METHOD FOR LIQUID FERMENTATION OF BLACK TEA JUICE BY USING AGED GREEN TEA

Abstract

The present disclosure discloses a method for liquid fermentation of black tea juice by using aged green tea and belongs to the technical field of tea leaf processing. The method comprises the following process steps: mixing aged green tea with hot water for a water bath-assisted extraction; adding a tannase into a crude catechin extract for a water bath-assisted enzymolysis; freeze-withering fresh tea leaves; homogenizing the freeze-withered leaves; pouring a homogenate into a primarily enzymolyzed crude catechin extract, adding a β-glucosidase for secondary enzymolysis and performing fermentation; and treating a fermentation broth by microwave, and performing filtration and cooling to a room temperature.

Claims

1. A method for liquid fermentation of black tea juice by using aged green tea, comprising the following process steps: 1) mixing aged green tea with hot water for a water bath-assisted extraction to prepare a crude catechin extract; 2) adding a tannase into the crude catechin extract obtained in step 1) for a water bath-assisted enzymolysis to obtain a primarily enzymolyzed crude catechin extract; 3) freeze-withering fresh tea leaves; 4) homogenizing the freeze-withered leaves obtained in step 3); 5) pouring a homogenate obtained in step 4) into the primarily enzymolyzed crude catechin extract, adding a β-glucosidase for secondary enzymolysis and performing fermentation; and 6) treating a fermentation broth obtained in step 5) by microwave heating, and performing filtration and cooling to a room temperature to obtain black tea juice by liquid fermentation using aged tea.

2. The method for liquid fermentation of black tea juice by using aged green tea according to claim 1, wherein the hot water in step 1) has a temperature of 85° C. and the water bath-assisted extraction is conducted for 20 min at a tea-to-water ratio w/v of 1:50.

3. The method for liquid fermentation of black tea juice by using aged green tea according to claim 1, wherein in step 2), the tannase has an enzyme activity higher than 5,000 U/g and is added at an amount w/w of 0.2%.

4. The method for liquid fermentation of black tea juice by using aged green tea according to claim 1, wherein in step 2), the water bath-assisted enzymolysis is performed at 50° C. for 7.5 min.

5. The method for liquid fermentation of black tea juice by using aged green tea according to claim 1, wherein in step 3), during the freeze-withering, the fresh tea leaves picked in any season are frozen at a temperature of −20° C. to −80° C. for 2 h or more and thawed for 1 h.

6. The method for liquid fermentation of black tea juice by using aged green tea according to claim 1, wherein in step 4), the homogenizing is performed with a ratio of fresh leaves and water w/v at 1:50 and at a 2nd gear for 2 min with an interval of 5-10 s every 30 s.

7. The method for liquid fermentation of black tea juice by using aged green tea according to claim 1, wherein in step 5), the β-glucosidase has an enzyme activity higher than 100 U/g and is added at an amount w/v of 1:400.

8. The method for liquid fermentation of black tea juice by using aged green tea according to claim 1, wherein in step 5), the fermentation is performed to control a temperature of the fermentation broth to 35° C., with a defoaming agent at 0.2% of a volume of the fermentation broth and in a manner of uniform ventilation for 1 h with a ventilation capacity 150 times of a total volume of the fermentation broth.

9. The method for liquid fermentation of black tea juice by using aged green tea according to claim 1, wherein in step 6), the microwave heating is performed to 90° C.

Description

DESCRIPTION OF THE EMBODIMENTS

[0026] The present invention is further illustrated by the following description in conjunction with the embodiments.

