Postharvest changes in essential oil content and quality of lavender flowers

• The lavender EO content and quality were studied during long term storage.
• A reduction in the EO content at a rate of about 2.56% per year was proved.
• Also the changes in EO quality were observed during long-term storage.
• A degradation and rearrangement of some compounds on the other was detected.

The aim of this study was to analyse both the essential oil (EO) content and quality changes of two Czech Lavandula angustifolia Mill. varieties, ‘Krajová’ and ‘Beta’, in the period between the harvesting and chemical analysis. An eight-year experiment proved that during the long-term storage of dried flowers a gradual reduction in the total content of EO occurs at a rate of about 0.007% per day, which means about 2.56% per year. The content of linalool, terpinen-4-ol, lavandulol, linalyl acetate, α-terpineol, and lavandulyl acetate varied between the varieties. In the case of ‘Krajová’ the value of the correlation coefficient showed a decreasing tendency of terpinen-4-ol, lavandulol, linalyl acetate, and linalool. In the case of the ‘Beta’ variety loss rates for linalyl acetate, lavandulyl acetate, and terpinen-4-ol were found. This can be partly explained by disappearance but also by degradation and rearrangement into other compounds, such as linalool, lavandulool, and α-terpineol, whose content increased. The residual moisture of the air-dried plant material and room temperature are sufficient for the changes in such compounds during long-term storage. Only the differences between the varieties that were tested and growing seasons in terms of the EO content and composition were statistically proven, although it can be assumed that the differences in the EO content and composition between determinations would also be statistically significant in longer-term monitoring. No relationship between the initial EO composition and its loss during storage was found.