Influence of post-harvesting period on quality of thyme and spearmint essential oils

The quality of essential oils of common thyme (Thymus vulgaris) and spearmint (Mentha spicata) during long storage and following experimental (25 weeks) period were studied. Samples of both plants were hydrodistilled periodically during the experimental period and evaluated for their composition, as well as for antioxidant activity. The quality of the oils was evaluated by analyzing the percentage composition of the constituents, but also by quantification of the major compounds via calibration method using authentic standards. Although the percentage composition did not show any significant changes during the experimental period, results from quantification of the major compounds revealed that the quality of both oils significantly decreases during this period. Consequently, the antioxidant activity of the oils also decreased. It was found that the first 15 - 20 weeks of the post-harvesting period are crucial for the quality of the essential oils. Presented results show that percentage content is not necessarily reliable way of presenting the quality of the essential oil as a crop product that will be used in the food and pharmaceutical industry.

Automated summary

The quality of essential oils of common thyme and spearmint significantly decreases during long storage and following a 25-week experimental period, affecting the antioxidant activity. The first 15-20 weeks post-harvesting are crucial for maintaining the quality of the essential oils. The percentage content is not a reliable indicator of the quality of essential oil as a crop product for the food and pharmaceutical industry.