydroxide solution to the ethanol solution to make the pH of the ethanol solution 13), and homogenize at 40°C for 2 hours to obtain a homogenate. The volume concentration of the ethanol solution is 90 v / v%. The mass ratio of the cake meal to the ethanol solution is 1:2; S6. Distill the homogenate to remove residual ethanol; adjust the pH of the homogenate after ethanol removal to 6 using hydrochloric acid solution (concentration of 10 mol / L), then add β-glucosidase and incubate at 40℃ for 2 h to obtain the enzymatic hydrolysate. The amount of β-glucosidase used is 4000U relative to 1g of the cake meal; S7. Mix the enzymatic hydrolysate with refined flaxseed oil, let it stand until the oil and water separate, remove the oil phase to obtain flaxseed oil; The mass ratio of the enzymatic hydrolysate to refined flaxseed oil is 1:8.

[0063] Example 6 S1. The rapeseed is dehulled using a rapeseed dehulling and sorting device to obtain rapeseed hulls and rapeseed kernels; The kernel content of the rapeseed husk is 1 wt%. S2. Stir-fry the rapeseed hulls at 180℃ for 35 minutes; S3. Mix the roasted rapeseed hulls and rapeseed kernels, roast at 120℃ for 40 minutes, and then press the roasted material in a screw press (pressure 180MPa) to obtain crude oil and oil cake. The mass ratio of the roasted rapeseed husk to the rapeseed kernel is 1:1. S4. The crude oil is subjected to conventional neutralization, decolorization, dewaxing, and deodorization to obtain refined rapeseed oil; S5. Mix the pressed cake with an ethanol solution with a pH of 13 (add sodium hydroxide solution to the ethanol solution to make the pH of the ethanol solution 13), and homogenize at 60°C for 4 hours to obtain a homogenate. The volume concentration of the ethanol solution is 75 v / v%. The mass ratio of the cake meal to the ethanol solution is 1:2; S6. Distill the homogenate to remove residual ethanol; adjust the pH of the homogenate after ethanol removal to 4.5 using hydrochloric acid solution (concentration of 10 mol / L), then add β-glucosidase and incubate at 70℃ for 6 h to obtain the enzymatic hydrolysate. The amount of β-glucosidase used is 1000U relative to 1g of the cake meal; S7. Mix the enzymatic hydrolysate with refined rapeseed oil, let it stand until the oil and water separate, remove the oil phase to obtain rapeseed oil; The mass ratio of the enzymatic hydrolysate to refined rapeseed oil is 1:8.

[0064] Example 7 The method of Example 1 is followed, except that in step S1, the kernel content of flaxseed hulls exceeds 30 wt%, while the other steps and conditions remain the same as in Example 1, to obtain flaxseed oil.

[0065] Example 8 The method of Example 1 was followed, except that in step S6, the amount of β-glucosidase was 100U relative to 1g of cake, while the other steps and conditions remained the same as in Example 1, to obtain flaxseed oil.

[0066] Example 9 The method of Example 1 was followed, except that in step S4, the pH of the ethanol solution was 9, while the other steps and conditions remained the same as in Example 1, to obtain flaxseed oil.

[0067] Example 10 The method of Example 1 is followed, except that in step S6, β-glucosidase is replaced with α-glucosidase (α-glucosidase was purchased from Shanghai Yuanye Biotechnology Co., Ltd.), while the other steps and conditions are the same as in Example 1, to obtain flaxseed oil.

[0068] Comparative Example 1 The method of Example 1 is followed, except that the temperature of the first and second roasting is 120°C, while the other steps and conditions are the same as in Example 1, to obtain flaxseed oil.

[0069] Comparative Example 2 The method is the same as in Example 1, except that the temperature of the first roasting is 100°C higher than that of the second roasting. Specifically, in step S1, the first roasting temperature is 140°C and the roasting time is 35 minutes; in step S3, the second roasting temperature is 40°C and the roasting time is 40 minutes. Other steps and conditions are the same as in Example 1, and flaxseed oil is obtained.

[0070] Comparative Example 3 The method is the same as in Example 1, except that the first roasting temperature is 60°C lower than the second roasting temperature. Specifically, the first roasting temperature in step S2 is interchanged with the second roasting temperature in step S3, that is, the flaxseed hulls are roasted at 120°C for 35 minutes, and then the roasted flaxseed powder is mixed with flaxseed and roasted at 180°C for 40 minutes. Other steps and conditions are the same as in Example 1 to obtain flaxseed oil.

[0071] Comparative Example 4 The method of Example 1 is followed, except that in step S6, β-glucosidase is replaced with rhamnosidase (rhamnosidase was purchased from Xiasheng Biotechnology Co., Ltd.), while the other steps and conditions are the same as in Example 1, and flaxseed oil is obtained.

[0072] Comparative Example 5 The method of Example 1 is different in that, in step S1, the flaxseed is not separated from the kernel and husk, but is directly subjected to the first roasting, second roasting, pressing and other steps. The other steps and conditions are the same as in Example 1 to obtain flaxseed oil.

