Bread rich in flax protein and preparation method thereof

Abstract

The present invention provides a bread rich in flax protein and a preparation method thereof. The flax protein is modified by pH shift treatment, and the modified flax protein is added to wheat flour, which not only increases the content of flax protein in the bread, but also forms a more stable gluten network structure. The bread rich in flax protein has the characteristics of high nutritional value, good taste, good storage stability, long shelf life, etc., and better meets the needs of today's consumers for healthy diet.

Description

[0001] This application claims the priority of the Chinese prior application, application number: 202210178548X, filing date February 25, 2022; all of its contents are regarded as part of the present invention. Technical Field

[0002] The invention relates to the technical field of food processing, in particular to bread rich in flax protein and a preparation method thereof. Background Art

[0003] my country is rich in flaxseed resources, with an annual output of more than 350,000 tons. The planting area and total output are second only to Canada, ranking second in the world. However, the commercial value of flaxseed is mainly reflected in its oil use, and its potential value has not yet been developed and utilized. With the development of society, the improvement of people's living standards and the continuous deepening of scientific research, the nutritional and health functions of flaxseed are attracting more and more attention. Flaxseed is a good source of protein, containing all the essential amino acids needed by the human body, of which the content of branched-chain amino acids is about 16%, making it the plant with the highest content of branched-chain amino acids found so far.

[0004] Existing flax bread is directly prepared by mixing flax seed powder and wheat flour. Since flax seeds contain cyanogenic glycosides, which will produce highly toxic HCN under the action of hydrolases, which is very harmful to humans and animals, flax seed powder must be detoxified before being used in the preparation of bread. In addition, flax bread directly prepared with flax seed powder has a darker color, a rough surface with lumps, a poor bite, and a strong flax cake smell. In addition, the high viscosity of flax gum affects the taste of the bread.

[0005] Since bread is mainly made of wheat flour and supplemented with other ingredients, and since wheat flour protein lacks lysine, branched-chain amino acids (isoleucine, leucine, valine), etc., while plant isolate protein such as flax protein is rich in various amino acids, adding flax protein to bread can be a perfect means of fortifying cereal foods.

[0006] Flax protein is one of the main nutrients in flaxseed powder. It is rich in branched-chain amino acids and has the effect of protecting the liver. However, adding flax protein to bread will reduce the specific volume of the product, deteriorate the texture, shorten the shelf life of the product, and make it difficult to increase the amount of flax protein added. As a result, the amount of flax protein added is very low and the nutritional value is low. This cannot meet consumers' demand for healthy diet to a large extent. Summary of the invention

[0007] To solve the above problems, the present invention provides a bread rich in flax protein and a preparation method thereof, wherein the flax protein is first modified by pH shift treatment and then high pressure treatment, and then the modified flax protein is added to wheat flour, which not only increases the content of flax protein in the bread, but also forms a more stable gluten network structure. The bread rich in flax protein has the characteristics of high nutritional value, good taste, good stability, long shelf life, etc., and better meets the needs of today's consumers for healthy diet.

[0008] In one aspect, the present invention provides a flax protein-rich bread, wherein the bread contains modified flax protein, wherein the modified flax protein is flax protein treated with pH shift.

[0009] pH shift treatment can significantly improve protein structure. When a protein is dissolved in an extreme pH solution, its molecular side chains carry a large number of charges of the same kind, causing the protein molecules to unfold due to electrostatic repulsion. When the pH value is adjusted back to neutral, the electrostatic repulsion disappears and the protein molecules refold. The refolded protein structure is looser than the initial state, and its functional properties also change accordingly.

[0010] As a plant protein, flax protein has the general properties of protein and its own structural and physical and chemical properties, and has the potential to be developed into flax bread with high nutritional value. Compared with other proteins, flax protein is rich in branched-chain amino acids and has the effect of protecting the liver. When flax protein is subjected to pH shift treatment, the charge carried by the amino acids increases, and the electrostatic repulsion between them increases. After a short period of maintenance, the protein structure can be folded, resulting in performance changes. The degree of change is more complex than that of other proteins, such as soy protein and pea protein, after pH shift treatment, and the performance change is more obvious; after that, the pH value is adjusted back to neutral, the electrostatic repulsion in the system is weakened, and the protein structure is refolded, but it can no longer be restored to the state before the pH shift treatment.

[0011] However, studies have shown that when 1.0% flax protein is added to flour, the baked bread will become harder and have worse chewiness. After the bread is stored at room temperature for 3 days, its hardness increases significantly, its elasticity decreases significantly, and its aging rate accelerates significantly. Therefore, the amount of flax protein added to bread should generally not exceed 2.0% of the flour content.

