Method for judging the strength of almond flavor of tea tree and tea leaf

Abstract

The present application relates to the field of tea processing and tea germplasm resources, and specifically relates to a method for judging the strength of almond aroma of tea tree and tea leaf. Benzaldehyde is a characteristic component of black tea almond aroma, and the higher the content, the stronger the almond aroma. The present application takes tea leaf processing process samples for drying, sensory evaluation, and determination of relative content of hydrocyanic acid and benzaldehyde. The results show that the content of hydrocyanic acid in rolled and twisted samples, fermented samples, and finished product samples is relatively high, the content of benzaldehyde also changes with the content of hydrocyanic acid, and the sensory evaluation results are consistent with the detection results. Therefore, by using a visible spectrophotometer to determine the content of hydrocyanic acid in rolled and twisted samples, fermented samples, and finished product samples, and without determining the content of benzaldehyde by using expensive gas chromatography, the strength of almond aroma of tea leaf can be accurately judged, which can also be used for risk assessment of tea product quality and safety, screening, identification, genetic map construction, population genetic relationship and evolution, or genetic breeding of specific tea tree germplasm resources, etc.

Description

Technical Field

[0001] This invention relates to the fields of tea processing and tea germplasm resources, specifically a method for determining the strength of almond aroma in tea trees and tea leaves. Background Technology

[0002] The aroma of tea is determined by the nature of the plant, the production process, and many other factors, and is a crucial factor in determining tea quality. Different compounds exhibit different aroma profiles. Almond aroma is a very unique aroma in tea. Tea tree resources with an almond aroma in black tea are rare worldwide; currently, only wild ancient tea tree resources in Luokeng Town, Guangdong Province, and Guangxi Province have been reported in China. Research has proven that benzaldehyde is a characteristic aroma component of almond aroma in black tea, and the higher the proportion of this component, the stronger the almond aroma. Currently, the strength of the almond aroma in tea trees is accurately determined mainly by measuring the benzaldehyde content in black tea and through sensory evaluation.

[0003] The determination of benzaldehyde aroma components is mainly performed using liquid chromatography, gas chromatography-mass spectrometry, or gas chromatography-tandem mass spectrometry. However, these instruments are expensive and many institutions do not possess them.

[0004] There are currently no reports of tea containing hydrocyanic acid.

[0005] Therefore, developing a method that can accurately determine the strength of almond aroma in tea is urgently needed. This method can be used for the precise screening, evaluation, and utilization of almond-scented tea germplasm resources, as well as for quality and safety risk assessment. Summary of the Invention

[0006] To address the aforementioned technical problems in the existing technology, the present invention provides a method for determining the strength of almond aroma in tea trees and tea leaves, as detailed below:

[0007] One method for judging the strength of almond aroma in tea trees and tea leaves involves measuring the content of hydrocyanic acid. The higher the hydrocyanic acid content in the tea leaves, the stronger the almond aroma in the tea trees and tea leaves.

[0008] Furthermore, the method of determining the strength of almond aroma by measuring the content of hydrocyanic acid is to determine the content of benzaldehyde by measuring the content of hydrocyanic acid.

[0009] Furthermore, the benzaldehyde content is determined by measuring the content of hydrocyanic acid, with a molar ratio of hydrocyanic acid to benzaldehyde of 1:1 and a mass ratio of hydrocyanic acid:benzaldehyde = 1:3.926.

[0010] Furthermore, the tea mentioned is black tea.

[0011] Furthermore, the tea leaves are measured after being kneaded.

[0012] Furthermore, the tea leaves were tested after fermentation.

[0013] The rolling and fermentation processes are the main stages for the formation and accumulation of hydrocyanic acid. Sensory evaluation results also show that the rolled sample already has an almond aroma, and the aroma and taste of the fermented sample and the finished product are both rich in almond aroma. The tea is baked at 120℃ for 6 minutes; after being removed and cooled, it is placed in a tea roasting and aroma-enhancing machine and dried at 80℃ with a moisture content of ≤6%, which generally takes more than 1 hour. To save time, the hydrocyanic acid content in the fermented sample can be measured after fermentation, which can accurately determine the strength of the almond aroma in the tea. Alternatively, the hydrocyanic acid content can be more accurately obtained by measuring the final finished tea.

