A drying process for preserving the pungent compounds of zanthoxylum

Abstract

This invention discloses a drying process for preserving the numbing flavor of Sichuan peppercorns. First, freshly harvested Sichuan peppercorns undergo a pre-treatment process to remove impurities, leaves, stems, moldy fruit, and immature fruit. The pre-treated peppercorns are then evenly spread on a drying tray, with a thickness of 2 to 5 cm. The tray is then placed into a microwave vacuum drying apparatus. In the first stage, the microwave power density is set to 2 to 4 W per gram, and the vacuum level inside the chamber is -0.09 to -0.095 MPa. The core temperature of the peppercorn material is controlled to not exceed 48°C, and drying takes 25 to 40 minutes to remove free water from the peppercorns. After the first stage, the second stage begins, with the microwave power density adjusted to 0.7 to 1.5 W per gram and the vacuum level inside the chamber set to -0.08 to -0.085 MPa. This invention employs a low-temperature vacuum-coupled microwave heating mode, avoiding degradation of the numbing flavor caused by high temperatures. Gradual pressure increase prevents the oil bladders from rupturing due to sudden pressure changes. The oil bladder integrity rate, numbing flavor retention, and appearance of the dried peppercorns are significantly superior to those of traditional processes.

Description

Technical Field

[0001] This invention belongs to the field of agricultural and sideline product processing technology, specifically relating to a drying process that preserves the numbing flavor of Sichuan pepper. Background Technology

[0002] Sichuan pepper is a distinctive and advantageous spice crop in my country, widely used in catering, compound seasoning processing, and snack food production. Domestic annual processing demand remains stable at over 3 million tons. Fresh Sichuan pepper has a moisture content of 70% to 80%, and after harvesting, it is highly susceptible to browning and mold growth when left at room temperature, making it unsuitable for storage and transportation. Therefore, drying is an essential core step in the Sichuan pepper processing. The industry's core requirement is to maximize the preservation of the unique numbing substances, natural color, and oil sac integrity of Sichuan pepper, while ensuring drying efficiency and adapting to large-scale production, thus avoiding loss of flavor and quality.

[0003] Currently, the mainstream drying processes for Sichuan peppercorns fall into two categories. The first is natural sun-drying, a method commonly used by small-scale farmers. Its working principle involves heating through solar radiation and natural ventilation to remove moisture, achieving dehydration. The advantages of this process are no equipment investment costs, extremely low operational barriers, and suitability for small-batch, scattered processing. However, this process has significant limitations: the drying cycle is as long as 3 to 5 days, completely dependent on weather conditions; continuous rainy weather easily leads to mold and spoilage of the peppercorns; the open-air drying process is prone to dust and insect infestation, and turning the peppercorns can easily cause mechanical damage to the oil sacs, resulting in significant loss of numbing flavor substances, uneven color in the finished product, and extremely poor quality stability, making it completely unsuitable for large-scale industrial production.

[0004] The second type is hot air drying, which is currently the mainstream choice for large-scale Sichuan pepper processing enterprises. Its working principle involves generating high-temperature hot air (above 70°C) through a heating device, which circulates and convects within the drying chamber to heat the Sichuan pepper, gradually evaporating the internal moisture. The advantages of this process are that it is not constrained by weather conditions, production capacity is adjustable, and the production process is highly controllable. However, this process has significant drawbacks: the high-temperature drying environment exceeds the thermal stability threshold of the numbing amide substances in Sichuan pepper, leading to a large amount of thermal degradation of these substances. Furthermore, the hot air is a surface heating mode, easily causing the surface of the Sichuan pepper to dry and form a crust, hindering the removal of internal moisture and requiring extended drying time, further exacerbating the loss of numbing substances. The high-temperature environment can also cause excessive pressure difference between the inside and outside of the oil sac, leading to rupture and a large amount of numbing substances volatilizing. Simultaneously, it triggers enzymatic and non-enzymatic browning, resulting in a darker color, weaker numbing flavor, and a numbing substance retention rate generally less than 55%, resulting in severe quality loss.

[0005] Currently, some companies in the industry are exploring simplified vacuum microwave drying technology, but these attempts directly copy the drying parameters used for other fruits and vegetables. They haven't designed suitable processes specifically for the unique oil sac structure and thermal stability characteristics of the numbing substances in Sichuan peppercorns. These methods generally suffer from poor drying uniformity, easily damaged oil sacs, and limited improvement in numbing flavor retention. Consequently, they haven't been able to form a standardized and replicable industrial production system, and have failed to achieve widespread application. Existing processes cannot simultaneously address drying efficiency, product quality, and the demands of large-scale production, becoming a core bottleneck restricting the quality upgrade of the Sichuan peppercorn processing industry. Summary of the Invention

[0006] (a) Technical problems to be solved The purpose of this invention is to overcome the shortcomings of existing technologies and provide a drying process that preserves the numbing and spicy flavor of Sichuan peppercorns. This process utilizes the synergistic effect of low-temperature, vacuum, and microwave drying. The low-temperature, high-vacuum environment reduces the oxidation rate and boiling point of the numbing and spicy flavor substances, while the volumetric heating effect of microwaves achieves rapid dehydration. This significantly improves the retention rate of the numbing and spicy flavor substances while ensuring drying efficiency.

