Industrialized fermentation process for bread by using complex natural bacteria to dynamically control acidity

Abstract

This invention discloses an industrial-scale fermentation bread process based on dynamic acidity regulation using a composite natural microbial strain, belonging to the field of food processing technology. This process involves screening composite natural microbial strains (Lactobacillus plantarum Lp-05, Lactobacillus brevis Lb-08, and Saccharomyces rouxii Zr-12, all preserved in CGMCC) that synergistically control acidity, flavor, and gas production, and optimizing the blending ratio through orthogonal experiments. A multi-dimensional monitoring system for pH, lactic acid / acetic acid / CO2 release rate, and dough elasticity is constructed, combined with PLC-based linkage control of parameters throughout the fermentation cycle. The process also optimizes raw material formulations and key equipment for industrial continuous production lines. Experiments show that, compared with traditional processes, the bread cultured using this process has a center-to-surface pH difference ≤0.2, specific volume ≥4.6mL / g, total ester flavor substances ≥35mg / kg, oligosaccharide content 1.2-1.5g / 100g, GI value 55-60, shelf life 12-15 days, and batch qualification rate ≥98.5%. It can be widely applied to the industrial production of bread such as toast and dinner rolls with a daily output of 10-50 tons, providing technical support for the preparation of clinical-grade nutritional bread.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, specifically to the industrial production of grain fermented products. In particular, it relates to an industrial process that optimizes bread quality, improves production stability, and enhances health attributes through metabolic regulation mediated by compound natural strains and dynamic intervention of acidity throughout the fermentation cycle. This process is suitable for the continuous production of functional products such as immune-nutritional bread and low-sugar bread on a large scale. Background Technology

[0002] The synergy between acidity, flavor, and production capacity in industrialized bread production is also a core bottleneck for the industry. Existing bread fermentation technologies have the following significant shortcomings, which severely restrict product quality and industrialization progress.

[0003] Single-strain yeast combined with exogenous acidification leads to an imbalance in quality. Current industrial processes commonly employ a combination of "pure Saccharomyces cerevisiae" and exogenous organic acids (citric acid, lactic acid) (e.g., the "rapid fermentation bread process" disclosed in CN202310251234.5): ① Yeast metabolites contain only ethanol and CO2, lacking the characteristic lactic acid (mild sour taste), acetic acid (refreshing aroma), and esters (ethyl hexanoate, ethyl acetate) flavor compounds of lactic acid bacteria, resulting in a single flavor profile in the bread. 1. Sensory evaluation score is only 65-70 points (out of 100, refer to SB / T10527-2022); 2. Exogenous acidification easily causes uneven acidity distribution, with the center of the dough pH 4.9-5.2 and the surface pH 4.4-4.6, a difference >0.5, and it destroys the disulfide bond structure of the gluten network, causing the bread specific volume to drop to 3.8-4.0 mL / g and the chewiness to increase by 20%-25% (refer to GB / T35862-2023 "Methods for Texture Analysis of Cereal Products").

[0004] Static acidity control leads to poor batch stability. Conventional processes achieve static control solely by setting the fermentation endpoint pH (4.8-5.0), failing to consider the stage-specific nature of microbial metabolism: ① In the early stage of primary fermentation (0-1h), lactic acid bacteria (if added) proliferate rapidly (generation time 30-40min), easily leading to excessive acid production and pH < 4.5, inhibiting yeast activity; ② In the later stage of secondary fermentation (1-1.5h), yeast aerobic metabolism increases, and if ventilation is insufficient, gas production efficiency decreases, resulting in dough expansion < 1.5 times; ③ During the proofing stage (35-45min), the temperature rises to 35-38℃, accelerating lactic acid bacteria metabolism and causing a sudden drop in pH of 0.3-0.4 units. These issues result in batch-to-batch pH fluctuations > 0.4 in industrial production, a product qualification rate of only 75%-80%, and daily raw material losses of 5%-8% (production data from a large baking company in 2024), leading to annual economic losses exceeding one million.

[0005] Natural strains used alone are difficult to adapt to industrial production capacity. Traditional sourdough fermentation relies on a single lactic acid bacteria or natural yeast, but has obvious limitations: ① Fermentation with a single lactic acid bacteria (such as Lactobacillus plantarum) (CN202110567890.1) produces acid quickly (pH drops from 6.0 to 4.2 within 4 hours), but produces insufficient gas, requiring the addition of leavening agents such as sodium bicarbonate, resulting in a bitter taste and excessive sodium content; ② Fermentation with a single natural yeast (such as Saccharomyces rouxii) (CN202010345678.9) produces sufficient gas, but the fermentation cycle is as long as 8-12 hours, which cannot meet the 5-6 hour / batch cycle requirements of industrial continuous production lines, resulting in a 30%-40% decrease in equipment utilization and severely limited production capacity.

[0006] Health benefits and shelf life are difficult to balance. Bread produced using exogenous acidification processes has organic acids concentrated on the surface, failing to create a uniform antibacterial environment, resulting in a shelf life of only 8-10 days (stored at 25℃). Furthermore, it lacks oligosaccharides produced by lactic acid bacteria fermentation (content <0.3g / 100g), resulting in a GI value as high as 70-75 (referencing GB / T22494-2008 "Determination of Carbohydrates in Plant-Based Foods"). This does not meet the functional needs of modern consumers for "low GI, high prebiotics, and long shelf life," and is especially difficult to meet the nutritional needs of special populations such as postoperative recovery patients and diabetic patients.

[0007] In summary, existing technologies have not yet broken through the technical bottleneck of "synergistic fermentation of natural microorganisms + dynamic acidity control + industrial adaptation". There is an urgent need for an innovative process that does not require the addition of exogenous acid, has rich flavor, stable batches and controllable costs, which is also the core research and development goal of this invention. Summary of the Invention

[0008] In view of the shortcomings of existing technologies, this invention aims to overcome the defects of existing industrial bread fermentation technologies and specifically solve the following core technical problems:

[0009] 1. Problems of poor bread flavor, uneven acidity distribution, and poor texture (low specific volume, high chewiness) caused by single strain of bacteria and exogenous acid addition;

[0010] 2. The problem of large batch-to-batch pH fluctuations and low product qualification rate (<80%) caused by relying solely on static pH control;

[0011] 3. The fermentation efficiency of natural strains is low or the gas production is insufficient when used alone, making them unsuitable for industrial continuous production lines (5-6 hours / batch);

[0012] 4. The problem of not being able to simultaneously achieve the product's health attributes (low GI, high prebiotics) and short shelf life (<10 days).

[0013] To achieve the above objectives, the present invention provides the following technical solution:

[0014] The core technical solution of this invention is a three-in-one system of "construction of a synergistic system of compound natural microbial strains + dynamic acidity control throughout the fermentation cycle + industrial adaptation and optimization", as detailed below:

[0015] The functional lipid complex is composed of cholesterol, sphingomyelin and phosphatidylserine in a mass ratio of (3-5):(2-4):1; (I) Construction of a "acid-flavor-gas production" complex natural microbial system.

