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 measured 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-enzymatic 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 applied to L* changes, while absorbance at 420 nm (A(420)) for liquid fractions was described using a zero order kinetic model. Thermally treated samples became more reddish and suffered a slight loss of yellow hues. The effect of temperature on kinetic constants was described by an Arrhenius type equation. The presence of pulp in the samples implied that the activation energy was lower than in clarified juices with the same soluble solids content. (C) 1999 Elsevier Science Ltd. All rights reserved.