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Cream formation and main chemical components of green tea infusions processed from different parts of new shoots
Food Chemistry 114 (2009) 665–670
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Cream formation and main chemical components of green tea infusions processed from different parts of new shoots Jun-Feng Yin a,1,*, Yong-Quan Xu a,1, Hai-Bo Yuan a, Long-Xin Luo b, Xiao-Jun Qian b a b
Engineering Research Center for Tea Processing, Tea Research Institute Chinese Academy of Agricultural Sciences, 9 Meiling Road, Hangzhou 310008, China Shenzhen Shenbao Huacheng Foods Co. Ltd., 22 Jinyuan Road, Shenzhen 518020, China
a r t i c l e
i n f o
Article history: Received 15 June 2008 Received in revised form 13 September 2008 Accepted 1 October 2008
Keywords: Cream Green tea Formation Chemical components
a b s t r a c t The formation of green tea cream and its chemical components were investigated. The green tea infusions were processed from different parts of new shoots: the bud and the first leaf, the second leaf and its implicative stem, the third leaf and its implicative stem, and the fourth leaf and its implicative stem, which were named as first part, second part, third part and fourth part, respectively. The results showed that the formation of tea cream and its settlement slowed down gradually from the first part to the fourth part, and that the amount of tea cream also decreased accordingly. The amount of tea cream was influenced remarkably by the chemical components in the green tea infusion. The main components of green tea cream were polyphenols (29.86 –78.66%), total sugar (14.47–27.62%) and caffeine (2.35–10.43%). Catechins (12.8–42.5%) were the main components of polyphenols which participated in tea cream formation. The main components in the catechins were found to be ( )-epigallocatechin (EGC), ( )-epigallocatechin gallate (EGCG), ( )-epicatechin (EC) and ( )-epicatechin gallate (ECG). Seven minerals were found in the tea cream, including Ca2+, K+, Mg2+, Mn2+, Na+, Zn2+ and Ni2+. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction Tea cream is formed whilst hot aqueous tea infusion cools down, which not only has an unattractive appearance but also damages both taste and colour of tea. The main constituents of black tea cream were thearubigins (TRs), theaflavina (TFs) and caffeine (Roberts, 1962, 1963; Smith, 1968). Collier, Mallows, and Thomas (1972), Rutter (1971) and Rutter and Stainsby (1975) concluded that the formation of tea cream was governed by various molecular types of interactions including polyphenol–caffeine complexation and polyphenol–polyphenol interactions. Polyphenol–caffeine complexation is influenced by a number of gallate and hydroxyl groups of the polyphenols. Protein (Nagalakshmi & Seshadri, 1983) and a lipid complex (Seshadri & Nagalakshmi, 1988) were identified in black tea cream. Tea cream also has been found in green tea infusion (Liang, Lu, & Zhang, 2002) and in semifermented tea infusion (Chao & Chiang, 1999a). However, most researches related to tea cream formation have focused on black tea. The primary components of semifermented tea cream were catechins (30%), caffeine (20%) and protein (16%), and EGCG and ECG were found to be the major catechins precipitated during cream-
* Corresponding author. Tel.: +86 571 86650594; fax: +86 571 86650056. E-mail address: [email protected] (J.-F. Yin). 1 These authors contributed equally to this work. 0308-8146/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2008.10.004
ing, constituting 19% and 5% of the tea cream, respectively (Chao & Chiang, 1999a). Liang and Bee (1992) investigated the morphology of green tea cream particles by using optical and electron microscopes, and revealed that tea cream could be formed in the absence of thearubigins and theaflavins. Liang et al. (2002) also observed that caffeine, gallocatechine (GC) and EGCG were predominant in green tea cream, and that gallated catechins had stronger creaming ability than un-gallated catechins. However, little information on the chemical components except catechins and caffeine has been reported, and the influence of chemical components in green tea infusions when tea cream formed was not noticed. The amount of tea cream formed in tea infusions is influenced by various parameters including chemical composition (Liang et al., 2002; Penders, Jones, Needham, & Pelan, 1998; Smith, 1989). There are different chemical compositions in different parts of new shoots. The contents of polyphenols, catechins, caffeine, free amino acids, protein, magnesium (Mg), zinc (Zn) and kalium (K) decrease gradually, whilst the contents of total sugar, flavones, starch, chlorophyll, calcium (Ca), manganese (Mn) and aluminium (Al) increase gradually, amongst one leaf and a bud, second leaf, third leaf and fourth leaf of the new shoots (Chen, 1982; Selvendran, Perera, & Selvendran, 1973; Wan, 2003). Consequently, green tea infusions processed from different parts of new shoots can demonstrate the effects of the chemical components in green tea infusion better when green tea cream formed. The objectives of this study were to investigate the formation of green tea cream,
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chemical compositions of the tea cream and the effects of the chemical components in the tea infusions processed from different parts of new shoots when tea cream formed. 2. Materials and methods 2.1. Tea leaves Shoots with four leaves and a bud from tea plant (Camellia sinensis (L.) O. Kuntze cv. Zhenghe dabaicha) were harvested in August 2007 from tea garden of the Tea Research Institute of Chinese Academy of Agricultural Sciences. Every new tea shoot was separated into four parts, which were the bud and the first leaf, the second leaf and its implicative stem, the third leaf and its implicative stem, and the fourth leaf and its implicative stem. These parts of new shoots were named as first part, second part, third part and fourth part, respectively. After withering for 3 h, every part of the tea leaves was panned at 130 °C for 8 min, rolled for 5 min, first dried at 95 °C for 30 min and then dried at 80 °C to a final moisture content of 4%. The dry tea leaves were stored in a freezer at 20 °C for further use. 2.2. Preparation of the tea infusion The ground tea leaves (20–60 mesh) were extracted with distilled water (1:20, w/w) at 70 °C for 10 min. The extract was filtered through 300 mesh screen and then quickly cooled down to 25 °C or lower with a glass condenser using water (15 °C) as a cooling medium. The cooled extract was then centrifuged at 10,000g at 10 °C for 15 min to obtain a clarified infusion. 2.3. Formation and separation of the tea cream The clarified infusion was sterilized at 90 °C for 5 min, and every 45 ml was filled in a lathy transparent bottle. The bottles were sterilized beforehand. Tea infusion in the bottles was cooled down to 25 °C, and then stored at 10 °C for 20 days to observe tea cream formation. Tea cream was separated by centrifuging at 10,000g at 10°C for 15 min, and the supernatant was discarded. The precipitated tea cream was rinsed with 10 ml distilled water, and then dissolved in 5 ml of 50% (v/v) ethanol solution, and then diluted to 50 ml with distilled water. 2.4. Observation of tea cream formation The observation team consisted of 10 members who were trained before. The infusions were observed by colour, clarity and the amount of tea cream at the bottom of the bottle during storage at 10 °C. The result was determined together by the team, and the observation indexes are described in Table 1. 2.5. Analysis of chemical constituents of tea infusion and tea cream 2.5.1. Analysis of total solids content and the amount of tea cream The total solids contents of the tea infusions were determined by drying 20 ml of the infusion at 80 °C for 48 h. The amount of Table 1 The observation index of phenomena for tea cream formation during storage at 10 °C. Index
1
2
3
4
Colour
Green Pellucid
Amount of tea cream
No deposit
A little deposit
Greenyellow A little turbid Visible deposit
Yellow
Clarity
Yellowgreen Sub-pellucid
Turbid Much visible deposit
