GB2618649A

GB2618649A - Method for improving quality of black tea juice with complex enzymes

Info

Publication number: GB2618649A
Application number: GB2303355.8A
Authority: GB
Inventors: Xu Yong-Quan; Liang Shuang; Yin Jun-Feng
Original assignee: Chinese Academy Of Agricultural Sciences Tea Res Institute
Current assignee: Chinese Academy Of Agricultural Sciences Tea Res Institute
Priority date: 2022-03-15
Filing date: 2023-03-08
Publication date: 2023-11-15
Anticipated expiration: 2043-03-08
Also published as: GB202303355D0; CN114747642B; CN114747642A; GB2618649B

Abstract

A method for improving the quality of black tea juice with complex enzymes comprising the process steps: freezing and withering fresh tea leaves picked in summer and autumn; subjecting the frozen withered leaves to homogenization treatment to obtain a homogenate; extracting the green tea in boiling water; adding tannase to the green tea extract to obtain a hydrolysed green tea extract; pouring the homogenate into the hydrolysed green tea extract, and adding β-glucosidase and cellulase for fermentation treatment to obtain a fermented solution. The fermented solution is subjected to microwave treatment before the hot black tea juice in filtered and then cooled to room temperature. The resulting black tea juice has a high content of theaflavin and a sweet aroma but has a weaker grass aroma. Preferably, the tannase has an activity of 5,000 U/g, the β-glucosidase has an activity of 100 U/g, and the cellulase has an activity of 50,000 U/g. Preferably, the ratio of the β-glucosidase to the cellulase to the fermentation solution is (0.5-2): (0.5-2):4,000 (w/w/v).

Description

METHOD FOR IMPROVING QUALITY OF BLACK TEA JUICE

WITH COMPLEX ENZYMES

FIELD OF TECHNOLOGY

The present disclosure belongs to the technical field of processing of tea leaves, and specifically relates to a method for improving the quality of a black tea juice with complex enzymes.

BACKGROUND

It) As a main substance affecting the flavor of black tea, theaflavin (TF) plays a decisive role in the sensory quality, such as color, aroma and taste, of black tea. According to recent studies, it is proved that TF has potential benefits for human health, such as preventing oxidation, lowering of blood lipids, treating and preventing cardiovascular diseases, resisting and preventing cancer, which makes TF a global concern. Since the 1960s, many tea-producing countries have tried to process fresh tea leaves as raw materials into tea drinks directly through liquid-fermentation, in order to simplify production processes of traditional tea drinks. The tea drinks not only contain many bioactive substances, but also have a red and bright color, a fresh and mellow taste, and a sweet aroma with a light grassy. According to CN108208216A, a double fermentation method for aerobic fermentation of a tea concentrate is used for increasing the content of the theaflavins (TFs). However, a relationship between catechins as a substrate and the TFs as a product is not deeply understood. According to CN113080281A, a liquid-fermentation method combined with tannase for changing the ratio of catechins is used for further increase of TFs content. However, the grassy aroma is not weakened. The method has not been widely accepted by entrepreneurs Cellulase can be used for degrading cellulose into oligosaccharides, and lysing cell walls promoting the dissolution of intercellular and intracellular substances. As a glycosidase for specifically hydrolyzing a non-reducing fl-D-glycosidic bond, fl-glucosidase can be used for hydrolyzing glycosidic flavor precursors rich in tea leaves to release natural aromatic substances, such as linalool, geraniol and other flowery substances, as well as benzyl alcohol and other fruity substances.

At present, most tea drinks on the market taste bitter in aftertaste and not mellow enough overall. The reason is that their initial tea components mainly come from tea powders or tea leaves. The increase of their dosage will increase the bitter and astringent taste of tea drinks. However, when a tea concentrate is added, the taste of the tea drinks get improved. Due to the lack of sugar for the modification of aftertaste, unsweetened tea even has greater bitterness.

