alexa Correlation between Sensory Evaluation Scores and Flavor Attributes of Black Teas from Around the World

ISSN: 2157-7110

Journal of Food Processing & Technology

  • Research Article   
  • J Food Process Technol 2018, Vol 9(4): 726
  • DOI: 10.4172/2157-7110.1000726

Correlation between Sensory Evaluation Scores and Flavor Attributes of Black Teas from Around the World

Duan Y1,2, Song X1,2, Yang Y3, Li L1,2, Zhao Y1,2, Wang Y, Fang W1,2* and Zhu X1,2*
1College of Horticulture, Nanjing Agricultural University, Nanjing, Jiangsu, P.R. China
2Tea Science Research Institute, Nanjing Agricultural University, Nanjing, Jiangsu, P.R. China
3Nanjing Rongdian Food Science and Technology Company Ltd, Nanjing, Jiangsu, PR China
*Corresponding Author(s): Fang W, College of Horticulture, Nanjing Agricultural University, No. 1, Weigang, Nanjing-210095, Jiangsu, PR China, Tel: 86- 25-8439-5182, Fax: 86- 25-8439-5182, Email: [email protected]
Zhu X, College of Horticulture, Nanjing Agricultural University, No. 1, Weigang, Nanjing-210095, Jiangsu, PR China, Tel: 86- 25-8439-5182, Fax: 86- 25-8439-5182, Email: [email protected]

Received Date: Mar 09, 2018 / Accepted Date: Mar 30, 2018 / Published Date: Apr 06, 2018

Abstract

Background: Black teas can be grouped into many types based on cultivar, region of origin, harvesting seasons, processing methods and other factors, all of which combine to produce different flavor attributes (taste and aroma). This study aimed to establish and predict the quality of different black teas based on the correlation between sensory evaluation scores and the principal chemical components.
Results and Discussion: Sensory evaluation, analysis of the principal chemical components, as well as correlation analysis of black teas from around the world, were performed in this study. Statistical analysis showed that sensory scores were significantly and positively correlated with tea polyphenols, caffeine, amino acids, thearubigins and thearubigins/theaflavins ratio, and the correlation coefficient was 0.4166, 0.6595, 0.4379, 0.4196, 0.4165, respectively, which determined black tea quality. Furthermore, the taste quality showed a significant and positive correlation with caffeine, thearubigins and the ratio of thearubigins/theaflavins, which correlation coefficient was 0.4396, 0.6109, 0.4938, respectively.
Conclusion: The aroma and taste of Chinese black teas were better than tea from other countries. The results may be attributed to the higher content of amino acids and caffeine in Chinese black teas.

Keywords: Black tea; Sensory quality; Chemical components; Correlation coefficient; Flavor comparison

Introduction

Tea (Camellia sinensis (L.) O. Kuntze) is a perennial crop and a very pleasant and popular beverage, which is consumed by over two-thirds of the world’s population [1,2]. The world’s tea production was around 5,561,339 metric tons in 2014. China is the world’s largest producer of tea, contributing 37.9% of the total global production, followed by India (21.7%), Kenya (8.0%), Sri Lanka (6.1%), Vietnam (4.1%), Turkey (4.1%), Indonesia (2.7%) and Iran (2.1%) [3].

Black tea is the most prevalent type of tea in the world, which accounts for approximately 75% of the world's tea trade. Black tea is manufactured through processes including, withering, rolling (cutting), fermenting and drying [4]. Fermentation plays a crucial role in the manufacturing of black tea, during which the chemical components and subsequent taste, aroma, color, and nutritional and biological properties of teas are greatly altered [5,6]. Furthermore, the taste and flavor in the tea brewing process were influenced by polyphenols, caffeine, amino acids and other components [7]. The polyphenols were oxidized and transformed to form the black tea pigments, theaflavins (TF, golden yellow) and thearubigins (TR, orange brown), during the manufacturing process. TF and TR are mainly responsible for the brightness, briskness and color of tea and improve tea quality [1,8,9]. Furthermore, the formation of black tea cream when the tea infusion became cold was related to TR, TF and caffeine contents [10,11]. Previous work also showed that the formation of tea cream was regulated by various chemical interactions including polyphenolcaffeine interactions and complex polyphenol-polyphenol interactions. Polyphenol-caffeine complexation was influenced by a number of gallate and hydroxyl groups of the polyphenol [12]. In summary, polyphenols and caffeine are crucial components, which have a strong influence on the taste of black tea brew.

