Making method of convenient crisp deep-fried dough sticks

Abstract

The invention discloses a making method of convenient crisp deep-fried dough sticks, and belongs to the field of deep-fried products. According to the method, the soybean protein isolate solution and the egg white protein solution are prepared and compounded to serve as dispersion phases to prepare the gel-like emulsion with the oil phase being 60%-80%, the freezing resistance of the gel-like emulsion is improved, and the compounded gel-like emulsion serves as a leavening agent to be added into dough. The making method of the fried bread sticks is green, the oil content and the oil oxidation degree of the fried bread sticks are reduced, the operation efficiency and convenience are improved, the color and luster of the fried bread sticks can be effectively regulated and controlled, and technical innovation and quality improvement in the field of fried foods are expected to be promoted.

Description

TECHNICAL FIELD

[0001] The application relates to a method for conveniently making crisp fried dough sticks, and belongs to the field of fried products. BACKGROUND

[0002] Fried dough sticks are an ancient kind of noodles, which are long hollow fried foods with golden color, crisp outer skin and porous inner part, and are classic foods on breakfast tables. A fried dough stick making process is as follows: flour, aluminum-free dough stick leavening agent, salt, sugar, soybean oil and water are mixed to obtain dough, the dough is allowed to rest for 15 min, and then is allowed to rest for 1 h after being kneaded, the dough is cut into rectangular dough sheets, two dough sheets are stacked together, the middle part is pressed, and then is gently stretched to be fried to obtain fried dough sticks. The leavening degree of the fried dough sticks is a key factor affecting the taste of the fried dough sticks, and the leavening taste of the fried dough sticks mainly depends on biological leavening and chemical leavening. The biological leavening is performed by using yeast fermentation, the yeast decomposes sugar to generate CO2 and alcohol, so that the dough is inflated, the fermentation time is relatively long (1-2 h), and the taste is slightly soft, which is not as crisp as the chemical leavening. The chemical leavening is performed by using a leavening agent to generate CO2, so that pores are formed in the dough, a porous structure is formed, the fried dough sticks are more crisp and leavened, and therefore the leavening agent is often used to increase the leavening degree of the fried dough sticks. Commonly used alum (potassium aluminum sulfate) + baking soda (sodium bicarbonate) are used for complex reaction to generate aluminum hydroxide, and long-term intake may affect health. Modern people often use aluminum-free leavening agents to replace the leavening agents. However, such leavening agents are contrary to the green label concept pursued by current consumers. In addition, it is worth noting that the leavening agent not only increases the leavening porosity of the fried dough sticks, but also easily leads to an increase in oil content and aggravates the oxidation of oil, and reduces the health and safety of products. Therefore, development of a method for increasing the leavening degree of the fried dough sticks with less oil content has attracted extensive attention of fried dough stick processing enterprises.

[0003] Gel-like emulsion is a new type of emulsion with good self-supporting property. Compared with ordinary emulsion, the gel-like emulsion can carry a higher proportion of fat, and has higher physical stability and oxidation stability. The use of the gel-like emulsion can replace the use of the leavening agent in the preparation of the fried dough sticks, as disclosed in patents CN 120283921 A and CN 120323629 A. However, the process of freezing the dough and then thawing the dough as needed is required in the large-scale preparation of the fried dough sticks, which is different from the preparation of fried foods. Therefore, the stability of the gel-like emulsion in the freezing and thawing process of the dough and the subsequent frying effect need to be further explored. SUMMARY

[0004] To solve the above problems, the present application first prepares a gel emulsion of 60% to 80% oil phase with soybean protein isolate solution and egg white protein solution as the dispersed phase, and then uses the gel emulsion as a pore-forming agent to achieve the increased crispness and bulkiness of the fried dough sticks. The soybean protein isolate and egg white protein synergistically inhibit ice crystal growth, so that the dough maintains good water content and structural integrity after freeze-thaw cycles, exhibits good freeze-resistant properties, and allows the emulsion to burst during high-temperature frying to form numerous bubbles, thereby achieving pore formation without a bulkiness agent. This not only can replace traditional bulkiness agents, but also can effectively reduce the oil content of the fried dough sticks, inhibit the oxidation of oil, and enable the dough to be stored in the frozen state, thereby improving the operation efficiency and convenience. This achievement provides a theoretical basis and practical operation guidance for the development of new technologies for making fried dough sticks, and can promote the innovation of fried food processing technology and the improvement of quality.