However, when a tea concentrate is added, the aftertaste is improved, and the sweetness after taste get enhanced. In recent years, the area of tea gardens and the production capacity of the tea leaves in China have increased rapidly, but the tea leaves consumption has been increasing slowly. 80%-90% of tea leaves in Chinese tea gardens are not picked in late spring, summer and autumn, so that these middle-and low-grade tea leaf resources, accounting for more than 50% of the capacity, will grow and die without outside interference, resulting in a low utilization rate and a great waste of tea leaf resources. Therefore, the preparation of black tea from the tea leaves picked in summer and autumn is carried out in the industry. High content of esterified catechins in them is hydrolyzed and oxidized by endogenous enzymes of fresh tea leaves, so that the bitterness of ultimate products is reduced, and the utilization way of the tea leaves picked in summer and autumn is expanded.

In view of the situation, a method for improving the aroma quality of black tea juice with complex enzymes is designed in the present disclosure based on the previous studies. Meanwhile, a high content of TFs is maintained, and a high-TF black tea juice with simple production technology, low cost and good aroma quality is obtained.

SUMMARY

In view of the problems in the prior art, the present disclosure aims to design and provide a technical solution of a method for improving the quality of a black tea juice with complex enzymes. Through treatment based on this method, the characteristic of a high content of theaflavins can be maintained, a grassy aroma can be weakened, and the aroma quality can be improved.

The present disclosure is specifically realized by the following technical solution A method for improving the quality of a black tea juice with complex enzymes includes the following process steps: 1) subjecting fresh tea leaves picked in summer and autumn to freezing and withering treatment to obtain frozen withered leaves; 2) adding boiling water to green tea for extraction treatment to obtain a green tea extract; 3) adding tannase to the green tea extract obtained in step 2) for enzymolysis treatment to obtain a hydrolyzed green tea extract; 4) subjecting the frozen withered leaves obtained in step 1) to homogenization treatment to obtain a homogenate; 5) pouring the homogenate obtained in step 4) into the hydrolyzed green tea extract obtained in step 3), and adding fl-glucosidase and cellulase for fermentation treatment to obtain a fermentation solution; and 6) subjecting the fermentation solution obtained in step 5) to microwave treatment, conducting filtration on a resulting hot black tea juice, and then cooling to room temperature. Further, in step 1), the freezing and the withering are conducted under the following conditions: the freezing is conducted at a temperature of -20°C to -80°C for more than 2 hours, 15 the withering is conducted at an environmental temperature of 20°C to 25°C, and thawing is conducted for 1 hour.

Further, in step 2), the extraction with the boiling water is conducted at a tea-water ratio of 1:(40-60) (w/v) for 15-25 min. Further, in step 3), the treatment with the tannase is conducted under the following conditions: the tannase has an activity of 5,000 (J/g, a weight ratio of the tannase to the green tea is 1:(400-600), and the enzymolysis is conducted at a temperature of 45-55°C for 7-8 min. Further, in step 4), the homogenization is conducted at a tea-water ratio of 1:(40-60) (w/v) at a grade 2 for 1-3 min. Further, in step 5), the fl-glucosidase has an activity of 100 U/g, the cellulase has an activity of 50,000 U/g, a ratio of the fl-glucosidase to the cellulase to the fermentation solution is (0.5-2):(0.5-2):4,000 (w/vv/v), and the temperature of the fermentation solution is controlled at 30-40°C; and a defoaming agent that is 0.2% of the volume of the fermentation solution is added for aerated fermentation at uniform speed for 1 hour, and the aeration volume is 150 times the total volume of the fermentation solution.

Further, in step 6), the microwave treatment is conducted by heating to 90°C.

