Annual Phytochemical Variations and Antioxidant Activity within the Aerial Parts of Lavandula angustifolia , an Evergreen Medicinal Plant

Acknowledging the importance of medicinal compounds, flavonoids, and phenolic acids in plants and human health; understanding the best time to harvest plants to get the most potentially therapeutic biological activity; and predicting and controlling the quality of medicinal plants are very useful. The rich chemical composition of medicinal lavender, as well as its antioxidant activity, has led to its wide application in the pharmaceutical, cosmetic, and food industries. In the current research, seasonal differences in phenolic content; the main constituents of essential oil, essential oil yield, and antioxidant activity; and flavonoid content were evaluated. In this investigation, for all the investigated factors, three replications were considered as completely randomized designs. The predominant natural components were α-pinene, camphene, 1,8-cineole, limonene, camphor, borneol, cryptone, isobornyl formate, cumin aldehyde, carvone, caryophyllene oxide, and epi-α-cadinol. The highest rate of 1,8-cineole was seen in summer, while camphor and borneol showed their highest percentages in the cold season. Some of the compounds such as caryophyllene oxide, isobornyl formate, and cumin aldehyde showed their highest amounts in the spring with the activation of some important plant enzymes such as peroxidase. The total content of flavonoids and some phenolic compounds (coumarin and p-coumaric acid) increased when plants received sunlight for a longer time than in the colder to warmer seasons. On the other hand, increases in chlorogenic acid and vanillin were observed in spring. Also, the highest antioxidant activity was observed in lavender, which was accompanied by an increase in the important phenolic composition of rosmarinic acid in the cold season. Generally, this investigation provides beneficial evidence about the most appropriate harvest time for lavender to produce the most favorable constituents for optimization in food, pharmaceutical, and herbal products.