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茶叶内含物质与外源污染物在冲泡过程中的浸出规律

2020-02-25陈红平刘新鲁成银邱静

茶叶科学 2020年1期
关键词:溶解度金属元素茶汤

陈红平,刘新,鲁成银*,邱静

茶叶内含物质与外源污染物在冲泡过程中的浸出规律

陈红平1,2,3,刘新2,鲁成银2*,邱静1*

1. 中国农业科学院农业质量标准与检测技术研究所,北京 100081;2. 中国农业科学院茶叶研究所农业部茶叶产品质量安全风险评估实验室,农业部茶叶质量安全控制重点实验室,浙江 杭州 310008;3. 中国农业科学院研究生院,北京 100081

在收集相关文献的基础上,总结分析茶叶内含物质、农药残留与金属元素在茶汤中的浸出规律。化合物的理化性质和茶叶冲泡方法是影响浸出率的内因和外因,其中内因起着决定性作用。茶汤中化合物浸出率与水溶解度呈正相关,与辛醇-水分配系数(辛醇/水)呈负相关。冲泡水温升高能显著提高茶叶内含物质与外源污染物的浸出率及其在茶汤中的浓度,冲泡时间与化合物浸出速率呈负相关,但随着时间增加,茶汤中化合物的浓度显著提高。新烟碱类农药和氨基甲酸酯类农药浸出率较高,大部分农药浸出率高于60%。金属元素在茶汤中的浸出率研究结果相差较大,氟、镍、钴在茶汤中浸出率较高,达到50%以上,铅的浸出率在20%~50%。基于质谱分析代谢组学技术将在茶叶冲泡过程的化学物质浸出规律研究中发挥重要作用,热力学理论基础和传质动力学模型将有利于更深层面认识外源有害物质在茶汤中的浸出行为。

茶叶冲泡;内含物质;农药残留;重金属;浸出规律

茶叶的色、香、味等品质是茶叶冲泡过程中内含物质在茶汤中溶解、释放的体现。茶多酚、咖啡碱、茶多糖、氨基酸、茶色素等特征成分溶解于茶汤中,形成茶叶独特的香气与滋味[1-2]。茶多酚是一类多酚化合物,主要有儿茶素、黄酮和黄酮类、酚酸及缩酚酸等。茶多酚易溶于热水,是构成茶汤品质的基础,一定程度上决定了茶汤的滋味及颜色。尽管咖啡碱呈苦味,但是咖啡碱与茶叶中的其他物质在茶汤温度下降后形成络合物,从而呈现鲜爽滋味。茶氨酸是茶叶游离氨基酸主要成分,占氨基酸总量50%~60%,具有焦糖香和鲜爽味,增加茶汤甜味和鲜味。茶叶呈香物质主要包括醇类、醛类、酸类、酯类、酮类、萜烯类,尽管呈香物质在茶汤中的溶解度差异较大,但茶叶冲泡过程中,呈香物质的释放通常与时间、水温及冲泡次数等因素密切相关。因此,茶叶内含物质在茶汤中溶解与释放是茶叶滋味与香气的化学物质基础,是茶叶品质的决定性条件。

茶汤既是茶叶特征成分的载体,同时也是茶叶中外源有害物质被人体吸收的主要途径之一。与其他农产品或食品不同,茶叶中外源有害物质在饮茶时并非完全进入人体,只有当有害物质溶解于茶汤后才被人体吸收,从而对人体构成潜在的健康风险。因此,有害物质在茶汤中的浸出率是茶叶中有害物质风险评估的关键参数。

本文在收集相关文献基础上,分别从茶叶特征成分、农药残留与金属元素(重金属)等三方面,总结分析茶叶内含物质和外源污染物在茶汤中的溶解、释放与转化规律,旨在探寻茶叶冲泡过程中物质迁移转化的基础规律,从而为茶叶品质调控、感官审评以及茶叶质量安全风险评估研究提供线索。

