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.