The method for improving the quality of a black tea juice with complex enzymes is reasonable in design. The fresh tea leaves picked in summer and autumn are subjected to the freezing and withering treatment. Compared with withering at room temperature, the withering time can be shortened, the activity of polyphenol oxidase is increased, the liquid-fermentation efficiency can be improved. Meanwhile, grassy aroma is reduced by reducing the added amount of fresh leaves. The green tea extract is subjected to hydrolysis with the tannase, so that ester catechin content is decreased, non-ester catechin content is increased, and the ratio of the non-ester catechin to the ester catechin is changed. During the homogenization treatment, spaced homogenization at medium or low speed is conducted, so that the activity of the polyphenol oxidase can be maintained. During the aerated fermentation, air is introduced to replace pure oxygen, so that the production cost can be reduced. The cellulase is added for breaking the cell walls of tea leaves, so as to promote the release of glycosidic aroma precursors, and the flglucosidase is used for hydrolyzing glycosides so as to obtain more flowery and fruity volatiles. During the microwave heating, the temperature is raised rapidly, and uniform heating is conducted. After the present disclosure is adopted, not only a high content of theaflavins in black tea juice for drinking can be maintained, but also grassy aroma can be weakened, and an obvious sweet aroma is obtained. Moreover, the content of flowery and fruity volatiles is significantly increased, and both the color and aroma quality are improved.

DESCRIPTION OF THE EMBODIMENTS

The process of the present disclosure is further illustrated below in combination with a method for improving the aroma quality of a high-theaflavins black tea juice in embodiments. Example 1: A method for improving the quality of a black tea juice with complex enzymes Step one: Raw fresh tea leaf materials with one bud and four leaves (Longjing 43) picked in the middle of September was subjected to freezing and withering treatment, where the freezing was conducted at -20°C for 4 hours, the withering was conducted at an environmental temperature of 25°C, and thawing was conducted for 1 hour.

Step two: 4 g of low-grade green tea was placed into a conical flask, and 200 mL of boiling water was poured for extraction for 20 min to prepare a green tea extract, where a tea-water ratio was 1:50.

Step three: 8 mg of 5,000 U/g tannase was added to the green tea extract obtained in step (2) for enzymolysis at 50°C for 8 min to obtain an hydrolyzed green tea extract.

Step four: 6 g of frozen withered leaves obtained in step one were weighed for homogenization treatment with 200 naL of water at a grade 2 (Philips blender 1-1R2084) for 30 s for a total of 4 times.

Step five: A homogenate obtained in step four was poured into the hydrolyzed green tea extract, 1 g, namely 0.25% (w/v), offi-glucosidase and 0.1 g, namely 0.25%0 (w/v), of cellulase were added, and a defoaming agent that was 0.2% of the volume of a fermentation solution was added for aerated fermentation at 35°C for 1 hour, where the aeration rate was 1 L/min, and the aeration volume was 150 times the total volume of the fermentation solution.

Step six: A fermentation solution obtained in step five was subjected to microwave treatment, heated to 90°C, filtered with a 500-mesh filter cloth, and then cooled to room temperature to obtain a black tea juice for drinking.

Table 1 Assessment of a black tea juice: 20 ml of the black tea juice for drinking was taken and poured into 80 ml of pure water at 50°C Example 2: A method for improving the quality of a black tea juice with a complex 20 enzyme Step one: Raw fresh tea leaf materials with one bud and four leaves (Longjing 43) picked in the middle of October was subjected to freezing and withering treatment, where the freezing was conducted at -40°C for 24 hours, the withering was conducted at an environmental Comment Aroma Score Treatment Comment Score Color A little sweet aroma, and a 91 light piled aroma A little grassy, fresh, and a 82 light coarse aroma, less sweet aroma, Little grassy, and a light piled aroma Little sweet aroma Control group Treatment with cellulase Treatment with /7-glucosidase Treatment with complex

enzymes (Example 1)

Orange-red Orange-red 87 Red and little 90 bright Red and 94 bright temperature of 20°C, and thawing was conducted for 1 hour.

Step two: 4g of low-grade green tea was placed into a conical flask, and 200 mL of boiling water was poured for extraction for 20 min to prepare a green tea extract, where a tea-water ratio was 1:50.

