Factors that influence the accumulation of antioxidant compounds in aromatic plants

The use of plant producing secondary metabolites as food preservatives is not a new invention but a rediscovered possibility, therefore in the last few years, besides medicinal and aromatic plants, vegetables, fruits and nuts were also analysed testing their possible advantageous effect on human health. The accumulation of phenolic compounds in aromatic plant species is affected by several factors. In accordance with literature data, the climatic conditions (mainly the temperature, the radiation and the amount of the precipitation) and the agrotechnology (time and the phenological phase of the harvesting) can be regarded as main influencing parameters. Based on these findings, the production parameters of a good quality plant material containing high amounts of antioxidant compounds have to be established especially for the pharmaceutical and food industry. In this review, the factors that can influence the production of secondary metabolites in a species recently introduced in the aromatic plant market (Prunella vulgaris L, self-heal), are reported in comparison with garden thyme (Thymus vulgaris L.), a popular and wellknown medicinal plant. Self-heal, from the Lamiaceae plant family, is a plant species accumulating phenolic compounds. It is native to Eurasia and traditionally used in the Chinese and Indian medicine. In the plant extract several active compounds are found possessing antioxidant effect: ursolic acid, oleanolic acid, rosmarinic acid, flavonoids, and antocyans. The summary of the literature data referring to the main compounds and their possible pharmacological effect is discussed in the article. As the extract of this plant is almost taste and odourless, its usage in the food industry seems to have interesting perspectives as natural food preservative; in some commercial products (Rosmol and Rosmol-P) this plant species has already been used as main ingredient. However, the main factors influencing the amount of its active compounds are under-evaluated. The chemical characteristics characteristics of self-heal could be compared to a well-know medicinal and aromatic plant, garden thyme, which is proved to have strong antioxidant properties. Garden thyme, also from the Lamiaceae family, shows one of the strongest antioxidant activity among medicinal plants. Its essential oil (mainly the components thymol and carvacrol) and the non volatile compounds (rosmarinic acid, carnosol, carnosic acid, flavonoids) are both responsible for the radical chain reaction inhibitor and the free radical scavenging effect. Several studies confirmed its strong antioxidant activity. However, similar to other plant species in the Lamiaceae family, it has a characteristic smell and taste, which are less desirable traits for an antioxidant food additive, on the contrary of self-heal.