Processing method of special wheat flour for baking low-bacteria low-heat-resistance spores

Abstract

The invention discloses a processing method of special wheat flour for baking low-bacteria and low-heat-resistance spores, and belongs to the field of wheat flour milling. The processing method disclosed by the invention comprises a specific wheat raw material sterilization method and grinding and milling. The wheat raw material sterilization method comprises the following steps: primary damp-heat isothermal sensitization, room-temperature standing, secondary heat treatment, low-temperature drying and post-conditioning. According to the processing method disclosed by the invention, microbiology and flour functionality are taken into consideration, the heat intensity requirement is reduced through sensitization-rekilling, and the gluten strength and the structure are retained through low-temperature drying-post-conditioning, so that double-low flour and bread-friendly flour are achieved at the same time.

Description

Technical Field

[0001] This invention belongs to the field of wheat milling, specifically relating to a processing method for wheat flour with low bacteria and low heat spores for baking. Background Technology

[0002] In recent years, with the popularization of the "Clean Label" concept, consumers have increasingly demanded natural, safe, and additive-free food. Chemical preservatives widely used in traditional baked goods, such as sodium dehydroacetate and potassium sorbate, are gradually being restricted or phased out. Sodium dehydroacetate, in particular, was once a commonly used preservative in bread production, significantly extending shelf life. However, with the national ban on sodium dehydroacetate and the rapid development of cold chain distribution and pre-packaged baked goods, the industry urgently needs to extend the shelf life of baked goods without relying on chemical preservatives. This trend has placed higher demands on the microbial control of raw wheat flour in the baking industry chain.

[0003] Wheat and its flour are core ingredients in baked goods, and microbial contamination has long been a problem. In particular, heat-resistant Bacillus bacteria can form spores under unfavorable conditions. These spores are extremely heat-resistant, surviving conventional sterilization and baking temperatures, and can regrow and multiply during product storage. This leads to a rapid increase in microbial numbers, manifesting as rancidity, flavor deterioration, and "rope-like spoilage," significantly shortening the shelf life of baked goods. Studies have shown that the higher the number of heat-resistant spores in raw flour, the shorter the shelf life of baked goods; when heat-resistant spore levels are controlled at low levels, the shelf life of products such as bread can be extended by 2 to 3 times. Therefore, reducing the number of heat-resistant spores in wheat flour is key to extending shelf life.

[0004] On the other hand, the total bacterial count in flour also affects the stability and quality safety of baked goods. Excessive bacteria can accelerate the deterioration of products such as bread and shorten their shelf life. Therefore, simply reducing the total bacterial count or simply controlling heat-resistant spores is insufficient to meet the requirements. Only flour with both low total bacterial count and low heat-resistant spore count can the quality and shelf life of baked goods under the conditions of preservative-free and clean labeling be truly guaranteed.

[0005] Currently, common wheat flour sterilization technologies include ozone treatment, irradiation, and hot air sterilization. However, these methods generally suffer from high costs, low consumer acceptance, or significant impacts on flour quality. For example, ozone may cause gluten protein oxidation, irradiation is restricted by regulations and the market, and while simple high-temperature heat treatment can reduce some bacteria, it has limited effect on heat-resistant spores. Meanwhile, the contamination rate of heat-resistant spores in domestically produced wheat flour is generally high (even exceeding 50% in southern regions), severely restricting its application in high-end baking.

[0006] In summary, existing wheat or wheat flour sterilization technologies suffer from problems such as incomplete sterilization, quality damage, high costs, or insufficient industrial adaptability. In particular, they cannot simultaneously achieve "double-low" wheat flour with low total bacterial count and low heat-resistant spore count. Therefore, there is an urgent need for a new clean wheat treatment method that can effectively control heat-resistant spores while maintaining the processing performance of wheat flour, providing a stable and safe raw material basis for preservative-free baked goods. Summary of the Invention

[0007] [Technical Issues] This invention aims to achieve a simultaneous, stable, and industrially sustainable reduction in total microbial count and heat-resistant spores for baking-specific wheat flour without relying on chemical preservatives and chemical inducers; at the same time, it maintains or improves key process quality indicators of flour (ash content, whiteness, protein, wet gluten, flour stability time, weakening degree, and tensile properties), providing a replicable raw material sterilization pathway for clean label baking flour.

[0008] [Technical Solution] To address the above problems, this invention provides a method for processing low-bacterial, low-heat-resistant spore wheat flour, comprising the following steps: (1) Raw grain cleaning and pretreatment: The raw wheat is screened, destoned, magnetically separated, threshed and winnowed in sequence to remove sand, metal and light impurities to obtain clean wheat; (2) First wet heat treatment: The cleaned wheat in step (1) is subjected to wet heat induction treatment; (3) Cooling and standing at room temperature: Cool the material after the wet heat induction treatment in step (2) to room temperature and let it stand at room temperature; (4) Second heat treatment: The material that has been left to stand in step (3) is subjected to heat treatment; (5) Low-temperature drying and cooling: Dry the material after heat treatment in step (4) at low temperature to a safe moisture content and cool it fully to prevent moisture absorption and condensation; (6) Post-conditioning and moistening of wheat: Add water to the cooled material in step (5) again to moisten the wheat so that the grains reach the target moisture content required for milling, and let it stand for a period of time to reach equilibrium; (7) Grind and sieve the wheat after moistening in step (6) to obtain wheat flour.

