English abstract
Fat soluble vitamins and fatty acids are nutrients that are sensitive to high temperature and oxidation which result in partial loss of the nutrients during frying operation. In this study, the stability of vitamin A and D and the physiochemical changes were investigated in two types of oils, oil blend of sunflower and Refined Bleached and Deodorized (RBD) palm olein in a ratio of 60:40 and Refined Bleached and Deodorized plam olein. About 12 L of oils were heated in the fryer to chosen temperature which were 160°C and 190°C and those temperature commonly used for commercial and industrial deep fat frying operation. The frying times were 5 min at 190°C and 7 min at 160°C. A batches of 500g of French fired were fried every 15 min for 5 hrs per day. The frying procedure was repeated for 4 days more, to give a total heating and frying time of 25 hrs. Oil samples were taken at the end of each day to measure vitamins A and D concentration, free fatty acid (FFA), peroxide value (PV), color index (CI), and fatty acids composition (FAs). The results of this study showed that depletion of vitamin A and D accelerated when both types of oil subjected to higher temperature and when time of frying increased. Using RBD palm olein, vitamin A was reduced by 96.7% at frying temperature of 160°C after 25hours. It was completed diminished (by 100 %) at 190°C after 15 hrs of frying. When oil blend is used, vitamin A was reduced by 72.2 % at 160°C after 25 hrs of frying, but at 190°C the depletion was 100 %. Vitamin D was reduced by 67 % and 80 % at 160°C and 190°C, respectively, when using RBD palm olein. Vitamin D was reduced by 50 % after 5 hrs of frying at 160°C and by 67 % at 190°C when oil blend was used. So we can conclude that oil blend was more stable compared to RBD palm olein based on the change in the FFA, PV, CI FAs and depletion of vitamin A and D. The results also showed that the PV, FFA, CI increased significantly as a function of frying temperature and time. The FFA increased sharply in RBD palm olein and reached 0.53% and 0.77% at 160°C and 190°C respectively after 25 hrs of frying operation. On the other hand, the FFA increased in oil blend up to 0.25 and 0.49 % at 160 °C and 190 °C respectively after 25 hrs of frying operation. The oil blend showed less increased in the PV compared to RBD plam olein. The PV was 2.57 and 1.53 at 160 °C and 190 °C after 25 hrs of frying operation. The CI was increased in both types of oils but in the RBD palm olein the CI were 59.17 and 72.50 at 160 °C and 190 °C respectively after 25 hrs of frying operation. On the other hand, the CI were 44.0 and 56.3 at 160 °C and 190 °C respectively after 25 hrs of frying operation by used oil blend. PUFA and MUFA increased slightly and SFA decreased slightly when used RBD plam olein and blend oil used for the frying operation for 25 hrs at 160 °C and 190 °C. It is recommended to use oil blend during deep fat frying due to the stability of vitamins and less oxidative compared to RBD palm olein under the same conditions of temperature and time of frying operation. According to the results, oil replenishment minimized the thermal oxidation, hydrolytic change and increased the stability of vitamin A and D in the frying oils and extended the frying life of the oil.
