"Real-World" Evaluation of Lipid Oxidation Products and Trace Metals in French Fries From Two Chain Fast-Food Restaurants

Abstract

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.

Keywords: French fries; aldehydes; fast-food restaurants; legislated metals; lipid oxidation products; proton nuclear magnetic resonance.

Figure 1

Stepwise process employed for the extraction of culinary oils and secondary aldehydic LOPs from FF samples purchased from restaurant chains X and Y. FF, French fries; rpm, revolutions per minute.

Figure 2

Percentage (w/w) total lipid acylglycerol contents of FF samples purchased from restaurants X and Y. XFF and YFF, French fries sampled from restaurants X and Y, respectively. All values are presented as mean ± SD values.

Figure 3

¹H NMR spectra of frying oils collected from restaurants X and Y, showing (A) major acylglycerol functions, and (B) expanded regions of resonances A, B, C, E, G, H, J, and K present within the 0.0–5.4 ppm regions of n-hexane-oil extracts of FF samples purchased from restaurants X and Y. XFF and YFF, Restaurant X and Y French fries, respectively; Ln, Linolenoylglycerol signal; L, Linoleoylglycerol signal; O, oleoylglycerol signal; S, saturated fatty acid acylglycerol signal. Letter assignments of resonances correspond to those provided in Table 1. ¹H NMR spectra of frying oils collected from restaurants X and Y, showing (A) major acylglycerol functions, and (B) expanded regions of resonances A, B, C, E, G, H, J, and K present within the 0.0–5.4 ppm regions of n-hexane-oil extracts of FF servings purchased from restaurants X and Y. XFF and YFF, Restaurant X and Y French fries, respectively; Ln, Linolenoylglycerol signal; L, Linoleoylglycerol signal; O, oleoylglycerol signal; S, saturated fatty acid acylglycerol signal. Letter assignments of signal resonances (A, B, C, E, G, H, J, and K) correspond to those provided in Table 1.

Figure 4

Concentrations of acylglycerol FA groups of n-hexane-extracts frying oils from FF samples purchased from restaurants X (A) and Y (B). All values are presented as mean ± SD values.

Figure 5

Iodine value (unit) of n-hexane-extracted culinary frying oils from FF samples purchased from restaurants X and Y. All values are presented as mean ± SD values.

Figure 6

¹H NMR spectra of frying oils collected from restaurants X and Y, showing minor compounds present with resonances within the 0.0–3.7 ppm regions of n-hexane-oil extracts of FFs purchased from restaurants X and Y. XFF and YFF, Restaurant X and Y French fries, respectively. Letter assignments of resonances correspond to those provided in Table 2.

Figure 7

(A) Secondary aldehydic LOPs concentrations of FF samples collected from restaurants X and Y on consecutive weekly days (Friday, Saturday, and Sunday), and their total lipid contents. These data reveal a significant correlation between aldehyde and total lipid levels. All values are presented as mean ± SD values. (B) Relationships between mean FF concentrations of aldehydic LOPs and total lipid contents of FF samples for restaurants X (filled spheres) and Y (unfilled triangles).

Figure 8

Aldehyde contents (mmol. aldehyde/mol. total fatty acid) of FFs normalized to total extracted acylglycerols for deuterochloroform (C²HCl₃) and exhaustive n-hexane methods employed for the ¹H NMR analyses of FF samples collected from restaurants X and Y. All values are presented as mean ± SD values. Data presented are consistent with those in Supplementary Table 6.

Figure 9

Plot of mean aldehyde concentrations determined using the direct C²HCl₃ and exhaustive hexane extraction techniques (designated as EXTRACTION-D and –H, respectively). The differential responses of aldehydes to these extractions are responsible for the highly significant first-order aldehyde x extraction technique source of variation observed for the model 2 ANOVA performed.

Figure 10

Concentrations of secondary aldehydic LOPs in culinary frying oil media extracted from FF samples purchased from restaurants X (A) and Y (B). All values are presented as mean ± SD values.