tea cream in tea infusions was determined by referring to the method described by Nagalakshmi, Ramaswamy, Natarajan, and Seshadri (1984). The tea liquor in the bottles was centrifuged at 10,000g at 10 °C for 15 min. The supernatant was discarded. The precipitated tea cream that was obtained was washed with two aliquots of 5 ml distilled water in a weighed glass dish having a diameter of 9 cm, and dried at 80 °C for 48 h. 2.5.2. Analysis of free amino acids The content of free amino acids in the tea infusions and tea cream was determined with a spectrophotometer (UV-2550, Shimadzu (Suzhou) Instruments Manufacturing, Co., Ltd., Suzhou, China) by ninhydrin colour reaction method (Zhong, 1989), which was performed at 540 nm with glutamic acids as the standard of free amino acids. The standard of the free amino acids graph is given as C = (A570 + 0.0868) 1.51 1, R2 = 0.9996. C was the concentration of the free amino acids, and A570 was the absorbance (A) at 570 nm. 2.5.3. Analysis of tea polyphenols The content of tea polyphenols in the tea infusions and tea cream was determined by the spectrophotometric method with FeSO4, 3.5 10 3 M potassium sodium tartrate and buffer described by Zhong (1989). Absorbance (E1) of the reaction solution was determined at 540 nm in a 1 cm photometer cuvette with Shimadzu UV-2550 spectrophotometer. Absorbance (E2) of the control reaction solution (containing 5 ml distilled water, 5 ml dyeing solution and 15 ml buffer) was determined at 540 nm as described earlier. The content of tea polyphenols was calculated using the following equation: TP (mg L 1) = (E1 E2) 3.9133 103. 2.5.4. Analysis of protein, pectin and flavones The protein content in the tea infusion and tea cream was determined by bicinchoninic acid (BCA) method (GENMED SCIENTIFICS INC., USA). The pectin content was determined by the procedure proposed by Blumenkrantz and Asoboe-Hansen (1973) using anhydrogalacturonic acid (AGA) as a standard. The flavones content in the tea infusions was determined at 420 nm by the spectrophotometric method with 1% AlCl3 as described by Zhong (1989). 2.5.5. Analysis of total sugar and polysaccharides The total sugar content was determined by the anthrone-sulphuric acid reaction, using glucose as a standard (Fu, Xie, Nie, Zhou, & Wang, 2001). Two milliliters of tea infusion was reacted with 8 ml anthrone reagent (2 g anthrone dissolves in 1000 ml analytically pure sulphuric acid) at 100 °C for 10 min, and then the absorbance (A620) was determined with SHIMADZU UV-2550 spectrophotometer after being cooled rapidly for 10 min. The standard glucose graph is given as C = 0.3589 * A620 0.0034, R2 = 0.999. C was the concentration of the glucose. Preparation of polysaccharides: 5 ml of tea infusion was precipitated with 10 ml 100% (v/v) ethanol at 10°C for 24 h, and centrifuged (10 min, 5000g) to get the sediment (Chen, Zhang, & Xie, 2005). Polysaccharides were dissolved and fixed to 25 ml with distilled water, and then analysed by referring to total sugar method. 2.5.6. Analysis of tea catechins and caffeine Analysis of tea catechins and caffeine was carried out by HPLC method (Liang et al., 2002). The tea infusion was filtered through a 0.2 lm Millipore filter before injection (Model Shimadzu LC2010A, Shimadzu Corporation, Kyoto, Japan). The HPLC conditions were as follows: injection volume, 5 ll; column, 5 lm – DiamonsilTM C18 (4.6 mm 250 mm); temperature, 40 °C; mobile phase A, acetonitrile/acetic acid/water (6:1:193); mobile phase B, acetonitrile/acetic acid/water (60:1:139); gradient, 100% mobile phase A to 100% mobile phase B by linear gradient during the early
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J.-F. Yin et al. / Food Chemistry 114 (2009) 665–670 Table 2 Phenomena (colour, charity and the amount of cream) of cream formation in the green tea infusions processed from different parts of new shoots during storage at 10 °C.
Time (day) 0
First part
Second part
Third part
Fourth part
Green-yellow, pellucid,
Green-yellow, pellucid,
Green-yellow,
Yellow-green, pellucid,
no deposit
no deposit
pellucid, no deposit
no deposit
1
Green-yellow, turbid, visible brown deposit
Green-yellow, turbid, a Green-yellow, turbid, little brown deposit
no deposit
Yellow-green, a little turbid, no deposit
10 Green-yellow, sub-pellucid, much visible brown deposit with white deposit around
Green-yellow, pellucid, visible
brown deposit
with white deposit
Green-yellow, pellucid, a little grey brown deposit
around
Flat green-yellow, pellucid, a little grey brown deposit with white deposit around
20 Green-yellow,
Green-yellow,
Green-yellow,
Flat green-yellow,
sub-pellucid, much
sub-pellucid, visible
sub-pellucid, a little
pellucid, a little brown
visible brown deposit
brown deposit with
brown deposit at the
deposit at the bottom
with white deposit
white deposit around
bottom with white
with white deposit
around (about one third
(about one fifth of the
deposit around
around
of the bottom)
bottom)
The observational infusion was 25 °C when on 0 day, 10°C from 1st day to 20th day.
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45 min and then 100% mobile phase B up to 60 min; flow rate, 1 ml min 1; detector, Shimadzu SPD ultraviolet detector (Shimadzu Corporation, Kyoto, Japan) at 280 nm. 2.5.7. Analysis of minerals The minerals in tea infusion and tea cream were determined by ICP-OES (IRIS/AP, Thermo Jarrell Ash Corp., America). Analytical conditions were as follows: Detector CID, low wavelength max intergration time: 15 s; high wavelength max intergration time: 5 s; nebulizer pressure: 28 psi; pump speed: 100 r min 1; auxiliary gas: medium (1.0 L min 1); RF power: 1150 W. 2.6. Statistical analysis Results are presented as mean value ± standard deviation (at least three replicates). Analysis of variance and significant differences amongst means, and correlation analysis were done by one-way ANOVA using SPSS (Version 11.5, SPSS Inc., Chicago, USA).
3. Results and discussion 3.1. Tea cream formation in the green tea infusion during storage at 10 °C Tea cream formation was observed in terms of colour, clarity and the amount of tea cream at the bottom of the bottle during storage at 10 °C. There was some difference between the infusions processed from different parts of the new shoots (Table 2). The infusions were pellucid at 25 °C, but appeared turbid after storage at 10 °C for 5 h, and then the infusions turned pellucid after the sedimentation of tea cream. The speed of deposit cumulating at the bottom of bottle was the fastest for the first part, followed by that of the second part and the fourth part, and that of the third part was the slowest. The amount of deposit of the first part was the largest, and then that of the second part, those of the third
and fourth parts were the smallest. It was found that the colour of the infusions changed from yellow-green to yellow during the storage, and the colour of the cream of the first part and the second part was darker than that of the third part and the fourth part as shown in the pictures (Table 2). In addition, there was demixing phenomena appeared in tea cream. A compact brown deposit was found at the bottom of the bottle, and an incompact white deposit was found on and around of the compact brown deposit. During the storage at 10 °C, the demixing phenomena of the first part and the second part appeared on the eighth day, whilst that of the third part on the 12th day and that of the fourth part on the 10th day. The appearance of demixing phenomena was concerned with the speed of the deposit cumulating at the bottom of the bottles. During the storage at 10 °C, a white deposit appeared after a brown deposit, which was the main deposit in the green tea infusion. Polyphenols, total sugar and caffeine (Table 3) were found to be the main components of the green tea cream. The white deposit of green tea cream might be caused by some chemical components such as free amino acids at low concentration. Demixing also has been reported by Penders et al. (1998) in the formation of black tea cream, and they observed that in the more concentrated region of the miscibility gap (>2% w/w), demixing (spinodal decomposition) was the predominant mechanism of tea cream formation, reflecting the substantial insolubility of polyphenols. Demixing in green tea cream may be caused by different speeds of aggregation and precipitation of different chemical components in the green tea infusion. 3.2. Comparison of chemical components in green tea cream and infusions processed from different parts of new shoots Content of some chemical components was found to be quite different in the infusions and tea creams between different disposals (Table 3). Obviously, the formation of tea cream was influenced by chemical components. This agreed with Harbron’s observation (1986) from black tea cream. The solids content of the infusions in-
Table 3 Main chemical components in green tea cream and infusions processed from different parts of new shoots (mg L Chemical components
Solids concentration Polyphenols Amino acids Flavones Total sugar Polysaccharides Protein Pectin Caffeine
Tea infusion
, mean ± s.d.).
Tea cream
First part
Second part
Third part
Fourth part
First part
Second part
Third part
Fourth part
16157.5 ± 10.6 9730.3 ± 22.6 699.2 ± 6.9 289.3 ± 1.3 4334.0 ± 184.0 374.2 ± 18.4 123.8 ± 15.6 2770.5 ± 705.3 1131.6 ± 8.0
17842.5 ± 88.4 8647.7 ± 39.1 888.2 ± 15.8 411.0 ± 1.8 4755.7 ± 260.1 354.0 ± 6.3 57.5 ± 0.0 2941.3 ± 163.3 1022.9 ± 10.5
18085 ± 81.3 8204.3 ± 125.8 953.9 ± 20.7 444.9 ± 0.8 5603.6 ± 253.8 369.2 ± 19.0 90.6 ± 0.0 3477.0 ± 84.9 997.7 ± 8.8
18397.5 ± 28.3 7513.0 ± 39.1 967.8 ± 18.2 425.2 ± 2.5 5827.9 ± 126.9 397.5 ± 1.9 118.2 ± 7.8 2613.5 ± 104.5 923.1 ± 11.3
1228.9 ± 20.5 966.7 ± 32.2 20.3 ± 0.5 28.4 ± 0.7 177.8 ± 6.5 10.6 ± 1.7 9.5 ± 4.0 31.1 ± 4.6 128.2 ± 10.8
517.2 ± 12.3 269.6 ± 13.6 19.2 ± 0.8 16.6 ± 0.4 100.9 ± 18.8 8.3 ± 2.2 4.7 ± 1.2 26.1 ± 2.1 17.1 ± 0.1
466.7 ± 15.3 194.2 ± 21.9 18.1 ± 0.3 12.8 ± 0.4 128.9 ± 5.6 10.5 ± 3.2 3.6 ± 1.1 20.6 ± 2.2 17.5 ± 0.3
434.4 ± 9.8 129.7 ± 18.9 12.5 ± 0.6 9.8 ± 0.5 89.4 ± 5.8 5.5 ± 1.5 5.2 ± 2.4 16.7 ± 1.7 10.2 ± 0.2
Table 4 Catechin components in green tea cream and infusions processed from different parts of new shoots (mg L Catechin components
1
Tea infusion
1
, mean ± s.d.).
