Color stability and change in bioactive compounds of red beet juice concentrate stored at different temperatures

In the present study, effect of storage temperature (25°, 35° and 45 ^°C) and light (with/without aluminum foil) on betalain content, color stability and bioactive compounds of concentrated red beet juice were investigated. Degradation of betalains and change in total phenolics content followed first-order kinetics while changes of L*, a*, b* and C* values and antioxidant capacity fitted zero-order kinetic. It was determined that the reaction rate constants of betacyanin and betaxanthin degradations in red beet juice concentrates increased with increasing storage temperature and time. The activation energies for betaxanthin degradation (E_a: 92.04-93.27 kJ mol^-1) in comparison with the activation energies for betacyanin degradation (E_a: 66.07-66.13 kJ mol^-1) in all samples demonstrate that susceptibility to temperature of betaxanthin is higher than that of betacyanin. According to L* and a* parameters it can be suggested that color stability in red beet juice concentrate stored with aluminum foil found better than that in the sample without aluminum foil. However, there was no significant difference (p > 0.05) between samples with and without foil as regards changes in total phenolics, betalains and antioxidant capacity. In addition, 25 °C can be proposed for providing betalain stability of red beet juice concentrates during storage.