浙江大学学报(农业与生命科学版)  2017, Vol. 43 Issue (3): 317-328
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不同品种大佛龙井茶的汤色与滋味属性特征[PDF全文]
徐鹏程1, 范方媛1, 陆德彪2, 金晶2, 龚淑英1    
1. 浙江大学茶叶研究所,杭州 310058;
2. 浙江省农业技术推广中心,杭州 310020
摘要: 通过对“浙农113” “、平阳特早茶”、“迎霜”、“龙井43”、“嘉茗1号”、“翠峰”、“白叶1号”、“鸠坑群体种” 8个品种加工的大佛龙井茶进行感官属性量化描述、品质成分定量检测及两者间的相关性分析,深入探究大佛龙井茶汤色与滋味的特征属性。结果表明,“龙井43”、“迎霜”和“嘉茗1号”的综合感官品质较优。色差分析结果表明,亮度高、黄绿度适中的大佛龙井茶汤品质较高,且杨梅素苷类和槲皮素苷类物质与大佛龙井茶汤色泽有显著相关性。在滋味属性因子中苦度及涩度与大佛龙井茶汤滋味有显著相关性,而厚度滋味的感受是对单独味觉的补充,可能会对茶汤风味起到至关重要的作用。不同品种大佛龙井茶的滋味成分含量差异显著,鲜味氨基酸与鲜度呈显著正相关,咖啡碱、表没食子儿茶素、表没食子儿茶素没食子酸酯、没食子儿茶素没食子酸酯和杨梅素苷类与苦度、涩度呈显著正相关,与甜度呈显著负相关。黄酮苷类物质虽然在茶汤中含量较少,但表现出与大佛龙井茶汤色和滋味属性较为显著的相关性。
关键词: 大佛龙井茶    汤色    滋味    定量描述    
Infusion color and taste characteristic of Dafo Longjing tea processed from different cultivars
XU Pengcheng1, FAN Fangyuan1, LU Debiao2, JIN jing2, GONG Shuying1    
1. Institute of Tea Science, Zhejiang University, Hangzhou 310058, China;
2. Zhejiang Agriculture-Technology Extension Center, Hangzhou 310020, China
Summary: Dafo Longjing tea, as one of top ten famous teas in Zhejiang Province, is mainly produced in Xinchang County and popular with consumers because of its fresh-tender aroma and soft-mellow taste. It is significantly different from other kinds of Longjing teas including famous Xihu-Longjing tea, and occupies large market share; however, studies on quality features and related components of Dafo Longjing tea are rather few at present. In order to delve deeply into the mechanism of quality formation of Dafo Longjing tea, systematic analyses of correlation between liquor-taste properties and chemical constituents were performed in this study. Dafo Longjing teas were processed by traditional processing procedure with fresh leaf from cultivars"Zhenong 113", "Pingyang-tezao tea", "Yingshuang", "Longjing 43", "Jiaming 1", "Cuifeng", "Baiye 1"and"Jiukeng". The quality of the made teas was assessed by sensory evaluation, which showed that all of the samples made from different cultivars were accorded with the typical characteristic of flat, straight and bright appearance. The overall qualities of samples from"Longjing 43", "Yingshuang"and"Jiaming 1"were superior to others, with the score of 94.80, 94.50 and 94.50 respectively. Characteristic constituents in tea samples were determined by high performance liquid chromatography. The result indicated that the"Jiukeng" and"Cuifeng"were with high content of catechins, and"Longjing 43"was with high content of gallic acid, and"Baiye 1"was with high content of amino acids. Flavonol glycosides, as essential functional ingredients with low content, were different in content among all the eight tea cultivars. As color indicators and representative of light-dark, red-green and yellow-blue degree respectively, values of L, a, and b were read to analyze the color difference of tea infusion. The result combined with sensory evaluation suggested that Dafo Longjing tea with high brightness and moderate yellow-green degree had good quality. What' s more, the result of tea infusion color difference analysis showed significant correlation with sensory evaluation, indicating that liquid quality of Dafo Longjing teas could be quantitative description by color indicators. Taken chemical determination together with color indicator analysis, we found that flavonol glycosides, especially myricetin glycosides and quercetin glycosides, had a significant impact on liquid color quality. Signal factor evaluation of taste characteristics could make sensory concept concretely and vividly, helping to understand product' s features. In this study, taste factors of umami, sweet, bitter, astringent and kokumi were scored by sensory experts. The result showed that bitter and astringent as important factors were speculated to have significant impact on taste quality of Dafo Longjing tea. In combination with quantitative analysis of chemical constituents, we found that flavonol glycosides were significantly correlated with taste factors of bitter, astringent and kokumi. Above all, color-indicator determination and signal factor evaluation can make sensory description of liquid and taste concretely and vividly. Moreover, flavonol glycosides as important chemical constituents have significant impact on liquid and taste quality, though with low content in Dafo Longjing tea. In the future, studies on the interaction between flavonol glycosides and other components will be explored further to illuminate the function mechanism of characteristic flavor.
Key words: Dafo Longjing tea    infusion color    taste    quantitative description    