[0005] The present application provides a soybean protein isolate-egg white protein gel emulsion, which is prepared by the following preparation method: (1) Preparation of soybean protein isolate solution: crush soybean powder to obtain soybean powder, add n-hexane, extract the oil in the soybean powder, then centrifuge to remove the supernatant, collect the precipitate, dry it to obtain defatted soybean meal powder, mix the defatted soybean meal with water, adjust the pH to alkaline, centrifuge, then adjust the pH of the supernatant to acidic, centrifuge to precipitate the protein, then redissolve the precipitate with water, adjust the pH of the solution to neutral until the precipitate is completely dissolved, then freeze-dry to obtain soybean protein isolate, dissolve the soybean protein isolate in water to obtain the soybean protein isolate solution; (2) Preparation of egg white protein solution: separate the yolk and egg white in the egg, then add water to obtain an egg white solution, then add an ethanol solution, stir and stand, freeze-dry to obtain egg white protein powder, then redissolve it with water to obtain the egg white protein solution; (3) Preparation of gel emulsion: mix the soybean protein isolate solution, egg white protein solution and soybean oil, and high-speed disperse to obtain a soybean protein isolate-egg white protein gel emulsion. Further, the soybean powder in step (1) is sieved to 60-100 mesh.

[0006] Further, the amount of n-hexane added in step (1) is 80-120 mL, based on the mass of 20 g of soybean powder.

[0007] Further, the n-hexane extraction conditions in step (1) are heating at 50-60 ℃ for 20-30 min.

[0008] Further, the centrifugation conditions after extraction in step (1) are 5000 rpm for 15 min.

[0009] Further, the defatted soybean meal is mixed with water in a ratio of 1:15-20.

[0010] Further, the alkaline in step (1) refers to pH 8-9.

[0011] Further, the centrifugal separation condition in step (1) is 8000-10000 g, and the time is 20-30 min.

[0012] Further, the acid in step (1) refers to pH 4.5-4.8.

[0013] Further, the neutral in step (1) refers to pH 7.0.

[0014] Further, the concentration of the soybean protein isolate solution in step (1) is 10-20%.

[0015] Further, the concentration of the egg white solution in step (2) is 1-5 wt%.

[0016] Further, the ratio of the egg white solution to the ethanol solution in step (2) is 1:0.5-1.5.

[0017] Further, the concentration of the ethanol solution in step (2) is 40-60 wt%.

[0018] Further, the concentration of the egg white protein solution in step (2) is 10-20%.

[0019] Further, the volume ratio of the soybean protein isolate solution to the egg white protein solution in step (3) is 1:1-3.

[0020] Preferably, the volume ratio of the soybean protein isolate solution to the egg white protein solution in step (3) is 1:2.

[0021] Further, the oil phase in the soybean protein isolate-egg white protein gel-like solution in step (3) is 60%-80% (v / v). Further, the concentration of the egg white protein in the water phase of the soybean protein isolate-egg white protein gel-like solution in step (3) is 5-7 wt%, and the concentration of the soybean protein isolate is 3-4 wt%.

[0022] Further, the high-speed dispersion condition in step (3) is 8000-10000 g for 1-5 min.

[0023] The soybean protein isolate-egg white protein gel-like emulsion provided by the application has the application in the field of food.

[0024] The application also provides a preparation method of a shortening oil stick, which comprises the following steps: The flour, salt, sugar and water are mixed, the soybean protein isolate-egg white protein gel-like emulsion is added, a dough is obtained, the dough is cut into a rectangular shape after being leavened, and the dough is fried to obtain the shortening oil stick. or, mixing flour, salt, sugar and water, adding the soybean protein isolate-egg white protein gelatinous emulsion to obtain a dough, after leavening, freezing and then thawing, cutting into a rectangular shape, frying to obtain a fried bread stick.

[0025] In an embodiment of the present application, the mass ratio of flour, salt, sugar and water is 60-65:1:1:30-35.

[0026] In an embodiment of the present application, the added amount of the soybean protein isolate-egg white protein gelatinous emulsion is 25-30wt% of the total mass of the dough.

[0027] In an embodiment of the present application, the leavening time is 1-2 hours.

[0028] In an embodiment of the present application, the freezing time is 8-72 hours.

[0029] In an embodiment of the present application, the frying is at 190-200℃ for 1-2 min.

[0030] Advantages (1) The present application discards traditional chemical additives such as alum and aluminum-free leavening agents, and uses two natural food ingredients, soybean protein isolate and egg white protein, to prepare a gelatinous emulsion as a key raw material for making fried bread sticks. This alternative not only meets the current consumer's pursuit of green label food, but also avoids the health risks that may be caused by chemical leavening agents from the source, while effectively reducing the oil content and the degree of fat oxidation of fried bread sticks. Compared with traditional methods of making fried bread sticks, the product of the present application has a significantly lower TBARs value, the oxidation of oil is effectively inhibited, and the health and safety of the product are greatly improved.