1 茶叶冲泡条件对内含物质浸出率的影响

多酚、咖啡碱、氨基酸、多糖、色素等特征成分在茶汤中的溶解与释放不仅与化合物的理化性质相关,而且与茶叶的种类、形状、水质、水温、茶水比、冲泡时间、冲泡次数等相关[3-5]。我国将茶叶分为绿茶、红茶、青茶(乌龙茶)、白茶、黄茶和黑茶,它们之间的差异不仅体现在茶叶品种、工艺和外形上,而且在冲泡方式和方法上也存在差异,从而体现茶叶品质特点。

1.1 冲泡温度对内含物特征成分的影响

茶叶中内含物质的浸出是溶质分子(浸出物)在固相(茶叶)与液相(水相)之间的分配,并逐渐达到平衡状态。浸出过程包括:水相进入茶叶固体内并溶解茶叶内含物,随后溶质从茶叶内部液体中扩散而达到茶叶表面,最后溶质从茶叶表面通过液膜扩散而达到外部水相的主体。在此过程中,水温是影响茶叶内含物浸出速度的关键影响因子之一。

茶叶冲泡温度不同,内含物在茶汤中的溶解度和溶解速率不同,从而影响茶汤中可溶性成分含量,形成不同口感,影响茶汤品质[6-8]。Jin等[9]采用非靶向UPLC-QTOF/MS结合组学分析,通过主成分分析(PCA)和正交偏最小二乘判别分析(OPLS-DA),发现60℃与90℃水温冲泡下的茶汤中内含物含量存在显著差异。李再兵[10]研究发现,绿茶冲泡时水温从60℃上升至100℃时,茶多酚、咖啡碱和氨基酸的浸出率均呈上升趋势,浸出率分别提高70.22%、59.30%和46.34%(图1)。金恩惠[11]研究发现,乌龙茶和普洱茶冲泡过程中可溶性物质的浸出量呈先上升至饱和浓度,再趋于平缓的趋势。通过温度对茶叶特征成分的影响分析,结合感官审评,乌龙茶与普洱茶的冲泡温度推荐为100℃。刘晓莎[12]利用核磁共振技术,发现乌龙茶冲泡过程中,随着水温的增加,水浸出物、茶多酚、可溶性糖、游离氨基酸和生物碱均显著增加(图2)。Kelebek[13]研究发现,随着水温提高(从80℃上升到100℃),茶汤颜色发生显著变化,抗氧化能力下降15.5%~36.6%,茶多酚、没食子酸衍生物、黄烷-3-醇、羟基肉桂酸酯、茶黄素、咖啡碱含量分别上升17.2%、30.1%、45.5%、7.5%、18.1%和17.3%。Pérez-Burilloa等[14]研究发现,茶叶冲泡水温60℃上升到98℃时,儿茶素和咖啡碱呈上升趋势,尤其在70℃~90℃区间,上升更为明显,同时茶汤抗氧化能力也显著上升。儿茶素在高温下(高于95℃)发生差向异构反应,由表没食子儿茶素没食子酸酯(EGCG)、表没食子儿茶素(EGC)转化为没食子儿茶素没食子酸酯(GCG)、没食子儿茶素(GC)。因此当水温从75℃上升到85℃时,茶汤中EGCG和EGC呈上升趋势,而水温从85℃上升到95℃时,EGCG和EGC呈下降趋势[15]。

由此可见,茶叶内含特征物质随着冲泡水温提高,在茶汤中的浸出率增加。水温增加,有助于提高化合物在水中的溶解度以及水对茶叶组织的渗透能力;同时水温提高,加速茶叶组织破坏,增加茶叶组织间的空隙,从而有利于茶叶内含物质的溶出。

注:浸泡时间5 min,茶叶∶水=3 g∶150 mL Note: infusion time for 5 min and tea∶water=3 g∶150 mL