茶叶作为世界三大饮料之一,是我国重要的经济作物。茶叶及其提取物具有抗氧化[1]、消炎杀菌[2]、舒缓神经[3]、抑制肿瘤细胞增殖[4]等生理作用。茶叶作为一种消费饮品,其汤色、滋味及香气是主要的风味品质特征,也是影响消费者选择的关键因素。大佛龙井茶是浙江省十大名茶之一,主要产自浙江省新昌县,其外形扁平(形似碗钉)、色泽嫩绿、汤色杏绿、清香持久、滋味鲜醇、叶底嫩绿匀整[5],品质优良,深受人们喜爱。本文利用感官审评及品质成分定量检测,结合汤色滋味属性与化学成分的相关性研究,对用不同茶树品种鲜叶制成的大佛龙井茶汤色及滋味进行全面分析,为进一步探究大佛龙井茶品质形成机制提供理论依据。

1 材料与方法 1.1 材料与试剂

选取“浙农113”、“平阳特早茶”、“迎霜”、“龙井43”、“嘉茗1号(乌牛早)”、“翠峰”、“白叶1号”、“鸠坑群体种”共8个不同茶树品种,于春季采摘其一芽二叶,按相同的工艺流程加工为成品茶样。

实验所用8种儿茶素单体、没食子酸、3种生物碱单体、20种氨基酸单体及8种黄酮苷类单体标准品纯度均≥98%,购于上海阿拉丁试剂公司;乙腈、甲醇、甲酸均为色谱纯,购于美国Tedia公司;邻苯二甲醛(ortho-phthalaldehyde, OPA)、氯甲酸芴甲酯(fluorenylmethyl chloroformate, FMOC)均购于上海阿拉丁试剂公司。

1.2 样品处理

准确称取3.00(±0.01)g茶样,加入沸水150 mL,浸提5 min后,将茶汤倒尽置于审评碗中,部分用于茶样感官审评及茶汤色度值检测,部分过0.45 μm膜后-20 ℃冻存备用。

1.3 感官审评

根据《茶叶感官审评方法》(GB/T 23776— 2009),由7位专业评茶师对各茶样进行感官审评。

滋味定量描述:根据《茶叶感官审评方法》(GB/ T 23776—2009)准备茶汤,由7位专业评茶师对各茶汤的鲜、甜、苦、涩、厚5项滋味特征进行评审赋分,采用10分制(0~2微强,2~4较强,4~6强,6~8很强,8~10极强)[6]

1.4 成分检测分析方法

水分含量:参照《茶水分测定》(GB/T 8304— 2013);水浸出物:参照《茶水浸出物测定》(GB/T 8305—2013);可溶性总糖:蒽酮-硫酸法。

儿茶素、生物碱组分采用高效液相色谱法(high performance liquid chromatography, HPLC),检测条件如下。色谱柱:Agilent TC-C18柱(4.6 mm× 250 mm,5 μm);流动相A:0.1%甲酸水溶液,流动相B:0.1%甲酸乙腈溶液;流速1 mL/min,柱温33 ℃,进样量10 μL,检测波长280 nm。洗脱梯度:0~25 min,10%~30% B;25 min下降至10% B;25~30 min,10% B。

黄酮苷类的HPLC检测分析条件如下。色谱柱:Agilent TC-C18柱(4.6 mm×250 mm,5 μm);流动相A:0.1%甲酸水溶液,流动相B:0.1%甲酸乙腈溶液;流速1 mL/min,柱温33 ℃,进样量10 μL,检测波长360 nm。洗脱梯度:0~55 min,20%~50% B;55 min下降至20% B;55~60 min,20% B。

氨基酸组分的HPLC检测分析条件如下。色谱柱:Zorbax Eclipse-AAA柱(4.6 mm×150 mm,3.5 μm);流动相A:40 mmol/L Na2HPO4,流动相B:V(乙腈):V(甲醇):V(水)=45:45:10;流速1.5 mL/min,柱温40 ℃,进样量10 μL,发射波长340 nm,接收波长450 nm。洗脱梯度:0~18 min,5%~60% B;18~23 min,60%~100% B;23 min下降至5% B;23~28 min,5% B。