[0031] (2) The present application effectively regulates the color of fried bread sticks through the complex system of soybean protein isolate and egg white protein, making them present a uniform golden yellow color, avoiding the uneven color, overcooking or overwhiting phenomenon that easily occurs in traditional production, and performing well in multiple dimensions such as color, odor, taste, shape and other sensory evaluations, with high overall acceptability.

[0032] (3) In the present application, soybean protein isolate and egg white protein are used to produce a gelatinous emulsion with anti-freezing properties, which is added to the dough to make a fried bread stick that can be frozen and thawed on demand, and still maintains good moisture and structural integrity after thawing, without affecting the subsequent frying effect. This feature greatly improves the flexibility and efficiency of production operations, facilitating industrialized mass production and overall scheduling. In addition, the production process of the present application is simple and easy to understand, the preparation of the gelatinous emulsion and the processing flow of the fried bread stick can be standardized, without the need for complex equipment and technology, easy to popularize and apply, and adapt to the needs of large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Microscopic images of soy protein isolate-egg white protein gel-like emulsions for Example 1, Example 2, Example 3.

[0034] Figure 2 Microscopic images of soy protein isolate-egg white protein gel-like emulsions for Example 1, Example 2, Example 3 after freezing.

[0035] Figure 3 Scanning electron microscopic images of soy protein isolate-egg white protein gel-like emulsions for Example 1, Example 2, Example 3 after freezing.

[0036] Figure 4 3D scanning images of soy protein isolate-egg white protein gel-like emulsions for Example 1, Example 2, Example 3.

[0037] Figure 5 Viscosity images of soy protein isolate-egg white protein gel-like emulsions for Example 1, Example 2, Example 3.

[0038] Figure 6 Scanning electron microscopic images of doughs for Example 4, Example 5, Example 6, Example 7, Comparative Example 1, Comparative Example 2, Comparative Example 3 after freezing.

[0039] Figure 7 Appearance images for Example 4, Example 5, Example 6, Example 7, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0040] Figure 8 Color L* test results for Example 4, Example 5, Example 6, Example 7, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0041] Figure 9 Color a* test results for Example 4, Example 5, Example 6, Example 7, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0042] Figure 10 Color b* test results for Example 4, Example 5, Example 6, Example 7, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0043] Figure 11 Texture test results for Example 4, Example 5, Example 6, Example 7, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0044] Figure 12 Sensory evaluation test results for Example 4, Example 5, Example 6, and Example 7.

[0045] Figure 13 Sensory evaluation test results for Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0046] Figure 14 TBARs test results for Example 4, Example 5, Example 6, Example 7, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0047] Figure 15 Oil content results for Example 4, Example 5, Example 6, Example 7, Comparative Example 1, Comparative Example 2, and Comparative Example 3. DETAILED DESCRIPTION

[0048] The following describes preferred embodiments of the present application, and it should be understood that the embodiments are for better explaining the present application and are not intended to limit the present application.

[0049] Test methods 1. Microscopic test: Place the gel emulsion in a glass slide, cover with a cover glass and gently press, and observe using a confocal microscope; freeze the gel emulsion for 24 h and then observe again using a confocal microscope.

[0050] 2. Heat stability test: Pour 10 mL of freshly prepared emulsion into a plastic tube and heat at 80°C for 30 min, and before measuring the physical properties of the emulsion, equilibrate the sample at room temperature for 12 h.

[0051] 3. When testing heat stability, periodically take samples and measure viscosity changes.

[0052] 4. Scanning electron microscopy (SEM): observe the microstructure of the dough using a scanning electron microscope at an acceleration voltage of 10 kV and a magnification of 100x. The dough is freeze-dried to remove moisture. At the same time, the dehydrated dough is deoiled in petroleum ether for 8 h, carefully cut into small cubes of 2 mm x 2 mm x 1 mm, and gold plated for imaging. Low-temperature scanning electron microscopy observation is performed.

[0053] 5. Colorimetry test: measure the color properties of the sticks in reflection mode using a colorimeter. The lightness (L*), red / green spectrum (a*), and yellow / blue spectrum (b*) values are recorded. The whiteness (W) is calculated as follows: (1) 6. Texture determination: determine after cooling the sticks to room temperature, using a P50 probe, in TPA mode (deformation 40%). Trigger type: automatic, trigger point load 5 g, 3 parallel tests.

[0054] 7. Oil content test: 5.00 g of the dried and constant weight of the oil strip was weighed in filter paper, and petroleum ether was selected as the solvent. Reflux extraction was performed for 6-8 h, and the petroleum ether was allowed to evaporate in a fume hood. Then, the sample was placed in an oven for drying until the constant weight was reached. The crude fat content in the sample was calculated.