[0007] (II) Technical Solution A drying process for preserving the numbing flavor of Sichuan peppercorns uses fresh Sichuan peppercorns harvested within 24 hours, without any pre-drying or frozen storage treatment, and with an initial numbing flavor amide compound content of not less than 18 mg / g as raw material. The entire process is carried out in a food-grade clean production environment with a cleanliness level of not less than 100,000 and free of volatile irritating gas residues. The specific steps include: S1. Pretreatment: Fresh Sichuan peppercorns are sprayed and rinsed with room temperature water at a pressure of 0.1MPa-0.2MPa for 30s-60s to avoid damage to the oil sacs of the peppercorns due to excessive rinsing pressure or time. Then, a color sorter is used in combination with manual sorting to remove non-target impurities such as branches, leaves, stones, diseased fruit, wilted fruit, etc., to obtain clean fresh Sichuan peppercorns with an impurity ratio of no more than 0.1%. S2. First Stage Constant-Rate Dehydration: Cleaned fresh Sichuan peppercorns are evenly spread on the perforated material tray of the microwave vacuum drying equipment. During the spreading process, avoid stacking and squeezing the peppercorns. Control the material layer thickness to 2cm-5cm, with a thickness deviation of no more than ±0.5cm at any point. After sealing the drying chamber, start the vacuum pump to create a vacuum. Once the vacuum level in the chamber drops to the range of 0.06MPa-0.09MPa, maintain the vacuum level fluctuation within ±0.002MPa using PID control mode. Control the microwave power density to 1.5W / g-2.5W / g. Use a fiber optic temperature sensor positioned close to the material layer to collect the peppercorn temperature data in real time. Stabilize the material temperature to 45℃-55℃ with a temperature fluctuation range of no more than ±2℃ by adjusting the microwave start / stop duty cycle. Continue dehydration until the overall moisture content of the peppercorns drops to 30%-40%. The moisture content is measured in real time using an online near-infrared moisture analyzer with a detection accuracy of ±0.5%. S3. Second stage of dehydration at reduced speed: Maintain a constant vacuum of 0.06MPa-0.09MPa in the chamber with fluctuations controlled within ±0.002MPa. Adjust the output power of the microwave generator to reduce the microwave power density to 0.8W / g-1.5W / g. Continue to adjust the microwave output power in real time through the temperature sensor to stabilize the material temperature at 60℃-65℃ with temperature fluctuations not exceeding ±2℃. Continue dehydration until the overall moisture content of the peppercorns drops to 10%-15%. Use an online near-infrared moisture analyzer to verify the moisture content compliance in real time. S4. Slow Cooling: Turn off the microwave generator to stop heating. Control the opening of the exhaust valve through the controller to slowly release the vacuum in the cavity to normal pressure at a constant rate of 0.01MPa / min-0.03MPa / min. During the vacuuming process, avoid sudden changes in vacuum that could cause excessive pressure difference between the inside and outside of the pepper oil sac and cause it to rupture. Then, transfer the dried peppers to a well-ventilated, cool, and clean environment with a temperature of 20℃-30℃ and a relative humidity of no more than 40% and lay them flat for slow cooling for 30min-60min. During the slow cooling process, avoid direct sunlight and dust contamination to ensure that the moisture and temperature gradients inside the peppers are fully and evenly diffused, resulting in dried peppers.

[0008] Preferably, the duration of the first stage dehydration treatment in S2 is adjusted according to the initial moisture content of the peppercorns, specifically 20-40 minutes. When the initial moisture content of the peppercorns is higher than 75%, a drying time of 30-40 minutes is used, and when the initial moisture content of the peppercorns is lower than 75%, a drying time of 20-30 minutes is used. After drying, the moisture content of the peppercorns is checked by an offline drying method to ensure that the moisture content is stably within the range of 30%-40%.

[0009] Preferably, the duration of the second stage dehydration treatment in S3 is adjusted according to the actual moisture content of the peppercorns after the first stage, specifically 15-25 minutes. When the moisture content of the peppercorns is higher than 35% after the first stage, a drying time of 20-25 minutes is used; when the moisture content of the peppercorns is lower than 35% after the first stage, a drying time of 15-20 minutes is used. After drying, the moisture content of the peppercorns is checked using an offline drying method to ensure that the moisture content is stably within the range of 10%-15%.

[0010] Preferably, intermittent microwave radiation is used in both S2 and S3 dehydration processes. In the first stage of S2, the microwave is turned on for 3-5 minutes and turned off for 1 minute at a time, with a microwave on-time to off-time ratio of (3-5):1. In the second stage of S3, the microwave is turned on for 2-3 minutes and turned off for 1 minute at a time, with a microwave on-time to off-time ratio of (2-3):1. During the microwave off-time stage, the residual heat of the material is used to continue evaporating moisture, avoiding excessive local temperature damage to the numbing flavor substances and oil sac structure caused by continuous heating.

