Vacuum low-temperature frying processing method for green-core broad beans

Abstract

The invention relates to the technical field of food processing engineering, and particularly discloses a vacuum low-temperature frying processing method of green-core broad beans. Comprising the following steps: S1, raw material pretreatment: selecting green-core broad beans, and removing mildewed particles to obtain cleaned broad beans; s2, soaking: putting the cleaned broad beans into a soaking solution, and soaking for 10-30 hours at the temperature of 18-28 DEG C under the assistance of ultrasonic waves with the frequency of 30-50 kHz to obtain softened broad beans; s3, performing micropore-airflow combined treatment; s4, carrying out two-stage variable-temperature fermentation; s5, carrying out gradient freezing-unfreezing circulation; s6, performing vacuum low-temperature segmented frying; s7, performing variable-frequency centrifugal deoiling; and S8, performing active seasoning and barrier packaging. The vacuum low-temperature frying processing method of the green-core broad beans can be used for producing high-quality healthy instant leisure broad bean products, and has the advantages that the oil content of the products is reduced, the crisp taste is kept, and the natural color, original nutritional ingredients and unique flavor of the green-core broad beans are reserved.

Description

Technical Field

[0001] This application relates to the field of food processing engineering technology, and more specifically, it relates to a method for vacuum low-temperature frying of green broad beans. Background Technology

[0002] Green-heart broad beans, as a high-quality grain raw material with both medicinal and edible properties, are applied in the field of food processing engineering technology, focusing on the high-value and diversified development of agricultural products. Through the deep integration of traditional techniques and modern processing technologies, they are widely used in the production of snack foods, condiments, canned foods, bean products, and fortified foods. The processing covers the entire process, including cleaning, sorting, color protection, dehydration, frying / baking / fermentation / puffing, seasoning, sterilization, and packaging, making them suitable for large-scale industrial production lines and specialty food processing scenarios. Their advantages lie in their strong adaptability to raw material characteristics. Green-heart broad beans are rich in protein, dietary fiber, vitamins, and minerals, and the green germ gives them a unique color and flavor. Through process optimization, nutrients and sensory characteristics can be efficiently preserved. The processing technology is highly compatible, adapting to traditional fermentation and braising processes to preserve flavor, and also combining modern technologies such as freeze-drying, microencapsulation, and ultra-high pressure sterilization to develop healthy and convenient products. Process parameters can be flexibly adjusted to meet upgraded requirements such as low oil, low salt, and no additives.

[0003] The green-hearted broad beans are processed through conventional washing, color preservation, frying or baking. However, these techniques often rely on high temperature and high oil processes, which can lead to products with high oil content, insufficient crispness, fading of natural color and loss of nutrients. It is difficult to meet the requirements of health, low fat and preservation of sensory quality at the same time. Summary of the Invention

[0004] To address the issues that lead to high oil content, insufficient crispness, fading of natural color, and loss of nutrients in green broad beans due to conventional washing, color protection, frying, or baking processes, this application provides a vacuum low-temperature frying method for green broad beans.

[0005] This application provides a method for vacuum low-temperature frying of green broad beans, employing the following technical solution:

[0006] A method for vacuum low-temperature frying green broad beans includes the following steps:

[0007] S1. Raw material pretreatment: Select green-hearted broad beans, remove moldy particles, and obtain cleaned broad beans;

[0008] S2. Soaking: Place the cleaned broad beans in the soaking solution and soak them at 18-28℃ for 10-30 hours with the assistance of ultrasound at a frequency of 30-50kHz to obtain softened broad beans.

[0009] S3. Micropore-airflow combined treatment: The softened broad beans are uniformly punctured with micropores to a depth of 1 / 5 to 1 / 3 of the thickness of the broad beans. After puncturing, the surface of the broad beans is impacted with airflow at a pressure of 0.2 to 0.5 MPa to obtain puffed broad beans.

[0010] S4. Two-stage variable temperature fermentation: The puffed broad beans are first fermented at 8-15℃ and 85%-90% relative humidity for 10-20 hours, and then left to stand at 0-5℃ for 5-10 hours to obtain fermented broad beans.

[0011] S5. Gradient freezing-thawing cycle: Fermented broad beans are first pre-frozen at -12℃ for 1 to 2 hours, then deep-frozen at -30℃ for 2 to 4 hours, and then thawed at -2 to 2℃ for 1 to 2 hours to obtain freeze-thawed broad beans;

[0012] S6. Vacuum low-temperature segmented frying: Frozen and thawed broad beans are placed under a vacuum of 0.088-0.095 MPa, first fried at 75-85℃ for 25-40 minutes, and then fried at 88-98℃ for 20-50 minutes to obtain pre-fried broad beans;

[0013] S7. Variable frequency centrifugal degreasing: The freshly fried broad beans are first degreased at a low speed of 300-500 r / min for 2-3 minutes under a vacuum of 0.080-0.085 MPa, and then degreased at a high speed of 600-800 r / min for 2-4 minutes to obtain low-fat broad beans.

[0014] S8. Active Flavoring and Barrier Packaging: Add a compound seasoning containing natural antioxidants to low-fat broad beans and use high-barrier aluminum film for nitrogen-filled packaging to obtain the finished product.

