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 froma local market. The Rosemary leaves (Rosemarinus Officinalis L.)used in this study were collected in October from the region ofZaghouan 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 wereof analytical grade. HPLC-grade acetonitrile and methanol wereboth from Carlo-Erba (Rodano, Italy), and formic acid was fromInterchim (Montluc¸ on, France). All of them were used without anyfurther purification.