[0012] The present invention creatively finds that the modified flax protein obtained after pH shift treatment has better protein cross-linking ability, which can not only increase the amount of flax protein added in bread, but also form a more stable gluten network structure with wheat flour. When 15% of the modified flax protein is added to the flour, the baked bread can still maintain good texture properties, and the hardness, elasticity and chewiness can still be maintained in an appropriate range after being stored at room temperature for 14 days. The color is golden, soft and palatable, and the nutritional value is high, which significantly improves the shelf life of the bread.

[0013] In some embodiments, the pH shift is a base shift.

[0014] In some embodiments, the pH shift is an acid shift.

[0015] In some embodiments, the pH shift includes a basic pH shift and an acidic pH shift.

[0016] Furthermore, the pH shift is performed by first performing an acidic pH shift and then performing an alkaline pH shift.

[0017] Furthermore, the pH shift operation method is: first titrate the flax protein solution to pH 2.0 with 1.0 mol / L HCl solution, and keep it for 1 hour; then titrate the flax protein solution to pH 12.0 with 1.0 mol / L NaOH solution, and keep it for 1 hour; and then adjust the pH back to 7.0 with 1.0 mol / L HCl.

[0018] Furthermore, wheat flour is also included, and the mass percentage of the modified flax protein in the wheat flour is 1.0% to 15%.

[0019] Furthermore, the mass percentage of the modified flax protein in the wheat flour is 8.0%.

[0020] In another aspect, the present invention provides a method for preparing bread rich in flax protein, the method comprising the following steps:

[0021] (1) Preparing modified flax protein;

[0022] (2) mixing wheat flour with modified flax protein, adding yeast, and fermenting;

[0023] (3) Divide into blocks, shape, and bake.

[0024] The preparation method of the modified flax protein comprises the following steps: the flax protein is subjected to pH shift treatment to obtain the modified flax protein.

[0025] Furthermore, in the preparation of the modified flax protein in step (1), the flax protein is first subjected to an acidic pH shift and then to an alkaline pH shift.

[0026] Furthermore, the pH shift operation method is: first titrate the flax protein solution to pH 2.0 with 1.0 mol / L HCl solution, and keep it for 1 hour; then titrate the flax protein solution to pH 12.0 with 1.0 mol / L NaOH solution, and keep it for 1 hour; and then adjust the pH back to 7.0 with 1.0 mol / L HCl.

[0027] Furthermore, the mass percentage of the modified flax protein in step (2) to the wheat flour is 1.0% to 15%.

[0028] Furthermore, the mass percentage of the modified flax protein in the wheat flour is 8.0%.

[0029] On the other hand, the present invention provides a use of modified flax protein for preparing flax protein-rich bread with high storage stability, wherein the modified flax protein is flax protein treated with pH shift; the pH shift is first an acidic pH shift and then an alkaline pH shift.

[0030] Furthermore, the storage stability refers to maintaining the hardness, elasticity and moisture content of the bread during storage.

[0031] The bread rich in flax protein provided by the present invention has the following beneficial effects:

[0032] 1. After modifying flax protein and adding it to wheat flour, it can form a more stable gluten network structure, improve the appearance, color and taste of bread, and extend the storage period;

[0033] 2. It can increase the amount of flax protein added in bread and improve the nutritional value of bread. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a hardness change trend diagram of the modified flax protein or unmodified flax protein in Example 2 after storage at 25° C. for 0 days, 3 days, and 14 days when the addition amount is 8.0%;

[0035] Figure 2 The elasticity change trend diagram of the modified flax protein or the unmodified flax protein in Example 2 after storage at 25° C. for 0 days, 3 days, and 14 days when the addition amount is 8.0%;

[0036] Figure 3 This is a trend chart of the moisture content after storage at 25° C. for 0 days, 3 days, and 14 days when the modified flax protein or unmodified flax protein in Example 2 is added at 8.0%. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on it. The raw materials and equipment used in the specific embodiments of the present invention are all known products and are obtained by purchasing commercially available products.

[0038] Example 1: Preparation of bread rich in flax protein

[0039] The preparation method of flax protein-rich provided in this embodiment comprises the following steps:

[0040] (1) Preparing modified flax protein;

[0041] Extract flax protein by alkali dissolution and acid precipitation method: Take 100g of defatted flax meal, mix it with 15 times deionized water, adjust the pH value to 7.5-8.0 with 2.0mol / L NaOH, stir for 1h, and centrifuge the suspension at 4℃. Take the supernatant and adjust the pH to 4.3 with 2.0mol / L HCl. Let it stand and centrifuge at 4℃; take the precipitate and disperse it in water, adjust the pH to 7.0 with 2.0mol / L NaOH, and freeze-dry the protein solution after dialyzing to obtain flax protein powder.

