Modified lipid-gluten protein mixture, preparation method and application thereof, frozen dough for baked food and preparation method of frozen dough

Abstract

The invention relates to the technical field of food processing, in particular to a modified lipid gluten protein mixture, a preparation method and application thereof, frozen dough for baking food and a preparation method of the frozen dough. The preparation process of the modified lipid gluten protein mixture comprises the following steps: mixing wheat flour with water to form a dough, washing with water, freeze-drying, and crushing; preliminarily and uniformly mixing gluten protein with water; adding lipid under stirring, and uniformly mixing to obtain a mixture M; treating the mixture M in a low-frequency alternating magnetic field, and then freeze-drying, dehydrating and crushing the mixture M to obtain a finished product. When the prepared modified lipid gluten protein mixture is applied to preparation of frozen dough for food baking, the frozen dough not only has the function similar to the function of adding grease without containing exogenous grease (vegetable oil), but also has the advantages that the network structure of gluten protein of the obtained frozen dough is stable, the anti-freezing capability is enhanced, and the frozen dough has a good anti-freezing effect. Therefore, the frozen dough has a soft internal structure and keeps good elasticity and water holding capacity.

Description

Technical Field

[0001] The present application relates to the field of food processing technology, and in particular to a modified lipid-gluten protein mixture and a preparation method and application thereof, and a frozen dough for baked food and a preparation method thereof. Background Art

[0002] Baked food is a popular food among the general public and is one of the most important application areas of wheat, and bread is the most representative product of baked food. As one of the oldest staple foods of mankind, bread has become an indispensable part of global food culture with its diverse forms and flavors. It is made from wheat flour as the main raw material and is made through fermentation, baking and other processes. It not only provides rich carbohydrates, but also presents a unique flavor and texture due to various chemical changes (such as Maillard and glycosylation reactions) during the production process.

[0003] The production of bread is inseparable from the gluten protein in wheat flour, which gives the dough elasticity and toughness, allowing the bread to expand during the fermentation process and form a soft internal structure. In order to control the quality of the final product, it is often necessary to add some raw materials to achieve this goal.

[0004] Among them, oil is an indispensable raw material in the processing of baked goods, especially bread and cakes. It improves the overall quality of baked goods by improving taste, flavor and appearance. However, chronic diseases such as cardiovascular disease, diabetes, hyperlipidemia, and hypertension caused by obesity have seriously threatened human health. However, the per capita fat intake in my country is significantly exceeded. Therefore, excessive intake of oil and the type of edible oil have always been the focus of the National Nutrition Society. In the process of baking, oil with triglycerides as the main component is often added to improve the quality, but at the same time, triglycerides will also inhibit the formation of gluten protein network structure and reduce its stability. Therefore, whether there are other substitutes in the field that can improve the viscoelasticity of dough and play a role similar to oil (triglycerides) by changing the secondary structure of gluten protein? Further exploration is needed.

[0005] Frozen dough has been around since the 20th century. Today, frozen dough is the most widely used raw material in bread production in Europe and the United States, and is favored by many bakery stores and convenience stores because it can improve production efficiency and reduce production costs. It can also promote the development of the Chinese fast food industry and bring considerable economic benefits to food companies.

[0006] However, the disadvantage is that, compared with freshly made dough on-site, the quality of products produced by the frozen dough technology deteriorates, and problems such as cracking, epidermal collapse, discoloration, small volume, and hard texture are likely to occur. This is because water is added during the dough preparation process, and the water absorbed by the key components of wheat forms ice crystals during the freezing process, filling the gluten network structure. The volume of the ice crystals continuously increases with the increase of the frozen storage time, damaging the gluten network structure, which is the key reason for the decline in the quality of frozen dough. Moreover, after the ice crystals recrystallize, they will have an extrusion and damaging effect on the gluten network. Therefore, at low temperatures, the depolymerization of gluten proteins into polymers occurs, and the reduction of properties such as water-holding capacity and viscoelasticity limits the wide application of frozen dough.