The quality of black tea depends on the chemical components of tea infusions and has traditionally been evaluated by a professional tea taster who has developed their own language to describe various quality attributes of the tea infusion [13]. The analytical methods available to identify chemical constituents impacting tea quality are precise [14], however, they are also complex, time consuming, labor-intensive, expensive and require large amounts of organic solvents. The use of organoleptic evaluation to identify tea quality is rapid but results may be inaccurate, and can be easily influenced by various factors, including the environment and the mood of the evaluator [15]. In this study, the quality of black tea was explored through the correlation of sensory scores and principal chemical components. Furthermore, the flavor attributes of tea samples from various countries were compared.

Materials and Methods

Samples

Thirty-seven teas, representing nine countries of origin, different manufacturing methods, varieties and prices were used in this study based on primary production regions for black tea. The black tea samples were collected from different countries including, China (n=22), Sri Lanka (n=5), Vietnam (n=2), Kenya (n=2), India (n=2), Nepal (n=1), Malawi (n=1), Indonesia (n=1), Arabia (n=1). There were 22 black tea samples from China, including samples from the southern Yangtze River area (n=11), the southern China area (n=9), the Southwest China area (n=1), and the northern Yangtze River area (n=1). Samples represented different manufacturing methods, including loose black tea of China that are coincident with Orthodox black tea and other countries, and CTC which is conventional black tea processed by cut, tear and curl methods. Details on samples collected are shown in Table 1.

No. Classification Sample name Producing areas Grade Country
CS001 CTC Uva tea Sri Lanka
CS002 CTC Vietnam tea Vietnam
CS003 CTC Ceylon tea Sri Lanka
CS004 CTC Malawi tea Malawi
CS005 CTC Assam tea India
CS006 CTC Darjeeling tea India
CS007 CTC Nepal tea Nepal
CS008 CTC Kenya tea Kenya
CS009 CTC  Indonesia tea  Indonesia
CS010 CTC Earl Grey Tea Sri Lanka
CS011 CTC FV523 Vietnam
CS012 CTC Pure Kenya tea Kenya
CS013 CTC KANDY Tea Sri Lanka
CS035 CTC Arab tea Arab
CS036 CTC Ceylon tea Sri Lanka
CS014 LBT Lapsang souchong SC Grade 1 China
CS015 LBT Golden junmee SC China
CS016 LBT Lapsang souchong SC Grade 1 China
CS017 LBT Golden junmee SC China
CS018 LBT Panyong congou SC Special grade China
CS019 LBT Lapsang souchong SC Grade 1 China
CS020 LBT Panyong congou SC Special grade China
CS021 LBT Keemun tea SYR China
CS022 LBT Keemun tea SYR China
CS023 LBT Hainan tea SC China
CS024 LBT Wild tea SC Grade 1 China
CS025 LBT Yunnan tea  SW Special grade China
CS026 LBT Fuliang tea SYR Grade 1 China
CS027 LBT Jiangxi tea SYR  Premium grade China
CS028 LBT Ninggong tea SYR Special grade China
CS029 LBT Jiangsu tea SYR China
CS030 LBT Jiangsu tea SYR China
CS031 LBT Jiangsu tea SYR Special grade China
CS032 LBT White leaf tea SYR Special grade China
CS033 LBT Xinyang tea NYR China
CS034 LBT Hunan tea SYR Grade 1 China
CS037 LBT Zijuan tea SYR China

Notes: LBT: represents Loose black tea; SC: represents the Southern China tea area; SW: represents the Southwest China tea area; SYR: represents the Southern Yangtze River tea area; NYR: represents the Northern Yangtze River tea area

Table 1: Information on 37 black tea samples.

Chemicals

Catechin, epicatechin, epigallocatechin, epigallocatechin gallate, epicatechingallate were purchased from Sigma-Aldrich (St. Louis, MO, USA). Methanol, acetic acid and ethanol were of HPLC-grade and were purchased from Honeywell (Morris, NJ, USA). Other reagents were of analytical grade.

Sensory evaluation of black tea infusion

According to GB/T23776-2009 [16], 3 g of each black tea sample was infused with 150 mL of freshly boiled water for 5 min in a tea pot. The black tea infusion was then filtrated through a stainless-steel strainer into a porcelain tea bowl.