Tea cream
First part
Second part
Third part
Fourth part
First part
Second part
Third part
Fourth part
GC EGC C EGCG EC GCG ECG CG
210.6 ± 2.3 1368.6 ± 12.5 166.4 ± 3.5 2871.8 ± 34.1 530.1 ± 2.7 39.6 ± 0.3 788.9 ± 5.5 22.8 ± 0.3
261.5 ± 3.2 1724.9 ± 18.1 110.7 ± 1.3 2338.0 ± 24.7 619.0 ± 9.2 35.4 ± 0.5 612.1 ± 6.7 44.2 ± 1.9
318.9 ± 1.8 1942.5 ± 44.7 88.3 ± 0.1 2155.9 ± 17.2 598.4 ± 5.6 47.5 ± 0.4 513.2 ± 5.4 47.1 ± 0.5
258.1 ± 6.8 1809.6 ± 18.2 84.2 ± 0.6 1875.7 ± 24.4 538.3 ± 5.4 23.7 ± 0.0 423.5 ± 5.6 45.6 ± 0.2
0 56.9 ± 0.7 12.1 ± 0.2 320.2 ± 10.6 21.6 ± 3.8 11.2 ± 0.0 97.6 ± 4.1 3.3 ± 0.3
0 23.9 ± 0.7 0 45.4 ± 1.8 8.8 ± 0.3 0 13.1 ± 0.7 0
0 36.7 ± 0.5 0 40.0 ± 0.4 9.7 ± 0.1 0 8.7 ± 0.1 0.5 ± 0.0
0 22.9 ± 0.9 0 22.1 ± 0.8 5.7 ± 0.2 0 4.6 ± 0.1 0
Total Gallated catechins
5998.7 ± 61.3 3723.0 ± 40.3
5745.8 ± 65.7 3029.7 ± 33.9
5711.8 ± 75.6 2763.7 ± 23.5
5058.6 ± 61.2 2368.4 ± 30.2
522.8 ± 18.2 432.3 ± 14.9
91.2 ± 3.6 58.5 ± 2.6
95.7 ± 1.1 49.3 ± 0.4
55.4 ± 2.1 26.7 ± 1.0
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creased gradually from the first part to the fourth part, but the amount of tea cream in the corresponding infusions reduced. In the tea cream, polyphenols were found to be 29.86–78.66%, and next, total sugar, 14.47–27.62%; caffeine, 2.35–10.43%; pectin, 2.53–5.05%; flavones, 2.26–3.21%; free amino acids, 1.65–3.88%; polysaccharides, 0.86–2.25% and protein, 0.59–0.91%. The amount of tea cream in the tea infusions, as well as the percentage (the amount of cream/solids content of tea infusion, w/ w%), reduced gradually from the first part to the fourth part. From the first part to the fourth part, the contents of polyphenols and caffeine in both tea infusion and tea cream reduced gradually, similar to the amount of the tea cream. Good positive correlation was found between the amount of tea cream and the content of polyphenols (c = 0.90, p 6 0.01) and caffeine (c = 0.91, p 6 0.01). However, the contents of the other chemical components except starch (c = 0.62, p 6 0.01) were all negatively correlated with the amount of tea cream. Both polyphenols and caffeine were found to be predominant in black tea (Rutter & Stainsby, 1975; Smith, 1968) and in semifermented tea (Chao & Chiang, 1999a). Therefore, in this study, because of the contents in tea cream and high positive correlation with the amount of tea cream, polyphenols and caffeine were considered as the principal chemical components in the formation of green tea cream. The content of most chemical components that participated in tea cream formation was much more in the first part than in the other parts. From the first part to the fourth part, free amino acids content in whole tea increased gradually, but free amino acids content in tea cream reduced gradually. No evident trend change in protein content was found. Free amino acid was also found to participate in cream formation in Paochung tea (Chao & Chiang, 1999a). The trend change in contents of flavones, total sugar and pectin amongst the four parts was similar to that in the free amino acids. There was no clear trend change in the content of polysaccharides, which have been shown to inhibit the precipitation of polyphenol–protein mixtures (Luck et al., 1994). These chemical components may not be the main factor of the tea cream formation, and we suspect that they may simply co-precipitate with insoluble complexes during tea cream formation. 3.3. Comparison of catechins components in green tea cream and infusions processed from different parts of new shoots Catechins are the main components of tea polyphenols, and they were regarded as the principal constituents of black tea cream (Powell et al., 1993; Roberts, 1963) and semifermented tea cream (Chao & Chiang, 1999a). It can be found from Table 4 that the catechins components that participated principally in tea cream formation were ( )-epigallocatechin (EGC), EGCG, ( )-epicatechin (EC) and ECG. They were all epi-catechins, thus epi-catechins may participate in
the formation of green tea cream. Gallated catechins (49.19– 82.69%) were the main component of the catechins in tea cream, which was also observed by Chao and Chiang (1999b) and Liang et al. (2002). Further, gallated catechins have a galloyl group and a hydroxylphenyl B ring acting like a claw (Chao & Chiang, 1999b). And gallated catechins having stronger creaming ability were considered to offer more hydroxyl groups for hydrogen bonding, which is thought to be an important force for aggregation of compounds involved in tea cream formation (Bee, Izzard, Harbron, & Stubbs, 1987; McManus, Davis, Beart, Gaffney, & Lilley, 1985). Similar to the amount of tea cream, the content of total catechins (12.8–42.5%) in tea cream, especially gallated catechins (Table 4), decreased gradually from the first part to the fourth part. The contents of ( )-catechin (C), EGCG and ECG in tea infusions, as well as the content of the total catechins in tea cream, reduced gradually from the first part to the fourth part. EGCG (39.89– 61.25%) and ECG (8.30–18.67%) were main components of catechins in tea cream, and EGCG (c = 0.93, p 6 0.01) and ECG (c = 0.91, p 6 0.01) were highly positively correlated with the amount of tea cream. Therefore, EGCG and ECG may be the crucial catechins components which participated in the tea cream formation. However, GC and EGCG were observed as the predominant compounds of catechins in green tea cream by Liang et al. (2002). The contents of GC, EGC and ( )-catechin gallate in tea infusions were highly negatively correlated with the amount of 0.56, p 6 0.01) and tea cream, whilst the contents of EC (c = ( )-gallocatechin gallate (GCG) (c = 0.23, p 6 0.01) were not correlated significantly. They may not be the pivotal catechin components which participated in the tea cream formation. 3.4. Comparison of minerals components in green tea cream and infusions processed from different parts of new shoots In the infusions of green tea, 11 main minerals were found according to the content (Table 5). The content of different minerals in tea infusion and tea cream was different. Seven minerals were found in the green tea cream, including Ca2+, K+, Mg2+, Mn2+, Na+, Zn2+ and Ni2+. And K+ (42.67–62.02%), Na+ (17.43– 28.82%) and Ca2+ (11.02–21.47%) were the main minerals in the green tea cream. Ca2+ was also found to be in high concentration in a tea infusion and to participated strongly in the cream formation by Pintauro (1977), and it was also found to enhance the self-association of caffeine, polyphenols and theaflavin, but had little effect on hetero-association (Jobstl, Fairclough, Davies, & Williamson, 2005). The main tea infusion components in the Ca2+ complex precipitation were polyphenols, and EGCG and ECG were the highest catechines found by Guo and Chen (1991), and it also had been substantiated that K+, Mg2+, Mn2+, Zn2+ and Ni2+ can be associated with tea infusion components.