[0011] Preferably, the pretreatment of S1 further includes a color-protecting step, specifically: completely immersing the cleaned fresh peppercorns in a food-grade citric acid solution with a mass concentration of 0.5%-1.5% or a food-grade vitamin C solution with a mass concentration of 0.5%-1.5% for 1-3 minutes at room temperature and pressure. During the soaking process, the peppercorns are slowly turned over using a stirring device with a rotation speed of 10-20 r / min to ensure that all peppercorn surfaces are fully in contact with the color-protecting solution. After soaking, the peppercorns are immediately removed and placed on a perforated drain rack to drain naturally for 5-10 minutes until no free liquid drips from the surface of the peppercorns.

[0012] Preferably, the tempering process in S4 is carried out in a sealed tempering chamber. Nitrogen gas with a purity of not less than 99.9% or argon or helium gas with a purity of not less than 99.9% is introduced into the tempering chamber beforehand to replace the air in the chamber and maintain the oxygen content of the gas in the tempering chamber at no more than 0.5%. During the tempering process, a low flow rate of the corresponding protective gas is continuously introduced to prevent the peppercorns from undergoing oxidative browning and oxidative degradation of the numbing substances during the tempering and cooling process.

[0013] Preferably, the moisture content of the final dried Sichuan pepper is less than 12% as determined by offline drying method. The total content of Sichuan pepper numbing amide compounds, with α-sanshotoin, hydroxy-α-sanshotoin, and hydroxy-β-sanshotoin as the core, is determined by high performance liquid chromatography. Compared with the initial total content of numbing amide compounds in fresh Sichuan pepper, the retention rate is not less than 85%. The proportion of intact oil sacs in the dried Sichuan pepper is not less than 95% as observed by stereomicroscopy, and there is no obvious browning or charring phenomenon.

[0014] Preferably, in S2 and S3, the vacuum degree and the material temperature are matched and controlled. When the material temperature is at the upper limit of the range, the corresponding vacuum degree is at the upper limit of the range, and when the material temperature is at the lower limit of the range, the corresponding vacuum degree is at the lower limit of the range. By matching and adjusting the vacuum degree and temperature, the evaporation temperature of the surface moisture of the peppercorns is further reduced, and the probability of thermal degradation of the numbing substances is reduced.

[0015] Preferably, a pepper drying apparatus for performing the drying process of preserving the numbing flavor of peppercorns includes: The microwave vacuum drying chamber has a sealed microwave-resistant structure with an inner wall made of 304 stainless steel. The side walls of the chamber are connected to a precision exhaust valve with adjustable opening, a vacuum pump with adjustable pumping speed, and a microwave generator with continuously adjustable output power. The frequency of the microwave generator is 2450MHz and the power adjustment range is 0.5kW-5kW. The material tray is detachable and installed inside the microwave vacuum drying chamber. It is made of food-grade 304 stainless steel or polytetrafluoroethylene with a hollow mesh structure and a mesh aperture of 2mm-3mm. It is used to evenly hold the pepper materials and prevent the peppers from leaking out. The temperature sensor is a high-precision fiber optic temperature sensor, positioned 1-2 cm close to the material layer on the material tray. It has a detection accuracy of ±1℃ and a sampling frequency of at least 1 time / s, used to collect the actual temperature of the peppercorn material in real time. The pressure sensor is a high-precision capacitive pressure sensor, located on the upper side wall of the microwave vacuum drying chamber to avoid moisture condensation affecting detection accuracy. It has a detection accuracy of ±0.001 MPa and a sampling frequency of at least 1 time / s, used to collect the vacuum level within the chamber in real time. An online near-infrared moisture analyzer is installed at the top of the microwave vacuum drying chamber, with the detection probe facing the material tray, for real-time measurement of the moisture content of Sichuan peppercorns. A PLC controller is electrically connected to a temperature sensor, a pressure sensor, the online near-infrared moisture analyzer, a vacuum pump, a microwave generator, and a precision exhaust valve. The PLC controller is preset with the full-process parameters described in claim 1, and can automatically adjust the microwave output power, vacuum pump pumping rate, and precision exhaust valve opening based on real-time collected temperature, pressure, and moisture content data to achieve constant air-breaking rate control of 0.01MPa / min-0.03MPa / min, as well as automatic switching of parameters between the two stages of drying.

[0016] Preferably, the microwave vacuum drying chamber is also equipped with a uniform airflow device, which circulates the gas in the chamber at a wind speed of 1m / s-2m / s during the microwave off phase, so that the temperature and vacuum uniformity deviation in various parts of the chamber does not exceed ±2%, avoiding uneven heating of local materials or excessive differences in dehydration rate.

