A soy-based nutritional powder enriched with linoleic acid with moderate protein oxidation and its preparation method and application

Abstract

The application discloses a soybean-based nutrition powder rich in linoleic acid with moderate protein oxidation and a preparation method and application thereof, and belongs to the technical field of soybean product processing. The method is that after soybean milk and linoleic acid are mixed, moderate heating is carried out, and a cold plasma technology is combined to moderately oxidize soybean powder, improve the solubility and the antioxidation during digestion, and effectively improve the functional properties and the nutritional value of the soybean-based nutrition powder.

Description

Technical Field

[0001] This invention belongs to the field of soybean product processing technology, specifically relating to a soybean-based nutritional powder rich in linoleic acid with moderate protein oxidation, its preparation method, and its application. Background Technology

[0002] Soy milk, also known as soy milk beverage, is rich in nutrients, especially plant protein, which provides the body with the necessary protein and energy for bodily functions. It is also rich in B vitamins, which help maintain normal metabolism. Furthermore, it contains plant amino acids and other components that can lower cholesterol and alleviate neurasthenia. Today, soy milk is popular overseas due to its excellent quality, unique taste, and superior nutritional value.

[0003] Currently, most soy milk products on the market are products with reduced sugar content, such as pumpkin powder mixed into soy milk as an additive. There is also a significant development of instant soy-based nutritional powders. While these soy-based nutritional powder products have good functionality and are nutritious and delicious, their effects are not comprehensive and their shelf life is short.

[0004] Linoleic acid is a polyunsaturated fatty acid belonging to the Omega-3 series of fatty acids. It is mainly found in flaxseed oil, flaxseed, and other plant-based foods. Linoleic acid is beneficial to human health, possessing anti-inflammatory, blood pressure-lowering, blood lipid-lowering, and cardiovascular health-improving effects. However, linoleic acid itself undergoes lipid peroxidation, generating ROS free radicals and reactive oxygen species that attack the protein backbone and amino acid side chains. Reactive oxygen species such as •OH abstract hydrogen atoms from protein molecules to form alkyl radicals (C•), which, in the presence of O2, generate alkyl peroxide radicals (COO•). These alkyl peroxide radicals are then converted to alkyl peroxide (COOH) through hydrogenation or protonation, further reacting with superoxide radicals (HO2•) in the system to form alkoxy radicals (CO•). At this point, the alkoxy radicals of the main peptide chain easily cause peptide chain breakage through α-amidation and diamide pathways, generating hydroxyl derivatives, ammonia, carboxylic acid derivatives, and polypeptide fragments, resulting in oxidative breakage of the protein's main peptide chain.

[0005] Cold plasma (CP) is the fourth state of matter, composed of charged particles generated from ionized gas atoms, ultraviolet photons, free radicals, reactive oxygen species (ROS), and reactive nitrogen species (RNS), among other substances. Due to its relatively low pressure and power, cold plasma lacks local thermodynamic equilibrium. Furthermore, current commercially available technologies primarily use cold plasma to directly modify proteins; methods combining cold plasma with nutrients such as linoleic acid for protein modification have not been reported. Summary of the Invention

[0006] To address the above issues, this invention provides a soybean-based nutritional powder rich in linoleic acid with moderate protein oxidation, along with its preparation method and applications. Its excellent antioxidant properties, digestibility, and high nutritional value make it suitable for various population groups and have promising market prospects.

[0007] This invention provides a method for preparing a soybean-based nutritional powder rich in linoleic acid with moderate protein oxidation, comprising the following steps:

[0008] Linoleic acid is added to soy milk, and the mixture is heated and treated with cold plasma. After homogenization, concentration and drying, a soy-based nutritional powder rich in linoleic acid with moderate protein oxidation is obtained.

[0009] The amount of linoleic acid added is 7-10%; the heating temperature is 40-50℃, and the heating time is 15-20min; for cold plasma treatment, the voltage is 10-18KV, the treatment time is 90-150min, and the power is 45-55W.

[0010] The 7-10% refers to the volume percentage of linoleic acid in soy milk, meaning 7-10 ml of linoleic acid is added to 100 ml of soy milk. Soy milk is made by mixing soy flour and water (the mass ratio of soy flour to water is 1:9-11) and then steaming it at 90-110℃ for 25-35 minutes.

