Changes in chemical quality indices during long-term storage of palm-olein oil under heated storage and transport-type conditions

Six quality indices, namely free fatty acids (FFA), peroxide value (PV), anisidine value (AV), oxidative stability index (OSI), total tocopherols and headspace volatiles (hexanal, t-2-hexenal and t,t-2,4-decadienal), were evaluated in a long-term storage trial of 52 weeks at 50 °C of palm-olein, a monounsaturated oil. Three concentrations of copper (0.035, 0.17 and 0.69 mg kg^-1) were added. FFA values for all the sample treatments increased slightly over the storage period but remained within acceptable limits. PV of the copper-containing samples declined initially and then remained stable up to week 40, after which it increased slightly for the 0.035 and 0.17 mg kg^-1 samples. However, PV of the control (no added copper) increased steadily to above the acceptable limit. AV of the copper-containing samples increased much more than that of the control. OSI and total tocopherol values of the copper-containing samples were markedly lower than those of the control. t-2-Hexenal did not increase during the storage period, whereas hexanal increased in the copper-containing samples but at a slower rate than in the control. Conversely, the copper-containing samples had high levels of t,t-2,4-decadienal but the control had none. AV, OSI and total tocopherols are the most valuable quality indices for assessing monounsaturated oil quality, whereas FFA, PV and headspace volatiles can be misleading