[0009] In one embodiment of the present invention, in step (2), the wet heat induction treatment causes the heat-resistant spores on or attached to the wheat surface to enter a germination or sub-germination state, thereby reducing their heat resistance.

[0010] In one embodiment of the present invention, in step (2), the damp heat induction treatment preferably adopts a dual-channel heat replenishment and water replenishment of "clean steam + sterile water atomization", and isothermal heat preservation in a saturated or near-saturated damp heat environment.

[0011] In one embodiment of the present invention, step (2) includes the following process: First, control the wet basis moisture content of wheat grains to reach 16%–32%, then place them in a temperature of 60℃–80℃ and a relative humidity of ≥95% for 5–15 minutes. Preferably, the wet basis moisture content of wheat grains reaches 30.0% ± 0.5%. Then, conduct isothermal treatment at 60℃ ± 1℃ for 10 ± 1 minutes.

[0012] In one embodiment of the present invention, in step (2), the thickness of the wheat raw material bed is ≤120 mm during wet heat treatment.

[0013] In one embodiment of the present invention, step (2) is carried out in a saturated or near-saturated humid and hot environment, with a relative humidity of ≥95% in the channel and a difference between the air dew point and the process temperature of ≤1.0℃ (preferably ≤0.5℃); the material bed thickness in the heat preservation channel is ≤150 mm and the material is turned over to ensure that the core temperature of the grain is ≥ the process temperature and continues until the heat preservation time.

[0014] In one embodiment of the present invention, step (2) adopts a dual-channel heating and water replenishment method of "clean steam + sterile water atomization" to enable the material to reach the target moisture and temperature within 90 seconds, and is equipped with temperature and dew point (or relative humidity) sensors and online near-infrared (NIR) moisture meter to implement dew point / temperature closed-loop control and discharge moisture release; step (2) does not add exogenous chemical inducers.

[0015] In one embodiment of the present invention, in step (2), the heat preservation channel is a sealed or basically sealed device for maintaining an isothermal and isohumid environment for a set time, and is composed of a heating / humidification unit, a circulating air distribution mechanism, a conveying and turning mechanism, and a temperature and humidity monitoring closed-loop control unit.

[0016] In one embodiment of the present invention, the cooling in step (3) involves cooling the material to 20–30°C and allowing it to stand at that temperature for 30–120 minutes to ensure that the spores are in a sensitized state of germination or sub-germination. Preferably, the standing time is 30–60 minutes.

[0017] In one embodiment of the present invention, the second heat treatment in step (4) is performed at a temperature of 65°C to 95°C for 10 to 20 minutes. Preferably, the treatment is performed at 85±5°C for 10 to 15 minutes.

[0018] In one embodiment of the present invention, in step (4), the thickness of the material bed is 20 to 80 mm (based on the thickness of the conveyor belt or the equivalent stacking height), preferably 30 to 60 mm.

[0019] In one embodiment of the present invention, the heat treatment method in step (4) may be one or a combination of steam, hot air, microwave, or radio frequency. When using a combination of microwave and radio frequency, the equivalent bed thickness is allowed to be **≤100 mm**, but the killing effect equivalent to the above temperature range should be verified by online monitoring of the core temperature within 10 to 20 minutes.

[0020] In one embodiment of the present invention, step (4) involves setting up multi-point temperature probes and (if applicable) penetrating temperature measurement or infrared temperature measurement, and recording the core temperature-time curve as the basis for release.

[0021] In one embodiment of the present invention, the drying conditions in step (5) are low-temperature hot air or room-temperature dry air drying with an air temperature below 40°C (optionally 30-40°C, preferably 30-38°C).

[0022] In one embodiment of the present invention, in step (5), the thickness of the material bed during drying is 20-80 mm (preferably 30-60 mm), the apparent wind speed is 0.5-1.5 m / s, and a dew point / temperature closed loop is used to avoid over-drying.

[0023] In one embodiment of the present invention, in step (5), the grains are dried until the wet basis moisture content is ≤14%.

[0024] In one embodiment of the present invention, in step (5), after drying, the material is cooled to room temperature ±5°C and left to stand for 10 to 30 minutes under slow cooling conditions at room temperature to balance the moisture and temperature and prevent condensation and re-moistening.

[0025] In one embodiment of the present invention, step (6) involves adding water by atomizing water spraying or humidifying air to adjust the wet basis moisture content of the grains to 15.5%, and then letting them stand at room temperature for 6 to 12 hours to allow the moisture to be evenly distributed inside the grains.

[0026] In one embodiment of the present invention, neither step (2) nor step (6) involves the addition of chemical inducers or chemical auxiliaries.

