This thesis provides new data on the levels of lipid and phytosterol oxidation products (POPs) in French fries and potato crisps consumed in Sweden. The levels of POPs in fried foods have attracted interest in recent years because of their potential harmful health effects. The analytical methods used here for the determination of POPs in commercial prefried French fries, French fries collected from fast food restaurants and commercial potato crisps included transesterification, SPE, GC and GC-MS. Higher amounts of total POPs were generally found in French fries prepared in restaurants (1.5-8.1 µg/g sample) than in prefried French fries (0.1-2.1 µg/g sample). In potato crisps, the total POPs content ranged from 0.5 to 6.8 µg/g sample. In general, no correlation could be established between the POPs content and the fatty acid profile, tocopherol, tocotrienol and sterol content in any of the fried potato products tested. However, these parameters provided information on the type of frying oil used in the preparation of the commercial fried potato products. The possibility of minimising lipid oxidation and POPs formation in some regular and oleic acid-dominated vegetable oils was examined. The oxidative stability was evaluated in these vegetable oils with and without addition of α-tocopherol and the results showed that addition of α-tocopherol (500-20000 µg/g) increased Rancimat stability only in refined olive oil. After heating at 180 ºC for up to 12 h, the levels of POPs generally increased over time in high oleic rapeseed oil, palm olein and refined olive oil. The addition of 0.2% α-tocopherol to refined olive oil decreased POPs formation significantly during heating. Studies on the quality of French fries prepared at 180 ºC in refined olive oil and palm olein in five batches at 1-hour intervals showed a higher content of POPs in French fries prepared in refined olive oil. However, all other frying quality parameters tested, such as total polar compounds, free fatty acids and p-anisidine value, were significantly lower in the French fries prepared in refined olive oil than in those prepared in palm olein
