Qualitative characteristics of hyssop (Hyssopus officinalis L.) under the influence of harvest time and drying methods

Abstract

Hyssop (Hyssopus officinalis L.) is one of the most important medicinal and aromatic crops (MACs) in the pharmaceutical, food and cosmetic industries. It has antioxidant, anticonvulsant, antifungal, antimicrobial, antihemolytic, antiulcer, antispasmodic and several other pharmacological activities. Determining suitable harvest time and most appropriate drying method has an important role in the production of high quality MACs for industry. In this study, aerial parts of hyssop were harvested every three hours over a 12-hour period, from 6:00 AM to 6:00 PM, during full-flowering stage. Subsequently, different drying methods such as shade-drying, freeze-drying, vacuum- and oven-drying (40, 50 and 60 °C) and microwave-drying (100, 300 and 600 W) were employed and the resulting qualitative traits (color, essential oil content and composition) were evaluated. Over time from morning to noon, the amount of essential oil (EO) was found to have increased, while in the afternoon a gradual decrease of EO content was observed. There were no specific trend changes in the EO components related to the passage of time during the day and only the amount of myrtenol was found to have increased gradually from morning to afternoon. With increasing temperature, in all drying methods applied, the amount of browning index was increased. The glandular trichomes were susceptible to drying method and microwave-dried samples at 600 W had defective and cracked trichomes. The highest EO content (1%) resulting from all drying methods was obtained from microwave drying at 100 W while the lowest (0.15%) was observed after microwave drying at 600 W. Increasing the temperature during drying reduced the EO content, which was higher in vacuum-drying treatments than oven-drying. Regarding the main components of EOs, the highest amount of cis-pinocamphone (65.6%) was obtained by microwave drying at 300 W and the lowest (36.7%) by oven-drying at 60 °C. Finally, it can be concluded from this study that the optimum harvest time for hyssop is 12 noon, during full-flowering stage, and that low power microwave drying (100 W), oven-drying at 40 °C and shade-drying were all able to preserve the desired main active ingredients.