[0015] By adopting the above technical solutions, a continuous and synergistic process is achieved, from ultrasonic-assisted soaking, micropore-airflow combined treatment, two-stage variable-temperature fermentation, gradient freezing-thawing to vacuum low-temperature segmented frying. Among these processes, the cavitation effect of ultrasound promotes the transfer of moisture and functional components into the broad beans, laying the foundation for subsequent processing. The combination of micropore puncture and airflow impact disrupts the cell wall structure, forming preliminary puffing channels, which is beneficial for moisture migration and oil penetration during subsequent freezing and frying. The subsequent two-stage variable-temperature fermentation regulates microbial activity while promoting the formation of flavor precursors and moderate softening of texture. The gradient freezing-thawing cycle further expands the internal microporous structure through the repeated formation and melting of ice crystals, providing uniform dehydration channels for the vacuum frying stage. Ultimately, the product achieves ideal crispness, low oil content, and retains the natural color and nutrients of green-hearted broad beans at low temperatures.

[0016] Preferably, based on 100 parts by weight of broad beans, the soaking solution in step S2 consists of the following components in parts by weight: 100-300 parts water, 1.5-3 parts trehalose, 0.2-0.6 parts L-ascorbic acid calcium, and 0.5-1.5 parts potassium citrate.

[0017] By adopting the above technical solution, a composite soaking solution is composed of trehalose, L-ascorbic acid calcium, and potassium citrate. Trehalose, as a heat-stabilizing protective agent, can form a protective layer on the surface of broad bean tissue, which helps to reduce the damage of heat-sensitive components and inhibit oil oxidation during the subsequent high-temperature frying stage. L-ascorbic acid calcium has both antioxidant and calcium ion strengthening effects, and can interact with pectin substances in broad beans to enhance cell wall strength, which is beneficial to maintaining structural integrity and preventing excessive breakage during subsequent puncture and puffing processes. Potassium citrate can regulate osmotic pressure, promote uniform water penetration, and act as a pH buffer to provide an environment for subsequent fermentation processes, thereby ensuring the stability of processing and the quality of the final product.

[0018] Preferably, the micro-perforation in step S3 is performed using laser drilling, with a single hole diameter of 0.3–1.0 mm, 5–10 holes per broad bean, and the holes are evenly spaced; the gas used for airflow impact is carbon dioxide, the airflow temperature is 10–20°C, and the impact time is 3–8 seconds.

[0019] By adopting the above technical solution, the combined treatment of laser precision drilling and low-temperature carbon dioxide gas impact ensures the consistency of drilling depth and pore size, forming regular and uniform microchannels on the surface and shallow layer of broad beans. These channels serve as preset paths for moisture escape and oil penetration in subsequent processes. Subsequently, the impact of low-temperature carbon dioxide gas further expands the micropores and penetrates them into the interior using airflow pressure, achieving preliminary physical puffing and forming a loose initial structure. On the other hand, the inert environment of carbon dioxide inhibits the enzymatic browning reaction caused by mechanical damage. This step provides a uniform textural basis for subsequent fermentation and freezing processes and facilitates rapid and uniform dehydration during the frying stage.

[0020] Preferably, before the two-stage variable temperature fermentation in step S4, a compound microbial agent, including Lactobacillus plantarum and Streptococcus thermophilus, is added at a rate of 0.15% to 0.35% of the weight of the broad beans, and the oxygen concentration in the fermentation environment is controlled at 3% to 8%.

[0021] By adopting the above technical solution, a compound microbial agent containing Lactobacillus plantarum and Streptococcus thermophilus is added, and a two-stage variable-temperature fermentation is carried out under controlled oxygen conditions. The initial medium-temperature and high-humidity stage is conducive to the proliferation and metabolism of microorganisms, producing organic acids and flavor substances, while partially degrading macromolecules to improve texture. The subsequent low-temperature static stage inhibits excessive microbial activity and promotes the fusion and stabilization of flavor substances. Controlling the low oxygen concentration can guide the fermentation to be dominated by lactic acid fermentation, inhibiting the growth of aerobic putrefactive bacteria and the generation of undesirable flavors. This fermentation process not only gives the product a unique base flavor, but the acidic environment it produces also helps stabilize the color of broad beans and moderately softens the broad bean tissue after microporous treatment, preparing it for the change of moisture state in the next step of gradient freezing treatment.

[0022] Preferably, between steps S5 and S6, microwave-assisted drying is also included: placing the frozen-thawed broad beans in a microwave environment with a frequency of 2450MHz and drying them at 50-60℃ for 10-20 minutes to uniformly reduce the moisture content of the broad beans to 15%-18%.

[0023] By adopting the above technical solution, microwave-assisted drying causes the internal moisture of frozen-thawed broad beans to migrate and evaporate evenly due to heat, quickly reducing the overall moisture content to a suitable low range. This treatment avoids the phenomenon of dry outside and wet inside caused by traditional hot air drying, so that the broad beans have a uniform moisture distribution before entering the frying process. The uniform low initial moisture content reduces the violent boiling at the beginning of vacuum frying, making the moisture evaporation process more gradual and controllable, which is conducive to the formation of a uniform porous structure and crispy texture. At the same time, it can also shorten the total time of subsequent frying and improve processing efficiency.

