WO2012069323A1

WO2012069323A1 - A tea product

Info

Publication number: WO2012069323A1
Application number: PCT/EP2011/069899
Authority: WO
Inventors: Matthew John; Gurmeet Singh; Purna Venkatesh; Joseph Vijay
Original assignee: Unilever Nv; Unilever Plc; Hindustan Unilever Limited
Priority date: 2010-11-24
Filing date: 2011-11-11
Publication date: 2012-05-31
Also published as: AR083962A1; EP2642863A1

Abstract

The present invention relates to a tea product. More particularly the present invention relates to a leaf tea product with enhanced amounts of theaflavins and catechins. The problem addressed by the present invention is to provide a tea product with significant amount of catechins without addition of any exogenous catechins, where the tea product has sensorial properties similar to those of black tea. The present inventors have surprisingly found that freezing the fresh tea leaf after plucking followed by exposing it to air and drying results a leaf tea product that has significant amount of catechins and theaflavins, and has sensorial properties similar to those of black tea.

Description

A TEA PRODUCT Technical Field

The present invention relates to a tea product. More particularly the present invention relates to a leaf tea product.

Background and prior art

The health benefits of tea are mainly due to the presence of polyphenols such as catechins, theaflavins etc. Catechins, which include epigallocatechin gallate (EGCG), epicatechin (EC), epicatechin gallate (ECG), and epigallocatechin (EGC), are the major polyphenolic compounds in green tea. Theaflavin and its derivatives, known collectively as theaflavins (TF), are antioxidant polyphenols, that are formed from catechins present in tea leaf during the enzymatic oxidation of tea leaf to form black tea.

Catechins and theaflavins both are known to provide potential health benefits. Most of the tea consumers in the world either consume green tea or black tea. Green tea contains a high amount of catechins with no perceivable amount of theaflavins whereas black tea contains a higher amount of theaflavins and a lower amount of catechins. The taste of black tea is different from that of green tea. Some consumers prefer green tea and others prefer black tea. Green tea is predominantly consumed in South-East Asia. Those consumers who prefer black tea are unable to get the health benefits of catechins because the amount of catechins in black tea is low. Therefore there is a need for a tea product which contains a significant amount of both catechins and theaflavins and which has the appearance and organoleptic properties of black tea, so that it is liked by consumers of black tea.

Black teas with high amouns of theaflavins are known in the literature. For example, CN 1729807 (Fujian Agriculture and Forestry University, 2006) discloses a process for manufacturing a black tea material having a high theaflavin content. The process includes plucking of leaf, withering, freezing, comminution and finally fermentation. GB593260 (Eric Howard Gridley, 1947) relates to the manufacture of tea, and discloses a process wherein the tea leaf received from the field is immediately suitably chilled and frozen without the preliminary process of withering followed by usual steps of rolling, green leaf shifting, fermenting etc.

GB51 1895 (J. Lyons & Company Limited, 1939) discloses an improvement in the manufacture of tea. In this process the plucked leaf is subjected to drying or withering, followed by freezing the tea leaf and then subjecting the tea leaf to usual manufacture. Freeze-withering the leaf to reduce the withering time is also known in the literature. Muthumani et al: ["Studies on freeze-withering in black tea manufacturing", Food Chemistry, Elsevier Ltd, NL, Vol. 101 , No.1 , 12 August 2006, pages 103-106] discloses that in order to reduce the withering time during black tea manufacture, freeze- withering was attempted. This resulted in flaccid leaves with increased cell membrane permeability in a shorter period of time. The freeze-withered leaves had similar amounts of quality precursors to conventionally withered leaves. The resultant black tea was better in quality than those manufactured without withering and after normal withering. Manufacturing of fresh leaves resulted in comparable levels of theaflavins, but the tea was not acceptable due to its harshness. Increased cell membrane permeability during freeze-withering showed that the leaf attained a sufficient degree of physical wither. The decreases in the levels of chlorophyll showed that chemical withering had also been achieved during freeze-withering, which was supported by the increased levels of caffeine. However none of these prior art documents discloses a method of producing a tea having similar properties to black tea with a significant amount of both catechins and theaflavins.

The problem addressed by the present invention is to provide a tea product with a significant amount of catechins and with a high amount of theaflavins, without the addition of any exogenous catechins; where the tea product has sensorial properties similar to that of black tea. Object of the invention

In view of the foregoing it is an object of the present invention to provide a leaf tea product and a process for producing a leaf tea product with significant levels of both catechins and theaflavins.

