Bread processing method capable of prolonging shelf life

Abstract

The invention discloses a bread processing method capable of prolonging shelf life, and relates to the field of bread processing, and the method comprises the following steps: S1, raw material pretreatment; s2, dough preparation and gluten strengthening; s3, performing variable-temperature dynamic fermentation; S4, performing segmented baking and vacuum top-speed cooling; s5, composite sterilization treatment; and S6, active packaging and storage. According to the preparation method, a natural antibacterial system is constructed by utilizing a nano-zinc antibacterial agent, lactobacillus acidophilus and the like, starch aging is delayed by combining beta-glucan microcapsules and resistant starch, and during processing, microorganisms are killed and a dough structure is kept under a non-thermal condition through PEF pretreatment, variable-temperature fermentation, segmented baking and HPP cold sterilization; the packaging is performed through the slow-release antibacterial film and the humidity self-adjusting film, a suitable storage environment is maintained, the shelf life of the bread is prolonged under the condition that no chemical preservative is added, the moisture retention rate is increased, the starch retrogradation degree is reduced, and meanwhile the high-quality taste of the bread is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of bread processing, and specifically to a bread processing method for extending the shelf life. Background Art

[0002] Bread is a food made by grinding grains and heating, with wheat flour as the main raw material, and yeast, eggs, oils, sugars, salts, etc. as auxiliary materials. It is made by adding water to form a dough, and then processed through processes such as dividing, shaping, proofing, baking, and cooling.

[0003] For example, in "A Bread and Its Preparation Method" with the publication number CN117441753A, the bread includes 100 parts to 150 parts of quinoa flour, 1000 parts of flour, 15 parts to 30 parts of eggs, 20 parts to 40 parts of vegetable oil, 60 parts to 100 parts of granulated sugar, 5 parts to 10 parts of dry yeast, 10 parts to 20 parts of edible salt, and 100 parts to 300 parts of water by weight.

[0004] In the prior art, as an instant food with high moisture and high carbohydrates, bread provides an ideal growth environment for molds, yeasts, and bacteria. During storage, the internal moisture of the bread migrates to the surface, resulting in softening of the surface and drying of the interior, which also creates conditions for the growth of microorganisms, leading to a short safe use period of the bread. When adding chemical preservatives to sterilize during the bread production process, a single preservative is difficult to cover all types of microorganisms, and some chemical preservatives will become ineffective due to high-temperature baking. At the same time, long-term intake of chemical preservatives can cause metabolic disorders and pose health risks. Summary of the Invention

[0005] The purpose of the present invention is to provide a bread processing method for extending the shelf life, so as to solve the problems proposed in the above background art that during storage, the internal moisture of the bread migrates to the surface, resulting in softening of the surface and drying of the interior, which also creates conditions for the growth of microorganisms, and the addition of chemical preservatives not only makes some chemical preservatives ineffective due to high-temperature baking, but also causes metabolic disorders when taken for a long time.

[0006] To achieve the above purpose, the present invention provides the following technical solution: A bread processing method for extending the shelf life, including the following steps:

[0007] S1. Raw material pretreatment: Prepare dry raw materials and then sieve to remove impurities. Dissolve and mix wet raw materials, and let it stand to obtain a pretreatment solution;

[0008] S2. Dough modulation and gluten strengthening: Stir and mix the pretreatment solution with dry raw materials, and send it to a high-voltage pulsed electric field device for pretreatment to strengthen the dough structure;

[0009] S3. Variable-temperature dynamic fermentation: Control the temperature and fermentation environment, and perform primary fermentation and secondary fermentation:

[0010] S4, Segmented Baking and Vacuum Rapid Cooling: Feed the dough into the oven for segmented baking, and transfer it to a vacuum cooler for cooling after baking.

[0011] S5, Composite Sterilization Treatment: Perform ultraviolet sterilization and ultra-high pressure sterilization on the bread to enhance sterilization.

[0012] Ultraviolet sterilization includes: The bread cooled to 25°C enters the tunnel-type UV-C sterilization line, and the bottom and gaps of the bread are irradiated for 10 seconds to kill hidden microorganisms.

[0013] Ultra-high pressure sterilization includes: Put the bread into a food-grade polypropylene bag, vacuum seal it and then put it into the HPP equipment to kill the internal heat-resistant spore bacteria.

[0014] S6, Active Packaging and Storage: The bread is packaged with an inner and outer double-layer packaging bag, filled with a mixed gas, heat-sealed and stored in a constant temperature warehouse at 5°C.