1.5 数据统计分析

各处理均设3次重复,利用Excel 2010进行数据处理,处理间比较采用最小显著差异法(least significant difference, LSD);采用SAS 9.2软件进行相关性和方差分析。

2 结果与分析 2.1 感官审评结果

不同茶树品种鲜叶经一致的工艺流程加工成大佛龙井成茶的感官审评结果如表 1所示。8个不同品种的成茶均符合大佛龙井茶扁平、挺直、尖削的外形要求。干茶在色泽上因品种差异而表现不同:“浙农113”与“翠峰”品种的大佛龙井成茶呈翠绿色,“鸠坑群体种”成茶呈尚绿带黄。在内质上,“迎霜”和“嘉茗1号”汤色嫩绿明亮,滋味鲜爽;“龙井43”汤色杏绿明亮,滋味醇爽。总体上,用“龙井43”、“迎霜”和“嘉茗1号”制得的大佛龙井茶感官品质较优,审评总分分别为94.80、94.50和94.50;而在本实验条件下,用“翠峰”制得的大佛龙井茶总得分最低,品质欠佳。

表1 不同品种大佛龙井茶感官审评结果 Table 1 Sensory evaluation results of Dafo Longjing tea processed from different cultivars
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2.2 茶汤品质成分定量分析

茶汤中生物碱含量如表 2所示,其范围为476.91~953.76 μg/mL,咖啡碱含量在3种生物碱中最高,占生物碱总量的60%以上,其中在“嘉茗1号”品种茶汤中咖啡碱可占到约96%。

表2 不同品种大佛龙井茶茶汤中生物碱质量浓度 Table 2 Contents of alkaloids in Dafo Longjing tea infusions processed from different cultivars
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不同品种大佛龙井茶汤中没食子酸及儿茶素单体含量如表 3所示。8个品种的儿茶素组分总量范围在1 060.71~2 129.46 μg/mL之间,其中“鸠坑群体种”与“翠峰”品种茶汤中儿茶素总量及EGCG含量显著高于其他几个品种,其他儿茶素单体在不同品种中的含量存在较大差异。“白叶1号”作为白化品种,其儿茶素总量及各单体含量均较低,与前人研究结果一致[7]。在8个茶树品种中,“嘉茗1号”的没食子酸质量浓度最低,为8.85 μg/mL,而其他品种均高于10 μg/mL,其中“龙井43”高达17.31 μg/mL。

表3 不同品种大佛龙井茶茶汤中没食子酸和儿茶素组分质量浓度 Table 3 Contents of GA and catechins in Dafo Longjing tea infusions processed from different cultivars
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表 4为不同品种大佛龙井茶汤中的氨基酸含量。结果显示,在茶汤中共检测到20种氨基酸。其中,茶氨酸的含量最高,占氨基酸总量的34%~47%,其次为天门冬氨酸(Asp)、谷氨酸(Glu)、谷氨酰胺(Gln)、精氨酸(Arg)和天门冬酰胺(Asn)。在本实验中不同品种大佛龙井茶汤氨基酸总量在320.37~698.68 μg/mL之间,其中“白叶1号”的氨基酸总量最高,为698.68 μg/mL,显著高于其他品种。已有研究显示,“白叶1号”是低温敏感型白化品种,在白化期间其氨基酸含量会显著上升[8]

表4 不同品种大佛龙井茶茶汤中氨基酸组分质量浓度 Table 4 Contents of amino acids in Dafo Longjing tea infusions processed from different cultivars
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此外,本实验在8个不同茶树品种制成的大佛龙井茶汤中共检测到7种黄酮苷类物质,主要为杨梅素苷、槲皮素苷及山柰酚苷类物质,其组分含量如表 5所示。7种黄酮苷总量在59.55~90.72 μg/mL之间,其中“鸠坑群体种”含量最高,“翠峰”品种含量最低;黄酮苷组分中山柰酚苷占比最小,仅为7种黄酮苷总量的1.08%~4.84%;杨梅素苷和槲皮素苷含量因茶树品种不同而存在一定的差异:“浙农113”的杨梅素苷含量最高,而“鸠坑群体种”的槲皮素苷含量最高;就黄酮苷单体含量而言,用“浙农113”、“翠峰”、“迎霜” 3个品种制成的大佛龙井茶汤中以杨梅素-3-O-鼠李糖苷含量最高,其他品种的大佛龙井茶汤中以槲皮素3-D-半乳糖苷含量最高。