It is another object of the present invention to provide a leaf tea product and a process for producing a leaf tea product with significant levels of both catechins and theaflavins without the addition of any exogenous catechins or theaflavins. It is a further object of the invention to provide a leaf tea product and a process for producing a leaf tea product with sensorial properties similar to that of black tea.

The present inventors have surprisingly found that freezing fresh tea leaf after plucking followed by exposing it to air under certain conditions and then drying results in a leaf tea product that has significant amounts of catechins and also sensorial properties similar to those of black tea.

Summary of the invention

In a first aspect the present invention provides a leaf tea product comprising:

a) 4-15 % catechins on a dry weight basis, and

b) 2- 4 % theaflavins on a dry weight basis.

In a second aspect the present invention provides a process for preparing a leaf tea product comprising the steps of:

a. providing fresh tea leaf,

b. freezing the leaf at a temperature in the range -2 to -200°C, c. exposing the frozen leaf to air at a temperature of 5-50° C for a duration of 1-6 hours; and

d. drying the leaf without comminution after step (c), to a moisture content of less than 10% by weight, to obtain the leaf tea product.

In a third aspect the present invention provides a leaf tea product of the first aspect prepared by the process of the second aspect. These and other aspects, features and advantages will become apparent to those of ordinary skill in the art from a reading of the following detailed description. For the avoidance of doubt, any feature of one aspect of the present invention may be utilised in any other aspect of the invention. The word "comprising" is intended to mean "including" but not necessarily "consisting of" or "composed of." In other words, the listed steps or options need not be exhaustive. It is noted that the examples given in the description below are intended to clarify the invention and are not intended to limit the invention to those examples per se. All percentages are weight/weight percentages unless otherwise indicated. Except in the operating and comparative examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts of material or conditions of reaction, physical properties of materials and/or use are to be understood as modified by the word "about". Numerical ranges expressed in the format "from x to y" are understood to include x and y. When for a specific feature multiple preferred ranges are described in the format "from x to y", it is understood that all ranges combining the different endpoints are also contemplated.

Detailed description of the invention

Tea product

The present invention provides a leaf tea product comprising:

a) 4-15 % catechins on a dry weight basis, and

b) 2- 4 % theaflavins on a dry weight basis.

Preferably the tea product comprises 4-12%, more preferably 4.5-10%, further more preferably 5-9 % and most preferably 6-8% of catechins on a dry weight basis.

The tea product preferably comprises 2.5-3.5 % and more preferably 2.5-3 % of theaflavins on a dry weight basis. One of the ways of characterizing a leaf tea product is by its colour characteristics, i.e. L*, a* and b* values. These values indicate the color characteristics of a particular tea product. The International Commission on Illumination (CIE) introduced the CIE L*a*b* scale of colour measurement in 1976. CIE L*a*b* is based on the opponent-colours theory, which assumes that the receptors in the human eye perceive colour following pairs of opposites:

- Light-Dark

Red-Green , and

- Yellow-Blue.

The CIE L*a*b* colour scale is an approximately uniform colour scale. In a uniform colour scale, the differences between points plotted in the colour space correspond to visual differences between the colours plotted. The CIE L*a*b* colour space is organized in a cubic form. The L* axis runs from top to bottom. The maximum value for L* is 100, which represents a perfect reflecting diffuser. The minimum is L*=0, which represents black. The a* and b* axes have no specific numerical limits. Positive a* is red and negative a* is green. Similarly, positive b* is yellow and negative b* is blue. CIE L*a*b* values can be measured using a color measuring instrument e.g. a spectrophotometer. A Hunterlab color measuring instrument is preferably used for this purpose. The colour measurements are preferably carried out under D65 illuminant. D65 is a standard illuminant defined by the CIE. The D65 illuminant is intended to represent average daylight throughout the visible spectrum.

Black tea and green tea have different CIE L*a*b* values. The lightness value (L*) of the leaf tea product of the present invention as measured on CIE L*a*b* scale using D65 illuminant at 25°C is preferably greater than 40, more preferably greater than 42, and further more preferably greater than 45. The yellowness or brightness (b*) value of the leaf tea product of the present invention as measured on CIE L*a*b* scale using D65 illuminant at 25°C is preferably greater than 8, more preferably greater than 10, further more preferably greater than 12. Although there is no particular upper limit for the value of L*, it may well be up to 80 or more preferably up to 70. Process for the preparation of the leaf tea product

The process for preparing the leaf tea product comprising the steps of:

a) providing fresh tea leaf,

b) freezing the leaf at a temperature in the range -2 to -200°C, c) exposing the frozen leaf to air at a temperature of 5-50° C for a duration of 1-6 hours; and

d) drying the leaf without comminution after step (c), to a moisture content of less than 10% by weight, to obtain the leaf tea product.