[0027] Measurement and Equivalence Explanation: Unless otherwise stated, "%" is the mass fraction, "moisture" is the wet basis moisture content, and "processing temperature" is the temperature of the processing medium (steam / hot air / humid air, or the equivalent material temperature corresponding to microwave / radio frequency). When the core temperature of the material reaches a killing effect equivalent to the above conditions, it is considered an equivalent condition.

[0028] The present invention also provides the application of the above-mentioned low-bacterial and low-heat-resistant spore wheat flour processing method in extending the shelf life of baked products.

[0029] In one embodiment of the invention, the baked product is, for example, bread.

[0030] This invention achieves a simultaneous and stable reduction in total microbial count and heat-resistant spores by introducing a coupled process of "two-stage moist heat treatment + static activation + low-temperature drying" at the wheat raw material level, while maintaining or even improving the processing quality of wheat flour. Compared with existing methods such as single-stage high-temperature sterilization or ozone and irradiation, the technical solution of this invention has the following significant advantages: First, the heat-sensitive treatment in the first stage transforms the heat-resistant spores on the surface of wheat grains from a dormant state to a sub-germination state, reducing their heat tolerance and thus significantly improving the killing efficiency of subsequent heat treatment. This process is carried out in an isothermal humid heat environment with relative humidity ≥95% and dew point difference ≤1℃, avoiding quality damage under traditional dry heat conditions.

[0031] Secondly, by setting a cooling and settling stage, the spores are further activated under suitable conditions, creating a "simultaneous killing window" for the second heat treatment. When the secondary heat treatment temperature is controlled at 65-95℃, the treatment time is 10-20 minutes, and the material thickness is 30-60 mm, the dual control of heat-resistant spores and total bacteria can be effectively achieved, which is significantly better than the control ratio that did not settle or was overheated.

[0032] Furthermore, the low-temperature drying and post-conditioning processes, while controlling moisture content, maximize the preservation of the natural enzyme activity and protein structure integrity of wheat flour. The total bacterial count of wheat flour treated by this invention can be stably controlled below 500 CFU / g, and the number of heat-resistant spores is below 50 CFU / g, significantly superior to products treated with conventional wet or dry heat. Simultaneously, the ash content, whiteness, protein, and wet gluten content of the wheat flour remain good, the flour stability time is increased to over 20 minutes, and the weakening degree decreases to around 25, indicating more stable flour properties and stronger gluten.

[0033] Finally, the process of this invention achieves a "low-intensity, high-efficiency" microbial control mode, without relying on any chemical preservatives or inducers, aligning with the trend of clean-label food production and applicable to the industrial production of bread flour and high-end baking powder. This method features a simple process, controllable parameters, and strong adaptability, and can be directly integrated into the front-end stages of conventional flour milling, possessing significant promotional value and industrialization potential. Attached Figure Description

[0034] Figure 1 This is a flowchart of a low-bacterial, low-spore wheat flour processing method.

[0035] Figure 2 This study investigates the effects of total bacterial count and heat-resistant spore count in commercially available bread flour on the storage stability of bread. Detailed Implementation

[0036] The specific implementation method of the present invention will be further described below. For ease of understanding and repetition, the embodiments and comparative examples following this specification are for illustrative purposes only and do not constitute a limitation.

[0037] Unless otherwise specified: percentages are mass fractions, moisture is wet basis moisture content, temperature is the temperature of the processing medium (equivalent material temperature corresponding to steam, hot air, humid air or microwave / RF), and the thickness of the material is measured by the thickness of the mesh belt material or the equivalent stack height; the target moisture content and dew point of the primary humid heat treatment are controlled in a closed loop by an online near-infrared moisture meter and a dew point / relative humidity sensor; the secondary heat treatment uses the core temperature-time curve recorded by multi-point probes as the basis for release; the temperature of the dry air is not higher than 40°C and slow cooling is set for equalization.

[0038] Unless otherwise specified, the test environment temperature is 20–30°C and the relative humidity is 30–60%; the raw materials are cleaned using the same cleaning process to obtain clean wheat; no chemical preservatives or chemical inducers are used throughout the process. Provided that the above parameter ranges and core temperature-time equivalence conditions are met, conventional substitutions of equipment structure, heating medium, conveying method, and online detection methods are considered equivalent.

[0039] In this invention, "wet basis moisture content" refers to the percentage of water content in a material relative to its total mass (water + dry matter).

[0040] Although this invention is illustrated and verified using the shelf life of bread, the technical principles and processing effects of the method are not limited to bread-specific wheat flour systems. Since the core of this invention lies in achieving a synergistic reduction of heat-resistant spores and total bacterial count at the grain level through a combined process of two-stage wet heat treatment—static activation—secondary heat sterilization—low-temperature drying, this method is also applicable to various baking-specific flours (including but not limited to toast flour, baguette flour, cake flour, biscuit flour, frozen dough flour, and general-purpose baking flour).

[0041] The processing parameters for different types of wheat (such as hard wheat, soft wheat, and mixed wheat) can be fine-tuned according to the flour characteristics of the target product to match its protein structure and water absorption properties. Experimental results of this invention show that this process can achieve a "double low" effect—total bacterial count below 500 CFU / g and heat-resistant spores below 50 CFU / g—in wheat with different protein levels and gluten strengths, while maintaining good flour properties. Therefore, this invention is applicable to the low-microbial processing and raw material control of a broad range of baking wheat flours.