[0042] Take 10g of flax protein powder and dissolve it in 90mL of distilled water (pH 7.0) to prepare a 10% flax protein solution. Stir at room temperature for 2 hours to ensure that the protein is fully dissolved. Titrate the flax protein solution to pH 2.0 with 1.0mol / L HCl solution and keep it for 1 hour; then titrate the flax protein solution to pH 12.0 with 1.0mol / L NaOH solution and keep it for 1 hour; then adjust the pH back to 7.0 with 1.0mol / L HCl.

[0043] (2) mixing wheat flour with modified flax protein, adding yeast, and fermenting;

[0044] 1.0 g of yeast was dissolved in water to prepare 50 mL of a solution with a mass concentration of 2.0%, and then placed in a constant temperature incubator at 26° C. to activate it for use.

[0045] Add 100g of weighed wheat flour, 80mL of modified flax protein solution (equivalent to 8.0g of flax protein, accounting for 8.0% of the mass of wheat flour), 10.0g of sugar, 1.5g of salt and 5.0g of oil, put them in a mixing bowl and mix them evenly, stir and knead at a low speed of 80 rpm for about 3min to fully hydrate the flour, continue to stir and knead at a medium speed of 110 rpm for about 4min, then add 50mL of activated yeast solution, continue to stir and knead at a medium speed of 110 rpm for about 5min, and then stir at a high speed of 180 rpm until dough is formed.

[0046] Knead the dough evenly and put it into a proofing box at a temperature of 30°C and a relative humidity of 75% to ferment for 30 minutes.

[0047] (3) Divide into blocks, shape, and bake.

[0048] Divide the fermented dough into 50g / piece, roll into balls until the surface is smooth, cover with plastic wrap and relax for 10 minutes, shape into olive shape and put into non-stick baking pan. Put the dough into a proofing box at 38℃ and relative humidity of 85% and proof for 60 minutes. Put the dough into the oven, control the bottom temperature at 215℃, the surface temperature at 220℃, steam for 3s, and the baking time for 15min, cool, package, and obtain the finished product.

[0049] Of course, based on the main dough ingredients provided in this embodiment, other ingredients such as butter, milk, eggs, bread improvers, dried fruits, nuts, etc. can be added as needed.

[0050] The baking characteristics of the finished bread were evaluated by sensory evaluation, and the specific volume and storage stability of the bread were measured.

[0051] The sensory evaluation method is as follows: a 30-member evaluation team is formed to evaluate the product from five aspects: bread color (10 points), shape (10 points), taste (10 points), aroma (10 points), and touch (10 points), and the total score is calculated. The evaluation criteria are shown in Table 1.

[0052] Table 1. Sensory evaluation criteria for flax bread

[0053]

[0054] The specific volume of bread is determined by the method of GB / T 20981-2007. The specific volume of bread (cm 3 / g) = volume (cm 3 ) / mass (g).

[0055] The texture analyzer was used to measure the changes in the hardness and elasticity of bread after being stored at room temperature (25°C) for different periods of time to reflect the aging degree of bread. The baked bread was packaged and stored after cooling naturally at room temperature for 2 hours. The changes in the hardness and elasticity of the bread core were measured after 1d, 2d, 3d, 4d, 5d, 6d, 7d, 10d, and 14d. The method is as follows: cut off the two ends of the bread (each 20mm thick), then cut a 20mm thick slice of bread from the middle, take the bread core with a diameter of 35mm at the center of the bread slice, and measure the hardness and elasticity of the bread slice when it is compressed on the texture analyzer. Each bread sample was measured 3 times in parallel and the average value was taken.

[0056] The moisture content of bread is determined according to GB500913-1985. Samples are taken from the same part of the bread core and the moisture content is determined by direct drying method.

[0057] After testing, the sensory score of the flax protein-rich bread prepared in this example reached more than 45 points, the specific volume of the bread was 3.46, and after being stored at 25° C. for 14 days, the hardness, elasticity and water content did not change significantly, and the bread had very good storage stability.

[0058] Example 2: Effect of the amount of modified flax protein added on bread properties

[0059] In this example, modified flax protein and unmodified flax protein were used respectively, and bread was prepared by the method provided in Example 1, wherein the addition ratio of flax protein to flour was shown in Table 1, and bread without flax protein was used as a blank control to examine the sensory score, specific volume, and hardness, elasticity and water content of the bread after storage at 25°C for 0d, 3d and 14d. The detection method was the same as in Example 1, and the detection results are shown in Tables 2 to 4.

