周子维, 魏莹莹, 吴晴阳, 范丽君, 饶泓婷, 陈援援, 吴灵贞, 戴彬彬, 蔡烈伟, 郑世仲, 王芳, 孙云. 气流因子差异化做青工艺对乌龙茶香气品质的影响[J]. 农业工程学报, 2022, 38(21): 240-248. DOI: 10.11975/j.issn.1002-6819.2022.21.028
    引用本文: 周子维, 魏莹莹, 吴晴阳, 范丽君, 饶泓婷, 陈援援, 吴灵贞, 戴彬彬, 蔡烈伟, 郑世仲, 王芳, 孙云. 气流因子差异化做青工艺对乌龙茶香气品质的影响[J]. 农业工程学报, 2022, 38(21): 240-248. DOI: 10.11975/j.issn.1002-6819.2022.21.028
    Zhou Ziwei, Wei Yingying, Wu Qingyang, Fan Lijun, Rao Hongting, Chen Yuanyuan, Wu Lingzhen, Dai Binbin, Cai Liewei, Zheng Shizhong, Wang Fang, Sun Yun. Effects of differential green-making by airflow factors on the aroma quality of oolong tea[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2022, 38(21): 240-248. DOI: 10.11975/j.issn.1002-6819.2022.21.028
    Citation: Zhou Ziwei, Wei Yingying, Wu Qingyang, Fan Lijun, Rao Hongting, Chen Yuanyuan, Wu Lingzhen, Dai Binbin, Cai Liewei, Zheng Shizhong, Wang Fang, Sun Yun. Effects of differential green-making by airflow factors on the aroma quality of oolong tea[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2022, 38(21): 240-248. DOI: 10.11975/j.issn.1002-6819.2022.21.028

    气流因子差异化做青工艺对乌龙茶香气品质的影响

    Effects of differential green-making by airflow factors on the aroma quality of oolong tea

    • 摘要: 为探究气流因子在乌龙茶做青工艺中对其香气品质的影响,以鲜叶(CK)、常氧摇青叶(Ta)和乏氧摇青叶(Tb)及相应的毛茶a(Ma)和毛茶b(Mb)为试材,利用半定量反转录聚合酶链式反应(Reverse Transcription and Polymerase Chain Reaction,RT-PCR)、顶空固相微萃取法(Head-Space Solid-Phase MicroExtraction,HS-SPME)与气相色谱-飞行时间质谱联用(Gas Chromatography-Time-Of-Flight Mass Spectrometry,GC-TOF MS)等技术,通过多元统计分析等方式,对不同气流因子介导做青工艺的乌龙茶挥发性组分进行分析。结果表明:Tb中低氧胁迫响应因子CsHIG4和CsHIG6基因的表达水平相较Ta和CK有所上调,基于毛茶中共鉴定出的205种挥发性组分,采用最小偏二乘法(Partial Least Squares,PLS)分析表明,以重要性投影指标值(Variable Important Projection,VIP)大于1.0为筛选条件,获得标志性差异挥发性成分有24个,其中吲哚的VIP值最大(4.75),α-法呢烯(3.06)、罗勒烯异构体混合物(2.77)、反式-橙花叔醇(2.75)等随后。乏氧摇青叶有5种特征差异挥发性组分,而常氧摇青叶中仅2种。毛茶感官审评结果发现,常氧摇青处理叶付制的乌龙茶香气清香持久,花香较显(香气感官得分90.67)。Ma中反式-橙花叔醇、2,3-二氢-3,5二羟基-6-甲基-4(H)-吡喃-4-酮、异植物醇、亚硫酸-2-乙基己基丁酯、6-氮杂双环3.2.1辛烷的含量均显著高于Mb(P<0.05),推测该5个物质可能是常氧摇青条件下形成较优品质乌龙茶的标志性代谢物,这有助于更好理解气流因子对摇青过程中香气物质代谢的影响,研究结果为探究环境因子介导下摇青工艺对乌龙茶香气品质的形成机制提供理论基础。

       

      Abstract: Oolong tea is one of the six major Chinese traditional tea categories, due to its naturally fruity and floral aroma. Unlike green and black tea, the quality of oolong tea is originated from the processing (named green-making), which also contributes to the semi-fermentation degree. The green-making includes turnover and indoor withering. The former refers to shaking the solar-withered tea leaves several times, while the latter is to pause for hours after turnover. The two steps are repeated alternately during the manufacturing process of oolong tea. Therefore, all process parameters can pose some influences on the aroma of oolong tea, such as the mode of green-making, the intensity of turnover, indoor withering, and the thickness of spread tea leaves. In addition, the environmental factors of green-making also play an important role in the formation of oolong tea quality, including environmental temperature, humidity, and atmosphere. The airflow is the carrier of temperature and humidity, particularly the indispensable determiner of oolong tea quality. However, it is still lacking in the effects of airflow on the oolong tea green-making during tea processing. This study aims to explore the effect of the airflow factor on the aroma quality of oolong tea during the process of green-making. The test materials were selected as fresh tea leaves (CK), normoxic tea leaves (Ta), hypoxic tea leaves (Tb), and their associated raw tea a (Ma) and raw tea b (Mb). The volatile components of oolong tea mediated by different airflow factors were analyzed by multivariate statistical analysis after the semi-quantitative Reverse Transcription and Polymerase Chain Reaction (RT-PCR), headspace solid-phase microextraction (HS-SPME), and Gas Chromatography Time-of-Flight Mass Spectrometry (GC-TOF MS). The result showed that both green-making rollers (named subroller a and subroller b) fully met the conditions of normoxia and hypoxia. The relative expression levels of hypoxic stress response factors CsHIG4 gene and CsHIG6 gene in Tb were up-regulated founded on the brightness of electrophoresis bands compared with the Ta and CK. 205 volatile components were identified in the raw tea. 33 kinds of shared differential metabolites were found among the CK, Ta and Tb, most of which were alcohol (8 kinds) and alkene (7 kinds). Partial Least Squares (PLS) analysis showed that there were 24 characteristic aroma components, whose Variable Important Projection (VIP) values were more than 1.0. Among them, the VIP value of indole was the largest (4.75), followed by α-farnesene (3.06), ocimene mixture of isomers (2.77), and trans-nerolidol (2.75). The analysis of variance showed that there were five characteristic aroma components in the Mb, whereas, only two in the Ma. The sensory evaluation of raw tea indicated that the aroma of Ma was clean, lasting and refreshing, indicating a distinct flowery scent, achieved the final score 90.67. More importantly, the final score was achieved in 90. By contrast, the aroma of the Mb was dull, less pleasant, lack of long and clean, particularly with the floral and characteristics variety fragrance. The contents of five volatiles in the Ma were extremely significantly higher than those in the Mb (P<0.05), including the trans-nerolidol, 2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one, isophytol, 2-ethylhexyl butyl sulfite, 6-azabicyclo 3.2.1 octane. It infers that these five substances can be the landmark metabolites to form better quality oolong tea under the normoxic turn-over condition. This finding can provide a strong reference to better understand the effect of airflow factors on the metabolism of aroma substances during the green-making process. A theoretical foundation was also laid to explore the formation mechanism of aroma quality during the green-making process of oolong tea mediated by environmental factors.

       

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