Kinetic models of non-enzymatic browning in apple puree

The effects of thermal treatments on 11 degrees Brix apple puree were studied at temperatures from 80 to 98 degrees C. Colour changes (measured by reflectance spectroscopy, colour difference, L*, a* and b* and the evolution of 5-hydroxymethylfurfural (HMF) and sugars (hexoses and sucrose) were used to evaluate non-enzymatic browning. A kinetic model based on a two-stage mechanism was applied to the evolution of colour difference and a*. A first-order kinetic model was applied to L* evolution, while the evolution of absorbance at 420 nm (A(420)) of the liquid fraction 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 the kinetic constants was described by an Arrhenius-type equation. The presence of pulp in the samples led to activation energies for A(420) and sucrose which were lower than those found previously for clarified juices with the same soluble solids content. (C) 2000 Society of Chemical Industry.