Example 1 Method for Liquid Fermentation of Black Tea Juice by Using Aged Green Tea

[0027] (1) fresh Longjing 43 tea leaves (autumn tea) with one bud and four leaves picked in mid-October were freeze-withered at a freezing temperature of −20° C. for 4 h and thawed for 1 h;

[0028] (2) 4 g of broken aged green tea (20-mesh) was put into a conical flask and 200 mL of 85° C. hot water was poured for extraction for 20 min to prepare a crude catechin extract;

[0029] (3) 8 mg (addition amount w/w of 0.2%) of a tannase at 5,000 U/g was added into the crude catechin extract obtained in step (2) for enzymalysis at 50° C. for 7.5 min to obtain an enzymolyzed crude catechin extract;

[0030] (4) 6 g of the freeze-withered leaves obtained in step (1) were homogenized with 300 mL of water at a 2nd gear for 30 s×4;

[0031] (5) a homogenate obtained in step (4) was poured into the enzymolyzed crude catechin extract, 1 g of a β-glucosidase (i.e. 0.25% (w/v)) was added at 35° C., a defoaming agent at 0.2% of a volume of a fermentation broth was added, and ventilation fermentation was performed at a ventilation rate of 1 L/min for 1 h; and

[0032] (6) a fermentation broth obtained in step (5) was heated by microwave to 90° C., the heated fermentation broth was filtered using a 500-mesh filter cloth, and the filtered fermentation broth was cooled to a room temperature to obtain black tea juice by liquid fermentation using aged tea.

TABLE-US-00001 TABLE 1 Assessment of black tea juice Color Aroma Taste Tea sample Comment Score Comment Score Comment Score (1) Aged tea Yellow and 7.6 Mature and 6.2 Heavy 4.2 bright stale odor bitter and stale taste (2) Aged tea-tea juice Reddish 6.5 Grass aroma 6.0 Moderately 7.0 subjected to liquid brown and mellow and fermentation turbid slightly astringent (3) Aged tea + tannase Moderately 8.3 Plant odor and 7.8 Moderately 7.8 treatment-tea juice red and slightly stuffy sweet and subjected to liquid bright and sweet odor mellow and fermentation slightly astringent (4) Aged tea + Bright red 8.8 Sweet and 8.2 Moderately 8.2 tannase + β-glucosidase delicate-flower sweet and treatment-tea juice tea aroma with mellow and subjected to liquid slight slightly fermentation astringency astringent

Example 2 Method for Liquid Fermentation of Black Tea Juice by Using Aged Green Tea

[0033] (1) fresh Longjing 43 tea leaves (Winter tea) with one bud and two leaves picked in mid-December were freeze-withered at a freezing temperature of −20° C. for 24 h and thawed for 1 h;

[0034] (2) 4 g of broken aged green tea (20-mesh) was put into a conical flask and 200 mL of 85° C. hot water was poured for extraction for 20 min to prepare a crude catechin extract;

[0035] (3) 8 mg (addition amount w/w of 0.2%) of a tannase at 5,000 U/g was added into the crude catechin extract obtained in step (2) for enzymalysis at 50° C. for 7.5 min to obtain an enzymolyzed crude catechin extract;

[0036] (4) 6 g of the freeze-withered leaves obtained in step (1) were homogenized with 300 mL of water at a 2nd gear for 30 s×4;

[0037] (5) a homogenate obtained in step (4) was poured into the enzymolyzed crude catechin extract, 1 g of a β-glucosidase (i.e. 0.25% (w/v)) was added at 35° C., a defoaming agent of 0.2% of a volume of a fermentation broth was added, and ventilation fermentation was performed at a ventilation rate of 1 L/min for 1 h; and

[0038] (6) a fermentation broth obtained in step (5) was heated by microwave to 90° C., the heated fermentation broth was filtered using a 500-mesh filter cloth, and the filtered fermentation broth was cooled to a room temperature to obtain black tea juice by liquid fermentation using aged tea.

