Abstract:
Repeated use of oils for frying can create products that are harmful for human
health. This study was aimed to evaluate the stability of three oils widely used in
Sri Lanka, namely, coconut oil (CO), sunflower oil (SO) and palm oil (PO) during
continuous deep frying. Oil samples were purchased from local markets. Frying
experiment was conducted by frying potato slices at 175±5 °C. Frying was done
for 15 minutes (one frying cycle). This process was conducted over a period of
12 hours using the same oil without replenishment. Samples were collected after
every two hours during frying and evaluated for the chemical changes [acid
value (AV), iodine value (IV) and total polar compounds (TPC)] and physical
changes (viscosity and smoke point) occurred during frying. Oxidative stability
of oil samples were determined by evaluation of peroxide value (PV), p-anisidine
value (p-AV) and conjugated dienes (CD) and conjugated trienes (CT) values.
Data were statistically analysed using ANOVA (α = 0.05) using SAS. Less changes
were observed in the parameters determined for the CO than SO and PO. Rates of
increase in AV (0.02/hour), p-AV (8.03/hour), PO (0.13/hour) and viscosity
(1.15/hour) were higher for SO than other oils. Smoke point of all oils decreased
significantly, however, the reduction was higher for PO (from 208.5 to 172 °C)
than others. TPC were increased significantly during frying in all three oils.
However, TPC of CO did not reach the maximum acceptable limit (24-27%)
throughout the frying, while, PO and SO reached the limit at 4 and 12 hours of
frying, respectively. The rate of reduction in the IV of the PO and SO was
0.03/hour and 1.15/hour, respectively. Based on the results of this study, it can
be concluded that the CO is more suitable for continuous deep frying up to the
duration studied compared to other two oils.