Table 5 Main minerals in green tea cream and infusions processed from different parts of new shoots (mg L Mineral components
Tea infusion
1
, mean ± s.d.). Tea cream
First part
Second part
Third part
Fourth part
First part
Second part
Third part
Fourth part
Al3+ Ca2+ Cu2+ Fe3+ K+ Mg2+ Mn2+ Na+ Zn2+ Ni2+
4.28 ± 0.19 14.51 ± 0.24 0.11 ± 0.004 0.05 ± 0.016 486.9 ± 6.15 35.64 ± 0.42 23.91 ± 0.81 14.45 ± 0.58 2.75 ± 0.15 0.207 ± 0.004
9.23 ± 0.27 19.22 ± 1.90 0.13 ± 0.009 0.04 ± 0.006 521.5 ± 12.14 40.60 ± 0.76 32.15 ± 0.59 14.90 ± 0.29 2.54 ± 0.02 0.186 ± 0.003
14.71 ± 0.31 20.54 ± 0.94 0.08 ± 0.001 0.06 ± 0.001 582.3 ± 7.34 43.44 ± 0.58 35.24 ± 0.29 16.04 ± 1.20 2.67 ± 0.04 0.190 ± 0.002
19.78 ± 0.15 23.97 ± 1.03 0.09 ± 0.007 0.05 ± 0.004 560.2 ± 2.08 38.05 ± 0.21 33.66 ± 0.55 15.90 ± 0.50 2.59 ± 0.14 0.196 ± 0.001
0 4.03 ± 0.12 0 0 8.01 ± 0.29 0.95 ± 0.02 0.48 ± 0.04 5.17 ± 0.34 0.097 0.020 ± 0.002
0 2.53 ± 0.15 0 0 8.27 ± 0.28 0.92 ± 0.02 0.45 ± 0.02 4.96 ± 0.26 0.058 0.014 ± 0.001
0 1.70 ± 0.08 0 0 9.57 ± 0.08 0.90 ± 0.05 0.52 ± 0.11 2.69 ± 0.08 0.046 0.009 ± 0.003
0 1.82 ± 0.13 0 0 6.68 ± 0.13 0.60 ± 0.03 0.35 ± 0.02 2.62±0.11 0.021 0.008 ± 0.001
Total
582.8 ± 8.5
640.5 ± 16.0
715.3 ± 10.7
694.4 ± 4.6
41.65 ± 1.67
35.95 ± 0.95
32.86 ± 0.06
25.67 ± 0.19
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The total content of main minerals in tea infusions, as well as Ca2+, K+, Mg2+, Mn2+ and Na+, increased from the first part to the third part, but the content of fourth part was a little less than that of the third part. Similar to the amount of tea cream (Table 2), the total content of minerals in tea cream, as well as Na+, Ca2+, Mg2+, Zn2+ and Ni2+, decreased from the first part to the fourth part. The trend change in minerals content in tea cream from the first part to the fourth part was not influenced directly by the content in tea infusion. Accordingly, we considered that mineral was not the predominant component of tea cream formation. 4. Conclusion The formation of tea cream was investigated, and the chemical components in green tea cream and infusions, which were processed from different parts of new shoots, were compared and investigated. There was visible demixing in green tea cream. The amount of tea cream decreased gradually from the first part to the fourth part, which was influenced remarkably by the chemical components in green tea infusion. The main components of green tea cream were polyphenols (29.86–78.66%), total sugar (14.47– 27.62%) and caffeine (2.35–10.43%). The main catechins components of green tea cream were EGC, EGCG, EC and ECG. And K+ (42.67–62.02%), Na+ (17.43–28.82%) and Ca2+ (11.02–21.47%) were the main minerals in the green tea cream. Polyphenols, caffeine, EGCG and ECG were found to be the principal constituents of green tea cream formation. Acknowledgements The authors thank Hua-Fu Wang, Liang Chen, and Wen-Yan Han for their revision, and Chun-Hong Feng, Yuan-Zhi Shi, Li-Feng Ma, Xin-Chao Wang, Can-Yan Xiao, Su-Qin Chen, Xiang-Feng Gao, Dan-Yu Shen and Fang Wang for offering their kind help. The authors also thank the two anonymous reviewers for their constructive comments. References Bee, R. D., Izzard, M. J., Harbron, S. R., & Stubbs, J. M. (1987). The morphology of black tea cream. Food Microstructure, 6, 47–56. Blumenkrantz, N., & Asoboe-Hansen, G. (1973). New method for quantitative determination of uronic acids. Analytical Biochemistry, 54, 484–490. Chao, Y. C., & Chiang, B. H. (1999a). Cream formation in a semifermented tea. Journal of the Science of Food and Agriculture, 79, 1767–1774. Chao, Y. C., & Chiang, B. H. (1999b). The roles of catechins and caffeine in cream formation in a semi-fermented tea. Journal of the Science of Food and Agriculture, 79(12), 1687–1690.
Chen, Q. K. (1982). Sample analyse of tea chemistry. Hangzhou: Zhejiang Agricultural University Press (in Chinese). Chen, H. X., Zhang, M., & Xie, B. J. (2005). Components and antioxidant activity of polysaccharide conjugate from green tea. Food Chemistry, 90, 17–21. Collier, P. D., Mallows, R., & Thomas, P. E. (1972). Interactions between theaflavins, flavanols and caffeine. Phytochemistry, 11, 867. Fu, B. Q., Xie, M. Y., Nie, S. P., Zhou, P., & Wang, Y. X. (2001). Determination of the contents of polysaccharides in tea. Chinese Journal of Food Science, 22(11), 69–73. Guo, B. Y., & Chen, Q. K. (1991). Complex of tea infusion components with metal ions. Journal of Tea Science, 11(2), 139–144. Harbron, R. S. (1986). A colloid-chemical study of tea cream from instant black tea infusion. PhD thesis, University of Bristol. Jobstl, E., Fairclough, J. P. A., Davies, A. P., & Williamson, M. P. (2005). Creaming in Black Tea. Journal of Agricultural and Food Chemistry, 53, 7997–8002. Liang, Y., & Bee, R. (1992). A study on morphology of green tea cream particles. Journal of Zhejiang Agricultural University, 8, 17–20. Liang, Y. R., Lu, J. L., & Zhang, L. Y. (2002). Comparative study of cream in infusions of black tea and green tea [Camellia sinensis (L.) O. Kuntze]. Journal of Food Science and Technology, 37, 627–634. Luck, G., Liao, H., Murray, N. J., Grimmer, H. R., Warminski, E. E., Williamson, M. P., et al. (1994). Polyphenols, astringency, and praline-rich proteins. Phytochemistry, 37, 357–371. McManus, J. P., Davis, K. G., Beart, J. E., Gaffney, S. H., & Lilley, T. H. (1985). Polyphenol interaction. Part I – Internation: Some observations on the reversible complexation of polyphenols with proteins and polysaccharides. Journal of Chemical Society Perkin Trans II, 1429–1438. Nagalakshmi, S., Ramaswamy, M. S., Natarajan, C. P., & Seshadri, R. (1984). The role of added carbohydrates in tea cream stabilization. Food Chemistry, 13, 69–77. Nagalakshmi, S., & Seshadri, R. (1983). A study of nitrogenous constituents of tea cream. Journal of Food Science and Technology, 20, 243–245. Penders, M. H. G. M., Jones, D. P., Needham, D., & Pelan, E. G. (1998). Mechanistic study of equilibrium and kinetic behaviour of tea cream formation. Food Hydrocolloids, 12, 9–15. Pintauro, N. D. (1977). Tea and soluble tea products manufacture. Food Technology Review, 38, 123–124. Powell, C., Clifford, M. N., Ople, S. C., Ford, M. A., Robertson, A., & Gibson, C. L. (1993). Tea cream formation: The contribution of black tea phenolic pigments determined by HPLC. Journal of the Science of Food and Agriculture, 63(1), 77–86. Roberts, E. A. H. (1962). Economic importance of flavonoid substances – Tea fermentation. In The Chemistry of Flavonoid Compounds (pp. 468–509). Oxford: Pergamon Press. Roberts, E. A. H. (1963). The phenolic substances of manufactured tea. X – The cream down of the liquors. Journal of the Science of Food and Agriculture, 14, 700–705. Rutter, P. (1971). A physico-chemical study of tea cream. PhD thesis, Leeds University. Rutter, P., & Stainsby, G. (1975). The solubility of tea cream. Journal of the Science of Food and Agriculture, 26, 455–463. Selvendran, R. R., Perera, B. P. M., & Selvendran, S. (1973). Changes in the ethanolinsoluble material of tea leaves (Camellia sinensis L.) during maturation. Journal of the Science of Food and Agriculture, 24, 161–165. Seshadri, R., & Nagalakshmi, D. (1988). New hydrophobic lipid interaction in tea cream. Food Science and Technology, India, 45, 79–86. Smith, R. F. (1968). Studies on the formation and composition of tea ‘cream’ in tea infusions. Journal of the Science of Food and Agriculture, 19, 530–534. Smith, M. A. (1989). A physico-chemical study of the processes involved in the formation of tea cream. PhD thesis, University of Bristol. Wan, X. C. (2003). Tea biochemistry. Beijing: China Agricultural Press (in Chinese). Zhong, L. (1989). Methods of chemical and physical evaluation of tea quality. Shanghai: Shanghai Science and Technology Press (in Chinese).