[0016] 1. Strain screening and functional localization

[0017] All strains were isolated and purified from traditional fermented dough from Kaifeng, Henan Province (collected in March 2024). Identification was performed by 16S rRNA gene sequencing (lactic acid bacteria) and 26S rRNA D1 / D2 region sequencing (yeast). The strains are deposited at the China General Microbiological Culture Collection Center (CGMCC, address: No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing). Preservation information and functional characteristics are as follows:

[0018] strains strain name Preservation Information Core Functions Key metabolic parameters Acid-controlling lactic acid bacteria Lactobacillus plantarum Lp-05 CGMCC No. 30021, deposit date July 10, 2024 Establishing basic acidity and controlling the acid production rate Within 4 hours, the pH decreased from 6.0 to 4.8±0.1, with lactic acid accounting for 82% of the total acid. The lowest acid-resistant pH was 3.5. Flavored lactic acid bacteria Lactobacillus brevis Lb-08 CGMCC No. 30022, deposit date July 10, 2024 Produces flavor compounds and balances acidity Acetic acid yield: 0.3-0.5 g / L; Ethyl hexanoate yield: ≥18 mg / kg; Inhibition zone diameter: ≥15 mm (against Escherichia coli) Acid-resistant gas-producing yeast Zr-12 of Zygosaccharomycesrouxii CGMCC No. 30023, deposit date July 10, 2024 Highly efficient gas production maintains dough fluffiness At pH 4.0-5.0, the gas production rate is ≥2.0 times the volume expansion, the maximum sugar concentration is 25%, and the ethanol yield is ≤1.2% (v / v).

[0019] 2. Optimization of strain compound ratio

[0020] via L9(3) 4 An orthogonal experiment was conducted, using "bread acidity uniformity (center-surface pH difference), specific volume, flavor score, and oligosaccharide content" as evaluation indicators to determine the optimal blending ratio.

[0021] Table 1: Orthogonal experimental design and results (n=3, mean)

[0022] Experiment No. Lp-05:Lb-08:Zr-12 pH difference between center and surface Specific volume (mL / g) Flavor rating Oligosaccharide content (g / 100g) Overall score 1 1:0.3:0.8 0.22 4.5 88 1.2 89 2 1:0.3:1.0 0.20 4.6 90 1.3 91 3 1:0.3:1.2 0.19 4.7 89 1.2 90 4 1:0.5:0.8 0.18 4.7 92 1.4 93 5 1:0.5:1.0 0.17 4.8 93 1.5 95 6 1:0.5:1.2 0.18 4.7 92 1.4 93 7 1:0.6:0.8 0.21 4.6 91 1.3 91 8 1:0.6:1.0 0.20 4.6 90 1.3 90 9 1:0.6:1.2 0.21 4.5 89 1.2 88

[0023] Compound mass ratio: Lactobacillus plantarum Lp-05 : Lactobacillus brevis Lb-08 : Saccharomyces rouxii Zr-12 = 1 : (0.3-0.6) : (0.8-1.2)

[0024] Verification results: At this ratio, the pH difference between the center and surface of the bread is ≤0.2, the specific volume is ≥4.6mL / g, the flavor score is ≥90 points, and the oligosaccharide content is ≥1.2g / 100g, which meets the synergistic requirements of "acid control-flavor-gas production-health" (orthogonal experimental data are shown in Table 1).

[0025] 3. Preparation of compound microbial seed solution (for industrial application)

[0026] The "anaerobic-aerobic segmented culture method" is adopted, combined with a compound protectant to enhance the activity and storage stability of the strain. The specific steps are as follows:

[0027] (1) Co-culture of lactic acid bacteria:

[0028] Lactobacillus plantarum Lp-05 and Lactobacillus brevis Lb-08 were inoculated at an optimized ratio into a modified MRS medium (formula: glucose 20 g / L, malt extract 10 g / L, yeast extract 5 g / L, sodium acetate 5 g / L, diammonium citrate 2 g / L, magnesium sulfate 0.1 g / L, manganese sulfate 0.05 g / L, pH adjusted to 6.2 ± 0.1 with 1 mol / L HCl or NaOH). The medium was incubated in a 37℃ anaerobic incubator (atmosphere: 10% H2, 5% CO2, 85% N2) for 18-20 h. Viable bacterial counts were determined using the plate count method, ensuring a count ≥ 1.2 × 10⁻⁶. 9 CFU / mL;

[0029] (2) Yeast culture alone:

[0030] Zr-12 *Saccharomyces rouxii* was inoculated into modified YPD medium (formulation: glucose 20 g / L, peptone 20 g / L, yeast extract 10 g / L, lactic acid 0.5 g / L, pH 5.5 ± 0.1) and cultured in an aerobic fermenter at 30°C (ventilation 1:1.2 vvm, stirring speed 180 r / min) for 22–26 h. Viable cell count was determined using the plate count method, ensuring a count ≥ 1.5 × 10⁻⁶. 9 CFU / mL;

[0031] (3) Mixing and protection of compound seed liquid:

[0032] The above-mentioned lactic acid bacteria solution and yeast solution were mixed in a compound ratio, and 2% (w / v) maltodextrin-trehalose complex protectant (mass ratio 2:1) was added. The mixture was stirred in a magnetic stirrer at 25℃ (speed 200 r / min) for 5 min to form a uniform mixture. After sterilization by filtration through a 0.22 μm sterile filter membrane, the mixture was dispensed into sterile centrifuge tubes and stored at 4℃. The viable cell loss rate was ≤10% within 7 days (protein concentration was determined by BCA method, and viable cell count was verified by plate count method).

[0033] (II) Dynamic acidity control system throughout the fermentation cycle

[0034] A closed-loop control system was constructed, consisting of "online multi-indicator monitoring → PLC linkage analysis → multi-parameter coordinated adjustment," covering three key stages: primary fermentation, secondary fermentation, and proofing. This system differs from conventional static pH control, as detailed below:

[0035] 1. Monitoring Indicators and Equipment Configuration

[0036] High-precision online detection equipment is used to capture real-time changes in microbial metabolism and dough quality parameters. The equipment selection and monitoring requirements are as follows:

[0037] Fermentation stage Core monitoring indicators Testing equipment model and parameters Target control range Monitoring frequency Single fermentation (1.5-2.5 hours) <![CDATA[①pH; ②Lactic acid concentration; ③CO2 release rate]]> <![CDATA[①Mettler Toledo S400 pH sensor (accuracy ±0.01, response time < 5 s); ②Thermo Fisher UltiMate 3000 online HPLC (detection wavelength 210 nm, flow rate 1.0 mL / min, mobile phase: 0.1% phosphoric acid aqueous solution - acetonitrile = 95:5); ③Hach POLARISCO2 infrared analyzer (accuracy ±0.1%, range 0 - 5%)]]> <![CDATA[①pH 4.8 - 5.2; ②Lactic acid 0.6 - 0.8 g / L; ③CO2 0.8 - 1.2 L / h]]> ① 1 time / 5 min; ② 1 time / 15 min; ③ 1 time / 10 min Secondary fermentation (0.8-1.2h) ① pH; ② acetic acid concentration; ③ dough expansion rate ① Same as above; ② Same as above (HPLC detection conditions are the same as above); ③ Keyence IV2 series laser diameter gauge (accuracy ±0.1mm, sampling frequency 1 time / s) ① pH 4.5-4.8; ② Acetic acid 0.2-0.3 g / L; ③ Expansion rate 1.5-1.8 times (relative to the volume of the divided dough) ① 1 time / 5 min; ② 1 time / 15 min; ③ 1 time / 20 min Awakening stage (35-45 minutes) ① pH; ② dough elasticity; ③ dough core temperature ① Same as above; ② Texture Technologies TA-XT2i online texture analyzer (probe P / 36R, compression rate 1mm / s, compression ratio 50%); ③ Rotronic HC2-AW temperature and humidity sensor (temperature accuracy ±0.1℃, humidity accuracy ±2%RH) ① pH 4.6-4.9; ② Elasticity ≥ 0.8 (texture parameter, unitless); ③ Temperature 35-38℃, humidity 80-85% ① 1 time / 5 min; ② 1 time / 15 min; ③ 1 time / 10 min

[0038] 2. The dynamic control strategy is based on a closed-loop mechanism of "online multi-indicator real-time monitoring → PLC system logic judgment → multi-parameter coordinated adjustment," covering the three core stages of primary fermentation, secondary fermentation, and proofing. The linkage logic of each stage is specifically executed in the following way to ensure that each adjustment matches the microbial metabolic pattern and dough quality requirements:

[0039] Primary fermentation stage (total duration 1.5-2.5 hours, core objective: to establish basic acidity and lay the foundation for the gluten network)

[0040] Initial parameter settings: After starting the intelligent fermentation chamber, first set the initial process parameters: temperature 30℃, relative humidity 72%, aseptic ventilation 0.5m³ / h (sterile air is treated by "primary 5μm filter + medium 1μm filter + high efficiency 0.3μm filter", and the total number of colonies is ≤10CFU / m³), without adding substrate; at the same time, start the online monitoring system, collect data at the frequency of "pH every 5min, lactic acid concentration every 15min, and CO2 release rate every 10min", and transmit it to the PLC control system (Siemens S7-1200) in real time.

[0041] Logical Judgment and Adjustment Measures: Based on real-time monitoring data, the PLC system performs conditional judgments and executes adjustments according to the following priorities:

[0042] Condition 1: pH > 5.2 and lactic acid concentration < 0.6 g / L (judged as "insufficient acid production by lactic acid bacteria, basic acidity not met")

[0043] Adjustment steps: Maintain a relative humidity of 72%, increase the fermentation temperature from 30℃ to 32℃ (to accelerate the proliferation of Lactobacillus plantarum Lp-05 and increase the acid production rate), and keep the ventilation rate at 0.5 m³ / h; after adjustment, reassess the pH and lactic acid concentration every 5 minutes until the pH drops below 5.2 and the lactic acid concentration rises above 0.6 g / L, then restore the temperature to 30℃.

[0044] Condition 2: pH < 4.8 and lactic acid concentration > 0.8 g / L (judged as "excessive acid production by lactic acid bacteria, inhibiting yeast activity")

[0045] Adjustments: Maintain a relative humidity of 72%, reduce the fermentation temperature from 30℃ to 27℃ (to slow down the metabolism of Lactobacillus plantarum Lp-05 and reduce the rate of acid production), and at the same time reduce the ventilation rate from 0.5 m³ / h to 0.3 m³ / h (to reduce oxygen supply and prevent lactic acid bacteria from producing more acid through aerobic respiration); review every 5 minutes after adjustment until the pH rises above 4.8 and the lactic acid concentration drops below 0.8 g / L, then restore the temperature and ventilation rate to their initial values.

[0046] Condition 3: CO2 release rate < 0.8 L / h and pH in the range of 4.8-5.2 (judged as "insufficient yeast gas production, slow dough expansion")

[0047] Adjustment procedure: Maintain the temperature at 30℃ and relative humidity at 72%, increase the ventilation rate from 0.5 m³ / h to 0.6 m³ / h (increase oxygen supply, promote aerobic metabolism of Zr-12 yeast, and improve gas production efficiency), and add 0.3% (w / v, relative to the total mass of dough) of maltose syrup through the built-in feeding device of the fermentation chamber (to supplement the yeast carbon source and further enhance gas production); after adjustment, reassess the CO2 release rate every 10 minutes until it rises to above 0.8 L / h, restore the ventilation rate to 0.5 m³ / h, and stop feeding.

[0048] Condition 4: pH 4.8-5.2, lactate concentration 0.6-0.8 g / L, CO2 release rate 0.8-1.2 L / h (judged as "metabolic state stable, meeting the stage target")

[0049] Adjustment steps: Keep all initial parameters unchanged and continue monitoring at the established frequency until the fermentation time reaches 1.5-2.5 hours and the dough volume expands to 1.8-2.2 times the initial volume (determined by the built-in laser volume detector in the fermentation box). The first fermentation is then complete.

[0050] Second fermentation stage (total time 0.8-1.2h, core objective: balance acidity and improve dough expansion rate)

[0051] Initial parameter settings: After the dough has undergone one fermentation, transfer it to a multi-layer fermentation rack equipped with a laser diameter gauge and set the initial parameters as follows: temperature 26-29℃ (default 27℃), relative humidity 68-72% (default 70%), and aseptic ventilation 0.3-0.6 m³ / h (default 0.4 m³ / h). The online monitoring system operates at a frequency of "pH collected every 5 minutes, acetic acid concentration collected every 15 minutes, and dough expansion rate collected every 20 minutes". The expansion rate is calculated by measuring the change in dough diameter using the laser diameter gauge (expansion rate = current dough volume / dough volume after division).

[0052] Logical Judgments and Adjustment Measures. The PLC system performs the following judgments and adjustments based on monitoring data:

[0053] Condition 1: pH > 4.8 and acetic acid concentration < 0.2 g / L (judged as "insufficient acid production by Lactobacillus brevis Lb-08, resulting in low flavor compound formation")

[0054] Adjustment procedure: Maintain the temperature at 27℃ and humidity at 70%, and reduce the ventilation rate from 0.4 m³ / h to 0.3 m³ / h (to create a micro-anaerobic environment and promote acetic acid production by Lactobacillus brevis Lb-08); reassess every 15 minutes after adjustment until the pH drops below 4.8 and the acetic acid concentration rises above 0.2 g / L, then restore the ventilation rate to 0.4 m³ / h.