[0024] Preferably, the frying oil used in step S6 is high-oleic sunflower oil or rice bran oil, and 0.02% to 0.06% of tea polyphenols are added to the oil as a natural antioxidant before frying.

[0025] By adopting the above technical solution, high-oleic sunflower seed oil or rice bran oil is selected as the frying medium, and tea polyphenols are added in advance. High-oleic oils are rich in monounsaturated fatty acids, which have high oxidative stability and can remain stable during long-term vacuum low-temperature frying, thus delaying the deterioration of the oil. The added tea polyphenols, as highly efficient natural antioxidants, can capture free radicals in the frying system and further inhibit the oxidation, polymerization, and hydrolysis reactions of the oil during the heating process, thereby ensuring the quality stability of the frying oil during the processing cycle. This reduces the risk of oxidative rancidity of the product during its shelf life. This, together with the subsequent barrier packaging, ensures the product's shelf life.

[0026] Preferably, the vacuum frying in step S6 adopts a dynamic temperature-changing process, wherein the initial frying is 0-20 minutes with the oil temperature controlled at 75-85℃; the middle frying is 20-40 minutes with the oil temperature rising to 88-92℃; and the later frying is 40-70 minutes with the oil temperature further rising to 92-98℃. Throughout the process, the oil-to-material mass ratio is controlled at 10:1-15:1.

[0027] By adopting the above technical solution, the dynamic temperature-controlled vacuum frying process aims to allow the residual ice crystals or moisture inside the broad beans to evaporate slowly in the initial low-temperature stage, avoiding excessively rapid surface crusting that would hinder internal dehydration. The appropriate temperature increase in the middle stage accelerates the moisture removal rate, forming a crispy structure. The final dehydration is completed at a higher vacuum and temperature in the later stage, ensuring the product achieves the required moisture content and crispness. Simultaneously, a sufficient oil-to-fat ratio ensures the stability of the frying system's temperature field, preventing a sudden drop in oil temperature and insufficient moisture evaporation due to excessive feed. This makes the heat transfer and moisture migration process more uniform and controllable. This process design is key to achieving low oil content, high crispness, and uniform color in the product.

[0028] Preferably, after the variable frequency centrifugal degreasing in step S7, the oil content of the broad beans is ≤10%, the moisture content is ≤2.5%, and the crispness of the product is ≥850g·s⁻¹.

[0029] By adopting the above technical solution, in the variable frequency centrifugal degreasing process of low speed followed by high speed, the initial low-speed degreasing removes free oils adhering to the surface of broad beans and in larger pores, while the subsequent high-speed degreasing uses centrifugal force to effectively remove oils hidden deep in the fine pores. This step-by-step approach can efficiently reduce the total oil content while reducing product breakage caused by single high-speed rotation. The vacuum environment avoids oxidation of materials during centrifugation. The oil content, moisture content, and crispness of the degreased product are used as quantitative indicators. Moisture content is a prerequisite for the product to maintain a crisp texture and have a long shelf life, while crispness defines the crispness standard that the product should achieve, providing a guarantee for the final quality.

[0030] Preferably, based on 100 parts by weight of low-fat broad beans, the compound seasoning in step S8 consists of the following components in parts by weight: 1-2 parts salt, 0.6-1.2 parts yeast extract, 0.2-0.6 parts Sichuan pepper oil, and 0.05-0.15 parts rosemary extract.

[0031] By adopting the above technical solution, an active seasoning is formulated from salt, yeast extract, Sichuan pepper oil, and rosemary extract. Salt provides a basic salty taste and enhances flavor perception; yeast extract is rich in amino acids and nucleotides, which can enhance the umami and mellow taste of the product, and form a synergistic flavor-enhancing effect with the flavor substances of fermented broad beans; Sichuan pepper oil then gives the product a fresh and numbing flavor; and rosemary extract, as a natural flavor substance, provides an additional antioxidant layer for the product during the seasoning stage due to its strong antioxidant properties. Together with the tea polyphenols added to the frying oil and the subsequent nitrogen-filled packaging, it forms a multi-level antioxidant system. This compound seasoning not only gives the product a rich and harmonious flavor, but also further enhances its storage stability.

[0032] Preferably, the packaging for step S8 uses an aluminum foil-polyamide composite film, is nitrogen-filled, and then stored in a light-proof environment at 4–25°C, resulting in a product shelf life of more than 18 months.

[0033] By adopting the above technical solution, nitrogen-filled packaging is performed using a high-barrier composite film such as aluminum foil-polyamide, and the packaged product is stored in a light-proof environment. The aluminum foil layer provides the ability to block moisture, oxygen, and light, while the polyamide layer gives the packaging high mechanical properties. Nitrogen filling provides a low-oxygen or anaerobic inert environment, inhibiting oil oxidation, microbial growth, and deterioration of flavor substances. Light-proof storage avoids photo-oxidation reactions caused by light. Combined with the control of microorganisms, moisture, and oxidation at each stage of processing, this packaging and storage condition, along with the product's inherent low water activity and added antioxidants, ensures that the product can achieve a long shelf life of more than 18 months under specified temperature conditions.