[0060] Table 2. Effect of the amount of modified flax protein added on bread performance (0d)

[0061]

[0062] Table 3. Effect of 3-day storage on the performance of bread

[0063]

[0064]

[0065] Table 4. Effect of 14-day storage on the performance of bread

[0066]

[0067] The texture characteristics of bread mainly include hardness, elasticity, chewiness, etc., which are important factors in determining the quality of bread. The harder the bread is, the harder it tastes, lacking elasticity, softness, and refreshing feeling. The more elastic the bread is, the softer it tastes, refreshing and non-sticky.

[0068] According to Table 2, compared with the blank control without flax protein, the sensory score of the bread prepared by adding unmodified flax protein decreased significantly, and the texture characteristics of the bread also decreased. Especially when the amount of flax protein added reached 2.0%, the hardness increased significantly, the elasticity decreased, the specific volume decreased, and the sensory score also decreased significantly. Therefore, when flax protein is added to bread, the maximum amount should not exceed 2.0%, otherwise it will greatly affect the texture characteristics of the bread and make the bread difficult to swallow. After adding flax protein modified by pH shift, not only did the texture characteristics of the bread not decrease, but it also improved the texture and taste of the bread. Even if the amount added reached 15%, it could still maintain very good hardness, elasticity and water content, and the sensory score was significantly improved. It can be seen that the modified flax protein obtained after pH shift treatment can increase the amount of protein added to bread. The reason may be that the modified flax protein has better protein cross-linking ability and can form a more stable gluten network structure with wheat flour, so that the bread can remain soft and improve the nutritional value of the bread. Among them, the more preferred addition amount of modified flax protein is 8.0%, and the texture characteristics and sensory scores of the prepared bread are at a higher level and have higher nutritional value.

[0069] When the amount of modified flax protein or unmodified flax protein added is 8.0%, the hardness change trend after storage at 25℃ for 0d, 3d, and 14d is as follows: Figure 1 As shown in the figure, the elasticity change trend is as follows Figure 2 As shown in the figure, the water content change trend is as follows Figure 3 As shown. Figure 1 to Figure 3 It can also be clearly seen that the storage stability of bread prepared with modified flax protein obtained after pH shift treatment is significantly improved, and the change trend of hardness, elasticity and water content is significantly slowed down.

[0070] According to the results in Tables 2 to 4, compared with unmodified flax protein, the modified flax protein obtained after pH shift treatment can significantly improve the storage stability of bread. In the range of 1.0% to 15% of modified flax protein addition, after storage at 25°C for 14 days, the bread can still maintain good texture characteristics, and the hardness, elasticity and water content have no obvious changes. However, after adding unmodified flax protein, the hardness is very high after storage for 3 days, and it cannot be stored and eaten for a long time. It can be seen that the modified flax protein obtained after pH shift treatment can maintain the texture characteristics of bread, improve storage stability, and extend the shelf life.

[0071] Example 3: Effects of flax protein prepared by different modification methods on bread properties

[0072] The method provided in Example 1 was used to prepare bread with 8.0% flax protein added. When preparing the modified flax protein solution, it was divided into 7 groups. The first group was an unmodified ordinary flax protein solution; the second group was a modified flax protein solution treated with alkaline pH shift (the flax protein solution was titrated to pH 12.0 with a 1.0 mol / L NaOH solution and maintained for 1 h); the third group was a modified flax protein solution treated with acidic pH shift (the flax protein solution was titrated to pH 12.0 with a 1.0 mol / L HCl solution); 2.0, maintained for 1h); the 4th group was treated with acidic pH shift for 1h and then alkaline pH shift for 1h; the 5th group was treated with alkaline pH shift for 1h and then acidic pH shift for 1h; the 6th group was treated with high pressure (350MPa, maintained for 15min) without pH shift; the 7th group was treated with acidic pH shift for 1h, alkaline pH shift for 1h and then high pressure (350MPa, maintained for 15min); the 7 groups of flax protein solutions were added respectively to prepare flax bread, and the sensory score, specific volume, hardness, elasticity and water content of the bread were investigated. The test results are shown in Table 5.