[0055] Condition 2: pH < 4.5 and acetic acid concentration > 0.3 g / L (judged as "excessive acid production by Lactobacillus brevis Lb-08, making the dough prone to sourness and astringency")

[0056] Adjustment procedure: Maintain the temperature at 27℃ and humidity at 70%, and increase the ventilation rate from 0.4 m³ / h to 0.6 m³ / h (to increase oxygen and promote the consumption of some acetic acid by the yeast Zr-12 to balance the acidity); reassess every 15 minutes after adjustment until the pH rises above 4.5 and the acetic acid concentration drops below 0.3 g / L, then restore the ventilation rate to 0.4 m³ / h.

[0057] Condition 3: Dough expansion rate < 1.5 times and pH 4.5-4.8, acetic acid concentration 0.2-0.3 g / L (judged as "low yeast gas production efficiency, insufficient dough fluffiness")

[0058] Adjustment steps: Maintain humidity at 70% and ventilation at 0.4 m³ / h, and raise the temperature from 27℃ to 29℃ (to enhance the metabolic activity of Zr-12 yeast and accelerate gas production); after adjustment, reassess the expansion rate every 20 minutes until it rises to more than 1.5 times, then restore the temperature to 27℃.

[0059] Condition 4: pH 4.5-4.8, acetic acid concentration 0.2-0.3 g / L, dough expansion rate 1.5-1.8 times (judged as "both acidity and fluffiness meet the standards")

[0060] Adjustment procedure: Keep all parameters unchanged and continue monitoring until the fermentation time reaches 0.8-1.2 hours, at which point the secondary fermentation is complete.

[0061] Proofing stage (total time 35-45 minutes, core objective: stabilize final acidity and ensure even dough expansion)

[0062] Initial parameter settings: After transferring the dough blocks after the second fermentation into the texture feedback proofing box, set the initial parameters as follows: temperature 35-38℃ (default 36℃), relative humidity 80-85% (default 82%), and aseptic ventilation 0.1-0.2m³ / h (default 0.15m³ / h). The online monitoring system runs at the frequency of "pH every 5 minutes, dough elasticity every 15 minutes, and dough center temperature every 10 minutes". The dough elasticity is detected by the TA-XT2i online texture analyzer (probe P / 36R, compression rate 1mm / s, compression ratio 50%), and the elasticity parameter must be ≥0.8 (unitless, characterizing the dough's recovery ability).

[0063] Logical judgment and adjustment measures: The PLC system, based on texture and acidity data, performs the following precise adjustments:

[0064] Condition 1: pH < 4.6 and dough elasticity < 0.8 (judged as "high acidity + insufficient cross-linking of gluten and mucopolysaccharides, dough is prone to collapse")

[0065] Adjustments: Maintain a relative humidity of 82%, increase the temperature from 36℃ to 38℃ (to accelerate gas production by Zr-12 yeast and dilute local acidity through gas expansion), and simultaneously increase the ventilation rate from 0.15 m³ / h to 0.2 m³ / h (to supplement oxygen and prevent excessive ethanol production by yeast anaerobic metabolism), and extend the proofing time by 5 minutes; reassess every 15 minutes after adjustment until the pH rises above 4.6 and the elasticity is ≥0.8, then restore the temperature and ventilation rate to their initial values.

[0066] Condition 2: pH > 4.9 and dough elasticity > 0.9 (judged as "low acidity + dough too soft, easily deformed after baking")

[0067] Adjustments: Maintain relative humidity at 82%, reduce temperature from 36℃ to 35℃ (to slow down gas production by *Saccharomyces rouxii* Zr-12, allowing sufficient time for *Lactobacillus brevis* Lb-08 to produce acid), and simultaneously reduce ventilation from 0.15 m³ / h to 0.1 m³ / h (to create a micro-anaerobic environment and promote acid production by lactic acid bacteria); reassess every 15 minutes after adjustment until pH drops below 4.9 and elasticity ≤ 0.9, then restore temperature and ventilation to their initial values.

[0068] Condition 3: The center temperature of the dough is <35℃ or >38℃ (judged as "temperature deviation, affecting microbial metabolism and dough expansion")

[0069] Adjustment steps: If the temperature is <35℃, turn on the heating element of the proofing box to raise the temperature to 36℃, while maintaining a ventilation rate of 0.15m³ / h (to avoid local overheating); if the temperature is >38℃, turn on the cooling fan of the proofing box to lower the temperature to 36℃, while maintaining a humidity of 82% (to prevent the dough from losing moisture); after the temperature stabilizes, reassess the pH and elasticity to ensure that the indicators are within the target range.

[0070] Condition 4: pH 4.6-4.9, dough elasticity 0.8-0.9, core temperature 35-38℃ (judged as "final acidity and texture both meet the standards")

[0071] Adjustment steps: Keep all parameters unchanged and continue monitoring until the proofing time reaches 35-45 minutes and the dough volume expands to 1.8-2.0 times its original volume after shaping (judged by a visual recognition system). The proofing stage ends, and the dough is transferred to the baking stage.

[0072] Coordinated support from the control system.

[0073] Throughout the entire control process, the PLC system has a "parameter memory and self-learning" function: after each batch ends, it automatically records the number of adjustment triggers, adjustment range, and final quality data (such as pH difference between the bread center and surface, specific volume) for each stage, and compares them with the historical best batch data; if a batch frequently triggers "insufficient acid production" or "insufficient gas production", the system will automatically fine-tune the initial parameters of the next batch (such as increasing the initial temperature of the first fermentation by 0.5℃ for the batch with insufficient acid production), gradually reducing batch fluctuations and improving the stability of industrial production.

[0074] 3. Coordinated regulation of acidity and texture during the awakening stage

[0075] The proofing stage is crucial for the final fluffiness and acidity setting of the dough. This invention adopts an "elastic feedback control" method: when "pH < 4.6 and dough elasticity < 0.8" is detected, the temperature is automatically raised to 38°C, the ventilation rate is increased to 0.2 m³ / h, and the proofing time is extended by 5 min (to accelerate yeast gas production to dilute acidity, while promoting Lactobacillus brevis to produce mucopolysaccharides and enhance the cross-linking stability of gluten and organic acids).

[0076] When the pH value is detected to be greater than 4.9 and the dough elasticity is greater than 0.9, the temperature is automatically reduced to 35°C and the ventilation rate is reduced to 0.1 m³ / h (to promote lactic acid bacteria production and prevent the dough from becoming too soft and collapsing after baking).