[0034] In summary, this application has the following beneficial effects:

[0035] 1. This application employs a continuous and synergistic process that includes ultrasonic-assisted soaking, micropore-airflow combined treatment, two-stage variable temperature fermentation, gradient freezing-thawing, and vacuum low-temperature segmented frying. The cavitation effect of ultrasound promotes the penetration of moisture and functional components, laying the foundation for subsequent processing. Meanwhile, micropore puncture and airflow impact form puffing channels, which, in conjunction with subsequent fermentation and freezing steps, further expand the internal microporous structure. Ultimately, the product achieves ideal crispness, low oil content, and retains the natural color and nutritional components of green broad beans under low-temperature frying conditions.

[0036] 2. In this application, a soaking solution composed of trehalose, L-ascorbic acid calcium and potassium citrate is preferably used, combined with micropore-airflow combined treatment of perforation and carbon dioxide airflow impact. The soaking solution regulates the osmotic pressure of broad beans and enhances cell wall strength under the assistance of ultrasound, providing whole broad beans for subsequent puncture. The perforation forms uniform microchannels and the airflow impact has a synergistic effect on the initial puffing. Combined with two-stage variable temperature fermentation to regulate flavor and texture, and gradient freezing-thawing cycle to expand pores, the effect is to improve the internal water migration path of broad beans, inhibit enzymatic browning, and provide uniform dehydration and oil penetration conditions for the vacuum frying stage.

[0037] 3. The method of this application uses dynamic temperature-controlled vacuum frying, frequency-controlled centrifugal degreasing, and the addition of compound seasonings containing natural antioxidants, followed by high-barrier nitrogen-filled packaging. The temperature gradient control during the frying stage and the vacuum environment during the degreasing step work together to reduce the oil and water content of the product. The rosemary extract in the seasoning and the tea polyphenols in the frying oil form a multi-level antioxidant system. Combined with the light-proof and oxygen-barrier storage of the aluminum foil composite film nitrogen-filled packaging, the product achieves stable crispness, meets the oil and moisture content standards, and has an extended shelf life. Attached Figure Description

[0038] Figure 1 This is a flowchart of a vacuum low-temperature frying method for green broad beans proposed in this application. Detailed Implementation

[0039] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0040] Example 1: This example provides a method for vacuum low-temperature frying of green broad beans, comprising the following steps:

[0041] S1. Raw material pretreatment: Select green-hearted broad beans, remove moldy particles, and obtain cleaned broad beans.

[0042] S2. Soaking: Place the cleaned broad beans in the soaking solution and soak them at 18°C ​​for 10 hours with the assistance of ultrasound at a frequency of 30kHz to obtain softened broad beans.

[0043] The soaking solution, with 100 parts by weight of broad beans, consists of the following components in parts by weight: 100 parts water, 1.5 parts trehalose, 0.2 parts L-ascorbic acid calcium, and 0.5 parts potassium citrate.

[0044] S3. Micropore-airflow combined treatment: The softened broad beans are uniformly punctured with micropores to a depth of one-fifth of the bean thickness. After puncturing, the surface of the broad beans is impacted with airflow at a pressure of 0.2 MPa to obtain puffed broad beans.

[0045] Among them, the micro-puncture is performed by laser drilling, with a single hole diameter of 0.3mm. Five holes are drilled per broad bean, and the spacing between the holes is evenly distributed. The gas used for airflow impact is carbon dioxide, the airflow temperature is 10℃, and the impact time is 3 seconds.

[0046] S4. Two-stage variable temperature fermentation: The puffed broad beans are first fermented at 8℃ and 85% relative humidity for 10 hours, and then left to stand at 0℃ for 5 hours to obtain fermented broad beans.

[0047] Before the two-stage variable temperature fermentation, a compound microbial agent, including Lactobacillus plantarum and Streptococcus thermophilus, is added at a rate of 0.15% of the weight of the broad beans, and the oxygen concentration in the fermentation environment is controlled at 3%.

[0048] S5. Gradient freezing-thawing cycle: Fermented broad beans are first pre-frozen at -12℃ for 1 hour, then deep-frozen at -30℃ for 2 hours, and then thawed at -2℃ for 1 hour to obtain frozen-thawed broad beans.

[0049] Between steps S5 and S6, microwave-assisted drying is also included: the frozen and thawed broad beans are placed in a microwave environment with a frequency of 2450MHz and dried at 50℃ for 10 minutes to reduce the moisture content of the broad beans to 15% evenly.

[0050] S6. Vacuum low-temperature segmented frying: Frozen and thawed broad beans are placed under a vacuum of 0.088 MPa, first fried at 75°C for 25 minutes, and then fried at 88°C for 20 minutes to obtain the first-fried broad beans.

[0051] The oil used for frying is high-oleic sunflower seed oil, with 0.02% tea polyphenols added as a natural antioxidant before frying. Vacuum frying adopts a dynamic temperature-changing process, with the initial frying time being 0-20 minutes and the oil temperature controlled at 75℃; the middle frying time being 20-40 minutes and the oil temperature rising to 88℃; and the later frying time being 40-70 minutes and the oil temperature further rising to 92℃. Throughout the process, the oil-to-seed mass ratio is controlled at 10:1.

[0052] S7. Variable frequency centrifugal degreasing: The freshly fried broad beans are first degreased at a low speed of 300 r / min for 2 minutes under a vacuum of 0.080 MPa, and then degreased at a high speed of 600 r / min for 2 minutes to obtain low-fat broad beans.