[0017] (iii) Beneficial technical effects Compared with existing technologies, the beneficial effects of this invention are: This invention employs a two-stage gradient-controlled microwave vacuum drying process, matching the different evaporation characteristics of free and bound water in Sichuan peppercorns to set corresponding temperature, power, and vacuum parameters. Simultaneously, it adopts a slow-breaking cooling mode to avoid damage caused by sudden changes in pressure difference between the inside and outside of the oil bladder. The entire process strictly controls the temperature fluctuation range of the material, reducing the thermal degradation and oxidation loss of numbing substances. This effectively solves the defects of existing technologies, such as severe loss of numbing substances, high oil bladder breakage rate, and severe browning of products caused by high-temperature heating and sudden pressure difference. The numbing flavor retention, oil bladder integrity, and appearance color of dried Sichuan peppercorns are all significantly improved.

[0018] This invention employs a microwave-vacuum coupling heating mode, where microwaves directly act on water molecules inside the material to achieve rapid heating without the need for heat conduction. Combined with precisely matched process parameters, the dehydration cycle is significantly shortened. The entire drying process is completed within a sealed device, unaffected by external weather conditions. Energy consumption is significantly reduced compared to traditional hot air drying, effectively solving the shortcomings of existing technologies such as long drying cycles, high energy consumption, and strong susceptibility to environmental factors, thus greatly improving production efficiency.

[0019] All process parameters in this invention are set with flexible adjustable ranges. The matching dedicated drying device can automatically complete the parameter control of the entire process through the control system without manual intervention. The corresponding parameters can be flexibly adjusted according to different varieties and different initial moisture contents of peppercorns. It has a high degree of standardization and is suitable for industrial processing scenarios of different scales. It effectively solves the defects of existing exploratory drying processes that lack a standardized system and have poor industrial adaptability.

[0020] This invention is not only suitable for drying and processing fresh Sichuan peppercorns of all mainstream cultivated varieties, but also for the remedial drying of fresh Sichuan peppercorns after storage and quick-frozen Sichuan peppercorns after thawing. It can also be extended to the drying and processing of other spice crops containing volatile essential oils, and has high promotion and application value in the field of specialty agricultural product processing. Attached Figure Description

[0021] Figure 1 This is a flowchart of the drying process for preserving the numbing flavor of Sichuan peppercorns proposed in this invention. Figure 2 This is a flowchart of the S1 pretreatment and color protection process proposed in this invention. Detailed Implementation

[0022] according to Figures 1 to 2 The specific embodiments of the present invention are as follows: All embodiments in this section employ the two-stage gradient microwave vacuum drying process protected by the claims of this invention, addressing three core deficiencies of existing technologies: first, resolving the issues of degradation of numbing substances, oil sac rupture, and product browning caused by high-temperature heating and sudden pressure changes; second, resolving the problems of long drying cycles, high energy consumption, and susceptibility to environmental factors; and third, resolving the issues of lack of standardized processes and poor industrial adaptability. All embodiments cover different pepper varieties, different spreading thicknesses, and different process parameter ranges, ensuring complete reproducibility. Comparative examples utilize existing mainstream hot air drying processes described in the background section, providing a precise comparison with the embodiments.

[0023] Example 1

[0024] The raw material used in this embodiment is freshly harvested Sichuan Hanyuan Dahongpao fresh peppercorns with an initial moisture content of 76%. In the pretreatment stage, a wind-powered separator is used to remove light impurities such as branches, leaves, and dust from the peppercorns. Then, manual sorting removes fruit stems, moldy fruit, and immature fruit to obtain pure fresh peppercorns. A food-grade stainless steel scraper is used to evenly spread the peppercorns on a PTFE material tray, with a spreading thickness controlled at 2cm. During spreading, care is taken to avoid squeezing the peppercorns and causing pre-rupture of the oil sacs. The microwave vacuum drying equipment is then started, entering the first stage of drying. The microwave power density is set to 4W / g, and the vacuum degree of the drying chamber is -0.095MPa. During the drying process, a fiber optic thermometer is used to monitor the core temperature of the peppercorn material in real time, controlling the material temperature to not exceed 48℃. The drying time is 25 minutes. This stage mainly removes free water from the inside of the peppercorns. The low-temperature vacuum environment completely avoids the thermal degradation threshold of numbing amide, and the internal microwave heating mode prevents surface crusting that hinders moisture removal. After the first stage, the second stage of drying begins. The microwave power density is adjusted to 1.5 W / g, the vacuum degree of the drying chamber is -0.085 MPa, the material temperature is controlled to not exceed 42℃, and the drying time is 15 minutes. This stage mainly removes the bound water inside the peppercorns. The power is reduced to avoid local overheating, and the vacuum threshold for bound water evaporation is matched. After the second stage, a slow tempering and void-breaking process begins. The chamber temperature is maintained at 30℃ throughout to prevent condensation. The chamber pressure is increased gradually by 0.01 MPa every 3 minutes until the chamber pressure matches the external atmospheric pressure. After void-breaking, the peppercorns are removed to obtain the dried peppercorn product. This embodiment is completed entirely in a sealed chamber, free from external dust and insect contamination, requiring no manual turning, and avoiding mechanical damage to the oil sacs.

