Abstract
The 2,2-diphenyl picrylhydrazyl (DPPH) method, which can be used to predict the oxidative stability of edible oils, was previously reported by our research group. Not only free radical scavenging antioxidants but also radicals from oxidized oils are capable of reacting with DPPH radicals, thereby reducing the absorbance of DPPH. In this study, the optimum sample size of edible oils for the DPPH method was determined, and the oxidation of the edible oils was monitored via DPPH, coupled with other conventional methods. The optimum sample size was determined as 1.5 g using soybean oil. Soybean, corn, virgin olive, and refined olive oils were thermally oxidized for 3 hr at $180^{\circ}C$ and analyzed via DPPH, conjugated dienoic acid (CDA) value, and p-anisidine value (p-AV) protocols. Soybean and corn oils were found to be more sensitive to thermal oxidation than virgin and refined olive oils, on the basis of the CDA value and p-AV measurements. The DPPH method can indicate the inherent radical scavenging activity of unoxidized samples, the time required for the depletion of antioxidants, and the rate of degradation of the antioxidants. The soybean and corn oils evidenced higher levels of free radical scavenging compounds, required more time for the consumption of inherent antioxidants, and also manifested steeper antioxidant degradation rates than olive oils, based on the results of DPPH analysis. The DPPH method, accompanied by other conventional methods, may prove useful in predicting the degree of oxidation of vegetable oils.
유지의 산화안정도 측정을 위해 개발된 DPPH법의 최적화를 위해 시료의 양에 따른 유지의 산화변화를 분석하였고, 결정도니 조건을 사용하여 시중에서 튀김유로 사용되는 4종류 식용유지의 열산화안정성을 측정하였다. CDA와 p-AV는 산화반응이 진행될수록 증가하였으며 시료간의 상대적인 산화안정성 차이를 확인할 수 있었다. 반면에 DPPH법은 유지의 산화라디칼과의 반응성을 이용하며 흡광도의 증가와 감소를 반복하는 경향을 나타냈고 이로부터 유지산화라디칼의 변화를 측정 할 수 있었다. 또한 유지의 초기 전자 혹은 수소공여능을 확인할 수 있었고, DPPH 흡광도 증가를 통해 산화방지물질의 소진속도 및 산화라디칼의 생성속도를 계산할 수 있었으며, 산화방지물질의 소진시점을 결정할 수 있었다. 따라서 DPPH법을 기존의 산화도 측정방법과 병용한다면 유지의 산화도는 물론 산화반응 단계를 측정 할 수 있고, 산화안정성을 예측하는데 도움이 될 것으로 기대된다.