[0042] Example 1 A method for processing low-bacterial, low-spore wheat flour includes the following steps: (1) Raw material pretreatment: 1000 kg of purchased wheat is selected and screened, destoned, magnetically separated, threshed and air-separated to remove impurities and obtain clean wheat.

[0043] (2) First wet heat treatment: The cleaned wheat is introduced into the wet heat mixing section, and clean steam and atomized sterile water are sprayed in simultaneously. Within 90 seconds, the wet basis moisture content of the grains is raised to 30.0%±0.5%, and the temperature is raised to 59℃. Then the material enters the saturated wet heat insulation channel and is kept at 60℃±1℃, relative humidity ≥95%, and bed thickness ≤120 mm for 5 minutes. The grain core temperature is kept consistent with the process temperature by turning the material.

[0044] (3) Cooling and standing: After the wheat was drained, it was air-cooled down to 25°C and then stood at room temperature for 30 minutes to allow the spores to be in a germination or sub-germination sensitive state.

[0045] (4) Second heat treatment: The wheat obtained in (3) is evenly spread in a mesh belt hot air tunnel with a thickness of 20 mm and treated at 85℃ for 10 minutes; the core temperature of the grains is monitored by multiple probes to ensure that the set sterilization conditions are met.

[0046] (5) Low-temperature drying and cooling: The heat-treated material is sent to the drying section, where hot air at 35℃ and wind speed of 1.0m / s is used, and the bed thickness is 40 mm. The material is dried until the wet basis moisture content of the grain is ≤12%. Then, it is allowed to stand for 15 minutes under normal temperature slow cooling conditions to balance the moisture and temperature and avoid condensation.

[0047] (6) Post-conditioning and moistening: After drying, add water to the material until the wet basis moisture content is 15.5%, and let it stand at room temperature for 4 hours to allow the moisture to be evenly distributed inside the grain.

[0048] (7) Grind and sieve the soaked wheat to obtain wheat flour.

[0049] Example 2 A method for processing low-bacterial, low-spore wheat flour includes the following steps: (1) Raw material pretreatment: 1000 kg of purchased wheat is selected and screened, destoned, magnetically separated, threshed and air-separated to remove impurities and obtain clean wheat.

[0050] (2) First wet heat treatment: The cleaned wheat is introduced into the wet heat mixing section, and clean steam and atomized sterile water are sprayed in simultaneously to raise the moisture content of the grains to 25%±0.5% and the temperature to 70℃ within 90 seconds. The material then enters the saturated wet heat insulation channel and is kept at 70℃±1℃, relative humidity ≥95%, and bed thickness ≤120 mm for 10 minutes, and the core temperature of the grains is kept consistent with the process temperature by turning the material.

[0051] (3) Cooling and standing: The treated wheat was cooled to 25°C by air and then stood at room temperature for 60 minutes to allow the spores to be in a germination or sub-germination sensitive state.

[0052] (4) Second heat treatment: The wheat obtained in (3) is evenly spread in a mesh belt hot air tunnel with a thickness of 30 mm and treated at 75℃ for 15 minutes; the core temperature of the grains is monitored by multiple probes to ensure that the set sterilization conditions are met.

[0053] (5) Low-temperature drying and cooling: The heat-treated material is sent to the drying section, where hot air at 35℃ and wind speed of 1.0m / s is used, and the bed thickness is 40 mm. The material is dried until the wet basis moisture content of the grain is ≤14%. Then, it is allowed to stand for 15 minutes under normal temperature slow cooling conditions to balance the moisture and temperature and avoid condensation.

[0054] (6) Post-conditioning and moistening: After drying, add water to the material until the wet basis moisture content is 15.5%, and let it stand at room temperature for 6 hours to allow the moisture to be evenly distributed inside the grain.

[0055] (7) Grind and sieve the soaked wheat to obtain wheat flour.

[0056] Example 3 A method for processing low-bacterial, low-spore wheat flour includes the following steps: (1) Raw material pretreatment: 1000 kg of purchased wheat is selected and screened, destoned, magnetically separated, threshed and air-separated to remove impurities and obtain clean wheat.

[0057] (2) First wet heat treatment: The cleaned wheat is introduced into the wet heat mixing section, and clean steam and atomized sterile water are sprayed in simultaneously to raise the moisture content of the grains to 27%±0.5% and the temperature to 70℃ within 90 seconds. The material then enters the saturated wet heat insulation channel and is kept at 65℃±1℃, relative humidity ≥95%, and bed thickness ≤120 mm for 5 minutes, and the core temperature of the grains is kept consistent with the process temperature by turning the material.

[0058] (3) Cooling and standing: The treated wheat was cooled to 25°C by air and then stood at room temperature for 120 minutes to allow the spores to be in a germination or sub-germination sensitive state.

[0059] (4) Second heat treatment: The wheat obtained in (3) is evenly spread in a mesh belt hot air tunnel with a thickness of 30 mm and treated at 90℃ for 10 minutes; the core temperature of the grains is monitored by multiple probes to ensure that the set sterilization conditions are met.