表5 不同品种大佛龙井茶茶汤中黄酮苷类组分质量浓度 Table 5 Contents of flavonol glycosides in Dafo Longjing tea infusions processed from different cultivars
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2.3 茶汤品质成分与茶汤色泽相关性分析 2.3.1 茶汤色泽属性量化分析

依据亨特-Lab表色系原理[9],对不同品种大佛龙井茶汤色的LabC值进行测定(表 6)。其中:L代表明度,其值越大说明样品明亮程度越高;a值代表红绿色度,正值表示红色程度,负值表示绿色程度;b值代表黄蓝色度,正值表示黄色程度,负值表示蓝色程度;C代表色调彩度。结果显示,大佛龙井茶汤L值较大,a值为负,b值为正,C值在10~23之间。这表明大佛龙井茶普遍具有茶汤明亮、汤色偏绿略带黄的典型特征。在不同色度指标中bC值的相对标准差较大,说明茶汤的黄度及色彩鲜艳度是影响不同品种大佛龙井茶汤色品质的主要因素。“浙农113”与“翠峰”品种的bC 值都明显高于其他几个品种,与感官审评中汤色得分低于其他品种的结果相一致;“嘉茗1号”的La值相对最大,bC值相对最小,其汤色得分也相对最高。相关性分析发现,L值、a值与汤色评分呈极显著正相关,而b值、C值与汤色评分呈极显著负相关,说明明亮度高、黄绿度适中的茶汤品质较高。该结果也表明色差分析能够较为精确科学的量化茶汤色泽属性。

表6 大佛龙井茶茶汤色度值 Table 6 Chromatic values of Dafo Longjing tea infusions
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2.3.2 呈色物质与茶汤色泽的相关性分析

对大佛龙井茶汤中各化学组分与茶汤色泽的相关性分析(表 7)表明:黄酮苷中杨梅素苷类与bC色度值指标呈极显著正相关,而与a值呈极显著负相关,与L值呈显著负相关;槲皮素苷类与L值、a值呈显著正相关,而与b值和C值呈显著负相关;山柰酚苷与各色度值指标的相关性都不显著。上述结果表明,在大佛龙井茶汤中槲皮素苷与茶汤的亮度及红绿色度有显著相关性,而杨梅素苷与茶汤的黄蓝度及色调彩度有极显著相关性。已有研究显示,茶叶中黄酮醇及其苷类物质有20多种,其水溶液为绿黄色,对绿茶汤色的形成作用较大[10-12]。WANG等[11]在对绿茶茶汤中3种黄酮醇与汤色的关系研究中发现,槲皮素与茶汤色泽红绿度有较高的相关性,而杨梅素、山柰素与汤色的相关性非常低。朱博等[12]在对六安瓜片茶汤贮藏过程中色度值及黄酮苷含量变化的研究中发现,只有杨梅素苷与茶汤的红绿度、黄蓝度呈显著负相关,而槲皮素和山柰素及其苷类与茶汤色泽变化关系不密切。推测上述研究表现出的结果差异主要是由于茶汤浸提方法不同及黄酮苷类物质检测差异造成的。赖凌凌等[13]在对福建绿茶色度值与呈色物质相关性的研究中发现,多酚类物质主要通过黄酮类物质间接影响茶汤亮度、绿度和黄度,并且其影响趋势均与黄酮类物质相反。本研究发现,茶汤中总儿茶素含量和色度指标间存在较弱的相关性,而黄酮苷类物质对汤色影响较大,尤其是杨梅素苷类和槲皮素苷类物质对大佛龙井茶汤色泽贡献较大。

表7 呈色物质与茶汤色度值的相关性 Table 7 Correlation between color ingredients and chromatic values
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2.4 茶汤品质成分与滋味属性相关性分析 2.4.1 茶汤滋味特征属性量化描述分析

对不同品种大佛龙井茶汤滋味分属性评审结果(表 8)表明,在供试的8个不同品种中,“白叶1号”及“龙井43”鲜度感最优,“嘉茗1号”表现出较高的甜度感,而“浙农113”、“鸠坑群体种”和“翠峰”品种的苦涩度较强,“翠峰”的厚度感最强。相关性分析发现,苦度和涩度属性与滋味得分呈显著负相关,推测苦涩度可能是影响大佛龙井茶滋味品质的关键属性因子。