[0015] Preferably, in step S1, the raw material pretreatment includes the following steps:

[0016] S11, Dry Raw Material Compound: Mix high-gluten flour, whole wheat flour, nano-zinc antibacterial agent, resistant starch, β-glucan microcapsule and trehalose, and sieve 3 times to remove impurities.

[0017] S12, Wet Raw Material Activation: Dissolve lactic acid powder and nisin in ice water at 4°C, add freeze-dried acidophilus lactobacillus powder and activated yeast, and let it stand for 10 minutes to obtain the pretreatment liquid.

[0018] Preferably, in step S11, the weight percentages of the dry raw materials for the bread are: 70 - 80% high-gluten flour, 20 - 30% whole wheat flour, 3 - 5% resistant starch, 0.05 - 0.1% nano-zinc antibacterial agent, 2 - 3% β-glucan microcapsule, 2 - 3% trehalose.

[0019] Preferably, in step S12, the weight percentages of the wet raw materials for the bread are: 0.8 - 1.2% lactic acid powder, 0.1 - 0.2% nisin, 1 - 2% freeze-dried acidophilus lactobacillus powder, 1.5 - 2% activated yeast.

[0020] Preferably, in step S2, the dough modulation and gluten strengthening include the following steps:

[0021] S21, Stir the pretreatment liquid and dry raw materials at low speed for 2 minutes, add 2 - 3% refrigerated butter, and stir at high speed for 8 - 10 minutes until the gluten is fully developed.

[0022] S22, High-voltage Pulsed Electric Field Treatment: Place the dough in the PEF equipment to destroy the cell membrane of microorganisms and strengthen the dough structure.

[0023] Preferably, in step S3, when performing the first fermentation, place the dough in an environment at 30 - 32°C and a humidity of 80 - 85%, and ferment for 30 - 40 minutes until the volume expands by 1.5 times; when performing the second fermentation, transfer the dough after the first fermentation to an environment at 15 - 18°C and a carbon dioxide atmosphere of 5 - 7%, and ferment for 90 - 120 minutes until the volume doubles.

[0024] Preferably, in step S4, the segmented baking of the dough includes the following steps:

[0025] S41. Steam stage: Preheat the oven to 220 - 230°C, inject saturated steam after the dough enters the oven, and maintain for 5 - 8 minutes;

[0026] S42. Hot air stage: Drain the steam, reduce the temperature to 180 - 190°C, and bake for 15 - 25 minutes to kill germs.

[0027] Preferably, in step S5, when performing ultraviolet sterilization, the ultraviolet wavelength is 254 nm and the irradiation intensity is 8 mJ / cm 2 , when performing ultra - high pressure sterilization, the pressure parameter is set to 600 - 650 MPa, the temperature is set to 25°C, and the treatment time is 2 - 4 minutes.

[0028] Preferably, in step S6, the active packaging includes an inner layer and an outer layer. The inner layer is a slow - release antibacterial film made of a polyethylene - based film, which is loaded with 5 - 8% rosemary essential oil microcapsules by melt - blending method to form a gas - phase antibacterial environment; the outer layer is a humidity self - regulating film, which is composed of a composite of a polypropylene film and a high - molecular water - absorbing resin.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] In the present invention, a composite antibacterial system is constructed using nano - zinc antibacterial agent, Lactobacillus acidophilus, and nisin to replace chemical preservatives. In combination with β - glucan microcapsules and resistant starch to delay starch retrogradation, and trehalose to lock in moisture. During processing, through PEF pretreatment, variable - temperature fermentation, segmented baking, and HPP cold sterilization, high - voltage pulsed electric field not only destroys the cell membranes of microorganisms but also strengthens the gluten structure, reduces baking cracks. Segmented baking combined with vacuum rapid cooling, the steam stage forms a dense film to lock in water, the hot air stage kills pathogenic bacteria, vacuum cooling inhibits the growth of microorganisms and retains moisture, ultraviolet light specifically kills microorganisms in dead corners, ultra - high pressure sterilization deeply destroys the structure of heat - resistant spore - forming bacteria, while preserving the moisture and taste of the bread. The packaging uses a slow - release antibacterial film and a humidity self - regulating film to maintain a suitable storage environment, inhibit mold growth and moisture loss, and construct a "gas - phase - solid - phase - structure" triple protection. Without adding chemical preservatives, the shelf life of the bread is extended, the total colony count and the risk of mold growth are effectively reduced, the moisture retention rate is increased, the degree of starch retrogradation is reduced, and at the same time, the high - quality taste of the bread is ensured. Brief Description of the Drawings