TABLE-US-00002 TABLE 2 Assessment of black tea juice Color Aroma Taste Tea sample Comment Score Comment Score Comment Score (1) Aged tea Yellow 5.0 Mature odor 2.8 Heavy 4.2 and bright bitter and stale taste (2) Aged tea-tea juice Reddish 4.0 Tea aroma with 5.2 Moderately 7.0 subjected to liquid brown and plant odor mellow and fermentation slightly slightly turbid astringent (3) Aged tea + tannase Slightly 7.5 Delicate-flower 7.2 Moderately 7.8 treatment-tea juice deep tea aroma sweet and subjected to liquid reddish mellow and fermentation slightly astringent (4) Aged tea + Red and 8.4 Delicate-flower 8.0 Moderately 8.2 tannase + β-glucosidase bright tea aroma with sweet and treatment-tea juice sweet aroma mellow and subjected to liquid slightly fermentation astringent

Example 3 Method for Liquid Fermentation of Black Tea Juice by Using Aged Green Tea

[0039] (1) fresh Longjing 43 tea leaves (Winter tea) with one bud and two leaves picked in mid-December were freeze-withered at a freezing temperature of −20° C. for 4 h and thawed for 1 h;

[0040] (2) 4 g of low-grade green tea was put into a conical flask and 200 mL of 85° C. hot water was poured for extraction for 20 min to prepare a crude catechin extract;

[0041] (3) 8 mg (addition amount w/w of 0.2%) of a tannase at 5,000 U/g was added into the crude catechin extract obtained in step (2) for enzymalysis at 50° C. for 7.5 min to obtain an enzymolyzed crude catechin extract;

[0042] (4) 4 g of the freeze-withered leaves obtained in step (1) were homogenized with 200 mL of water at a 2nd gear for 30 s×4;

[0043] (5) a homogenate obtained in step (4) was poured into the enzymolyzed crude catechin extract, 1 g of a β-glucosidase (i.e. 0.25% (w/v)) was added at 35° C., a defoaming agent at 0.2% of a volume of a fermentation broth was added, and ventilation fermentation was performed at a ventilation rate of 1 L/min for 1 h; and

[0044] (6) a fermentation broth obtained in step (5) was heated by microwave to 90° C., the heated fermentation broth was filtered using a 500-mesh filter cloth, and the filtered fermentation broth was cooled to a room temperature to obtain black tea juice by liquid fermentation using aged tea.

TABLE-US-00003 TABLE 3 Assessment of black tea juice Color Aroma Taste Tea sample Comment Score Comment Score Comment Score (1) Aged tea Yellow and 7.6 Mature and 6.2 Heavy 4.2 bright stale odor bitter and stale taste (2) Aged tea-tea juice Reddish 6.5 Grass aroma 6.0 Moderately 7.0 subjected to liquid brown and mellow and fermentation turbid slightly astringent (3) Aged tea + tannase Moderately 8.3 Plant odor and 7.8 Moderately 7.8 treatment-tea juice red and slightly stuffy sweet and subjected to liquid bright and sweet odor mellow and fermentation slightly astringent (4) Aged tea + Bright red 8.8 Sweet and 8.2 Moderately 8.2 tannase + β-glucosidase delicate-flower sweet and treatment-tea juice tea aroma with mellow and subjected to liquid slight slightly fermentation astringency astringent

TABLE-US-00004 TABLE 4 Detection of theaflavins in black tea juice (GB/T 30483-2013) Theaflavin (TF) content (μg/mL) Tea sample TF TFs (total content) (1) Aged tea — — (2) Aged tea-tea juice subjected  21.326 ± 0.074.sup.b  61.373 ± 4.185.sup.c to liquid fermentation (3) Aged tea + tannase 193.846 ± 0.514.sup.a 258.757 ± 0.429.sup.a treatment-tea juice subjected to liquid fermentation (4) Aged 191.906 ± 0.906.sup.b 237.378 ± 0.340.sup.b tea + tannase + β-glucosidase treatment-tea juice subjected to liquid fermentation

[0045] Note: it should be noted that compared with tea sample (3), the β-glucosidase (lower activity with an addition amount of 1 g) in the “3-glucosidase treatment” in tea sample (4) would complex with theaflavins (TFs), thus the total content of TFs was decreased, a certain amount of the TFs was lost, but the tea has better color, aroma and taste (Table 3).