[0011] In a preferred embodiment, the aforementioned preparation method includes the following steps:

[0012] 1) Prepare soybean flour to form soy milk, then add honey, xanthan gum, sodium polyacrylate, lecithin, and vanilla syrup;

[0013] 2) Linoleic acid is added and the mixture is heated and subjected to cold plasma treatment to obtain processed soy milk;

[0014] 3) After homogenization, concentration and drying, a soybean-based nutritional powder rich in linoleic acid with moderate protein oxidation is obtained.

[0015] The steps for preparing soybean flour are as follows: Soybeans and water are mixed at a mass ratio of 1:9-11 and soaked for 10-14 hours. The soybeans are washed by changing the water 2-4 times (soaking the soybeans in water for 10-14 hours after each water change). The soybeans are then ground into powder using a high-speed blender at 20,000-40,000 r / min to obtain soybean flour.

[0016] The process of making soy milk is as follows: Soy flour and water are mixed at a mass ratio of 1:9-11, and cooked at 90-110℃ for 25-35 minutes while stirring constantly to form soy milk; the soy milk is then filtered to separate it from the residue; and the pH of the soy milk is adjusted to 6.0-6.5. Under these pH conditions, the soy milk is relatively stable and has a better taste.

[0017] In a preferred embodiment, 4-6 wt% honey, 0.05-0.15 wt% xanthan gum, 0.05-0.2 wt% sodium polyacrylate, 0.03-0.07 wt% lecithin, and 0.5-1.5 wt% vanilla syrup are added to the soy milk; more preferably, 5 wt% honey, 0.1 wt% xanthan gum, 0.1 wt% sodium polyacrylate, 0.05 wt% lecithin, and 1 wt% vanilla syrup are added. Honey and vanilla syrup provide sweetness and aroma, xanthan gum and sodium polyacrylate increase viscosity and stability, and lecithin prevents oil-water separation, making the soy flour more delicate and smooth. The synergistic effect of xanthan gum and sodium polyacrylate, along with the emulsifying properties of lecithin, effectively prevents the soy flour from deteriorating and separating during storage and use. The percentages in this section refer to the mass percentage of each component to the soy milk. The soy milk is obtained by mixing soy flour and water (the mass ratio of soy flour to water is 1:9-11) and then steaming it at 90-110℃ for 25-35 minutes. That is, add 4-6g of honey, 0.05-0.15g of xanthan gum, 0.05-0.2g of sodium polyacrylate, 0.03-0.07g of lecithin and 1g of vanilla syrup to 100g of soy milk.

[0018] Homogenization is performed in two stages. The first stage of high-pressure homogenization is set at a homogenization pressure of 20-30 MPa and a processing time of 5-10 minutes. The second stage of low-pressure homogenization is set at a homogenization pressure of 10-15 MPa and a processing time of 3-5 minutes. More preferably, the first stage of high-pressure homogenization is set at a homogenization pressure of 25 MPa and a processing time of 8 minutes. The second stage of low-pressure homogenization is set at a homogenization pressure of 12 MPa and a processing time of 4 minutes.

[0019] During concentration, the vacuum degree is 82.6-98.6 kPa and the temperature is 45-55°C; more preferably, the vacuum degree is 90.6 kPa, the temperature is 50°C, and the steam pressure is less than 196 kPa.

[0020] Low-temperature spray drying is adopted, with the inlet air temperature set at 150-170℃, the outlet air temperature controlled at 80-90℃, and the feed concentration adjusted to 25-40%, where feed concentration refers to the mass fraction of solid components in the processed soy milk. The atomization speed is in the range of 250-300 r / s. More preferably, the inlet air temperature is set at 160℃, the outlet air temperature controlled at 85℃, the feed concentration adjusted to 30%, where feed concentration refers to the mass fraction of solid components in the processed soy milk, and the atomization speed is 270 r / s.

[0021] The present invention also discloses a moderately oxidized soy-based nutritional powder rich in linoleic acid obtained by the aforementioned preparation method.

[0022] The present invention also provides the application of the aforementioned preparation method in the preparation of soybean-based nutritional powder rich in linoleic acid.

