Unveiling the effect of leaf maturity on biochemical constituents and quality of CTC black tea: insights from Northeast India’s commercial cultivars

The maturity of tea shoots is a key factor influencing its biochemical composition, which in turn affects the quality of processed tea. This study aimed to assess the impact of leaf maturity—specifically, two-leaf and bud (2LB), three-leaf and bud (3LB), and four-leaf and bud (4LB)—on the biochemical constituents in fresh leaves and the quality of CTC black tea. The study was carried out with five commercial cultivars TV9, TV11, TV12, TV23 and S.3 A/3 from Northeast India. As the leaves matured, total polyphenol (TP), total catechin, and caffeine content decreased, while theanine levels increased. Key black tea quality components such as theaflavins, TP, caffeine, thearubigins, and water extract declined significantly (p ≤ 0.05) with increasing leaf maturity, while crude fiber and theanine levels increased. Antioxidant activity in the black tea samples also decreased with leaf maturity, showing a strong positive correlation with TP (R² = 0.84–0.98) and theaflavins (R² = 0.79–0.98). Sensory evaluations indicated a preference for 2LB black tea over the others. The chromatic analysis highlighted noticeable differences in the liquor color of black tea made from leaves at the three stages of maturity. These insights can help the tea industry optimize the quality of CTC black tea.