Lipids and phytosterol oxidation in commercial French fries commonly consumed in Sweden

Industrial frying oils continuously evolve as efforts are made to improve their overall quality because of health concerns. The objectives of this study were to determine fatty acids, tocopherols, sterols, and phytosterol oxidation products (POPs) in French fries, which are commonly consumed in Sweden. Five different commercial prefried French fries and four samples of French fries prepared in different fast food restaurants were studied. POPs were determined with transesterification, purification of oxides by solid-phase extraction, quantification by GC and identification by GC–MS. The method of POPs analysis was validated by spiking with standard samples of cholesterol oxidation products which showed good recoveries of those compounds. The results showed that the samples were generally prepared in frying oils dominated by saturated and monounsaturated fatty acids, except for two prefried samples which were dominated by a di-unsaturated fatty acid. In prefried samples, only α-tocopherol could be quantified whereas restaurant samples generally contained both α- and γ-tocopherols. Sitosterol was the dominating sterol in the all samples. The POPs content in prefried commercial French fries ranged from 0.01 to 0.21 mg/100 g, and the values in restaurant samples were considerably higher, ranging from 0.15 to 0.81 mg/100 g. The increased levels of POPs in the restaurant samples may be partially due to higher contents of fat, saturated and monounsaturated fatty acids and sterols. Further studies are required to identify other factors for the formation of POPs in French fries and their long-term implications to human health.