Drying Method-Dependent Variations in Phenolics, Color, and Volatile Profile of Thymus praecox subsp. skorpilii

This study investigated the effects of different drying methods, including freeze drying, oven drying, shade drying, and microwave drying (360, 600, and 900 W), on the volatile profile, total phenolic content (TPC), and color characteristics of wild-grown Thymus praecox subsp. skorpilii. Headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME/GC-MS) analysis identified 26 volatile compounds in the fresh sample, with α-pinene, 3-octanone, limonene, and β-caryophyllene as the predominant constituents. Drying induced pronounced shifts in volatile composition, characterized by an overall increase in isoprenoid compounds and a reduction in fatty acid derivatives, alongside the emergence of compounds such as nonanal and hexadecane. Increasing microwave power led to a decrease in monoterpenes and an increase in sesquiterpenes. TPC (19.5-40.21 mg gallic acid equivalent [GAE]/g), and color parameters were also significantly affected (p < 0.05), with freeze drying and high-power microwave drying showing improved phenolic retention and color preservation compared to oven and shade drying. Overall, the results indicate that drying influences multiple quality attributes in a method-dependent manner, with variations in processing conditions leading to distinct compositional outcomes. These findings highlight the importance of aligning drying conditions with specific quality targets when processing wild thyme. PRACTICAL APPLICATIONS: This study establishes a practical framework for selecting drying strategies in wild thyme (Thymus praecox subsp. skorpilii) by linking processing conditions to changes in volatile composition, color, and phenolic content. The results demonstrate that drying induces method-dependent transformations rather than uniform quality changes. Accordingly, drying methods should be chosen on the basis of the targeted product profile together with processing efficiency, enabling more tailored production of high-quality dried thyme.