1.2 冲泡时间对内含物特征成分的影响

茶叶中内含物在茶汤中的浸出过程是一个动态平衡过程,但不是简单的溶质分子在水相中快速达到平衡状态,而是溶质分子从固相(茶叶)到液相(茶汤)中溶解、扩散和传质的过程。在这个动态平衡过程中,时间是影响溶质分子在水相(茶汤)中含量的关键因素,在一定范围内符合一级动力学方程。李再兵[10]发现绿茶中氨基酸的浸出率和冲泡时间符合一级动力学方程,如公式(1):

=7.504ln()+18.708(2=0.993)·······························(1)

式中为每100 mL的含量(mg),为时间(min)。

İlyasoğlu等[16]采用响应面统计软件分析了冲泡时间和温度对茶叶抗坏血酸、茶多酚的影响,并建立了数学模型(2)和(3),用于预测抗坏血酸和茶多酚在茶汤中的浸出率。

=3.229+0.002-0.1292+0.100-0.0542·······························(2)

=61.411+1.835-2.0112+1.358-2.5212·······························(3)

式中为每100 mL的含量(mg),为时间(min),为温度(℃)

Jin等[9]研究发现,水温为60℃时,在60 min内,茶汤中儿茶素总量随温度升高而增加,主要是由于GC、C、GCG和CG在茶汤中含量上升;在90℃时,茶汤中儿茶素总量在10 min内迅速上升,然后在10~30 min内呈下降趋势,其主要原因是EGC、EC、EGCG和ECG向对应的差向异构体转化。Gani等[17]采用273 nm波长作为HPLC-UV检测波长,考查了监测信号与茶叶冲泡时间的关系,结果表明信号强度与冲泡时间呈正相关,由此说明,茶汤中内含物质随冲泡时间延长而增加。Nikniaz等[18]发现散装红茶和袋泡红茶随着冲泡时间延长,茶汤中的多酚含量增加,抗氧化能力提升。Zhang等[19]研究了冲泡参数对白茶品质的影响,在冲泡6 min后,儿茶素、咖啡碱和茶氨酸均呈上升趋势,但在第7分钟,EGCG、EC、ECG和咖啡碱有所下降,结合茶汤特征成分分析和感官审评,白茶推荐冲泡参数为冲泡时间7 min,温度100℃,料液比1∶30或1∶40,冲泡2次。Gan等[20]考查了泡时间对不同茶叶茶汤中多酚物质与抗氧化能力的影响,结果表明,10 min内多酚物质和抗氧化能力均上升,并推荐红茶、绿茶冲泡2次,但袋泡茶只冲泡1次。

由此可见,冲泡时间与茶汤中内含物质浓度呈正相关,与单位时间浸出量呈负相关。冲泡时间越长,茶汤中内含物质浓度越高,但单位时间浸出量降低。茶叶冲泡起始阶段(1~2 min),茶多酚、氨基酸、咖啡碱、水溶性多糖等内含物质迅速溶解于茶汤中,茶汤中内含物质浓度比例与茶叶中内含物质比例相近。当冲泡时间延长时,茶汤中茶多酚、咖啡碱等高含量内质成分浸出浓度高于氨基酸,从而导致酚氨比增大,苦涩味更为明显。

1.3 水质对茶叶内含物质浸出的影响

水质对茶叶品质的影响包括两方面,一方面水中有机物质和无机物质添加到茶汤中,不与茶叶内含物作用,由于添加物质本身的物理化学属性,从而改变茶汤滋味、汤色和香气等;另一方面,水中有机物或无机物与茶叶内含物质相互作用,产生新的化合物,从而改变茶汤滋味、汤色和香气等品质特征。对茶叶品质及其化学成分影响的水质因子主要包括金属离子、矿物质离子、pH、水中气体分子等[21-23]。大量研究表明,Ca2+、Fe3+/Fe2+、Al3+等金属离子是影响茶汤品质关键因子之一,其原因是金属离子与茶叶内含物相互作用,形成络合物从而改变茶汤滋味、汤色或香气[24-27]。由于茶叶富含多酚、氨基酸等弱酸性物质,茶汤具有较强的缓冲能力,pH范围明显窄于饮用水pH范围,因而水中pH对茶叶内含物浸出的影响并不显著[28-29]。

