Evaluation of yield and constituent compounds of fresh and dried Lavandula angustifolia L. essential oil in different harvesting times

Background and Objectives: Lavandula angustifolia L. is a perennial and aromatic plant which belongs to Lamiaceae family. The drying process is very expensive, but if it is done correctly, it significantly increases the efficiency and components of the essential oil after harvesting. In large-scale agriculture, L. angustifolia raw materials needs a lot of space and high cost for drying process due to the large volume of material at harvest time. In this case, if it is possible to directly extract the essential oil with the desired quantity and quality from the fresh plant, the production cost will be significantly reduced from the economic point of view. The aim of the current study was to evaluate the performance and quality of essential oil of L. angustifolia in different harvesting times of fresh and dried plants.
Materials and methods: For these goals, aerial parts of L. angustifolia in full flowering stage were collected from selected plants from a 3-year farm located in Saadatshahr city of Fars province. A Factorial experiment as a completely randomized blocks design with three replications and two factors include three different harvesting times (25th of May, 8th of August and 21st of October, 2020) and two types of plant materials (fresh and dry) was performed in the farm. The essential oils of different L. angustifolia samples were extracted by hydro-distillation using Clevenger apparatus and with three replications. The yields were calculated based on dry weight and the oils were analyzed by a combination of GC-FID and GC-MS techniques, to check for chemical variability based on British Pharmacopoeia. At the end of the experiment, data analysis was performed using SAS software (version: 9.4). The means were compared by Duncan's multi-range test.
Results: The results of the present study demonstrated that the interaction effects of harvesting times and plant materials on the essential oil yield was not significant. However, the results of variance analysis of the main compounds identified in the L. angustifolia essential oil showed that the characteristics of linalool, borneol and camphor compounds were significant at the 1% probability level, and the characteristics of the type of plant material on the linalool and linalool acetate compounds were significant at the level of 1%. The probability of 5% was significant on the borneol and camphor compounds at the 1% probability level. The interaction effect of harvest time and type of plant material had a significant effect on the two compounds of linalool and 1,8-cineole at the 1% probability level. Mean comparison of the effect of plant materials in harvest times the main compounds identified in essential oil of L. angustifolia showed that the percentage of linalool composition in the treatment of fresh plant matter and the third harvest time was the highest with an average of 21.63% and the lowest amount in the treatment of dry plant matter and the third harvest time was observed with an average of 7.53%. Also, the highest amount of 1,8-cineole compound was obtained in the treatment of fresh plant material and in the first harvest with an average of 13.90% and the lowest amount of this compound in the treatment of fresh plant material and the second harvest with an average of 4.30%.
Conclusion: The findings of this study showed that due to the very valuable essential oil of L. angustifolia and the world's increasing demand for essential oil, this plant is used in the pharmaceutical, food and cosmetic industries, and according to the research on the efficiency of the L. angustifolia essential oil in different harvest times, the best harvesting time was the Spring harvesting in the full flowering stage.