Abstract
This paper reported a potential analytical technique based on NMR spectroscopy for the determination of quality of olive oil. The model compounds with active hydrogen, including free sterols, free aliphatic alcohols, phenolics, and free fatty acids were determined by 19 F NMR upon derivation with 4-fluorobenzoyl chloride. Integration of the appropriate signals of the derivatives of the compounds in the corresponding 19 F NMR spectrum allows for the quantification of these compounds. 37 Samples of commercial olive oil and 5 samples of other plant oils were determined by 19 F NMR. The amount of diglycerides and the ratio of 1,2-diglycerides to the total amount of diglycerides were analyzed to monitor whether extra virgin olive oil was adulterated with low price olive oil and other plant oils or not. The results showed that the total diglyceride content should not be higher than 2.5% and the ratio (D) of 1,2-diglycerides to total diglycerides should be higher than 0.35 for extra virgin olive oil. This method is an easier, simpler, safer, faster and more reliable technique for the determination of the quality of olive oil and can also be extended to monitoring the quality of ordinary edible oils.
Highlights
Olive oil is essential culinary oil of the Mediterranean diet
In order to increase profits there is the possibility of mixing seed oil or low-quality olive oil such as refined olive oil (ROO) and pomace olive oil (POO) with the highest quality product, extra virgin olive oil (EVOO)
The deriving reagent (4-fluorobenzoyl chloride) (98%) and 4-tert-butylphenol were purchased from SigmaAldrich (SHH, CHN). 1,3-Stearin (DG) was synthesized from glycerol and stearic acid catalyzed by Lipozyme RM IM in the laboratory according to the method used by Berger et al (1992). 1,2-Stearin was made available from the partial hydrolysis of triglycerides through pancreatic lipase and separation of the formed mono- and diglycerides using thin-layer chromatography (IUPAC, 1987)
Summary
Olive oil is essential culinary oil of the Mediterranean diet. Olive oil is a genuine fruit juice with excellent nutritional, sensory and functional qualities obtained from the fruit of olive trees (Benito et al, 2013). Besides infringing the benefits of consumers, the adulteration of extra virgin olive oil may cause serious safety problems. Olive oil adulteration resulted in over 20,000 people becoming sick and over 400 people died in 1981. For the past 10 years the percentages of diacylglycerols (DGs) in olive oil have been investigated for their usefulness as a marker of possible adulteration (Pérez-Camino et al, 2001). Several studies suggest that the content of the percentages of total DGs and the ratio of 1,2-DGs to the total amount of DGs are useful indices to assess the freshness and quality of olive oil (Fronimaki et al, 2002; Pérez-Camino et al, 2001; Sacchi et al, 1991)
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