[0073] Comparative Example 6 The method of Example 1 is different in that, in step S2, the flaxseed hulls are not roasted for the first time, but are directly mixed with the flaxseed kernels for roasting and pressing. The other steps and conditions are the same as in Example 1 to obtain flaxseed oil.

[0074] Comparative Example 7 The method of Example 1 is different in that, in step S3, after the flaxseed hulls and flaxseed kernels are mixed, they are not roasted a second time, but are directly pressed. The other steps and conditions are the same as in Example 1 to obtain flaxseed oil.

[0075] Comparative Example 8 The method is the same as in Example 1, except that only flaxseed kernels are roasted, while the other steps and conditions remain the same. Specifically, the flaxseed kernels are roasted, roasted, and pressed in sequence to obtain cake; the cake is mixed with ethanol and homogenized to obtain a homogenate; the homogenate is mixed with an enzyme preparation and enzymatically hydrolyzed to obtain an enzymatic hydrolysate; the enzymatic hydrolysate is mixed with vegetable oil, and the oil phase is retained to obtain flaxseed oil.

[0076] Comparative Example 9 S1. Flaxseeds are dehulled using a flaxseed dehulling and sorting device to obtain flaxseed hulls and flaxseed kernels; The kernel content of flaxseed hulls is 1 wt%. S2. Stir-fry flaxseed hulls at 180℃ for 35 minutes; S3. Mix the roasted flaxseed hulls and flaxseed kernels, roast at 120℃ for 40 minutes, and then press the roasted material in a screw press (pressure of 180MPa) to obtain crude flaxseed oil. The mass ratio of the roasted flaxseed hulls to the flaxseed kernels is 1:1.

[0077] Comparative Example 10 S1. The rapeseed is dehulled using a rapeseed dehulling and sorting device to obtain rapeseed hulls and rapeseed kernels; The kernel content of the rapeseed husk is 1 wt%. S2. Stir-fry the rapeseed hulls at 180℃ for 35 minutes; S3. Mix the roasted rapeseed hulls and rapeseed kernels, roast at 120℃ for 40 minutes, and then press the roasted material in a screw press (pressure 180MPa) to obtain crude rapeseed oil. The mass ratio of the roasted rapeseed husk to the rapeseed kernel is 1:1.

[0078] Comparative Example 11 The method of Example 1 is followed, except that in step S5, the ethanol solution is replaced with a propylene glycol solution, while the other steps and conditions remain the same as in Example 1, to obtain flaxseed oil.

[0079] Test case The total polyphenol content, SECO content, and Canolol content of the edible oils prepared in the above examples and comparative examples were determined, and the oxidative stability of the edible oils was tested. The specific results are shown in Table 1.

[0080] The total amount of polyphenols was determined in accordance with the People's Republic of China grain industry standard "LS / T 6119-2017 Determination of Polyphenols in Grain and Oil Plants by Spectrophotometry".

[0081] The content of SECO (secrocinol) was determined by high-performance liquid chromatography (HPLC) using an external standard method. The specific steps included: accurately preparing a standard solution of SECO within a specific concentration range, filtering it through a 0.22 μm filter membrane, and then administering it to the HPLC. The oil sample to be tested was extracted three times with 80% methanol-water solution, and the extracts were combined and filtered through a 0.22 μm filter membrane before administration. Instrumental analysis conditions: Waters ultra-high performance liquid chromatograph, diode array detector (DAD); column: Waters Acquity BEH Shield RP18 (100 mm × 2.1 mm × 1.7 μm); mobile phase: methanol (A), 0.5% acetic acid aqueous solution (B), gradient elution; flow rate: 0.2 mL / min; injection volume: 2 μL; run time: 35 min; detection wavelength range: 200-400 nm.

[0082] The content of Canolol (Chinese name: 4-vinyl-2,6-dimethoxyphenol, also known as rapeseed polyphenol) was quantitatively determined by high-performance liquid chromatography (HPLC) using the external standard method. The specific steps included: accurately preparing a standard solution of Canolol standard material to a specific concentration range, filtering it through a 0.22 μm filter membrane before HPLC; diluting the oil sample to be tested to the mark with n-hexane and mixing thoroughly; if the solution was not clear, filtering it through a 0.45 μm microporous membrane before HPLC. Instrument analysis conditions: Thermo Fisher Scientific Ultra High Performance Liquid Chromatography (Thermo UltiMate 3000 UHPLC) with a fluorescence detector; column: glycol-based silica gel column (250 mm long, 4.6 mm inner diameter, 5 μm particle size); excitation wavelength: 298 nm; emission wavelength: 325 nm; mobile phase: n-hexane + isopropanol = 96:4 (v / v); flow rate: 0.8 mL / min; injection volume: 20 μL; column temperature: 30℃.

