低温发酵工艺与发酵时间对夏季径山红茶香气品质的影响

Effects of low-temperature fermentation process and fermentation time on aromatic quality of summer-harvested Jingshan black tea

中文关键词:  夏季红茶  径山茶  低温发酵  气相色谱-质谱法

英文关键词:summer black tea  Jingshan tea  low-temperature fermentation  gas chromatography-mass spectrometry

中文摘要:

      目的 探究低温发酵工艺与发酵时间对径山夏季红茶香气成分与香气特征的影响。方法 首先, 采用顶空固相微萃取-气相色谱-质谱(headspace solid phase microextraction-gas chromatography-mass spectrometry, HS-SPME-GC-MS)技术结合感官审评, 对在25、28、35 ℃ 3个发酵温度, 以及在4个发酵温度下发酵不同时间(2.5、4.0、5.5、7.0 h)的12个样品的香气成分进行分析。其次, 采用主成分分析(principal component analysis, PCA)和层次聚类分析(hierarchical cluster analysis, HCA)方法探究夏季径山红茶在不同发酵条件(温度和时间)下样品间的差异性。最后, 通过正交偏最小二乘判别分析(orthogonal partial least squares discriminant analysis, OPLS-DA)结合变量投影重要性(variable importance projection, VIP)指标, 并结合相对香气活度值(odorant activity value, OAV)筛选出夏季径山红茶样品中与发酵条件相关的差异性挥发性化合物。结果 通过上述方法共分析鉴定出86种香气成分, 其中二甲基硫、芳樟醇、(E,E)-2,4-庚二烯醛、吲哚、香叶醇等15种物质被鉴定为不同发酵条件(温度和时间)的关键差异挥发性化合物。发酵4.0 h的样品相较其他发酵时间的样品, 其挥发性化合物的浓度较高, 品质较好。在发酵时间为4.0 h的样品中, 发酵温度为25 ℃与28 °C的样品感官评分较高, 且表现出不同香气轮廓。25 ℃发酵4.0 h的样品主要呈现花香的品质特征, 主要由二甲基硫、脱氢芳樟醇、芳樟醇、橙花醛等物质共同组成了这一独特香气特征。而28 ℃发酵4.0 h的样品果香味更为突出, 由月桂烯、柠檬醛、香叶醇等物质构建了其独特的香气轮廓。结论 低温发酵工艺与发酵时间对径山红茶香气品质具有显著影响。

英文摘要:

      Objective To investigate the effects of low-temperature fermentation processes and fermentation duration on the aroma composition and aromatic characteristics of summer-harvested Jingshan black tea. Methods First, headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) combined with sensory evaluation was used to analyze the aroma components of 12 samples fermented at 3 temperatures (25, 28 and 35 ℃) and four durations (2.5, 4.0, 5.5 and 7.0 h). Second, principal component analysis (PCA) and hierarchical cluster analysis (HCA) were employed to explore the differences among samples under varying fermentation conditions (temperature and duration). Finally, Orthogonal partial least squares-discriminant analysis (OPLS-DA) with variable importance projection (VIP) scores and relative odorant activity value (OAV) was conducted to screen differential volatile compounds related to fermentation conditions. Results A total of 86 kinds of aroma components were analyzed and identified by the above-mentioned methods. Among them, 15 kinds of substances, such as dimethyl sulfide, linalool, (E,E)-2,4-heptadienal, indole and geraniol, were identified as the key differential volatile compounds under different fermentation conditions (temperature and time). Compared with other fermentation time samples, 4.0 h samples had higher concentration of volatile compounds and better quality. Among the samples with a 4.0 h fermentation duration, the samples fermented at 25 ℃ and 28 ℃ obtained higher sensory scores and presented distinct aroma profiles. At this duration, 25 ℃ and 4.0 h-fermented samples displayed floral aromas dominated by dimethyl sulfide, dehydro-linalool, linalool and neral, while 28 ℃ and 4.0 h-fermented samples exhibited fruity notes characterized by myrcene, citral and geraniol. Conclusion Low-temperature fermentation processes and fermentation duration critically influence the aromatic quality of Jingshan black tea.