[0025] Example 2

[0026] The raw material used in this embodiment is the same batch of Sichuan Hanyuan Dahongpao fresh peppercorns as in Example 1, with an initial moisture content of 76%. In the pretreatment stage, a wind-powered separator was used to remove light impurities such as branches, leaves, and dust from the peppercorns. Then, manual sorting was used to remove fruit stalks, moldy fruit, and immature fruit, resulting in pure fresh peppercorns. A food-grade stainless steel scraper was used to evenly spread the peppercorns on a PTFE material tray, with a spreading thickness controlled at 5 cm. During spreading, compression of the peppercorns was avoided to prevent pre-rupture of the oil sacs. The microwave vacuum drying equipment was started, entering the first stage of drying. The microwave power density was set to 2.5 W / g, and the vacuum degree of the drying chamber was -0.09 MPa. During the drying process, a fiber optic thermometer was used to monitor the core temperature of the peppercorn material in real time, controlling the material temperature to not exceed 48℃. The drying time was 35 minutes. This stage mainly removes free water from the peppercorns. The low-temperature vacuum environment completely avoids the thermal degradation threshold of numbing amide, and the internal microwave heating mode prevents surface crusting that hinders moisture removal.

[0027] After the first stage, the second stage of drying begins. The microwave power density is adjusted to 0.8 W / g, the vacuum degree of the drying chamber is -0.08 MPa, the material temperature is controlled to not exceed 42℃, and the drying time is 25 minutes. This stage mainly removes the bound water inside the peppercorns. The power is reduced to avoid local overheating, and the vacuum threshold for bound water evaporation is matched. After the second stage, a slow tempering and void-breaking process begins. The chamber temperature is maintained at 30℃ throughout to prevent condensation. The chamber pressure is increased gradually by 0.01 MPa every 3 minutes until the chamber pressure matches the external atmospheric pressure. After void-breaking, the peppercorns are removed to obtain the dried peppercorn product. This embodiment is completed entirely in a sealed chamber, free from external dust and insect contamination, requiring no manual turning, and avoiding mechanical damage to the oil sacs.

[0028] Example 3

[0029] The raw material used in this embodiment is freshly harvested green Sichuan peppercorns from Jiangjin, Chongqing, with an initial moisture content of 78%. In the pretreatment stage, a wind-powered separator is used to remove light impurities such as branches, leaves, and dust from the peppercorns. Then, manual sorting removes fruit stalks, moldy fruit, and immature fruit to obtain pure fresh peppercorns. A food-grade stainless steel scraper is used to evenly spread the peppercorns on a PTFE material tray, with a spreading thickness controlled at 2cm. During spreading, care is taken to avoid squeezing the peppercorns and causing pre-rupture of the oil sacs. The microwave vacuum drying equipment is then started, entering the first stage of drying. The microwave power density is set to 3.5W / g, and the vacuum degree of the drying chamber is -0.095MPa. During the drying process, a fiber optic thermometer is used to monitor the core temperature of the peppercorn material in real time, controlling the material temperature to not exceed 46℃. The drying time is 28 minutes. This stage mainly removes free water from inside the peppercorns. A lower temperature threshold is set to accommodate the lower thermal stability of the numbing amide in green Sichuan peppercorns. The low-temperature vacuum environment completely avoids the critical threshold for thermal degradation of the numbing amide, and the internal microwave heating mode prevents surface crusting from hindering moisture removal.

[0030] After the first stage, the second stage of drying begins. The microwave power density is adjusted to 1.2 W / g, the vacuum degree of the drying chamber is -0.085 MPa, the material temperature is controlled to not exceed 40℃, and the drying time is 18 minutes. This stage mainly removes the bound water inside the peppercorns. The power is reduced to avoid local overheating, and the vacuum threshold for bound water evaporation is matched. After the second stage, a slow tempering and void-breaking process begins. The chamber temperature is maintained at 28℃ throughout to prevent condensation. The chamber pressure is increased by 0.01 MPa every 3 minutes until the chamber pressure matches the external atmospheric pressure. After void-breaking, the peppercorns are removed to obtain the dried peppercorn product. This embodiment is completed entirely in a sealed chamber, free from external dust and insect contamination, requiring no manual turning, and avoiding mechanical damage to the oil sac.

[0031] Example 4

[0032] The raw material used in this embodiment is the same batch of Chongqing Jiangjin green Sichuan peppercorns as in Example 3, with an initial moisture content of 78%. In the pretreatment stage, a wind-powered separator was used to remove light impurities such as branches, leaves, and dust from the peppercorns. Then, manual sorting was used to remove fruit stalks, moldy fruit, and immature fruit, resulting in pure fresh peppercorns. A food-grade stainless steel scraper was used to evenly spread the peppercorns on a PTFE material tray, with a spreading thickness controlled at 5cm. During spreading, compression of the peppercorns was avoided to prevent pre-rupture of the oil sacs. The microwave vacuum drying equipment was started, entering the first stage of drying. The microwave power density was set to 2.2W / g, and the vacuum degree of the drying chamber was -0.09MPa. During the drying process, a fiber optic thermometer was used to monitor the core temperature of the peppercorn material in real time, controlling the material temperature to not exceed 46℃. The drying time was 40 minutes. This stage mainly removes free water from inside the peppercorns. A lower temperature threshold was set to accommodate the lower thermal stability of the numbing amide in green Sichuan peppercorns. The low-temperature vacuum environment completely avoids the critical threshold for thermal degradation of the numbing amide. The internal microwave heating mode prevents surface crusting from hindering moisture removal.

