Abstract
The deterioration of palm oil during deep frying was mainly examined at 180°C by measuring the acid value (AV) of the oil to which water was continuously fed at a constant rate. The addition of water simulated importing water from the material being fried. In most cases, the AV rapidly increased after an induction period, reached a plateau, and then gradually decreased in most cases. The addition rate of water significantly affected the change in the AV. The changes in the AV were also exmined for the mixtures of the constituent fatty acids of palm oil with or without glycerol. Based on these experimental results, a kinetic model was proposed for describing the change in the AV during deep frying. The rate constants of the model were evaluated at various feed rates of water. The rate constant for the degradation of the AV-positive compound scarcely depended on the feed rate of water, but the rate constants for the hydrolysis and reverse-hydrolysis of the ester bond were mostly affected by the feed rate. The changes in the AV were also measured at 160 to 200°C at a constant feed rate of water. The AV continued to increase at 160°C, while the AV increased, reached a plateau and then gradually decreased at 180 and 200°C during the late stage of the test period.
