Sterilization is the most relevant technique to guaranty safety of shelf-stable highly hydrated food products at ambient temperature. However, these thermal processes are often optimised to microbiological aspect and consequently are not without consequences on food quality. Ascorbic acid's degradation at sterilization temperature (>100 °C) is poorly documented. Using a new instrumented reactor (thermoresistometer Mastia®), the behavior of ascorbic acid was studied in food model solution at pH = 3.5, in aerobic and anaerobic conditions from 95 °C to 125 °C. In anaerobic conditions, degradation was slow and followed first order kinetics (k125°C = 2.88*10-3 min-1, Ea = 96 kJ/mol). In aerobic conditions, reactions were faster with total elimination of ascorbic acid in about 4 h, and the data were best fitted using 0.5-order, while reaction speed varied little with temperature.