Turek, C: Investigations into the Stability of Essential Oil

In recent years, essential oils have reached great popularity and their possible applications are numerous. Biosynthesized by a number of aromatic plants, they represent naturally occurring mixtures of a huge variety of secondary metabolites. It is generally known that essential oils are prone to chemical alterations upon aging, triggered by air, light, and heat. Thus, quality monitoring of essential oils during storage to reveal chemical changes is not only mandatory due to sensory reasons but also to ensure pharmacological safety.Still, only little has been known about underlying processes that essential oils may go through after production and systematic approaches investigating the impact of differing extrinsic factors on the stability of essential oils are rare to be found. Furthermore, only a limited number of analytical parameters were hitherto taken into account that, however, have been reported not to fully assess possible changes upon storage. Therefore, an HPLC method combining diode array detection as well as mass spectrometry to comprehensively assess both genuine essential oil volatiles of different chemical classes as well as storage-induced chemical alterations such as the formation of polymeric oxidation products or thermolabile substances was implemented in the course of the present thesis (CHAPTER 1).In addition, a range of suitable physicochemical parameters complementing HPLC was established in the present work (CHAPTER 2) assessing both primary as well as secondary oxidation processes to comprehensively reveal alterations in essential oils. In the course of storage, refractive index, color, peroxide value (POV), pH, conductivity, as well as HPLC analyses were applied on essential oils and individual parameters were discussed with respect to their capability to track aging processes. The hitherto new approach of combined pH and conductivity assessment in essential oils turned out to be an appropriate quality parameter complementing the POV, as