[0033] After the first stage, the second stage of drying begins. The microwave power density is adjusted to 0.7 W / g, the vacuum degree of the drying chamber is -0.08 MPa, the material temperature is controlled to not exceed 40℃, and the drying time is 28 minutes. This stage mainly removes the bound water inside the peppercorns. The power is reduced to avoid local overheating, and the vacuum threshold for bound water evaporation is matched. After the second stage, a slow tempering and void-breaking process begins. Throughout the process, the chamber temperature is maintained at 28℃ to prevent condensation. The chamber pressure is increased gradually by 0.01 MPa every 3 minutes until the chamber pressure matches the external atmospheric pressure. After void-breaking, the peppercorns are removed to obtain the dried peppercorn product. This embodiment is completed entirely in a sealed chamber, free from external dust and insect contamination, requiring no manual turning, and avoiding mechanical damage to the oil sacs.

[0034] Comparative Example This comparative example uses the existing mainstream hot air drying process described in the background art. The raw material is fresh Sichuan Hanyuan Dahongpao peppercorns from the same batch as in Examples 1 and 2, with an initial moisture content of 76%. In the pretreatment stage, a wind separator was used to remove light impurities such as branches, leaves, and dust from the peppercorns. Then, fruit stalks, moldy fruits, and immature fruits were manually removed to obtain pure fresh peppercorns. A food-grade stainless steel scraper was used to evenly spread the peppercorns on a stainless steel material tray, with a spreading thickness controlled at 5 cm. During spreading, care was taken to avoid squeezing the peppercorns and causing pre-rupture of the oil sacs. The tray was placed in a hot air drying chamber, with the hot air temperature set at 75℃ and the hot air velocity at 2 m / s. During the drying process, the peppercorns were manually turned over every 2 hours using a wooden shovel to avoid uneven drying. Excessive squeezing of the peppercorns was avoided during turning. The total drying time was 540 minutes. The drying endpoint was determined by sampling and testing the moisture content. Drying was stopped when the moisture content dropped to approximately 10%. After removal, the peppercorns were placed in a cool, ventilated place to cool to room temperature, yielding the dried peppercorn product.

[0035] Performance testing methods All dried Sichuan peppercorns from all groups were tested for performance indicators using a standardized method: moisture content was tested using the atmospheric pressure drying method specified in GB5009.3-2016 "National Food Safety Standard - Determination of Moisture in Food"; oil sac integrity rate was determined by randomly selecting 100 Sichuan peppercorns under a stereomicroscope, observing and counting them, and counting the percentage of peppercorns with undamaged surface oil sacs; numbing amide retention rate was determined by high performance liquid chromatography, testing the content of hydroxy-α-sanshool in dried Sichuan peppercorns, and comparing it with the initial content of hydroxy-α-sanshool in fresh Sichuan peppercorns to obtain the retention rate; color was determined by measuring the L value using a colorimeter, with a higher value indicating lower browning and better color; and unit energy consumption was calculated based on the electricity consumption per kilogram of fresh Sichuan peppercorns processed.

[0036] Test Results and Explanation

[0037] This table simplifies and removes unnecessary staged sub-parameters, retaining only core identifiers, clearly showing the differences in material selection and process control logic among different groups. All implementation groups adopted the two-stage microwave vacuum heating mode of this invention, with an upper temperature control limit below 50℃, far lower than the 75℃ temperature control parameter of the comparative hot air drying. The total drying time was only 1 / 8 to 1 / 13 of the comparative. The parameters cover two mainstream pepper varieties in China and two material thicknesses of 2cm and 5cm, intuitively demonstrating the parameter adaptability of this invention's process and its core differences from existing processes.

[0038] Table 2 Performance test results of each embodiment and comparative example

[0039] This table summarizes the core performance test results of four examples and one comparative example. The final moisture content of all groups meets the standard of approximately 10% for dried Sichuan pepper storage, demonstrating horizontal comparability. It can be seen that the oil sac integrity rate of all four examples exceeds 94%, the numbing flavor amide retention rate exceeds 89%, the color L value is significantly higher than the comparative example, the unit energy consumption is only about half that of the comparative example, and the total drying time is only about one-tenth that of the comparative example. All indicators are significantly superior to the comparative example. The performance of examples with different layering thicknesses and different varieties remains stable, proving that the process of this invention effectively solves the defects of existing technologies, such as severe loss of numbing flavor substances, high oil sac breakage rate, severe browning, long drying cycle, and high energy consumption. The process has strong adaptability and can meet the processing needs of different scenarios.

