Abstract
Vegetable oil analyses, especially due to the complexity of the oil components, are commonly laborious, requiring several analytical techniques. In this work, electrospray ionization mass spectrometry with direct injection (DIMS), along with 18-crown-6 ether (crown ether) chelating agent and trifluoroacetic acid (TFA), was used to characterize and semi-quantitatively evaluate commercial vegetable oils. As a result, an unprecedented DIMS method of triacylglycerols (TAGs) analysis for semi-quantitative profiling of fatty acids in commercial oils (e.g., soybean, sunflower, corn, oil, canola), without sample derivatization, was developed. The results of the ion abundances related to the analyzed TAGs, with quantitative percentage analyzed by gas chromatography with flame ionization detector (GC-FID), allowed generating correction factors for each oil. DIMS analysis with crown ether/TFA resulted in the elimination of isobaric interferences from sodium and potassium adducts, facilitating the ion assignments, due to the one-ion-per-molecule observation in the mass spectrum. Chemometric analyses by principal component analysis (PCA) and heatmap, to evaluate the ionic profile of the oils, grouped them accordingly to their TAG content. Olive oil was identified as the most different from the other oils. Overall, a semi-quantitative approach to investigate the vegetable oils, reaching low percentage variation for DIMS, with 2 min analyses and 30 min sample preparation, was proposed.
Highlights
Lipids are a large and diverse group of chemical compounds related by their solubility in nonpolar organic solvents.[1]
We propose an unprecedented method of TAG analysis in commercial oils, which could be applied to animal fats and add important information to the techniques already used for this purpose.[15,16,17,18]
To compare the vegetable oils of this study, a representative mass spectrum of each type of oil was used, since the TAG profiles observed among the various brands were very similar
Summary
Lipids are a large and diverse group of chemical compounds related by their solubility in nonpolar organic solvents.[1] Lipids perform two critical functions: as the major structural components of biological membranes and a form of energy storage. Among the most commonly identified lipids, high molecular mass esters, such as fats, oils, and natural waxes, must be highlighted.[2]. Vegetable oils are complex chemical mixtures composed primarily of lipid structures, such as triacylglycerols (TAGs), and small amounts of free fatty acids (FAs) and mono- and diacylglycerides from degradation processes. Crude vegetable oils contain a variety of minor components, such as sterols, tocopherols, and phospholipids, but their distributions are characteristic of different types of oils.[3,4] Lipid has a fundamental nutritional role, but its consumption is directly related to cardiovascular diseases, obesity, and insulin resistance.[5]
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