Effect of precision harvesting on the quality of herbal distillates (Case study of Hyssopus officinalis L. )

​Distillates are one of the most popular consumer products of medicinal plants. High essential oil and low methanol contents have always been considered as two desirable factors by experts in the food and pharmaceutical industries. In order to investigate the effect of harvest height on Hyssop (Hyssopus officinalis L.) distillate quality, an experiment was conducted in a randomized complete block design with three replications. Four harvesting heights of 15, 25, 35 and 45 cm (measured from the highest point of the plant), as well as the remaining stalk, were the treatments in this research. The measured traits were: methanol and essential oil content in the distillates. The results of statistical analysis showed a significant effect of treatments on the studied traits. It can be said that methanol values significantly increased with the harvesting height measured from the top. It varied from 71.64 ± 2.7 mg/l for the height of 15 cm to 219.77 ± 3.52 mg/l for 45 cm. In the remaining stalk, methanol values increased from 142.33 ± 1.34 mg/l for 15 cm height to 393.86±24.65 mg/l for 35 cm height. It should be mentioned that at 45 cm height of cut, there was no remaining stalk. The amount of essential oil in the distillate increased with harvesting height. The findings of this study showed that the harvesting height of 15 cm from the highest part of the plant is recommended for obtaining a higher distillate quality with lower methanol content, and the possibility of increasing the number of harvesting cuts for the production of medicinal and nutritional products.