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Cream formation and main chemical components of green tea infusions processed from different parts of new shoots Jun-Feng Yin a,1,*, Yong-Quan Xu a,1, Hai-Bo Yuan a, Long-Xin Luo b, Xiao-Jun Qian b a b
Engineering Research Center for Tea Processing, Tea Research Institute Chinese Academy of Agricultural Sciences, 9 Meiling Road, Hangzhou 310008, China Shenzhen Shenbao Huacheng Foods Co. Ltd., 22 Jinyuan Road, Shenzhen 518020, China
a r t i c l e
i n f o
Article history: Received 15 June 2008 Received in revised form 13 September 2008 Accepted 1 October 2008
Keywords: Cream Green tea Formation Chemical components
a b s t r a c t The formation of green tea cream and its chemical components were investigated. The green tea infusions were processed from different parts of new shoots: the bud and the first leaf, the second leaf and its implicative stem, the third leaf and its implicative stem, and the fourth leaf and its implicative stem, which were named as first part, second part, third part and fourth part, respectively. The results showed that the formation of tea cream and its settlement slowed down gradually from the first part to the fourth part, and that the amount of tea cream also decreased accordingly. The amount of tea cream was influenced remarkably by the chemical components in the green tea infusion. The main components of green tea cream were polyphenols (29.86 –78.66%), total sugar (14.47–27.62%) and caffeine (2.35–10.43%). Catechins (12.8–42.5%) were the main components of polyphenols which participated in tea cream formation. The main components in the catechins were found to be ( )-epigallocatechin (EGC), ( )-epigallocatechin gallate (EGCG), ( )-epicatechin (EC) and ( )-epicatechin gallate (ECG). Seven minerals were found in the tea cream, including Ca2+, K+, Mg2+, Mn2+, Na+, Zn2+ and Ni2+. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction Tea cream is formed whilst hot aqueous tea infusion cools down, which not only has an unattractive appearance but also damages both taste and colour of tea. The main constituents of black tea cream were thearubigins (TRs), theaflavina (TFs) and caffeine (Roberts, 1962, 1963; Smith, 1968). Collier, Mallows, and Thomas (1972), Rutter (1971) and Rutter and Stainsby (1975) concluded that the formation of tea cream was governed by various molecular types of interactions including polyphenol–caffeine complexation and polyphenol–polyphenol interactions. Polyphenol–caffeine complexation is influenced by a number of gallate and hydroxyl groups of the polyphenols. Protein (Nagalakshmi & Seshadri, 1983) and a lipid complex (Seshadri & Nagalakshmi, 1988) were identified in black tea cream. Tea cream also has been found in green tea infusion (Liang, Lu, & Zhang, 2002) and in semifermented tea infusion (Chao & Chiang, 1999a). However, most researches related to tea cream formation have focused on black tea. The primary components of semifermented tea cream were catechins (30%), caffeine (20%) and protein (16%), and EGCG and ECG were found to be the major catechins precipitated during cream-
* Corresponding author. Tel.: +86 571 86650594; fax: +86 571 86650056. E-mail address: [email protected] (J.-F. Yin). 1 These authors contributed equally to this work. 0308-8146/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2008.10.004
ing, constituting 19% and 5% of the tea cream, respectively (Chao & Chiang, 1999a). Liang and Bee (1992) investigated the morphology of green tea cream particles by using optical and electron microscopes, and revealed that tea cream could be formed in the absence of thearubigins and theaflavins. Liang et al. (2002) also observed that caffeine, gallocatechine (GC) and EGCG were predominant in green tea cream, and that gallated catechins had stronger creaming ability than un-gallated catechins. However, little information on the chemical components except catechins and caffeine has been reported, and the influence of chemical components in green tea infusions when tea cream formed was not noticed. The amount of tea cream formed in tea infusions is influenced by various parameters including chemical composition (Liang et al., 2002; Penders, Jones, Needham, & Pelan, 1998; Smith, 1989). There are different chemical compositions in different parts of new shoots. The contents of polyphenols, catechins, caffeine, free amino acids, protein, magnesium (Mg), zinc (Zn) and kalium (K) decrease gradually, whilst the contents of total sugar, flavones, starch, chlorophyll, calcium (Ca), manganese (Mn) and aluminium (Al) increase gradually, amongst one leaf and a bud, second leaf, third leaf and fourth leaf of the new shoots (Chen, 1982; Selvendran, Perera, & Selvendran, 1973; Wan, 2003). Consequently, green tea infusions processed from different parts of new shoots can demonstrate the effects of the chemical components in green tea infusion better when green tea cream formed. The objectives of this study were to investigate the formation of green tea cream,
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chemical compositions of the tea cream and the effects of the chemical components in the tea infusions processed from different parts of new shoots when tea cream formed. 2. Materials and methods 2.1. Tea leaves Shoots with four leaves and a bud from tea plant (Camellia sinensis (L.) O. Kuntze cv. Zhenghe dabaicha) were harvested in August 2007 from tea garden of the Tea Research Institute of Chinese Academy of Agricultural Sciences. Every new tea shoot was separated into four parts, which were the bud and the first leaf, the second leaf and its implicative stem, the third leaf and its implicative stem, and the fourth leaf and its implicative stem. These parts of new shoots were named as first part, second part, third part and fourth part, respectively. After withering for 3 h, every part of the tea leaves was panned at 130 °C for 8 min, rolled for 5 min, first dried at 95 °C for 30 min and then dried at 80 °C to a final moisture content of 4%. The dry tea leaves were stored in a freezer at 20 °C for further use. 2.2. Preparation of the tea infusion The ground tea leaves (20–60 mesh) were extracted with distilled water (1:20, w/w) at 70 °C for 10 min. The extract was filtered through 300 mesh screen and then quickly cooled down to 25 °C or lower with a glass condenser using water (15 °C) as a cooling medium. The cooled extract was then centrifuged at 10,000g at 10 °C for 15 min to obtain a clarified infusion. 2.3. Formation and separation of the tea cream The clarified infusion was sterilized at 90 °C for 5 min, and every 45 ml was filled in a lathy transparent bottle. The bottles were sterilized beforehand. Tea infusion in the bottles was cooled down to 25 °C, and then stored at 10 °C for 20 days to observe tea cream formation. Tea cream was separated by centrifuging at 10,000g at 10°C for 15 min, and the supernatant was discarded. The precipitated tea cream was rinsed with 10 ml distilled water, and then dissolved in 5 ml of 50% (v/v) ethanol solution, and then diluted to 50 ml with distilled water. 2.4. Observation of tea cream formation The observation team consisted of 10 members who were trained before. The infusions were observed by colour, clarity and the amount of tea cream at the bottom of the bottle during storage at 10 °C. The result was determined together by the team, and the observation indexes are described in Table 1. 2.5. Analysis of chemical constituents of tea infusion and tea cream 2.5.1. Analysis of total solids content and the amount of tea cream The total solids contents of the tea infusions were determined by drying 20 ml of the infusion at 80 °C for 48 h. The amount of Table 1 The observation index of phenomena for tea cream formation during storage at 10 °C. Index
1
2
3
4
Colour
Green Pellucid
Amount of tea cream
No deposit
A little deposit
Greenyellow A little turbid Visible deposit
Yellow
Clarity
Yellowgreen Sub-pellucid
Turbid Much visible deposit
tea cream in tea infusions was determined by referring to the method described by Nagalakshmi, Ramaswamy, Natarajan, and Seshadri (1984). The tea liquor in the bottles was centrifuged at 10,000g at 10 °C for 15 min. The supernatant was discarded. The precipitated tea cream that was obtained was washed with two aliquots of 5 ml distilled water in a weighed glass dish having a diameter of 9 cm, and dried at 80 °C for 48 h. 2.5.2. Analysis of free amino acids The content of free amino acids in the tea infusions and tea cream was determined with a spectrophotometer (UV-2550, Shimadzu (Suzhou) Instruments Manufacturing, Co., Ltd., Suzhou, China) by ninhydrin colour reaction method (Zhong, 1989), which was performed at 540 nm with glutamic acids as the standard of free amino acids. The standard of the free amino acids graph is given as C = (A570 + 0.0868) 1.51 1, R2 = 0.9996. C was the concentration of the free amino acids, and A570 was the absorbance (A) at 570 nm. 2.5.3. Analysis of tea polyphenols The content of tea polyphenols in the tea infusions and tea cream was determined by the spectrophotometric method with FeSO4, 3.5 10 3 M potassium sodium tartrate and buffer described by Zhong (1989). Absorbance (E1) of the reaction solution was determined at 540 nm in a 1 cm photometer cuvette with Shimadzu UV-2550 spectrophotometer. Absorbance (E2) of the control reaction solution (containing 5 ml distilled water, 5 ml dyeing solution and 15 ml buffer) was determined at 540 nm as described earlier. The content of tea polyphenols was calculated using the following equation: TP (mg L 1) = (E1 E2) 3.9133 103. 2.5.4. Analysis of protein, pectin and flavones The protein content in the tea infusion and tea cream was determined by bicinchoninic acid (BCA) method (GENMED SCIENTIFICS INC., USA). The pectin content was determined by the procedure proposed by Blumenkrantz and Asoboe-Hansen (1973) using anhydrogalacturonic acid (AGA) as a standard. The flavones content in the tea infusions was determined at 420 nm by the spectrophotometric method with 1% AlCl3 as described by Zhong (1989). 2.5.5. Analysis of total sugar and polysaccharides The total sugar content was determined by the anthrone-sulphuric acid reaction, using glucose as a standard (Fu, Xie, Nie, Zhou, & Wang, 2001). Two milliliters of tea infusion was reacted with 8 ml anthrone reagent (2 g anthrone dissolves in 1000 ml analytically pure sulphuric acid) at 100 °C for 10 min, and then the absorbance (A620) was determined with SHIMADZU UV-2550 spectrophotometer after being cooled rapidly for 10 min. The standard glucose graph is given as C = 0.3589 * A620 0.0034, R2 = 0.999. C was the concentration of the glucose. Preparation of polysaccharides: 5 ml of tea infusion was precipitated with 10 ml 100% (v/v) ethanol at 10°C for 24 h, and centrifuged (10 min, 5000g) to get the sediment (Chen, Zhang, & Xie, 2005). Polysaccharides were dissolved and fixed to 25 ml with distilled water, and then analysed by referring to total sugar method. 2.5.6. Analysis of tea catechins and caffeine Analysis of tea catechins and caffeine was carried out by HPLC method (Liang et al., 2002). The tea infusion was filtered through a 0.2 lm Millipore filter before injection (Model Shimadzu LC2010A, Shimadzu Corporation, Kyoto, Japan). The HPLC conditions were as follows: injection volume, 5 ll; column, 5 lm – DiamonsilTM C18 (4.6 mm 250 mm); temperature, 40 °C; mobile phase A, acetonitrile/acetic acid/water (6:1:193); mobile phase B, acetonitrile/acetic acid/water (60:1:139); gradient, 100% mobile phase A to 100% mobile phase B by linear gradient during the early
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J.-F. Yin et al. / Food Chemistry 114 (2009) 665–670 Table 2 Phenomena (colour, charity and the amount of cream) of cream formation in the green tea infusions processed from different parts of new shoots during storage at 10 °C.
