CN113567580A

CN113567580A - Method for evaluating freshness of Keemun black tea based on volatile component content

Info

Publication number: CN113567580A
Application number: CN202110808012.7A
Authority: CN
Inventors: 刘政权; 陶勐; 肖志鹏; 郭雯丽; 黄嫒
Original assignee: Anhui Agricultural University AHAU
Current assignee: Anhui Agricultural University AHAU
Priority date: 2021-07-16
Filing date: 2021-07-16
Publication date: 2021-10-29

Abstract

The invention provides a method for evaluating the freshness of Qimen black tea based on the content of volatile components, comprising the following steps: (1) taking Qi black tea leaves or tea soup, and extracting the volatile components with an organic solvent; Non-volatile components, concentrated injection; (3) Data collection for volatile components, and quantification of geraniol, methyl salicylate, linalool, dihydroanemone lactone and rye lactide; (4) Calculate the ratio between the total amount of geraniol, methyl salicylate, and linalool to the total amount of dihydroanemone lactone and rye lactide, as the freshness value; when the freshness value is greater than 4, it indicates that The sample is fresh Qihong; when the freshness value is 1-4, it indicates that the sample is mature Qihong; when the freshness value is less than 1, it indicates that the sample is aged Qihong. The present invention is the first to propose a method for objectively evaluating the freshness of Qimen black tea, which not only fills the gap in the field, but also provides a basis for evaluating the freshness of other black teas and oolong teas.

Description

Method for evaluating freshness of Keemun black tea based on volatile component content

Technical Field

The invention relates to the field of tea quality chemistry, in particular to a method for evaluating the freshness of Keemun black tea based on the content of volatile components.

Background

Keemun, due to its very characteristic and high-fragrance, has been called three major high-fragrance black teas in the world together with the black teas of slylan kawa and of digiin greens. The keemun tea is black tea prepared by taking tea tree varieties and fresh leaves as raw materials, wherein the tea tree varieties are mainly selected from the keemun county in Anhui province, and the keemun county is taken as a core production area, and the tea tree varieties are mainly selected from the keemun chinquan leaf seeds and clone improved seeds which are selected and bred by taking the keemun chinquan leaf seeds as resources. The characteristic aroma of keemun is broadly described as "keemun" and is an important quality attribute.

Like oolong tea, white tea and black tea, black tea is a type of tea which can be stored properly, the fragrance of the black tea is obviously changed during the storage period, and the black tea is popular or advocated by some consumers in recent years.

Fresh keemun fragrance is mainly tender sweet, blue and white and sweet flower fragrance, and the keemun fragrance is mainly sweet and fragrant and costustoot when stored for a period of time. As long-aged white tea and dark tea have been receiving wide attention from consumers so far, research on volatile and non-volatile components of tea leaves has been focused on white tea and dark tea, accordingly. In contrast, there has been little research on the storage of volatile components or aromas of keemun or black tea, and no extensive attention has been paid. In addition, currently, the keemun freshness degree is evaluated almost completely by means of sensory evaluation, subjectivity exists, and no method for objectively evaluating the keemun freshness degree exists.

Disclosure of Invention

The invention aims to provide a method for evaluating the freshness of Keemun black tea based on the content of volatile components.

The invention adopts the following technical scheme to solve the technical problems:

a method for evaluating freshness of Keemun black tea based on volatile component content comprises the following steps:

(1) extracting volatile components from QIHONG tea or tea soup with organic solvent;

(2) removing the extracted non-volatile components, and concentrating and sampling;

(3) collecting data of volatile components, and quantifying geraniol, methyl salicylate, linalool, dihydroactinolide and secaline;

(4) calculating the ratio of the total amount of geraniol, methyl salicylate and linalool to the total amount of dihydroactinol and secaline, and taking the ratio as a freshness degree value for representing the keemun freshness degree;

wherein, when said freshness value is greater than 4, it indicates that the keemun tea sample is fresh keemun; when the freshness value is 1-4, the keemun tea sample is mature keemun; when the freshness value is less than 1, the keemun tea sample is aged keemun.