Fresh tea leaf collected by plucking from a tea plantation is preferably used. The tea leaf may include leaf, buds, stem and other parts of Camellia Sinensis.

The plucked leaf is subjected to freezing. In the freezing step the leaf is exposed to a temperature in the range of -2 to -200°C thereby freezing the tea leaf. The temperature is preferably in the range of -20 to -200°C, more preferably -50 to -200°C, further more preferably -100 to -200°C and most preferably -150 to -200°C.

The freezing temperature may be attained by adding liquid nitrogen, dry-ice or any other suitable substance used for the purpose of freezing or by keeping the leaf at a low temperature in a freezer. Liquid nitrogen (~ -196°C) is preferably used for freezing the tea leaf. The freezing step is preferably carried out by contacting the leaf with liquid nitrogen. The freezing step is preferably carried out on tea leaf which has a moisture content of at least 75%, more preferably 78 % and most preferably 80%. This may be achieved by not exposing the tea leaf to open air or accelerated high temperature conditions where it can lose moisture. The desired moisture content may be achieved by keeping the fresh tea leaf, after plucking, in a closed container or in an air tight bag.

After freezing, the frozen tea leaf is exposed to air at a temperature of 5-50°C preferably 10-40°C and more preferably 15-35°C. Exposure of the frozen tea leaf to air at these specified temperatures is carried out for a duration of 1 -6 hours, preferably 1-5 hours, more preferably 1-4 hours, further more preferably 1-3 hours and most preferably 1-2 hours.

The step of exposing the tea leaf to air under these specified conditions may also be considered as withering (without prejudice to any particular definition). Withering in the conventional tea manufacturing process is carried out for a long time, typically from 16- 20 hours.

After the exposure of the tea leaf to air, the leaf is then subjected to drying. The tea leaf is dried to a moisture content of less than 10%, preferably less than 5% by weight. Drying preferably takes place by contacting the tea leaf with air at a temperature of 50- 100°C, during which the leaf loses moisture and enzyme activity is stopped. By drying, the moisture content of the tea leaf is brought down to less than 10% preferably 2-3%. A tray drier or fluidized bed drier is preferably used for drying the tea leaf.

In the process of the invention, there is no step of comminution between exposure to air and drying. However, the process preferably comprises a step of comminuting the tea leaf after the drying step. Comminution (i.e. size reduction of the tea leaf, which is also known as maceration) can be carried out by rolling, twisting and/or cutting the tea leaf. Preferebly comminution is achieved by crushing, tearing and curling which is known as CTC. CTC machines are widely used in the tea industry. One or more CTC steps may be carried out. Comminution damages the tea leaf and therefore releases enzymes which convert catechins into theaflavins during the fermentation process in conventional black tea production.

Now the invention will be demonstrated with the help of examples. The examples are for illustration only and do not limit the scope of the invention in any manner.

Examples

Example 1 : Process for the preparation of the tea product

1.5 kg of freshly plucked tea leaf was collected from a plantation in Southern India. This was divided into three parts which were processed in three different ways.

Example 1 a: Conventional black tea was made by taking 0.5 kg of the freshly plucked tea leaf (having a moisture content of -80% by weight). The tea leaf was exposed to air at room temperature (~25°C) for 4 hours followed by comminution by CTC. After comminution, the tea leaf was kept for 1.5 hours at the same temperature for fermentation. After fermentation the leaf was dried at 100°C in a tray drier to a moisture content of 3%. Example 1 b: Black tea was made after an initial step of freezing. 0.5 kg of the freshly plucked tea leaf (having a moisture content of -80% by weight) was frozen by adding 2 L of liquid nitrogen at -196°C to it. The frozen leaf was exposed to air at room temperature (~25°C) for 4 hours followed by comminution by CTC. After comminution, the tea leaf was kept for 1.5 hours at room temperature for fermentation. After fermentation the leaf was dried at 100°C in a tray drier to a moisture content of 3%.

Example 1 c: A tea product according to the invention was made using an initial freezing step followed by exposing to air and drying. 0.5 kg of the freshly plucked tea leaf (having a moisture content of -80% by weight) was frozen by adding 2 L of liquid nitrogen at -196°C to it. After freezing, the frozen leaf was exposed to air at room temperature (~25°C) for 4 hours. The leaf was then dried to a moisture content of 3% in a tray-drier at 100°C.

The catechin and theaflavin contents of the leaf teas of Examples 1 a, 1 b and 1 c were measured using the following analysis methods. The results are shown in Table 1.