Six highly trained tea tasting panelists, who had previously achieved Chinese national certificates as senior tea panelists, participated in this study. During the process of sensory evaluation, the panelists used the method of collective evaluation of tea quality grade [17]. Five factors of sensory evaluation, including dry leaf appearance, liquor color, aroma, taste and infused leaf appearance [9,18]. were determined (Table 2). In case of CTC (Crush, Tear and Curl) black tea, that is usually graded on one of four scales of quality (such as whole leaf, broken leaf, fannings and dust), and an infusion of CTC was poured on the tea pot cover which had been used to brew tea for evaluation [9].

Classification Appearance Liquor Aroma Taste Infused
Loose black tea 25 10 25 30 10
CTC 20 10 30 30 10

Table 2: The proportion of five factors in different types of black tea.

Polyphenols and caffeine analysis

The tea infusion was filtered through a 0.45 μm Millipore (Tianjin Branch billion Lung Experimental Equipment Co., Ltd) filter before determination using a HPLC system (Shimadzu LC-5P, Kyoto, Japan) fitted with a C18 column. The measurement was described as follows: flow rate: 1.0 mL min-1; injection volume: 10 μL; mobile phase: A: methanol, B: 98% water and 2% acetic acid; gradient elution: 20%-25% A, 0-1 min; 25%-45% A, 1-12 min; 45%-90% A, 12-15 min; 90%-20% A, 15-16 min; maintained for 4 min.

Determination of free amino acids

The content of free amino acids in the tea infusions was estimated with a spectrophotometer (Model UV-5800; Shanghai yuan Analytical Instrument Co., Ltd., China). The ninhydrin dying method was used as described by GB/T8314-2003 for determination of total amino acid content, which was established at 570 nm, using glutamic acid as the standard.

Determination of TF and TR

Biochemical assessment of tea quality was carried out by estimation of TF and TR in black tea. A system analysis method for estimating TF, TR and TB in black tea was employed, using the simplified Roberts' method [19] as described previously [20], with slight modifications. The absorbance was measured on a UV spectrophotometer. The tea infusion was prepared by refluxing 3 g tea with 125 mL freshly boiled distilled water for 10 min on a water bath. The infusion (30 mL) was mixed with 30 mL ethyl acetate by shaking for 5 min. On separation of the two phases, the bottom layer (A1) was drained off and the ethyl acetate extract (A2) contained the TF and part of TR. A quantity (2 mL) of the ethyl acetate extract (A2) was diluted with 25 mL ethanol (E1). The tea infusion (15 mL) was mixed with 15 mL N-butyl alcohol by shaking for 3 min. Then to 2 mL of the bottom layer (B1), 2 mL of aqueous saturated oxalic acid solution and 6 mL of water was added, and it was made up to 25 mL with ethanol (E2). The ethyl acetate extract (15 mL, A2) was mixed with 15 mL aqueous 2% sodium bicarbonate by shaking for 30 s and left aside. On separation of the two phases, the bottom layer (C1) was drained off and the ethyl acetate extract (C2) contained the TF. A quantity (4 mL) of ethyl acetate extract (C2) was diluted with 25 mL of ethanol (E3). To 2 mL of the bottom layer (A1), 2 mL of aqueous saturated oxalic acid solution and 6 mL water was added and it was made up to 25 mL with ethanol (E4). E1, E2, E3, E4 were measured at 380 nm with a spectrometer. The tea pigments were calculated as follows:

TF (%)=E3 × 2.25

TR (%) = (2 × E1 + 2 × E4 – E3 – 2 × E2) × 7.06

TB (%) = 2 × E2 × 7.06

Statistical analysis

Results are presented as mean values (at least 3 replicates), the statistical significance of the sensory attributes and chemical components of black tea was evaluated by nonparametric testing at a 5% significance level and 1% significance level (Microsoft Office 2010). Differences were considered to be significant at p ≤ 0.05, and to be extremely significant at p ≤ 0.01.

Results and Discussion

Analysis of sensory evaluation and quality scores of tea samples

Full-type black tea from China and broken-type tea from other countries was collected and sensory evaluation analyses were performed. The aroma of Chinese black tea was relatively better than tea from other countries, and included some unique aroma characters, such as the orchid fragrance in CS020, the sugar aroma of CS025, smoky flavor of CS019, and the aroma of high sharpness persisting (Tables 3 and 4). The aroma characters of black tea samples collected from other countries were mainly sweet and fruity fragrances, and a slightly flat aroma. The durability of aroma from Chinese black tea was better than that from other samples. In addition, Sri Lankan Black Tea (CS036) was only one sample from other countries had a floral scent.