[0077] (III) Industrialization process adaptation and optimization

[0078] To meet the requirements of a continuous production line with a daily output of 10-50 tons, optimizations were made in three dimensions: raw material formulation, key equipment modification, and quality control, as detailed below:

[0079] 1. Raw material formulation optimization (adapting to the metabolic characteristics of compound microbial strains)

[0080] Based on the sugar tolerance and mucopolysaccharide production characteristics of the compound strain, the raw material ratio (by weight) was optimized to ensure synergistic metabolism between each component and the strain, as detailed below:

[0081] Raw material name Quality Selection Criteria Industrial control requirements High-gluten flour 100 The wet gluten content is ≥30% (GB / T8607-2018), which enhances the cross-linking stability with mucopolysaccharides produced by Lactobacillus brevis. For each batch, sample and test the gluten content. If the deviation is >1%, add 0.5-1.0 parts of wheat gluten to ensure gluten formation degree ≥85%. Reverse osmosis drinking water 55-60 Hardness ≤150mg / L (GB5749-2022), to avoid calcium and magnesium ions affecting the metabolic activity of the strain. An online hardness monitor (model: Hach HQ40d) will be installed; if the hardness exceeds the standard, the secondary reverse osmosis treatment system will be activated. white sugar 3-5 Adapted to the sugar tolerance of Saccharomyces rouxii Zr-12 (tolerant to 25% concentration), providing a carbon source for fermentation. Grind to 80 mesh (standard sieve) to avoid large particles affecting bacterial dispersion. Add after premixing with flour. Edible butter 2-4 Melting point 32-35℃ (GB19646-2010) to avoid high temperature damaging the activity of the bacterial strain and improve the bread's texture. Melt at a constant temperature of 25-28℃ (melting tank model: JRH-500), filter to remove impurities, then add. salt 1-1.5 It regulates osmotic pressure, inhibits the growth of unwanted bacteria, and enhances the elasticity of gluten. Food-grade refined salt (NaCl content ≥ 97%) is used, dissolved and then mixed with water before being added to avoid excessively high local concentrations. Compound microbial seed liquid 8-12 <![CDATA[The viable count is ≥ 1.0×10 8 CFU / mL, providing fermenting microorganisms]]> Add in batches (add 50% first, stir for 5 minutes, then add the remaining 50%) to ensure even dispersion.

[0082] 2. Key equipment modification and integration

[0083] Based on the need for dynamic control, existing industrial equipment will be modified or have new functional modules added to ensure seamless connection between all stages, as detailed below:

[0084] Production process conventional equipment This invention modifies / adds equipment Core functions and parameters dough mixing Ordinary dough mixer Vacuum dough mixer with temperature monitoring (Model: FM-1000, modified by adding a PT100 temperature sensor, vacuum level -0.08 to -0.06 MPa) To prevent gluten oxidation and ensure even distribution of the starter culture, the total mixing time is 12-15 minutes (2-3 minutes for dry mixing → 5-8 minutes for wet mixing → 5-7 minutes for oil mixing). single fermentation ordinary fermentation box <![CDATA[Intelligent fermentation chamber (Model: HF-2000, New addition: Online HPLC + CO2 analyzer + PLC control system)]]> Real-time monitoring of metabolic indicators, with PLC (Siemens S7-1200) adjusting temperature (28-32℃), humidity (70-75%), and ventilation volume (0.3-0.6 m³ / h). Dough Division Ordinary dividing machine Fully automatic cutting machine with weight detection (Model: DF-500, new feature: weight sensor, accuracy ±1g) Divide the dough into portions weighing 50-100g each, ensuring each portion is of uniform quality and avoiding uneven fermentation. Secondary fermentation Multi-layer fermentation rack Multi-layer fermentation rack with laser diameter gauge (Model: HJ-1000, newly added: Keyence IV2 laser diameter gauge) The system monitors the dough's expansion rate online and automatically alarms when it reaches 1.5-1.8 times its original size, prompting the user to proceed to the next step. Awaken Standard proofing box Texture feedback proofing box (Model: XF-1500, New addition: TA-XT2i online texture analyzer) Simultaneously monitor pH, elasticity, and temperature, and adjust parameters accordingly to ensure that the elasticity after proofing is ≥0.8. Baking Tunnel oven Segmented temperature control + steam injection tunnel oven (Model: TB-3000, newly added: steam injection device) Segmented temperature control: Preheating section 180-190℃ / 160-170℃, baking section 190-210℃ / 170-190℃, cooling section 100-120℃, steam humidity 80-85%. cool down Natural cooling Air-cooled tunnel (Model: FL-2000, wind speed 1.5-2.0m / s) Quickly cool the bread to 20-25℃ to prevent condensation from causing mold growth. Cooling time is 30-40 minutes. Package Ordinary packaging machine Fully automatic vacuum packaging machine (Model: DZ-600, vacuum degree ≤ -0.09MPa) Packaging is made of PET / PE composite film, with an oxygen permeability of ≤5cc / (m²・24h・atm) and a water vapor permeability of ≤3g / (m²・24h).

[0085] 3. Full-process quality control system

[0086] Establish a comprehensive testing standard covering the entire process from raw materials to intermediate products to finished products to ensure stable product quality. Specific testing points and requirements are as follows:

[0087] Detection Node Testing items Detection methods Qualification Standard Raw material warehousing Gluten content and moisture content of high-gluten flour; hardness of drinking water; viable bacterial count of microbial strains. GB / T5506.2-2021; GB / T5750.4-2023; Plate Counting Method <![CDATA[Gluten ≥ 30%, moisture 13 - 14%; hardness ≤ 150 mg / L; viable bacteria ≥ 1.0×10 8 CFU / mL]]> After seed liquid preparation viable count, protein concentration, pH Plate count method; BCA method; pH meter (Mettler-Toledo FE28) <![CDATA[Viable bacteria ≥ 1.0×10 8 CFU / mL; Protein concentration 1.0 - 1.5 mg / mL; pH 5.5 - 6.0]]> After the dough is mixed Gluten formation degree, pH, temperature SB / T10526-2021; pH meter; temperature sensor Gluten ≥85%; pH 5.8-6.2; temperature 25-30℃ After one fermentation pH, lactic acid concentration, expansion rate pH meter; HPLC; water displacement method pH 4.8-5.2; lactic acid 0.6-0.8 g / L; expansion ratio 1.8-2.2 times. After secondary fermentation pH, acetic acid concentration, expansion rate pH meter; HPLC; laser diameter measuring instrument pH 4.5-4.8; acetic acid 0.2-0.3 g / L; expansion ratio 1.5-1.8 times. After waking up pH, elasticity, core temperature pH meter; texture analyzer; temperature sensor pH 4.6-4.9; elasticity ≥0.8; temperature 35-38℃ After baking Specific volume, core temperature, moisture GB / T20981-2021; Needle thermometer; Rapid moisture meter (Ohaus MB25) Specific volume ≥ 4.6 mL / g; core temperature ≥ 90℃; moisture content 28-32%. Finished product Acidity uniformity, flavor score, GI value, shelf life pH meter; Sensory evaluation (SB / T10527-2022); GB / T22494-2008; Accelerated test method Center-surface pH difference ≤ 0.2; Flavor score ≥ 90; GI 55-60; Shelf life ≥ 12 days (25℃)

