Determining the Degree of Deterioration of Cooking Oil by Assessing Polar Compound Content (FS14-07-19)

OBJECTIVES: Degradation of oil is characterized by oxidation, polymerization and hydrolysis of the chemical compounds of the oil. This process of deterioration increases the amount of several types of compounds, including polar compounds, such as alcohols, ketones and free fatty acids. Currently, there is no universal assay for measuring the quality of frying oil, and tests that do exist to examine frying oil are often costly and time consuming. This study set out to examine the utility of Reichardt's dye, a solvatochromic dye that indicates degrees of solvent polarity, as a possible way to accurately predict the degree of degradation of cooking oils. METHODS: Several pH indicators were used to indicate the pH of the substances tested. Reichardt's dye was first tested against well-known indicators, including Bromophenol blue, Bromothymol blue, Bromocresol purple, and Phenolphthalein. One milliliter of each oil sample was combined with 0.5 milliliters of the Reichardt's dye solution and the color changes were observed. To determine the percentage of free fatty acids in each of the three oils, approximately 2 grams of oil with a pH indicator was dissolved in 100% ethanol and titrated with 1 M potassium hydroxide solution. The titrations assigned quantitative values to the color changes observed when Reichardt's dye was used. RESULTS: The addition of Reichardt's dye solution to all three oils indicated presence of polarized substances through varying degrees of color change whereby the fresh vegetable oil had the lowest concentration of polar compounds (dark blue) and the degraded oil had the highest concentration of polar compounds (greenish-orange). The degree of color change correlated with the results of titrations which demonstrated increasing amounts of free fatty acid (FFA) content in the fresh vegetable oil (0.17% FFA), the slightly degraded kitchen oil (2.7% FFA) and the degraded oil (15% FFA). CONCLUSIONS: Our experiment showed that Reichardt's dye was effective in indicating the polarity of oil substances, a reflection of the degree of degradation in oil. Given that oxidized oil is harmful to health, it is important to measure this oxidation process. This study warrants future research into the utility of Reichardt's dye. FUNDING SOURCES: National Institute of Environmental Health Sciences, NIH; University of Pennsylvania TREES Program (R25 ES021649).