Kinetic models for colour changes in pear puree during heating at relatively high temperatures

The effect of thermal treatments on 11 degrees Brix pear puree were studied at temperatures from 80 degrees C to 98 degrees C. Changes in colour measu red with colorimetric parameters (reflectance spectra, colour difference, L *, a* and b* parameters), and the variation in 5-hydroxymethylfurfural (HMF ) and sugars (hexoses and sucrose) content were used to evaluate non-enzyma tic browning. A kinetic model based on a two-stage mechanism was applied to the changes in colour difference and a*. A first order kinetic model was a pplied to L* changes, while absorbance at 420 nm (A(420)) for liquid fracti ons was described using a zero order kinetic model. Thermally treated sampl es became more reddish and suffered a slight loss of yellow hues. The effec t of temperature on kinetic constants was described by an Arrhenius type eq uation. The presence of pulp in the samples implied that the activation ene rgy was lower than in clarified juices with the same soluble solids content . (C) 1999 Elsevier Science Ltd. All rights reserved.