[0007] Therefore, in this field, there is an urgent need to develop a certain technology that can maintain the overall quality of baked goods with low or no oil addition, while regulating the network structure of gluten proteins to make the dough form a soft internal structure, and improving the structural stability of the dough at low temperatures (such as maintaining good water-holding capacity and other properties), and overcoming the adverse effects of low temperature on its quality. Summary of the Invention

[0008] To solve the problems mentioned in the above-mentioned background art in the prior art, the present application provides the following technical solutions: The present application provides a method for preparing a modified lipid gluten protein mixture, which comprises the following steps: Gluten protein extraction: After mixing wheat flour and water into a dough, wash away the starch part in the dough with water to obtain gluten protein with a certain color; then freeze-dry and pulverize for standby; Lipid mixing: Under dynamic stirring, preliminarily mix the gluten protein and water; then add lipids under stirring and mix evenly until the lipids are completely absorbed by the gluten protein to obtain a mixture M; wherein, the lipid is one or a combination of fatty acids, monoglycerides, diglycerides, vegetable oils, and the mass of the lipid is 1% - 10% of the mass of the gluten protein; Low-frequency alternating magnetic field treatment: Place the mixture M in a low-frequency alternating magnetic field for treatment, and then freeze-dry and dehydrate the mixture M and pulverize it to obtain the modified lipid gluten protein mixture; wherein, the intensity of the low-frequency alternating magnetic field is 3 - 7 mT.

[0009] In some embodiments, in the gluten protein extraction step, wheat flour and water are mixed into a dough at a mass ratio of (2-3):1; the starch part in the dough is washed away with water, wherein the mass ratio of the washing water to the dough is 1:30-1:45; in the lipid mixing step, under dynamic stirring, the gluten protein and water are preliminarily mixed evenly at a mass ratio of 1:0.95-1:1.25, and then lipids are added under high-speed stirring and mixed evenly until the lipids are completely absorbed by the gluten protein to obtain mixture M; in the low-frequency alternating magnetic field treatment step, the mixture M is placed in a low-frequency alternating magnetic field for treatment for (1-2) h.

[0010] In some embodiments, the fatty acids include one or more combinations of stearic acid, palmitic acid, and oleic acid; the monoglycerides include one or more combinations of stearic acid monoglyceride, palmitic acid monoglyceride, and oleic acid monoglyceride; the diglycerides include one or more combinations of oleic acid diglyceride, palmitic acid diglyceride, and stearic acid diglyceride; the vegetable oils include one or more combinations of rapeseed oil, soybean oil, and shortening.

[0011] In some embodiments, the lipid is oleic acid.

[0012] In some embodiments, the lipid is oleic acid, the mass of the oleic acid is 5% of the mass of the gluten protein, and the intensity of the low-frequency alternating magnetic field is 5 mT; In some embodiments, the lipid is monoglyceride, the mass of the monoglyceride is 5% of the mass of the gluten protein, and the intensity of the low-frequency alternating magnetic field is 5 mT.

[0013] The present application also provides a modified lipid gluten protein mixture prepared by the preparation method described above.

[0014] The present application also provides an application of the modified lipid gluten protein mixture in making frozen dough, characterized in that: the modified lipid gluten protein mixture is prepared by the preparation method described above.

[0015] The present application also provides a preparation method of a frozen dough for baked foods, which includes the following preparation steps: fully mixing the modified lipid gluten protein mixture and starch evenly, then adding water and yeast, and stirring until a uniform dough is formed; finally, storing it in an environment of (-16 to -20) °C to obtain the frozen dough; wherein, the modified lipid gluten protein mixture is prepared by the preparation method described above.

[0016] In some embodiments, in the step of preparing the frozen dough, the mass ratio of the modified lipid gluten protein mixture to the starch is 12:88 to 15:85; the mass of the yeast is (2-5)% of the mass of the modified lipid gluten protein mixture; wherein, the starch is one or a combination of corn starch, wheat starch, and potato starch.

[0017] The present application also provides a frozen dough for baked foods, which is prepared by the preparation method described above.

[0018] Based on the above, compared with the prior art, the preparation method of the modified lipid gluten protein mixture provided by the present application has the following technical principles and effects: The solution of the present application provides a method that can improve the processing properties of gluten proteins. The prepared modified lipid gluten protein mixture, when applied to the preparation of frozen dough for food baking, not only enables the frozen dough to have functions similar to those with added oil in the absence of oil, but also makes the network structure of the gluten proteins in the obtained frozen dough stable and the anti-freezing ability enhanced, so that the frozen dough has a soft internal structure and maintains good elasticity and water-holding capacity, is suitable for processing into healthier flour-based foods, and expands the types of frozen dough.