[0014] If it is necessary to determine more quickly whether tea tree germplasm resources have almond aroma and the strength of almond aroma, the content of hydrocyanic acid can be measured after rolling to determine the strength of almond aroma of tea tree resources or whether the variety has almond aroma. This saves about 6 hours (after fermentation time + drying time) compared to fermentation sample and about 7 hours compared to finished tea sample.

[0015] A method for determining the benzaldehyde content in tea leaves involves measuring the content of hydrocyanic acid to determine the benzaldehyde content. The molar ratio of hydrocyanic acid to benzaldehyde in tea leaves is 1:1; the mass ratio is hydrocyanic acid:benzaldehyde = 1:3.926.

[0016] A method for determining the hydrocyanic acid content in tea leaves includes the following steps:

[0017] (1) Tea sample solution: The tea sample was steam distilled to obtain the sample solution;

[0018] (2) Preparation of standard solutions: The standard substance for cyanide analysis in water is prepared into an intermediate standard solution using sodium hydroxide solution, and then water is added to prepare solutions of different concentrations;

[0019] (3) Determination of cyanide content in tea samples: Add 1 mL of 10 g / L sodium hydroxide solution and 1 drop of phenolphthalein-ethanol indicator (10 g / L) to each of the tea sample solution and standard series solutions. Slowly adjust the solution with acetic acid solution (1+24) until the red color fades. Then add 5 mL of phosphate buffer solution [(0.5 mol / L) pH 7.0]. Incubate in a 37℃ constant temperature water bath for 10 min. Then add 0.25 mL of chloramine T (10 g / L) solution, stopper and shake to mix thoroughly, and let stand for 5 min. Then add 5 mL of isonicotinic acid- Pyrazolone solution [Weigh 1.5g of isonicotinic acid and dissolve it in 24mL of sodium hydroxide solution (20g / L), add water to 100mL, separately weigh 0.25g of pyrazolone and dissolve it in 20mL of anhydrous ethanol, then mix the two solutions together and shake well; prepare immediately before use], add water to 25mL and mix well, place in a 37℃ constant temperature water bath for 40min; use a 2cm cuvette, adjust the zero point of the visible spectrophotometer with the zero tube, and measure the absorbance at a wavelength of 638nm;

[0020] (4) The cyanide content (calculated as CN-) in the sample is calculated according to the formula:

[0021] X = A × 1000 / m × V 2 × V 1 × 1000

[0022] X - Cyanide content in sample (calculated as CN-), in milligrams per kilogram (mg / kg);

[0023] A - Determine the mass of cyanide in the sample solution (as CN-), in micrograms (μg);

[0024] 1000 - Conversion factor;

[0025] m - Sample mass, in grams (mg);

[0026] V1 - The volume of distilled liquid used for determination is measured in milliliters (mL);

[0027] V2 - Total volume of the sample distillate, in milliliters (mL);

[0028] The calculation results should be retained to three significant figures; the absolute difference between two independent measurements should not exceed 10% of the arithmetic mean.

[0029] Furthermore, the tea sample solution is prepared by the following steps: Weigh 20g of tea sample (accurate to 0.001g), with two replicates for each sample, place it in a 500mL steam distillation apparatus, add approximately 200mL of water, seal the bottle tightly, and stir magnetically at room temperature for 2 hours; then add 20mL of zinc acetate solution (100g / L) and 2.0g of tartaric acid, quickly connect the distillation apparatus, and insert the lower end of the condenser into a container containing 10mL of... Place a 100mL Erlenmeyer flask ① containing 20g / L sodium hydroxide solution below the liquid surface; perform steam distillation, collecting approximately 100mL of distillate, then remove Erlenmeyer flask ①; simultaneously, insert the lower end of the condenser into a 100mL Erlenmeyer flask ② containing 10mL of 20g / L sodium hydroxide solution below the liquid surface, and repeat distillation until approximately 80mL of distillate is collected, then stop heating and continue collecting approximately 100mL of distillate, removing Erlenmeyer flask ②; remove distillation flask ② and thoroughly stir and mix its contents, then insert the lower end of the condenser into a 100mL Erlenmeyer flask ③ containing 10mL of 20g / L sodium hydroxide solution below the liquid surface, and perform steam distillation until approximately 50mL of distillate is collected in Erlenmeyer flask ③, then remove Erlenmeyer flask ③; completely transfer the distillate collected in Erlenmeyer flasks ①, ②, and ③ into a 250mL (V1) volumetric flask, and dilute to the mark with water. Measure 10mL of the solution (V2) into a 25mL colorimetric tube as the sample solution.