[0031] Figure 1 It is a flowchart of a bread processing method for extending the shelf life of the present invention. Detailed Description of the Invention

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0033] Example 1: Refer to Figure 1 As shown: A bread processing method for extending the shelf life includes the following steps:

[0034] S1. Raw material pretreatment: After preparing the dry raw materials and sieving to remove impurities, dissolve and mix the wet raw materials, and let it stand to obtain the pretreatment liquid;

[0035] In step S1, the raw material pretreatment includes the following steps:

[0036] S11. Dry raw material compounding: Mix high-gluten flour, whole wheat flour, nano-zinc antibacterial agent, resistant starch, β-glucan microcapsule and trehalose, sieve 3 times to thoroughly remove impurities in the raw materials, such as small particle stones, plant debris, etc., and at the same time ensure that each component is evenly distributed, laying a foundation for subsequent dough modulation;

[0037] S12. Wet raw material activation: Dissolve lactic acid powder and nisin in ice water at 4°C. Controlling the ice water temperature at 4°C can maintain the stability of lactic acid powder and nisin, preventing the decomposition or inactivation of their active ingredients, stir and dissolve to form an acidic solution, providing a suitable growth environment for Lactobacillus acidophilus. Add freeze-dried powder of Lactobacillus acidophilus and activated yeast. The activated yeast is pre-activated with warm water at 35°C for 10 minutes to ensure yeast activity. After stirring evenly, let it stand for 10 minutes. During this process, Lactobacillus acidophilus starts to metabolize and produce acid, further inhibiting the growth of miscellaneous bacteria, and the yeast also gradually adapts to the environment, preparing for subsequent fermentation, and obtaining the pretreatment liquid.

[0038] In step S1, the weight percentages of the dry ingredients for the bread are as follows: 75% high-gluten flour, 25% whole wheat flour, 4% resistant starch, 0.07% nano-zinc antibacterial agent, 2.5% β-glucan microcapsules, and 2.5% trehalose. The high-gluten flour and whole wheat flour serve as the base flours, and their combination can balance the toughness and texture of the bread. The resistant starch enhances the structural stability and prevents collapse during baking. The addition of the nano-zinc antibacterial agent utilizes the high specific surface area property of the nanoparticles to continuously release zinc ions and inhibit the synthesis of the microbial cell membrane. The β-glucan microcapsules delay starch crystallization, and trehalose locks in moisture and improves the anti-aging ability of the bread. Trehalose, as a natural humectant, locks in moisture and maintains the softness of the bread.

[0039] The weight percentages of the wet ingredients for the bread are as follows: 1% lactic acid powder, 0.15% nisin, 1.5% freeze-dried acid-tolerant lactobacillus powder, and 1.5% activated yeast.

[0040] S2. Dough modulation and gluten strengthening: Stir and mix the pretreatment liquid with the dry ingredients, and send them to a high-voltage pulsed electric field device for pretreatment to strengthen the dough structure.

[0041] In step S2, the dough modulation and gluten strengthening include the following steps:

[0042] S21. Stir the pretreatment liquid and the dry ingredients at a low speed for 2 minutes at a speed of 60 rpm, add 2% cold butter with a temperature of 4°C, cut the cold butter into small pieces of 5 mm, which can be evenly melted during stirring and will not be dispersed prematurely due to being too small. Then stir at a high speed for 8 minutes at a speed of 200 rpm. During the stirring process, gluten proteins gradually form a network structure until the gluten is fully developed and the dough can pull out a translucent film. Control the dough temperature below 24°C through an ice-water bath to prevent premature over-fermentation of the yeast due to excessive temperature, which may affect the subsequent process.

[0043] S22. High-voltage pulsed electric field treatment: Place the dough in a high-voltage pulsed electric field (PEF) device before dividing. Set the electrode distance to 2 cm to ensure that the electric field intensity acts uniformly on the dough. The electric field intensity is 30 kV / cm, the pulse frequency is 100 Hz, and the treatment time is 2 minutes. Destroy the microbial cell membrane through the electroporation effect, and at the same time promote the oxidation and cross-linking of the sulfhydryl groups of gluten proteins, improve the gas-holding property of the dough, strengthen the dough structure, and reduce the generation of cracks during baking.