[0019] Other features and beneficial effects of the present application will be described in the subsequent specification, and part of them will become obvious from the specification or be understood by implementing the present application. The objectives and other beneficial effects of the present application can be achieved and obtained through the content shown in the specification, claims, and drawings. Description of the Drawings

[0020] Figure 1 It is a diagram of the secondary structure detection results of the experimental group samples; wherein Figure 1 (a) is an infrared spectrogram, Figure 1 (b) is the secondary structure of the protein; Figure 2 It is a diagram of the X-ray diffraction results of the experimental group samples; Figure 3 It is a fluorescence spectrogram and an ultraviolet-visible absorption spectrum of the experimental group samples; wherein Figure 3 (a) is a fluorescence spectrogram, Figure 3 (b) is an ultraviolet-visible absorption spectrum; Figure 4 It is a diagram of the results of the rheological behavior of the experimental group samples, Figure 4 (a) represents the creep characteristics of gluten proteins, Figure 4 (b) represents the elastic modulus of gluten proteins under temperature scanning, Figure 4 (c) represents the viscous modulus of gluten proteins under temperature scanning; Figure 5It is a diagram of molecular simulation docking of the experimental group samples, where Figure 5 (a) is the diagram of molecular simulation docking of different lipids with high molecular weight gliadin samples, Figure 5 (b) is the diagram of molecular simulation docking of different lipids with low molecular weight glutenin, Figure 5 (c) is the diagram of molecular simulation docking of different lipids with high molecular weight glutenin. Specific implementation manners

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application; the technical features designed in different implementation manners of the present application described below can be combined with each other as long as they do not conflict with each other; based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0022] In the description of the present application, it should be noted that all terms (including technical terms and scientific terms) used in the present application have the same meanings as those generally understood by those of ordinary skill in the art to which the present application belongs, and should not be construed as a limitation to the present application; it should be further understood that the terms used in the present application should be understood as having meanings consistent with their meanings in the context of this specification and the relevant art, and should not be understood in an idealized or overly formal sense, unless otherwise clearly defined in the present application.

[0023] The present application provides the following experiments to verify the effects of the solutions of the present application: 1. Experimental process: Explore the influence of glycerolipid types on the elasticity of gluten proteins (1) Extraction of gluten proteins: After mixing wheat flour and water in a mass ratio of 2:1 into a dough, add water in a mass ratio of 1:35 to wash away the starch part, obtain gluten proteins with a certain color, and then freeze-dry and pulverize for standby; (2) After preliminarily mixing gluten proteins and water in a ratio of 1:1.1 under dynamic stirring, add fatty acids (stearic acid, oleic acid), monoglycerides, diglycerides, and vegetable oil (soybean oil) in a mass ratio of 5% respectively under the condition of high-speed stirring, and mix until the lipids are completely absorbed by the gluten proteins, and then freeze-dry to obtain gluten protein-lipid complexes.

[0024] The elasticity of the dough is an important indicator to measure the gel structure and represents the stability of the gel network structure. Elasticity tests were performed on the samples prepared above, and the results are shown in Table 1: Table 1 Effects of Glycerolipid Types on the Elasticity of Gluten Proteins

[0025] Through the above elasticity tests, it was found that when monoglyceride dough, diglyceride dough, stearic acid, and oleic acid were used as lipid additives, the elasticity of the dough remained at a relatively good level. Among them, stearic acid and oleic acid could significantly improve the elasticity of gluten, indicating that their interaction with gluten proteins strengthened the network structure of gluten proteins.

[0026] Explore the Effects of Glycerolipid Dosages on the Elasticity of Gluten Proteins (1) Extraction of gluten proteins: After kneading wheat flour and water in a mass ratio of 2:1 into a dough, the starch part was washed away by adding water in a mass ratio of 1:35 to obtain gluten proteins with a certain color. Then, they were freeze-dried and pulverized for standby. (2) Under dynamic stirring, gluten proteins and water were preliminarily mixed in a ratio of 1:1.1, and then fatty acids (stearic acid, palmitic acid, oleic acid), monoglycerides, diglycerides, and vegetable oils (rapeseed oil, soybean oil) with mass ratios of 2.5% - 10% were added respectively under high-speed stirring conditions. The mixture was stirred until the lipids were completely absorbed by the gluten proteins, and then freeze-dried to obtain gluten protein-lipid complexes.

[0027] Elasticity tests were conducted on the samples prepared above, and the results are shown in Table 2.

[0028] Table 2 Effects of Glycerolipid Dosages on the Elasticity of Gluten Proteins

[0029] Elasticity characterization: The data results in Table 2 show that although the elasticity of gluten proteins decreased with the increase in the dosage of exogenous lipids, oleic acid and stearic acid could still significantly improve the elasticity of gluten proteins at a 10% addition level, indicating that oleic acid and stearic acid could strengthen the cross-linking of the gluten protein network structure and make the dough form a soft internal structure.

[0030] The samples prepared above were characterized for the following items, and the results are as Figures 1 - 5 shown.

[0031] (1) Secondary structure (infrared spectroscopy analysis) As Figure 1 shown, the addition of lipids changed the secondary structure of gluten proteins, and different types of lipid additives had different effects. Among them, oleic acid could significantly increase the proportion of α-helices in gluten proteins, and α-helices are closely related to the structural stability of gluten proteins.

