Metabolomics Analysis of Effects of Low-temperature Baking on the Flavor of Albino Green Tea

To investigate the effect of baking on the flavor of albino green tea, Baiye 1 green tea samples with different treatment (0, 40, 80, and 120 min at 60 ℃) were conducted in the study. The dynamic changes of metabolites were detected and analyzed by UHPLC-Q-Exactive/MS and GC-MS. The result showed that green tea sample treated by 40 min at 60 ℃ exhibited a better quality than other green tea samples. The thickness of green tea infusions and the aroma intensity went a downtrend with the increase of baking time, while the intensity of astringency increased. The content of total free amino acids and caffeine increased remarkable with time up (P<0.05). Except for GC, C and GCG, the contents of catechins initially increased and then decreased during baking. A total of 61 nonvolatiles were identified in the study by UHPLC-Q-Exactive/MS, including 38 differential metabolites (P<0.05). Partial least squares discriminant analysis showed that there were 7 key metabolites (VIP>1, P<0.05, and FC≥1.1 or ≤0.9) among green tea samples. It contained 5 flavonoid glycosides, strictinin, and proanthocyanidin B4, which declined significantly after baking for 80 min and 120 min. The volatiles analysis showed that the total volatiles concentration increased significantly with time up. In addition, dimethyl sulfide, 2-methylbutanal, 3-methylbutanal, heptanal, 2-hexenal, nonanal, benzaldehyde, 1-octene-3-ol, linalool, trans-linalool oxide (furanoid), geraniol, β-ionone, and cedrol were identified as the key aroma components of Baiye 1 green tea in the study, which had relative odor activity values above one hundred. Aroma character impact values analysis showed that tea samples baked for 40 min had the lowest ACI of complex odor and the highest ACI of pleasant aroma, while tea samples baked for 120 min showed the opposite. This study provides a theoretical basis for understanding the effect of baking on albino green tea.