No. Aroma Liquor Taste
China
CS014 Sweet and flower fragrance, umami, lasting Orange and redness, clarity and brightness Sweet and mellow, umami
CS015 Sweet and potato fragrance, lasting Orange and redness, clarity and brightness Longan flavour, slightly umami
CS016 Longan fragrance, lasting Orange and redness, clarity and brightness Longan flavour, umami
CS017 Caramel-like, slightly lasting Redness, brightness More mellow, slightly taster-after
CS018 Longan fragrance, slightly lasting Redness, brightness Mellow, umami
CS019 Smoke-like, lasting Orange and redness, clarity Mellow, smoked odour, little umami
CS020 Sweet and orchid fragrance,high and lasting Orange and redness, clarity and brightness More mellow, umami
CS021 Sweet and fruity fragrance, slightly high and lasting Orange and redness, clarity and brightness Mellow, umami
CS022 Sweet fragrance, stuffy smell, none high and none lasting Redness, brightness Mellow, slightly umami
CS023 Sweet and loquat fragrance, high and lasting Redness, brightness Briskness and strength, little umami
CS024 Stuffy smell, none high and none lasting Deep redness, slightly brightness More mellow, slightly taster-after, slightly umami
CS025 Sweet and sugar-like, high and lasting Orange and redness, clarity and brightness Sweet and mellow, umami
CS026 Sweet and flower fragrance, high and lasting Redness, clarity More mellow, umami
CS027 Potato fragrance, slightly high and slightly lasting Redness, slightly brightness More mellow, slightly umami
CS028 Sweet and flower fragrance, slightly high and little lasting Orange and redness, clarity and brightness Mellow, umami
CS029 Sweet and little smoked, slightly lasting Redness, little brightness More mellow, little umami
CS030 Sweet fragrance, slightly high and slightly lasting Redness, little brightness More mellow, none umami
CS031 Sweet fragrance, little lasting Orange yellow little, brightness Mellow, little umami
CS032 Sweet and little flower fragrance Orange yellow, clarity and brightness Mellow, little umami
CS033 Sweet and longan fragrance Golden yellow, most clarity and brightness More mellow, umami, astringency
CS034 potato fragrance Golden yellow, clarity and brightness More mellow, little umami
CS037 Sweet fragrance, slightly high and slightly lasting Orange yellow, clarity and brightness Sweet and mellow, umami
Other countries
CS001 Sweet and little rose fragrance Redness, little brightness Pure, little umami, little strength
CS002 sweet fragrance and staleness odour, slightly lower Deep redness, little brightness Flat and staleness flavour, none umami
CS003 Stuffy smell Deep redness, slightly brightness Mellow, little umami
CS004 Staleness odour Deep redness, little dark More mellow, slightly strength, little umami
CS005 Sweet fragrance, pure, little high Redness, clarity and brightness Briskness and strength, slightly umami
CS006 Chinese herbaceous peony fragrance, flat Orange and redness, clarity and brightness More mellow, slightly umami
CS007 Sweet fragrance, flat Redness, little brightness Briskness and strength, little umami
CS008 Sweet fragrance, flat Deep redness, little brightness Mellow, little staleness flavour little umami
CS009 Sweet fragrance, little staleness odour, flat Redness, clarity Mellow, staleness flavour, little umami
CS010 Bergamot odour, high Redness, brightness Mellow, fries flavour, slightly umami
CS011 Sweet fragrance, little staleness odour Orange and redness, slightly brightness Pure, little umami
CS012 Sweet and little caramel fragrance, little high Redness, slightly brightness Flat flavour, none umami
CS013 Sweet fragrance, flat Redness, little brightness Mellow, little umami
CS035 Sweet fragrance and bergamot odour, soft and high Deep redness, little brightness More mellow, slightly sour
CS036 Sweet and flower fragrance, slightly high and slightly lasting Orange and redness, slightly brightness More mellow, slightly umami

Table 3: The sensory evaluation of different black teas.