[0032] (2) X-ray diffraction As Figure 2As shown, significant crystal diffraction peaks are exhibited at approximately 2θ = 9.8° and 20°, corresponding to the characteristic peaks of α-helix and β-sheet in the secondary structure of proteins, respectively. Adding a 2.5% dose of lipid does not significantly affect the crystal structure of gluten proteins, while a 10% dose of lipid significantly changes the crystal structure, increasing the peak intensity at 2θ = 20°.

[0033] (3)Spectroscopy As Figure 3 shown, characteristic peaks corresponding to the π-π* transitions of C=O in peptide bonds and aromatic amino acid side chains (such as tryptophan (Trp), tyrosine residues (Tyr), and phenylalanine (Phe), etc.) appear near 225 nm and 278 nm for all gluten protein samples. The addition of exogenous lipids reduces the intensities of the characteristic peaks near 225 nm and 278 nm. This may be because exogenous lipids cause changes in the protein spatial structure, and some amino acid residues that were originally in the hydrophobic environment of the protein molecule are not exposed on the protein molecule surface, exacerbating the concealment of aromatic amino acids.

[0034] (4)Rheology Generally, materials with the largest creep compliance have the lowest stiffness, indicating poor resistance to permanent deformation. As Figure 4 shown, compared with gluten proteins without adding exogenous lipids, the addition of oleic acid results in a decrease in the creep compliance of gluten proteins, indicating that oleic acid improves the strength of gluten proteins.

[0035] (5)Molecular simulation docking Figure 5 The four diagrams in (a) show the molecular simulation docking of different lipid molecules with gliadin samples. From left to right, they represent the binding mechanisms of oleic acid, monoolein (a typical representative of monoglycerides), diolein (a typical representative of diglycerides), and triolein (a typical representative of vegetable oils) with gliadin; Figure 5 The four diagrams in (b) show the molecular simulation docking of different lipid molecules with low-molecular-weight glutenin molecules. From left to right, they represent the binding mechanisms of oleic acid, monoolein, diolein, and triolein with low-molecular-weight glutenin; Figure 5 The four diagrams in (c) show the molecular simulation docking of different lipids with high-molecular-weight glutenin molecules. From left to right, they represent the binding mechanisms of oleic acid, monoolein, diolein, and triolein with high-molecular-weight glutenin.

[0036] As Figure 5As shown, the total binding energy of all lipid - proteins (≤ -7 kJ / mol) is negative, indicating good binding between all lipids and gluten protein components. Among them, compared with other oleic acid - rich glycerides, the gliadin - monooleate (-20.6 kJ / mol), LMW - GS - trioleate (-14.7 kJ / mol), and HMW - GS - monooleate (-15.4 kJ / mol) systems exhibit the highest binding energy. Although theoretically, from the binding energy data shown by molecular docking, the three lipids other than oleic acid perform better. However, in essence, the binding energy of oleic acid is also excellent, and from a comprehensive analysis of various properties during practical application (such as the elastic effect on gluten proteins), the overall effect of oleic acid application is better. This may be due to more complex interactions in real conditions compared to simulation conditions.

[0037] Therefore, in summary, oleic acid can be considered as a preferred choice in the selection of lipid additives.

[0038] Exploring the effect of low - frequency alternating magnetic field treatment on the properties of gluten proteins (1) Extraction of gluten proteins: After mixing wheat flour and water in a mass ratio of 2:1 to form a dough, then washing away the starch part by adding water in a mass ratio of 1:35 to obtain gluten proteins with a certain color, and then freeze - drying and pulverizing for standby; (2) Under dynamic stirring, gluten proteins and water are preliminarily mixed in a mass ratio of 1:1.1, and then 5% by mass of oleic acid is added respectively under high - speed stirring conditions, and mixed until the lipid is completely absorbed by the gluten proteins to obtain a gluten protein - lipid complex.

[0039] (3) Treat the gluten protein - lipid mixture with low - frequency alternating magnetic fields of different intensities (0, 3, 5, or 7 mT) for 1 h to further regulate the secondary structure of gluten proteins. Then freeze - dry and dehydrate the mixture and pulverize it to obtain a modified lipid - gluten protein mixture.