[0088] Beneficial effects

[0089] This invention, through its innovative approach of "synergistic effects of compound microbial strains + dynamic regulation + industrial adaptation," achieves the following breakthrough improvements compared to existing technologies, fully demonstrating its novelty and inventiveness:

[0090] 1. Significantly optimized quality characteristics

[0091] Acidity uniformity: The pH difference between the center and surface of the bread was reduced from 0.5-0.6 in conventional processes to ≤0.2, avoiding local over-acidity or under-acidity, and the taste harmony score was improved from 65 points to 92 points;

[0092] Flavor compounds: The total amount of esters increased from 10-15 mg / kg to ≥35 mg / kg, and the ratio of lactic acid to acetic acid remained stable at 3-4:1, forming a complex flavor of "mild sour aroma + fruity aroma", with a 40% improvement in sensory acceptance;

[0093] Texture characteristics: Specific volume increased from 3.8-4.0 mL / g to ≥4.6 mL / g, chewiness decreased from 250-300g to 150-180g, and anti-aging properties were enhanced (hardness increase rate decreased from 50% to 20% after 5 days of storage).

[0094] 2. Industrial stability has been greatly improved.

[0095] Batch consistency: Data from 30 production batches showed that pH fluctuation decreased from >0.4 to ≤0.15, specific volume fluctuation decreased from 0.4 mL / g to ≤0.2 mL / g, and the product qualification rate increased from 78% to ≥98.5%.

[0096] Capacity adaptation: The total fermentation cycle is controlled at 4.5-6 hours, which matches the cycle time of existing industrial production lines. The equipment utilization rate is increased from 70% to 100%, and the annual capacity of the 30-ton-per-day production line is increased by 1095 tons.

[0097] Cost control: Eliminating the cost of purchasing exogenous organic acids (citric acid 8 yuan / kg, added at 0.3%), saving 24 yuan per batch (1000kg dough), and 87,600 yuan per year; at the same time, the raw material loss rate is reduced from 8% to 2.5%, saving more than 600,000 yuan in raw material costs per year.

[0098] 3. Enhanced health benefits and shelf life

[0099] Low GI characteristics: The content of oligosaccharides produced by lactic acid bacteria fermentation increases from <0.3g / 100g to 1.2-1.5g / 100g, and the GI value decreases from 70-75 to 55-60, which meets the "Low GI Food Certification Standard" (GI<60) and is suitable for diabetic patients and postoperative recovery groups;

[0100] Long shelf life: The evenly distributed organic acids (lactic acid + acetic acid) form a broad-spectrum antibacterial environment, extending the shelf life from 8-10 days to 12-15 days (stored at 25℃), and no preservatives are added (complies with GB2760-2024 "National Food Safety Standard for the Use of Food Additives"), reducing distribution losses.

[0101] 4. Environmental Protection and Industrialization Prospects

[0102] Green production: avoids the high energy consumption and high pollution of organic acid preparation in the exogenous acid addition process, and reduces the discharge of microbial waste liquid (the amount of waste liquid in the preparation of compound microbial seed liquid is only 1 / 5 of that in the traditional process).

[0103] Industrialization adaptability: The compound ratio and process parameters can be flexibly adjusted to adapt to the production of different categories such as toast, dinner rolls, and European bread. Moreover, the cost of core equipment modification is only 30% of that of new equipment, making it easy to promote and apply in existing baking enterprises. Detailed Implementation

[0104] Example 1: Optimal plan for producing 30 tons of toast bread per day (standard ratio)

[0105] 1. Preparation of compound microbial seed liquid

[0106] Compound ratio: Lactobacillus plantarum Lp-05: Lactobacillus brevis Lb-08: Saccharomyces rouxii Zr-12 = 1:0.5:1.0 (mass ratio);

[0107] Culture parameters: Lactic acid bacteria were anaerobically cultured at 37℃ for 19 h, with a viable count of 1.3 × 10⁻⁶. 9 CFU / mL; yeast cultured aerobically at 30℃ for 24 h, viable count 1.6 × 10⁻⁶ 9 CFU / mL;

[0108] Compound seed culture: After mixing, add 2% maltodextrin-trehalose protectant (2:1), viable count 1.1×10⁻⁶ 8 CFU / mL, pH 5.8, store at 4℃ for later use.

[0109] Ingredient recipe (1000kg dough)

[0110] 1000 kg of high-gluten flour (31% wet gluten, 13.5% moisture), 580 kg of reverse osmosis drinking water (hardness 120 mg / L), 40 kg of white sugar (80 mesh), 30 kg of edible butter (melted at 26℃), 12 kg of salt (added after dissolution), and 100 kg of compound microbial seed solution.

[0111] 2. Industrialized production steps

[0112] (1) Dough mixing:

[0113] Start the vacuum dough mixer (FM-1000), first add high-gluten flour, white sugar, and salt, and dry mix at 25℃ for 2 minutes (300 rpm); add reverse osmosis drinking water and compound bacterial seed solution, and wet mix at 28℃ for 7 minutes (250 rpm); finally add melted edible butter, vacuum to -0.07 MPa, and stir for 6 minutes (200 rpm) to obtain a dough with 88% gluten formation, pH 6.0, and temperature 27℃.

[0114] (2) Primary fermentation:

[0115] The dough was transferred to the intelligent fermentation chamber (HF-2000), with initial parameters set as follows: temperature 30℃, humidity 72%, and ventilation 0.5 m³ / h. Online monitoring showed that after 1 hour of fermentation, the pH was 5.4, lactic acid was 0.5 g / L, and CO2 was 0.7 L / h, triggering the "CO2 deficiency" condition. The ventilation was automatically increased to 0.6 m³ / h, and 0.3% maltose syrup (3 kg) was added. After 2 hours of fermentation, the pH was 5.0, lactic acid was 0.7 g / L, and CO2 was 1.0 L / h, reaching the target range. The first fermentation was completed, and the dough expansion rate was 2.0 times.

[0116] (3) Segmentation and relaxation:

[0117] The dough was divided into 80g pieces (weight deviation ±1g) using a fully automatic dividing machine (DF-500), and then transferred into a relaxation tunnel (temperature 26℃, humidity 73%) for 18 minutes to prevent gluten shrinkage.

[0118] (4) Secondary fermentation:

[0119] The relaxed dough was transferred to a multi-layer fermentation rack (HJ-1000) equipped with a laser diameter measuring instrument. The initial parameters were set as follows: temperature 27℃, humidity 70%, and ventilation 0.4m³ / h. After 0.8h of fermentation, the pH was 4.7, the acetic acid was 0.25g / L, and the expansion rate was 1.6 times, reaching the target range, and the second fermentation was completed.

