AccuTOF TM with DART TM “No-prep” Analysis of Lipids in Cooking Oils and Detection of Adulterated Olive Oil Introduction DART source was operated with helium and the gas heater was set to 375oC. Melting point tubes were Dietary fats are categorized according to the level of dipped in oil samples and placed in front of the DART unsaturation. Oils are a mixture of triglycerides and free ion source for a few seconds. A cotton swab dipped in fatty acids. Olive oil contains a high concentration of dilute ammonium hydroxide was placed nearby to + monounsaturated fatty acids, while other oils such as enhance formation of [M+NH4] from triglycerides. A Canola and safflower oil contain larger amounts of spectrum of PEG 600 was measured between samples polyunsaturated fatty acids. Characterizing the type of to permit exact mass measurements. lipids present is important for quality control and for detecting adulteration of more expensive oils (e.g. olive Results oil) with cheaper products. Analysis by HPLC is time- consuming and requires solvents and consumables. Figure 1 shows the DART mass spectrum of a grocery- DART provides a convenient alternative: no solvents are store olive oil and Figure 2 shows a comparison of required and the analysis can be completed in seconds. mass spectra for different cooking oils. Free fatty acids (Figure 3), squalene and di- and triglycerides + Experimental (Figure 4) are detected as [M+NH4] . The relatively high abundance of free fatty acids in Figure 1 (bottom) Analysis was carried out by using a JEOL AccuTOF- is a result of thermal decomposition and is only DARTtm mass spectrometer operated in positive-ion observed at higher gas temperatures for large amounts mode at a resolving power of >6000 (FWHM). The of (neat) oil. However, the abundant peaks for the free

TRIGLYCERIDES Triolein OOP

Diolein

200 400 600 800 1000 m/z

Oleic acid TRIGLYCERIDES Triolein Squalene Diolein OOP Linoleic acid Triolein-O

200 400 600 800 1000 m/z

Figure 1. Medium-quality grocery store olive oil. Top: dilute solution of olive oil in hexane, bottom: neat oil (DART at 375oC).

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Oleic Acid Gourmet Olive Oil

200 400 600 800 1000 m/ z Oleic Acid Grocery-Store Olive Oil

200 400 600 800 1000 m/ z Linoleic Acid Spray-on Oil Triglycerides

200 400 600 800 1000 m/ z Linoleic Acid Sesame Oil

200 400 600 800 1000 m/ z

Figure 2. Comparison of cooking oils

fatty acids under these conditions make it easy to see while increasing unsaturation is observed for the Canola/ differences in the overall fatty acid content of the oil. safflower oil blend and the sesame oil. Elemental compositions were confirmed for the Of the C18 fatty acids, oleic acid (O) comprises 55- 1 + 85% of olive oil , while the Omega-6 fattty acid linoleic triglyceride [M+NH4] peaks by exact mass acid (L) is present at about 9% and the Omega-3 fatty measurements and isotope pattern matching. Examples acid linolenic acid (Ln) is present at less than 1.5%. for triolein (OOO) and OOP are shown in Table 1. Figure 5 shows the DART mass spectrum of an olive oil Other fatty acids including the C16 palmitic acid (P) are also detected. sample to which 50% of the Canola/safflower oil blend The triglyerides are readily detected (Figure 4) and has been added. In comparison with the unadulterated their elemental compositions confirmed by exact mass olive oil (Figures 3 and 4), the adulterated oil is easily measurements (Table 1) and isotope pattern matching. recognized by the higher degree of unsaturation and the Triolein (OOO) is the major component in olive oil, relatively higher abundance of linoleic and linolenic acids.

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Oleic Gourmet Olive Oil Linoleic Linolenic

29 0 2 95 30 0 3 05 31 0 m/ z Oleic Linoleic Grocery-Store Olive Oil Linolenic

29 0 2 95 30 0 3 05 31 0 m/z Linoleic Canola/Safflower Oil Linolenic Oleic (Spray-Can)

29 0 2 95 30 0 3 05 31 0 m/ z Linoleic Oleic Sesame Oil

Linolenic

29 0 2 95 30 0 3 05 31 0 m/ z

Figure 3. Enlarged view of free fatty acid region

C57H104O6 (OOO)

C55H102O6 (OOP)

C53H100O6 (PPO) Olive Mostly Monounsaturated 840 860 880 900 920 940 960 980 m/ z C57H100O6 (LLO) C57H102O6 (OOL)

C57H98O6 (LLL) Canola/Safflower

m/z 840 860 880 900 920 940 960 980

C57H102O6 (OOL) C55H100O6 (POL) C H O 55 98 6 Sesame (LLP) Polyunsaturated

840 860 880 900 920 940 960 980 m/z Figure 4. Enlarged view of triglycerides in cooking oils

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876.801270 25.14 -0.75 3.5 C55 H106 O6 N1 (OOP) 902.816040 35.62 -1.61 4.5 C57 H108 O6 N1 (OOO)

Table 1. Elemental compositions from exact mass measurements

OOO

298.27428Linoleic acid OOL LLO LLL Linolenic acid Oleic acid

296 298 300 302 840 860 880 900 920 940 960 m/z m/z

20 40 60 80 100 m/z

Figure 5. DART mass spectrum of adulterated olive oil

Conclusion Reference

DART can characterize lipids such as fatty acids and 1.http://www.oliveoilsource.com/olivechemistry.htm mono-, di-, and triglycerides in cooking oils and detect adulterated olive oil within seconds and with no sample preparation.

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