[0040] The prepared samples are tested for disulfide bond content and water - holding capacity, and the results are shown in Table 3: Table 3 Effect of low - frequency alternating magnetic field intensity treatment on the properties of gluten proteins

[0041] Sulfur elements in wheat gluten proteins mainly exist in the form of disulfide bonds, which endow gluten proteins with a unique network structure. SH oxidation and the exchange reaction with S - S bonds are the two major mechanisms for the formation of S - S bonds. The formation of S - S bonds gathers amino acid residues in different parts of the same peptide chain or different peptide chains, making the arrangement of protein molecules in the formed network structure more orderly, thus stabilizing the conformation of proteins.

[0042] Before freeze-drying, the dough of the present application was pretreated with a low-frequency alternating magnetic field of a specific intensity for 1 h. From the above test results, it can be seen that the low-frequency alternating magnetic field slightly reduced the disulfide bond content of gluten protein, but the treatment with a magnetic field of moderate intensity significantly improved the water-holding capacity of gluten protein.

[0043] The low-frequency alternating magnetic field is a new non-thermal processing technology (frequency < 300 kHz). The magnetic field affects the migration of charged proteins by inducing radiative energy transitions, thereby changing protein properties. However, during frozen storage, frozen dough often suffers from the weakening of the gluten protein network structure due to the destruction of ice crystals, resulting in the deterioration of its functional properties such as water-holding capacity. Through the action of the low-frequency alternating magnetic field, while maintaining the disulfide bond content of gluten protein in the dough at a good level and improving the water-holding capacity of gluten protein, the protein network structure will also become more uniform, overcoming the defect that the gluten network structure is damaged at low temperature, resulting in the deterioration of its water-holding capacity and elasticity. Therefore, it will have potential application prospects in frozen dough.

[0044] The present application controls the intensity of the low-frequency alternating magnetic field at 3 - 7 mT to obtain better comprehensive effects. If the intensity is lower than the limited range, the magnetic field effect is not ideal. However, the higher the intensity is not necessarily better. When it is higher than the limited range, while the disulfide bond content decreases, the water-holding performance also deteriorates.

[0045] Explore the effects of modified lipid gluten protein mixtures prepared by different preparation processes on the quality of frozen dough (1) Extraction of gluten protein: After mixing wheat flour and water in a ratio of 2:1 to form a dough, the starch part was washed away by adding water in a ratio of 1:35 to obtain gluten protein with a certain color, and then freeze-dried and pulverized for standby; (2) After initially mixing gluten protein and water in a ratio of 1:1.1 under dynamic stirring, fatty acids (stearic acid, oleic acid), monoglyceride, diglyceride, and soybean oil with a mass ratio of 5% were respectively added under high-speed stirring conditions, and mixed until the lipids were completely absorbed by the gluten protein to obtain a gluten protein-lipid complex.

[0046] (3) Treat the gluten protein-lipid mixture with a low-frequency alternating magnetic field of 5 mT with different intensities to further regulate the secondary structure of gluten protein, and then freeze-dry and dehydrate and pulverize the mixture to obtain a modified lipid gluten protein mixture.

[0047] (4) Mix the above-obtained lipid-gluten protein mixture and corn starch evenly in a mass ratio of 14:86, add an appropriate amount of water, and yeast with a mass ratio of 4%, stir until a uniform dough is formed, and finally store it in a refrigerator at -18°C to obtain frozen dough.

[0048] The samples prepared above were tested, and the results are shown in Table 4 as follows: Table 4 Effects of modified gluten proteins on the properties of frozen dough (frozen dough stored at -18 °C for 14 days)

[0049] The complex chemical reactions occurring among the dough components make the relationship between different treatments and dough quality not a simple linear one. Different treatment processes (with the variables being the types of lipid additives and the action of low-frequency alternating magnetic fields) have different effects on the lipid-gluten protein mixture, and thus different effects on the properties of frozen dough. In this application, exploratory experiments were conducted on what kind of combinations of additive types and low-frequency alternating magnetic field actions are beneficial to achieving better comprehensive effects. Among them, the application lists the combined schemes for achieving better comprehensive performance in Table 4; It can be seen from Table 4 that the two preferred combined design schemes of 5% oleic acid + magnetic field treatment and 5% monoglyceride + magnetic field treatment achieved better comprehensive effects.

[0050] Monoglycerides belong to emulsifiers. Their lipophilic groups and hydrophilic groups can combine with glutenin and gliadin respectively to improve the gas-holding property of the dough. They can also combine with gluten proteins and starches to improve the freeze-thaw stability of the dough, reduce the migration of water. Emulsifiers can also inhibit the retrogradation of starch, reduce the surface tension of water in the dough, and form smaller ice crystal structures, ultimately reducing the damage to the gluten network structure. The combination of specific exogenous lipids and magnetic fields can significantly improve the water-holding capacity of frozen dough. This may be because the synergistic effect of the two promotes the binding strength of proteins, starches and water, reduces the proportion of free water, and thus inhibits the formation of ice crystals.