2 茶叶中农药残留在茶汤中的浸出规律

农药残留是茶叶外源污染物,茶树鲜叶吸附农药后,经过茶叶加工渗透到茶叶组织内,或与茶叶内含物质相互作用。农药在茶叶中的分布包括叶表面、组织间和组织内。因此,农药在茶汤中的溶出规律与茶叶内含物浸出规律存在较大差异。

2.1 农药在茶汤中的浸出率

目前,国内外针对在茶叶中使用的农药进行了浸出规律研究,已查明60种农药在茶汤中的浸出率,包括有机磷农药(15种)、新烟碱类农药(5种)、拟除虫菊酯农药(7种)、苯甲酰脲类(7种)、有机氯类农药(5种)、氨基甲酸酯类(3种)和其他农药(18种)(表1)。总体上,新烟碱类农药和氨基甲酸酯类农药浸出率较高,大部分浸出率高于60%。有机氯农药、拟除虫菊酯农药和苯甲酰脲类农药浸出率较低,均低于10.5%,部分浸出率为0。有机磷农药浸出率差异较大,甲胺磷、乙酰甲胺磷和乐果的浸出率高于80%,三唑磷、水胺硫磷、杀扑磷和磷铵浸出率为27%~65%,其他有机磷农药浸出率较低。另外,多菌灵和噻苯唑农药浸出率较高,均高于80%。

2.2 影响农药浸出率的主要因素

农药在茶汤中的浸出率取决于农药理化性质(内因)和冲泡方法、茶叶属性及其农药残留量等(外因)。农药的浸出率与水溶解度、辛醇/水比和蒸汽压密切相关,水溶解度越大、辛醇/水比越小、蒸汽压越小,农药浸出率就越大[31,42,45]。图3与图4说明了19种农药的水溶解度和辛醇/水比与浸出率的关系,农药浸出率随着其在水中的溶解度增加而提高,当在水中的溶解度低于20 mg·L-1时,农药浸出率低于15%;当在水中的溶解度从35 mg·L-1(三唑磷)上升到4 100 mg·L-1(噻虫嗪)时,农药浸出率从22.6%上升到90.6%。因此,在水中的溶解度20 mg·L-1可能是农药浸出率的关键参数。农药浸出率与辛醇/水比成负相关,辛醇/水比越低,浸出率就越高。当辛醇/水比(Logow)从1.52(多菌灵)上升到2.48(水胺硫磷)时,农药浸出率从80%下降到30%。由此可见,辛醇/水比Logow=2可能是农药浸出率的阈值[31]。Wan等[55]研究表明,水溶解度低于10 mg·L-1或高于179 mg·L-1时,农药浸出率与水溶解度相关性不显著,农药浸出率分别在1%~4%和大于90%范围;但水溶解度为10~150 mg·L-1时,农药浸出率与水溶解度几乎呈线性上升关系。Hou等[37]比较了3种新烟碱类农药在茶汤中的浸出率,吡虫啉、噻虫嗪和啶虫脒的水溶解度分别为0.51、4.10 g·L-1和4.25 g·L-1,3种农药在茶汤中平均浸出率为63.1%、80.5%和78.3%。尽管农药浸出率与农药理化性质和冲泡方法相关,但Wang等[56]认为水溶解度是影响浸出率最主要的因素,浸出率符合热力学行为,并建立了浸出率(Log)与水溶解度(Log)数学预测模型,用于预测农药在茶汤中的浸出率。

茶叶冲泡方法,包括水温、冲泡时间和冲泡次数等外因对农药浸出率起到重要影响。浸泡水温升高,有助于提高农药的水溶解度,加大水对茶叶基质的渗透能力,加快农药的溶出速率。因此,冲泡温度升高,农药在茶汤中浸出率显著提升[56-57]。甲氰菊酯、氯氰菊酯、氰戊菊酯和三氟氯氰菊酯随着冲泡水温度从60℃提高到100℃时,浸出率分别从0.76%、0、0.72%和0上升到5.82%、5.58%、4.87%和3.96%[42]。

