In this study, degree of rancidity and trans fatty acid formation were examined in fat and oils, including soybean oil (SB), canola oil (CA), corn germ oil (CO), olive oil (OL), palm oil (PO), and beef tallow (BT), during heating for 10-130 minutes at 160-200℃. In order to determine the rancidity of the fat and oils, acid values (AV), iodine values (IV), viscosity, and color were measured. Changes in the amounts of fatty acids and the formation of trans fatty acids were measured using GC and HPLC. For all groups, AV increased, IV decreased, and coefficients of viscosity and color increased as the heating temperature and heating time increased, indicating there were positive correlations between the heating temperature and time and AV. In addition, all groups had similar amounts of trans fatty acids, with the exception of the beef tallow; however, its level only slightly increased with heating. The olive oil had the lowest trans fatty acid content and the lowest amount created by heating. The order of trans fatty acid amounts generated while heating was BT〉PO〉CO〉CA〉SB〉OL. According to the study results, the deep frying temperature during cooking should be 160-180℃ in order to reduce AV and the amount of trans fatty acids that are formed. In addition, it is better to remove beef tallow during cooking and avoid heating at high temperatures since it results in high levels of trans fatty acids. The correlation between the amount of trans fatty acids and AV was positive, while the correlation between the amount of trans fatty acids and IV was negative, indicating that AV and trans fatty acid levels increase while IV decreases as the deep frying temperature and time increase. From the results, it was found that reducing the deep frying temperature and time can lessen increases in AV and trans fatty acids, and decrease IV. Accordingly, to reduce AV and trans fatty acid formation, the ideal deep frying conditions would be to use olive oil or soybean oil rather than beef tallow or palm oil at a temperature of 160-180℃.

대두유의 탈취과정에서 탈취온도, 진공도, cycle time 및 stripping steam 주입량의 4대 요소를 조정하여 탈취를 행한 후 탈취유의 산가, 과산화물가 및 trans 지방산 함량을 측정한 결과는 다음과 같았다. 즉, 탈취온도가 높을수록 AV, POV는 하락하였으나 trans 지방산 함량이 비례적으로 증가하였다. 진공도는 4torr 수준이 적정하였으며, CT는 길어질수록 효과가 우수하였다. SS주입량은 2.0%(w/w) 수준이 가장 적절한 조건이었다. 이러한 결과를 종합적으로 볼 때, 대두유에서 trans 지방산 함량을 상대적으로 낮게 할 수 있는 탈취조건은 최고 탈취온도 235℃, 진공도 4torr, CT 14~15분 및 SS주입량 2.0%(w/w)내외의 조건에서 trans 지방산 함량 0.31% 내외의 우수한 탈취유의 생산이 가능하였다. 결과적으로 탈취과정에서 trans 지방산 생성량을 극소화하기 위하여는 탈취온도가 가장 중요하였는데, AV, POV 등 다른 품질 요인들을 동시에 고려할 때, 더 이상의 탈취온도 하락은 어려운 것으로 판단된다.