Classification of Edible Oils by Employing ³¹P and ¹H NMR Spectroscopy in Combination with Multivariate Statistical Analysis. A Proposal for the Detection of Seed Oil Adulteration in Virgin Olive Oils

Abstract

A combination of (1)H NMR and (31)P NMR spectroscopy and multivariate statistical analysis was used to classify 192 samples from 13 types of vegetable oils, namely, hazelnut, sunflower, corn, soybean, sesame, walnut, rapeseed, almond, palm, groundnut, safflower, coconut, and virgin olive oils from various regions of Greece. 1,2-Diglycerides, 1,3-diglycerides, the ratio of 1,2-diglycerides to total diglycerides, acidity, iodine value, and fatty acid composition determined upon analysis of the respective (1)H NMR and (31)P NMR spectra were selected as variables to establish a classification/prediction model by employing discriminant analysis. This model, obtained from the training set of 128 samples, resulted in a significant discrimination among the different classes of oils, whereas 100% of correct validated assignments for 64 samples were obtained. Different artificial mixtures of olive-hazelnut, olive-corn, olive-sunflower, and olive-soybean oils were prepared and analyzed by (1)H NMR and (31)P NMR spectroscopy. Subsequent discriminant analysis of the data allowed detection of adulteration as low as 5% w/w, provided that fresh virgin olive oil samples were used, as reflected by their high 1,2-diglycerides to total diglycerides ratio (D > or = 0.90).

Effect of J‐coupling on lipid composition determination with localized proton magnetic resonance spectroscopy at 9.4 T

“…The frequency of the narrow-bandwidth PRESS sequence was optimized separately for the 2.1, 2.3, or 2.8 ppm peak. (14,(29)(30)(31)(32). For the high purity linoleic acid, analysis was performed to compare the estimated amount of linoleic acid determined by each method.…”

31P NMR spectroscopy in the quality control and authentication of extra‐virgin olive oil: A review of recent progress

“…5,10,17,28 The repeatability was measured on the basis of several consecutive 31 P NMR spectra recorded for the same model compound (e.g. phosphitylated hydroxytyrosol), whereas the reproducibility was tested by performing measurements on several different solutions of model compounds and using the same experimental protocol for each measurement.…”

“…35 A further application of the NMR methodology to the EVOO authentication is the classification of several edible oils and the detection of EVOO adulteration with refined seed oils. 28 For this purpose, 192 samples of 13 types of edible oils including EVOO were analyzed by employing NMR spectroscopy. Total free sterols, free acidity, 1,2-DGs, 1,3-DGs, total DGs and the ratio D were determined with 13 P NMR spectroscopy.…”

“…Total free sterols, free acidity, 1,2-DGs, 1,3-DGs, total DGs and the ratio D were determined with 13 P NMR spectroscopy. In addition, 1 H NMR spectroscopy has been employed for determining the fatty acid composition and iodine value, 1,6,28 in order to increase the number of variables for statistical analysis. Selection of variables with the highest discriminatory power was made as before by employing one-way ANOVA.…”

“…The use of 2 of the 8 canonical functions or roots of the model obtained by DA with the highest discriminating power succeeded in classifying the 192 oil samples into 13 different groups. 28 For adulteration studies, a series of artificial mixtures of EVOO-hazelnut oil, EVOO-corn oil, EVOO-sunflower oil and EVOO-soybean oil were prepared at concentrations ranging from 5 to 50% w/w and analyzed by 1 H NMR and 31 P NMR spectroscopy. Subsequent DA of the data allowed detection of adulteration as low as 5% w/w for each seed oil including hazelnut oil.…”