Differences in lipid oxidation products (LOPs) and trace metal concentrations of French fry samples found between two global chain fast-food restaurants in the UK were investigated using high-resolution proton nuclear magnetic resonance (1H NMR) and inductively coupled plasma-optical emission spectrometry (ICP-OES) analyses, respectively, of extracts derived therefrom. Over the course of 3 days and 3 different diurnal time periods, samples of French fries (FFs) were analyzed, and comparisons of two different oil extraction methods were undertaken for the two restaurants involved. The magnitude of concentrations of LOPs extracted from FFs is discussed. Significant differences between 6/7 aldehyde classifications, and aluminum, manganese, vanadium, lead, iron, copper and nickel levels between samples from the two restaurants are also reported. Redox-active transition and further trace metal concentrations inversely correlated with FF oil sample LOP contents; this suggested an antioxidant rather than a pro-oxidant role for them.
Over the course of 3 days and 3 different diurnal time periods, the present study established that between the two UK fast-food restaurants, the total lipid acylglycerol content extracted and established as a percentage of FF mass, was directly proportional to the levels of LOPs identified and quantified in these samples. Total lipid acylglycerol contents were consistently higher in YFF [13.2-17.3% (w/w)] than in XFF [8.2-11.9% (w/w)], and hence so were the identified and quantified aldehydic LOPs. Overall, with regards to the 1H NMR analyses of the major acyl function resonances, the classes of the fatty acid contents were quite distinct between XFF and YFF oil extracts. Moreover, small differences in the amounts of the fatty acid contents between XFF and YFF oils were observed. For example, the total ω-3 acylglycerols and linolenoylglycerol levels were both higher in the XFF than the YFF FF oils extracted. Although both primary and secondary LOPs identified in the oil extracts of FFs across the sampling time-points were similar, YFF oil extracts were found to be richer in all LOPs determined. In retrospect, the presence of LOPs in FFs studied present a health hazard to consumers regarding the use of UFA-rich culinary oils for high-temperature, peroxidation-promoting frying episodes. Moreover, levels of redox-active metals measured with the aid of ICP-OES in oil extracts of FFs were found to be inversely correlated with FF oil LOP concentrations, and this may indicate that the redox-active ones monitored (e.g., those of Fe, Cu, and Mn) may exert antioxidant rather than pro-oxidant roles.