[0055] 8. TBARs test: 0.1 g of the oil strip was taken and mixed with 5 mL of thiobarbituric acid mixture. The mixture was heated in boiling water for 10 min. After centrifugation, the supernatant was collected, and the absorbance at a wavelength of 532 nm was measured using a microplate reader. The MDA content in the sample was calculated using a standard curve, and the result was expressed as thiobarbituric acid reactive substances (TBRAS) value.

[0056] 9. Sensory evaluation: A sensory evaluation panel consisting of 10 food science students (5 males and 5 females) trained in sensory evaluation was invited to evaluate the oil strips. The sensory evaluation criteria are shown in Table 1.

[0057] Table 1. Sensory evaluation criteria

[0058] Instrumentation The high-speed disperser was model LC-ES-10SH from Likang Technology.

[0059] Example 1 A method for preparing a gel-like emulsion using a soybean protein isolate-egg white protein solution as the dispersed phase, comprising the following steps: (1) Preparation of soybean protein isolate solution: First, the soybeans were pulverized using a pulverizer to obtain soybean powder, which was sieved through a 60-mesh stainless steel screen to remove impurities. Then, n-hexane (20 g of soybean powder was added to 100 mL) was added, and the soybean was extracted in a constant-temperature water bath at 60°C for 30 min to dissolve the oil in the soybean. After centrifugation at 5000 rpm for 15 min, the supernatant was removed, and the precipitate was collected and dried in an oven at 50°C for 20 min to obtain defatted soybean meal. The defatted soybean meal was mixed with deionized water at a ratio of 1:15, and the soybean protein was alkali-dissolved using a 2 M NaOH solution. The pH was adjusted to 7.0-9.0, and the alkali-dissolved soybean protein was thoroughly stirred and extracted. The centrifugation conditions were 8000 g for 30 min. The pH of the supernatant was then adjusted to 4.5-4.8 using a 2 M HCI solution, and the protein was precipitated by acid. The centrifugation conditions were 6500 r / min for 20 min. The precipitate was then re-dissolved in deionized water, and the pH of the solution was adjusted to 7.0 until the precipitate was completely dissolved. The solution was freeze-dried to obtain soybean protein isolate, which was dissolved in deionized water containing 0.02 wt% sodium azide. The solution was stirred at room temperature for 2 h until it was fully dissolved, and it was hydrated overnight to obtain a soybean protein isolate solution (concentration of 10 wt%).

[0060] (2) Preparation of egg white protein solution: first separate the yolk from fresh eggs, then add water to adjust the concentration of egg white to 2wt%, then slowly add an equal volume of 50% ethanol aqueous solution, and stir continuously, stand for 1 hour, then rotary evaporate, then freeze dry into egg white protein powder, and then reconstitute into egg white protein solution (concentration of 10wt%).

[0061] (3) Preparation of soybean protein isolate-egg white protein stabilized gel-like emulsion: mix soybean protein isolate solution, egg white protein solution and soybean oil, then high-speed disperse, to obtain a gel-like emulsion with soybean protein isolate-egg white protein as the dispersed phase, the oil phase of the gel-like emulsion is 60%, and the volume ratio of soybean protein isolate solution and egg white protein solution in the water phase is 1:2. Example 2 Adjust the oil phase ratio in step (3) of Example 1 to 70%, and keep the rest the same as Example 1, to obtain a soybean protein isolate-egg white protein stabilized gel-like emulsion.

[0062] Example 3 Adjust the oil phase ratio in step (3) of Example 1 to 80%, and keep the rest the same as Example 1, to obtain a soybean protein isolate-egg white protein stabilized gel-like emulsion.

[0063] Figure 1 、 Figure 2 The laser confocal scanning images of the emulsions of Example 1, Example 2 and Example 3 before and after freezing are shown in Figure 1. Figure 1 It can be seen that: the soybean protein isolate-egg white protein stabilized gel-like emulsions of Example 1, Example 2 and Example 3 can all form oil-in-water type gel-like emulsions under the conditions of soybean protein isolate-egg white protein with oil phase ratio of 60%, 70% and 80%, the emulsion droplet size is uniform and relatively large, and the emulsion droplets are in a close arrangement state; Figure 2 The emulsion was observed again by confocal microscope after being frozen for 24h, and compared with the emulsion before freezing. Figure 1 There is basically no change. Freezing has no effect on the state of the emulsion.

[0064] Figure 3 The scanning electron microscope images of the emulsions of Example 1, Example 2 and Example 3 after freezing are shown in Figure 2. Figure 3 It can be seen that: the emulsion droplet size in Example 1 is the smallest, and the emulsion droplet size in Example 3 is the largest. With the increase of oil phase ratio, the emulsion droplet size increases. The emulsions of Example 1-3 all do not appear obvious rupture after freezing, showing good anti-freezing properties.

