Determination of Flavor and Off Flavor Compounds in Dairy Products using Stir Bar Sorptive Extraction (SBSE) and Thermal Desorption GC/MSD/PFPD


App Note 4/2000

The analysis of flavor compounds in dairy products such as milk, cream, yogurt and cheese as well as their blends with several ingredients usually requires cumbersome sample preparation steps such as liquid/liquid extraction, solid phase extraction or distillation techniques, often with the drawback of organic solvent use. Headspace and purge & trap methods do not use organic solvents, but their analyte range is restricted to volatile compounds and therefore characterize compounds that contribute to the aroma/smell of a sample, not flavor/taste. In addition heating of the sample should be avoided since this would lead to reaction products which dramatically modify the flavor and taste of any dairy product. The sensitivity of solid phase microextraction (SPME) is limited by the small amount of sorptive material that can be coated on the fibers. A new extraction technique, Stir Bar Sorptive Extraction (SBSE), that overcomes the major problems with classical extraction techniques is applied in this paper. With this technique, a small stir bar is coated with polydimethylsiloxane, placed directly in the sample, and stirred for about 1 hour. During this time, analytes are extracted into the PDMS phase, which acts as an immobilized liquid phase. The stir bar is removed, rinsed with distilled water, and placed into a thermal desorption unit. Due to the hydrophobic character of PDMS, a drying step is not necessary. Heating the stir bar releases the extracted compounds into a GC/MS system for sub sequent analysis with very low detection limits (parts per trillion).