Aromatic Quality of Mingguancha White Tea Differentiated by Withering Methods

Objective Effects of different withering methods applied in processing Mingguancha white tea on aromatic characteristics were determined.

Method One bud and two leaves plucked from the yellow-leaf 'Mingguancha' tea bushes were processed with air-conditioned control withering (AW), combination withering (CW) or indoor natural withering (NW). Sensory evaluation, electronic (E-) nose detection, and headspace solid-phase microextraction–gas chromatography–tandem mass spectrometry (HS-SPME-GC-MS) were conducted on the white teas. The analytic data were used to calculate odor activity value (OAV) and for a multivariate statistical analysis to determine the chemical and sensory effects of the varied withering on tea aroma.

Result The highest overall sensory quality of 88.61 was scored for the rich floral and fruity aroma, mellow taste, and outstanding refined flavor of the CW-processed Mingguancha white tea. The principal components of E-nose responses effectively differentiated the teas made with the different withering methods. Notably, the E-nose W5S (nitrogen oxides), W1W (sulfides), and W2W (aromatic compounds) sensors yielded significantly higher responses on the CW-processed sample than the others. Among the 73 volatiles identified by GC-MS, the CW treated tea displayed the highest total aromatic content of 173.49 μg·g⁻¹, which included the floral–fruity benzyl alcohol, phenethyl alcohol, and nonanal. Based on the OPLS-DA model at VIP ＞1, |FC|＜0.5 or ＞2, 12 compounds including (E,E)-2,4-heptadienal, heptanal, benzyl alcohol, and phenethyl alcohol were crucial for distinguishing the teas processed with varied withering methods. The OAV analysis indicated that nerol, citral, linalool, and nonanal were the key aromatics in teas produced by CW and AW, while linalool and nonanal were in that made by NW.

Conclusion It appeared that, with the combined effects of sunlight exposure and controlled atmosphere, CW not only promoted the accumulation of floral and fruity volatiles but also enhanced the flavor harmonization in Mingguancha white tea to achieve the superior overall quality among the three tried withering methods.