[0065] Figure 4 The 3D printing appearance images of Example 1, Example 2 and Example 3 are shown in Figure 3. Figure 4It can be seen that the surface pattern of the cubic gel-like emulsion printed by Examples 1-3 is clear and no obvious collapse phenomenon occurs. The results show that the three emulsions all have good self-supporting properties.

[0066] Figure 5 The viscosity diagram of the emulsions of Example 1, Example 2, and Example 3 after freezing is shown in the following figure: Figure 5 It can be seen that the viscosity of Example 3 is the highest, which is always higher than that of Example 1 and Example 2, and the viscosity of Example 1 is the lowest overall. The gel-like emulsions in Example 2 and Example 3 are more stable in the middle.

[0067] The above results show that the soybean protein isolate-egg white protein gel-like emulsion prepared by the method of the present application has good freeze resistance, self-supporting performance, and thermal stability, and the effects of Example 2 and Example 3 are better, which can be applied in the preparation of fried dough sticks.

[0068] Example 4 A method for preparing fried dough sticks based on a soybean protein isolate-egg white protein stable gel-like emulsion, comprising the following steps: (1) Preparation of soybean protein isolate solution: first, grind the soybeans with a grinder to obtain soybean powder, sieve the soybean powder with a 60-mesh stainless steel screen to remove impurities; then add n-hexane (20 g of soybean powder is added to 100 mL), immerse in a constant temperature water bath at 60°C for 30 min to dissolve the oil in the soybeans, centrifuge at 5000 rpm for 15 min, remove the supernatant, collect the precipitate, and dry it in an oven at 50°C for 20 min to obtain defatted soybean meal. Mix the defatted soybean meal with deionized water at a ratio of 1:15, alkali-dissolve the soybean protein with 2 M NaOH solution, adjust the pH to 7.0-9.0, and fully stir and extract the alkali-dissolved soybean protein. The centrifugal separation conditions are 8000 g and 30 min. Then adjust the pH of the supernatant to 4.5-4.8 with 2 M HCl solution, and acid-precipitate the protein. The centrifugal separation conditions are 6500 r / min and 20 min. Then redissolve the precipitate with deionized water, and adjust the pH of the solution to 7.0 until the precipitate is completely dissolved. Freeze-dry to obtain soybean protein isolate, dissolve it in deionized water (containing 0.02 wt% sodium azide), stir at room temperature for 2 h until it is fully dissolved, and hydrate overnight to obtain a soybean protein isolate solution (concentration of 10 wt%).

[0069] (2) Preparation of egg white protein solution: first, separate the yolk from fresh eggs, then adjust the concentration of egg white to 2 wt% by adding water, then slowly add an equal volume of 50% ethanol aqueous solution while stirring, let it stand for 1 hour, then rotary evaporate, then freeze-dry to obtain egg white protein powder, and redissolve it to obtain an egg white protein solution (concentration of 10 wt%).

[0070] (3) Preparation of a stable gel emulsion of soy protein isolate-egg white protein: Soy protein isolate solution, egg white protein solution and soybean oil are mixed and then dispersed at high speed to obtain a gel emulsion with soy protein isolate-egg white protein as the dispersed phase. The oil phase of the gel emulsion is 60% and the volume ratio of soy protein isolate solution to egg white protein solution in the aqueous phase is 1:2. (4) Application of soy protein isolate-egg white protein stabilized gel emulsion in fried dough sticks: Mix flour, salt, sugar and water in a mass ratio of 62:1:1:32, add soy protein isolate gel emulsion to obtain dough, let it rise for 1-2 hours, freeze for 24 hours, after thawing, cut the dough into rectangular pieces and fry them. When frying, gently stretch them, oil temperature 200℃, time 90s, to obtain fried dough sticks; the amount of soy protein isolate gel emulsion added is 25wt% of the total mass of the dough with added gel emulsion.

[0071] Example 5 The amount of gel emulsion added in step (4) of Example 4 was adjusted to 30wt%, while the rest remained the same as in Example 4, and fried dough sticks were obtained.

[0072] Example 6 Adjust the oil phase of the gel solution in step (3) of Example 4 to 80%, while keeping the other components the same as in Example 4, to obtain fried dough sticks.

[0073] Example 7 Adjust the gel emulsion oil phase in step (4) of Example 4 to 80% and the addition amount to 30wt%, while keeping the other steps the same as in Example 4, to obtain fried dough sticks.

[0074] Comparative Example 1 Mix flour, salt, sugar and water in a mass ratio of 62:1:1:32 to obtain dough. Let it rest for 1-2 hours, then freeze for 24 hours. After thawing, cut the dough into rectangular pieces and deep-fry them. Gently stretch the dough while deep-frying at 200℃ for 90 seconds to obtain fried dough sticks.

