Biochemical Quality Profile of Black Tea from Upper Assam and North Bank Region of Assam, India

Black tea quality is fundamentally determined by its biochemical composition, providing essential baseline data for producers, traders, and consumers. This study comprehensively evaluates key biochemical quality components of 32 black tea samples from Upper Assam and North Bank regions of Assam, India, produced by both orthodox and CTC methods, using standardized International Organization for Standardization (ISO) analytical protocols for total polyphenols (TP), theaflavins, catechins, water extract (WE), caffeine, thearubigins (TR), theanine, crude fibre (CF), and ash characteristics. The results reveal substantial variation in TP (83.54–184.52 mg g−1, avg. 134.07 mg g−1), theaflavins (4.88–15.54 mg g−1, avg. 8.61 mg g−1), caffeine (15.51–39.24 mg g−1, avg. 30.09 mg g−1), and theanine (2.47–8.16 mg g−1, avg. 5.53 mg g−1), demonstrating substantial biochemical variation reflecting differences in cultivation practices, leaf maturity, processing conditions and agroclimatic conditions. The orthodox and CTC methods yielded comparable WE (avg. 404.34 vs. avg. 407.91 mg g−1) and theanine levels (avg. 5.65 vs. avg. 5.35 mg g−1) indicating that both processing types successfully retain key quality components. All analyzed biochemical attributes with established minimum or maximum limits set by the ISO and Food Safety and Standards Authority of India (FSSAI) demonstrated compliance with national and international quality standards. These findings establish contemporary benchmarks for key quality indicators in Assam black teas and confirm the consistency of quality across diverse processing methodologies and cultivation practices.