采用PLS-DA分析毛火方式对工夫红茶品质的影响

为探究不同毛火方式对工夫红茶品质的影响,明确新型电磁内热式滚筒-热风耦合干燥设备的毛火效果,该研究以一芽一二叶初展嫩度的"福鼎大白"品种为原料进行工夫红茶加工,设定电磁滚筒-热风耦合(Rotary pot-Hot air coupling First-Drying with electromagnetic heat,RHFD)、链板热风(Chain plate Hot air First-Drying,CHFD)、箱式热风(Box Hot air First-Drying,BHFD)、滚筒式滚炒(Rotary pot First-Drying,RFD)等4种毛火方式,比较所制茶样的茶多酚、儿茶素、茶色素、可溶性糖、咖啡碱、氨基酸等29个非挥发性指标,114个气相色谱-质谱技术(GasChromatography-Mass Spectrometry,GC-MS)检测的挥发性香气指标,10个外形和汤色色泽客观评价指标,同时进行了毛火方式的热效率、生产效率、生产成本等性能指标的分析比较,通过偏最小二乘判别统计(PartialLeastSquaresDiscriminationAnalysis,PLS-DA)分析毛火方式对优质工夫红茶品质的影响,并获得标志性差异化合物。结果表明:电磁内热式滚筒-热风耦合毛火处理下茶多酚和儿茶素总量显著最低(P<0.05),简单儿茶素含量较高,茶红素和可溶性糖含量、茶黄素综合指标TDE和茶色素综合指标10TFRB最高(P<0.05),毛火方式对茶黄素总量影响不显著(P>0.05);挥发性化合物总量以RHFD方式最高,RFD方式次之,CHFD方式最低;RHFD毛火方式芳香类、萜烯类等化合物含量最高。电磁内热式滚筒-热风耦合毛火升温快、温度分布均匀且稳定性好,热效率和生产效率高(分别为50.0%、220 kg/h),生产成本较低(仅0.32元/kg),预热时间仅14min;所制红茶在汤色透亮度、香气甜久度、滋味甜醇度等方面均得到提升,感官总分最高(P<0.05),达88.1。PLS-DA分析从挥发性和非挥发性角度均可将工夫红茶4种毛火方式显著区分,并分别获得了43种和18种差异化合物,结合差异性分析获得标志性差异化合物,2,4,6-三(1,1-二甲基乙基)-4-甲基环己-2,5-二烯-1-酮、香叶醇、3-辛酮、水杨酸甲酯、茶黄素、茶褐素、可溶性糖、表儿茶素等,可作为区分工夫红茶毛火方式,以及定向加工甜香、甜醇、高亮等优质工夫红茶的指标物质。该研究为红茶加工基础和品质提升提供技术参考和理论指导。

Influences of first-drying methods on the quality of Congou black tea using partial least squares-discrimination analysis

Processing of Congou black tea usually includes five procedures: withering, rolling, fermentation, first-drying and second-drying. Water content of a tea leaf is an important indicator for the black tea processing, particularly water loss most in first-drying, from 58%-64% of the fermented leaves to 20%-25% of the first-drying leaves. With a large amount of evaporation from leaf water and a rapid rise of leaf temperature, the enzymatic reaction in the leaves can be inhibited, while a large number of violent thermochemical reactions occur, in order to promote the transformation and upgrade of quality substances, and thereby to obtain the formation of excellent aroma, taste, color and other qualities of black tea. In this paper, two leaves and a bud of Fuding Dabai species were selected as raw material to make trial production of Congou black tea, in order to explore the influence of rotary pot-hot air coupling first-drying with electromagnetic heat on first-drying characteristic and quality formation of Congou black tea. Four methods were used, including chain plate hot air first-drying (CHFD), box hot air first-drying (BHFD), rotary pot first-drying (RFD), and rotary pot - hot air coupling first-drying with electromagnetic heat (RHFD). Multiple features and indicators were compared, such as 29 kinds of non-volatile tea indexes (polyphenols, catechins, tea pigments, soluble sugar, caffeine, amino acids, et al), 114 kinds of volatile aroma indexes that tested by GC-MS/MS, 10 kinds of evaluation indexes of leaf shape and liquor color, quality evaluation of artificial sensory and performance indexes of first-drying methods (production efficiency, energy cost, thermal efficiency, etc.). Partial least squares-discrimination analysis (PLS-DA) was then used to analyze the influence of first-drying methods on the taste, liquor color, and aroma quality formation of high-quality Congou black tea, finally to obtain the typical features of difference compounds. The results show that: 1) in RHFD treatment, the contents of tea polyphenols and total amount of catechins were the lowest, and the contents of total simple catechins, thearubigins, soluble sugar, TDE and 10TFRB were the highest, whereas the effect of first-drying methods on the content of theaflavins was not significant (P<0.05); 2) the total amount of volatile compounds was observed in the order of RHFD, RFD, BHFD, and CHFD; 3) the RHFD treatment can achieve the highest content of aromatic hydrocarbons, and terpenes. The rotary pot-hot air coupling first-drying (RHFD) method indicated some advantages, including fast heating (only 14 minutes), uniform temperature distribution and good stability, high thermal efficiency (50.0%), high production efficiency (220 kg/h), and low production cost (only 0.32 Yuan/kg). Moreover, the black tea after RHFD treatment has been significantly improved, indicating soup color brightness (La value), aroma sweetness, taste sweetness and refreshing, and the total score of sensory quality reaches the highest (88.1). PLS-DA also shows that Congou black tea can be distinguished by four kinds of first-drying methods from non-volatile (43 types obtained) and volatile (18 types obtained) compounds. The typical compounds are obtained, such as 2,4,6-tris(1,1-dimethylethyl)-4-methylcyclohexa-2,5-dien-1-one, geraniol, 3-octanone, methyl salicylate, theaflavin (TF), theabrownins (TBs), total soluble sugar (SSs), epicatechin (EC). These compounds can be used as indicators to identify the first-drying methods of Congou black tea, and then to produce "sweet fragrance aroma", "sweet alcohol taste", "high brightness liquor color" and other high-quality Congou black tea. This study can provide a technical reference and theoretical guidance to process much high quality of black tea.