No. Appearance Aroma Liquor Taste Infuse leaves Total score
China
CS014 22.5 22.5 8.5 25.5 7.25 86.25
CS015 21.25 22.5 8.65 25.5 8 85.9
CS016 20 22.5 8.5 27 7.25 85.25
CS017 21.25 20 9.15 25.5 8 83.9
CS018 20 20 9 24 7.75 80.75
CS019 18.75 21.25 8 24 7.25 79.25
CS020 20 23.75 8.5 27 8.5 87.75
CS021 19.38 22.5 8.5 27 8.5 85.88
CS022 20 19.38 9 25.5 7 80.88
CS023 21.25 22.5 8.75 24 9 85.5
CS024 20 17.88 8.5 25.5 8 79.88
CS025 21.25 22.5 8.5 27 7.4 86.65
CS026 22.25 22.5 8 27 9 88.75
CS027 22.5 21.38 8.5 25.5 8 85.88
CS028 21.25 22.5 8.25 27 8 87
CS029 20 20.63 8.3 23.25 8.15 80.33
CS030 21.25 21.25 8.15 21 8.5 80.15
CS031 21.25 21 7.9 24 8.5 82.65
CS032 22.5 22.5 8.5 25.5 8.65 87.65
CS033 21.25 21.25 9 27 7.75 86.25
CS034 21.25 21.25 8.5 25.2 8.3 84.5
CS037 22.5 23.75 7.9 27 8 89.15
Other countries
CS001 16 25.5 7.9 24 8 81.4
CS002 16 22.95 8 21 7 74.95
CS003 16 21 8.4 24 7.5 76.9
CS004 15 21.3 7 24 7.5 74.8
CS005 16 25.5 9.25 26.25 8 85
CS006 14 25.5 8.85 26.4 8 82.75
CS007 14.5 24 8.8 25.5 8 80.8
CS008 16 24.75 8 24 7 79.75
CS009 15 22.5 8.4 22.5 7.5 75.9
CS010 17 25.5 8.5 22.5 7.75 81.25
CS011 16 23.25 8 25.5 8 80.75
CS012 16 25.5 8.25 21 7 77.75
CS013 15.6 24 8 24.75 8 80.35
CS035 17 24 8 23.25 8 80.25
CS036 18 26.25 8 25.5 7.5 85.25

Notes: Tea samples conduct two sensory evaluation of different times of the same day, the scores are calculated according to score coefficient of table 2

Table 4: The scores of individual attributes of sensory evaluation.

The tea infusion color of Assam black tea (CS005) was especially good in redness and brightness, and the evaluation score of liquor was the highest of all the black tea samples, after sensory evaluation scores. The score of tea liquor of Malawi black tea (CS004) was the lowest of all the samples, and the liquor had a deep red and dark color. The sensory evaluation results of the tea liquor samples from other countries indicated no significant differences. However, the tea liquor from the southern Yangtze River and the northern Yangtze River were mostly orange-yellow in color, while a yellow tea infusion was not apparent in teas from other areas in China. The degree of redness of black teas from the southern and the northern Yangtze River areas was slightly weaker than that found in teas from other areas in China and from other countries in the world, and this may be due to the different tea cultivars and the degree of fermentation used. The liquor color of teas from the southern and the northern Yangtze River areas were mostly orange in color. The quantities of TF and TR produced largely govern the liquor characters (color, brightness, briskness, strength and ‘quality’) of teas [21,22]. It is therefore likely that the degree of the withering conducted on the tea leaf may influence the development of liquor characters and the overall quality of black teas [4].

The briskness, umami and strength of infusion were the most important factors for evaluating the taste of black tea. The umami taste of Chinese black teas (except CS030) was better than that of teas from other countries. From Table 3, it can be seen that the umami taste of CS016, CS020, CS021, CS025, CS026, CS028, CS033 and CS037 was relatively high, while the umami taste scores of Chinese black tea (CS030), Vietnamese black tea (CS002) and Kenyan black tea (CS012) was the lowest. Furthermore, the briskness and strength of Assam black tea and Nepal black tea were the best.

In particular, the difference in tea taste between tea samples may have been due to the different manufacturing methods employed. Chinese black tea is mainly full-type black tea, while the black tea from the other countries is mainly broken-type tea (crush, tear and curl) [23-25].

Analysis of chemical constituents in tea samples

The variation in content of polyphenols in Chinese black tea samples was relatively larger than that in other samples, and although there was no obvious trend, the content of polyphenols in sample CS037 was higher than in other samples. Sample CS037 was made from a purple leaf cultivar, named ‘Zijuan’, which is a specific cultivar in Yunnan big-leaf tea population with a national improved tea variety, Menghai big-leaf tea, which has high levels of tea ployphenols (TPs) [26], and good pharmacological effects [27]. Moreover, the polyphenol content in Vietnamese Black Teas, CS002 and CS011, was lower than that in samples from other countries. The polyphenol content was highest in tea samples CS005 and CS006, which were from India (except CS037).