(a) Theaflavin content:

The total theaflavin content was measured as follows: 0.2 g of tea leaf was extracted twice in 10 mL of 70% methanol solution at 75°C for 15 minutes. Then 800 μΙ_ of the supernatant was diluted with 1200 μΙ_ of stabilizing solution (10% v/v acetonitrile with 500 μg/mL of EDTA and 500 μg/mL of ascorbic acid). The diluted samples were analysed by HPLC using an octadecylsilica (C18) column (Nova-pak ex. Waters, 3.9 mm i.d. ^χ 150 mm) with detection at a wavelength of 380 nm, column temperature of 40°C, injection volume of 20 μΙ_ and flow rate of 1 mL/min. The mobile phases for the theaflavin analysis were 2% (v/v) acetic acid in water (as mobile phase A) and acetonitirile (as mobile phase B). A linear gradient from 8% B to 69% B over 50 min was used to separate the theaflavins following which the column was equilibrated with 8% of buffer A for 5 min. Pure theaflavins ( Sigma Aldrich, > 90%, HPLC grade) were used as the standard for quantification.

(b) Catechin content:

The total catechin content was determined using the ISO method for the determination of catechins in green and black tea, using high performance liquid chromatography (ISO/CD 14502-2).

(c) Colour measurement:

Colour (CIE L*a*b* values) were measured using a Hunterlab Ultrascan XE (Model- USXE/UNI version 3.4, Hunterlab Associates Laboratories Inc. Virginia). A halogen cycle lamp was used as the light source. The illuminant used was D65 and the measurements were made at 10° Observer angle. Tea leaf was filled up to the brim of a quartz cuvette of 10 mm path length which was placed in the instrument for colour measurement. The instrument was calibrated using a standard white tile (Hunterlab Duffuse/8°, mode-RSEX, Port-1 " and area- large) in accordance with the instruction manual. The L*a*b* values were measured at room temperature (~25°C). The L* and b* values for the different teas are shown in Table 2. Table 1

From Table 1 , it is evident that the tea of Example 1 c (according to the invention) has a higher amount of catechins and theaflavins than the tea as made according to Examples 1 a or 1 b or conventional a Japanese green tea known as Sencha (comparative examples). Freezing freshly plucked tea leaf with a moisture content of -80%, followed by exposing to air at 25°C for 4 hours and then drying it to a moisture content of 3% produced a tea that has significant amount of both catechins and theaflavins. Comparison of examples 1 b and 1 c shows that it is not simply the presence of a freezing step which resultedn the increased amount of catechins. It is also necessary that there is no comminution step. Without wishing to be limited by theory, it is believed that freezing causes a certain amount of damage to the structure of the leaf, thereby allowing a limited degree of enzyme release. However, in the absence of a comminution step, no further damage to the leaf took place in Example 1 c. Thus the extennt of fermentation in Example 1c was much less than in Example 1 b. Hence only some of the catechins were converted to theaflavins during the step of exposing the tea leaf to air at 25°C. Once enzyme activity had been stopped by drying, the resulting tea leaf hada significant amount of both catechins and theaflavins.

Table 2:

From Table 2 it is evident that the tea product of Example 1 c (according to the invention) has much higher L* and b* valuesthan those of example 1 a (conventional black tea), 1 b or green tea. This shows that the tea product of the invention can be distinguished from conventional green and black teas by its L* and b* values. However, it is believed that the tea product of the invention nonetheless has an appearance which for the consumer is sufficiently similar to conventional black tea, because the red / brown colouration, which is characteristic of black tea, is largely reflected by the a* value rather than the L* and b* values.

A tea beverage was produced by infusing the leaf tea product of example 1c in hot water. The beverage was tasted and found to be similar to a black tea beverage. Example 2: Effect of time of exposure to air on theaflavin and catechin contents

The effect of the exposure time to air on the catechin and theaflavin contents was studied. Tea leaf was prepared as in example 1 c, except that the frozen leaf was exposed to air at 25°C for times up to 8 hours. The total theaflavins and catechins were measured after 0, 2, 3 and 8 hours exposure using the procedures described in Example 1. As a comparison, some of the tea leaf was exposed to air at 25°C without having undergone freezing. The results are summarized in Table 3. Table 3:

From Table 3 it is evident that freezing carried out before exposure of the fresh leaf to air at 25°C resulted in high amounts of theaflavins, whilst retaining a relatively high amount of catechins (whereas in a conventional black tea does not contain a perceivable amount of catechins). In contrast exposing the fresh tea leaf to air 25°C without the freezing step resulted in a high catechin content but a much lower theaflavin content. From Table 3 it is also evident that very long exposure to air (8 hours - outside the scope of the invention) reduced the catechin content. Example 3: Effect of freezing temperature on theaflavin and catechin contents

Freshly plucked tea leaves from the tea plantation in Southern India were divided into four batches and subjected to four different freezing temperature regimes:

(a) no freezing;

(b) freezing at -20°C in a freezer;

(c) freezing at -80°C in a freezer.