TABLE-US-00005 TABLE 5 Odor activity value (OAV) analysis of aroma components in black tea juice (OAV = compound concentration/threshold and OAV > 1 means the compound can be smelled) Threshold OAV Compound (μg/L) (1) (2) (3) (4) Hexanal 4.5  0.16 ± 0.03.sup.c  0.34 ± 0.02.sup.bc  0.38 ± 0.04.sup.b  1.09 ± 0.08.sup.a (E)-2-hexenal 17  0.02 ± 0.01.sup.c  0.06 ± 0.02.sup.bc  0.08 ± 0.01.sup.b  0.12 ± 0.01.sup.a (E)-3-hexen-l-ol 110  0.00 ± 0.00.sup.b  0.22 ± 0.05.sup.a  0.19 ± 0.02.sup.a  0.26 ± 0.00.sup.a n-hexanol 5.6  0.08 ± 0.01.sup.b  2.04 ± 0.42.sup.a  1.94 ± 0.16.sup.a  2.40 ± 0.03.sup.a Methyl salicylate 40  0.03 ± 0.01.sup.c  0.49 ± 0.08.sup.a  0.39 ± 0.02.sup.ab  0.36 ± 0.01.sup.b Benzaldehyde 350  0.01 ± 0.00.sup.b  0.01 ± 0.00.sup.b  0.01 ± 0.00.sup.b  0.02 ± 0.00.sup.a D-limonene 34  0.01 ± 0.00.sup.b  0.18 ± 0.03.sup.a  0.16 ± 0.00.sup.a  0.17 ± 0.00.sup.a Benzyl alcohol 20000  0.00 ± 0.00  0.00 ± 0.00  0.00 ± 0.00  0.00 ± 0.00 Citral 53  0.01 ± 0.01.sup.b  5.04 ± 0.81.sup.a  4.16 ± 0.18.sup.a  4.44 ± 0.26.sup.a Phenylacetaldehyde 4  0.59 ± 0.03.sup.a  0.60 ± 0.15.sup.a  0.51 ± 0.12.sup.a  0.52 ± 0.10.sup.a Linalool oxide II 190  0.00 ± 0.00.sup.b  0.05 ± 0.01.sup.a  0.04 ± 0.01a  0.04 ± 0.00.sup.a Linalool 0.22 10.53 ± 2.29.sup.b 339.91 ± 69.34.sup.a 264.91 ± 17.51.sup.a 259.79 ± 2.24.sup.a Nonaldehyde 1.1  1.95 ± 0.02.sup.a  2.42 ± 0.76.sup.a  2.06 ± 0.25.sup.a  1.81 ± 0.06.sup.a Phenethyl alcohol 390  0.00 ± 0.00.sup.b  0.02 ± 0.00.sup.a  0.02 ± 0.00.sup.a  0.03 ± 0.01.sup.a Nerol 49  0.03 ± 0.00.sup.c  0.11 ± 0.01.sup.a  0.09 ± 0.01.sup.ab  0.09 ± 0.00.sup.b Geraniol 7.5  0.65 ± 0.06.sup.b  35.64 ± 5.77.sup.a  29.54 ± 1.16.sup.a  31.46 ± 1.70.sup.a

[0046] In the example, tea sample (2) was treated without adding the tannase and the β-glucosidase, and other conditions were the same as those in the example; and tea sample (3) was treated only with the tannase, and other conditions were the same as those in the example.

[0047] To sum up, the method for preparing liquid-fermented black tea juice by using aged tea provided by the present disclosure uses endogenous enzymes (mainly polyphenol oxidase and peroxidase) of fresh tea leaves (picked in any season) and exogenous enzymes (tannase and β-glucosidase) to catalyze conversion of the aged tea catechin extract, promotes conversion of catechins in aged tea to theaflavins (increased by nearly 3 times, see Table 4-(4)), promotes hydrolysis of glycosides to release bound aroma (OAVs of two characteristic aroma compounds of black tea, linalool and geraniol, are significantly increased, see Table 5-(4)), successfully removes stale odor of aged tea, and enables the black tea juice to have a main sweet aroma and a slight floral aroma, a red and bright color and a sweet and mellow taste. The method solves a problem of a large inventory of aged tea, further promotes high-value utilization of summer and autumn tea, and has a low cost and high economic benefits.