[0060] (5) Low-temperature drying and cooling: The heat-treated material is sent to the drying section, where hot air at 35℃ and wind speed of 1.0m / s is used, and the bed thickness is 40 mm. The material is dried until the wet basis moisture content of the grain is ≤14%. Then, it is allowed to stand for 15 minutes under normal temperature slow cooling conditions to balance the moisture and temperature and avoid condensation.

[0061] (6) Post-conditioning and moistening: After drying, the material is sprayed with water to a wet basis moisture content of 15.5%, and left to stand at room temperature for 8 hours to allow the moisture to be evenly distributed inside the grain.

[0062] (7) Grind and sieve the soaked wheat to obtain wheat flour.

[0063] Example 4 Referring to Example 1, the only difference is that the heat treatment parameters in step (4) are 85°C for 15 minutes.

[0064] Example 5 Referring to Example 1, the only difference is that in step 4, the heat treatment parameters are 95°C for 15 minutes.

[0065] Example 6 Referring to Example 1, the only difference is that in step 4, the heat treatment parameters are 75°C for 10 minutes.

[0066] Comparative Example 1 Compared to Example 1, steps (2)-(3) are omitted, and heat treatment is performed directly: (1) Raw material pretreatment: 1000 kg of purchased wheat is selected and screened, destoned, magnetically separated, threshed and air-separated to remove impurities and obtain clean wheat.

[0067] (2) Heat treatment: The cleaned wheat is evenly spread in the mesh belt hot air tunnel with a thickness of 20 mm and treated at 85℃ for 10 minutes; the core temperature of the grain is monitored by multiple probes to ensure that the set sterilization conditions are met.

[0068] (3) Low-temperature drying and cooling: The heat-treated material is sent to the drying section, where hot air at 35℃ and wind speed of 1.0m / s is used, and the bed thickness is 40 mm. The material is dried until the wet basis moisture content of the grain is ≤12%. Then, it is allowed to stand for 15 minutes under normal temperature slow cooling conditions to balance the moisture and temperature and avoid condensation.

[0069] (4) Post-conditioning and moistening: After drying, add water to the material until the wet basis moisture content is 15.5%, and let it stand at room temperature for 4 hours to allow the moisture to be evenly distributed inside the grain.

[0070] (5) Grind and sieve the soaked wheat to obtain wheat flour.

[0071] Comparative Example 2 Compared to Example 1, steps (3)-(4) are omitted, and only wet heat treatment is performed: (1) Raw material pretreatment: 1000 kg of purchased wheat is selected and screened, destoned, magnetically separated, threshed and air-separated to remove impurities and obtain clean wheat.

[0072] (2) Moist heat treatment: The cleaned wheat is introduced into the moist heat mixing section, and clean steam and atomized sterile water are sprayed in simultaneously. Within 90 seconds, the moisture content of the grains on a wet basis is raised to 30.0%±0.5%, and the temperature is raised to 59℃. The material then enters the saturated moist heat insulation channel and is kept at a constant temperature for 5 minutes under the conditions of 60℃±1℃, relative humidity ≥95%, and bed thickness ≤120 mm. The grain core temperature is kept consistent with the process temperature by turning the material.

[0073] (3) Low temperature drying and cooling: The material after wet heat treatment is sent to the drying section, using 35℃ hot air, wind speed of 1.0m / s, and bed thickness of 40 mm, to dry until the wet basis moisture content of the grains is ≤12%; then it is left to stand for 15 minutes under normal temperature slow cooling conditions to balance the moisture and temperature and avoid condensation.

[0074] (4) Post-conditioning and moistening: After drying, add water to the material until the wet basis moisture content is 15.5%, and let it stand at room temperature for 4 hours to allow the moisture to be evenly distributed inside the grain.

[0075] (5) Grind and sieve the soaked wheat to obtain wheat flour.

[0076] Comparative Example 3 (1) Raw material pretreatment: 1000 kg of purchased wheat is selected and screened, destoned, magnetically separated, threshed and air-separated to remove impurities and obtain clean wheat.

[0077] (2) First wet heat treatment: The cleaned wheat is introduced into the wet heat mixing section, and clean steam and atomized sterile water are sprayed in simultaneously to raise the moisture content of the grains to 23%±0.5% and the temperature to 59℃ within 90 seconds. The material then enters the saturated wet heat insulation channel and is kept at 60℃±1℃, relative humidity ≥95%, and bed thickness ≤120 mm for 5 minutes, and the core temperature of the grains is kept consistent with the process temperature by turning the material.

[0078] (3) Cooling and standing: After the wheat was drained, it was air-cooled down to 25°C and then stood at room temperature for 30 minutes to allow the spores to be in a germination or sub-germination sensitive state.

[0079] (4) Second heat treatment: The wheat obtained in (3) is evenly spread in a mesh belt hot air tunnel with a thickness of 50 mm and treated at 65°C for 10 minutes; the core temperature of the grains is monitored by multiple probes to ensure that the set sterilization conditions are met.