[0040] refer to Figure 1This diagram illustrates the entire lifecycle of Sichuan peppercorns, from fresh raw materials to final dried peppercorns. The process begins with the selection of high-quality fresh peppercorns, followed by a pre-treatment stage where impurities are removed and color is protected through low-pressure spraying and color sorting. Next comes the core microwave vacuum dehydration stage, divided into constant-rate dehydration (stage one) and decreasing-rate dehydration (stage two), achieving efficient moisture removal through differentiated power and temperature settings. After drying, the crucial tempering and cooling stage begins. Precise control of the air-breaking rate protects the oil sac structure, and combined with inert gas protection and a constant temperature and humidity environment, ensures uniform diffusion of moisture and temperature gradients. The entire process aims to maximize the retention of numbing amides and volatile oils in the peppercorns.

[0041] refer to Figure 2 This diagram details the technical aspects of the pretreatment stage. The raw Sichuan peppercorns are first sprayed with room-temperature water at a pressure strictly limited to 0.1 MPa to 0.2 MPa to protect the sensitive surface oil sacs. After washing, impurities exceeding 0.1% are removed using a color sorter in conjunction with manual labor. The core step is color-protecting soaking, where the peppercorns are completely immersed in a citric acid or vitamin C solution, and low-speed agitation ensures a uniform film formation on the surface, preventing browning during drying. Finally, they are naturally drained using a perforated drain rack to ensure that the vacuum efficiency within the subsequent drying chamber is not affected by free droplets.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A drying process for preserving the numbing flavor of Sichuan peppercorns, characterized in that, Using fresh Sichuan peppercorns harvested within 24 hours, without any pre-drying or frozen storage treatment, and with an initial content of numbing amide compounds of not less than 18 mg / g, the process includes the following steps: S1. Pretreatment: Fresh Sichuan peppercorns are sprayed and rinsed with room temperature water at a pressure of 0.1MPa-0.2MPa for 30s-60s. Then, a color sorter is used in combination with manual sorting to remove non-target impurities such as branches and leaves, stones, diseased fruit, and wilted fruit, so as to obtain clean fresh Sichuan peppercorns with an impurity ratio of no more than 0.1%. S2. First stage constant-rate dehydration: The cleaned fresh peppercorns are evenly spread on the perforated material tray of the microwave vacuum drying equipment. After the drying chamber is sealed, the vacuum pump is started to draw a vacuum. After the vacuum degree in the chamber drops to the range of 0.06MPa-0.09MPa, the vacuum degree fluctuation range is maintained by the PID adjustment mode. The temperature data of peppercorns is collected in real time by a fiber optic temperature sensor placed close to the material layer. The material temperature is stably controlled by adjusting the microwave start-stop duty cycle. The dehydration process continues until the overall moisture content of peppercorns drops to 30%-40%. The moisture content is measured in real time by an online near-infrared moisture detector. S3, Second Stage Deceleration Dehydration: Maintain a constant vacuum level of 0.06MPa-0.09MPa within the chamber, with fluctuations controlled within ±0.002MPa. Adjust the microwave generator output power to reduce the microwave power density to 0.8W / g-1.5W / g. Continue to adjust the microwave output power in real time using the temperature sensor to stabilize the material temperature at 60℃-65℃ with temperature fluctuations not exceeding ±2℃. Continue dehydration until the overall moisture content of the peppercorns drops to 10%-15%. S4. Slow Cooling: Turn off the microwave generator to stop heating. Control the opening of the exhaust valve through the controller to slowly release the vacuum in the cavity to normal pressure at a constant rate of 0.01MPa / min-0.03MPa / min. During the vacuuming process, avoid sudden changes in vacuum that could cause excessive pressure difference between the inside and outside of the pepper oil sac and cause it to rupture. Then, transfer the dried peppers to a well-ventilated, cool, and clean environment with a temperature of 20℃-30℃ and a relative humidity of no more than 40% and lay them flat for slow cooling for 30min-60min. During the slow cooling process, avoid direct sunlight and dust contamination to ensure that the moisture and temperature gradients inside the peppers are fully and evenly diffused, resulting in dried peppers.

2. The drying process for retaining the numbing flavor of Sichuan pepper according to claim 1, characterized in that, The duration of the first stage of dehydration in S2 is adjusted according to the initial moisture content of the peppercorns, specifically 20-40 minutes. When the initial moisture content of the peppercorns is higher than 75%, a drying time of 30-40 minutes is used, and when the initial moisture content of the peppercorns is lower than 75%, a drying time of 20-30 minutes is used. After drying, the moisture content of the peppercorns is checked using an offline drying method to ensure that the moisture content is stable within the range of 30%-40%.

3. The drying process for retaining the numbing flavor of Sichuan pepper according to claim 1, characterized in that, The duration of the second stage dehydration treatment in S3 is adjusted according to the actual moisture content of the peppercorns after the first stage, specifically 15-25 minutes. When the moisture content of the peppercorns is higher than 35% after the first stage, a drying time of 20-25 minutes is used; when the moisture content of the peppercorns is lower than 35% after the first stage, a drying time of 15-20 minutes is used. After drying, the moisture content of the peppercorns is checked using an offline drying method.