Researches show that geraniol, methyl salicylate and linalool are volatile components derived from glycoside hydrolysis and show an exponential decline trend in the 20-year storage process; the dihydroactinolactone and secaline are volatile components from the oxidative degradation of carotenoid, and tend to rise first and then fall in the storage process of 20 years. According to the invention, geraniol, methyl salicylate, linalool, dihydroactinia lactone and secaline are selected as volatile components for evaluating the freshness of keemun. As for the fact that the freshness degree of keemun is characterized by the specific ratio of the total amount of geraniol, methyl salicylate and linalool to the total amount of dihydroactinolate and secaline, based on the results of multiple experiments, in the process of implementing the invention, it is found that the difference between keemun samples (caused by production area, grade, processing technology and the like) can be better eliminated by calculating the content ratio of the two compounds.

As one of the preferable modes of the invention, in the step (1), the organic solvent can be selected from one or more of n-pentane, diethyl ether, methyl tert-butyl ether and dichloromethane. In the process of the invention, the organic solvent can better extract the volatile components in the keemun.

As one of the preferred embodiments of the present invention, in the step (2), the method for removing the non-volatile components can be selected from, but not limited to, Solid Phase Extraction (SPE) and Solvent assisted flavor distillation (SAFE), so as not to pollute the sample analysis system and not to affect the analysis of the volatile components. In the process of implementing the invention, the method can better remove the extracted nonvolatile impurities.

In a preferred embodiment of the present invention, in the step (3), data collection is performed on the volatile component by using Gas chromatography-mass spectrometry (GC-MS) or Gas chromatography-flame ionization detector (GC-FID). In the process of implementing the invention, the instrument can conveniently acquire data.

In a preferred embodiment of the present invention, in the step (3), the quantitative method may be selected from, but not limited to, an internal standard method or a standard substance addition method, so as to obtain an accurate quantitative result. In the process of implementing the invention, the method is found to be more convenient for carrying out semi-quantitative/quantitative analysis on geraniol, methyl salicylate, linalool, dihydroactinol and secaline.

In a preferred embodiment of the present invention, in step (4), fresh keemun refers to keemun stored for 0 to 6 months, aged keemun refers to keemun stored for 6 to 24 months, and aged keemun refers to keemun stored for 24 months or more.

In a preferred embodiment of the present invention, in the step (4), one or more compounds selected from geraniol, methyl salicylate, linalool, and actide, dihydroactide, and secaline may be used as the ratio of the total amount to each other and calculated as the freshness value. For example, the ratio of the total amount of geraniol to the total amount of dihydroactinols is used as the freshness value.

In a preferred embodiment of the present invention, in the step (4), the freshness degree value for dividing the keemun bodies with different freshness degrees may be adjusted according to actual conditions. In the process of implementing the invention, the Qihong with different freshness degrees can be better classified by adjusting the freshness degree value according to the actual situation.

As one of the preferred embodiments of the present invention, the present invention is also applicable to other black teas and oolong teas than keemun black teas. In the practice of the present invention, it was found that other black and oolong teas have similar trends in aroma during storage.

Compared with the prior art, the invention has the advantages that:

(1) the freshness of keemun can be judged approximately by traditional sensory evaluation of keemun fragrance, but the subjective property of sensory evaluation is strong, and long-time professional training is needed; in order to objectively evaluate the keemun freshness, the invention designs a novel method for evaluating the keemun freshness based on the content of volatile components, namely, the keemun freshness is evaluated in a mode of extracting, analyzing and quantifying compounds and calculating the ratio of the compounds; the invention provides a method for objectively evaluating the freshness of Keemun black tea for the first time, fills the blank of the field, and provides a powerful basis for application and popularization of Keemun and continuous development of industries.