[0023] More specifically, the preparation method of the present invention includes the following steps:

[0024] Soak soybeans in water (mass ratio 1:9-11) for 12-14 hours, changing the water 2-4 times to wash the soybeans (soaking them in water for 12-14 hours after each water change). Longer soaking time allows the soybeans to absorb water and swell, loosening their cell structure and making it easier for proteins and other components to dissolve, thus increasing the yield of soy milk.

[0025] Place the washed soybeans into a high-speed blender and process them at 20,000-40,000 rpm for 2-3 minutes until they are dry-ground into powder.

[0026] Soy flour and water are steamed at 90-110℃ for 25-35 minutes, stirring constantly, to form soy milk.

[0027] A 200-mesh sieve is used to filter and separate the soy milk from the residue.

[0028] Adjust the pH of the soy milk to 6.0-6.5 using acetic acid or sodium hydroxide.

[0029] Add 4-6 wt% honey, 0.05-0.15 wt% xanthan gum, 0.05-0.2 wt% sodium polyacrylate, 0.03-0.07 wt% lecithin and 0.5-1.5 wt% vanilla syrup.

[0030] Add 7-10% linoleic acid and perform combined heating and cold plasma treatment. Heating temperature: 40-50℃, heating time: 15-20 min. During cold plasma treatment, voltage: 10-18KV, treatment time: 90-150 min. After adding linoleic acid, heating and cold plasma treatment are performed simultaneously, but the heating time is shorter than the cold plasma treatment time.

[0031] Perform two-stage homogenization. The first-stage high-pressure homogenization is set at a homogenization pressure of 20-30 MPa and a processing time of 5-10 minutes. The second-stage low-pressure homogenization is set at a homogenization pressure of 10-15 MPa and a processing time of 3-5 minutes.

[0032] The soy milk is concentrated under vacuum conditions of 82.6-98.6 kPa, at a temperature of 45-55°C, and with a steam pressure of less than 196 kPa.

[0033] Low-temperature spray drying is performed with the inlet air temperature set at 150-170℃, the outlet air temperature controlled at around 80-90℃, the feed concentration adjusted to 25-40wt%, and the atomization speed in the range of 250-300r / s.

[0034] Packaged finished products.

[0035] The advantages of this invention compared to existing technologies are as follows:

[0036] The combination of thermally induced linoleic acid (TIA) and cold plasma treatment, under the same degree of oxidation, resulted in soybean-based nutritional powder with better solubility and antioxidant properties than soybean-based nutritional powder treated with TIA alone or cold plasma alone. This indicates that under certain concentration and process parameters, the synergistic modification of soybean protein by TIA and cold plasma treatment can improve the solubility and antioxidant properties of soybean-based nutritional powder.

[0037] The reasons why heat-induced linoleic acid combined with cold plasma treatment enhances the antioxidant properties of soybean flour include: cold plasma treatment can further enhance the antioxidant effect of linoleic acid by activating intracellular antioxidant defense mechanisms, such as the Nrf2 pathway. In addition, various active substances generated by cold plasma treatment, such as reactive oxygen species (ROS), free radicals, and ultraviolet photons, can react with linoleic acid to generate oxidation products with specific functions, which have stronger antioxidant capabilities. Furthermore, cold plasma treatment helps retain or increase the antioxidant components in soybean flour, such as polyphenols and flavonoids. These components can synergistically work with the oxidation products of linoleic acid to further improve antioxidant capacity.

[0038] Cold plasma treatment generates almost no heat, which allows it to be effectively combined with heat treatment to avoid the adverse effects of secondary heating on the protein in soybean flour. This invention effectively improves the nutritional value of soybean flour, providing high-quality protein for the human body. Attached Figure Description

[0039] Figure 1 The graph shows the carbonyl content of Examples 1-3 and Comparative Examples 1-5;

[0040] Figure 2 The graph shows the free thiol content of Examples 1-3 and Comparative Examples 1-5;

[0041] Figure 3 These are schematic diagrams illustrating the solubility of Examples 1-3 and Comparative Examples 1-5;

[0042] Figure 4 DPPH diagrams for Examples 1-3 and Comparative Examples 1-4;

[0043] Figure 5 The ABTS diagrams are for Examples 1-3 and Comparative Examples 1-4. Detailed Implementation

[0044] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the embodiments. All chemical reagents used in the experiments were purchased through commercial channels.

[0045] The cold plasma described in this article is dielectric barrier discharge (DBD) cold plasma, using helium as the working medium and a power of 50W.