4. The drying process for retaining the numbing flavor of Sichuan pepper according to claim 1, characterized in that, In the dehydration processes of S2 and S3, intermittent microwave radiation is used. In the first stage of S2, the microwave is turned on for 3-5 minutes and turned off for 1 minute at a time, with a microwave on-time to off-time ratio of (3-5):

1. In the second stage of S3, the microwave is turned on for 2-3 minutes and turned off for 1 minute at a time, with a microwave on-time to off-time ratio of (2-3):

1. During the microwave off-time stage, the residual heat of the material is used to continue evaporating moisture.

5. The drying process for retaining the numbing flavor of Sichuan pepper according to claim 1, characterized in that, The pretreatment of S1 also includes a color-protecting step, specifically: completely immersing the cleaned fresh peppercorns in a food-grade citric acid solution with a mass concentration of 0.5%-1.5% or a food-grade vitamin C solution with a mass concentration of 0.5%-1.5% for 1-3 minutes at room temperature and pressure. During the soaking process, the peppercorns are slowly turned over using a stirring device with a rotation speed of 10-20 r / min to ensure that all peppercorn surfaces are fully in contact with the color-protecting solution. After soaking, the peppercorns are immediately removed and placed on a perforated drain rack to drain naturally for 5-10 minutes until no free liquid drips from the surface of the peppercorns.

6. The drying process for retaining the numbing flavor of Sichuan pepper according to claim 1, characterized in that, The S4 tempering process is carried out in a sealed tempering chamber. Nitrogen gas with a purity of not less than 99.9% or argon or helium gas with a purity of not less than 99.9% is introduced into the tempering chamber beforehand to replace the air in the chamber and maintain the oxygen content of the gas in the tempering chamber at no more than 0.5%. During the tempering process, a low flow rate of the corresponding protective gas is continuously introduced.

7. The drying process for retaining the numbing flavor of Sichuan pepper according to claim 1, characterized in that, The final dried Sichuan peppercorns had a moisture content of less than 12% as determined by offline drying. The total content of Sichuan pepper numbing amide compounds, with α-sanshotoin, hydroxy-α-sanshotoin, and hydroxy-β-sanshotoin as the core, was determined by high performance liquid chromatography. Compared with the initial total content of numbing amide compounds in fresh Sichuan peppercorns, the retention rate was not less than 85%. The percentage of intact oil sacs in the dried Sichuan peppercorns was not less than 95% as observed by stereomicroscopy.

8. The drying process for retaining the numbing flavor of Sichuan pepper according to claim 1, characterized in that, In S2 and S3, the vacuum degree and the material temperature are matched and controlled. When the material temperature is at the upper limit of the range, the corresponding vacuum degree is at the upper limit of the range. When the material temperature is at the lower limit of the range, the corresponding vacuum degree is at the lower limit of the range. By matching and adjusting the vacuum degree and temperature, the evaporation temperature of the surface moisture of the peppercorns is further reduced.

9. A Sichuan pepper drying apparatus for performing the drying process for retaining the numbing flavor of Sichuan pepper as described in any one of claims 1 to 8, characterized in that, include: The microwave vacuum drying chamber has a sealed microwave-resistant structure with an inner wall made of 304 stainless steel. The side walls of the chamber are connected to a precision exhaust valve with adjustable opening, a vacuum pump with adjustable pumping speed, and a microwave generator with continuously adjustable output power. The frequency of the microwave generator is 2450MHz and the power adjustment range is 0.5kW-5kW. The material tray is detachable and installed inside the microwave vacuum drying chamber. It is made of food-grade 304 stainless steel or polytetrafluoroethylene with a hollow mesh structure and a mesh aperture of 2mm-3mm. It is used to evenly hold the pepper materials and prevent the peppers from leaking out. The temperature sensor is a high-precision fiber optic temperature sensor, which is placed 1cm-2cm close to the material layer on the material tray. The detection accuracy is ±1℃ and the sampling frequency is not less than 1 time / s. It is used to collect the actual temperature of the pepper material in real time. The pressure sensor is a high-precision capacitive pressure sensor, located on the upper side wall of the microwave vacuum drying chamber to avoid water vapor condensation affecting the detection accuracy. The detection accuracy is ±0.001MPa, and the sampling frequency is not less than 1 time / s. It is used to collect the vacuum level in the chamber in real time. An online near-infrared moisture analyzer is installed at the top of the microwave vacuum drying chamber, with the detection probe facing the material tray, for real-time measurement of the moisture content of Sichuan peppercorns; The PLC controller is electrically connected to the temperature sensor, pressure sensor, online near-infrared moisture detector, vacuum pump, microwave generator, and precision exhaust valve. The PLC controller is preset with the full-process parameters as described in claim 1, and automatically adjusts the microwave output power, vacuum pump pumping rate, and precision exhaust valve opening based on the real-time collected temperature, pressure, and moisture content data.

10. The Sichuan pepper drying apparatus according to claim 9, characterized in that, The microwave vacuum drying chamber is also equipped with a uniform airflow device, which circulates the gas in the chamber at a wind speed of 1m / s-2m / s during the microwave off phase, so that the temperature and vacuum uniformity deviation in the chamber does not exceed ±2%.

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