[0073] Table 5. Effects of flax protein prepared by different modification methods on bread properties

[0074] Group Sensory Rating <![CDATA[Specific volume (cm 3 / g)]]> Hardness(g) Elasticity(mm) Water content (%) Group 1 19.5 2.58 445.03 0.72 29.2 Group 2 18.4 2.64 478.75 0.70 30.4 Group 3 32.8 3.01 382.49 0.75 31.0 Group 4 44.5 3.44 285.39 0.88 31.5 Group 5 30.2 3.15 390.17 0.74 30.2 Group 6 15.7 3.09 537.61 0.70 28.8 Group 7 30.7 3.23 438.53 0.72 30.3

[0075] It can be seen from Table 5 that the modified flax protein obtained by different modification methods will have completely different effects when used to prepare bread.

[0076] Compared with Groups 1 to 5, ideal modified flax protein could not be obtained by performing acidic pH shift alone, alkaline pH shift alone, or first alkaline pH shift and then acidic pH shift; only the modified flax protein obtained by first acidic pH shift for 1 hour and then alkaline pH shift for 1 hour was most suitable for preparing flax protein-rich bread, and the resulting bread had better texture characteristics, was more elastic and had a better taste.

[0077] Compared with groups 1 to 7, the modified flax protein prepared by high pressure treatment is not suitable for making bread, and it is difficult to obtain the ideal modified flax protein by pH shift treatment and then high pressure treatment.

[0078] In summary, the most preferred modification method is to use the fourth group of acidic pH shift treatment for 1 hour and then alkaline pH shift treatment for 1 hour. The modified flax protein obtained can be used to prepare bread that is truly rich in flax protein, with good taste and high nutritional value.

[0079] Example 4: Amino Acids in Modified Flax Protein

[0080] In this example, pepsin was used to hydrolyze the modified flax protein (Example 1) and the unmodified flax protein, and then the amino acid content was measured by nanofiltration and high performance liquid chromatography to determine the nutritional components of the modified flax protein. The test results are shown in Table 6.

[0081] Table 6. Amino acid composition of flax protein hydrolysate

[0082]

[0083] It can be seen from Table 6 that the content of branched-chain amino acids in modified flax protein is higher than that in unmodified flax protein. The reason may be that pH shift modification of flax protein can promote the release of free amino acids. At the same time, the nutritional components in modified flax protein not only do not decrease, but have higher nutritional value than unmodified flax protein, and are more suitable for preparing flax bread with high nutritional value.

[0084] Although the present invention is disclosed as above, the present invention is not limited thereto. For example, it can be expanded according to its application range in medicine. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A bread rich in flax protein, characterized in that: The invention relates to a method for treating a flax protein containing modified flax protein, wherein the modified flax protein is flax protein treated with a pH shift; the method for treating the pH shift is as follows: firstly titrating the flax protein solution with a 1.0 mol / L HCl solution to a pH of 2.0, and maintaining the pH for 1 hour; then titrating the flax protein solution with a 1.0 mol / L NaOH solution to a pH of 12.0, and maintaining the pH for 1 hour, and then adjusting the pH back to 7.0 with 1.0 mol / L HCl.

2. The bread according to claim 1, characterized in that It also includes wheat flour, wherein the mass percentage of the modified flax protein in the wheat flour is 1.0% to 15%.

3. The bread according to claim 2, characterized in that The mass percentage of the modified flax protein in the wheat flour is 8.0%.

4. A method for preparing bread rich in flax protein, characterized in that: The following steps are involved: (1) Preparation of modified flax protein; (2) Mix wheat flour and modified flax protein, add yeast, and ferment; (3) Dividing, shaping and baking; The preparation method of the modified flax protein comprises: the flax protein is subjected to pH shift treatment to obtain the modified flax protein; The operation method of the pH shift treatment is: first, the flax protein solution is titrated to pH 2.0 with 1.0 mol / L HCl solution, and maintained for 1 hour; then, the flax protein solution is titrated to pH 12.0 with 1.0 mol / L NaOH solution, and maintained for 1 hour, and then the pH is adjusted back to 7.0 with 1.0 mol / L HCl.

5. The method according to claim 4, characterized in that The mass percentage of the modified flax protein in step (2) to the wheat flour is 1.0% to 15%.

6. Use of modified flax protein in preparing bread rich in flax protein with high storage stability, characterized in that: The modified flax protein is flax protein that has been subjected to a pH shift treatment; the pH shift is firstly an acidic pH shift and then an alkaline pH shift; The operation method of the pH shift treatment is: first, the flax protein solution is titrated to pH 2.0 with 1.0 mol / L HCl solution, and maintained for 1 hour; then, the flax protein solution is titrated to pH 12.0 with 1.0 mol / L NaOH solution, and maintained for 1 hour, and then the pH is adjusted back to 7.0 with 1.0 mol / L HCl.

7. The use according to claim 6, characterized in that The storage stability refers to maintaining the hardness, elasticity and moisture content of the bread during storage.

Images