表8 茶汤滋味分属性量化分析结果 Table 8 Analysis of taste quality attributes of tea infusions
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2.4.2 呈味物质含量与滋味感官特征评分的相关性分析

不同品种大佛龙井茶因茶汤中可溶性糖、儿茶素、生物碱、氨基酸、黄酮苷类等化合物的含量、比例不同,形成了不同的滋味特征。呈味物质含量与感官特征的相关性分析结果(表 9)显示,水浸出物含量与甜度呈极显著负相关,与苦度呈极显著正相关,与涩度和厚度呈显著正相关。其中,儿茶素类物质中的EGC、EGCG及咖啡碱与苦度、涩度呈显著正相关;该结论与前人的研究结果相一致[14-17]。在20种被检测到的氨基酸中,谷氨酸(Glu)、谷氨酰胺(Gln)、茶氨酸(The)与大佛龙井茶汤鲜度呈显著正相关,说明氨基酸是绿茶茶汤鲜度感的重要来源[18]。已有相关研究显示,黄酮苷类物质在达到阈值之后不仅能产生柔和的涩感,还能增强咖啡碱的苦味[19-20],如在冲泡过程中西湖龙井茶槲皮素-3-O-芸香糖苷的Dot值(滋味物质实际浓度与其阈值的比值)最高可达4万,比其他黄酮苷类高出3~4个数量级[21]。在本实验条件下,黄酮苷类物质中的杨梅苷类与大佛龙井茶汤的苦度、涩度及厚度呈显著正相关,而与甜度呈极显著负相关。由此可见,黄酮苷类物质虽含量相对较低,但对茶汤滋味具有较大的贡献作用。

表9 呈味物质含量与滋味感官特征评分的相关性 Table 9 Correlation between taste ingredient contents and sensory characteristic scores
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厚度滋味通常被描述为浓厚的、复杂的、满口感。对人体感官神经的研究发现,通过刺激一系列的钙离子受体(CaSR)可以引起浓厚滋味[22]。能引起浓厚滋味的物质很多,如γ-谷酰基二肽及三肽能提升满口感和味觉复杂感[23-25],但是目前对于茶汤中厚味呈味物质的研究还很少。在本实验中发现咖啡碱、部分儿茶素、杨梅苷类物质及水浸出物含量与厚度有显著相关性,而这些物质都同时与苦涩度呈显著正相关;因此,推测茶汤滋味中的厚度感可能与苦涩感密切相关,它们相互作用形成茶汤滋味品质特征。

3 讨论

目前普遍认为,绿茶的汤色以黄绿色为主,滋味以涩味和苦味为主,辅以较强的鲜味和较弱的甜味[26]。龙井茶作为茶中珍品,以汤色“杏绿明亮”及滋味“甘醇鲜爽”而著称,其优异的品质倍受人们喜爱。在本实验条件下,用8种不同品种制得的大佛龙井茶均能较好地满足其品质特征要求,其中“龙井43”品种的大佛龙井茶综合感官品质最优。

本研究应用色度指标及单因子评分分别对用8种不同品种制得的大佛龙井茶汤色和滋味属性进行量化分析。结果显示:明度L、红绿度a、黄蓝度b及色调彩度C等色度指标能够较好地反映大佛龙井茶汤黄绿明亮的典型特征;同时,分属性量化及相关性分析显示,茶汤苦涩度可能是影响大佛龙井茶滋味品质的关键属性因子。通过进一步研究茶汤品质成分含量对大佛龙井茶汤色和滋味品质的影响发现,在本实验条件下检测到的7种黄酮苷总量仅为儿茶素总量的5%左右,虽然在茶汤中含量较少,但与大佛龙井茶汤色和滋味属性具有较为显著的相关性。其中,槲皮素苷及杨梅素苷与大佛龙井茶汤的亮度、红绿度及黄蓝度等色度指标显著相关;而杨梅苷类与茶汤滋味属性中的苦涩度、厚度呈显著正相关,与甜度呈显著负相关。由此表明,黄酮苷类物质作为茶汤中的微量物质能够显著影响大佛龙井茶汤色泽和滋味属性,对茶汤特征风味的形成起到至关重要的作用。已有研究显示,茶汤特征属性是各种内含物质作用的综合表现,各成分间的协同/拮抗作用也是影响茶汤滋味属性的重要因素[27]。因此,未来可进一步针对黄酮苷类物质与其他成分间的相互作用进行深入探究,以明确特征风味物质的作用机制。

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