不同干燥温度对萎凋叶压制白茶饼品质的影响

为探明不同干燥温度对萎凋叶压制白茶饼品质的影响，本研究采用顶空固相微萃取法结合气相色谱-飞行时间质谱联用技术及靶向代谢组学方法，研究了不同干燥温度（60、70、80、90、100 ℃）对萎凋叶压制白茶饼香气、糖组分、多酚类物质和氨基酸等品质成分的影响。结果表明：萎凋叶压制白茶饼感官品质得分随干燥温度的升高呈先升后降的趋势，80 ℃干燥茶饼的感官审评得分最高，为90.2 分。80 ℃和90 ℃干燥的白茶饼儿茶素总含量显著低于60、70、100 ℃干燥的白茶饼（P＜0.05）；80 ℃干燥的白茶饼总氨基酸和鲜爽类氨基酸含量显著高于70 ℃干燥的样品（P＜0.05）；70、80 ℃干燥的白茶饼糖类物质含量显著高于低温干燥（60 ℃）和高温干燥（90 ℃和100 ℃）（P＜0.05）；各干燥温度白茶饼主要挥发性物质种类总体一致，其中醇类物质所占比例较大，80 ℃干燥处理白茶饼的十三酸甲酯、辛酸甲酯、己酸甲酯和二氢猕猴桃内酯等酯类香气物质含量显著高于90、100 ℃干燥样品（P＜0.05）。综上，80 ℃干燥能提高萎凋叶压制白茶饼的鲜爽度和甜度及愉悦香气物质的含量，更有利于品质形成，是萎凋叶压制白茶饼干燥的适宜温度。结果可为萎凋叶压制白茶饼加工工艺提供参考。

Effect of Drying Temperature on the Quality of Pressed White Tea Cake from Withered Leaves

This study was undertaken in order to investigate the effects of different drying temperatures (60, 70, 80, 90 and 100 ℃) on the quality of pressed white tea cake made from withered leaves. Various quality components of white tea cake such as aroma, sugar components, polyphenols and amino acids were analyzed using targeted metabolomics based on headspace solid-phase microextraction combined with gas chromatography-time-of-flight mass spectrometry (HS-SPME-GC-TOF-MS). The results showed that the sensory quality score of white tea cake increased first and then decreased with increasing drying temperature, reaching its maximum (90.2) at 80 ℃. The total catechin content of white tea cake dried at 80 and 90 ℃ was significantly lower than that of white tea cake dried at 60, 70 and 100 ℃ (P < 0.05). The contents of total amino acids and refreshing taste amino acids in white tea cake dried at 80 ℃ were significantly higher than those in white tea cake dried at 70 ℃ (P < 0.05). The sugar contents of white tea cake dried at 70 and 80 ℃ were significantly higher than those of white tea cake dried at low temperature (60 ℃) and high temperature (90 and 100 ℃) (P < 0.05). The main volatile substances of white tea cake were generally consistent across all drying temperatures, in which alcohols accounted for a large proportion. The contents of ester aroma substances such as methyl tridecanoate, methyl octanoate, methyl nonanoate and acetic acid lactone in white tea cake dried at 80 ℃ were significantly higher than those in white tea cake dried at 90 and 100 ℃ (P < 0.05). In general, drying at 80 ℃ can improve the refreshing taste and sweetness of pressed white tea cake and the content of pleasant aroma substances, thereby conducing to the quality formation. The appropriate drying temperature for pressed white tea cake, therefore, is 80 ℃. The results can provide reference for the processing technology of white tea cake pressed by withered leaves.