The polyphenols content in Sri Lanka`s black tea samples were similar to the polyphenol levels in Chinese black tea (Table 5).

No. Polyphenols Caffeine Amino acids Theaflavins Thearubigins Theabrownins TR/TF
China
CS014 14.81 6.07 0.13 1.02 10.69 8.7 10.48
CS015 20.77 9.89 0.36 1.04 12.93 4.14 12.43
CS016 12.54 8.54 0.25 1.5 15.09 5.72 10.06
CS017 12.64 6.46 0.34 0.94 10.16 7.47 10.81
CS018 15.76 7.55 0.27 1.24 13.75 5.87 11.09
CS019 10.41 4.91 0.18 0.72 11.3 4.76 15.69
CS020 14.02 6.64 0.45 0.93 10.11 5.27 10.87
CS021 17.66 7.73 1.08 1.05 13.59 5.39 12.94
CS022 13.2 7.21 0.76 1.08 13.52 7.6 12.52
CS023 28.28 8.43 0.52 0.99 12.07 7.16 12.19
CS024 15.13 7.9 0.56 1.26 13.16 7.37 10.44
CS025 26.16 8.69 0.48 0.91 12.95 5.69 14.23
CS026 20.8 8.36 1.06 1.02 11.36 7.88 11.14
CS027 17.36 7.13 0.75 0.8 10.65 6.38 13.31
CS028 17.4 7.21 0.92 0.98 12.18 7.79 12.43
CS029 17.78 7.06 0.66 1.25 10.87 6.75 8.7
CS030 18.68 7.74 0.55 1.03 8.66 8.02 8.41
CS031 17.82 7.36 0.97 0.67 8.26 5.93 12.33
CS032 17.73 6.54 1.24 1.34 14.74 4.39 11
CS033 13.66 7.56 0.71 1.36 13.72 5.78 10.09
CS034 21.55 7.72 0.74 1.12 11.48 4.21 10.25
CS037 31.73 7.79 0.48 0.78 10.18 4.94 13.05
Other countries
CS001 15.8 4.86 0.24 0.72 7.77 7.78 10.79
CS002 11.86 5.44 0.19 0.68 7.85 7.85 11.54
CS003 16.58 4.39 0.12 1.11 12.32 9.26 11.1
CS004 14.73 5.05 0.33 0.84 9.57 8.98 11.39
CS005 17.52 5.94 0.46 1.05 16.3 8.74 15.52
CS006 24.02 6.72 0.19 1.15 13.8 2.95 12
CS007 25.53 5.05 0.37 1.13 12.52 7.24 11.08
CS008 18.15 5.37 0.09 1.33 10.31 5.65 7.75
CS009 15.63 4.44 0.75 0.96 6.18 7.06 6.44
CS010 17.51 6.2 0.46 1.35 11.75 5.79 8.7
CS011 10.25 5.88 0.23 1.62 12.29 5.21 7.59
CS012 17.04 5.64 0.54 1.24 8.23 7.7 6.64
CS013 17.72 5.48 0.16 1.36 11.24 9.45 8.26
CS035 14.52 5.73 0.24 0.83 5.75 9.05 6.93
CS036 26.86 9.01 0.79 0.8 9.3 5.62 11.63

Table 5: Determination of the chemical components (%) in different black teas.

Caffeine is an important flavor substance in black tea infusion and is responsible for the stimulating effect of tea liquor [9]. The caffeine content of Chinese tea samples was higher than that in teas from other countries, probably due to differences in tea varieties and processing methods as caffeine content did not significantly change during the processing of black tea [28]. In addition, the caffeine content in tea samples from the southern Yangtze River area was not significantly different (Table 5). Furthermore, sample CS036 from Sri Lanka was significantly higher in caffeine content which was 9.01%.

