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CN-121878089-B - Online pretreatment method for real-time measurement of aromatic substances in tea processing process

CN121878089BCN 121878089 BCN121878089 BCN 121878089BCN-121878089-B

Abstract

The invention discloses an online pretreatment method for real-time measurement of aromatic substances in a tea processing process. The method comprises the steps of carrying out heat tracing and heat preservation on wet and hot carrier gas, carrying out airflow shearing to obtain homogeneous mixed gas, introducing the mixed gas into a cold trap tube with multiple adsorbent beds, adsorbing and enriching at low temperature, switching through a six-way valve, reversely purging with inert gas at low temperature to remove residual moisture, switching through the six-way valve, and rapidly pulsing the cold trap tube to heat so as to enable aromatic substances to be instantaneously desorbed and be brought into a gas chromatograph-mass spectrometer by carrier gas for analysis. The invention solves the technical problem of capturing trace aromatic substances in real time in a high-humidity dynamic processing environment through the synergistic effect of heat tracing shearing, grading low-temperature enrichment, low-temperature blowing and pulse heating, realizes high-time resolution monitoring of the dynamic change of aroma in the tea processing process, and can be used for tea quality control and process optimization.

Inventors

  • HUANG JIANFENG
  • SHI HONGYAN

Assignees

  • 福建鸿钧农业发展有限公司

Dates

Publication Date
20260508
Application Date
20260320

Claims (6)

  1. 1. The on-line pretreatment method for real-time measurement of aroma substances in the tea processing process is characterized by comprising the following steps of: Extracting wet and hot carrier gas containing aromatic substances from tea processing equipment in real time, carrying out heat tracing and heat preservation on the wet and hot carrier gas, carrying out airflow shearing treatment on the carrier gas after heat tracing and heat preservation, and crushing and separating water mist particles carried in the carrier gas by utilizing shearing force generated by high-speed airflow to obtain homogeneous mixed gas; b, introducing the homogeneous mixed gas obtained in the step a into a cold trap tube filled with a multi-adsorbent bed layer, and carrying out adsorption enrichment at a low temperature of-10 ℃ to 5 ℃; Step c, after adsorption enrichment is finished, switching through a six-way valve, and reversely purging the cold trap tube by adopting inert gas under the condition of maintaining low temperature, so as to selectively remove and drain co-adsorbed residual moisture, wherein target aromatic substances are reserved on the adsorbent; D, after purging, switching through a six-way valve, quickly programming the temperature of the cold trap tube to 280-300 ℃ at the temperature rising rate of 40-60 ℃ per second, enabling adsorbed aromatic substances to be instantaneously desorbed, and carrying out back flushing by carrier gas in a narrow pulse mode and transferring to a gas chromatography-mass spectrometer for analysis; The six-way valve is provided with three working positions, namely a sampling position, a purging position, a carrier gas source, a cold trap pipe outlet, a cold trap pipe inlet and a sample inlet, wherein the sampling position is communicated with a sample inlet, the cold trap pipe outlet and a sampling pump, so that sample gas passes through the cold trap pipe in the forward direction for adsorption enrichment; The shearing chamber is made of quartz glass, and comprises an inlet contraction section, a throat section and an outlet diffusion section in sequence along the airflow direction, wherein the length of the inlet contraction section is 12 mm, the diameter of the inlet is 6mm, the contraction angle is 21 degrees, the length of the throat section is 2 mm, the diameter of the throat section is 2 mm, and the length of the outlet diffusion section is 18 mm, the diameter of the outlet is 6mm, and the diffusion angle is 12 degrees; The multi-adsorbent bed layer in the step b sequentially comprises hydrophobic high-crosslinked polystyrene resin for adsorbing high-boiling-point volatile components, graphitized carbon black for adsorbing terpene compounds and carbon molecular sieves for adsorbing low-boiling-point small-molecular sulfur compounds along the airflow direction, wherein the tea processing process comprises the steps of de-enzyming, drying or baking, and the aromatic substances comprise terpene alcohols, pyrazines, sulfur compounds and Maillard reaction intermediates.
  2. 2. An on-line pretreatment method for real-time measurement of aroma substances in tea processing according to claim 1, wherein the extraction flow rate of the wet and hot carrier gas in step a is 50-200 mL/min, and the temperature of heat tracing and heat preservation is 110-130 ℃.
  3. 3. An on-line pretreatment method for real-time measurement of aroma substances in tea processing according to claim 1, wherein the hydrophobic highly crosslinked polystyrene resin is Porapak Q with a particle size of 80-100 mesh, the graphitized carbon black is Carbopack B with a particle size of 60-80 mesh, and the carbon molecular sieve is Carbosieve S-III.
  4. 4. An on-line pretreatment method for real-time measurement of aroma substances in tea processing according to claim 1, wherein the adsorption enrichment time in step b is 1-5 minutes.
  5. 5. An on-line pretreatment method for real-time measurement of aroma substances in tea processing according to claim 1, wherein the inert gas in step C is high-purity nitrogen, the purge flow rate is 20-50 mL/min, the purge time is 30-90 seconds, and the cold trap tube temperature is maintained at 0-10 ℃ in the purge process.
  6. 6. An on-line pretreatment method for real-time measurement of aroma substances in tea processing according to claim 1, wherein in step d, said carrier gas is helium gas, the back flushing flow rate is 1.5-3 mL/min, and the peak width in the form of narrow pulse is less than 3 seconds.