Step three: Then, 8 mg of 5,000 U/g tannase was added to the green tea extract obtained in step (2) for enzymolysis at 55°C for 8 mm to obtain an hydrolyzed green tea extract.

Step four: 6 g of frozen withered leaves obtained in step one were weighed for homogenization treatment with 200 mL of water at a grade 2 (Philips blender BR2084) for 30 s for a total of 4 times.

Step five: A homogenate obtained in step four was poured into the hydrolyzed green tea extract, 1 g, namely 0.25% (w/v), offi-glucosidase and 0.1 g, namely 0.25°/00 (vv/v), of cellulase were added, and a defoaming agent that was 0.2% of the volume of a fermentation solution was added for aerated fermentation at 30°C for 1 hour, where the aeration rate was 1 L/min, and the aeration volume was 150 times the total volume of the fermentation solution.

Table 2 Assessment of a black tea juice: 20 mL of the black tea juice was taken and poured into 80 mL of pure water at 50°C Color Aroma Treatment Comment Score Comment Score Control group Treatment with cellulase Treatment with /3-glucosidase Treatment with complex

enzymes (Example 1)

Dark orange-red Orange-red and bright Red and less bright Red and bright 83 A little grassy, fresh, and a 82 coarse aroma, a light sweet aroma 88 Little grass, and a light piled 85 aroma Little sweet aroma 87 92 A little sweet aroma 90 Example 3: A method for improving the quality of a black tea juice with a complex enzyme Step one: Raw fresh tea leaf materials with one bud and four leaves (Longjing 43) picked in the middle of October was subjected to freezing and withering treatment, where the freezing 5 was conducted at -60°C for 4 hours, the withering was conducted at an environmental temperature of 20°C, and thawing was conducted for 1 hour.

Step two: 4g of low-grade green tea was placed into a conical flask, and 200 mL of boiling water was poured for extraction for 25 min to prepare a green tea extract, where a tea-water ratio was 1:50.

Step three: 8 mg of 5,000 U/g tannase was added to the green tea extract obtained in step (2) for enzymolysis at 45°C for 7min to obtain an hydrolyzed green tea extract.

Step four: 4 g of frozen withered leaves obtained in step one were weighed for homogenization treatment with 200 mL of water at a grade 2 (Philips blender 1-1R2084) for 30 s for a total of 4 times.

Step five: A homogenate obtained in step four was poured into the hydrolyzed green tea extract, and 0.25% (w/v) of fl-glucosidase and 0.1 g, namely 0.25%0 (w/v), of cellulase were added for aerated fermentation at 40°C for 1 hour, where the aeration rate was 1 L/min. Step six: A fermentation solution obtained in step five was subjected to microwave treatment, heated to 90°C, filtered with a 500-mesh filter cloth, and then cooled to room temperature to obtain a black tea juice for drinking.

Table 3 Assessment of a black tea juice: 20 mL of the black tea juice was taken and poured into 80 nth of pure water at 50°C Color Aroma Comment Score 83 A little grass aroma, fresh, 80 and a light coarse aroma 86 Little grassy, and a piled 84 aroma 91 Little sweet aroma 88 94 Obvious sweet aroma 92 Treatment Control group Treatment with cellulase Treatment with fl-glucosidase Treatment with a complex

enzymes (Example 1)

Comment Score Dark orange-red Orange-red Red and little bright Red and bright After the treatment with the tannase in Example 1 and Example 2, the ratio of non-ester catechins to ester catechins is greater than 10, and subsequent fermentation is facilitated so as to obtain a high content of theaflavins, as shown in Table 4.