[0075] Comparative Example 2 Mix flour, salt, aluminum-free leavening agent, sugar, soybean oil, and water in a mass ratio of 62:1:1:2.5:6.25:32 to obtain dough. Let it rest for 1-2 hours, then freeze it for 24 hours. After thawing, cut the dough into rectangular pieces and deep-fry them. Gently stretch the pieces while deep-frying at 200℃ for 90 seconds to obtain fried dough sticks.

[0076] Comparative Example 3 (1) Preparation of soybean protein isolate solution: First, soybeans were crushed using a grinder to obtain soybean powder, which was then sieved through a 60-mesh stainless steel sieve to remove impurities. Next, n-hexane was added (20 g soybean powder was added to 100 mL), and the mixture was extracted in a constant temperature water bath at 60℃ for 30 min to dissolve the oil in the soybeans. After centrifugation at 5000 rpm for 15 min, the supernatant was discarded, and the precipitate was collected and dried in an oven at 50℃ for 20 min to obtain defatted soybean meal. The defatted soybean meal was mixed with deionized water at a ratio of 1:15, and the soybean protein was dissolved in 2 M NaOH solution to adjust the pH to 7.0~9.0. The mixture was stirred thoroughly to extract the alkali-dissolved soybean protein, and centrifuged at 8000 g for 30 min. The pH of the supernatant was then adjusted to 4.5~4.8 using 2 M HCl solution to precipitate the protein, and centrifuged at 6500 r / min for 20 min. The precipitate was then re-dissolved in deionized water, and the pH of the solution was adjusted to 7.0 until the precipitate was completely dissolved. The solution was freeze-dried to obtain soy protein isolate, which was then dissolved in deionized water (containing 0.02 wt% sodium azide), stirred at room temperature for 2 hours until fully dissolved, and hydrated overnight to obtain a soy protein isolate solution (concentration 10 wt%).

[0077] (2) Preparation of soy protein isolate stabilized gel emulsion: Mix soy protein isolate solution and soybean oil, and then disperse at high speed to obtain soy protein isolate stabilized gel emulsion; the oil phase of soy protein isolate gel solution is 80%. (3) Preparation of fried dough sticks: Mix flour, salt, sugar and water in a mass ratio of 62:1:1:32, add soy protein isolate gel emulsion to obtain dough, let it rise for 1-2 hours, freeze for 24 hours, then thaw, cut the dough into rectangular pieces, and fry them. When frying, gently stretch them, oil temperature 200℃, time 90s, to obtain fried dough sticks; the amount of soy protein isolate gel emulsion added is 30 wt% of the total mass of the dough.

[0078] Comparative Example 4 Referring to Example 7, only the volume ratio of soy protein isolate solution and egg white protein solution in the aqueous phase in step (3) is adjusted to 1:1.

[0079] The results showed that when soy protein isolate and egg white protein were mixed in a 1:1 ratio, although they complemented each other in terms of amino acid composition, this ratio had obvious drawbacks in practical applications: functionally, the gel properties and foaming properties of the two were significantly different, and it was difficult to form a stable internal network structure when mixed in equal amounts, which easily led to mutual interference of the network structure and weakened the overall texture stability and elasticity; sensorily, the beany taste of soybeans would increase, which would easily produce an uncoordinated complex odor and affect the flavor acceptance.

[0080] Comparative Example 5 Referring to Example 7, only the volume ratio of soy protein isolate solution and egg white protein solution in the aqueous phase in step (3) is adjusted to 3:1.

[0081] The results showed that a 3:1 blend of soy protein isolate and egg white protein had key defects. Nutritionally, the dominant position of soy protein meant that its methionine limitation remained prominent, limiting the improvement in amino acid complementarity. Functionally, the excellent gelling and foaming properties of egg white protein were significantly diluted, making it difficult to effectively improve the textural deficiencies of soy protein, which could easily result in a product with a powdery or coarse texture. At the same time, the beany taste of soybeans might still dominate in terms of flavor.

[0082] The parameter settings for Examples 1-7 and Comparative Examples 1-5 are shown in Tables 2 and 3 below: Table 2

[0083] Table 3

[0084] The obtained fried dough sticks were subjected to performance testing, and the test results are as follows: Figure 6 The images show scanning electron microscope (SEM) images of the dough from Examples 4-7 and Comparative Examples 1, 2, and 3 after freezing. In Examples 4-7, Examples 5 and 7, compared to Examples 4 and 6, showed an increased emulsion content while maintaining the same oil ratio. The images show a more compact dough structure, with the compound emulsion and gluten proteins combining to form a network structure with uniform internal pore distribution. The increased oil phase ratio further enhances the synergistic effect between the oil phase and the emulsion, resulting in a uniformly sized and densely distributed pore structure. Comparative Example 1 shows virtually no pores inside the dough; Comparative Example 2 exhibits a larger pore structure due to gas expansion; Comparative Example 3, with the addition of soy protein isolate gel emulsion, shows a more random surface pore distribution with significant size variations. These results indicate that the synergistic addition of the oil phase and the compound gel emulsion effectively improves the uniformity and density of the dough's microporous structure, thereby contributing to improved texture and mouthfeel of fried dough products.