[0030] Furthermore, the standard solution is prepared as follows: a cyanide analysis standard substance in water (50 μg / mL), whose standard substance number is GBW(E)080115, is prepared into an intermediate standard solution of 1 μg / mL using sodium hydroxide solution (2 g / L); 0.0 mL, 0.1 mL, 0.2 mL, 0.3 mL, 0.4 mL, and 0.5 mL of the intermediate standard solution are respectively measured by pipette and placed in 25 mL colorimetric tubes, and water is added to 10 mL.

[0031] Compared with the prior art, the technical effects of this invention are reflected in:

[0032] (1) This invention confirms that the relative content of benzaldehyde aroma components in tea increases with the increase of hydrocyanic acid content, and the two are positively correlated. The reason is that under the action of enzymes, one molecule of amygdalin can be decomposed into one molecule of benzaldehyde and one molecule of hydrocyanic acid. The higher the benzaldehyde content, the richer and longer-lasting almond aroma of the tea. The ratio of hydrocyanic acid to benzaldehyde is 1:3.926. The content of benzaldehyde can be determined by measuring the content of hydrocyanic acid in tea, and the strength and presence of almond aroma in tea can be accurately determined. Therefore, the strength of almond aroma in tea can be accurately determined by measuring the content of hydrocyanic acid in rolled, fermented and finished samples using a visible spectrophotometer instead of measuring the content of benzaldehyde using expensive gas chromatography. This can further determine the strength of almond aroma in tea trees, and can also be used for tea product quality and safety risk assessment, screening and identification of special tea tree germplasm resources, construction of genetic maps, kinship and evolution or genetic breeding of populations, etc.

[0033] (2) This invention provides a method for determining the hydrocyanic acid content in tea, which can accurately determine the hydrocyanic acid content in tea.

[0034] (3) This invention confirms that during the black tea production process, the dried sample after rolling already exhibits an almond aroma, while the fermented and finished samples have a rich and lasting almond aroma. The tea soup of both the fermented and finished samples also has a strong almond aroma. From the above results, it can be seen that the rolling and fermentation processes are the main stages for the formation and accumulation of hydrocyanic acid. Sensory evaluation results also show that the rolled sample already has an almond aroma, and the aroma and taste of the fermented and finished samples are both rich in almond fragrance. The tea is dried at 120℃ for 6 minutes; after cooling, it is placed in a tea roasting and aroma-enhancing machine and dried at 80℃ with a moisture content ≤6%, generally requiring about 1 hour. To save time, the hydrocyanic acid content in the fermented sample can be measured after fermentation, thus accurately determining the strength of the almond aroma in the tea. Alternatively, the hydrocyanic acid content can be more accurately obtained by measuring the final finished tea. If it is necessary to determine more quickly whether tea tree germplasm resources have almond aroma and the strength of almond aroma, the content of hydrocyanic acid can be measured after rolling to determine the strength of almond aroma of tea tree resources or whether the variety has almond aroma. This saves about 6 hours (after fermentation time + drying time) compared to fermentation sample and about 7 hours compared to finished tea sample. Detailed Implementation

[0035] The technical solution of the present invention will be further defined below with reference to specific embodiments, but the scope of protection is not limited to the description made.