[0046] Example 1

[0047] The preparation method of a soybean-based nutritional powder rich in linoleic acid with moderate protein oxidation is as follows:

[0048] Soak soybeans in water at a ratio of 1:10 for 12 hours, changing the water twice, soaking for 12 hours after each water change, and then washing the soybeans.

[0049] Place the washed soybeans into a high-speed blender and process them at 30,000 rpm for 2 minutes until they are ground into powder.

[0050] After mixing soybean flour and water (the mass ratio of soybean flour to water is 1:10), steam at 100℃ for 30 minutes, stirring constantly, to form soy milk.

[0051] A 200-mesh sieve is used to filter and separate the soy milk from the residue.

[0052] Adjust the pH of the soy milk to 6.5 using acetic acid or sodium hydroxide.

[0053] Add 5% honey, 0.1% xanthan gum, 0.1% sodium polyacrylate, 0.05% lecithin, and 1% vanilla syrup.

[0054] Linoleic acid (8%) was added, and the mixture was subjected to a combined heating and cold plasma treatment. Heating temperature: 45℃, heating time: 15 min. Voltage: 14 kV, time: 120 min.

[0055] Two-stage homogenization is performed. The first-stage high-pressure homogenization is set at a homogenization pressure of 25 MPa and a processing time of 8 minutes. The second-stage low-pressure homogenization is set at a homogenization pressure of 12 MPa and a processing time of 4 minutes.

[0056] The soy milk is concentrated. Vacuum degree: 90.6 kPa, temperature: 50℃, steam pressure: less than 196 kPa.

[0057] Low-temperature spray drying is performed with the inlet air temperature set at 160℃, the outlet air temperature controlled at 85℃, the feed concentration adjusted to 30wt%, and the atomization speed at 270r / s.

[0058] Packaged finished products.

[0059] Example 2

[0060] The preparation method of a soybean-based nutritional powder rich in linoleic acid with moderate protein oxidation is as follows:

[0061] 1) Soak soybeans in water at a ratio of 1:9 for 12 hours. Change the water twice, soaking for 12 hours after each water change. Wash the soybeans thoroughly.

[0062] 2) Put the washed soybeans into a high-speed blender and process them at 25,000 rpm for 3 minutes until they are ground into powder.

[0063] 3) Mix soybean flour and water (the mass ratio of soybean flour to water is 1:9), then steam at 100℃ for 30 minutes, stirring constantly, to form soy milk.

[0064] 4) Filter the soy milk and residue through a 200-mesh sieve.

[0065] 5) Adjust the pH of the soy milk to 6.0 using acetic acid or sodium hydroxide.

[0066] 6) Add 4% honey, 0.15% xanthan gum, 0.15% sodium polyacrylate, 0.05% lecithin, and 1% vanilla syrup.

[0067] 7) Add 7% linoleic acid and treat with heating combined with cold plasma. Heating temperature: 50℃, heating time: 15min. Voltage: 16KV, time: 90min.

[0068] 8) Perform two-stage homogenization. The first-stage high-pressure homogenization is set to a homogenization pressure of 20 MPa and a processing time of 5 minutes; the second-stage low-pressure homogenization is set to a homogenization pressure of 10 MPa and a processing time of 3 minutes.

[0069] 9) Concentrate the soy milk. Vacuum degree: 82.6 kPa, temperature: 45℃, steam pressure: less than 196 kPa.

[0070] 10) Low-temperature spray drying: the inlet air temperature is set to 170℃, the outlet air temperature is controlled at 90℃, the feed concentration is adjusted to 40wt%, and the atomization speed is 250r / s.

[0071] 11) Packaging finished products.

[0072] Example 3

[0073] The preparation method of a soybean-based nutritional powder rich in linoleic acid with moderate protein oxidation is as follows:

[0074] 1) Soak soybeans in water at a ratio of 1:11 for 12 hours, changing the water twice, and soaking for 12 hours after each water change. Wash the soybeans thoroughly.

[0075] 2) Put the washed soybeans into a high-speed blender and process them at 40,000 rpm for 2 minutes to grind the soybeans into powder.

[0076] 3) Mix soybean flour and water (the mass ratio of soybean flour to water is 1:11), then steam at 100℃ for 30 minutes, stirring constantly, to form soy milk.

[0077] 4) Filter the soy milk and residue through a 200-mesh sieve.