[0120] (5) Awakening:

[0121] The dough was transferred to a texture feedback proofing chamber (XF-1500) with initial parameters set at 36°C, 82% humidity, and 0.15 m³ / h ventilation. After 35 minutes of proofing, the pH was 4.8, elasticity was 0.85, and temperature was 37°C, which met the target range. Proofing was then stopped, and the dough expansion was 1.9 times (relative to the volume after shaping).

[0122] (6) Shaping and baking:

[0123] The dough was pressed into a loaf shape (12×8×6cm) using a loaf forming machine (model: TS-800) and then transferred to a segmented temperature-controlled tunnel oven (TB-3000). The parameters were set as follows: preheating section 185℃ / 165℃ (5m), baking section 200℃ / 180℃ (20m), cooling section 110℃ (5m), total baking time 18min, and bread center temperature 93℃.

[0124] (7) Cooling and Packaging:

[0125] After baking, the toast is transferred to a cooling tunnel (FL-2000) with a wind speed of 1.8 m / s and cooled for 35 minutes until the center temperature reaches 23°C. It is then packaged using a fully automatic vacuum packaging machine (DZ-600) with a PET / PE composite film (oxygen permeability 4cc / (m²・24h・atm)) and a vacuum degree of -0.095MPa.

[0126] Test results

[0127] Testing items Numerical values / results Compliance with standards central pH 4.8 The target range is 4.6-4.9, which is in line with expectations. Surface pH 4.6 The pH difference between the center and the surface is 0.2, which meets the requirement of ≤0.2. specific volume 4.7 mL / g The target range is ≥4.6 mL / g, which meets the requirements. Total amount of esters 38.5 mg / kg The target range is ≥35mg / kg, which meets the requirements. Oligosaccharide content 1.4g / 100g The target range is 1.2-1.5g / 100g, which is in line with... GI value 56 The target range is 55-60, which is in line with the requirements. chewing 165g The target range is 150-180g, which is in line with... Shelf life (25℃) 14 days The target range is ≥12 days, which meets the requirements. Batch pass rate (30 batches) 99% The target range is ≥98.5%, which meets the requirements.

[0128] Example 2: A low-sugar meal pack production plan for 10 tons per day (low yeast ratio)

[0129] 1. Adjust parameters

[0130] Compound strain ratio: Lp-05:Lb-08:Zr-12=1:0.6:0.8 (reduced yeast ratio to suit low sugar environment);

[0131] Raw material adjustments: The amount of white sugar was reduced to 2kg / 100kg of flour, and 1kg / 100kg of fructooligosaccharides (prebiotic fortification) was added.

[0132] 2. Process adjustments: The ventilation rate for secondary fermentation was increased to 0.6 m³ / h (to compensate for insufficient gas production caused by the reduced yeast ratio), and the baking time was shortened to 15 minutes (to avoid over-baking due to the small size of the bread rolls).

[0133] 3. Test results: pH difference between center and surface is 0.20, specific volume is 4.6 mL / g, ester content is 35.2 mg / kg, oligosaccharide content is 1.3 g / 100 g (total prebiotics after including fructooligosaccharides are 1.8 g / 100 g), GI value is 55, shelf life is 13 days, which meets the functional requirements of low sugar meal packs.

[0134] Example 3: A high-fiber bread production plan for 50 tons per day (high lactic acid bacteria ratio)

[0135] 1. Adjust parameters

[0136] Compound strain ratio: Lp-05:Lb-08:Zr-12=1:0.3:1.2 (the proportion of lactic acid bacteria is reduced to avoid excessive acid production in a high-fiber environment);

[0137] 2. Raw material adjustment: Add 5 kg / 100 kg of wheat dietary fiber (GB14881-2023) to the flour, and increase the amount of drinking water to 60 kg / 100 kg of flour (to improve fiber dispersibility).

[0138] 3. Process adjustment: The primary fermentation temperature is reduced to 28℃ (to slow down the acid production of lactic acid bacteria and adapt to the buffering effect of fiber on pH), and the proofing time is extended to 45 minutes (the fiber needs more time to expand after absorbing water).

[0139] 4. Test results: pH difference between center and surface is 0.17, specific volume is 4.5 mL / g, ester content is 36.8 mg / kg, oligosaccharide content is 1.5 g / 100 g, dietary fiber content is 4.8 g / 100 g, GI value is 55, shelf life is 15 days, which meets the health requirements of high fiber and low GI.

[0140] Example 4: Immobilized microbial strain recycling scheme (cost optimization)

[0141] 1. New step: Microbial immobilization and recovery

[0142] Immobilization carrier: Magnetic chitosan microspheres (particle size 50-100nm, surface amino-modified, preparation method refers to CN202210887654.3);

[0143] Immobilization process: The composite bacterial seed solution was mixed with magnetic microspheres at a ratio of 1:0.3 (mass ratio), and the mixture was shaken at 25°C for 30 min (rotation speed 150 r / min), with a binding rate of 92%.

[0144] Recovery and recycling: After the first fermentation, a 0.5T external magnetic field (magnetic field generator model: GMW5403) is applied to adsorb the magnetic microsphere-strain complex, and the mechanical scraping recovery rate is 80%. After rinsing twice with sterile water, it is inoculated into a modified medium and rejuvenated at 30℃ for 1 hour. The viable number is restored to more than 90% of the initial value, and it is recycled 3 times.

[0145] 2. Test results (after 3 cycles): pH difference between center and surface 0.16, specific volume 4.6 mL / g, esters 35.5 mg / kg, oligosaccharide content 1.4 g / 100 g, shelf life 14 days; the cost of strain preparation was reduced from 8.5 yuan / kg to 2.8 yuan / kg (after 3 cycles), saving 5700 yuan per batch (1000 kg dough), significantly reducing the cost of industrial production.

[0146] Comparative Example 1: Conventional single-strain + exogenous acidification process

[0147] process parameters

[0148] Microbial strain: Commercial brewing yeast (live count 1.0 × 10⁻⁶) 8 CFU / mL, addition amount 5kg / 1000kg dough);

[0149] Exogenous acid addition: Citric acid (addition amount 3kg / 1000kg dough, added on the 3rd day of fermentation);

[0150] Control method: Static control of the fermentation endpoint pH 5.0, without adjusting the temperature or ventilation (primary fermentation temperature 30℃, ventilation 0.5m³ / h, secondary fermentation temperature 27℃, ventilation 0.4m³ / h).

[0151] Test results:

[0152] The pH difference between the center and the surface is 0.65, the specific volume is 4.0 mL / g, the ester content is 15.0 mg / kg, the oligosaccharide content is 0.2 g / 100 g, the GI value is 71, the shelf life is 10 days, and the batch qualification rate is 78%. Compared with Example 1 of the present invention, the quality, stability and health properties are significantly inferior.

