Abstract
Long-used frying oil may pose health risks. In the last few decades, consumption of commercially deep-fried foods has increased drastically, thus drawing attention to the thermal deterioration of the frying oil used in their preparation. The purpose of this study was to collect basic information about deteriorated frying oil ingested through foods. We analyzed the acid value (AV), carbonyl value (COV), contents of polar compounds (PC) and triacylglycerol (TG) and Gardner color in oils used in the kitchen of a campus restaurant and in oils contained in batter coatings of commercially deep-fried foods purchased randomly in Kobe, Japan. The results of the restaurant investigation indicated that the properties of frying oil were almost within the safe limit when one batch of oil was used at 180°C for 3 hours a day for 5 consecutive days. Among oils extracted from the batter coatings, 4-22% samples, depending on the analytical items, showed properties worse than those of oil recovered from food manufacturing companies after use. It seems that deep-fried foods containing deteriorated frying oil were produced on some occasions but not others by certain companies and that deep-fried foods were sometimes prepared with long-used thermally deteriorated oil. Thus, to ensure the safety of deep-fried foods, measures should be taken to shorten the usage span of frying oil.