冲泡时间对农药浸出率的影响取决于农药的溶出速率、挥发速率和其在茶汤中的稳定性。冲泡时间延长会提高农药的浸出率,尤其对于水溶解度低的农药影响更大。在2、5、10、20、30 min内,甲氰菊酯、氯氰菊酯、氰戊菊酯和三氟氯氰菊酯在浸泡10 min时浸出率最大,比2 min时的浸出率提高了6.5倍以上[42]。Ozbey等[58]发现随着浸出时间的延长,杀螟硫磷、毒死蜱、乐果、马拉硫磷和乙基嘧啶磷等有机磷农药后期的浸出速率呈下降趋势,在10 min下降不明显,但在20 min后,杀螟硫磷、毒死蜱、乐果、马拉硫磷和乙基嘧啶磷分别下降了28.5%、35.4%、12.6%、39.8%和39.1%。噻虫嗪和噻虫啉在茶汤中的浸出率随着时间延长而增加,并在20 min达到最大值[38]。

图3 农药水溶解度与浸出率的关系[31]

Fig 3. Relationship of water solubility and extraction rate of pesticides during tea brewing[31]

图4 农药辛醇/水比(LogKow)与浸出率的关系[31]

Fig 4. Relationship of octanol/water ratio (Logow) and extraction rate of pesticides during tea brewing[31]

茶叶一般冲泡2~3次,每次冲泡过程中农药浸出率存在显著差异,一般第一次冲泡农药浸出率大于第二次。Chen等[31]研究发现,当农药总浸出率大于20%时(冲泡2次),第一泡和第二泡农药浸出率比例为(2∶1)~(5∶1);当农药总浸出率小于10%时,第一泡和第二泡农药浸出率相当。这一结果与茶叶中邻苯二甲酸酯在茶汤中的浸出率相近[59]。Fang等[38]研究发现,噻虫嗪在第一泡和第二泡中的浸出率分别为30.7%和3.8%,噻虫啉在第一泡和第二泡中的浸出率分别为12.5%和2.8%,在第三泡中均未检出两种农药。一般来讲,农药浸出率与茶水比呈负相关,茶水比越大,浸出率越小[42]。然而,当茶水比(g∶mL)从1∶30上升到1∶100时,噻虫嗪和噻虫啉农药浸出率分别从8.8%上升到31.5%和4.8%上升到16.5%[42]。同时,冲泡器具密闭或敞开对茶汤中农药含量有一定影响,与茶杯密闭相比,茶杯无盖时,噻虫嗪和噻虫啉浸出率分别下降3.1%和2.5%[42]。

茶叶种类及其残留量对农药浸出率的影响不明显[31,37]。Chen等[31]研究发现,茶叶中农药残留量与浸出率无显著关系,但Kumar等[51]研究发现,茶叶中已唑醇在茶汤中浸出率与其残留量呈正相关,浓度越高,浸出率越大。

Gao等[60]为了查明茶叶淋洗对农药去除效果,考察了8种农药(乐果、马拉硫磷、啶虫脒、吡虫啉、噻虫嗪、联苯菊酯、氯氰菊酯和氰戊菊酯)在不同时间(5、10、20、30 s)内在绿茶、红茶和乌龙茶中的浸出规律。结果表明,在5~30 s,乐果、马拉硫磷、啶虫脒、吡虫啉、噻虫嗪等5种农药在绿茶中的浸出率分别为10.8%~16.7%、8.4%~12.6%、7.1%~13.3%、7.8%~10.5%和3.8%~5.6%,红茶浸出率结果与绿茶相近,但乌龙茶中5种农药浸出率与绿茶、红茶不一致,农药浸出率与冲泡时间关系不显著。另外,短时间内联苯菊酯、氯氰菊酯和氰戊菊酯等3种农药浸出率几乎为0。由此推测,茶叶饮用前,沸水洗茶弃去后重新泡茶,可以减少水溶解度较高的农药对人体的暴露水平。

