Changes in the quality of hive commercial brands of cooking oil were s
tudied under the frying conditions traditionally used in the Portugues
e hospitality trade. Three hundred rissoles were fried at a temperatur
e of 160-170 degrees C for 1 hour. Values of peroxide, p-anisidine, To
tox, acidity and total polar compounds were determined. Isomeric cis a
nd trans fatty acids were quantified using CP-Sil 88-packed capillary
column via gas chromatography.