绿茶茶汤色泽的变化规律及其调控研究
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摘要
随着社会经济的快速发展,茶饮料特别是纯茶饮料因具有显著的保健价值而倍受广大消费者青睐,成为当今茶叶深加工的重点研发方向。然而,由于绿茶饮料在生产和销售期间色泽极易发生褐变,在一定程度上影响了其产品的货架期和外观质量。本研究从绿茶饮料的主要呈色物质如黄酮醇及其苷类、儿茶素的氧化产物等入手,对绿茶茶汤常温贮藏期间色泽的变化规律和调控进行分析研究,旨在揭示绿茶饮料的色泽褐变规律,并探索有效的调控技术。主要研究结果如下:
1、建立了黄酮醇物质的HPLC检测方法,即采用phenomenex-c18(150×4.60mm)柱;磷酸-甲醇流动相体系,A相为0.2%磷酸溶液,B相为100%甲醇;洗脱梯度为,0～20 min B相从55%降到20%,20～21min B相从20%升到55%;流速1 mL?min-1;柱温25℃;检测波长360 nm;进样量5μL,此方法可对黄酮醇类物质进行有效分离。利用上述的HPLC检测方法,采取正交实验,对影响黄酮醇苷水解的条件进行了优化,建立了黄酮醇苷的定量方法,即将5mL茶汤,置于15mL纯甲醇和5mL6mol?L-1盐酸的水解溶液中,在75℃下水解2h;利用HPLC检测水解体系的槲皮素、山柰素和杨梅素含量;利用公式黄酮醇苷(μg?mL-1)=黄酮醇增加量/芦丁水解率来计算茶汤中黄酮醇苷的含量。
2、利用黄酮醇及其苷的定量方法,对不同贮藏期间茶汤的黄酮醇类物质变化进行了研究,并对茶汤色泽变化与黄酮醇及其苷类变化的相关性进行了研究,结果表明茶汤贮藏过程中随着茶汤的红绿度(a)和黄蓝度(b)不断升高,杨梅素苷含量逐步下降,它与茶汤的红绿度、黄蓝度的相关系数分别为-0.9821**、-0.8826*,但与茶汤明亮度(L)的相关性不显著;槲皮素和山柰素及其苷类与茶汤色泽变化关系不密切。
3、本文采用体外模拟体系(含与鲜叶比例相同的儿茶素标准品混合体系),进行儿茶素的自动氧化和酶促氧化研究,并利用HPLC鉴定氧化产物。结果发现,在常温贮藏过程中,不含酶液的儿茶素模拟体系发生了自动氧化,其色泽从无色转变为淡黄色;而含酶液的儿茶素模拟体系发生了酶促氧化,色泽变成红色;HPLC检测显示了两者产物的差异。
HPLC检测发现,常温贮藏期间,绿茶茶汤中酯型儿茶素类明显下降,非酯型儿茶素变化规律不明显,而没食子酸则明显上升;茶汤中茶褐素的含量略有增加,但没有发现酶促氧化产物,由此推测,常温贮藏期间茶汤中发生了自动氧化和脱没食子化反应。
4、在绿茶茶汤贮藏初期,Vc可有效延缓杨梅素苷、槲皮素苷、山奈素苷,EGCG、ECG、EGC的氧化,稳定了茶汤汤色,但对绿茶茶汤长期贮藏的护色效果不够理想。
With the rapid socio-economic development, tea beverage especially pure tea beverage is preferred by consumers with their distinctive health-care function. Tea beverage has become the interested R&D fields in tea further processing industry. However, it is liable to undergo browning during the production and storage of green tea beverage, which shortens the shelf life and affects the external appearance. Attempted to dissolve this problem, this paper focus on the components as flavonols glycosides and oxidized products of catechins in green tea which play a vital role in the formation of tea beverage color. With the investigation of the beverage color variation at the room temperature storage, this paper was attempted to explore an efficient technology to keep the color of green tea beverage. The major results acquired in this paper were as follows:
1. A HPLC method assaying for flavonol in green tea infusion has been achieved by using the mobile phase system of phosphate– methanol. The protocol could be described as following: using phenomenex-c18(150×4.60mm) column, mobile phase A was phosphate/water in ratio of 2/998(v/v),mobile phase B was methyl alcohol and phase B decreased gradiently from 55% to 20% in early 20 minutes, then increased gradiently from 20% to 55% for next 1minutes. The linear gradient elution with the flow rate of 1mL?min-1 was detected at the wavelength of 360nm. The hydrolyzed flavonols were further separated successfully with the HPLC method.
With the orthogonal design, the optimal hydrolytic conditions of flavonol glycosides in green tea infusion (5mL) were explored by 2 hours hydrolysis at 75℃in the hydrolytic solution of methyl alcohol(15mL) supplemented with 6 mol?L-1 hydrochloric acid(5mL). Quercetin,myricetin and kaempferol from the hydrolytic system of tea infusion were detected by using the HPLC.