Description

Online pretreatment method for real-time measurement of aromatic substances in tea processing process Technical Field The invention relates to the technical field of sample pretreatment, in particular to an online pretreatment method for real-time measurement of aromatic substances in a tea processing process. Background The quality of the aroma of the tea is a core index of sensory evaluation, the economic value of the tea is directly determined, the formation of characteristic aroma is a dynamic and nonlinear chemical conversion process, the characteristic aroma mainly occurs in the hot processing stages of fixation, drying, baking and the like, and the real-time monitoring of the generation and growth regulation of the aromatic substances has great significance for precisely controlling the processing end point and stabilizing the quality of the tea. However, the prior art faces the difficult bottleneck that the traditional tea aroma analysis methods, such as headspace solid-phase microextraction (HS-SPME), solvent Assisted Flavor Evaporation (SAFE) and the like, belong to an off-line or off-line-on-line combination mode, need to sample, cool, weigh, extract and enrich at specific processing nodes, take longer time in the whole process, and cannot completely match the rapid chemical change in seconds in the tea processing process. More importantly, the existing off-line pretreatment technology has a dead zone which is difficult to detect by a person skilled in the art, the adaptability of the characteristic of a semi-finished product matrix in the middle of processing is lost, the conventional method is mostly used for optimizing the finished dry tea (the water content is less than 5% and the cell structure is stable), however, in the tea processing process, especially in the late fixation stage and the rolling primary drying stage, the water content of the leaf is still as high as 10% -40%, the cell is in a semi-damaged state, the matrix presents a colloid characteristic of high humidity and high adhesiveness, fragrance extraction is carried out in the dynamic matrix, a serious matrix competitive adsorption effect exists, namely a large number of water molecules with strong polarity and oligosaccharide fragments generated in the middle period can preferentially occupy active sites of extraction fibers or adsorbents, so that the enrichment efficiency of trace target aromatic substances (such as sulfur compounds and pyrazines) is drastically reduced or even false negative, meanwhile, the sampling process of the off-line method breaks the processing continuity, and the sample leaves a thermal reaction environment, and partially unstable intermediates (such as Maillard reaction intermediates) can react or degrade, so that the detection result cannot truly reflect the instantaneous state of the processing. Therefore, the development of an online pretreatment method which can overcome the interference of a high-humidity matrix, realize second-level time resolution and stably capture unstable intermediates solves the technical problems of real-time capture and unbiased analysis of trace aromatic substances and unstable intermediates in a high-humidity dynamic processing environment, and is a key problem to be solved in the field. Disclosure of Invention The invention aims to solve the technical problems of solving the technical problems of real-time capturing and unbiased analysis of trace aromatic substances and unstable intermediates in a high-humidity dynamic processing environment by developing an on-line pretreatment method which can overcome high-humidity matrix interference, realize second-level time resolution and stably capture the unstable intermediates. In order to solve the technical problems, the invention adopts the following technical scheme: an on-line pretreatment method for real-time measurement of aroma substances in a tea processing process comprises the following steps: Extracting wet and hot carrier gas containing aromatic substances from tea processing equipment in real time, carrying out heat tracing and heat preservation on the wet and hot carrier gas, carrying out airflow shearing treatment on the carrier gas after heat tracing and heat preservation, and crushing and separating water mist particles carried in the carrier gas by utilizing shearing force generated by high-speed airflow to obtain homogeneous mixed gas; b, introducing the homogeneous mixed gas obtained in the step a into a cold trap tube filled with a multi-adsorbent bed layer, and carrying out adsorption enrichment at a low temperature of-10 ℃ to 5 ℃; Step c, after adsorption enrichment is finished, switching through a six-way valve, and reversely purging the cold trap tube by adopting inert gas under the condition of maintaining low temperature, so as to selectively remove and drain co-adsorbed residual moisture, wherein target aromatic substances are reserved on the adsorbent; D, after purging, switching through a six-