[0080] (5) Low-temperature drying and cooling: The heat-treated material is sent to the drying section, where hot air at 35℃ and wind speed of 1.0m / s is used, and the bed thickness is 40 mm. The material is dried until the wet basis moisture content of the grain is ≤12%. Then, it is allowed to stand for 15 minutes under normal temperature slow cooling conditions to balance the moisture and temperature and avoid condensation.

[0081] (6) Post-conditioning and moistening: After drying, the material is sprayed with water to a wet basis moisture content of 15.5%, and left to stand at room temperature for 6 hours to allow the moisture to be evenly distributed inside the grain.

[0082] (7) Grind and sieve the soaked wheat to obtain wheat flour.

[0083] Comparative Example 4 Referring to Example 1, the only difference is that the heat treatment conditions in step (4) are set to 80°C and 20 minutes, while the other steps and conditions are the same.

[0084] Comparative Example 5 Referring to Example 1, the only difference is that the heat treatment conditions in step (4) are set to 65°C and 15 min, while the other steps and conditions are the same.

[0085] Comparative Example 6 Referring to Example 1, the only difference is that the heat treatment conditions in step (4) are set to 95°C and 20 min, while the other steps and conditions are the same.

[0086] The total bacterial count in wheat flour was determined according to the national standard GB4789.2-2016, "National Food Safety Standard - Microbiological Examination of Food: Determination of Total Bacterial Count". The total number of thermoresistant Bacillus was determined according to the method of Berghofer et al. (Berghofer LK, Hocking AD, Miskelly D, et al. Microbiology of wheat and flour milling in Australia[J]. International Journal of Food Microbiology, 2003, 85(1):137-149.). The test results are shown in Tables 1 and 2.

[0087] Table 1: Total bacterial count in flour, bran, and grains (unit: CFU / g)

[0088] Blank refers to wheat flour made from untreated wheat grains. Table 2: Heat-resistant spore count of flour, bran, and grains (unit: CFU / g)

[0089] Blank refers to wheat flour made from untreated wheat grains.

[0090] For powder physicochemical and powder quality / stretch testing, refer to the corresponding methods of GB / T and AACC (such as farinograph, stretching tester, protein, ash, whiteness, damaged starch, etc.); each result should be obtained by taking the mean of no less than three parallel determinations, and the standard deviation or method detection limit should be given if necessary.

[0091] The wheat flour quality of each embodiment and some comparative examples was tested, and the results are shown in Table 3.

[0092] Table 3

[0093] Note: "-" indicates that gluten could not be extracted. Blank refers to wheat flour made from untreated wheat grains.

[0094] To make bread, follow the method in GB / T 14611-2008: Mix 600g wheat flour, 270ml water, 60g egg liquid, 120g sugar, 6g salt, 60g butter, and 6g yeast in a dough mixer until smooth. Shape the mixture into a ball, place it on a tray, and proof in a proofing box at 35℃ and 85% humidity for 55 minutes. Deflate the dough, proof for another 25 minutes, deflate again, shape into a ball, place in a bread mold, and continue proofing for 50 minutes. Once proofed, bake in an oven at 190℃ (top heat) and 200℃ (bottom heat) for 20 minutes. After baking, cool and store in a resealable bag until ready for testing.

[0095] Dough water absorption (%), formation time (min), stability time (min), weakening degree (FU), stretching area (cm²) 2 The test methods for tensile resistance / BU, maximum tensile resistance / BU, and elongation / mm are in accordance with GB / T 14614-2019 and GB / T 14615-2019.

[0096] The results are shown in Table 4.

[0097] Table 4

[0098] Blank refers to bread made from wheat flour prepared from untreated wheat grains.

[0099] Example 7 Referring to Example 1, another batch of wheat raw materials was selected for a single-factor control experiment.

[0100] Comparison 1: Adjust the wet basis moisture content of the grains in step (2) and control the standing time in step (3) to 60 min. Other process conditions are the same as in Example 1.

[0101] Comparison 2: Adjust the wet heat treatment temperature in step (2) and control the standing time in step (3) to 60 min. Other process conditions are the same as in Example 1.

[0102] Comparison 3: Adjust the wet heat treatment time in step (2) and control the settling time in step (3) to 60 min, and other process conditions are the same as in Example 1.

[0103] Comparison 4: Adjust the settling time in step (3), and keep other process conditions the same as in Example 1.

[0104] The total bacterial count and the number of heat-resistant spores in the seeds were tested, and the results are shown in Table 5.

[0105] Table 5

[0106] Blank refers to untreated wheat grains.

[0107] Choose from several types of bread flour available on the market: Bread flour 1: Total bacterial count (TPC) = 260 CFU / g, heat-resistant spore count (TSC) < 10 CFU / g; Bread flour 2: TPC=370 CFU / g, TSC<10 CFU / g; Bread flour 3: TPC=1550 CFU / g, TSC<25 CFU / g; Bread flour 4: TPC=2900 CFU / g, TSC<75 CFU / g; Bread flour 5: TPC=4350 CFU / g, TSC<50 CFU / g; Bread flour 6: TPC=5550 CFU / g, TSC<90 CFU / g.