Free amino acids in tea can play an essential role in tea aroma and taste qualities [29] and are major contributors to the freshness of tea [30]. The amino acid content in tea samples from the southern Yangtze River area in China was higher than that in teas produced in other areas in China or in other countries. This southern Yangtze River area is a major tea production area, due to the occurrence of optimum climatic conditions, such as mild temperatures, abundant rainfall, high humidity and moderate sunshine [31]. Hence, the high content of amino acids in the teas was mainly due to the suitable climatic characteristics. The amino acid content was highest in sample CS032, which was made from a white-leaf cultivar. White-leaf is a typical albino tea cultivar found in China that has a high level of amino acids, which are essential components affecting tea taste quality [32]. The content of amino acids in the Vietnamese black teas, CS002 and CS011, were relatively lower, compared to samples from other countries, and amino acids contents in the Kenyan sample CS008 was the lowest. In addition, the amino acid levels in black teas from China were similar to levels in Sri Lankan teas. However, amino acids contents in Chinese black teas were higher than in Sri Lankan teas due to geographical locations [33], which were similar to results reported in previous studies [34,35].

There was no obvious difference in TF content or in the TR/TF ratio between samples (Table 5). The TR content in samples CS005 and CS006 from India were the highest, while sample CS009 from Indonesia had the lowest, which was consistent with the liquor and taste of tea samples (Table 3). The TR contents in samples from the Southern China area were higher than those in other tea producing areas, while CS030 and CS031 from the southern Yangtze River area had lower TR contents than other samples from the same area. This may be due to differences in the production processes employed. In addition, the highest TB content was in Sri Lankan tea samples. Black tea pigment is a key factor in forming the color and taste of tea infusion, and polyphenols in fresh tea leaves are consumed and chemically transformed into various oxidation products including dimeric, oligomeric and polymeric constituents, such as TF, theasinensins, TR and TB [36,37]. TF mainly determine the brightness of the tea infusion, with higher levels of TF forming better brightness. The TR level is mainly related to liquor and concentration and is a very important chemical component with regard to taste and concentration of tea infusion. In general, TB have a negative impact on black tea quality, with high contents resulting in the tea infusion becoming dark in color and losing astringency properties, while moderate levels of TB are essential to form the red infusion of black tea. The TR/TF ratio is another important factor in determining the quality of black tea, which levels ranging from 10 to 12 resulting in balanced liquor and taste [38].

Correlation analysis between tea liquor, taste and pigments

The relevance of sensory score of black tea color, taste and tea pigments (TF, TR and TB) was performed through correlation coefficient statistical analysis. Table 6 shows that the correlation coefficient of sensory quality (liquor and taste) and tea pigments had a correlation. The score of tea liquor was extremely significant and positive correlation with TR content, which correlation coefficient was 0.5839, TF content and the TR/TF value with tea liquor`s correlation coefficient was 0.3028 and 0.2122, only showed positive correlation. However, TB showed a negative correlation with tea liquor score. Therefore, it is feasible to employ the TR content to reflect the color of black tea infusion. In addition, there were extremely positive and significant correlations between tea taste scores and TR content and TR/TF values, the correlation coefficient was 0.6109 and 0.4938, respectively. However, the TB content showed a significantly negative correlation with tea taste. The results imply that the TR content and TR/ TF values could be used to evaluate the taste quality of black tea.

Variables Liquor score Taste score Theaflavins Thearubigins Theabrownins TR/TF
Liquor score 1          
Taste score 0.3002 1        
Theaflavins 0.3028 0.1159 1      
Thearubigins 0.5839** 0.6109** 0.5384 1    
Theabrownins -0.1874 -0.3327* -0.1521 -0.3118 1  
TR/TF 0.2122 0.4938** -0.4757 0.4651 -0.2127 1

*P<0.05; **P<0.01

Table 6: The correlation coefficient between sensory quality (liquor and taste) and black tea pigment.

Correlation analysis of tea taste, polyphenols and caffeine

The correlation coefficients of tea polyphenols, caffeine and black tea taste scores are shown in Table 7. The tea taste scores were positively correlated with contents of polyphenols and caffeine, indicating that determination of polyphenols and/or caffeine contents can assay black tea taste.

Variables Taste score Polyphenols Caffeine
Taste score 1 -- --
Polyphenols 0.2232 1 --
Caffeine 0.4396** 0.4331 1

*P<0.05; **P<0.01

Table 7: The correlation coefficient of black tea taste score and chemical components (polyphenols and caffeine).

Correlation analysis of tea taste, aroma and amino acids

As shown in Table 8, the amino acid contents were positively correlated with tea taste and aroma scores. Therefore, amino acids levels can also be considered as important chemical components to estimate tea taste and aroma.