[0083] The oxidative stability of edible oils was tested using a Rancimat oil oxidative stability analyzer. The specific steps included: heating a specific weight of oil to 90°C and continuously passing air through a glass tube to collect the volatile substances produced after heating; passing deionized water through the oil and monitoring the conductivity of the deionized water; and identifying the time point at which the conductivity changed most rapidly and the time point at which the oil underwent a significant oxidation reaction. The heating time at this point is the oxidation induction time of the oil. The longer the oxidation induction time, the better the oxidative stability of the oil, and the less likely it is to undergo rancid oxidative deterioration during storage.

[0084] Table 1

[0085] As can be seen from the data in Table 1, comparing Examples 1-5 with Examples 7-10, Comparative Examples 1-9, and Comparative Example 11, it can be seen that the preferred method significantly increases the content of polyphenols and SECO in flaxseed oil, thereby improving the oxidative stability of flaxseed oil.

[0086] As shown in Table 1, comparing Example 6 with Comparative Example 10, it can be seen that the preferred method significantly increased the content of polyphenols and Canolol in rapeseed oil, thereby improving the oxidative stability of rapeseed oil.

[0087] In summary, the method of the present invention significantly improves the polyphenol and SECO content in the prepared flaxseed oil, or the method of the present invention significantly improves the polyphenol and Canolol content in the prepared rapeseed oil, and the flaxseed oil or rapeseed oil has high oxidative stability.

[0088] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing oils with improved oxidative stability, characterized in that, The method includes the following steps: S1. Remove the outer skin from the oilseeds to obtain the seed coat and kernel; S2. The seed coat is first stir-fried; S3. Mix the roasted seed coat with the seed kernel, and then perform a second roasting and pressing to obtain cake meal; S4. The cake is mixed with an alkaline substance and ethanol and homogenized to obtain a homogenate. S5. Mix the homogenate with glucosidase and perform enzymatic hydrolysis to obtain the enzymatic hydrolysate; S6. Mix the enzymatic hydrolysate with vegetable oil, retaining the oil phase; The temperature of the first stir-fry is 50-90℃ higher than that of the second stir-fry.

2. The method according to claim 1, wherein, The temperature of the first stir-frying is 50-80℃ higher than that of the second stir-frying; And / or, in S1, the peeling conditions result in the kernel content of the seed coat being less than 5 wt%; And / or, in S1, the oilseed is selected from at least one of rapeseed, peanut, flaxseed, soybean, safflower seed, cottonseed, sesame, walnut, camellia seed, evening primrose seed, borage seed, perilla seed, pumpkin seed, maple seed, chia seed, wheat germ, pine nut, almond, rice bran, hazelnut, tomato seed, pomegranate seed, avocado, grape seed, coconut, milk thistle seed, jojoba seed, shea butter, babassu seed, hemp seed, and sunflower seed.

3. The method according to claim 1, wherein, In S2, the conditions for the first stir-frying include: a temperature of 150-190℃ and a time of 20-40 minutes.

4. The method according to any one of claims 1-3, wherein, In S3, the conditions for the second stir-frying include: a temperature of 60-140℃ and a time of 20-60 minutes; And / or, in S3, the mass ratio of the roasted seed coat to the seed kernel is 1:(1-6). And / or, in S3, the pressing method includes pressing the kernel and seed coat after the second roasting in a screw press.

5. The method according to any one of claims 1-3, wherein, In S4, the alkaline substance is selected from at least one of sodium hydroxide, potassium hydroxide, and ammonia water; And / or, in S4, the conditions for homogenization include: a temperature of 40-60°C and a time of 2-4 hours; And / or, in S4, the mass ratio of the cake and ethanol is 1:(1-2).

6. The method according to claim 5, wherein, The amount of alkaline substance used makes the pH of the ethanol 10-13; And / or, in S4, the ethanol is provided in the form of an aqueous ethanol solution.

7. The method according to any one of claims 1-3, wherein, In S5, the enzymatic hydrolysis conditions include: pH 3-6, temperature 60-75℃, and time 1-6h. And / or, in S5, the amount of glucosidase used is 200-4000U relative to 1g of the cake meal; And / or, in S5, the glucosidase is selected from α-glucosidase and / or β-glucosidase.

8. The method according to any one of claims 1-3, wherein, In S6, the mass ratio of the enzymatic hydrolysate to the edible oil is 1:(2-20).

9. The method according to any one of claims 1-3, wherein, In S6, the vegetable oil is selected from refined vegetable oil; And / or, the refined vegetable oil is selected from at least one of refined rapeseed oil, refined peanut oil, refined flaxseed oil, refined soybean oil, refined corn oil, refined safflower seed oil, refined cottonseed oil, refined sesame oil, refined walnut oil, refined camellia oil, refined evening primrose oil, refined borage oil, refined perilla seed oil, refined pumpkin seed oil, refined maple seed oil, refined chia seed oil, refined wheat germ oil, refined pine nut oil, refined almond oil, refined rice bran oil, refined hazelnut oil, refined tomato seed oil, refined pomegranate seed oil, refined avocado oil, refined grape seed oil, refined coconut oil, refined milk thistle seed oil, refined jojoba oil, refined shea butter, refined babassu oil, refined hemp seed oil, and refined sunflower seed oil.

10. Edible oil prepared by the method according to any one of claims 1-9.

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