In the present work, two oils are selected for the formula-tion of the frying oil: sunflower oil and soybean oil. These oilsand fresh potatoes for sensorial analysis were purchased from a local market. The Rosemary leaves (Rosemarinus Officinalis L.)used in this study were collected in October from the region of Zaghouan in the north-east of Tunisia. Vouchers specimens arekept in the herbarium of the National Institute of Applied Scienceand Technology (Tunis, Tunisia). All chemical reagents used were of analytical grade. HPLC-grade acetonitrile and methanol wereboth from Carlo-Erba (Rodano, Italy), and formic acid was from Interchim (Montluc¸ on, France). All of them were used without any further purification.