2. The correlations between flavonol and its glycosides and color of tea infusion during storage were investigated. The results showed that the redness(a)and yellowness (b) increased as the decrease of myricetin glycosides in green tea infusion, which suggested that myricetin glycosides have a significant relation to the redness(a)and yellowness(b) of green tea infusion with -0.9821** and -0.8826* of the correlation coefficients, respectively. The correlations between the color of tea infusion and quercetin, myricetin, kaempferol and their glycosides were not remarkable.
3. Simulated model in vitro of catechins in green tea infusion comparatively studied on auto-oxidation and enzymatic oxidized of catechins and detected their oxidized products using HPLC. As a result, the model of the standard solution of catechins at room temperature storage, catechins underwent auto-oxidation and the solution color varied from colorless into light yellow. However, the model of the standard solution of catechins with polyphenol oxidase, catechins underwent enzymatic oxidation and the solution color varied from colorless into redish brown. The auto-oxidation products of catechins were different from their enzymatic oxidized products too.
During the storage of green tea infusion at room temperature, catechin esters in tea infusions decreased significantly while gallic acid and theabrownins (TBs) increased gradually. However,enzymatic oxidized products were not found. It is supposed that catechin esters have degallated to simple catechins and catechins have underwent enzymatic oxidation during the storage of green tea infusion.
4. The color of green tea infusion can be stabilized at the initial storage with the supplement of ascorbic acid (Vc), which led to the minimal changes of the glycosides of myricetin, quercetin and kaempferol and catechins as EGCG, ECG and EGC. With the elongation of tea infusion’s storage, the color changes were similar to those without the Vc supplement. The protective method of the color of tea beverage is still under exploration.
1、建立了黄酮醇物质的HPLC检测方法,即采用phenomenex-c18(150×4.60mm)柱;磷酸-甲醇流动相体系,A相为0.2%磷酸溶液,B相为100%甲醇;洗脱梯度为,0～20 min B相从55%降到20%,20～21min B相从20%升到55%;流速1 mL?min-1;柱温25℃;检测波长360 nm;进样量5μL,此方法可对黄酮醇类物质进行有效分离。利用上述的HPLC检测方法,采取正交实验,对影响黄酮醇苷水解的条件进行了优化,建立了黄酮醇苷的定量方法,即将5mL茶汤,置于15mL纯甲醇和5mL6mol?L-1盐酸的水解溶液中,在75℃下水解2h;利用HPLC检测水解体系的槲皮素、山柰素和杨梅素含量;利用公式黄酮醇苷(μg?mL-1)=黄酮醇增加量/芦丁水解率来计算茶汤中黄酮醇苷的含量。
2、利用黄酮醇及其苷的定量方法,对不同贮藏期间茶汤的黄酮醇类物质变化进行了研究,并对茶汤色泽变化与黄酮醇及其苷类变化的相关性进行了研究,结果表明茶汤贮藏过程中随着茶汤的红绿度(a)和黄蓝度(b)不断升高,杨梅素苷含量逐步下降,它与茶汤的红绿度、黄蓝度的相关系数分别为-0.9821**、-0.8826*,但与茶汤明亮度(L)的相关性不显著;槲皮素和山柰素及其苷类与茶汤色泽变化关系不密切。
3、本文采用体外模拟体系(含与鲜叶比例相同的儿茶素标准品混合体系),进行儿茶素的自动氧化和酶促氧化研究,并利用HPLC鉴定氧化产物。结果发现,在常温贮藏过程中,不含酶液的儿茶素模拟体系发生了自动氧化,其色泽从无色转变为淡黄色;而含酶液的儿茶素模拟体系发生了酶促氧化,色泽变成红色;HPLC检测显示了两者产物的差异。
HPLC检测发现,常温贮藏期间,绿茶茶汤中酯型儿茶素类明显下降,非酯型儿茶素变化规律不明显,而没食子酸则明显上升;茶汤中茶褐素的含量略有增加,但没有发现酶促氧化产物,由此推测,常温贮藏期间茶汤中发生了自动氧化和脱没食子化反应。
4、在绿茶茶汤贮藏初期,Vc可有效延缓杨梅素苷、槲皮素苷、山奈素苷,EGCG、ECG、EGC的氧化,稳定了茶汤汤色,但对绿茶茶汤长期贮藏的护色效果不够理想。
With the rapid socio-economic development, tea beverage especially pure tea beverage is preferred by consumers with their distinctive health-care function. Tea beverage has become the interested R&D fields in tea further processing industry. However, it is liable to undergo browning during the production and storage of green tea beverage, which shortens the shelf life and affects the external appearance. Attempted to dissolve this problem, this paper focus on the components as flavonols glycosides and oxidized products of catechins in green tea which play a vital role in the formation of tea beverage color. With the investigation of the beverage color variation at the room temperature storage, this paper was attempted to explore an efficient technology to keep the color of green tea beverage. The major results acquired in this paper were as follows:
1. A HPLC method assaying for flavonol in green tea infusion has been achieved by using the mobile phase system of phosphate– methanol. The protocol could be described as following: using phenomenex-c18(150×4.60mm) column, mobile phase A was phosphate/water in ratio of 2/998(v/v),mobile phase B was methyl alcohol and phase B decreased gradiently from 55% to 20% in early 20 minutes, then increased gradiently from 20% to 55% for next 1minutes. The linear gradient elution with the flow rate of 1mL?min-1 was detected at the wavelength of 360nm. The hydrolyzed flavonols were further separated successfully with the HPLC method.