[0053] Among them, the oil content of broad beans after variable frequency centrifugal degreasing is ≤10%, the moisture content is ≤2.5%, and the crispness of the product is ≥850g·s⁻¹.

[0054] S8. Active Flavoring and Barrier Packaging: Add a compound seasoning containing natural antioxidants to low-fat broad beans and use high-barrier aluminum film for nitrogen-filled packaging to obtain the finished product.

[0055] The compound seasoning, with 100 parts by weight of low-fat broad beans, consists of the following components by weight: 1 part salt, 0.6 parts yeast extract, 0.2 parts Sichuan pepper oil, and 0.05 parts rosemary extract. The packaging uses aluminum foil-polyamide composite film, and after nitrogen filling, it is placed in a light-proof environment and stored at 4°C. The product has a shelf life of more than 18 months.

[0056] Example 2: This example provides a method for vacuum low-temperature frying of green broad beans, comprising the following steps:

[0057] S1. Raw material pretreatment: Select green-hearted broad beans, remove moldy particles, and obtain cleaned broad beans.

[0058] S2. Soaking: Place the cleaned broad beans in the soaking solution and soak them at 23°C for 20 hours with the assistance of ultrasound at a frequency of 40kHz to obtain softened broad beans.

[0059] The soaking solution, with 100 parts by weight of broad beans, consists of the following components in parts by weight: 200 parts water, 2.3 parts trehalose, 0.4 parts L-ascorbic acid calcium, and 1.0 parts potassium citrate.

[0060] S3. Micropore-airflow combined treatment: The softened broad beans are uniformly punctured with micropores to a depth of one-quarter of the thickness of the broad bean. After puncturing, the surface of the broad bean is impacted by an airflow with a pressure of 0.35 MPa to obtain puffed broad beans.

[0061] Among them, the micro-perforation is performed by laser drilling, with a single hole diameter of 0.6 mm. Seven holes are drilled in each broad bean, and the holes are evenly distributed. The gas used for airflow impact is carbon dioxide, the airflow temperature is 15℃, and the impact time is 6 seconds.

[0062] S4. Two-stage variable temperature fermentation: The puffed broad beans are first fermented at 12℃ and 87% relative humidity for 15 hours, and then left to stand at 2℃ for 8 hours to obtain fermented broad beans.

[0063] Before the two-stage variable temperature fermentation, a compound microbial agent, including Lactobacillus plantarum and Streptococcus thermophilus, is added at a rate of 0.25% of the weight of the broad beans, and the oxygen concentration in the fermentation environment is controlled at 6%.

[0064] S5. Gradient freezing-thawing cycle: Fermented broad beans are first pre-frozen at -12℃ for 1.5 hours, then deep-frozen at -35℃ for 3 hours, and then thawed at 0℃ for 1.5 hours to obtain freeze-thawed broad beans.

[0065] Between steps S5 and S6, microwave-assisted drying is also included: the frozen and thawed broad beans are placed in a microwave environment with a frequency of 2450MHz and dried at 55℃ for 15 minutes to reduce the moisture content of the broad beans to 17% evenly.

[0066] S6. Vacuum low-temperature segmented frying: Frozen and thawed broad beans are placed under a vacuum of 0.092 MPa, first fried at 80℃ for 33 minutes, and then fried at 93℃ for 35 minutes to obtain the first fried broad beans.

[0067] The oil used for frying is rice bran oil, with 0.04% tea polyphenols added as a natural antioxidant before frying. Vacuum frying adopts a dynamic temperature-changing process, with the initial frying time being 0-20 minutes and the oil temperature controlled at 80℃; the middle frying time being 20-40 minutes and the oil temperature rising to 90℃; and the later frying time being 40-70 minutes and the oil temperature further rising to 95℃. Throughout the process, the oil-to-oil mass ratio is controlled at 12:1.

[0068] S7. Variable frequency centrifugal degreasing: The freshly fried broad beans are first degreased at a low speed of 400 r / min for 2.5 minutes under a vacuum of 0.083 MPa, and then degreased at a high speed of 700 r / min for 3 minutes to obtain low-fat broad beans.

[0069] Among them, the oil content of broad beans after variable frequency centrifugal degreasing is ≤10%, the moisture content is ≤2.5%, and the crispness of the product is ≥850g·s⁻¹.

[0070] S8. Active Flavoring and Barrier Packaging: Add a compound seasoning containing natural antioxidants to low-fat broad beans and use high-barrier aluminum film for nitrogen-filled packaging to obtain the finished product.

[0071] The compound seasoning, with 100 parts by weight of low-fat broad beans, consists of the following components by weight: 1.5 parts salt, 0.9 parts yeast extract, 0.4 parts Sichuan pepper oil, and 0.1 parts rosemary extract. The packaging uses aluminum foil-polyamide composite film, and after nitrogen filling, it is placed in a light-proof environment and stored at 15°C. The product has a shelf life of more than 18 months.

[0072] Example 3: This example provides a method for vacuum low-temperature frying of green broad beans, comprising the following steps:

[0073] S1. Raw material pretreatment: Select green-hearted broad beans, remove moldy particles, and obtain cleaned broad beans.

