NMR Provides Characterization of Complex Lipid Emulsifier Mixture
“…this research showed how 1H NMR, 13C NMR, and 31P NMR techniques can be used to analyze HMMS without the need for purification”
Emulsifying agents enhance the mixing of two components with a natural tendency to separate by forming a film around the dispersed globules to form an emulsion. Functional emulsifiers comprising a mixture of monoesters and diesters, such as propylene glycol (1,2-propanediol) esters, at high concentrations are widely used in the food industry to improve the appearance and properties of their final products. For example, such emulsifiers are added to ice cream to inhibit the recrystallization of ice during freezing and to determine the consistency; either foamy so it can be extruded onto cones, or firm so it retains its shape on scooping. Similarly, the addition of lipid emulsifiers to cake mixture and bread dough can increase the volume of the final product and ensure uniform structure to improve their quality.
Success in achieving the desired effect is determined by the precise composition and concentration of the emulsifier mixture. These in turn may be affected by the way in which the emulsifier is produced or the conditions in which it is used. It is thus important that an emulsifier can be accurately characterized. Furthermore, the requirement to include nutritional labeling on food products mean that the fatty acid composition of the lipid emulsifier must be known.
There are many high-performance analytical techniques that can be used to characterize lipid mixtures, such as high-performance liquid chromatography (HPLC), mass spectroscopy, and nuclear magnetic resonance spectroscopy (NMR). Unfortunately, none has yet provided the ideal solution for analyzing complex lipid emulsifier mixtures and it is often necessary to use a combination of different methodologies, which can be time-consuming and wasteful.
The search thus continues for a fast and reliable methodology for the easy and complete analysis of the lipid emulsifiers. NMR, being a particularly desirable technique due to its non-destructive analysis and minimal necessity for sample preparation, has been central to this research. It has already proved to be an effective methodology for the determination of fatty acid composition. The fatty acid contents of sunflower, olive, and linseed oils have been determined in less than a minute using an optimized 1H NMR methodology.
An NMR study has now analyzed a complex lipid mixture derived from soybean oil by enzymatic alcoholysis reactions. The enzymatic alcoholysis produced a high monoester mixture of soybean oil (HMMS). Both the original soybean oil and the HMMS were analyzed, without any purification steps, by 1H NMR, 13C NMR, and 31P NMR using a Bruker Avance III 500 spectrometer.
All three NMR methodologies enabled effective qualitative and quantitative analysis of the HMMS complex mixture of emulsifiers.
13C NMR provided greater spectral dispersion than 1H NMR and this enabled better characterization and quantification of mono- and diesters. Greater sensitivity was achieved with 31P relative to 13C allowing detection of partially esterified glycerols, tocopherol, and free fatty acids.
The fatty acids within the HMMS were shown to be more unsaturated than saturated. Both polyunsaturated fatty acids and monounsaturated fatty acids were detected in the HMMS.
Overall, the authors concluded that 31P NMR spectroscopy represents the most practical and useful methodology for the precise detection and quantification of the components of complex lipid mixtures.
Reference:
Vafaei N, et al. J Am Oil Chem Soc 2020;97:125–133.