Time (day) 0
First part
Second part
Third part
Fourth part
Green-yellow, pellucid,
Green-yellow, pellucid,
Green-yellow,
Yellow-green, pellucid,
no deposit
no deposit
pellucid, no deposit
no deposit
1
Green-yellow, turbid, visible brown deposit
Green-yellow, turbid, a Green-yellow, turbid, little brown deposit
no deposit
Yellow-green, a little turbid, no deposit
10 Green-yellow, sub-pellucid, much visible brown deposit with white deposit around
Green-yellow, pellucid, visible
brown deposit
with white deposit
Green-yellow, pellucid, a little grey brown deposit
around
Flat green-yellow, pellucid, a little grey brown deposit with white deposit around
20 Green-yellow,
Green-yellow,
Green-yellow,
Flat green-yellow,
sub-pellucid, much
sub-pellucid, visible
sub-pellucid, a little
pellucid, a little brown
visible brown deposit
brown deposit with
brown deposit at the
deposit at the bottom
with white deposit
white deposit around
bottom with white
with white deposit
around (about one third
(about one fifth of the
deposit around
around
of the bottom)
bottom)
The observational infusion was 25 °C when on 0 day, 10°C from 1st day to 20th day.
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45 min and then 100% mobile phase B up to 60 min; flow rate, 1 ml min 1; detector, Shimadzu SPD ultraviolet detector (Shimadzu Corporation, Kyoto, Japan) at 280 nm. 2.5.7. Analysis of minerals The minerals in tea infusion and tea cream were determined by ICP-OES (IRIS/AP, Thermo Jarrell Ash Corp., America). Analytical conditions were as follows: Detector CID, low wavelength max intergration time: 15 s; high wavelength max intergration time: 5 s; nebulizer pressure: 28 psi; pump speed: 100 r min 1; auxiliary gas: medium (1.0 L min 1); RF power: 1150 W. 2.6. Statistical analysis Results are presented as mean value ± standard deviation (at least three replicates). Analysis of variance and significant differences amongst means, and correlation analysis were done by one-way ANOVA using SPSS (Version 11.5, SPSS Inc., Chicago, USA).
3. Results and discussion 3.1. Tea cream formation in the green tea infusion during storage at 10 °C Tea cream formation was observed in terms of colour, clarity and the amount of tea cream at the bottom of the bottle during storage at 10 °C. There was some difference between the infusions processed from different parts of the new shoots (Table 2). The infusions were pellucid at 25 °C, but appeared turbid after storage at 10 °C for 5 h, and then the infusions turned pellucid after the sedimentation of tea cream. The speed of deposit cumulating at the bottom of bottle was the fastest for the first part, followed by that of the second part and the fourth part, and that of the third part was the slowest. The amount of deposit of the first part was the largest, and then that of the second part, those of the third
and fourth parts were the smallest. It was found that the colour of the infusions changed from yellow-green to yellow during the storage, and the colour of the cream of the first part and the second part was darker than that of the third part and the fourth part as shown in the pictures (Table 2). In addition, there was demixing phenomena appeared in tea cream. A compact brown deposit was found at the bottom of the bottle, and an incompact white deposit was found on and around of the compact brown deposit. During the storage at 10 °C, the demixing phenomena of the first part and the second part appeared on the eighth day, whilst that of the third part on the 12th day and that of the fourth part on the 10th day. The appearance of demixing phenomena was concerned with the speed of the deposit cumulating at the bottom of the bottles. During the storage at 10 °C, a white deposit appeared after a brown deposit, which was the main deposit in the green tea infusion. Polyphenols, total sugar and caffeine (Table 3) were found to be the main components of the green tea cream. The white deposit of green tea cream might be caused by some chemical components such as free amino acids at low concentration. Demixing also has been reported by Penders et al. (1998) in the formation of black tea cream, and they observed that in the more concentrated region of the miscibility gap (>2% w/w), demixing (spinodal decomposition) was the predominant mechanism of tea cream formation, reflecting the substantial insolubility of polyphenols. Demixing in green tea cream may be caused by different speeds of aggregation and precipitation of different chemical components in the green tea infusion. 3.2. Comparison of chemical components in green tea cream and infusions processed from different parts of new shoots Content of some chemical components was found to be quite different in the infusions and tea creams between different disposals (Table 3). Obviously, the formation of tea cream was influenced by chemical components. This agreed with Harbron’s observation (1986) from black tea cream. The solids content of the infusions in-
Table 3 Main chemical components in green tea cream and infusions processed from different parts of new shoots (mg L Chemical components
Solids concentration Polyphenols Amino acids Flavones Total sugar Polysaccharides Protein Pectin Caffeine
Tea infusion
, mean ± s.d.).
Tea cream
First part
Second part
Third part
Fourth part
First part
Second part
Third part
Fourth part
16157.5 ± 10.6 9730.3 ± 22.6 699.2 ± 6.9 289.3 ± 1.3 4334.0 ± 184.0 374.2 ± 18.4 123.8 ± 15.6 2770.5 ± 705.3 1131.6 ± 8.0
17842.5 ± 88.4 8647.7 ± 39.1 888.2 ± 15.8 411.0 ± 1.8 4755.7 ± 260.1 354.0 ± 6.3 57.5 ± 0.0 2941.3 ± 163.3 1022.9 ± 10.5
18085 ± 81.3 8204.3 ± 125.8 953.9 ± 20.7 444.9 ± 0.8 5603.6 ± 253.8 369.2 ± 19.0 90.6 ± 0.0 3477.0 ± 84.9 997.7 ± 8.8
18397.5 ± 28.3 7513.0 ± 39.1 967.8 ± 18.2 425.2 ± 2.5 5827.9 ± 126.9 397.5 ± 1.9 118.2 ± 7.8 2613.5 ± 104.5 923.1 ± 11.3
1228.9 ± 20.5 966.7 ± 32.2 20.3 ± 0.5 28.4 ± 0.7 177.8 ± 6.5 10.6 ± 1.7 9.5 ± 4.0 31.1 ± 4.6 128.2 ± 10.8
517.2 ± 12.3 269.6 ± 13.6 19.2 ± 0.8 16.6 ± 0.4 100.9 ± 18.8 8.3 ± 2.2 4.7 ± 1.2 26.1 ± 2.1 17.1 ± 0.1
466.7 ± 15.3 194.2 ± 21.9 18.1 ± 0.3 12.8 ± 0.4 128.9 ± 5.6 10.5 ± 3.2 3.6 ± 1.1 20.6 ± 2.2 17.5 ± 0.3
434.4 ± 9.8 129.7 ± 18.9 12.5 ± 0.6 9.8 ± 0.5 89.4 ± 5.8 5.5 ± 1.5 5.2 ± 2.4 16.7 ± 1.7 10.2 ± 0.2
Table 4 Catechin components in green tea cream and infusions processed from different parts of new shoots (mg L Catechin components
1
Tea infusion
1
, mean ± s.d.).