(2) The method analyzes the keemun volatile components in different storage periods by utilizing solvent extraction, SPE/SAFE, GC-MS/GC-FID combined with an internal standard method/standard addition method; wherein, the volatility of the keemun tea or the tea soup can be fully and effectively extracted by utilizing a solvent with proper proportion; the SPE/SAFE can be used for effectively removing the extracted nonvolatile components so as to protect a sample introduction system; the GC-MS/GC-FID can be used for effectively separating and identifying complex volatile components; the volatile components can be quantified quickly and effectively by using an internal standard method/standard addition method. Wherein, GC-MS is a kind of instrument widely used for the separation and identification of volatile components in tea; selecting a semi-quantitative/quantitative method, extracting and concentrating volatile components in the tea leaves, removing non-volatile impurities, and performing quantitative analysis on each volatile component in the tea leaves by using GC-MS; at present, no method for judging the freshness of keemun black by analyzing the content of volatile components in the keemun black by using GC-MS (gas chromatography-Mass spectrometer) exists.

(3) According to the invention, analysis of keemun volatile components with different storage times discovers that a part of glycoside-derived volatile components (such as geraniol, methyl salicylate, linalool and the like) have strong negative correlation with the storage time, a part of carotenoid-derived volatile components (such as dihydroactinolactone, secaline and the like) have strong positive correlation with the storage time, and the ratio of the total amount of the two parts of compounds is reduced in a high correlation index type along with the storage time, so that the keemun volatile components can be used for objectively characterizing the freshness of the keemun.

(4) The method is suitable for evaluating the freshness of keemun black tea and oolong tea and provides a basis for evaluating the freshness of other black tea and oolong tea.

Drawings

FIG. 1 is a graph showing the trend of geraniol content of different Keemun samples stored at different times in example 1;

FIG. 2 is a graph showing the trend of the content of methyl salicylate in different keemun samples according to example 1;

FIG. 3 is a graph showing the trend of linalool content in different keemun samples according to example 1;

FIG. 4 is a graph showing the trend of the change in the content of dihydroactine lactone in the keemun samples of example 1 at different storage times;

FIG. 5 is a graph showing the trend of change in lactide content of rye in different keemun samples at different storage times in example 1;

FIG. 6 is a graph showing the change of freshness among different keemun samples at different storage times in example 1.

Detailed Description

The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.

Example 1

The method for evaluating the freshness of Keemun black tea based on the content of volatile components comprises the following steps:

(1) selecting a tea sample:

3 fresh Qihong tea samples are purchased in Jindong tea markets in Qimen county in batches in 2019 and 4 months; the Qihong Kongfu from 1 to 20 years is from Anhui national tea industry Co.

(2) Traditional sensory evaluation:

the collected samples were subjected to traditional sensory evaluation according to GB/T23776-. The sensory evaluation results are shown in Table 1.

TABLE 1 sensory evaluation results of different storage time keemun samples

Tea sample	Fragrance
		FKBT1	High sweet and fragrant, with fragrant flower
FKBT2	Sweet, long-lasting and flower-like fragrance
		FKBT3	Sweet and fragrant
1 year congou	Higher sweet and slightly fragrant smell
		2 years old congou	Sweet and pure, with aucklandia root
3 years congou	Sweet and pure, mu Xiang Zhi
		5 years old congou	Old and sweet
10 years old congou	Chen Chun, mu Xiang
		15 years old congou	Old, sweet, fragrant and high cool
20 years old congou	Display for old fragrance

Note: FKBT, fresh keemun; numbers represent different qihong samples

Sensory evaluation results show that the difference and gradient change of the keemun fragrance are obvious in different storage times.

(3) Extracting volatile components:

weighing 6g of tea leaves, adding 300mL of ultrapure water for brewing for 5min, then quickly filtering, and placing in ice water for cooling for 5 min; then, a certain amount of 2-octanol and ethyl decanoate internal standard are added, and the mixture is continuously extracted three times by utilizing pentane: MTBE (methyl tert-butyl ether) with the ratio of 4:1, and a clear organic layer is obtained by high-speed centrifugation, and nitrogen is blown to 1 mL.