[0044] S3. Variable-temperature dynamic fermentation: Control the temperature and fermentation environment to carry out the first fermentation and the second fermentation:

[0045] In step S3, during the first fermentation, the dough is placed in an environment with a temperature of 30°C and a humidity of 80% and fermented for 30 minutes. At this stage, the yeast actively proliferates, decomposes the fermentable sugars in the dough to produce carbon dioxide and alcohol, causing the dough volume to expand by 1.5 times, forming a preliminary pore structure, which lays the foundation for the fluffy texture of the bread. During the second fermentation, the dough after the first fermentation is transferred to an environment with a temperature of 15°C, and a mixed gas of 5% carbon dioxide (the rest is nitrogen) is introduced and fermented for 100 minutes until the volume doubles. During this period, sterile air filtered through a 0.2μm pore size is introduced every 30 minutes to maintain a pressure of 0.1 MPa, preventing the dough from collapsing due to insufficient gas. The low temperature inhibits the growth rate of miscellaneous bacteria (such as molds and Escherichia coli), and the CO2 reduces the pH of the dough surface, further inhibiting the reproduction of miscellaneous bacteria. At the same time, the slow fermentation allows the accumulation of more flavor substances (such as esters and aldehydes).

[0046] S4. Segment baking and vacuum rapid cooling: The dough is sent into the oven for segment baking, and after being taken out of the oven, it is transferred to a vacuum cooler for cooling. In a vacuum environment, the water evaporation rate is accelerated, and the center temperature of the bread can be reduced to below 30°C within 10 minutes, and the surface condensate content is low, inhibiting the growth of microorganisms during the cooling stage and retaining the internal moisture of the bread;

[0047] In step S4, the segment baking of the dough includes the following steps:

[0048] S41. Steam stage: The oven is preheated to 220°C in advance. After the dough is put into the oven, saturated steam is injected, the humidity is set to 90%, and it is maintained for 6 minutes. The high-temperature steam rapidly gelatinizes the dough epidermis, forming a dense film with a thickness of 60μm, effectively locking in the internal moisture, and at the same time endowing the bread epidermis with gloss and crispness;

[0049] S42. Hot air stage: The steam is discharged, the oven temperature is reduced to 180°C, and baked for 20 minutes until the center temperature of the bread reaches 98°C and is maintained for a period of time. During this stage, through hot air circulation, the internal moisture of the bread is evenly evaporated, and at the same time, pathogenic bacteria such as Salmonella are killed, forming a golden-yellow and crispy epidermis, while the internal tissue remains soft.

[0050] S5. Composite sterilization treatment: The bread is subjected to ultraviolet sterilization and ultra-high pressure sterilization to strengthen sterilization;

[0051] In step S5, the ultraviolet sterilization includes the following: The bread cooled to 25°C enters the tunnel-type ultraviolet sterilization line, using ultraviolet light with a wavelength of 254nm and an irradiation intensity of 8mJ / cm 2 , irradiate the bottom and gaps of the bread for 10 seconds. The ultraviolet light penetrates the microbial cells and destroys the DNA pyrimidine dimer structure, killing the microorganisms hidden in these dead corners;

[0052] In step S5, the ultra-high pressure sterilization includes the following: put the bread into a food-grade polypropylene bag, vacuum seal it and then put it into the HPP equipment. Set the pressure parameter to 600 MPa, the temperature to 25 °C, and the treatment time to 3 minutes. Under high pressure, the three-dimensional structure of the proteins of microorganisms is destroyed, while the moisture, vitamins and other nutrients and the taste of the bread are basically not affected, and it can kill the heat-resistant bacilli inside while maintaining the moisture content of the bread.

[0053] S6. Active packaging and storage: Set up an inner and outer double-layer packaging, fill it with a mixed gas, the mixed gas is 88% nitrogen and 12% carbon dioxide gas, displace the air, inhibit the growth of aerobic microorganisms, and store it in a constant temperature warehouse at 5 °C after heat sealing;

[0054] In step S6, the active packaging includes an inner packaging and an outer packaging. The inner layer is a slow-release antibacterial film, which uses a polyethylene-based film and loads 5% rosemary essential oil microcapsules by the melt blending method. The capsule particle size is 50-100 μm, and 0.4 μL of essential oil is released daily at 20 °C to form a gas-phase antibacterial environment. Components such as thymol and carvacrol in the rosemary essential oil can penetrate the cell membrane of mold spores and inhibit the germination of mold spores; the outer layer is a humidity self-regulating film, which is composed of a composite of a polypropylene film and a high molecular weight water-absorbing resin. When the humidity in the packaging > 70%, the high molecular weight water-absorbing resin quickly absorbs the excess water, and when the humidity < 60%, it releases the bound water to maintain the stability of the humidity in the packaging, avoiding the bread from getting moldy due to too high humidity or becoming dry and hard due to too low humidity.

