An Improved Silver Ion HPLC Combined with Capillary Gas Chromatography of cis/trans Fatty Acids in Alimentary Fats and Human Milk Fat

A convenient route to mono-trans polyunsaturated free fatty acids

Trans unsaturated fatty acids in humans may be originated both from dietary supplementation and from an endogenous free-radical-catalyzed cis−trans isomerization of fatty acid residues in naturally occurring cis lipids. The latter process affords geometrical isomers and the polyunsaturated fatty acid mono-trans isomers were demonstrated to be connected with stress conditions in living organisms. Synthesis of mono-trans polyunsaturated fatty acid is useful for analytical and biological research, and in this case, the availability of free fatty acids is needed as well as the possibility of mg scale of the synthetic protocol. Herein, we report a simple synthetic route to mono-trans isomers of arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid, which includes thiyl radical-catalyzed isomerization reaction of polyunsaturated fatty acid methyl esters and fraction isolation of mono-trans mixture isomers followed by optimization of hydrolysis condition to free fatty acids and purification of each mono-trans polyunsaturated fatty acid. Our approach to mono-trans polyunsaturated fatty acids as free acids can reach the mg scale, thus fostering more applications to biochemical and biological studies.

trans Fatty Acids in Polish Pastry

HIGHLIGHTS

A multichannel Au nanosensor for visual and pattern inspection of fatty acids

Fatty acids (FAs) are important dietary sources of fuel for animals and structural components for cells. The number, position and configuration of olefins in the alkyl chains play important roles in the impacts of FAs on human health. Currently, structural profiling of FAs in edible oils and fats is an important issue in nutrition industries and food safety. Due to the lack of distinct functional groups, it is extremely difficult to discriminate FAs with structural differences by facile and in situ sensing methods. A few chemosensors have been developed for shape selective sensing of FAs, but their capability and performance were still limited. Herein, for the first time, we proposed a multichannel Au nanosensor for visual and pattern-generating inspection of FAs based on the highly selective binding ability of Ag⁺ to olefinic bonds and Ag⁺ regulable color variation of Au nanoparticles. As a result, the nanosensor showed good selectivity for five FAs with subtle structural difference as low as 5 nM. By further deriving three channel signals in respect of color and color depth, a signature-like signal pattern could be generated by principal component analysis for each FA and even different FA mixtures such as edible oils. Hence, structural variation of FAs in edible hot pot oils with heat treatment was successfully monitored by this Au nanosensor over time. This sensor holds great promise in point-of-care inspection of edible oils and fats.

Silver nanoparticles-coated monolithic column for in-tube solid-phase microextraction of monounsaturated fatty acid methyl esters

Based on our developed sodium hyaluronate-functionalized urea-formaldehyde (HA-UF) monolith, a silver nanoparticles-coated monolithic column has been fabricated via the interaction between silver nanoparticles (Ag NPs) and HA. The successful coating of Ag NPs on the parent monolith was proven by SEM, EDAX, UV-vis spectrum and XPS. Nitrogen adsorption desorption isotherms and Barret-Joyner-Halenda (BJH) pore size distributions of the parent and resultant monolith were also performed. Due to the Ag⁺-like affinity interaction caused by the contact of unsaturated compounds and Ag NPs, the Ag NPs-coated monolith showed satisfactory extraction efficiency towards these compounds, and was applied for in-tube solid-phase microextraction (SPME) of monounsaturated fatty acid methyl esters (MUFAMEs). Several factors for in-tube SPME, such as ACN percentage in the sampling solution, elution volume, sampling and elution flow rate, were investigated with respect to the extraction efficiency of model MUFAMEs. Under the optimized SPME conditions, a simple in tube SPME-Ag⁺-HPLC method for detection of model MUFAMEs has been proposed, the limits of detection (LODs) were less than 5.2 μg/kg, and the recoveries of spiked French fry samples were ranged from 86.6% to 96.1% with relative standard deviations (RSDs) less than 5.2%. This study provided an Ag NPs-coated monolith with good reproducibility and repeatable extraction performance, and developed an efficient method for in-tube SPME of MUFAMEs in practical food samples.

Test Paper for Colorimetric Inspection of Fatty Acids and Edible Oils

Fatty acids (FAs) are of interest to the areas of food science and medicine because they are important dietary sources of fuel for animals and play important roles in many biological processes. The health effects of FAs are different due to the diversity of olefinic bonds in the alkyl chains including number, position and configuration. However, the discrimination of FAs is difficult from a chemical sensing perspective due to the lack of diversity in terms of functional groups. Until now, only a few chemosensors have been developed for selective sensing of FAs based on their overall shape, however they are still limited in discrimination of FAs with subtle structural differences, moreover, they cannot be used for rapid and in situ inspections. Herein, for the first time, we designed a test paper for in situ colorimetric inspection for FAs based on the combination of the highly selective binding of Ag⁺ to olefinic bonds and Ag⁺ mediated color variation of 3,3′,5,5′,-tetramethylbenzidine. As a result, the sensor exhibited high sensitivity and good selectivity for five FAs with subtle structural differences. Furthermore, our method described herein was successfully applied to monitor the structural variations of FAs and quality changes in mixture edible hot pot oils with heat treatment in time course. Hence, the test paper presented herein holds great potential in the inspection of fats and edible oils in food industries.