[0108] Dinner rolls and toast were made using these bread flours, and the total bacterial count was tested every 24 hours. The test results are as follows: Figure 2 As shown, it was found that as the number of heat-resistant spores in flour increased from 10 CFU / g to 90 CFU / g, the shelf life of bread decreased from 8 days to 4 days, and the shelf life of bread was significantly negatively correlated with the number of heat-resistant spores and the total bacterial count in the raw flour. p<0.05). Therefore, for bread, the total bacterial count and the number of heat-resistant spores in the raw wheat flour have a significant impact on the shelf life of bread. Reducing the number of heat-resistant spores and the total bacterial count in the raw wheat flour is of great significance for extending the shelf life of bread.

[0109] Parallel testing of the examples and comparative examples shows that the sterilization method of the present invention—first wet heat isothermal sensitization, room temperature standing, second heat treatment, low temperature drying, and post-conditioning—can stably suppress the level of microorganisms at key sampling sites. Taking Example 1 as an example, the heat-resistant spores in most powder samples were at a low level of ≤10-20 CFU / g (e.g., 1B=10, 2B<10, 3B<10, 1M<10, 2M<10, 3M=20), and the levels of bran and grains also decreased significantly (branchinek approximately 950 CFU / g, grains approximately 65 CFU / g), forming a difference of one to two orders of magnitude compared to the bran / grain ratio of the blank sample (approximately 27500 / 8900 CFU / g). The total bacterial count also decreased simultaneously, with the grains in Example 1 reaching approximately 760 CFU / g. This indicates that first drawing the spores into a germination or sub-germination state, and then using a short-term, medium-temperature treatment to achieve targeted killing, is more effective than applying weak or strong heat separately. When the secondary heat treatment is weaker (e.g., 65 ℃ × 10-15 min), the total bacterial count and spore count in both powder and grain samples often rebounded to 10. 3 ~10 4 The scale is insufficient to meet the dual requirements of low bacterial count and low concentration. When using excessively high-intensity single heat treatment (corrected to Comparative Example 3), although the bacterial count can be further reduced, the resulting quality cost is significant, as seen in Comparative Examples 4 and 6. Based on the results of multiple batches, a secondary heat treatment at 85±5 ℃ for 10–15 min, with a substrate thickness controlled at 20–80 mm, is more conducive to achieving steady-state output in the sensitization-re-sterilization tandem process.

[0110] The powder quality followed the same pattern as described above. At the physicochemical level, the ash content of Examples 1 and 6 was 0.47 and 0.46 respectively (0.53 for the blank), and the whiteness was 79.6 and 79.4 (78.8 for the blank), with no side effects such as ash rising or darkening of color observed. The protein and wet gluten content remained within the target range, at 13.23% / 33.7% for Example 1 and 13.15% / 34.9% for Example 6, which were at the same level as or slightly improved from the blank's 12.94% / 34.9%. The powder quality and stretchability indicators are more intuitive: with the blank stabilization time of 14.2 min as the baseline, Examples 1 and 6 reached 21.7 / 21.9 min respectively, and the weakening degree decreased to 25 / 19 FU; the maximum stretching resistance and stretching area of ​​Example 1 increased to 680 and 176 (blank 539 and 142), and the elongation was basically the same (205 vs 207), showing a bread-friendly structure with improved strength, enhanced stability, and no damage to stretchability. In contrast, Comparative Example 6 showed typical heat damage signals after high-intensity heat treatment: stabilization time of about 3.2 min, weakening degree of about 85 FU, and simultaneous collapse of the stretching curve; while the lower treatment temperatures and times (65 ℃ × 10~15 min) in Comparative Examples 3 and 5 were not able to achieve the double lows, nor did they show any substantial improvement in powder stability.

[0111] Based on the mechanism, the single-factor experimental results in Example 7 clearly show the central region: the first wet-heat stage increases the wet basis moisture content of the grains to 30%, and the temperature is maintained at 60-80 °C; then, after standing for about 60 min, the heat-resistant spores can be compressed to <10-15 CFU / g; insufficient standing (30 min) or excessive standing (120 min) is not ideal, and the latter may also result in rebound. Under this premise, a medium-temperature short-time secondary heat treatment is implemented, and drying at below 40 °C and 15.5% post-conditioning are used as the finishing touches. Stable results of total bacteria ≤500 CFU / g and heat-resistant spores ≤50 CFU / g can be repeatedly obtained at multiple flour paths and grain / bran sites, while maintaining key quality indicators such as ash content, whiteness, protein, wet gluten, stability time, degree of weakening, and tensile strength / area within the working range required for bread flour. It can be considered that the parameter limitation of the present invention is not simply about high temperature and time, but about achieving a balance around the two red lines of sufficient sensitization and controllable thermal damage: insufficient strength will result in the failure of the two low-temperature and low-temperature closure; excessive strength will result in quality loss; only within the medium temperature and short time window can the two indicators be stabilized at the same time.

