Phytochemicals and antioxidant activity degradation kinetics during thermal treatments of sour cherry extract

The present study focuses on the kinetics of degradation of polyphenolics during thermal treatment of sour cherry extract solutions heated at temperatures ranging from 100 to 160 °C. The study includes a comparative study of kinetics of phytochemicals, as anthocyanins, total polyphenols and flavonoids in correlation with changes in antioxidant activity. The heat induced changes in anthocyanins were evaluated also by using fluorescence spectroscopy technique. Therefore, fluorescence emission spectra of extract at pH 3.5 in aqueous solution have been studied. The most effective fluorescence excitations were at UV absorption maxima of 270 nm, whereas the extract exhibited fluorescence emission maxima at 320 nm. When excited at 270 nm, a significant decrease in fluorescence intensity was recorded above 130 °C, whereas the λmax had constant values around 320 nm. A second emission band centered at around 375 nm was measured at temperature higher than 130 °C. The degradation kinetics in terms of reaction rate constant and activation energy are discussed. An increase in the degradation rate constant with increasing temperature was evidenced. The estimated activation energies were 74.23 ± 3.17, 54.19 ± 5.88, 38.38 ± 3.78 and 31.47 ± 3.51 kJ/mol for heat-induced changes in fluorescence intensity at excitation wavelengths of 270 nm, monomeric anthocyanins, total flavonoids content and antioxidant activity, respectively.