Applications of supercritical fluid technologies to the analysis of food components
Calvey, Elizabeth Madigan
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Supercritical fluid (SF) technologies are being investigated extensively by the food industry for a variety of applications. Carbon dioxide in the supercritical state is of particular interest to the food industry due to its extremely low toxicity in comparison with organic solvents. Three applications of chromatography or extraction employing SFs in the analysis of food components and natural products were investigated. These applications related to carbohydrate, lipid, and coumarin derivative analyses. The peracetylated nitrogen derivatives of carbohydrates were analyzed by supercritical fluid chromatography (SFC) with flame ionization detection (FID), Fourier-transform infrared (FT-IR) detection, and mass spectrometry (MS) detection. Although reports in the literature indicated that only one derivatized component was detected under GC conditions, the SFC analysis of peracetylated aldonitrile derivatives of monosaccharides resulted in detection of multiple reaction products. The identification of the peracetylated nitrile and acyclic oxime was accomplished using both SFC/FT-IR and SFC/MS. The spectroscopic data indicated that an additional reaction product was a peracetylated cyclic oxime. The data was not conclusive enough to determine if the structure contained a pyranose or furanose ring. Changes in chemical composition of vegetable oils due to processing were observed employing SFC/FT-IR. Refined soybean oil and soybean oil that was hydrogenated with a NI or a Ni-S catalyst were analyzed. SFC/FT-IR provided an opportunity to determine the extent of unsaturation and isomerization in a single analysis. The C-H deformation of trans R₁HC=CHR₂ groups was observed at 972 cm⁻¹. The double bond in the cis configuration was evident by absorptions above 3000 cm⁻¹l. On-line FT-IR spectra of triacylglycerols and free fatty acids readily revealed conversion to trans isomers in those samples that were hydrogenated with the Ni-S. Quantitation was not possible due to the incomplete resolution of the cis and trans isomers present in the hydrogenated samples. Apparent threshold densities were determined for a series of coumarin derivatives using a supercritical fluid chromatograph with a flame ionization detector. The extraction cell was a LC stainless steel precolumn. Milligram quantities of the model compounds were extracted. Functionality, extraction temperature, and matrix affected the measured threshold densities of the compounds. The addition of two hydroxyl groups onto the coumarin structure caused the compound to be unextractable at 60°C and densities up to 0.90 g/mL. For those compounds that were completely extracted, coumarin, 7-methoxycoumarin, 3-phenylcoumarin, and psoralen, the apparent threshold density increased with increasing melting point. The melting or decomposition points of those compounds that were partially extracted ranged between 200 and 240°C. For those compounds that were not extracted, under the constraints of the experiment, the melting or decomposition points were greater than 240°C. A higher extraction temperature resulted in a lower threshold density. Corn starch was found to be a noninteractive matrix.
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