[0085] Figure 7Images show the appearance of the dough after frying in Examples 4-7 and Comparative Examples 1, 2, and 3. Examples 4 and 5 show slightly smaller pores; Example 6 shows larger pores, but the surface is not sufficiently fluffy; Example 7 shows larger and more uniform pores with a greater distribution. Comparative Example 1, without any added emulsion, has inconspicuous internal pores and almost no surface fluff; Comparative Example 2 shows larger and more uniform pores and a sufficiently fluffy surface; Comparative Example 3, with an emulsion containing a single soy protein isolate dispersed phase, produces more fluffy fried dough sticks, superior to Comparative Example 1, but slightly inferior to Comparative Example 2. The results indicate that gel-like emulsions can significantly increase the pore structure of fried dough sticks, and the porosity is directly proportional to the amount added, which is beneficial for internal pore formation and increased crispness.

[0086] Figure 8 , 9 10 represents the brightness (L*) value, red / green spectral (a*) value, and yellow / blue spectral (b*) value of Examples 4-7 and Comparative Examples 1, 2, and 3, respectively. Figures 6-8 It can be seen that Comparative Examples 1, 2, and 3 have the highest L* values, while a* and b* values ​​are the lowest, indicating that the color of the control group is whitish. Examples 4-7 show a decreasing L* value and a significant increase in a* and b* values, exhibiting a golden-yellow color. The results indicate that the addition of soy protein isolate-egg white protein gel emulsion can improve the color of fried dough sticks.

[0087] Figure 11 The results show the textural hardness test results for Examples 4-7 and Comparative Examples 1, 2, and 3. Figure 11 It can be seen that Comparative Example 1 has the highest hardness, followed by Comparative Example 3, which also has relatively high hardness, while Comparative Example 2 has the lowest hardness. In Examples 4-7, the overall hardness difference is not significant, and is close to that of Comparative Example 2. Among them, Example 7 has the highest hardness, and Example 4 has the lowest hardness. The results indicate that the addition of soy protein isolate-egg white protein gel emulsion can improve the hardness of fried dough sticks.

[0088] Figure 12 , 13 The sensory evaluation test results of Examples 4-7 and Comparative Examples 1, 2, and 3 are presented. Figure 12 , 13It can be seen that, firstly, Comparative Example 2 performed best in terms of color, smell, taste, appearance, and overall acceptability; secondly, Example 5 performed well in terms of color, smell, taste, appearance, and overall acceptability; Examples 4, 5, and 6 performed worse than Example 7 in all aspects, with Example 4 being the worst; Comparative Example 1 had lower brittleness, poor leavening, and a worse taste compared to Examples 4-7; Comparative Example 3 was closer to the sensory effects of Examples 4-7, but worse than Examples 4-7. The results show that the fried dough sticks made by adding compound gel emulsion to the dough can achieve a level close to that made with aluminum-free fried dough stick leavening agent.

[0089] Figure 14 The results of the determination of oil oxidation in Examples 4-7 and Comparative Examples 1, 2, and 3 are as follows: Figure 14 It can be seen that the TBARs values ​​of Comparative Examples 1, 2, and 3 are relatively high. The TBARs values ​​of Examples 4 and 5 gradually decrease, as do those of Examples 7 and 8. The TBARs value of Example 4 is greater than that of Example 5, and the TBARs value of Example 6 is greater than that of Example 7; all are lower than those of Comparative Examples 1, 2, and 3. With the addition of the compound emulsion, the oxidation values ​​of Examples 4, 5, 6, and 7 decrease, and the antioxidant properties gradually increase. Among Examples 4, 5, 6, and 7, Example 6 is greater than Example 7, and Example 5 is greater than Example 4. The results indicate that as the proportion of oil in the fried dough sticks increases, the degree of oxidation of the fried dough sticks increases; and as the amount of compound emulsion added increases, the degree of oxidation of the fried dough sticks decreases.

