Evolution of oxidative values during kinetic studies on olive oil oxidation in the Rancimat test.

摘要

A comparative study was carried out in order to evaluate the kinetics of the formation of a number of primary and secondary oxidation products during oxidation of olive oil in the Rancimat test at 100-130 degrees C. There were good correlations between the Rancimat index (OSI) and stability indices (IP) measured in the Rancimat test with no significant differences in kinetic parameters calculated from them. Mean values of the temperature coefficient, Q₁₀ number, activation energy (E_a), frequency factor (A), and free energy of activation ( Delta G++) for olive oil oxidation were calculated to be -3.44x10-2 degrees C-1, 2.21, 98.91 kJ/mol, 12.17x1012 h-1, and 128.25 kJ/mol, respectively. Each unit change in E_a was accompanied by an average 1.43x1012 change in A, indicating a higher contribution for factor A than for E_a to the olive oil stability. The E_a and A correlated well with the values of enthalpy and entropy, respectively. The values of OSI or IP could be described well by the Delta G++ values. Kinetic data indicated that olive oil stability is more affected by the indigenous antioxidants than by the fatty acid composition.