[0078] 5) Adjust the pH of the soy milk to 6.3 using acetic acid or sodium hydroxide.

[0079] 6) Add 5% honey, 0.1% xanthan gum, 0.1% sodium polyacrylate, 0.06% lecithin, and 1.5% vanilla syrup.

[0080] 7) Add 9% linoleic acid and treat with heating combined with cold plasma. Heating temperature: 40℃, heating time: 20min. Voltage: 10KV, time: 150min.

[0081] 8) Perform two-stage homogenization. The first-stage high-pressure homogenization is set to a homogenization pressure of 30 MPa and a processing time of 10 minutes; the second-stage low-pressure homogenization is set to a homogenization pressure of 15 MPa and a processing time of 5 minutes.

[0082] 9) Concentrate the soy milk. Vacuum degree: 98.6 kPa, temperature: 55℃, steam pressure: less than 196 kPa.

[0083] 10) Low-temperature spray drying: the inlet air temperature is set to 160℃, the outlet air temperature is controlled at 85℃, the feed concentration is adjusted to 25wt%, and the atomization speed is 300r / s.

[0084] 11) Packaging finished products.

[0085] Comparative Example 1

[0086] Compared to Example 1, step 7) is modified as follows: add 8% linoleic acid, do not heat, and maintain for 15 minutes. Everything else is the same as in Example 1.

[0087] Comparative Example 2

[0088] Compared to Example 1, step 7) is modified as follows: 8% linoleic acid is added and heated; heating temperature: 45℃, heating time: 15min. Everything else is the same as in Example 1.

[0089] Comparative Example 3

[0090] Compared to Example 1, step 7) is modified as follows: no linoleic acid is added and no heating is performed; only cold plasma treatment is conducted. The cold plasma voltage is 14KV, and the time is 120min. Everything else is the same as in Example 1.

[0091] Comparative Example 4

[0092] Compared to Example 1, step 7 is omitted. Everything else is the same as in Example 1.

[0093] Comparative Example 5

[0094] Compared to Example 1, step 7) is modified as follows: 12% linoleic acid is added, and the mixture is treated with a combination of heating and cold plasma. Heating temperature: 45°C, heating time: 30 min. Voltage: 22 kV, time: 200 min.

[0095] Example 4

[0096] Carbonyl determination

[0097] Test samples: Soy-based nutritional powders prepared in Examples 1-3 and Comparative Examples 1-5.

[0098] Test method: Dilute the sample concentration to 5 mg / ml with phosphate buffer (20 mmol / L, pH 6.0). Place two 0.8 mL aliquots of the sample solution into 5 mL centrifuge tubes. One aliquot serves as the treatment group, adding 1600 μL of DNPH solution containing 2 mol / L (0.2%, w / v) HCl; the other group serves as the blank group, adding 1600 μL of HCl solution (2 mol / L). React at room temperature for 30 min, then add 800 μL of trichloroacetic acid (40%, w / v) to precipitate the protein. Centrifuge (5000 g, 4℃, 5 min). After removing the supernatant, wash the precipitate three times with 2 mL of ethanol-ethyl acetate mixture (1:1). Wash 3 mL with 20 mmol / L phosphate buffer containing 6 mol / L guanidine hydrochloride, pH 6.5 to completely dissolve the precipitate. Measure the absorbance at 370 nm, and determine the molar extinction coefficient (22,000 mmol / L). -1 ·L·cm -1 Calculate the carbonyl content of proteins.

[0099] Figure 1 This is a graph showing the carbonyl content of Examples 1-3 and Comparative Examples 1-5. (See figure) Figure 1 Comparative Example 5 had the highest carbonyl content, at 9 nmol / mg. Comparative Example 4 had the lowest carbonyl content, at 3 nmol / mg. Examples 1, 2, and 3 had moderate carbonyl contents, around 7.5 nmol / mg. This indicates that the soybean protein in Examples 1, 2, and 3 exhibited moderate oxidation. The addition of linoleic acid can act as a substrate for lipoxygenase, generating a large number of free radicals and lipid oxides. These free radicals can attack the side chains of proteins (especially Pro, Arg, Thr, Lys, etc.) or the main chain, leading to an increase in the carbonyl content of the protein. Additionally, some free radicals introduced by cold plasma treatment can also attack the protein side chains, causing protein oxidation. When cold plasma encounters lipoxygenase, its activity decreases. Under appropriate concentrations and conditions, the combined use of linoleic acid and cold plasma does not cause excessive protein oxidation.