表1 农药在茶汤中的浸出率

续表1

由此可见,农药在茶汤中的浸出率取决于农药的理化性质(内因)和冲泡方法(外因)。水溶解度和辛醇/水比是影响农药浸出率最主要因素,农药浸出率与水溶解度呈正相关,与辛醇/水比呈负相关。农药浸出率与茶叶冲泡温度、时间在一定范围内呈正相关,但与茶叶种类、茶叶农药残留量的相关性较小。

3 茶叶中金属元素与氟在茶汤中的溶解规律

金属元素与氟作为茶叶外源污染物之一,主要通过土壤-根系或大气-茶树鲜叶之间的吸附、转化与累积作用,导致不同化学形态的金属元素与氟在茶树新梢中累积。因此,与茶叶内含物和农药在茶汤中的浸出规律不同,影响金属元素或氟在茶汤中的浸出率内因主要是金属元素或氟的存在形态,而不仅是无机态金属元素或氟的溶解度。然而,茶叶中金属元素的化学形态研究集中于土壤-茶树系统间吸附、转运、累积作用以及茶叶中含量测定等方面研究,浸出规律以总量计算,尚未有不同化学形态的金属元素在茶汤中浸出规律研究[61-63]。目前,茶汤中金属元素的浸出规律主要集中在冲泡温度、时间、冲泡次数等外因的影响。茶叶中氟的存在形式包括无机氟离子、有机氟和氟化物。Zhang等[64]调查了19个中国生产的茶叶样品中氟含量及其存在形态,结果表明,茶叶中氟主要以无机氟离子存在,有机氟仅有0.023%~0.41%,且50%~99%的氟化物是短链化合物,碳原子的数量不多于6,而大部分有机氟尚未鉴定出是何种化合物。

金属元素(重金属)与氟在茶汤中的浸出率差异非常大,不仅表现在不同金属元素(重金属)之间,而且同一种元素在不同茶叶中或不同分析方法中差异也很大(表2)。总体来看,氟在茶汤中的浸出率较高,达到60%~98.8%,其次是镍(51.13%~82.4%)和钴(31.04%~74.48%)。茶汤中氟含量差异较大,浸出率分布范围也非常广。Das等[76]调查了中草药、红茶、绿茶、乌龙茶、白茶和普洱茶冲泡后茶汤中氟含量,分别为0.06~0.69、1.47~5.45、2.43~6.94、3.08~5.63、5.39 mg·L-1和2.87~4.96 mg·L-1,平均浸出率为57.6%、60%、72.8%、76.2%、98.9%和65.9%。铅的浸出率分布范围很广,达到1.17%~49.76%,其主要原因除了茶叶中铅含量差异、分析方法差异等因素外,铅在茶叶中的化学形态也是导致浸出率差异极大的主要原因之一。

刘锐[80]研究发现,茶叶中各元素在不同温度冲泡下,浸出率差异较大。其中As、Cd、Mn、Ni、Pb、Ti和Zn的浸出率随温度升高而增加,Cu呈下降趋势,而Cr和Fe变化不大。傅仙玉等[81]研究了不同温度(60、80、100℃)对水仙和肉桂两种乌龙茶中氟浸出率的影响,随着温度升高,水仙茶汤中氟的含量分别为0.752、1.106 mg·L-1和1.681 mg·L-1,而肉桂茶汤中氟含量分别为1.095、1.388 mg·L-1和1.761 mg·L-1。

表2 属元素(重金属)与氟在茶汤中的浸出率

冲泡时间对茶中金属元素(重金属)的浸出率提取有着显著影响。研究表明,碧螺春、金骏眉和铁观音中Cu和Zn在3、5、7、10 min内浸出率几乎呈倍数增加,但10 min后(10~120 min)浸出率呈平稳水平[82]。Miri等[83]研究发现,冲泡时间在5、10 min和15 min时,肯尼亚红茶、绿茶、伊朗茶中氟的浸出率随冲泡时间延长而增加,以绿茶为例,5、10、15 min冲泡后,茶汤中氟含量分别为1.35、1.80、1.98 mg·L-1,10 min后分别提高了33.3%和46.7%。傅仙玉等[81]发现随着冲泡时间延长(5、15、30 s),乌龙茶中氟的浸出量与时间呈正相关,且肉桂中浸出量高于水仙。紧压茶通常采用煮沸形式饮用,但煮茶时间(5、10、20 min)对氟的浸出量影响不大,未达到极显著差异[77]。