Tea cream
First part
Second part
Third part
Fourth part
First part
Second part
Third part
Fourth part
GC EGC C EGCG EC GCG ECG CG
210.6 ± 2.3 1368.6 ± 12.5 166.4 ± 3.5 2871.8 ± 34.1 530.1 ± 2.7 39.6 ± 0.3 788.9 ± 5.5 22.8 ± 0.3
261.5 ± 3.2 1724.9 ± 18.1 110.7 ± 1.3 2338.0 ± 24.7 619.0 ± 9.2 35.4 ± 0.5 612.1 ± 6.7 44.2 ± 1.9
318.9 ± 1.8 1942.5 ± 44.7 88.3 ± 0.1 2155.9 ± 17.2 598.4 ± 5.6 47.5 ± 0.4 513.2 ± 5.4 47.1 ± 0.5
258.1 ± 6.8 1809.6 ± 18.2 84.2 ± 0.6 1875.7 ± 24.4 538.3 ± 5.4 23.7 ± 0.0 423.5 ± 5.6 45.6 ± 0.2
0 56.9 ± 0.7 12.1 ± 0.2 320.2 ± 10.6 21.6 ± 3.8 11.2 ± 0.0 97.6 ± 4.1 3.3 ± 0.3
0 23.9 ± 0.7 0 45.4 ± 1.8 8.8 ± 0.3 0 13.1 ± 0.7 0
0 36.7 ± 0.5 0 40.0 ± 0.4 9.7 ± 0.1 0 8.7 ± 0.1 0.5 ± 0.0
0 22.9 ± 0.9 0 22.1 ± 0.8 5.7 ± 0.2 0 4.6 ± 0.1 0
Total Gallated catechins
5998.7 ± 61.3 3723.0 ± 40.3
5745.8 ± 65.7 3029.7 ± 33.9
5711.8 ± 75.6 2763.7 ± 23.5
5058.6 ± 61.2 2368.4 ± 30.2
522.8 ± 18.2 432.3 ± 14.9
91.2 ± 3.6 58.5 ± 2.6
95.7 ± 1.1 49.3 ± 0.4
55.4 ± 2.1 26.7 ± 1.0
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creased gradually from the first part to the fourth part, but the amount of tea cream in the corresponding infusions reduced. In the tea cream, polyphenols were found to be 29.86–78.66%, and next, total sugar, 14.47–27.62%; caffeine, 2.35–10.43%; pectin, 2.53–5.05%; flavones, 2.26–3.21%; free amino acids, 1.65–3.88%; polysaccharides, 0.86–2.25% and protein, 0.59–0.91%. The amount of tea cream in the tea infusions, as well as the percentage (the amount of cream/solids content of tea infusion, w/ w%), reduced gradually from the first part to the fourth part. From the first part to the fourth part, the contents of polyphenols and caffeine in both tea infusion and tea cream reduced gradually, similar to the amount of the tea cream. Good positive correlation was found between the amount of tea cream and the content of polyphenols (c = 0.90, p 6 0.01) and caffeine (c = 0.91, p 6 0.01). However, the contents of the other chemical components except starch (c = 0.62, p 6 0.01) were all negatively correlated with the amount of tea cream. Both polyphenols and caffeine were found to be predominant in black tea (Rutter & Stainsby, 1975; Smith, 1968) and in semifermented tea (Chao & Chiang, 1999a). Therefore, in this study, because of the contents in tea cream and high positive correlation with the amount of tea cream, polyphenols and caffeine were considered as the principal chemical components in the formation of green tea cream. The content of most chemical components that participated in tea cream formation was much more in the first part than in the other parts. From the first part to the fourth part, free amino acids content in whole tea increased gradually, but free amino acids content in tea cream reduced gradually. No evident trend change in protein content was found. Free amino acid was also found to participate in cream formation in Paochung tea (Chao & Chiang, 1999a). The trend change in contents of flavones, total sugar and pectin amongst the four parts was similar to that in the free amino acids. There was no clear trend change in the content of polysaccharides, which have been shown to inhibit the precipitation of polyphenol–protein mixtures (Luck et al., 1994). These chemical components may not be the main factor of the tea cream formation, and we suspect that they may simply co-precipitate with insoluble complexes during tea cream formation. 3.3. Comparison of catechins components in green tea cream and infusions processed from different parts of new shoots Catechins are the main components of tea polyphenols, and they were regarded as the principal constituents of black tea cream (Powell et al., 1993; Roberts, 1963) and semifermented tea cream (Chao & Chiang, 1999a). It can be found from Table 4 that the catechins components that participated principally in tea cream formation were ( )-epigallocatechin (EGC), EGCG, ( )-epicatechin (EC) and ECG. They were all epi-catechins, thus epi-catechins may participate in
the formation of green tea cream. Gallated catechins (49.19– 82.69%) were the main component of the catechins in tea cream, which was also observed by Chao and Chiang (1999b) and Liang et al. (2002). Further, gallated catechins have a galloyl group and a hydroxylphenyl B ring acting like a claw (Chao & Chiang, 1999b). And gallated catechins having stronger creaming ability were considered to offer more hydroxyl groups for hydrogen bonding, which is thought to be an important force for aggregation of compounds involved in tea cream formation (Bee, Izzard, Harbron, & Stubbs, 1987; McManus, Davis, Beart, Gaffney, & Lilley, 1985). Similar to the amount of tea cream, the content of total catechins (12.8–42.5%) in tea cream, especially gallated catechins (Table 4), decreased gradually from the first part to the fourth part. The contents of ( )-catechin (C), EGCG and ECG in tea infusions, as well as the content of the total catechins in tea cream, reduced gradually from the first part to the fourth part. EGCG (39.89– 61.25%) and ECG (8.30–18.67%) were main components of catechins in tea cream, and EGCG (c = 0.93, p 6 0.01) and ECG (c = 0.91, p 6 0.01) were highly positively correlated with the amount of tea cream. Therefore, EGCG and ECG may be the crucial catechins components which participated in the tea cream formation. However, GC and EGCG were observed as the predominant compounds of catechins in green tea cream by Liang et al. (2002). The contents of GC, EGC and ( )-catechin gallate in tea infusions were highly negatively correlated with the amount of 0.56, p 6 0.01) and tea cream, whilst the contents of EC (c = ( )-gallocatechin gallate (GCG) (c = 0.23, p 6 0.01) were not correlated significantly. They may not be the pivotal catechin components which participated in the tea cream formation. 3.4. Comparison of minerals components in green tea cream and infusions processed from different parts of new shoots In the infusions of green tea, 11 main minerals were found according to the content (Table 5). The content of different minerals in tea infusion and tea cream was different. Seven minerals were found in the green tea cream, including Ca2+, K+, Mg2+, Mn2+, Na+, Zn2+ and Ni2+. And K+ (42.67–62.02%), Na+ (17.43– 28.82%) and Ca2+ (11.02–21.47%) were the main minerals in the green tea cream. Ca2+ was also found to be in high concentration in a tea infusion and to participated strongly in the cream formation by Pintauro (1977), and it was also found to enhance the self-association of caffeine, polyphenols and theaflavin, but had little effect on hetero-association (Jobstl, Fairclough, Davies, & Williamson, 2005). The main tea infusion components in the Ca2+ complex precipitation were polyphenols, and EGCG and ECG were the highest catechines found by Guo and Chen (1991), and it also had been substantiated that K+, Mg2+, Mn2+, Zn2+ and Ni2+ can be associated with tea infusion components.
