A study of the thermal degradation of l-ascorbic acid indifferent buffer systems (pH 4, 7, and 8)and in real products (juice from squeezed oranges and tomatoes)revealed that l-ascorbic acid ismost thermosensitive in real products. These products wereselected to investigate in detail thedegradation kinetics of l-ascorbic acid by heat (120−150°C) as well as by combined pressure−temperature treatment (8.5 kbar and 65−80 °C). In both casesthe l-ascorbic acid degradation wasconfirmed to be a first-order reaction. The z values ofthermal destruction of l-ascorbic acid insqueezed oranges and tomatoes were respectively 27.15 and 30.15 °Cand were shown to be similarfor pressure−temperature degradation. Keywords: l-Ascorbic acid; thermal stability; pressurestability; kinetics; pH