Kinetic models of non-enzymatic browning in apple puree

The effects of thermal treatments on 11 degrees Brix apple puree were studi ed at temperatures from 80 to 98 degrees C. Colour changes (measured by ref lectance spectroscopy, colour difference, L*, a* and b* and the evolution o f 5-hydroxymethylfurfural (HMF) and sugars (hexoses and sucrose) were used to evaluate non-enzymatic browning. A kinetic model based on a two-stage me chanism was applied to the evolution of colour difference and a*. A first-o rder kinetic model was applied to L* evolution, while the evolution of abso rbance at 420 nm (A(420)) of the liquid fraction was described using a zero -order kinetic model. Thermally treated samples became more reddish and suf fered a slight loss of yellow hues. The effect of temperature on the kineti c constants was described by an Arrhenius-type equation. The presence of pu lp in the samples led to activation energies for A(420) and sucrose which w ere lower than those found previously for clarified juices with the same so luble solids content. (C) 2000 Society of Chemical Industry.