Kinetics for Isobaric−Isothermal Degradation of<scp>l</scp>-Ascorbic Acid

Abstract

A study of the thermal degradation of l -ascorbic acid in different buffer systems (pH 4, 7, and 8) and in real products (juice from squeezed oranges and tomatoes) revealed that l -ascorbic acid is most thermosensitive in real products. These products were selected to investigate in detail the degradation 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 cases the l -ascorbic acid degradation was confirmed to be a first-order reaction. The z values of thermal destruction of l -ascorbic acid in squeezed oranges and tomatoes were respectively 27.15 and 30.15 °C and were shown to be similar for pressure−temperature degradation. Keywords: l -Ascorbic acid; thermal stability; pressure stability; kinetics; pH