Variables  Taste score Aroma score Amino acids
Taste score 1 -- --
Aroma score 0.4528 1 --
Amino acids 0.2396 0.3108 1

*P<0.05; **P<0.01

Table 8: The correlation coefficient between sensory quality (taste and aroma) and amino acids.

In particular, the aroma and taste characteristics of Chinese black tea were better than tea from other countries, while the black tea liquor from all samples were not significantly different. A possible explanation is that Chinese full-type black tea is usually brewed with freshly boiled water and is drank directly, whereas milk and sugar may be added to broken-type black tea infusion during consumption [39-41]. Although the aroma and taste of the broken-type tea were relatively lower, the taste could be improved via addition of other substances, which may mask the original taste of the tea. Therefore, Chinese black tea aroma and taste are quite important for tea quality formation, and the appearance of dry tea is also an essential factor in the evaluation of tea quality.

Correlation analysis between sensory quality and chemical composition of black tea

The correlation between the sensory quality of black tea and the chemical composition is shown in Table 9. The sensory quality score was extremely significant and positively correlated with the content of tea polyphenols, caffeine, amino acids, TR and TR/TF, which correlation coefficient was 0.4166, 0.6595, 0.4379, 0.4196, 0.4165, respectively. There was a significant and negative correlation between the TB content and sensory evaluation scores. Surprisingly, TF showed a negative correlation with the sensory quality of black tea. However, there was a positive correlation between the tea taste, color and TF (Table 6). It may be that the appearance, aroma and infusion of black tea impacted the sensory quality scores, or they may have been impacted by other factors. Therefore, the effect of TF on the sensory quality of black tea warrants further investigation.

Variables  Sensory evaluation score Polyphenols Caffeine Amino acids Theaflavins Thearubigins Theabrownins TR/TB
Sensory evaluation score 1 -- -- -- -- -- -- --
Polyphenols 0.4166** 1 -- -- -- -- -- --
Caffeine 0.6595** 0.4331 1 -- -- -- -- --
Amino acids 0.4379** 0.2008 0.4183 1 -- -- -- --
Theaflavins -0.0042 -0.1812 0.0422 -0.0749 1 -- -- --
Thearubigins 0.4196** 0.073 0.354 0.1067 0.5384 1 -- --
Theabrownins -0.3943* -0.2491 -0.4198 -0.1912 -0.1521 -0.3118 1 --
TR/TF 0.4165** 0.2388 0.2943 0.1492 -0.4757 0.4651 -0.2127 1

*P<0.05; **P<0.01

Table 9: The correlation coefficient between sensory quality and chemical compositions.

Moreover, the comprehensive effects of these chemical compounds in forming the unique quality of black tea needs to be studied further, including their effects on high and lasting aroma, mellowness, umami taste, astringency, sweet taste, redness and brightness of liquor etc. [42-50]. TF is an important chemical component of the color and taste quality of black tea infusion, which was positively correlated with the quality of the liquor and taste of black tea [35,51].

Conclusion

In summary, a comprehensive analysis of 37 different black tea samples from nine countries was performed. The aroma and taste of Chinese black teas were better than teas from other countries, with the aroma of sharpness persisting from Chinese black tea. Teas from other countries had mainly sweet and fruity fragrances, but the aroma of teas from other countries was also slightly flat. The liquor colors of teas from the southern and northern regions of the Yangtze River were mostly orange in color. The umami tastes of Chinese black teas were better than those from other countries, and the umami tastes of teas from Vietnam and Kenya were relatively lower. This study indicated that the evaluated sensory scores were extremely significant and positively correlated with tea polyphenols, caffeine, amino acids and TR/TF values.

Acknowledgements

The authors thank Profs Lucheng Yang for performing sensory evaluation of tea samples. This work was supported by National Natural Science Foundation of China (31370688, 31400584), The earmarked fund for China Agriculture Research System (CARS-19), Modern Agriculture Industry System in Jiangsu (SXGC[2017]279), Keypoint Research and Invention Program of Jiangsu Province (BE2016417) and FuJian Province “2011 Collaborative Innovation Center” Chinese Oolong Tea Industry Innovation Center (Cultivation) special project (J2015-75).

References

Citation: Duan Y, Song X, Yang Y, Li L, Zhao Y, et al. (2018) Preparation and Evaluation of Carrot and Apple Blended Jam. J Food Process Technol 9: 726. Doi: 10.4172/2157-7110.1000726

Copyright: © 2018 Duan Y, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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