[0051] In addition, the modified lipid-gluten protein mixture and frozen dough prepared by the application scheme of this application add glycerol lipids, which do not contain oil but have similar functions to those with added oil, specifically reflected in: Compared with the widely used oil as a dough quality improver, adding lipids such as oleic acid or adding lipids such as oleic acid combined with low-frequency magnetic field treatment can improve the elasticity of frozen dough. The relatively high content of disulfide bonds indicates that the above treatments improve the frost resistance of gluten proteins and alleviate the damage to the secondary structure of proteins at low temperatures. It shows that the modified lipid-gluten protein mixture and frozen dough prepared by the application scheme of this application add glycerol lipids, do not contain oil (vegetable oil) but already have similar functions and performance characteristics to those with added oil (vegetable oil).

[0052] 2. The index measurement methods used in this article are as follows: (1) Elasticity: The texture distribution of MP / WM-TS gels was obtained using a texture analyzer (TA XTplus, Stable Micro Systems, Surry, UK) equipped with a probe P / 36R. The gluten protein gels were cut into cylinders with a diameter of 15 mm and a height of 20 mm, and then compressed at a compression degree of 50%. The pre-test and test speeds were both set to 1 mm / s, and the post-test speed was set to 5 mm / s. The trigger type was set to automatic, and the trigger force was 5 g.

[0053] (3) Disulfide bonds: Determined with reference to the method of Gao Xueli (Gao Xueli. Mechanism study on the effects of soybean 7S, 11S globulins and isolated proteins on dough properties and steamed bread quality [D]. Northwest A&F University, 2015.). Take 50 mg of the prepared freeze-dried sample, mix it with 1 mL of Tris-glycine buffer (pH = 8.0), add 4.7 g of guanidine hydrochloride, and make up the volume to 10 mL with the buffer. Measurement of sulfhydryl groups: Add 1 mL of the sample solution to 4 mL of (8 mol / L urea + 5 mol / L guanidine hydrochloride) solution and 0.1 mL of DTNB with a mass concentration of 4 mg / mL. After mixing, perform colorimetry at 412 nm to obtain the absorbance value. Measurement of total sulfhydryl groups: Add 1 mL of the sample solution to 4 mL of (8 mol / L urea + 5 mol / L guanidine hydrochloride) solution, then add 0.1 mL of mercaptoethanol. React at room temperature for 1 h, then add 10 mL of 12% trichloroacetic acid solution, continue to react for 1 h, and then centrifuge at 5000 r / min for 10 min. Pour off the supernatant, wash the precipitate twice with 5 mL of 12% trichloroacetic acid, centrifuge at 5000 r / min for 10 min each time. Then dissolve the precipitate in 10 mL of 8 mol / L urea, add 0.08 mL of DTNB with a mass concentration of 4 mg / mL, and finally take 1 mL of this solution, add 5 mL of buffer solution to it, mix well, and perform colorimetry at 412 nm to obtain the absorbance value.

[0054] (3) Water holding capacity: Mix 2 g of gluten protein with 10 ml of water, put it into a centrifuge tube, record the weight as w1. After centrifugation (3000×g, 10 min), discard the supernatant, and record the weight as W2. The calculation formula for water holding capacity is as follows: Water holding capacity = 100*(W1 - W2) / 2.

[0055] (4) Infrared spectroscopy: Weigh an appropriate amount of freeze-dried and sieved sample. The test parameters are as follows: the wavelength range is 4000–600 cm−1, the resolution is 4 cm-1, the total number of scans is 32 times, and the secondary structure of the sample is analyzed by peakfit4.2 software. (5) X-ray diffraction: The crystal structure of the sample was determined using an X-ray diffractometer. The test conditions were as follows: The diffraction condition was a copper target, the voltage was 40 kV, the current was 40 mA, and CuKα radiation was used. The measurement angle 2θ was 4 - 40 °, the step size was 0.02, and the scanning speed was 2 ° / min. The crystallinity was calculated using Origin 2019 software.

[0056] (6) Ultraviolet-visible absorption spectroscopy: 0.1 g of the sample was weighed and dispersed in 20 mL of 0.01 M phosphate buffer solution (pH 7.2). After stirring for 30 min, it was centrifuged (3000 ×g, 10 min). The supernatant was taken and placed in a quartz cuvette, and scanned using a TU-1950 double-beam ultraviolet-visible spectrophotometer (Beijing Purkinje General Instrument Co., Ltd.) at 25 °C with a scanning rate of 50 nm / min.

