Determining nutritional labeling data for fats and oils by 1H NMR

The nutrition labeling compositional data (NLCD) required for fat-containing food products consists of the percentages of saturated, cis-monounsaturated, and cis-polyunsaturated fat as well as trans content. The capability of H-1 NMR spectroscopy to determine the NLCD components in oils that do not contain significant levels of trans isomers has already been established in the literature, but not its capability to differentiate between cis- and trans-unsaturation. In the present study, the determination of all four NLCD components in fats and oils has been demonstrated for the first time. A preliminary analysis of the intensity-normalized H-1 NMR spectra of defined mixtures of pure triacylglycerols (TAG) by partial least squares (PLS) regression revealed that the (mono)allylic proton resonances of cis and trans bonds were sufficiently well separated to allow for accurate quantitation of trans content by simple peak integration. This chemometric approach also served to facilitate the identification of optimal integration limits for these cis- and trans-allylic resonances. Fixed integration limits were also set for the other resonances employed in the determination of the four NLCD components, and a standardized spectral preprocessing procedure was established. The H-1 NMR NLCD data obtained for the TAG mixtures by this methodology was a good match to the actual values, calculated from the known molar composition of these gravimetrically prepared mixtures. A procedure for the conversion of the NMR mol% NLCD to units of wt%, previously developed for C-13 NMR, was adapted for H-1 NMR and shown to be effective in compensating for the overestimation of wt% saturates and underestimation of wt% unsaturates by H-1 NMR if this conversion is not made. The H-1 NMR methodology for NLCD determination was validated by analyzing AOCS Laboratory Proficiency Program GC samples as well as samples taken from a hydrogenator over time and analyzed for trans content by GC and IR spectroscopy. Comparison of the H-1 NMR mol% and wt% NLCD obtained for these validation samples with the data obtained from the reference methods indicated that H-1 NMR can deliver high-quality, accurate NLCD, much like C-13 NMR, but in a much shorter time frame. Thus, H-1 NMR provides a more rapid and cost-effective means of obtaining NLCD than C-13 NMR and can replace GC as a primary reference method for the calibration of simpler and automatable instrumental methods such as Fourier transform infrared (FTIR) spectroscopy.