[0074] S2. Soaking: Place the cleaned broad beans in the soaking solution and soak them at 28°C for 30 hours with the assistance of ultrasound at a frequency of 50kHz to obtain softened broad beans.

[0075] The soaking solution, with 100 parts by weight of broad beans, consists of the following components in parts by weight: 300 parts water, 3 parts trehalose, 0.6 parts L-ascorbic acid calcium, and 1.5 parts potassium citrate.

[0076] S3. Micropore-airflow combined treatment: The softened broad beans are uniformly punctured with micropores to a depth of one-third of the thickness of the broad bean. After puncturing, the surface of the broad bean is impacted by an airflow with a pressure of 0.5 MPa to obtain puffed broad beans.

[0077] Among them, the micro-perforation is performed by laser drilling, with a single hole diameter of 1.0 mm. Ten holes are drilled in each broad bean, and the holes are evenly distributed. The gas used for airflow impact is carbon dioxide, the airflow temperature is 20℃, and the impact time is 8 seconds.

[0078] S4. Two-stage variable temperature fermentation: The puffed broad beans are first fermented at 15℃ and 90% relative humidity for 20 hours, and then left to stand at 5℃ for 10 hours to obtain fermented broad beans.

[0079] Before the two-stage variable temperature fermentation, a compound microbial agent, including Lactobacillus plantarum and Streptococcus thermophilus, is added at a rate of 0.35% of the weight of the broad beans, and the oxygen concentration in the fermentation environment is controlled at 8%.

[0080] S5. Gradient freezing-thawing cycle: Fermented broad beans are first pre-frozen at -12℃ for 2 hours, then deep-frozen at -40℃ for 4 hours, and then thawed at 2℃ for 2 hours to obtain freeze-thawed broad beans.

[0081] Between steps S5 and S6, microwave-assisted drying is also included: the frozen and thawed broad beans are placed in a microwave environment with a frequency of 2450MHz and dried at 60℃ for 20 minutes to reduce the moisture content of the broad beans to 18% evenly.

[0082] S6. Vacuum low-temperature segmented frying: Frozen and thawed broad beans are placed under a vacuum of 0.095 MPa, first fried at 85°C for 40 minutes, and then fried at 98°C for 50 minutes to obtain the first-fried broad beans.

[0083] The oil used for frying is high-oleic sunflower seed oil, with 0.06% tea polyphenols added as a natural antioxidant before frying. Vacuum frying adopts a dynamic temperature-changing process, with the initial frying time being 0-20 minutes and the oil temperature controlled at 85℃; the middle frying time being 20-40 minutes and the oil temperature rising to 92℃; and the later frying time being 40-70 minutes and the oil temperature further rising to 98℃. Throughout the process, the oil-to-seed mass ratio is controlled at 15:1.

[0084] S7. Variable frequency centrifugal degreasing: The freshly fried broad beans are first degreased at a low speed of 500 r / min for 3 minutes under a vacuum of 0.085 MPa, and then degreased at a high speed of 800 r / min for 4 minutes to obtain low-fat broad beans.

[0085] Among them, the oil content of broad beans after variable frequency centrifugal degreasing is ≤10%, the moisture content is ≤2.5%, and the crispness of the product is ≥850g·s⁻¹.

[0086] S8. Active Flavoring and Barrier Packaging: Add a compound seasoning containing natural antioxidants to low-fat broad beans and use high-barrier aluminum film for nitrogen-filled packaging to obtain the finished product.

[0087] The compound seasoning, with 100 parts by weight of low-fat broad beans, consists of the following components in parts by weight: 2 parts salt, 1.2 parts yeast extract, 0.6 parts Sichuan pepper oil, and 0.15 parts rosemary extract. The packaging uses aluminum foil-polyamide composite film, and after nitrogen filling, it is placed in a light-proof environment and stored at 25°C. The product has a shelf life of more than 18 months.

[0088] Comparative Example 1: This comparative example refers to the content of Example 1, except that the ultrasonic frequency in step S2 is 18kHz, and the rest is the same as Example 1.

[0089] Comparative Example 2: This comparative example refers to the content of Example 1, except that the airflow pressure in step S3 is 0.12 MPa, and the rest is the same as Example 1.

[0090] Comparative Example 3: This comparative example refers to the content of Example 1, except that the amount of compound microbial agent added in step S4 is 0.09% of the weight of broad beans, and the rest is the same as Example 1.

[0091] Comparative Example 4: This comparative example refers to the content of Example 1, except that the deep freezing temperature in step S5 is -21°C, and the rest is the same as Example 1.

[0092] Comparative Example 5: This comparative example refers to the content of Example 1, except that the first stage of vacuum low-temperature segmented frying in step S6 is 105°C, and the rest is the same as in Example 1.

[0093] Comparative Example 6: This comparative example refers to the content of Example 1, except that the low-speed deoiling speed of the variable frequency centrifugal deoiling in step S7 is 180 r / min, and the rest is the same as Example 1.

[0094] Performance testing

[0095] Sample preparation: The samples for performance testing were prepared according to the process flow of Examples 1-3, and comparative samples of Comparative Examples 1-6 were also prepared. After frying, degreasing and seasoning, all samples were temporarily sealed and stored under the same environmental conditions to ensure that the pretreatment conditions were consistent and to eliminate the interference of external factors on the test results.

