Fig. 4: The response surface regression analysis.

a–f The effects of brewing conditions on preference (a), bitterness-astringency (b), TPP (c), FAA (d), ABTS (e), and DPPH (f). TPP total polyphenols, FAA free amino acids. ABTS/DPPH the antioxidant activity of tea infusion in ABTS/DPPH assays, respectively.