[0036] Example:

[0037] I. Materials and Methods

[0038] 1. Preparation of Almond-Scented Black Tea Samples: ① Fresh leaves with one bud and two or three leaves were picked in spring (fresh leaf sample); ② Withered at room temperature for about 15 hours until the moisture content dropped to 70-75%, then left to stand for 10 minutes (withering sample); ③ Lightly rolled for 15 minutes, then rolled under pressure for 60 minutes, and then lightly rolled for another 15 minutes (rolling sample); ④ The rolled tea leaves were fermented at 25℃ for 4.5 hours (fermentation sample); ⑤ The fermented tea leaves were dried in a tea roasting and aroma-enhancing machine (finished product sample). The control sample was the Meizhan tea variety harvested from the Tea Germplasm Resource Garden of the Guangxi Subtropical Crops Research Institute, processed according to the conditions of the almond-scented black tea sample.

[0039] 2. Sample Preparation: At the end of each process ① to ⑤ above, take tea samples, namely fresh leaf samples, withered samples, rolling samples, fermented samples, and finished product samples, and place them in a tea roasting and aroma-enhancing machine, and bake at 120℃ for 6 minutes; remove and let cool, then place them in the tea roasting and aroma-enhancing machine again, and dry at 80℃ with a moisture content ≤6%. The dried samples are used to determine the hydrocyanic acid content of the tea. The reference sample is commercially available almond-scented black tea from Guixin Tea Cooperative, and the control sample is a finished Meizhan black tea sample.

[0040] 3. Sensory Evaluation Method: Four technicians with senior tea appraiser qualifications conducted sensory evaluations of the dried fresh leaves, withered leaves, rolled leaves, fermented leaves, and finished tea samples. The reference sample was the commercially available almond-scented black tea from Guixin Tea Cooperative, and the control sample was Meizhan black tea.

[0041] 4. Determination of hydrocyanic acid content in tea samples

[0042] (1) Tea sample solution: Weigh 20g of tea sample (accurate to 0.001g), with two replicates for each sample, and place it in a 500mL steam distillation apparatus. Add about 200mL of water, seal the bottle tightly, and stir magnetically for 2 hours at room temperature. Then add 20mL of zinc acetate solution (100g / L) and 2.0g of tartaric acid, quickly connect the distillation apparatus, and insert the lower end of the condenser into the liquid surface of a 100mL conical flask ① containing 10mL of 20g / L sodium hydroxide solution. Perform steam distillation. When the distillate reaches approximately 100 mL, remove the conical flask ①. Simultaneously, insert the lower end of the condenser into the liquid surface of a 100 mL conical flask ② containing 10 mL of 20 g / L sodium hydroxide solution. Repeat distillation until approximately 80 mL of distillate is collected. Stop heating and continue collecting approximately 100 mL of distillate. Remove the conical flask ②. Remove the distillation flask ② and thoroughly stir and mix its contents. Then, insert the lower end of the condenser into the liquid surface of a 100 mL conical flask ③ containing 10 mL of 20 g / L sodium hydroxide solution. Perform steam distillation until approximately 50 mL of distillate is collected in the conical flask ③. Remove the conical flask ③. Transfer the distillate collected from conical flasks ①, ②, and ③ completely into a 250 mL (V1) volumetric flask and dilute to the mark with water. Measure 10 mL of the solution (V2) into a 25 mL colorimetric tube as the sample solution.

[0043] (2) Preparation of standard solutions: A cyanide analysis standard (50 μg / mL) was prepared in water, with the standard number GBW(E)080115. An intermediate standard solution of 1 μg / mL was then prepared using sodium hydroxide solution (2 g / L). 0.0 mL, 0.1 mL, 0.2 mL, 0.3 mL, 0.4 mL, and 0.5 mL of the intermediate standard solution were pipetted into 25 mL colorimetric tubes, and water was added to a final volume of 10 mL.