[0112] The core of this invention lies in first "sensitizing" and then "targeted killing." During the initial humid-heat stage, heat-resistant spores enriched on the surface and in the grooves of the grain undergo a transformation from dormancy to germination / sub-germination under high-humidity isothermal conditions: the water content of the spore core increases, Ca-DPA (calcium dipyridine carboxylic acid) efflux and SpoVA channel opening occur simultaneously, cortical peptidoglycan begins to loosen, and the SASP small acidic protein bound to DNA is gradually cleaved by endogenous enzymes, resulting in a series of signs of decreased thermal stability. This process substantially reduces the D-value and equivalent z-value of the spores, lowering their upper limit of tolerance to subsequent heat loads; while the high-humidity environment inhibits surface evaporative cooling and "shell formation," avoiding the formation of a temperature / moisture gradient that is dry on the outside and moist on the inside, thereby reducing the cold spot.

[0113] The room temperature resting (step (3)) is not simply waiting, but rather allowing the heat-activated spores to complete the "commitment" stage: membrane structure rearrangement, proton dynamics recovery, and initial metabolic initiation, so that the population tends to be synchronized in time and enters the window most susceptible to heat-induced killing. At this time, the second heat treatment is carried out, and the heat mainly acts on the target population that has germinated or is sub-germinating. The required process temperature and time can be significantly lower than the intensity of directly heating dormant spores, which is more economical and gentler from the perspective of thermodynamics and heat transfer. By constraining the bed thickness (20-80 mm) and using saturated or near-saturated media, the convection / condensation heat transfer coefficient can be improved, ensuring that the core temperature curve reaches and maintains the set threshold within the specified residence time, and avoiding "missed killing" caused by excessively thick bed or evaporative cooling.

[0114] The subsequent low-temperature drying and slow cooling (step (4)) serves to quickly bring the moisture and water activity back to a safe range, cut off the continued growth of the germinated cells, and avoid the secondary thermal damage and color deterioration of the gluten protein and starch structure caused by high-temperature drying. Then, the 15.5% post-conditioning restores the plasticity and brittleness balance required for milling, which is conducive to the clean separation of bran and endosperm. Common manifestations include a decrease in ash content and a stable or slightly increased whiteness.

[0115] In summary, this mechanism takes into account both microbiology and flour functional science: by reducing the heat intensity requirement through "sensitization → sterilization" and by preserving gluten strength and structure through "low-temperature drying → post-conditioning", it achieves both low heat content and bread-friendly flour texture.

[0116] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A process for the production of a low bacteria, low heat resistant spore, bakery specialty wheat flour, characterized in that, It comprises the following steps: (1) raw grain cleaning and pretreatment: the raw material wheat is sequentially screened, stoned, magnetically selected, threshed and air selected to remove sand, metal and light impurities to obtain clean wheat; (2) first wet heat treatment: the clean wheat in step (1) is subjected to wet heat induction treatment; (3) cooling and room temperature standing: the material after wet heat induction treatment in step (2) is cooled to room temperature and stands at room temperature; (4) second heat treatment: the material after standing in step (3) is subjected to heat treatment; (5) low-temperature drying and cooling: the material after heat treatment in step (4) is dried to a safe moisture content under low-temperature conditions and is fully cooled to prevent moisture return and condensation; (6) post-conditioning and wheat moistening: the material after cooling in step (5) is moistened again to make the grain reach the target moisture content required for flour milling, and stands for equalization; (7) the wheat after moistening in step (6) is ground and screened to obtain wheat flour.

2. The method of claim 1 wherein, In step (2), the process of wet heat treatment comprises: First, control the wet basis moisture content of wheat grains to reach 16% to 32%, and then place it in a temperature of 60℃ to 80℃ and a relative humidity of ≥95% for 5 to 15 minutes of holding time.

3. The method of claim 2, wherein, In step (2), the wet basis moisture content of the wheat grains reaches 30.0% ± 0.5%; and it is held at an isothermal temperature of 60℃ ± 1℃ for 10 ± 1 minutes.

4. The method of claim 1 wherein, In step (3), the material is cooled to 20 to 30℃ and stands for 30 to 120 minutes.

5. The method of claim 1 wherein, The second heat treatment in step (4) has a treatment temperature of 65℃ to 95℃ and a treatment time of 10 to 20 minutes.

6. The method of processing according to claim 5, wherein, In step (4), the second heat treatment conditions are: 85 ± 5℃ for 10 to 15 minutes.

7. The method of claim 1 wherein, In step (5), the drying is performed until the wet basis moisture content of the grains is ≤14%.

8. The method of claim 1 wherein, In step (5), after drying, the material is cooled to room temperature ± 5℃, and stands for 10 to 30 minutes under normal temperature slow cooling conditions to equalize the moisture and temperature and prevent condensation and moisture return.

9. The process according to any one of claims 1 to 8, characterized in that, In step (6), after moistening, the wet basis moisture content of the grains reaches 15.5% and stands at room temperature for 4 to 8 hours to achieve uniform distribution of internal moisture.

10. Use of the processing method of a low-bacteria and low-heat-resistant spore baking special-purpose wheat flour according to any one of claims 1 to 9 to extend the shelf life of baked products.

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