(d) freezing by pouring liquid nitrogen at -196° C onto the fresh leaf.

The leaf was then exposed to air at 25°C for two different times (2 hours and 4 hours). The catechin and theaflavin contents were measured using the procedures described in Example 1. The results are shown in Table 4. Table 4:

From Table 4 it is evident that the amount of theaflavins in the tea leaf increased as the freezing temperature was lowered. The exposure time after freezing also had an effect on the theaflavin and catechin contents: the longer the exposure, the greater the theaflavin content and the lower the catechin content. The most preferred freezing process was liquid N₂, where it was possible to get a high amount of theaflavins whilst retaining a significant amount of catechins. Example 4: Effect of freezing temperature on physical appearance of the leaf

Freshly plucked tea leaf from the tea plantation in Southern India was treated as in example 3. All the samples were exposed to air at 25°C for 4 hours, and then their physical appearance was observed in terms of colour and texture of the leaf (using the terms Turgid' - filled with fluid, firm; and 'Flaccid' - lacking firmness, drooping). The results are summarized in Table 5.

Table 5:

Freezing temperature Leaf Characteristics

Colour Texture

Fresh Leaf Green Turgid

No freezing Green Turgid

-20° C Predominantly green Flaccid

with some browning

-80° C Predominantly green Flaccid

with some browning

Liquid N₂ (-196° C) Predominantly brown Flaccid with some regions of green

It is evident that as the freezing temperature decreased, the appearance of the leaf became brown, and thus resembled black tea leaf. Example 5: Effect of freezing after exposure to air at 25°C for 4 hours

Freshly plucked tea leaf from the tea plantation in Southern India was divided into two batches. In batch (a) 0.5 kg of the leaf was simply left in the open atmosphere of temperature ~ 25°C for 4 hours. In batch (b) 0.5 kg of the leaf was first subjected to 4 hours of exposure to air as in (a). After 4 hours the moisture content of the tea leaf was found to be 72%. Freezing was then carried out by adding 2 L of liquid nitrogen (at - 196°C). The catechin and theaflavin contents were measured using the procedures described in Example 1. The results are shown in Table 6.

Table 6:

From Table 6 it is evident that carrying out the freezing step after exposure to air at 25°C for 4 hours (i.e. outside the scope of the invention) did not result in a tea which had significant amounts of both catechins and theaflavins. Freezing carried out after exposure to air 25°C for 4 hours had almost no effect on the theaflavin content. Thus the order of carrying out the freezing and exposure steps is important in order to obtain a tea which has significant amount of both catechins and theaflavins.

In summary, it is evident that the present invention provides a leaf tea product with significant amount of both catechins and theaflavins without the addition of any exogenous catechins or theaflavins. The tea product has an appearance similar to that of black tea, and produces beverages which have similar organoleptic properties to black tea.

Claims

1. A leaf tea product comprising:

a) 4-15 % catechins on a dry weight basis, and

b) 2- 4 % theaflavins on a dry weight basis.

2. A leaf tea product as claimed in claim 1 wherein the lightness value (L*) of the leaf tea product as measured on CIE L*a*b* scale using D65 illuminant is greater than 40.

3. A leaf tea product as claim in claim 1 or claim 2 wherein the yellowness value (b*) of the leaf tea product as measured on CIE L*a*b* scale using D65 illuminant is greater than 8.

4. A process for preparing a leaf tea product comprising the steps of:

a) providing fresh tea leaf,

b) freezing the leaf at a temperature in the range -2 to -200°C,

c) exposing the frozen leaf to air at a temperature of 5-50° C for a duration of 1-6 hours; and

5. A process as claimed in claim 4 wherein the freezing step is carried out by contacting the leaf with liquid nitrogen.

6. A process as claimed in claim 4 or 5 wherein the freezing step (b) is carried out on a tea leaf from step (a) which has a moisture content of at least 75% by weight.

7. A process of preparing a leaf tea product as claimed in any of claims 4, 5 or 6 further comprising a step of comminuting the tea leaf after drying.

8. A leaf tea product as claimed in any of claims 1 to 3 made by the process of any of claims 4 to 7.