[0055] The present invention constructs a bread processing system without chemical preservatives through six core steps: raw material compounding → dough treatment → fermentation process → segmented baking → composite sterilization → active packaging, achieving the goals of extending the shelf life, inhibiting the growth of microorganisms, maintaining moisture and taste.

[0056] (I) Technical solution:

[0057] 1. Raw material pretreatment (S1): including the treatment of dry raw materials and wet raw materials;

[0058] 2. Dough modulation and gluten strengthening (S2)

[0059] Mixing process (S21)

[0060] After the pretreatment liquid and the dry raw materials are stirred at a low speed, add 4 °C refrigerated butter and stir at a high speed until the gluten is fully developed.

[0061] Function: The butter evenly wraps the gluten, enhancing the extensibility of the dough; the low temperature inhibits the early proliferation of miscellaneous bacteria.

[0062] High-voltage pulsed electric field treatment (S22)

[0063] Function: The electroporation effect destroys the microbial cell membrane and promotes the oxidative cross-linking of gluten protein sulfhydryl groups, thereby improving the dough's gas retention and reducing baking cracks.

[0064] 3. Dynamic fermentation with variable temperature (S3)

[0065] Primary fermentation

[0066] Conditions: temperature 30°C, humidity 80%, time 30 minutes, until the volume expands to 1.5 times.

[0067] Objective: To achieve initial proliferation of yeast and construct basic stomatal structure.

[0068] Secondary fermentation

[0069] Conditions: Temperature 15-18°C, 5% CO2 (the rest is N2) is introduced for 100 minutes until the volume doubles; 0.2 μm filtered sterile air is introduced every 30 minutes to maintain the air pressure at 0.1 MPa.

[0070] Purpose: Low temperature inhibits the growth of bacteria, CO2 creates a low-oxygen environment to delay the germination of mold spores, and at the same time promotes the accumulation of flavor substances and avoids dough collapse.

[0071] 4. Segmented baking and vacuum rapid cooling (S4)

[0072] Staged baking

[0073] Steaming stage (S41): preheat the oven to 220°C, inject saturated steam, and maintain for 6 minutes to form a 50μm dense epidermal film to lock in internal moisture.

[0074] Hot air stage (S42): exhaust steam, reduce the temperature to 180°C, bake for 20 minutes, until the center temperature of the bread reaches 98°C, killing pathogens such as salmonella.

[0075] Vacuum rapid cooling

[0076] After being taken out of the oven, it is immediately transferred to a vacuum cooler to reduce the core temperature to below 30°C, reduce surface condensation water, and inhibit the growth of microorganisms during the cooling stage.

[0077] 5. Composite sterilization treatment (S5)

[0078] UV sterilization

[0079] Parameters: Wavelength 254nm, irradiation intensity 8mJ / cm 2 , irradiate the bottom and gaps of the bread for 10 seconds.

[0080] Function: Targeted killing of hidden microorganisms that are difficult to cover with traditional sterilization (such as mold spores in gaps).

[0081] High pressure sterilization (HPP)

[0082] Parameters: Vacuum seal with food-grade polypropylene bag, pressure 600 MPa, temperature 25 °C, treatment time 3 minutes.

[0083] Function: Hydrostatic pressure destroys the protein structure of internal heat-resistant spore-forming bacteria, retains the high moisture content and texture of the bread, and avoids the destruction of nutrients by high temperature.

[0084] 6. Active Packaging and Storage (S6)

[0085] Inner layer slow-release antibacterial film

[0086] Material: Polyvinyl film loaded with 5% rosemary essential oil microcapsules.

[0087] Function: Releases 0.3 μL of essential oil per day at 20 °C to form a gas-phase antibacterial environment and inhibit the growth of mold spores.

[0088] Outer layer humidity self-regulating film

[0089] Material: Composite of polypropylene film and high molecular weight water-absorbing resin.

[0090] Function: Maintains the humidity stability inside the package, prevents epidermal softening and internal drying.

[0091] (II) Core principle:

[0092] 1. Composite antibacterial system (replacing chemical preservatives)

[0093] Use nano-zinc antibacterial agent, biological antibacterial agent and gas-phase antibacterial in combination to construct an antibacterial system and achieve multi-dimensional antibacterial;

[0094] Nano-zinc antibacterial agent: Destroys the cell membrane permeability of microorganisms and inhibits DNA replication;

[0095] Biological antibacterial agent: Lactose powder (reduces pH value and inhibits bacteria), nisin (specifically inhibits Gram-positive bacteria), acid-tolerant lactobacillus (secretes antibacterial peptides and competes for nutrients);

[0096] Gas-phase antibacterial: Rosemary essential oil microcapsules release slowly and form an antibacterial gas environment inside the package through volatilization to inhibit the germination of mold spores;

[0097] Advantages: Covers various microorganisms such as bacteria, molds, and yeasts, avoids the limitations of single preservatives, and has no risk of chemical residues.