[0100] Example 5

[0101] Determination of free thiol groups

[0102] Test samples: Soy-based nutritional powders prepared in Examples 1-3 and Comparative Examples 1-5.

[0103] Test method: Add 1 ml of sample solvent to 5 ml of Tris-Gly, then add 40 μl of DTNB (4 mg / ml), and react at room temperature in the dark for 30 min. Measure the absorbance of the reactants at 412 nm using a UV-Vis spectrophotometer. The reactants without DTNB serve as the control group. Lipid oxidation produces ROS, which extract hydrogen atoms from the sulfhydryl groups of cysteine, causing protein cross-linking and reducing sulfhydryl content.

[0104] C SH = 73.53 × A 412 × D / C

[0105] C SH The free thiol content is expressed in μmol / mg.

[0106] A 412 The absorbance value is for the 412 nm sample.

[0107] D represents the dilution factor.

[0108] C represents the protein concentration of the sample (mg / mL).

[0109] Figure 2 This is a graph showing the free thiol content of Examples 1-3 and Comparative Examples 1-5. Figure 2 Comparative Example 5 had the lowest free thiol content, at 4.2 μmol / mg. Comparative Example 4 had the highest free thiol content, at 13 μmol / mg. Examples 1, 2, and 3 had moderate free thiol content, around 6 μmol / mg, indicating a moderate degree of oxidation.

[0110] Example 6

[0111] Solubility determination

[0112] Test samples: Soy-based nutritional powders prepared in Examples 1-3 and Comparative Examples 1-5.

[0113] Test method: Prepare a 1 mg / ml solution using phosphate buffer (10 mmol / L pH 7.4). Determine the protein content in the supernatant using the BCA method. Dissolve the sample solution in 2 mol / L NaOH and determine the total protein content.

[0114] Solubility (%) = N1 / N0 × 100

[0115] N0: Total protein content.

[0116] N1: Protein content in the supernatant. Unit: mg / ml.

[0117] Figure 3 This diagram illustrates the solubility of Examples 1-3 and Comparative Examples 1-5. Protein solubility is closely related to its functional properties. Compared to Comparative Examples 1-5, Examples 1, 2, and 3 exhibit higher solubilities (82%, 80%, and 79%, respectively), indicating that moderate oxidation caused by heating linoleic acid combined with cold plasma is beneficial for improving protein solubility. Comparative Example 4 shows the lowest solubility at 42%, indicating that the solubility of untreated soybean protein is significantly lower than that of soybean protein treated with linoleic acid heating combined with cold plasma. Comparative Example 5 shows lower solubility than the Examples 1-3, indicating that excessive oxidation leads to a decrease in solubility.

[0118] Furthermore, the solubility of chickpea nutritional powder treated with linoleic acid heating combined with cold plasma (prepared using the same method as in Example 1, except that soybeans were replaced with chickpeas) was 68%, which was lower than the solubility of soybean protein under the same treatment. This experiment shows that linoleic acid heating combined with cold plasma treatment increases the solubility of soybean protein, which is beneficial to the utilization of soy milk powder.

[0119] Example 7

[0120] Antioxidant assay

[0121] Test samples: Sample solutions of soybean-based nutritional powders prepared in Examples 1-3 and Comparative Examples 1-4 after in vitro enteric digestion, and sample solutions of chickpea nutritional powders treated with linoleic acid heating and cold plasma after in vitro enteric digestion.

[0122] Test method: A sample solution (0.5 mg / ml, 2 ml) after in vitro enteric digestion was incubated with an equal volume of DPPH solution (0.08 mmol / L) in the dark at 25°C for 30 min. The absorbance of the resulting solution was measured at 517 nm. DPPH free radical scavenging rate (%) = [1 - (A... i -A j ) / A c ] × 100%. A i : Absorbance of the sample solution after adding DPPH. A j : Absorbance of the sample solution. A c : Absorbance of DPPH solution.

