Storage-related changes of terpene constituents in caraway (Carum carvi L.) under real-time storage conditions
2021
Bitterling, Hannes | Lorenz, Peter | Vetter, Walter | Kammerer, Dietmar R. | Stintzing, Florian C.
Caraway is a widespread agricultural crop that has been utilized by humans since ancient times. It is known as a kitchen spice, medicinal plant in phytotherapy and, due to its high essential oil content, as a fragrant plant and raw material for terpene production. Limonene and carvone, which in turn are used as precursors for the synthesis of further flavorings and fine chemicals, account for more than 90 % of the essential oil. However, the quality of essential oils can quickly deteriorate due to inadequate storage and by external impacts such as heat, oxygen, and light. In the present study, caraway seeds, caraway essential oil as well as pure standards of limonene and carvone were stored in parallel under real-time conditions at 25 °C and 40 °C to assess the effect of the plant matrix and the natural blend of compounds on essential oil stability. GC and HPLC analyses were used to show that the volatile compounds were well protected in the caraway seeds as no significant changes were determined. In comparison, a remarkable loss of limonene (22.4 %) due to oxidation-induced alterations was observed for the pure substance, while carvone contents remained almost constant over the entire storage period. The decline of limonene (9.2 %) as part of the essential oil was much lower while carvone again remained unchanged. The formation of novel minor compounds such as limonene-1,2-epoxide, carveol, and limonene-1,2-diol was mainly due to limonene downstream oxidation and increased with elevated storage temperatures. Volatile compounds were best protected in the intact plant seeds, and storage of the entire essential oil is preferable compared with isolated terpenes due to higher stability as representatively demonstrated for the major compound limonene.
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