Table 5 Main minerals in green tea cream and infusions processed from different parts of new shoots (mg L Mineral components
Tea infusion
1
, mean ± s.d.). Tea cream
First part
Second part
Third part
Fourth part
First part
Second part
Third part
Fourth part
Al3+ Ca2+ Cu2+ Fe3+ K+ Mg2+ Mn2+ Na+ Zn2+ Ni2+
4.28 ± 0.19 14.51 ± 0.24 0.11 ± 0.004 0.05 ± 0.016 486.9 ± 6.15 35.64 ± 0.42 23.91 ± 0.81 14.45 ± 0.58 2.75 ± 0.15 0.207 ± 0.004
9.23 ± 0.27 19.22 ± 1.90 0.13 ± 0.009 0.04 ± 0.006 521.5 ± 12.14 40.60 ± 0.76 32.15 ± 0.59 14.90 ± 0.29 2.54 ± 0.02 0.186 ± 0.003
14.71 ± 0.31 20.54 ± 0.94 0.08 ± 0.001 0.06 ± 0.001 582.3 ± 7.34 43.44 ± 0.58 35.24 ± 0.29 16.04 ± 1.20 2.67 ± 0.04 0.190 ± 0.002
19.78 ± 0.15 23.97 ± 1.03 0.09 ± 0.007 0.05 ± 0.004 560.2 ± 2.08 38.05 ± 0.21 33.66 ± 0.55 15.90 ± 0.50 2.59 ± 0.14 0.196 ± 0.001
0 4.03 ± 0.12 0 0 8.01 ± 0.29 0.95 ± 0.02 0.48 ± 0.04 5.17 ± 0.34 0.097 0.020 ± 0.002
0 2.53 ± 0.15 0 0 8.27 ± 0.28 0.92 ± 0.02 0.45 ± 0.02 4.96 ± 0.26 0.058 0.014 ± 0.001
0 1.70 ± 0.08 0 0 9.57 ± 0.08 0.90 ± 0.05 0.52 ± 0.11 2.69 ± 0.08 0.046 0.009 ± 0.003
0 1.82 ± 0.13 0 0 6.68 ± 0.13 0.60 ± 0.03 0.35 ± 0.02 2.62±0.11 0.021 0.008 ± 0.001
Total
582.8 ± 8.5
640.5 ± 16.0
715.3 ± 10.7
694.4 ± 4.6
41.65 ± 1.67
35.95 ± 0.95
32.86 ± 0.06
25.67 ± 0.19
670
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The total content of main minerals in tea infusions, as well as Ca2+, K+, Mg2+, Mn2+ and Na+, increased from the first part to the third part, but the content of fourth part was a little less than that of the third part. Similar to the amount of tea cream (Table 2), the total content of minerals in tea cream, as well as Na+, Ca2+, Mg2+, Zn2+ and Ni2+, decreased from the first part to the fourth part. The trend change in minerals content in tea cream from the first part to the fourth part was not influenced directly by the content in tea infusion. Accordingly, we considered that mineral was not the predominant component of tea cream formation. 4. Conclusion The formation of tea cream was investigated, and the chemical components in green tea cream and infusions, which were processed from different parts of new shoots, were compared and investigated. There was visible demixing in green tea cream. The amount of tea cream decreased gradually from the first part to the fourth part, which was influenced remarkably by the chemical components in green tea infusion. The main components of green tea cream were polyphenols (29.86–78.66%), total sugar (14.47– 27.62%) and caffeine (2.35–10.43%). The main catechins components of green tea cream were EGC, EGCG, EC and ECG. And K+ (42.67–62.02%), Na+ (17.43–28.82%) and Ca2+ (11.02–21.47%) were the main minerals in the green tea cream. Polyphenols, caffeine, EGCG and ECG were found to be the principal constituents of green tea cream formation. Acknowledgements The authors thank Hua-Fu Wang, Liang Chen, and Wen-Yan Han for their revision, and Chun-Hong Feng, Yuan-Zhi Shi, Li-Feng Ma, Xin-Chao Wang, Can-Yan Xiao, Su-Qin Chen, Xiang-Feng Gao, Dan-Yu Shen and Fang Wang for offering their kind help. The authors also thank the two anonymous reviewers for their constructive comments. References Bee, R. D., Izzard, M. J., Harbron, S. R., & Stubbs, J. M. (1987). The morphology of black tea cream. Food Microstructure, 6, 47–56. Blumenkrantz, N., & Asoboe-Hansen, G. (1973). New method for quantitative determination of uronic acids. Analytical Biochemistry, 54, 484–490. Chao, Y. C., & Chiang, B. H. (1999a). Cream formation in a semifermented tea. Journal of the Science of Food and Agriculture, 79, 1767–1774. Chao, Y. C., & Chiang, B. H. (1999b). The roles of catechins and caffeine in cream formation in a semi-fermented tea. Journal of the Science of Food and Agriculture, 79(12), 1687–1690.
Chen, Q. K. (1982). Sample analyse of tea chemistry. Hangzhou: Zhejiang Agricultural University Press (in Chinese). Chen, H. X., Zhang, M., & Xie, B. J. (2005). Components and antioxidant activity of polysaccharide conjugate from green tea. Food Chemistry, 90, 17–21. Collier, P. D., Mallows, R., & Thomas, P. E. (1972). Interactions between theaflavins, flavanols and caffeine. Phytochemistry, 11, 867. Fu, B. Q., Xie, M. Y., Nie, S. P., Zhou, P., & Wang, Y. X. (2001). Determination of the contents of polysaccharides in tea. Chinese Journal of Food Science, 22(11), 69–73. Guo, B. Y., & Chen, Q. K. (1991). Complex of tea infusion components with metal ions. Journal of Tea Science, 11(2), 139–144. Harbron, R. S. (1986). A colloid-chemical study of tea cream from instant black tea infusion. PhD thesis, University of Bristol. Jobstl, E., Fairclough, J. P. A., Davies, A. P., & Williamson, M. P. (2005). Creaming in Black Tea. Journal of Agricultural and Food Chemistry, 53, 7997–8002. Liang, Y., & Bee, R. (1992). A study on morphology of green tea cream particles. Journal of Zhejiang Agricultural University, 8, 17–20. Liang, Y. R., Lu, J. L., & Zhang, L. Y. (2002). Comparative study of cream in infusions of black tea and green tea [Camellia sinensis (L.) O. Kuntze]. Journal of Food Science and Technology, 37, 627–634. Luck, G., Liao, H., Murray, N. J., Grimmer, H. R., Warminski, E. E., Williamson, M. P., et al. (1994). Polyphenols, astringency, and praline-rich proteins. Phytochemistry, 37, 357–371. McManus, J. P., Davis, K. G., Beart, J. E., Gaffney, S. H., & Lilley, T. H. (1985). Polyphenol interaction. Part I – Internation: Some observations on the reversible complexation of polyphenols with proteins and polysaccharides. Journal of Chemical Society Perkin Trans II, 1429–1438. Nagalakshmi, S., Ramaswamy, M. S., Natarajan, C. P., & Seshadri, R. (1984). The role of added carbohydrates in tea cream stabilization. Food Chemistry, 13, 69–77. Nagalakshmi, S., & Seshadri, R. (1983). A study of nitrogenous constituents of tea cream. Journal of Food Science and Technology, 20, 243–245. Penders, M. H. G. M., Jones, D. P., Needham, D., & Pelan, E. G. (1998). Mechanistic study of equilibrium and kinetic behaviour of tea cream formation. Food Hydrocolloids, 12, 9–15. Pintauro, N. D. (1977). Tea and soluble tea products manufacture. Food Technology Review, 38, 123–124. Powell, C., Clifford, M. N., Ople, S. C., Ford, M. A., Robertson, A., & Gibson, C. L. (1993). Tea cream formation: The contribution of black tea phenolic pigments determined by HPLC. Journal of the Science of Food and Agriculture, 63(1), 77–86. Roberts, E. A. H. (1962). Economic importance of flavonoid substances – Tea fermentation. In The Chemistry of Flavonoid Compounds (pp. 468–509). Oxford: Pergamon Press. Roberts, E. A. H. (1963). The phenolic substances of manufactured tea. X – The cream down of the liquors. Journal of the Science of Food and Agriculture, 14, 700–705. Rutter, P. (1971). A physico-chemical study of tea cream. PhD thesis, Leeds University. Rutter, P., & Stainsby, G. (1975). The solubility of tea cream. Journal of the Science of Food and Agriculture, 26, 455–463. Selvendran, R. R., Perera, B. P. M., & Selvendran, S. (1973). Changes in the ethanolinsoluble material of tea leaves (Camellia sinensis L.) during maturation. Journal of the Science of Food and Agriculture, 24, 161–165. Seshadri, R., & Nagalakshmi, D. (1988). New hydrophobic lipid interaction in tea cream. Food Science and Technology, India, 45, 79–86. Smith, R. F. (1968). Studies on the formation and composition of tea ‘cream’ in tea infusions. Journal of the Science of Food and Agriculture, 19, 530–534. Smith, M. A. (1989). A physico-chemical study of the processes involved in the formation of tea cream. PhD thesis, University of Bristol. Wan, X. C. (2003). Tea biochemistry. Beijing: China Agricultural Press (in Chinese). Zhong, L. (1989). Methods of chemical and physical evaluation of tea quality. Shanghai: Shanghai Science and Technology Press (in Chinese).