[0090] Figure 15 The oil content results for Examples 4-7 and Comparative Examples 1, 2, and 3 are derived from... Figure 15 It can be seen that the oil content of Examples 4 and 5 gradually increases, as does the oil content of Examples 6 and 7. The oil content of Example 5 is significantly higher than that of Example 4, and the oil content of Example 7 is significantly higher than that of Example 6. The oil content of Example 6 is higher than that of Example 4; the oil content of Example 7 is higher than that of Example 5. The oil content of Comparative Example 2 is 35.86%, which is higher than that of Comparative Examples 1 and 3, and Comparative Examples 1-3 are all higher than those of Examples 4-7. The results show that compared with commercial leavening agents, gel emulsions reduce the oil content of fried dough sticks, and compound gel emulsions have a better oil-reducing effect. However, the higher the proportion of oil phase in the gel emulsion, the higher the oil content of the fried dough sticks.

[0091] Based on the results of the comparative examples and embodiments, this invention enhances the dough's moisture retention and structural integrity by adding a compound gel-like emulsion, thereby increasing the dough's antifreeze properties, improving the fluffiness and crispness of the fried dough sticks, and simultaneously reducing the oil content and degree of oil oxidation, effectively controlling the color of the fried dough sticks. This provides a convenient new method for enhancing the crispness of fried dough sticks, and is expected to drive technological innovation and quality improvement in the processing of other fried dough-based foods.

[0092] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A soy protein isolate-egg white protein gel emulsion, characterized in that, The gel-like emulsion was prepared by the following method: (1) Preparation of soy protein isolate solution: Soybeans are crushed and sieved to obtain soy flour. Hexane is added and extracted to dissolve the oil in the soy flour. Then, the supernatant is removed by centrifugation. The precipitate is collected and dried to obtain defatted soybean meal powder. The defatted soybean meal is mixed with water, and the pH is adjusted to alkaline. After centrifugation, the pH of the supernatant is adjusted to acidic and centrifuged to precipitate the protein. The precipitate is then re-dissolved in water, and the pH of the solution is adjusted to neutral until the precipitate is completely dissolved. After that, it is freeze-dried to obtain soy protein isolate. The soy protein isolate is dissolved in water to obtain soy protein isolate solution. The concentration of soy protein isolate solution is 10~20%; (2) Preparation Prepare egg white protein solution: Separate the egg yolk and egg white from the egg, add water to the egg white to obtain egg white solution, then add ethanol solution, stir and let stand, freeze dry to obtain egg white protein powder, then add water to reconstitute to prepare egg white protein solution; the concentration of egg white protein solution is 10~20%; (3) Prepare gel emulsion: Mix soy protein isolate solution, egg white protein solution and soybean oil, disperse at high speed to obtain soy protein isolate-egg white protein gel emulsion; the volume ratio of soy protein isolate solution and egg white protein solution is 1:1~3, the oil phase in soy protein isolate-egg white protein gel emulsion is 60%~80%, v / v.

2. The soy protein isolate-egg white protein gel emulsion according to claim 1, characterized in that, In step (1), the hexane extraction conditions are heating at 50-60 °C for 20-30 min.

3. The soy protein isolate-egg white protein gel emulsion according to claim 1, characterized in that, In step (1), alkalinity refers to a pH of 8-9, acidity refers to a pH of 4.5-4.8, and neutrality refers to a pH of 7.

0.

4. The soy protein isolate-egg white protein gel emulsion according to claim 1, characterized in that, The concentration of the egg white solution in step (2) is 1~5wt%.

5. The soy protein isolate-egg white protein gel emulsion according to claim 1, characterized in that, In step (2), the ratio of egg white solution to ethanol solution is 1:0.5~1.5; the concentration of ethanol solution is 40~60wt%.

6. The soy protein isolate-egg white protein gel emulsion according to claim 1, characterized in that, In step (3), the conditions for high-speed dispersion are 8000~10000 g for 1~5 min.

7. The application of the soy protein isolate-egg white protein gel emulsion according to any one of claims 1 to 6 in the food industry.

8. A method for preparing flaky fried dough sticks, characterized in that, Includes the following steps: Mix flour, salt, sugar and water, add soy protein isolate-egg white protein gel emulsion to get dough, let it rise and then cut it into rectangular pieces, deep-fry them to get fried dough sticks; Alternatively, mix flour, salt, sugar, and water, add soy protein isolate-egg white protein gel emulsion to obtain dough, let it rise, freeze it, thaw it, cut it into rectangular pieces, and deep-fry it to obtain fried dough sticks; The amount of soy protein isolate-egg white protein gel emulsion added is 25-30 wt% of the total dough mass.

9. The preparation method according to claim 8, characterized in that, The mass ratio of flour, salt, sugar, and water is 60~65:1:1:30~35.

10. The preparation method according to claim 8, characterized in that, Deep-frying is done at 190~200℃ for 1~2 minutes.

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