(4) Removing non-volatile impurities using SPE column:

6mL of 1:1 pentane, MTBE, was weighed out and the SPE cartridge (LC-Si,500mg/6mL) was activated; subsequently, 1mL of the concentrated sample was loaded and eluted with 10mL of 1:1 pentane: MTBE; finally, the eluate was collected and concentrated to 200. mu.L, sealed after concentration and stored at-20 ℃. All sample analyses were performed in triplicate.

(5) And (3) GC-MS data acquisition:

volatile component data collection was performed using Agilent 7890A-5975C with a DB-5MS column.

The carrier gas for the GC-MS system was 99.999% high purity helium at a flow rate of 1 mL/min. The injection port temperatures were 250 ℃ (DB-5MS) and 230 ℃ (DB-WAX), respectively, and 1 μ l of the sample was aspirated and manually injected in split mode at a split ratio of 5: 1.

For the DB-5MS column, the temperature rise pattern is as follows: keeping the temperature at 50 ℃ for 5min, heating to 230 ℃ at the speed of 5 ℃/min and keeping the temperature for 2 min; subsequently, the temperature was raised to 280 ℃ at 15 ℃/min and maintained for 1 min.

The key parameters of the mass spectrometer are as follows: the ionization mode is Electron Ionization (EI); ionization energy is 70 eV; the temperature of the ionization source is 150 ℃; the quadrupole mass scan range is 30-450 Atomic mass units (amu).

(6) Qualitative and semi-quantitative analysis of GC-MS data:

the collected GC-MS data was deconvoluted and qualitatively analyzed using an agilent workstation equipped with NIST17 database and AMDIS equipped with a self-built tea volatile component database. In addition, Retention Indices (RI) of all volatile components (DB-5MS and DB-WAX columns) were calculated and compared to RI of volatile components in published literature for secondary characterization.

Semi-quantitative analysis of the collected GC-MS data was performed (again using agilent workstation equipped with NIST17 database and AMDIS equipped with self-built tea volatile component database). For the component with RI less than 2-octanol, performing semi-quantitative calculation by using the peak area of 2-octanol; and if the component is larger than the component of the 2-octanol, performing semi-quantitative calculation by using the peak area of the ethyl decanoate.

(7) Screening of compounds:

screening compounds related to storage time, and screening five volatile components represented by geraniol, methyl salicylate, linalool, dihydroactilactone and rye estolide. Wherein, geraniol, methyl salicylate and linalool are derived from glycoside, and the content trend along with storage time is respectively shown in figure 1 and figure 2 and figure 3; the actides of dihydroactins and secalins are derived from carotenoids, and the content trend with storage time is shown in fig. 4 and 5.

As can be seen from fig. 1 to 5, the contents of geraniol, methyl salicylate and linalool are much higher in fresh keemun than in keemun stored for a certain period of time, and show an exponential decrease in the storage period of 1 to 20 years; the content of dihydroactins and secalins in fresh keemun is far lower than that in storage for a period of time, and the keemun is in a linear rising trend within 1 to 5 years of storage, and then has a certain descending trend.

(8) Calculating a freshness value:

the ratio of the total amount of "geraniol, methyl salicylate, linalool" to the total amount of "dihydroactinols, secalins" was calculated for each sample and taken as the freshness value, i.e., the freshness value (geraniol + methyl salicylate + linalool)/(dihydroactinols + secalins). The results are shown in FIG. 6.

As can be seen from FIG. 6, the freshness of keemun is greatly different from that of keemun stored for a certain period of time, and the freshness of keemun stored in a range of 1 to 20 is in a power-down trend, and the correlation coefficient is 0.997.

Accordingly, based on freshness value, the keemun can be divided into three categories, namely, fresh keemun (0-6 months) is one category (freshness value is more than 4), mature keemun (6-24 months) is one category (freshness value is 1-4) within shelf life, and aged keemun (more than 24 months) is one category (freshness value is less than 1). Correspondingly, when the method of the embodiment is adopted to evaluate the keemun freshness, the freshness can be accurately judged according to the freshness value of each sample.