[0098] 2. Delay starch retrogradation (maintain texture)

[0099] Raw material compounding: β-glucan microcapsules (inhibit starch molecule recrystallization) and resistant starch (form a spatial network structure to hinder starch molecule aggregation) act synergistically to reduce the degree of starch retrogradation.

[0100] Process assistance: Variable-temperature fermentation (secondary low-temperature fermentation slows down enzyme activity) and segmented baking (the steam stage quickly forms an epidermal film to reduce internal water loss) further delay aging and maintain the soft texture of the bread.

[0101] 3. Non-thermal sterilization technology (preserving nutrition and structure)

[0102] High-voltage pulsed electric field (PEF): Instantaneous high voltage forms irreversible pores in the microbial cell membrane, leading to cell death. At the same time, it promotes the cross-linking of gluten proteins, enhances the structural stability of the dough, and reduces baking cracks.

[0103] High-pressure sterilization (HPP): At room temperature (25°C), 600 MPa high pressure destroys the proteins and nucleic acids of microbial spores, causing little damage to heat-sensitive nutrients (such as vitamins and flavor substances), and avoiding the problem of preservative failure caused by traditional high-temperature baking.

[0104] 4. Structure strengthening and moisture regulation

[0105] Gluten optimization: Slow stirring of refrigerated butter at low speed promotes the combination of fat and gluten. PEF treatment enhances protein cross-linking, improves the gas-holding property of the dough, makes the internal pores uniform after baking, and reduces the moisture migration channels.

[0106] Moisture locking control: The combined action of trehalose (humectant), vacuum rapid cooling (reducing water evaporation), and outer layer humidity self-regulating film (dynamic balance of moisture) improves the moisture retention, avoiding epidermal softening and internal dryness.

[0107] 5. Triple protection packaging (gas phase - solid phase - structure)

[0108] Inner layer slow-release antibacterial film: Microcapsules of rosemary essential oil continuously release antibacterial components, forming a gas-phase barrier to inhibit mold growth.

[0109] Outer layer humidity regulating film: Superabsorbent polymer absorbs / releases moisture to maintain stable humidity inside the package, destroying the high-humidity environment for microbial growth.

[0110] Physical structure: The double-layer film isolates external oxygen and moisture. Combined with nitrogen filling packaging (reducing oxygen content), it constructs a low-oxygen and humidity-stable storage environment, prolonging the microbial reproduction cycle.

[0111] Through the systematic design of "raw material antibacterial + process sterilization + packaging protection", a long-term fresh-keeping system without chemical preservatives is constructed, solving the core problems of traditional bread such as water loss, microbial contamination, and starch aging, and achieving the dual goals of extended shelf life and improved quality.

[0112] Example 2: A method for processing bread with an extended shelf life provided in this example is generally the same as that in Example 1, and the main difference lies in that the weight percentages of the dry ingredients of the bread are: 70% high-gluten flour, 20% whole wheat flour, 3% resistant starch, 0.05% nano-zinc antibacterial agent, 2% β-glucan microcapsules, 2% trehalose; the weight percentages of the wet ingredients of the bread are: 0.8% lactic acid powder, 0.1% nisin, 1% freeze-dried powder of acid-tolerant lactobacillus, 1.5% activated yeast.

[0113] Example 3: A method for processing bread with an extended shelf life provided in this example is generally the same as that in Example 1, and the main difference lies in that the weight percentages of the dry ingredients of the bread are: 80% high-gluten flour, 30% whole wheat flour, 5% resistant starch, 0.1% nano-zinc antibacterial agent, 3% β-glucan microcapsules, 3% trehalose; the weight percentages of the wet ingredients of the bread are: 1.2% lactic acid powder, 0.2% nisin, 2% freeze-dried powder of acid-tolerant lactobacillus, 2% activated yeast.

[0114] Comparative Example 1: A method for processing bread with an extended shelf life provided in this example is generally the same as that in Example 1, and the main difference lies in that no freeze-dried powder of acid-tolerant lactobacillus is added.

[0115] Comparative Example 2: A method for processing bread with an extended shelf life provided in this example is generally the same as that in Example 1, and the main difference lies in that in step S5, ultra-high pressure sterilization is not carried out.