[0123] Add 7 mmol / L ABTS and 2.45 mmol / L potassium persulfate to 4 ml of deionized water and dilute 40-fold in the dark for 8-12 hours to obtain an ABTS solution. Mix 4 ml of the ABTS solution with 50 μl of the sample solution in the dark for 10 minutes. Measure the absorbance of the resulting solution at 734 nm. Deionized water was used as a blank. ABTS free radical scavenging rate (%) = [1-(A i -A j ) / A c ] × 100%. A i : Absorbance of the sample solution after adding ABTS. A j : Absorbance of the sample solution. A c : Absorbance of ABTS solution.

[0124] Figure 4 The graph shows the DPPH free radical scavenging rates of Examples 1-3 and Comparative Examples 1-4. Compared with Comparative Examples 1-4, Examples 1, 2, and 3 have higher DPPH values ​​(i.e., DPPH free radical scavenging rates), at 78%, 76%, and 75%, respectively, indicating that the moderate oxidation caused by linoleic acid heating combined with cold plasma is beneficial to increasing the DPPH value of proteins. Comparative Example 4 has the lowest DPPH value at 44%, indicating that the DPPH value of untreated soybean protein is much lower than that of soybean protein treated with linoleic acid heating combined with cold plasma.

[0125] Figure 5 The figures show the ABTS values ​​for Examples 1-3 and Comparative Examples 1-4. Example 1 showed the highest ABTS value (i.e., ABTS radical scavenging rate) at 69%. The ABTS values ​​for Examples 1, 2, and 3 were similar, at 69%, 68%, and 67.5%, respectively. Comparative Example 4 showed the lowest ABTS value at 30%, indicating that the ABTS value of untreated soybean protein was significantly lower than that of soybean protein treated with linoleic acid heating combined with cold plasma.

[0126] For soybean protein, after linoleic acid heating combined with cold plasma treatment (Example 1), compared with untreated soybean protein (Comparative Example 4), its DPPH and ABTS values ​​increased by 34% and 39%, respectively (data from Example 1 minus data from Comparative Example 4). For chickpea protein, after linoleic acid heating combined with cold plasma treatment (soybeans were replaced with chickpeas in Example 1, and the preparation process was the same as described in Example 1), its DPPH and ABTS values ​​increased by 25% and 30%, respectively, compared with untreated chickpea protein (soybeans were replaced with chickpeas in Comparative Example 4, and the preparation process was the same as described in Comparative Example 4). It is evident that the effect of linoleic acid heating combined with cold plasma treatment on antioxidant properties is also related to the type of protein, and the modification of soybean protein by linoleic acid heating combined with cold plasma treatment has a more significant effect on improving the final antioxidant properties.

[0127] Example 8

[0128] Comparison of solubility and antioxidant capacity under the same degree of oxidation

[0129] Prepare soybean-based nutritional powders with the same degree of oxidation, either heat-induced linoleic acid treatment only or cold plasma treatment only.

[0130] The preparation of the soy-based nutritional powder treated only with heat-induced linoleic acid was basically the same as in Comparative Example 2, except that the amount of linoleic acid added was 12% and the linoleic acid treatment time was extended to 40 min. Carbonyl and free thiol groups were determined according to Examples 4 and 5, respectively, with results of 7.4 nmol / mg and 5.9 μmol / mg, which are comparable to the carbonyl and free thiol group determination results of 7.5 nmol / mg and 6 μmol / mg in Example 1.

[0131] The preparation of soy-based nutritional powder with only cold plasma treatment was basically the same as in Comparative Example 3, except that the voltage was increased to 25 kV and the plasma treatment time was extended to 200 min. Carbonyl and free thiol groups were determined according to Examples 4 and 5, respectively, with results of 7.3 nmol / mg and 5.8 μmol / mg, which are comparable to the carbonyl and free thiol group determination results of 7.5 nmol / mg and 6 μmol / mg in Example 1.

[0132] Solubility tests were conducted according to Example 6. The results for soy-based nutritional powder treated with only heat-induced linoleic acid and soy-based nutritional powder treated with only cold plasma were 50% and 48%, respectively, which were inferior to those of Example 1. It can be seen that the solubility of soy-based nutritional powder treated with only heat-induced linoleic acid or only cold plasma with the same degree of oxidation is not as good as that of Example 1.

