Rapid simultaneous determination by proton NMR of unsaturation and composition of acyl groups in vegetable oils

Abstract

Abstract1H NMR spectra of 66 samples of edible oils from 14 different botanical origins were acquired. Assignment of signal spectra to the different types of hydrogen atoms was made and the areas of the signals determined. Considering that the area of the signals of the spectra is proportional to the number of hydrogen atoms of each type in the sample, it is possible to calculate not only the iodine value, but also the proportion of different acyl groups from the data. Determination of both parameters requires only a few minutes and one spectroscopic run. Classical methodology however, requires two separate wet methods for determining the unsaturation degree (iodine value) and the proportions of different acyl groups; both of them involve chemical transformations of the sample and considerable time and cost. Determination of acyl group proportions in samples by 1H NMR, which was validated with mixtures of standard triglycerides, provides accurate results and is able to detect small differences between samples of very similar composition.

Chemical Characterization of Oils and Fats from Amazonian Fruits by ¹H NMR

“…The results are shown in Table 1. Oleic acid is an unsaturated fatty acid (ω9) and characteristic signals of its structure observed in the oils 1 H NMR spectra (Supplementary materials: Figures S1-S10) are in accordance with data described in the literature [15]. The contents of this acid, as estimated by the evaluation of corresponding signals in the NMR spectra of the oils analyzed, varied between 26.18% (Red Pupunha) to 75.38% (Tucumanzinho) in samples studied (Table 1).…”

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.…”

“…The high spectral resolution is necessary to enable separate quantification of relevant lipid peaks such as the %2.1 ppm (allylic protons) and the %2.3 ppm (protons in a position to the carbonyl group) resonances. High-resolution NMR has been employed to identify the constituents of oils, animal fats, and extracts of rat adipose tissue (13)(14)(15)(16). Recently, in vivo MRS measurements of rodents (12,17,18) and humans (11) have been performed at high field strengths to calculate adipose tissue composition from the areas of the 2.1 ppm, 2.3 ppm, and 2.8 ppm (diallylic protons) proton lipid peaks.…”

“…It was assumed that the mouse adipose tissue was composed of SFA, MUFA, DUFA, in addition to a 2% fixed amount of triunsaturated fatty acids (TUFA) (18). The lipid compositions can be calculated from the NMR spectra by the following equations (14,18), Equation 1, where PUFA is the total amount of polyunsaturated fatty acids, and %TUFA ¼ 0 for the oils and 2% for the mouse.…”

Monitoring the Effect of Different Storage Conditions of Cold-Pressed Rice Bran Oil

“…2. Method A [13] based on proportional methyl group in sample and method B [14] based on the methylenic hydrogen atom in α position. From Table II, it can be observed that 1 H NMR technique was analyzed and calculated the intensity for the unsaturated fatty acid compositions of RBO samples and GC-MS technique was provided all the saturated fatty acid compositions of the RBO samples.…”