冲泡次数对乌龙茶中氟的浸出量影响呈先升后降的趋势,第二泡中氟的浸出量最高,而第一泡和第三泡中氟的含量相当[81]。但在紧压茶中,铅的浸出率随着冲泡次数增加而显著降低,在第一泡、第二泡和第三泡中铅的浸出率分别为15.9%、5.4%和2.0%[78]。茶水比的提高,有助于增大铅在茶汤中的浸出率[77]。

金属元素与氟在茶汤中浸出规律相对复杂,浸出率不仅与金属元素的理化性质相关,而且与金属元素在茶叶组织中的位置、金属元素的形态与价态相关。因此,金属元素在茶汤中的浸出率研究结果相差较大。总体来看,氟、镍、钴在茶汤中浸出率较高,达到50%以上,铅的浸出率在20%~50%。

4 总结与展望

化合物的理化性质和茶叶冲泡方法是影响浸出率的内因和外因,前者起决定性作用,后者对茶叶内含物质浸出率的影响更突出。茶多酚、咖啡碱、氨基酸酸、可溶性多糖等茶叶内含物质由于分子量小,水溶解度高,因而在茶汤中浸出速率高,且浓度随着冲泡温度提高与冲泡时间延长而增加,直至饱和呈平稳状态。农药在茶汤中浸出率差异较大,新烟碱类农药、氨基甲酸酯类农药由于水溶解高,因而在茶汤中的浸出率高,但有机氯农药和拟除虫菊酯农药浸出率极低。由于分析方法、金属元素存在形式等方面的差异,金属元素(含重金属)与氟在茶汤中浸出率研究结果差异较大,氟、镍和钴的浸出率较大,铅次之,其他金属元素(重金属)大部分低于30%。

茶叶品质是一个系统物质基础,不仅仅是由几类特征成分的叠加反应决定的。因此,茶叶冲泡过程中全组分分析(或大数据分析)则更能反应冲泡方法对茶汤浸出物质的变化规律,更全面揭示冲泡温度、冲泡时间和冲泡次数对茶叶品质的影响。由此可见,基于质谱分析技术,尤其是高分辨质谱分析技术,结合大数据软件分析系统,将成为茶叶-茶汤品质化学研究的有力工具。茶汤是茶叶农药残留、重金属等外源污染物暴露人体最主要的途径之一,其浸出率是评价外源有害物质安全性的关键参数。从热力学理论基础和传质动力学模型解析茶汤中外源有害物质浸出机理,预测外源有害物质在茶汤中的浸出率,将有利于更深层面认识外源有害物质在茶汤中的浸出行为,从而为制定茶叶中最大残留限量标准提供基础数据和理论依据。

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《茶叶科学》第八届编辑委员会副主任委员刘仲华教授当选中国工程院院士

11月22日,中国工程院公布了2019年院士增选结果,我刊第八届编辑委员会副主任刘仲华教授当选中国工程院院士。继陈宗懋院士之后,我刊迎来了第二位中国工程院院士编委。

刘仲华,湖南农业大学教授、博士生导师、学术委员会副主任、茶学学科带头人,浙江大学兼职教授。现任国家植物功能成分利用工程技术研究中心主任、国家茶叶产业技术体系加工研究室主任、国家农产品加工技术研发中心茶叶分中心(湖南)主任。兼任国务院学位委员会园艺学科评审组成员、教育部科技委农林学部委员、中国茶叶学会监事、中国茶叶流通协会副会长、中国国际茶文化研究会副会长、国家茶叶标准化技术委员会顾问兼黑茶工作组和茯茶工作组组长、湖南省茶叶学会名誉理事长、湖南省大湘西茶业发展促进会会长等职。