[0133] Antioxidant properties were tested according to Example 7. The DPPH values ​​of the soybean-based nutritional powder treated with only heat-induced linoleic acid and the soybean-based nutritional powder treated with only cold plasma were 53% and 55%, respectively. The ABTS values ​​of the soybean-based nutritional powder treated with only heat-induced linoleic acid and the soybean-based nutritional powder treated with only cold plasma were 52% and 48%, respectively. It can be seen that the antioxidant properties of soybean-based nutritional powder treated with only heat-induced linoleic acid or only cold plasma with the same degree of oxidation are not as good as those in Example 1.

[0134] Finally, it should be noted that the above embodiments do not limit the present invention in any way. Those skilled in the art can make modifications and improvements based on the present invention.

Claims

1. A method for preparing a soybean-based nutritional powder rich in linoleic acid with moderate protein oxidation, characterized in that, Includes the following steps: Linoleic acid is added to soy milk, and the mixture is then heated and treated with cold plasma. After homogenization, concentration, and drying, a soy-based nutritional powder rich in linoleic acid with moderate protein oxidation is obtained. After adding linoleic acid, heating and cold plasma treatment are carried out simultaneously, but the heating time is shorter than the cold plasma treatment time. The amount of linoleic acid added is 7-10%; the heating temperature is 40-50℃, and the heating time is 15-20min; for cold plasma treatment, the voltage is 10-18KV, the treatment time is 90-150min, and the power is 45-55W.

2. The method for preparing a moderately oxidized, linoleic acid-rich soybean-based nutritional powder according to claim 1, characterized in that, Includes the following steps: 1) Prepare soybean flour to form soy milk, then add honey, xanthan gum, sodium polyacrylate, lecithin, and vanilla syrup; 2) Linoleic acid is added and the mixture is heated and subjected to cold plasma treatment to obtain processed soy milk; 3) After homogenization, concentration and drying, a soybean-based nutritional powder rich in linoleic acid with moderate protein oxidation is obtained.

3. The method for preparing a moderately oxidized protein-rich linoleic acid-based nutritional powder according to claim 2, characterized in that, The steps for preparing soybean flour are as follows: Soybeans and water are mixed at a mass ratio of 1:9-11 and soaked for 10-14 hours, then washed; the soybeans are ground into powder using a high-speed blender at 20000-40000r / min to obtain soybean flour.

4. The method for preparing a moderately oxidized protein-rich linoleic acid-based nutritional powder according to claim 2, characterized in that, The process of making soy milk is as follows: Soy flour and water are mixed at a mass ratio of 1:9-11, and the mixture is steamed at 90-110℃ with constant stirring to form soy milk; the soy milk is filtered to separate the soy milk from the residue; and the pH of the soy milk is adjusted to 6.0-6.

5.

5. The method for preparing a moderately oxidized, linoleic acid-rich soybean-based nutritional powder according to claim 2, characterized in that, Add 4-6 wt% honey, 0.05-0.15 wt% xanthan gum, 0.05-0.2 wt% sodium polyacrylate, 0.03-0.07 wt% lecithin, and 0.5-1.5 wt% vanilla syrup to the soy milk.

6. The method for preparing a moderately oxidized protein-rich linoleic acid-based nutritional powder according to claim 1, characterized in that, Two-stage homogenization is used. The first-stage high-pressure homogenization is set with a homogenization pressure of 20-30 MPa and a processing time of 5-10 minutes. The second-stage low-pressure homogenization is set with a homogenization pressure of 10-15 MPa and a processing time of 3-5 minutes.

7. The method for preparing a moderately oxidized, linoleic acid-rich soybean-based nutritional powder according to claim 1, characterized in that, During concentration, the vacuum level is 82.6-98.6 kPa, the temperature is 45-55℃, and the steam pressure is less than 196 kPa.

8. The method for preparing a moderately oxidized, linoleic acid-rich soybean-based nutritional powder according to claim 1, characterized in that, Low-temperature spray drying is adopted, with the inlet air temperature set at 150-170℃, the outlet air temperature controlled at 80-90℃, and the feed concentration adjusted to 25-40%. The feed concentration refers to the mass fraction of solid components in the processed soy milk. The atomization speed is in the range of 250-300r / s.

9. A moderately oxidized, linoleic acid-rich soybean-based nutritional powder prepared by the preparation method according to any one of claims 1-8.

10. The application of the preparation method according to any one of claims 1-8 in the preparation of linoleic acid-rich soybean-based nutritional powder.

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