In order to determine the biological significance of the changes which occur when fats are heated to high temperatures in air, cottonseed oils were heated and aerated under several controlled conditions. In general, the data indicate that the changes induced are proportional to the severity of the conditions and that treatments more severe than those usually encountered in processing or cooking are necessary to produce detectable damage.
Oils which had been subjected to prolonged aeration at 60C (16 days or more) or exposed to air in thin layers maintained at 180舑220C supplied less available energy and caused development of larger livers than untreated samples when compared in rat feeding tests. Heating in deep layers caused less damage than heating to the same temperatures in thin films, indicating that exposure to oxygen accelerates nutritional impairment.
The cooking of food in fats changes condition so greatly that direct extrapolation of data obtained in tests using fat alone is not justified. Fat extracted from foods has not been found to contain harmful substances by the tests used.
Summary
Cottonseed oil, partially hydrogenated cottonseed oil and corn oil, were fed at 4% and 10% of the diets with two levels of protein, 19% and 25%, and with 0.5% cholesterol to cockerels 21 days of age for a period of 38 days. Blood samples were obtained at 0, 14, 24, and 38 daysvia heart puncture.
The data indicate that the serum cholesterol value, irrespective of the level or type of fat, was significantly lower in those groups of birds which were fed the higher level of protein. Excluding the combination of 19% protein and 10% cottonseed oil, the degree of saturation did not have any apparent effect upon serum cholesterol because the mean differences among the oils and between the fat levels were not statistically significant.
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