Oxidative stress study. (a) Intracellular ROS level of strains Y1EK (wt), AACK (production of α-amylase in wt strain), Y6EK (SEC16 overexpression), and YIGS16 (production of α-amylase in SEC16 overexpression) in shake flask cultivation. (b) The final yield of α-amylase with different concentrations of vitamin C (VC) supplied to the medium, with tube fermentation. *, P < 0.05; **, P < 0.01. Measurements are reported as the average values ± standard deviations from independent triplicates (for ROS) and duplicates (for VC test).