With the orthogonal design, the optimal hydrolytic conditions of flavonol glycosides in green tea infusion (5mL) were explored by 2 hours hydrolysis at 75℃in the hydrolytic solution of methyl alcohol(15mL) supplemented with 6 mol?L-1 hydrochloric acid(5mL). Quercetin,myricetin and kaempferol from the hydrolytic system of tea infusion were detected by using the HPLC.
2. The correlations between flavonol and its glycosides and color of tea infusion during storage were investigated. The results showed that the redness(a)and yellowness (b) increased as the decrease of myricetin glycosides in green tea infusion, which suggested that myricetin glycosides have a significant relation to the redness(a)and yellowness(b) of green tea infusion with -0.9821** and -0.8826* of the correlation coefficients, respectively. The correlations between the color of tea infusion and quercetin, myricetin, kaempferol and their glycosides were not remarkable.
3. Simulated model in vitro of catechins in green tea infusion comparatively studied on auto-oxidation and enzymatic oxidized of catechins and detected their oxidized products using HPLC. As a result, the model of the standard solution of catechins at room temperature storage, catechins underwent auto-oxidation and the solution color varied from colorless into light yellow. However, the model of the standard solution of catechins with polyphenol oxidase, catechins underwent enzymatic oxidation and the solution color varied from colorless into redish brown. The auto-oxidation products of catechins were different from their enzymatic oxidized products too.
During the storage of green tea infusion at room temperature, catechin esters in tea infusions decreased significantly while gallic acid and theabrownins (TBs) increased gradually. However,enzymatic oxidized products were not found. It is supposed that catechin esters have degallated to simple catechins and catechins have underwent enzymatic oxidation during the storage of green tea infusion.
4. The color of green tea infusion can be stabilized at the initial storage with the supplement of ascorbic acid (Vc), which led to the minimal changes of the glycosides of myricetin, quercetin and kaempferol and catechins as EGCG, ECG and EGC. With the elongation of tea infusion’s storage, the color changes were similar to those without the Vc supplement. The protective method of the color of tea beverage is still under exploration.
引文
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[2]戴前颖.绿茶饮料加工中沉淀和褐变的形成机理及解决方案[D],安徽农业大学,2007
[3]潘顺顺.绿茶鲜汁饮料色素物质组成及其护绿措施研究[D],浙江大学,2007
[4]高新蕾.绿茶饮料防褐变的研究[J].饮料工业,2002 (05):4 :22-25
[5]宁井铭、王华、周天山.绿茶饮料护色技术的研究[J].中国茶叶加工.2004(02):22-24
[6]戴前颖、夏涛、高俊等.β-环糊精对茶汤体系的动力学影响[J].江苏大学学报(自然科学版),2009(02):14-18
[7]中华人民共和国国家标准.茶饮料.GB/T 21733-2008
[8]孙其富、梁月荣、陆建良,不同杀菌处理对绿茶茶汤生化成分的影响[J].茶叶.2004,30(3):146-168
[9]宛晓春.茶叶生物化学[M].中国农业出版社2003,15-18,23-24,31-32,301-306
[10] Zheng-Yu chen,Qin Yan Zhu,David Tsang. Degradation of Green Tea Catechins in Tea Drinks[J].J.Agric.Food Chem.2001,49,477-482
[11] Qin Yan zhu、Anqi zhang、David Tsang,etal. Stability of green tea catechins[J]. J Agric Food Chem.1997,45(12):4624～4628
[12]林亲录,刘冠民.绿茶饮料保色的探讨[J],食品科学,1994,9:18～20
[13]梁月荣、陆建良.马辉.罐装绿茶饮料防褐变研究[J],浙江大学学报(农业与生命科学版) 1999 25(03):260-26.
[14]尤新辉.影响茶叶及茶饮料品质因素之探讨[J].食品工业,1994,26(10): 37-43.
[15] Mikuni K,Shibata E, Kagri N. Prevention of milk down of tea extract by cyclodextrins[J].Seito Gijntsu Kenkyn Kaishi, 1993,41:71-75.
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