刘仲华教授长期从事茶叶深加工与功能成分利用、茶叶加工理论与技术、饮茶与健康等领域的研究与教学,致力于创新茶叶加工理论技术、提高茶叶资源利用率和产业综合效益。创新黑茶加工和茶叶深加工理论与技术体系,揭示了黑茶加工品质风味形成机理及黑茶健康属性,创建了黑茶优质高效安全加工关键技术体系,强力推进了我国黑茶产业提质增效与快速发展;揭示了茶叶功能成分的生物活性及作用机制,创制的茶叶提取物制品催生了一批国际主流健康产品,引领我国茶叶深加工从追踪日本和欧美发达国家到领先国际同行。为我国茶叶科技进步、茶叶产业提质增效与转型升级做出了突出贡献。

刘仲华教授先后主持国家和部省级项目30多项,以第一完成人获国家科技进步二等奖2项、湖南省科技进步一等奖3项、湖南省科技进步二等奖1项,并荣获首届湖南省十大科技创新奖、湖南省光召科技奖、国际茶叶科技创新杰出贡献奖等荣誉;先后在国内外学术刊物发表论文400多篇,其中SCI收录60多篇,授权发明专利60多件。2019年获得了“何梁何利基金”科学与技术进步奖(农学奖)。

Leaching Pattern of Internal Substances and Xenobiotic Pollutants during Tea Brewing

CHEN Hongping1,2,3, LIU Xin2, LU Chengyin2*, QIU Jing1*

1. Institute of Quality Standard and Testing Technology for Agro-Products of Chinese Academy of Agricultural Sciences, Beijing 100081, China; 2. Tea Research Institute, Chinese Academy of Agricultural Sciences, Tea Quality and Supervision Testing Center, Key Laboratory ofTea Quality and Safety & Risk Assessment, Ministry of Agriculture, Ministry of Agriculture R. P. China, Hangzhou, 310008, China; 3. Graduate School of Chinese Academy of Agricultural Sciences, Beijing 100081, China

Based on the recent literatures, the dissolving, releasing and transformation patterns of tea internal compounds and exogenous contaminants were summarized and discussed in this study. Physicochemical properties of chemicals and tea brewing methods are the internal and external cause affecting extraction rates of chemicals during tea brewing. Internal cause plays a crucial role in extraction rates, while external cause is more prominent for the leaching of tea internal substances. Water solubility of chemicals is positively correlated with extraction rates, while octanol-water partition is negatively correlated with extraction rates. Increasing water temperature is helpful for increasing extraction rates of chemicals and their concentrations in tea infusion. Brewing time is negatively correlated with extraction rates in a period of time, while the concentrations of chemicals in tea infusion increase with the brewing time. Compared with other pesticides, most of neonicotine pesticides and carbamate pesticides have higher extraction rates over 60%. The results of extraction rates of metal elements in tea infusion are quite different, and extraction rates of fluorine, nickel and cobalt have high extraction rates over 50%, while extraction rates of lead range from 20% to 50%. Metabonomic analysis based-high resolution mass spectrometry technique is a promising and powerful method for profiling extracting pattern of chemicals during tea brewing. Meanwhile, extracting behavior of toxic compounds during tea brewing will be deeply understood by using thermodynamic theory and kinetic model of mass extraction.

tea brewing, internal substance, pesticide residues, heavy metals, leaching pattern

S571.1;TS201.6

A

1000-369X(2020)01-063-14

2019-06-27

2019-07-25

中国农业科学院创新团队茶叶质量与风险评估团队(CAAS-ASTIP-2014-TRICAAS-06)、浙江省公益应用项目(2017C32059)、现代农业产业技术体系建设专项基金资助项目(nycytx-26)、国家自然科学基金(31671941)

陈红平,男,副研究员,主要从事茶叶质量安全检测与研究方面的研究。

lchy@mail.tricaas.com,qiujing@caas.cn

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