Fig. 4

Concentration (a) and calculated oxidation rate (b) of ascorbic acid during enzymatic saccharification of Avicel. Reactions were initially supplied with 1000 µM ascorbic acid and were run under anaerobic conditions with H₂O₂ feeding. Feed rates used: black symbols, no feeding of H₂O₂; blue, 50 µmol h⁻¹ H₂O₂: magenta, 100 µmol h⁻¹ H₂O₂: red, 150 µmol h⁻¹ H₂O₂. The straight lines in panel (a) are trendlines obtained from fitting a kinetic model assuming a first-order reaction for the rate of ascorbic acid oxidation (see Materials and methods). The trendlines were used for calculation of oxidation rates in panel (b), using discrete steps of a few hours. The magenta and red arrows indicate the approximate time points where the rate of H₂O₂ accumulation in the medium started increasing for the reactions with 100 and 150 µmol h⁻¹, respectively