Table 4 Hydrolysis of catechins in green tea extract with tannase Ester Non-ester Non-ester EGC/E catechins catechins catechins/ester

GCG

(mg/mL) (mg/mL) catechins 0.8 2.1 0.3 0.1 0.04 1.6 40 130.7 0.1 1.5 15 23.0 Green tea extract Treatment with

tannase (Example 1)

Treatment with

tannase (Example 2)

On the basis of Example 1, the step of treatment with an enzyme was changed. Treatment with an enzyme was not conducted in a control group, and treatment with tannase was conducted in Comparative Example 1, and treatment with tannase and cellulase was conducted in Comparative Example 2, and treatment with tannase and f3-glucosidase was conducted in Comparative Example 3. Results are as shown in Tables 5 and 6.

Table 5 Test results of theaflavins in a black tea juice (GB/T 30483-2013) Tea sample Content of theaflavins (mg/m1)) TF TFs (total content) Control group 21.326+0.073e 223.505+0.799d 245.570+0.060c 247.942±0.860b 61.372±4.184d 266.893+1.624c 284.391+0.176b 287.070+0.474b (I) Treatment with tannase 263.963±1.213a 312.214±0.094a (Z Treatment with tannase and cellulase (3) Treatment with tannase and fl-glucosidase (4) Treatment with tannase, cellulase, and /3-glucosidase Table 6 OAV analysis of the aroma of a black tea juice treated with a complex enzyme Thres OAV hold Compound value (tig/L Arom a type Control group CL Hexanal (E)-2-licxenal (E)-3-hcxenol V-hcxanol Methyl salicylate Benzaldchyd Grass 4.5 Grass Grass Grass 5.6 Grass 350 Baked 0.74+0.03c 0.67+0.02c 0.63+0.01c 0.32+0.01d 0.11±0.00b 0.13±0.00b 1.99+0.04b 1.24+0.00c 0.68+0.046 0.92+0.03a 0.01+0.00b 0.01+0.00b 0.32+0.02a 0.27+0.02abc 4.28±0.28c 5.36+0.5 lab 1.68+0.02a 0.93+0.05a 0. 14±0.00b 1.29+0.00c 0.88+0.01a 0.03+0.00a 0.24+0.01c 4.90±0.09bc 1.28+0.0 lb 0.71+0.03b 0.15±0.00b 1.30+0.00c 0.99+0.08a 0.03+0.00a 0.29+0.01 ab 6.17+0.11a 0.87±0.07be 114+0 14ab 1.3210 04a 1.52+0.30a 0.08+0.00c 506.33+21.15b 0.43+0.18ab 0.02+0.00bc 0.07±0.00c 30.29+I.99c 0.09+0.00a 575.59+30.I2a 0.60+0.06a 0.03+0.00a 0.08±0.00ab 0.08+0.00ab 526.05+8.26b 0.54+0.13ab 0.03+0.00ab 0.08±0.00be 0.09+0.00ab 590.52+8.40a 0.47+0.01 ab 0.03+0.00a 0.09+0.00a 43.60+0.8 I a 37.85+3.58ab 34.62+0 67bc 0.57+0.05d 0.06+0.01e 0.30±0.06a 2.5 I +0. Ilta 0.5 1 +0.03c 0.01+0.00b D-limonenc 34 Fruity 0.26+0.03bc Citral 53 Fruity 4.15±0.45c Flowe 4 ry and 0.5410.08c fruity Flowe 0.09+0.01ab Iy Howe Linalool 0.22 509.36+2.346 Flowe Nonanal 1.1 0.30+0.02b Phenylethan Howe ol Flowe Nerol 49 0.08+0.0 1 b y Howe rv Phenylacetal dehyde Linalool oxide 11 0.02+0.00c Gcraniol 7.5 29.32+3.19c Note: OAV is represented as relative concentration of a compound/threshold valve of the compound; when OAV is greater than 1, it indicates that the compound can be smelled, and thus the aroma quality is affected; and different letters indicate significant differences (P<0.05). According to the method for improving the quality of black tea juice, namely, a method for producing a black tea juice by combining tannase, cellulase, and /3-glucosidase, provided by the present disclosure, the color and aroma quality of the black tea juice can be obviously improved, the influence of grassy aroma can be weakened. Meanwhile, the characteristic of a high content of theaflavins is maintained. Specific effects are as shown as follows: The sensory color is improved and changed from "orange-red" in the control group to "red and bright" in the complex enzymes treatment group. The sensory aroma quality is improved and changed from "A little grassy" in the control group to "Obvious sweet aroma (without grassy aroma)" in the complex enzymes treatment group (with reference to Tables 1-3). According to the test results of theaflavins, the content of theaflavin (TF) is increased from 21 mg/mL in the control group to 263 ing/naL, which is increased by nearly 12 times, and the total content of theaflavins (TFs) is also increased by 4 times (with reference to Table 5). According to the OAV analysis, compared with the control group, the complex enzymes treatment group has the advantages that the OAV of flowery substances such as linalool, geraniol, and phenacetaldehyde, as well as the OAV of fruity citral can be significantly increased. Meanwhile, the OAV of N-hexanol is significantly decreased (with reference to Table 6).

