Kinetic studies of L-ascorbic acid degradation in fruit juices for the improvement of pasteurization plants

Abstract

Pasteurization especially high-temperature short time (HTST) heating is a widely used preservation method which inactivates microorganisms and enzymes, but also degrades compounds as L-ascorbic acid. For a gentle dimensioning of a pasteurization plant the knowledge of the kinetic figures is important. Activation energy, reaction order and pre-exponential factor of the L-ascorbic acid degradation in a model solution, apple, orange and black currant juice were determined. Lines of equal effects, which indicate different time-temperature combinations for the degradation, could be derived and compared with the lethal effect on microorganisms. The activation energies were located in the area of 25 to 44 kJ/mol for all samples except of orange juice (74 kJ/mol) in the range of 40–90 °C with a zeroth reaction order. Based on these values, the lines of equal effects showed a lesser degradation at higher temperatures and shorter holding times even in the typical setting range of pasteurization plants.