[0116] Test experiment

[0117] The breads prepared by Examples 1-3 were respectively designated as Experimental Example Groups 1-3, and the breads prepared by Comparative Examples 1-2 were designated as Comparative Groups 1-2. The shelf life at room temperature (25°C), mold detection time, starch retrogradation degree, moisture retention degree, and total number of colonies of the bread were tested, and the relevant data were experimentally recorded in Table 1.

[0118] Table 1: Test data record form

[0119]

[0120] As can be seen from Table 1, the normal temperature shelf life of Comparative Groups 1-2 was only 2-3 days, while that of Example Groups 1-3 reached 15-20 days, indicating that the process of the present invention extended the normal temperature shelf life of bread. Mold was detected in Comparative Groups 1-2 on the 3rd day, while the mold detection time in Example Groups 1-3 was delayed to the 12th - 15th day. The present invention effectively inhibited the growth of mold through a composite antibacterial technology and extended the safe consumption period of bread. The retrogradation degree of starch in Comparative Groups 1-2 was 35% - 38%, while that in Example Groups 1-3 decreased to 17% - 20%. The lower the retrogradation degree of starch, the better the anti-aging effect of bread. The present invention effectively delayed the recrystallization of starch and maintained the soft texture of bread through the compounding of raw materials such as β-glucan microcapsules and resistant starch and a variable-temperature fermentation process. The moisture retention rate in Comparative Groups 1-2 was 72% - 75%, while that in Example Groups 1-3 increased to 82% - 88%. The high moisture retention rate indicates that the present invention reduced water loss and avoided bread from becoming dry and hard through technologies such as trehalose moisturization, vacuum cooling, and humidity self-regulating film. From the total number of colonies, it can be seen that by combining non-thermal sterilization technologies of high-voltage pulsed electric field and ultra-high pressure sterilization, the number of microorganisms can be effectively controlled, ensuring the safety of bread and achieving an overall improvement in bread quality and preservation effect.

[0121] The present invention first prepares dry raw materials and wet raw materials according to weight percentages. After mixing the dry raw materials, they are sieved 3 times to ensure uniform composition. After mixing the wet raw materials, they are left standing for 10 minutes to activate microbial metabolism, forming a pretreatment solution rich in antibacterial substances, laying a foundation for subsequent fermentation and antibacterial. After stirring the pretreatment solution with the dry raw materials, 4°C refrigerated butter is added and stirred at high speed until the gluten is fully developed, inhibiting the early proliferation of miscellaneous bacteria. High-voltage pulsed electric field treatment is carried out to destroy the cell membrane of microorganisms using the electropermeabilization effect, and at the same time promote the oxidation cross-linking of sulfhydryl groups in gluten proteins, improving the gas-holding property of the dough and reducing baking cracks.

[0122] Controlling the temperature and fermentation environment, two fermentations are carried out. The first fermentation completes the initial proliferation of yeast and the construction of the pore structure. The second fermentation is transferred to a low-temperature and low-oxygen environment. The low temperature inhibits the growth of miscellaneous bacteria, synergistically delays the germination of mold spores, and at the same time promotes the accumulation of flavor substances. During baking, steam baking and hot air baking are carried out in sequence. After taking out of the oven, it is immediately transferred to a vacuum cooler to reduce the central temperature from 90°C to below 30°C, reducing surface condensate and inhibiting the growth of microorganisms during the cooling stage.

[0123] The bread cooled to 25°C is sterilized through a tunnel-type ultraviolet sterilization line, using a wavelength of 254 nm and 8 mJ / cm 2Irradiate with strong ultraviolet light for 10 seconds to specifically kill the hidden microorganisms at the bottom and in the gaps of the bread, solving the problem of traditional sterilization dead angles. Subsequently, put the bread into the HPP equipment to destroy the protein structure of heat-resistant bacilli through hydrostatic pressure while maintaining the high moisture content and taste of the bread. Use double-layer packaging inside and outside. The inner layer is a polyethylene film loaded with rosemary essential oil microcapsules to inhibit mold spores through gas-phase diffusion. The outer layer is a composite film of a polypropylene film and a superabsorbent polymer to adjust the humidity in real time, avoiding the dryness of the bread core and the softening of the crust. Fill the package with a mixed gas of 85% nitrogen and 15% carbon dioxide to displace the air and inhibit aerobic bacteria. After heat sealing, store it in a constant temperature warehouse at 5°C to achieve long-term freshness preservation.