[0096] Crispness testing: A puncture test was performed using a texture analyzer. A cylindrical probe with a diameter of 2 mm was used to penetrate the broad bean sample at a speed of 1 mm / s. The maximum puncture force and the area of ​​the fracture curve were recorded. Crispness was expressed as fracture energy value, with the unit being g·s. -1The higher the value, the better the crispness; this test directly reflects the puffing effect of micropore-airflow combined treatment and gradient freezing on cell structure; the test standard refers to GB / T30767-2014 "Food Texture Evaluation Method".

[0097] Oil content detection: Soxhlet extraction was used with petroleum ether as solvent. The crushed broad bean sample was continuously extracted for 6 hours. The oil content was obtained by the difference in mass before and after extraction. This index is used to verify the inhibitory effect of vacuum segmented frying and variable frequency centrifugation on oil penetration. The oil content must be less than 10% to meet the design requirements. The test standard refers to GB5009.6-2016 "National Food Safety Standard - Determination of Fat in Food".

[0098] Moisture content detection: The direct drying method was used, and the sample was dried at 105℃ to constant weight. The mass loss rate was obtained to determine the moisture content. This test can evaluate the regulatory effect of microwave-assisted drying and gradient freezing on moisture distribution. The test standard refers to GB5009.3-2016 "National Food Safety Standard - Determination of Moisture in Food".

[0099] Accelerated Oxidative Stability Test: Samples were stored in a 60℃ constant temperature chamber for 14 days to simulate long-term storage conditions; peroxide value was measured weekly using the iodometric method; this test was used to verify the effectiveness of the antioxidant system constructed from tea polyphenols and rosemary extract, as well as the inhibitory effect of nitrogen-filled packaging on lipid oxidation; the test standards were in accordance with GB5009.227-2016 "National Food Safety Standard - Determination of Peroxide Value in Food" and GB5009.229-2016 "National Food Safety Standard - Determination of Acid Value in Food".

[0100] Table 1: Comparison of Detection Data between Examples and Comparative Examples

[0101] Group <![CDATA[Crispness (g·s -1 )]]> Oil content (%) Moisture content (%) Peroxide value (meq / kg) after 14 days of storage Example 1 892 9.8 2.1 2.5 Example 2 915 9.2 2.3 2.8 Example 3 948 8.6 2.4 3.1 Comparative Example 1 712 11.5 3.8 4.7 Comparative Example 2 735 13.2 3.5 5.2 Comparative Example 3 698 14.0 3.2 6.8 Comparative Example 4 765 12.8 3.0 4.0 Comparative Example 5 580 18.5 1.5 10.5 Comparative Example 6 625 16.4 2.8 7.6

[0102] Example Conclusion:

[0103] Based on Examples 1-3 and Comparative Example 1, and in conjunction with Table 1, it can be seen that an appropriate ultrasonic frequency during the soaking step can promote the penetration of moisture and functional components, thereby improving the textural basis of broad beans; insufficient frequency will lead to insufficient softening, weaken the subsequent puffing and dehydration effects, thereby reducing the crispness of the product and increasing the oil content and oxidation risk.

[0104] Based on Examples 1-3 and Comparative Example 2, and in conjunction with Table 1, it can be seen that appropriate airflow pressure in the micropore-airflow combined treatment is an influencing factor in the formation of a uniform pore structure. Insufficient pressure will limit the puffing degree of broad beans, affect the uniformity of moisture evaporation and oil distribution during frying, and ultimately lead to a decrease in product crispness and an increase in oil content.

[0105] Based on Examples 1-3 and Comparative Example 3, and in conjunction with Table 1, it can be seen that the amount of compound microbial agent added in the two-stage variable temperature fermentation affects the degree of fermentation and flavor formation; insufficient addition will weaken the effect of microorganisms on the structure of broad beans, reduce the porosity of cell walls, and thus affect the crispness and oxidative stability of the final product.

[0106] Based on Examples 1-3 and Comparative Example 4, and in conjunction with Table 1, it can be seen that the deep freezing temperature in gradient freezing affects the formation and distribution of ice crystals. Insufficient deep freezing temperature leads to coarse ice crystals, which damages the integrity of cell structure, weakens the synergistic effect of subsequent freeze-thaw cycles, and results in insufficient product texture and high oil content.

[0107] Based on Examples 1-3 and Comparative Example 5, and in conjunction with Table 1, it can be seen that the initial temperature control of vacuum low-temperature segmented frying can regulate the balance between moisture evaporation and oil penetration. If the initial temperature is too high, it will cause the surface to harden rapidly, hindering the removal of internal moisture, and at the same time exacerbating oil penetration and thermal oxidation reactions, resulting in a decrease in the crispness of the product and a deterioration in oxidative stability.

[0108] Based on Examples 1-3 and Comparative Example 6, and in conjunction with Table 1, it can be seen that the speed setting in the low-speed stage of variable frequency centrifugal degreasing affects the removal efficiency of free oil on the surface; insufficient speed will lead to incomplete degreasing, causing residual oil to oxidize more rapidly during storage, and also affecting the crispness of the product texture, highlighting the importance of the synergy between segmented degreasing and speed in controlling the oil content.

