Abstract:
To investigate the effects of different drying methods on the quality of Tanyang Gongfu black tea, five drying processes were employed in this study: Vacuum-freeze drying (FD), hot-air drying (HD), hot-air-vacuum-freeze combined drying (HFD), vacuum-freeze-hot-air combined drying (FHD), and microwave drying (MD). The five dried tea samples were compared by combining sensory evaluation, physicochemical component determination, aroma compound detection, and chemometric analysis. The results indicated that the Tanyang Gongfu black tea was characterized mainly by sweet floral aroma and sweet mellow taste. Among them, the FHD sample was characterized by a pure, sweet, refreshing taste and a pronounced sweet floral aroma, achieving the highest sensory score (90.90 points). Significant differences were observed in the quality components of the tea samples subjected to different drying methods. FD treatment was found to be conducive to increasing the thearubigins content (3.08%). The free amino acid (6.69%) and tea polyphenol (12.28%) contents in the FHD sample were significantly higher than those in the other groups (
P<0.05). The highest water extract content (38.23%) was found in the HFD sample. Soluble sugars (44.34 mg/g) in the HD sample were found to contribute to its sweet mellow taste characteristic. Flavonoids were maximally retained (24.61 mg/g) in the MD sample. A total of 99 aroma compounds were detected in the five tea samples, mainly including aldehydes, esters, and alcohols. The FD sample possessed unique grassy and floral characteristics, mainly contributed by hexanal (OAV=33.51), linalool (OAV=75.45), and geraniol (OAV=239.77). The sweet and honey-like aroma characteristics of the HD sample were associated with the enrichment of isovaleraldehyde (OAV=254.73) and phenylacetaldehyde (OAV=41.44). Geraniol (OAV=210.22) was identified as the characteristic aroma compound for the FHD treatment. Geraniol (OAV=130.04) and isovaleraldehyde (OAV=122.23) were determined to be the main aroma-contributing components for HFD. Nonanal (OAV=71.89) was identified as the key aroma component for MD treatment. This study systematically elucidated the influence of different drying processes on the quality of Tanyang Gongfu black tea, providing a theoretical basis for optimizing black tea processing technology.