[0057] (7) Intrinsic fluorescence spectroscopy: 10 mg of gluten protein was weighed and dispersed in 10 mL of 0.05 M acetic acid solution under stirring conditions. After continuing to stir for 2 h, the mixture was centrifuged at 10000 ×g for 20 min at 4 °C, and then the fluorescence characteristics of the gluten protein solution were measured using a fluorescence spectrophotometer. The emission wavelength was set to 290 - 500 nm, the excitation wavelength was 280 nm, the excitation slit and emission slit widths were both 5 nm, the voltage was 400 V, and the scanning speed was 240 nm / min.

[0058] (8) Rheology: Stress relaxation test: The stress relaxation test of the gluten protein sample was carried out in the stress relaxation mode on a rheometer using a PP25 probe in the single compression measurement mode.

[0059] Temperature scan: The rheological behavior of gluten protein during heating and cooling processes was measured. The test parameters were a strain of 1% and a frequency of 1 Hz. The test temperature range during the heating process was 25 °C - 95 °C; the temperature range during the cooling process was 95 °C - 25 °C. The heating / cooling rate was 2 °C / min.

[0060] (9) Molecular simulation docking: The amino acid sequences of gliadin (A27319), low molecular weight glutenin (LMW-GS) (CAA27052.1), and high molecular weight glutenin (HMW-GS) (ACF93467.1) were retrieved from the NCBI database. Since low-confidence regions were detected in the predictions of AlphaFold3, AlphaFold2, RoseTTAFold2, and iTASSER, the three-dimensional (3D) structures of gliadin, LMW-GS, and HMW-GS were obtained using "AlphaFlow". The SAVES v6.1 program was used to evaluate the quality of the final refined model.

[0061] In addition, it should be noted that the "low frequency" in the low-frequency alternating magnetic field described in this application refers to a magnetic field frequency < 100 kHz. And the magnetic field frequency selected for the experimental group in this application is 80 kHz.

[0062] In summary, the solution provided by this application has at least the following design concepts and beneficial effects: Baked goods are wheat foods deeply loved by residents. In order to improve the processing characteristics of dough and the flavor and appearance of the final product, a certain dose of oil needs to be added during the processing. However, a high dose of oil will inhibit the formation and stability of the three-dimensional network structure of gluten proteins. And when producing frozen dough in the prior art, at low temperatures, the gluten proteins depolymerize, and properties such as water-holding capacity and viscoelasticity decrease, thus restricting the wide application of frozen dough.

[0063] To improve or solve the above-mentioned problems, this application has developed a chemical combined with physical dual-regulation technology. First, a lipid gluten protein mixture that does not contain oil but has a function similar to that of added oil and is more in line with the health concept is prepared. Then, combined with the low-frequency alternating magnetic field treatment technology, the secondary structure of gluten proteins is regulated to improve its storage stability during low-temperature storage, and a modified lipid gluten protein mixture is obtained. Applying this modified lipid gluten protein mixture to the preparation of frozen dough, the types of frozen dough that can be developed: The solution of this application can improve the processing characteristics of gluten proteins. When the prepared modified lipid gluten protein mixture is applied to the preparation of frozen dough for food baking, the frozen dough not only has a function similar to that of added oil without containing oil, but also the network structure of the gluten proteins in the obtained frozen dough is stable, the anti-freezing ability is enhanced, making the frozen dough have a soft internal structure and maintain good elasticity and water-holding capacity, and is suitable for processing into healthier wheat-based foods.

[0064] Among them, in the process scheme for preparing the modified lipid gluten protein mixture in this application, the core design points lie in these two steps: lipid mixing and low-frequency alternating magnetic field treatment: (1) In the solution of this application, the lipid is selected from one or a combination of fatty acids, monoglycerides, diglycerides, and vegetable oils. A mixture is formed by mixing lipids of specific types and proportions with gluten proteins, and the mixture before frozen storage is treated by low-frequency alternating magnetic field treatment with specific parameters to regulate the secondary structure of gluten proteins. After subsequent freezing treatment, the frozen dough not only has a function similar to that of added oil without containing oil, but also the network structure of the gluten proteins in the obtained frozen dough is stable, and the anti-freezing ability is enhanced.

[0065] The above extraction steps are all indispensable. Without the addition of lipids and the treatment with a low-frequency alternating magnetic field, the effects required by this application cannot be obtained. Moreover, this application also optimizes the combined design of lipids and a low-frequency alternating magnetic field, and pre-selects two preferred combined design schemes: treatment with 5% oleic acid + treatment with a low-frequency alternating magnetic field and treatment with 5% monoglyceride + treatment with a low-frequency alternating magnetic field.

