Modelling Kinetics of Thermal Colour Degradation in Production of Beetroot Juice Concentrate by Various Heating Methods

Preservation of natural colour, as a quality attribute and characteristic of beetroot concentrate might be considered as a possibility if the knowledge of kinetic of color change is studied thoroughly.
Three different heating/evaporation processes were employed for the production of beetroot juice concentrate. The juice was concentrated to a final 40 Brix from an initial °Brix of 10 by microwave heating, rotary vacuum evaporator and evaporating at atmospheric pressure.
The concentration of the final juice at 40 °Brix was achieved in 40, 43 and 70 minutes by using microwave, rotary vacuum and atmospheric heating processes, respectively. The changes in colour during the concentration processes were investigated. Total colour differences (KE) and L, a and b parameters were used to estimate the extent of colour changes by using Hunter Lab equipment. All colour parameters were decreased with time. The zeroorder, first-order and a combined kinetics model were applied to the changes in colour parameters.
The results indicated that the variation in TCD followed both first order and combined kinetics models, and parameters L, a and b followed only the combined model. This model implied that the colour formation and pigment destruction occurred during concentration processes of beetroot juice.