Abstract
Thermooxidative stabilities of soybean oil, beef tallow and palm oil were studied during frying of steamed noodles. Steamed noodles were fried in $150^{\circ}C$ oils for 70 sec at the interval of 30 min. The frying oil was taken every 8 hrs for the analysis of peroxide value (PV) and free fatty acid (FFA) content, fatty acid composition, and tocopherol and tocotrienol content. A little change was shown in PV and FFA content in soybean oil during frying; on the other hand, rapid increase in beef tallow and palm oil was observed. Unsaturated fatty acid content was the highest in soybean oil, followed by palm oil and beef tallow. While fatty acid composition in soybean oil was not changed during frying, unsaturated fatty acid content decreased and saturated fatty acid increased in beef tallow and palm oil, which showed susceptibility to the oxidation. The ratio of linoleic acid to palmitic acid did not show difference with frying time in soybean oil: however, it decreased in other oils with a high correlation with frying time and higher decreasing rate in palm oil was observed. These suggested that soybean oil was the most stable to thermooxidation and the stability was followed by beef tallow and palm oil. Tocopherol was disappeared during frying and 87.5, 81.1, and 73.1% were remained in soybean oil after 8, 16 and 24 hour frying, respectively. Also the rate decreased in the order of ${\gamma}-,\;{\beta}-\;and\;{\alpha}-tocopherol$. However, 34.2 and 169.0 ppm tocopherol and tocotrienol which were present in control samples of beef tallow and palm oil were completely disappeared by 8 hr frying. Therefore, high thermooxidative stability of soybean oil resulted from higher residual amount of tocopherol during frying, and lower stability of palm oil than beef tallow was partly due to high degree of unsaturation.
대두유, 우지, 팜유에서 증숙면을 튀겨내면서 튀김유의 가열산화안정성을 살펴보았다. 튀김유를 $150^{\circ}C$로 가열하고 증숙면을 30분 간격으로 70초간 튀기는 도중 8시간 간격으로 튀김유를 채취하여 과산화물가와 유리지방산의 함량, 지방산 조성의 변화, 토코페롤 및 토코트리엔올을 분석하였다. 튀김과정중 대두유에서의 과산화물가 및 유리지방산가는 별다른 변화를 보이지 않은 반면, 우지와 팜유에서는 급격한 증가를 보였다. 구성 지방산의 불포화도는 대두유가 가장 높았고 다음이 팜유, 우지의 순이었다. 대두유의 지방산 조성은 튀김과정 동안 거의 변하지 않았으나 우지와 팜유에서는 불포화지방산의 함량이 줄어드는 대신 포화지방산의 함량이 증가하여 산화에 대한 민감성을 나타내었다. 리놀레산과 팔미틴산의 함량비는 대두유의 경우 튀김시간에 따라 큰 차이를 보이지 않았으나 우지와 팜유에서는 튀김시간에 따라 높은 상관관계로 감소하였고 우지보다는 팜유에서 그 속도가 빨랐다. 이것은 대두유가 가열 산화에 가장 안정하고 우지, 팜유가 그 뒤를 따르고 있음을 암시한다. 토코페롤은 대두유에서 튀김과정에 의해 파괴되어 8, 16, 24시간 후 87.5, 81.1, 73.1%가 잔존하였으며 그 파괴 속도는 ${\gamma}$-토코페롤이 가장 컸고 ${\beta}-,\;{\alpha}$-토코페롤 순으로 나타났다. 그러나 대조군 우지와 팜유에 각각 34.2, 169.0 ppm 존재하던 토코페롤과 토코트리엔올은 튀김 8시간을 지나면서 모두 파괴되었다. 따라서 높은 불포화도에도 불구하고 대두유에서 나타난 가열산화안전성은 토코페롤의 높은 잔존량에 기인하였고, 팜유가 우지보다 낮은 가열산화안전성을 보인 것은 구성 지방산의 높은 불포화도에서 일부 기인한 것으로 생각된다.
(Department of Food Science and Nutrition, The Inha University)
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