[0044] (3) Determination of cyanide content in tea samples: Add 1 mL of 10 g / L sodium hydroxide solution and 1 drop of phenolphthalein-ethanol indicator (10 g / L) to each of the tea sample solution and standard series solutions. Slowly adjust the solution with acetic acid solution (1+24) until the red color fades. Then add 5 mL of phosphate buffer solution [(0.5 mol / L) pH 7.0]. Incubate in a 37℃ constant temperature water bath for 10 min. Then add 0.25 mL of chloramine T (10 g / L) solution, stopper and shake to mix evenly, and let stand for 5 min. Then add 5 mL of isonicotinic acid-pyrazolone solution [weigh 1.5 g of isonicotinic acid and dissolve it in 24 mL of sodium hydroxide solution (20 g / L), add water to 100 mL, and weigh 0.25 g of pyrazolone and dissolve it in 20 mL of anhydrous ethanol. Mix the two solutions and shake well. Prepare immediately before use]. Add water to 25 mL and mix well. Incubate in a 37℃ constant temperature water bath for 40 min. Using a 2cm cuvette, the absorbance of the visible spectrophotometer is measured at a wavelength of 638nm by adjusting the zero point with the zero tube.

[0045] (4) The cyanide content (calculated as CN-) in the sample is calculated according to the formula:

[0046] X = A × 1000 / m × V 2 × V 1 × 1000

[0047] X - Cyanide content in sample (calculated as CN-), in milligrams per kilogram (mg / kg);

[0048] A - Determine the mass of cyanide in the sample solution (as CN-), in micrograms (μg);

[0049] 1000 - Conversion factor;

[0050] m - Sample mass, in grams (mg);

[0051] V1 - The volume of distilled liquid used for determination is measured in milliliters (mL);

[0052] V2 - Total volume of the sample distillate, in milliliters (mL).

[0053] The calculation results should be retained to three significant figures; the absolute difference between two independent measurements should not exceed 10% of the arithmetic mean.

[0054] 5. Determination of aroma components in tea

[0055] Accurately weigh 3.00 g of sample that has passed through a 40-mesh sieve and place it in a 250 mL headspace extraction bottle. Add 150 mL of boiling water and equilibrate in a 60 °C water bath for 5.0 min. Then, insert a 50 / 30 μm DVB / CAR / PDMS extraction head that has been pre-aged at 250 °C for 30 min at the GC-MS inlet. Perform headspace extraction for 60 min at 60 °C to enrich the aroma. After removing the extraction head, immediately insert it into the inlet of a Thermo Finigan TRACE DSQ GC-MS instrument for thermal desorption and adsorption for 5.0 min. Use high-purity helium gas (>99.99%), splitless injection at a flow rate of 1.0 mL / min; inlet temperature 250 °C, ECD detector temperature 250 °C; column temperature initial temperature 50 °C, hold for 5 min, increase to 180 °C at 3 °C / min, hold for 2 min, then increase to 250 °C at 10 °C / min, hold for 3 min. Helium flow rate: 1.0 mL / min; ionization method: EI; total ion current intensity: 100 mA; ion source temperature: 230 °C; mass spectrometry interface temperature: 280 °C; electron energy: 70 eV; electron multiplier tube voltage: 1800 V; mass scan range: 50–600 amu. Each sample was analyzed independently and repeatedly three times, and the average value was taken. The mass spectrometry data obtained by GC-MS were searched in the database, and the chemical structure and name of aroma substances were confirmed based on the retention time, base peak, mass-to-nucleus ratio, and relative abundance of volatile components. The peak area normalization method was used to analyze the percentage of the peak area of ​​each aroma component to the total peak area, which represents the relative content of the aroma component.

[0056] II. Results

[0057] 1. Sensory evaluation of fresh leaf samples, withered samples, rolled samples, fermented samples, finished product samples, reference samples, and control samples was conducted, and the results are shown in Table 1. The sensory evaluation results show that during the black tea production process, the dried samples after rolling already exhibited an almond aroma, while the fermented and finished samples had a rich and lasting almond aroma. The tea liquor of both the fermented and finished samples had a rich almond aroma.

[0058] Table 1. Sensory evaluation results of almond-scented black tea samples.