[0153] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. An industrial process for fermenting bread using a complex natural microbial strain to dynamically regulate acidity is characterized by, Includes the following steps: (1) Preparation of compound natural fungal seed liquid The mixture is prepared according to the following mass ratio: Lactobacillus plantarum Lp-05: Lactobacillus brevis Lb-08: Saccharomyces rouxii Zr-12 = 1:(0.3-0.6):(0.8-1.2); Lactobacillus plantarum Lp-05 and Lactobacillus brevis Lb-08 were inoculated into a modified MRS medium and anaerobically cultured at 37°C for 18-20 h to obtain a viable count ≥1.2×10⁻⁶. 9 Lactic acid bacteria solution with CFU / mL; *Saccharomyces rouxii* Zr-12 was inoculated into modified YPD medium and cultured aerobicly at 30℃ for 22-26 h, yielding a viable count ≥1.5 × 10⁻⁶. 9 Yeast liquid at CFU / mL; Lactic acid bacteria broth and yeast broth were mixed in a compound ratio, and 2% (w / v) maltodextrin-trehalose complex preservative was added. After stirring evenly, the mixture was filtered to remove bacteria, yielding a viable count ≥1.0 × 10⁻⁶. 8 CFU / mL compound bacterial seed solution; (2) Dynamic regulation of dough preparation and fermentation throughout the entire cycle By weight, 100 parts of high-gluten flour, 55-60 parts of reverse osmosis drinking water, 3-5 parts of white sugar, 2-4 parts of edible butter, 1-1.5 parts of salt and 8-12 parts of the compound bacterial seed liquid from step (1) are put into a vacuum dough mixer and stirred in stages at 25-30℃ for 12-15 minutes to obtain a dough with gluten formation degree ≥85%. First fermentation: Transfer the dough to an intelligent fermentation chamber with initial parameters of 28-32℃, 70-75% humidity, and 0.3-0.6 m³ / h ventilation. Monitor the pH at 4.8-5.2, lactic acid concentration at 0.6-0.8 g / L, and CO2 release rate at 0.8-1.2 L / h, and adjust the temperature, ventilation, and substrate replenishment accordingly. Cultivate for 1.5-2.5 hours. Dividing and Relaxation: Divide the dough after the first fermentation into 50-100g pieces and relax at 25-28℃ for 15-20 minutes; Second Fermentation: Transfer the dough pieces to a multi-layer fermentation rack with initial parameters of temperature 26-29℃, humidity 68-72%, ventilation 0.3-0.6m³ / h, real-time monitoring of pH 4.5-4.8, acetic acid concentration 0.2-0.3g / L, expansion rate 1.5-1.8 times, and incubation for 0.8-1.2 hours; Proofing: Transfer the dough block into a texture feedback proofing chamber with initial parameters of 35-38℃, 80-85% humidity, and 0.1-0.2m³ / h ventilation. Monitor the pH at 4.6-4.9 and the dough elasticity at ≥0.8 in real time. Proof for 35-45 minutes. (3) Baking and post-processing After proofing, transfer the dough to a segmented temperature-controlled tunnel oven and bake for 15-20 minutes. Then cool it to 20-25°C and vacuum pack it to obtain the finished bread.

2. The process according to claim 1, characterized in that, The modified MRS medium in step (1) has the following formula: glucose 20 g / L, malt extract 10 g / L, yeast extract 5 g / L, sodium acetate 5 g / L, diammonium citrate 2 g / L, magnesium sulfate 0.1 g / L, manganese sulfate 0.05 g / L, pH 6.2 ± 0.1; the modified YPD medium has the following formula: glucose 20 g / L, peptone 20 g / L, yeast extract 10 g / L, lactic acid 0.5 g / L, pH 5.5 ± 0.

1.

3. The process according to claim 1, characterized in that, The mass ratio of the maltodextrin-trehalose composite protectant in step (1) is 2:1, and the viable bacteria loss rate of the composite bacterial seed liquid after refrigeration at 4°C for 7 days is ≤10%.

4. The process according to claim 1, characterized in that, The vacuum degree of the vacuum dough mixer mentioned in step (2) ① is -0.08 to -0.06 MPa. The staged mixing includes: dry mixing for 2-3 min, wet mixing for 5-8 min, and oil mixing for 5-7 min. The mixing speeds are 300 r / min, 250 r / min, and 200 r / min, respectively.

5. The process according to claim 1, characterized in that, The linkage adjustment logic for the primary fermentation described in step (2) ② is as follows: When pH > 5.2 and lactic acid concentration < 0.6 g / L, the temperature is raised to 32℃, and the ventilation rate is maintained at 0.5 m³ / h. When pH < 4.8 and lactic acid concentration > 0.8 g / L, the temperature is reduced to 27℃ and the ventilation rate is reduced to 0.3 m³ / h. When the CO2 release rate is <0.8L / h and the pH is in the range of 4.8-5.2, the ventilation rate is increased to 0.6m³ / h, and 0.3% (w / v) maltose syrup is added.

6. The process according to claim 1, characterized in that, The multi-layer fermentation rack mentioned in step (2) ④ is equipped with a laser diameter measuring instrument. The laser diameter measuring instrument has an accuracy of ±0.1mm and a sampling frequency of 1 time / s, and is used to monitor the dough expansion rate online.

7. The process according to claim 1, characterized in that, The activation linkage adjustment logic mentioned in step (2) ⑤ is as follows: When pH < 4.6 and dough elasticity < 0.8, the temperature is increased to 38℃, the ventilation rate is increased to 0.2m³ / h, and the proofing time is extended by 5min; When pH > 4.9 and dough elasticity > 0.9, the temperature is reduced to 35℃ and the ventilation rate is reduced to 0.1 m³ / h.

8. The process according to claim 1, characterized in that, The parameters of the segmented temperature-controlled tunnel oven mentioned in step (3) are: preheating section 180-190℃ / 160-170℃, baking section 190-210℃ / 170-190℃, cooling section 100-120℃, bread center temperature ≥90℃.

9. The process according to claim 1, characterized in that, The vacuum packaging in step (3) uses a PET / PE composite film with an oxygen permeability of ≤5cc / (m²・24h・atm), a water vapor permeability of ≤3g / (m²・24h), and a vacuum degree of ≤-0.09MPa.

10. The process according to claim 1, characterized in that, The composite strain mentioned in step (1) is immobilized by magnetic chitosan microspheres. The mass ratio of the magnetic microspheres to the composite strain seed liquid is 1:0.

3. After fermentation, it is recovered by a 0.5T magnetic field and recycled 3-5 times. The recovery rate is ≥80%. After rejuvenation, the number of viable bacteria is restored to more than 90% of the initial value.