As noted in our previous publications (1-3), frying oil is replaced after use at 180 for about 20 h in the Japanese food manufacturing industry; 50% of the browning of frying oil is attributable to the thermal deterioration of the oil itself (Gardner color increases to 5), and the rest most probably to amino-carbonyl compounds formed from thermally oxidized oil/fatty acids and amino acids exuded from frying foodstuffs. Depending on the type of amino acids included, 200-2000 ppm of amino acids are enough to brown oil to G>10. Other substances, such as protein, starch, sugar, coloring substances, and blood, have little to do with the browning of oil in frying practice. Koga et al. (4) found that Gly, Ala, and Leu were browning substances but did not compare these amino acids with other substances related to frying or conduct a quantitative inves-441 JOS

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After Swedish researchers reported that heated foods such as potato chips and French fries contain acrylamide, the potential for health damage resulting from the consumption of these foods became a widespread concern. Used frying oils collected from food manufacturing companies were subjected to acrylamide determination using GC/MS-SIM, but the compound was not detected. Thus, we conclude that frying oil used in deep frying would not contaminate foodstuffs with acrylamide and that the recovered oil, much of which is used as a component of animal feeds, would be safe for livestock. Model experiments heating oil at 180 degrees C suggested that no acrylamide was formed either from a mixture of major amino acids exuded from frying foodstuffs and carbonyl compounds generated from oxidized oil, or from oil and ammonia generated from amino acids.

Although the abolition ratio of edible oil depends on usage and where it is used, the amount of abolished oil in Japan seems to be vast; presumably, 20% of annual consumption of edible tallow vegetable oil, 2.5 million tons (1), is abolished at present. But one half of the used oil is rarely recovered because of domestic use (2). In spite of enthusiastic efforts of some groups making soap from it, most used frying oil is discarded after it is solidified with a gelling agent or bottled or is discarded directly to soil or kitchen drains (3). Thus, complete recovery of used edible oil will be a difficult goal to achieve immediately. The rest of the used oil is generated from food manufacturing industries, restaurants, supermarkets, and other food-related businesses and recovered by renderers, oil collectors, and blenderers, then classified by appearance and other properties and reused after simple treatments or burned. In short, some used edible oil ends up as a fatty acid source, feed oil for animals, paint, ink, fuel oil, or soap or is burned/discarded (2,4). Insufficient reuse of recovered oil is primarily due to tough competition between the price of good-grade oil coming from fancy restaurants and other such sources and the cost of refining low-grade, poorcolored oil (Gardner color 11), as well as to the relationship between the demand and the supply of both oils.

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