Abstract: The kinetic study reactions like rate constants, half-life, and thermodynamic parameters like enthalpy activation energies (?E*) (?H*), change of activation free energy (?G*), change of entropy activation (?S*) are measured to determine the stability of anthocyanins extracted from onions skins. The extracted anthocyanins from onions skins in aqueous and ethanol solvent, were stored under darkness for one day at 5 °C. The effect of temperatures, and solvents were determined by kinetic study of the anthocyanins degradation using Spectrophotometric UV/visible techniques Thermodynamic parameters were determined, highest stabilities being observed for the anthocyanins extracted by using water at lower temperatures, such as 40°C than the stabilities of anthocyanins at higher temperatures 70 0C, and 100°C). The half-life values found for anthocyanins extracted by using water are ,(t 1/2 5 40=27.72 ; t 1/2 50= 13.86 t 1/2 70= 2.69; , t 1/2 70= 6.3; t 1/2 100=8.66). The half-life values, for anthocyanins extracted by using ethanol were found were (t 1/2 40= 55.44h; t 1/2 50= 83.49; t 1/2 70= 27.8; t 1/2 100=10.5).The rate constants for anthocyanins extracted by water at 400C, 500C, 700C,1000C were (k h-1 =2.5, 5, 7.5, 81) respectively; and the results extracted by the ethanol solvent at 400C, 500C, 700C, 1000C ( K h-1=1.25, 8.3, 25, 66 ) respectively. The effect of different temperatures on the degradation of anthocyanins from onion skins extracted by water and ethanol were determined by the found values of the activation energies were; Ea (kJ/mol) were 39.10 and 27.88 respectively and Ko (h-1) 1.73, and 4.26. The temperature coefficient Q10 at 40–50 °C for water and ethanol were 2, and 1.1respectively, but for Q10 at 70–100 °C were 6.79and 2.64 respectively.
Keywords: Anthocyanins; Red-onion ,degradation kinetics, water, Ethanol.