[0124] Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A bread processing method for extending the shelf life, characterized in that, The following steps are involved: S1. Raw material pretreatment: prepare dry raw materials, sieve and remove impurities, dissolve and mix wet raw materials, and let stand to obtain pretreatment liquid; S2, dough preparation and gluten strengthening: the pretreatment liquid is mixed with the dry raw materials and sent to the high-voltage pulse electric field equipment for pretreatment to strengthen the dough structure; S3. Dynamic fermentation with variable temperature: Control the temperature and fermentation environment to carry out primary and secondary fermentation: S4, segmented baking and vacuum rapid cooling: the dough is placed in an oven for segmented baking, and then transferred to a vacuum cooler for cooling after being taken out of the oven; S5. Composite sterilization treatment: UV sterilization and ultra-high pressure sterilization are performed on the bread to enhance sterilization; Ultraviolet sterilization includes: bread cooled to 25°C enters the tunnel-type UV-C sterilization line, irradiating the bottom and crevices of the bread for 10 seconds to kill hidden microorganisms; Ultra-high pressure sterilization includes: packaging the bread into food-grade polypropylene bags, vacuum sealing them, and then putting them into the HPP equipment to kill the heat-resistant spore bacteria inside; S6. Active packaging and storage: Bread is packaged in double-layer bags, filled with mixed gas, heat-sealed and stored in a constant temperature warehouse at 5°C.

2. A method for processing bread with an extended shelf life according to claim 1, characterized in that: In step S1, the raw material pretreatment includes the following steps: S11. Compounding of dry ingredients: Mix high-gluten flour, whole wheat flour, nano-zinc antimicrobial agent, resistant starch, β-glucan microcapsules and trehalose, and sieve three times to remove impurities; S12. Activation of wet raw materials: dissolve lactic acid powder and nisin in 4°C ice water, add freeze-dried acid-resistant Lactobacillus powder and activated yeast, and let stand for 10 minutes to obtain a pre-treated solution.

3. A method for processing bread with an extended shelf life according to claim 2, characterized in that: In step S11, the weight percentages of the dry bread ingredients are: 70-80% high-gluten flour, 20-30% whole wheat flour, 3-5% resistant starch, 0.05-0.1% nano zinc antibacterial agent, 2-3% β-glucan microcapsules, and 2-3% trehalose.

4. A method for processing bread with an extended shelf life according to claim 2, characterized in that: In step S12, the weight percentages of the bread wet ingredients are: 0.8-1.2% lactic acid powder, 0.1-0.2% nisin, 1-2% acid-resistant Lactobacillus freeze-dried powder, and 1.5-2% activated yeast.

5. A method for processing bread with an extended shelf life according to claim 1, characterized in that: In step S2, the dough preparation and gluten strengthening comprises the following steps: S21, stirring the pre-treated liquid and dry ingredients at low speed for 2 minutes, adding 2-3% refrigerated butter, and stirring at high speed for 8-10 minutes until the gluten is fully expanded; S22, high-voltage pulsed electric field treatment: Place the dough in PEF equipment to destroy the microbial cell membrane and strengthen the dough structure.

6. A method for processing bread with an extended shelf life according to claim 1, characterized in that: In step S3, during the primary fermentation, the dough is placed in an environment of 30-32°C and 80-85% humidity for 30-40 minutes until the volume increases by 1.5 times; during the secondary fermentation, the dough after the primary fermentation is transferred to an atmosphere of 15-18°C and 5-7% carbon dioxide for 90-120 minutes until the volume increases by 2 times.

7. A method for processing bread with an extended shelf life according to claim 1, characterized in that: In step S4, the dough is baked in sections, including the following steps: S41, steam stage: preheat the oven to 220-230℃, inject saturated steam into the dough after it is placed in the oven, and maintain for 5-8 minutes; S42, hot air stage: exhaust steam, reduce the temperature to 180-190℃, bake for 15-25 minutes to kill bacteria.

8. A method for processing bread with an extended shelf life according to claim 1, characterized in that: In step S5, when performing ultraviolet sterilization, the ultraviolet wavelength is 254 nm and the irradiation intensity is 8 mJ / cm 2 , when performing ultra-high pressure sterilization, the pressure parameter is set to 600 - 650 MPa, the temperature is set to 25 °C, and the treatment time is 2 - 4 minutes.

9. A method for processing bread with an extended shelf life according to claim 1, characterized in that: In step S6, the active packaging includes an inner layer and an outer layer. The inner layer is a slow-release antibacterial film made of a polyvinyl film, which is loaded with 5-8% rosemary essential oil microcapsules by melt blending to form a gas-phase antibacterial environment. The outer layer is a humidity self-regulating film, which is composed of a composite of a polypropylene film and a superabsorbent polymer.

Images