A fraction conversion kinetic model for thermal degradation of color in red chilli puree and paste

The kinetics of degradation of color was evaluated using a fraction conversion model during thermal treatment of red chilli puree at 60, 70, 80 and 90degreesC (up to 20 min) and storage of red chilli paste at 5, 25 and 37degreesC (up to 6 mo). Red chilli puree was subjected to heat treatment at different temperatures in a well-stirred water bath. Test samples were removed from the bath at selected time intervals (0-20 min after come-up), cooled immediately and analysed for color using a Hunterlab colorimeter. Chilli paste was prepared by a standard formulation by adding common salt (8%) and the required volume of citric acid to bring the pH to 4.0. The paste was thermally processed at 85 degreesC for 15 min, filled into glass bottles and stored at selected temperatures for 6 mo. Red chilli color it-as expressed as a tristimulus combination value (L.a.b) as well as the total color difference (DeltaE). The fraction conversion model adequately described the kinetic changes in both color values during thermal treatment of puree and storage of puree. The process activation energies were 24.2 and 24.8 kJ/mol, respectively, for DeltaE and L.a.b during the thermal treatment, and during the storage the respective values were 24.1 and 25.0 kJ/mol. Up to the end of the 6-mo storage, the paste was microbiologically stable with no major changes in other physico-chemical characteristics.