[0059]

[0060] 2. The relative content of hydrocyanic acid in tea leaves and benzaldehyde in aroma components are shown in Table 2. The processing of black tea reveals that the hydrocyanic acid content reaches its highest point in the final black tea sample, followed by the sample after fermentation. After approximately 15 hours of withering, the withered sample only had a 7.56 mg / kg higher content than the fresh leaf sample, but after 90 minutes of rolling, it increased by 13.40 mg / kg, indicating a sudden change in hydrocyanic acid content due to cell breakage during rolling. After 4.5 hours of fermentation, the hydrocyanic acid content in the fermented sample increased by 12.6%. After approximately 1 hour of drying, the hydrocyanic acid content increased by only 2.0 mg / kg, indicating that the hydrocyanic acid content in the fermented sample was already close to its peak after fermentation. The relative content of benzaldehyde aroma components also increased with increasing hydrocyanic acid content, showing a positive correlation.

[0061] Table 2. Results of determination of hydrocyanic acid and benzaldehyde content in tea leaves

[0062]

[0063] 3. Plant cyanogenic glycosides, under the action of enzymes, can decompose one molecule of amygdalinone into one molecule of benzaldehyde and one molecule of hydrocyanic acid. The higher the benzaldehyde content, the richer and longer-lasting the almond aroma of the tea. The ratio of hydrocyanic acid to benzaldehyde is 1:3.926. The above test results show that the rolling and fermentation processes are the main stages for the formation and accumulation of hydrocyanic acid. Sensory evaluation results also show that the rolled sample already has an almond aroma, and the aroma and taste of the fermented and finished samples are both rich in almond aroma. The tea is baked at 120℃ for 6 minutes; after cooling, it is placed in a tea roasting and aroma-enhancing machine and dried at 80℃ with a moisture content ≤6%, generally requiring about 1 hour. To save time, the hydrocyanic acid content in the fermented sample can be measured after fermentation to accurately determine the strength of the almond aroma in the tea. Alternatively, the hydrocyanic acid content can be more accurately obtained by measuring the final finished tea.

[0064] If it is necessary to determine more quickly whether tea tree germplasm resources have almond aroma and the strength of almond aroma, the content of hydrocyanic acid can be measured after rolling to determine the strength of almond aroma of tea tree resources or whether the variety has almond aroma. This saves about 6 hours (after fermentation time + drying time) compared to fermentation sample and about 7 hours compared to finished tea sample.

[0065] Based on the black tea making process, sensory evaluation results, and test results, combined with the black tea production technology, the grades are classified as shown in Table 3.

[0066] Table 3. Hydrocyanic Acid Content and Grade Classification of Tea

[0067]

[0068] Finally, it should be noted that the above embodiments are merely representative examples of the present invention. Obviously, the technical solution of the present invention is not limited to the above embodiments, and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the content disclosed in this invention should be considered within the scope of protection of this invention.

Claims

1. A method for determining the strength of almond aroma in tea trees and tea leaves, characterized in that, The strength of the almond aroma is determined by measuring the content of hydrocyanic acid; the higher the hydrocyanic acid content in tea, the stronger the almond aroma.

2. The method for determining the strength of almond aroma in tea trees and tea leaves according to claim 1, characterized in that, The method of determining the strength of almond aroma by measuring the content of hydrocyanic acid is to determine the content of benzaldehyde by measuring the content of hydrocyanic acid.

3. The method for determining the strength of almond aroma in tea trees and tea leaves according to claim 2, characterized in that, The benzaldehyde content is determined by measuring the content of hydrocyanic acid, with a molar ratio of hydrocyanic acid to benzaldehyde of 1:1 and a mass ratio of hydrocyanic acid:benzaldehyde = 1:3.

926.

4. The method for determining the strength of almond aroma in tea trees and tea leaves according to claim 1, characterized in that, The tea mentioned is black tea.

5. The method for determining the strength of almond aroma in tea trees and tea leaves according to claim 1, characterized in that, The tea leaves were measured after being kneaded.

6. The method for determining the strength of almond aroma in tea trees and tea leaves according to claim 1, characterized in that, The tea leaves were tested after fermentation.