[0066] (2) This application designs a mixing step of specific types and proportions of lipids and a cooperation with a low-frequency alternating magnetic field treatment with specific parameters, and short-time regulation treatment of the dough composition is carried out before the dough is frozen, without the need for low-frequency alternating magnetic field treatment during freezing, with higher overall efficiency and lower energy consumption.

[0067] It should be noted that: In this article, "~" is used to represent a numerical range, and both endpoint values are included within the represented range.

[0068] In addition, those skilled in the art should understand that although there are many problems in the prior art, each embodiment or technical solution of this application can be improved in only one or several aspects, without having to solve all the technical problems listed in the prior art or the background art at the same time. Those skilled in the art should understand that content not mentioned in a claim should not be regarded as a limitation to that claim.

[0069] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them; although this application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a modified lipid gluten protein mixture, characterized in that: The following steps are involved: Gluten protein extraction: After wheat flour and water are mixed into a dough, the starch part in the dough is washed away with water to obtain gluten protein with a certain color; then freeze-dried and crushed for later use; Lipid mixing: preliminarily mixing the gluten protein and water under dynamic stirring; then adding lipid under stirring, mixing evenly until the lipid is completely absorbed by the gluten protein, to obtain a mixture M; wherein the lipid is one or more combinations of fatty acids, monoglycerides, diglycerides, and vegetable oils, and the mass of the lipid is 1% to 10% of the mass of the gluten protein; Low-frequency alternating magnetic field treatment: placing the mixture M in a low-frequency alternating magnetic field for treatment, and then freeze-drying, dehydrating and crushing the mixture M to obtain the modified lipid gluten protein mixture; wherein the intensity of the low-frequency alternating magnetic field is 3 to 7 mT.

2. The method for preparing the modified lipid gluten protein mixture according to claim 1, characterized in that: In the gluten protein extraction step, wheat flour and water are mixed into a dough in a mass ratio of (2-3):1; starch in the dough is washed with water, wherein the mass ratio of washing water to dough is 1:30-1:45; In the lipid mixing step, the gluten protein and water are preliminarily mixed at a mass ratio of 1:0.95 to 1:1.25 under dynamic stirring, and then lipid is added under high-speed stirring and mixed evenly until the lipid is completely absorbed by the gluten protein to obtain a mixture M; In the low-frequency alternating magnetic field treatment step, the mixture M is placed in a low-frequency alternating magnetic field for treatment for (1 to 2) hours.

3. The method for preparing the modified lipid gluten protein mixture according to claim 1, characterized in that: The fatty acid includes one or more combinations of stearic acid, palmitic acid, and oleic acid; The monoglyceride includes one or more combinations of stearic acid monoglyceride, palmitic acid monoglyceride, and oleic acid monoglyceride; The diglyceride includes one or more combinations of oleic acid diglyceride, palmitic acid diglyceride, and stearic acid diglyceride; The vegetable oil includes one or a combination of rapeseed oil, soybean oil and shortening.

4. The method for preparing the modified lipid gluten protein mixture according to claim 1, characterized in that: The lipid is oleic acid.

5. The method for preparing the modified lipid gluten protein mixture according to claim 1, characterized in that: The lipid is oleic acid, the mass of the oleic acid is 5% of the mass of the gluten protein, and the intensity of the low-frequency alternating magnetic field is 5 mT; Or, the lipid is monoglyceride, the mass of the monoglyceride is 5% of the mass of the gluten protein, and the intensity of the low-frequency alternating magnetic field is 5 mT.

6. A modified lipid gluten protein mixture, characterized in that: The method is prepared according to any one of claims 1 to 5.

7. Application of a modified lipid-gluten protein mixture in making frozen dough, characterized in that: The modified lipid gluten protein mixture is prepared by the preparation method according to any one of claims 1 to 5.

8. A method for preparing frozen dough for baked food, characterized in that: The method comprises the following preparation steps: The modified lipid gluten protein mixture is fully mixed with starch, and then water and yeast are added and stirred until a uniform dough is formed; finally, the dough is stored at (-16 to -20)°C to obtain frozen dough; Wherein, the modified lipid gluten protein mixture is prepared by the preparation method as described in any one of claims 1-5.

9. The method for preparing frozen dough for baked food according to claim 8, characterized in that: In the frozen dough preparation step, the mass ratio of the modified lipid gluten protein mixture to the starch is 12:88-15:85; the mass of the yeast is (2-5)% of the mass of the modified lipid gluten protein mixture; Wherein, the starch is one or a combination of corn starch, wheat starch and potato starch.

10. A frozen dough for baked food, characterized in that: The method is prepared according to any one of claims 8 to 9.

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