The descriptions above are merely general embodiments of the present disclosure, and the implementation scope of the present disclosure cannot be limited thereby. All equivalent changes and modifications made according to the patent scope of the present disclosure and the content of the specification shall still fall within the scope covered by the present disclosure. I'

Claims

CLAIMS1. A method for improving the quality of a black tea juice with complex enzymes, comprising the following process steps: 1) subjecting fresh tea leaves picked in summer and autumn to freezing and withering treatment to obtain frozen withered leaves; 2) adding boiling water to green tea for extraction treatment to obtain a green tea extract; 3) adding tannase to the green tea extract obtained in step 2) for enzymolysis treatment to obtain an hydrolyzed green tea extract; 4) subjecting the frozen withered leaves obtained in step 1) to homogenization treatment to obtain a homogenate; 5) pouring the homogenate obtained in step 4) into the hydrolyzed green tea extract obtained in step 3), and adding fl-glucosidase and cellulase for fermentation treatment to obtain a fermentation solution; and 6) subjecting the fermentation solution obtained in step 5) to microwave treatment, conducting filtration on a resulting hot black tea juice, and then cooling to room temperature 2. The method for improving the quality of a black tea juice with complex enzymes according to claim 1, wherein in step 1), the freezing and the withering treatment are conducted under the following conditions: the freezing is conducted at a temperature of -20°C to -80°C for more than 2 hours, the withering is conducted at an environmental temperature of 20°C to 25°C, and thawing is conducted for 1 hour 3. The method for improving the quality of a black tea juice with a complex enzyme according to claim 1, wherein in step 2), the extraction with the boiling water is conducted at a tea-water ratio of 1:(40-60) (w/v) for 15-25 min. 4. The method for improving the quality of a black tea juice with complex enzymes according to claim 1, wherein in step 3), the treatment with the tannase is conducted under the following conditions: the tannase has an activity of 5,000 (J/g, a weight ratio of the tannase to the green tea is 1(400-600), and the enzymolysis is conducted at a temperature of 45-55°C for 7-8 min. 5. The method for improving the quality of a black tea juice with complex enzymes according to claim 1, wherein in step 4), the homogenization is conducted at a tea-water ratio of 1:(40-60) (w/v) at a grade 2 for 1-3 min 6. The method for improving the quality of a black tea juice with complex enzymes according to claim 1, wherein in step 5), the /3-glucosidase has an activity of 100 U/g, the cellulase has an activity of 50,000 U/g, a ratio of the fl-glucosidase to the cellulase to the fermentation solution is (0.5-2): (0.5-2):4,000 (w/w/v), and the temperature of the fermentation solution is controlled at 30-40°C; and a defoaming agent that is 0.2% of the volume of the fermentation solution is added for aerated fermentation at uniform speed for 1 hour, and the aeration volume is 150 times the total volume of the fermentation solution.7. The method for improving the quality of a black tea juice with complex enzymes according to claim 1, wherein in step 6), the microwave treatment is conducted by heating to 90°C