Impact of Different Brewing Water on the Quality and Antioxidant Activity of Toona sinensis Fermented Tea Infusions

Water is the important medium of the tea infusions, which plays a crucial role in the development of tea quality. Tooma sinensis (TS) fermented tea was brewed with tap water, mineral water and purified water. The physicochemical indexes, biochemical components, antioxidant activity and flavor compounds of three types tea infusions were analyzed using ultraviolet spectrophotometer, electronic tongue and gas chromatography-mass spectrometry (GC-MS) to elucidate the influence of different brewing water on the quality of TS fermented tea infusions. The results demonstrated that the quality and antioxidant activity of TS fermented tea infusions were significant influenced by different brewing water (P<0.05). Among the three samples, the purified water tea infusion with weak acidity and conductivity close to 1 μS/cm exhibited superior characteristics, including the highest levels of tea polyphenols (669.45 mg/L), total flavonoids (645.83 mg/L), soluble sugar (731.91 mg/L) and free amino acids (2738.96 mg/L). Additionally, it demonstrated the strongest scavenging capacity of DPPH free radicals (IC₅₀ was 0.17 mg/mL) and total reducing ability. Moreover, tap water tea infusions showed the highest caffeine content (67.98 mg/L) and the significant OH radical scavenging ability with IC₅₀ value of 12.27 mg/mL. The electronic tongue effectively discriminated between TS fermented teas prepared using different brewing water, with the tea infusions made from pure water exhibiting the most abundant taste profile characterized by bitterness, bitter aftertaste, sweetness and richness. A total of 29 volatile components were identified using GC-MS, with sulfur-containing compounds and aldehydes were found to be the predominant volatile components in the TS fermented tea infusions, accounts for more than 50% of the total. 24, 17 and 16 volatile components were detected in tap water, mineral water and purified water tea infusions, respectively. The aroma components of tap water tea infusions exhibited the most abundant, and purified water tea infusions displayed obvious floral and fruity aroma. Comprehensive analysis of pure water was deemed most suitable for the TS fermented tea, the tea infusion exhibits an optimal overall quality. The present study elucidated the impact of water quality on the biochemical composition, antioxidant activity and volatile components of TS fermented tea, thereby establishing a theoretical foundation for the scientific brewing of TS fermented tea and the development of TS fermented tea beverages.