Non-volatile and volatile metabolite analyses and objective quantitative technique reveal the effect of fixation methods on the flavor quality and metabolites of green tea

Fixation methodology serves as the critical determinant in shaping green tea's multi-dimensional quality attributes; however, the impact of different fixation methods and the corresponding combinations on the overall metabolites and quality of in green tea remains unclear. In this study, non-volatile metabolites (NVMs) and volatile metabolites (VMs) analyses and objective quantitative techniques were used to determine the effects of electromagnetic roller-hot air coupling fixation (ROHF), electromagnetic roller-steam coupling fixation (ROSF), electromagnetic roller-hot air-steam coupling fixation (RHSF), electromagnetic single roller fixation (ROLF), and carding fixation (CDF) on the quality of green tea. Forty-four NVMs, 99 VMs, and 15 flavor objective quantitative indexes were identified, with 12 differential NVMs and 9 differential VMs statistically screened. The green tea processed via ROLF was lustrous and emerald green with a bright and clear liquor; ROSF resulted in low caffeine and flavonoid glycosides contents and an umami (UMS) taste; and RHSF was associated with high trans-β-ionone, hexanal and 1-octen-3-ol levels, with a floral and fresh aroma. These findings provide a precise control scheme for the customized processing of green tea, and promote the upgrading of traditional fixation process to intelligent standardization.