7. A method for determining the benzaldehyde content in tea, characterized in that, The content of benzaldehyde was determined by measuring the content of hydrocyanic acid. The molar ratio of hydrocyanic acid to benzaldehyde in tea was 1:1; the mass ratio was hydrocyanic acid:benzaldehyde = 1:3.

926.

8. A method for determining the hydrocyanic acid content in tea, characterized in that, Includes the following steps: (1) Tea sample solution: The tea sample was steam distilled to obtain the sample solution; (2) Preparation of standard solutions: The standard substance for cyanide analysis in water is prepared into an intermediate standard solution using sodium hydroxide solution, and then water is added to prepare solutions of different concentrations; (3) Determination of cyanide content in tea samples: Add 1 mL of 10 g / L sodium hydroxide solution and 1 drop of phenolphthalein-ethanol indicator to each of the tea sample solution and standard series solutions. Slowly adjust the solution with acetic acid solution (1+24) until the red color fades. Then add 5 mL of phosphate buffer solution and keep warm in a 37℃ water bath for 10 min. Then add 0.25 mL of chloramine T solution, stopper and shake to mix evenly, and let stand for 5 min. Then add 5 mL of isonicotinic acid-pyrazolone solution, add water to 25 mL and mix well. Let stand in a 37℃ water bath for 40 min. Use a 2 cm cuvette and a visible spectrophotometer with the zero tube adjusted to zero to measure the absorbance at a wavelength of 638 nm. (4) The cyanide content (calculated as CN-) in the sample is calculated according to the formula: X = A × 1000 / m × V 2 × V 1 × 1000 X - Cyanide content in sample (calculated as CN-), in milligrams per kilogram (mg / kg); A - Determine the mass of cyanide in the sample solution (as CN-), in micrograms (μg); 1000 - Conversion factor; m - Sample mass, in grams (mg); V1 - The volume of distilled liquid used for determination is measured in milliliters (mL); V2 - Total volume of the sample distillate, in milliliters (mL); The calculation results should be retained to three significant figures; the absolute difference between two independent measurements should not exceed 10% of the arithmetic mean.

9. The method according to claim 8, characterized in that, The tea sample solution was prepared as follows: 20g of tea sample was weighed, with two replicates per sample, and placed in a 500mL steam distillation apparatus. Approximately 200mL of water was added, and the flask was sealed tightly. The mixture was magnetically stirred at room temperature for 2 hours. Then, 20mL of zinc acetate solution (100g / L) and 2.0g of tartaric acid were added. The distillation apparatus was quickly connected, and the lower end of the condenser was inserted below the surface of a 100mL conical flask ① containing 10mL of 20g / L sodium hydroxide solution. Steam distillation was performed, and when nearly 100mL of distillate was collected, conical flask ① was removed. Simultaneously, the lower end of the condenser was inserted below the surface of a 100mL conical flask ② containing 10mL of 20g / L sodium hydroxide solution. Distillation was repeated until approximately 80mL of distillate was collected. Heating was stopped, and nearly 100mL of distillate was collected. Conical flask ② was removed. The contents of conical flask ② were thoroughly stirred and mixed. The lower end of the condenser was then inserted below the surface of a 100mL conical flask ② containing 10mL of 20g / L sodium hydroxide solution. Steam distillation is performed with 20 g / L sodium hydroxide solution submerged in a 100 mL conical flask ③ until approximately 50 mL of distillate is collected. The conical flask ③ is then removed. The distillate collected in conical flasks ①, ②, and ③ is completely transferred to a 250 mL (V1) volumetric flask and diluted to the mark with water. 10 mL of this solution (V2) is measured and placed in a 25 mL colorimetric tube as the sample solution.

10. The method according to claim 8, characterized in that, The standard solution was prepared as follows: a cyanide analysis standard substance (50 μg / mL) with the standard substance number GBW(E)080115 was prepared with sodium hydroxide solution (2 g / L) to form an intermediate standard solution of 1 μg / mL; 0.0 mL, 0.1 mL, 0.2 mL, 0.3 mL, 0.4 mL and 0.5 mL of the intermediate standard solution were respectively measured with a pipette and placed in 25 mL colorimetric tubes, and water was added to 10 mL.

Images