Monthly fluctuations in total polyphenol content of Sri Lankan tea cultivars in relation to climatic factors and drying techniques

Diverse and variable climatic conditions of Sri Lanka significantly influence the biochemical properties of tea leaves. Therefore, tea manufacturers regulate oxidation/aeration durations during processing to optimize black tea quality and market value. The sensory qualities and health benefits of tea are primarily attributed to its polyphenolic compounds. This study aimed to evaluate monthly variations in total polyphenolic content of black tea and tea leaves over two years, offering insights into seasonal fluctuations. Analyses were conducted on black tea (BT), oven-dried (OD, at 60 °C), and freeze-dried (FD) tea leaves from two widely cultivated Sri Lankan tea cultivars, TRI 2025 and DT-1. A distinct seasonal variation in total phenolic content (TPC) was observed in both black tea and tea leaves. For TRI 2025, average dry-season TPC was 25.03% (FD), 24.76% (OD), and 21.27% (BT); for DT-1, values were 24.60% (FD), 23.97% (OD), and 20.30% (BT). In contrast, wet-season TPC levels declined: TRI 2025 showed 22.99% (FD), 22.85% (OD), and 18.59% (BT), while DT-1 recorded 23.84% (FD), 21.77% (OD), and 16.82% (BT). TPC in tea is strongly affected by seasonal climate, processing method, and tea cultivars. Dry months consistently produced higher TPC in both fresh leaves and processed teas, whereas wet months were associated with the lowest levels. Among processing methods, freeze-drying retained the most TPC, followed by oven drying at 60 °C, while black tea processing resulted in the lowest TPC retention.