[0109] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for vacuum low-temperature frying of green-fleshed broad beans, characterized in that, Includes the following steps: S1. Raw material pretreatment: Select green-hearted broad beans, remove moldy particles, and obtain cleaned broad beans; S2. Soaking: Place the cleaned broad beans in the soaking solution and soak them at 18-28℃ for 10-30 hours with the assistance of ultrasound at a frequency of 30-50kHz to obtain softened broad beans. S3. Micropore-airflow combined treatment: The softened broad beans are uniformly punctured with micropores to a depth of 1 / 5 to 1 / 3 of the thickness of the broad beans. After puncturing, the surface of the broad beans is impacted with airflow at a pressure of 0.2 to 0.5 MPa to obtain puffed broad beans. S4. Two-stage variable temperature fermentation: The puffed broad beans are first fermented at 8-15℃ and 85%-90% relative humidity for 10-20 hours, and then left to stand at 0-5℃ for 5-10 hours to obtain fermented broad beans. S5. Gradient freezing-thawing cycle: Fermented broad beans are first pre-frozen at -12℃ for 1 to 2 hours, then deep-frozen at -30℃ for 2 to 4 hours, and then thawed at -2 to 2℃ for 1 to 2 hours to obtain freeze-thawed broad beans; S6. Vacuum low-temperature segmented frying: Frozen and thawed broad beans are placed under a vacuum of 0.088-0.095 MPa, first fried at 75-85℃ for 25-40 minutes, and then fried at 88-98℃ for 20-50 minutes to obtain pre-fried broad beans; S7. Variable frequency centrifugal degreasing: The freshly fried broad beans are first degreased at a low speed of 300-500 r / min for 2-3 minutes under a vacuum of 0.080-0.085 MPa, and then degreased at a high speed of 600-800 r / min for 2-4 minutes to obtain low-fat broad beans. S8. Active Flavoring and Barrier Packaging: Add a compound seasoning containing natural antioxidants to low-fat broad beans and use high-barrier aluminum film for nitrogen-filled packaging to obtain the finished product.

2. The method for vacuum low-temperature frying green broad beans according to claim 1, characterized in that, Based on 100 parts by weight of broad beans, the soaking solution in step S2 consists of the following components in parts by weight: 100-300 parts water, 1.5-3 parts trehalose, 0.2-0.6 parts L-ascorbic acid calcium, and 0.5-1.5 parts potassium citrate.

3. The method for vacuum low-temperature frying green broad beans according to claim 1, characterized in that, The micro-perforation in step S3 is performed using laser drilling, with a single hole diameter of 0.3–1.0 mm. Each broad bean has 5–10 holes, and the holes are evenly spaced. The gas used for airflow impact is carbon dioxide, with a gas temperature of 10–20°C and an impact time of 3–8 seconds.

4. The method for vacuum low-temperature frying green broad beans according to claim 1, characterized in that, Before the two-stage variable-temperature fermentation in step S4, a compound microbial agent, including Lactobacillus plantarum and Streptococcus thermophilus, is added at a rate of 0.15% to 0.35% of the weight of broad beans. The oxygen concentration in the fermentation environment is controlled at 3% to 8%.

5. The method for vacuum low-temperature frying green broad beans according to claim 1, characterized in that, Between steps S5 and S6, microwave-assisted drying is also included: the frozen and thawed broad beans are placed in a microwave environment with a frequency of 2450MHz and dried at 50-60℃ for 10-20 minutes to reduce the moisture content of the broad beans to 15%-18% evenly.

6. The method for vacuum low-temperature frying green broad beans according to claim 1, characterized in that, In step S6, the frying oil is high-oleic sunflower oil or rice bran oil, and 0.02% to 0.06% of tea polyphenols are added to the oil as a natural antioxidant before frying.

7. The method for vacuum low-temperature frying green broad beans according to claim 1, characterized in that, The vacuum frying process in step S6 adopts a dynamic temperature-changing process. The initial frying time is 0-20 minutes, with the oil temperature controlled at 75-85℃; the middle frying time is 20-40 minutes, with the oil temperature rising to 88-92℃; and the later frying time is 40-70 minutes, with the oil temperature further rising to 92-98℃. Throughout the process, the oil-to-material mass ratio is controlled at 10:1-15:

1.

8. The method for vacuum low-temperature frying green broad beans according to claim 1, characterized in that, After the variable frequency centrifugal degreasing in step S7, the oil content of the broad beans is ≤10%, the moisture content is ≤2.5%, and the crispness of the product is ≥850g·s⁻¹.

9. A method for vacuum low-temperature frying green broad beans according to claim 1, characterized in that, Based on 100 parts by weight of low-fat broad beans, the compound seasoning in step S8 consists of the following components in parts by weight: 1-2 parts salt, 0.6-1.2 parts yeast extract, 0.2-0.6 parts Sichuan pepper oil, and 0.05-0.15 parts rosemary extract.

10. A method for vacuum low-temperature frying green broad beans according to claim 1, characterized in that, The packaging for step S8 uses an aluminum foil-polyamide composite film. After nitrogen-filled packaging, it is placed in a light-proof environment and stored at 4–25°C. The product has a shelf life of more than 18 months.

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