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Last Update: 01/31/00

Comparison Of Cooking Oils By Direct Thermal Extraction and Purge and Trap GC/MS

INTRODUCTION

Volatile and semi-volatile organic compounds present both in the matrix and the headspace aroma are primarily responsible for the flavor/fragrance qualities of commercial cooking oils. There is a concern in the food industry over the quality as well as the level of residual solvents that may be present in cooking oils due to plant origin, plant maturity, adulteration or dilution of the final product. In determining an oil's plant origin and assessing its overall flavor quality, it would be extremely advantageous to have a reliable and efficient method for the detection, identification and quantification of the volatile organic compounds responsible for the unique flavors and aromas in these oils. Because oils possess highly characteristic aromas due to specific volatile organic components, it can be anticipated that the chemical analysis of the aroma and flavor components of a given oil could give a fingerprint which could be dependent on the fruit or floral source. In previous studies of flavors and aromas in oils and food products, headspace GC techniques have been the methods of choice. However, headspace techniques are limited in their level of detection and identification of many organic volatiles, especially the semi-volatile organics.

More sensitive analytical techniques are needed to profile and identify flavors, fragrances, off-flavors, off-odors and potential contaminants that may be present as flavor and fragrance additives at lower concentrations. The purge and trap (P&T) technique permits the analysis of a wider range of both volatile and semi-volatile organic compounds and is more sensitive by a factor of at least 100 as compared to the static headspace technique. In addition, a new technique entitled Direct Thermal Extraction using a thermal desorption apparatus attached to the injection port of a GC/MS system permits the direct thermal extraction of volatile and semi-volatile organics directly from small sample sizes (mg) without the need for solvent extraction or other sample preparation. The samples are ballistically heated and together with the carrier gas flow through the samples the volatiles are outgassed into the injection port and onto the front of the GC column for subsequent analysis via the GC and/or GC/MS. For this study, cooking oils were analyzed by both the Direct Thermal Extraction and P&T techniques to determine the best suitable technique for possible development of a quality control method for the food industry. The volatile organics present in the oils were quantified using matrix spiked deuterated internal standards.

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