Volatile metabolomics reveals the regulation mechanisms of aroma formation in Scutellaria baicalensis Georgi herbal under different roasting methods

Roasting is a critical process that influences the aroma of traditional teas. In this study, the effects of microwave roasting (MR), electric conduction roasting (ER), charcoal conduction roasting (CR), steam roasting (SR), and natural shade drying (ND) on the aroma quality of <i>Scutellaria baicalensis</i> Georgi herbal tea (HHT) were systematically evaluated using gas chromatography-mass spectrometry (GC-MS) and electronic nose (E-nose) analysis, and sensory evaluation. The results indicated that MR generated moderate floral-fruity notes and pronounced pyrazines exhibiting roasted characteristics, primarily driven by a balanced Maillard reaction. However, the accumulation of aldehydes and ketones indicated potential oxidation risks. ER further enhanced the roasted characteristics but weakened the floral-fruity notes compared with MR, as intensified lipid oxidation at higher temperatures produced undesirable fatty odors. CR exhibited the most comprehensive aroma profile, characterized by fully released floral-fruity notes, a balanced roasted note, and minimal fatty off-odors. The synergistic effect of radiant heat and a smoky environment promoted terpene glycoside hydrolysis, lipid oxidation, and the Maillard reaction, yielding a harmonious blend of fresh notes and a woody base with the highest complexity. In contrast, SR suppressed the formation of most aroma compounds because of enzyme inactivation and volatile loss under high-temperature, high-humidity conditions, resulting in reduced terpene content and inhibition of the Maillard reaction, though it most effectively eliminated undesirable odors. Due to slow dehydration at low temperatures, ND preserved aroma precursors but exhibited low conversion efficiency, limited enzymatic activity, and continuous degradation of aldehydes and ketones, producing the lowest levels of fresh green and woody notes. Weighted compound co-expression network analysis revealed antagonism between the turquoise module (roasted aroma) and the brown module (fresh floral notes), with the latter demonstrating higher sensitivity to quality variations. The blue module independently reflected oxidative stability. Monitoring the S9/S7 signal ratio enabled precise regulation of roasting parameters, thereby optimizing the Maillard reaction, maintaining aroma balance, and providing early warning of deterioration. Overall, this study elucidated the regulatory mechanisms of different roasting processes on the aroma quality of HHT, providing a basis for production optimization.