In addition, it should be noted that in this embodiment, besides pentane and MTBE, the organic solvent used in the volatile component extraction process may also be selected from ether, dichloromethane or other organic solvents commonly used in the art. The method for removing the nonvolatile components can adopt a SAFE method commonly used in the art in addition to the SPE method. Meanwhile, the data acquisition and analysis process can adopt a GC-FID system besides a GC-MS system.

Moreover, when the GC-FID system is adopted for book note acquisition and analysis, the corresponding data acquisition and analysis processes are as follows:

and (3) GC-FID data acquisition: for GC-FID, the GC parameters were the same as those for GC-MS, and the FID temperature was set at 300 ℃.

Qualitative and semi-quantitative analysis of GC-FID data: comparing and confirming the selected compounds by using the standard substance; for the component with RI less than 2-octanol, performing semi-quantitative calculation by using the peak area of 2-octanol; and if the component is larger than the component of the 2-octanol, performing semi-quantitative calculation by using the peak area of the ethyl decanoate.

Meanwhile, it should be noted that, in the process of carrying out the present invention, it was found that other black teas and oolong teas have similar changes in aroma during storage, and therefore, the freshness evaluation method of the present embodiment is also applicable to other black teas and oolong teas other than keemun black teas.

In addition, when defining the freshness value, the ratio of the total amount of geraniol to the total amount of dihydroactinolactone can be used as the freshness value. Correspondingly, the freshness degree values of the tea leaves with different freshness degrees can be adjusted to a certain extent according to actual conditions.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. a method for evaluating Qimen black tea freshness based on volatile component content, is characterized in that, comprises the steps:

(1) get Qi black tea leaves or tea soup, and utilize organic solvent to extract its volatile components;

(2) remove the extracted non-volatile components, concentrate and inject;

(3) Data collection for volatile components, and quantification of geraniol, methyl salicylate, linalool, dihydroanemone lactone and rye lactide;

(4) Calculate the ratio between the total amount of geraniol, methyl salicylate, and linalool to the total amount of dihydroanemone lactone and rye lactide, and use it as a freshness value that characterizes the freshness of Qihong;

Wherein, when the freshness value is greater than 4, it indicates that the Qihong tea sample is fresh Qihong; when the freshness value is 1-4, it indicates that the Qihong tea sample is mature Qihong; When the degree value is less than 1, it indicates that the Qihong tea sample is aged Qihong.

2. the method for evaluating Qimen black tea freshness based on volatile component content according to claim 1, is characterized in that, in described step (1), organic solvent adopts n-pentane, ether, methyl tert-butyl One or more mixtures of ether and dichloromethane.

3. the method for evaluating Qimen black tea freshness based on volatile component content according to claim 1, is characterized in that, in described step (2), the method for removing non-volatile component adopts solid phase extraction method or Solvent-assisted flavor distillation.

4. the method for evaluating Qimen black tea freshness based on volatile component content according to claim 1, is characterized in that, in described step (3), utilize gas chromatography-mass spectrometry or gas chromatography-flame ionization Detector coupling is used for data collection of volatile components.

5. the method for evaluating the freshness of Qimen black tea based on volatile component content according to claim 1, is characterized in that, in described step (3), used quantitative method is internal standard method or standard substance addition method.

6. the method for evaluating Qimen black tea freshness based on volatile component content according to claim 1, is characterized in that, in described step (4), fresh Qihong refers to the Qihong that stores 0-6 months, Aged Qihong refers to Qihong that has been stored for 6-24 months, and aged Qihong refers to Qihong that has been stored for more than 24 months.

7. the method for evaluating Qimen black tea freshness based on volatile component content according to claim 1, is characterized in that, in described step (4), also can from " geraniol, methyl salicylate, One or more compounds were selected from "Linalool" and "Dihydroanemon lactide, rye lactide" to calculate the ratio between the total amount and take it as the freshness value.

8. The method for evaluating the freshness of Keemun black tea based on the content of volatile components according to any one of claims 1-7, characterized in that it is also applicable to other black teas and oolong teas other than Keemun black tea.