LED Light Sources Improved the Essential Oil Components and Antioxidant Activity of Two Genotypes of Lemon Balm (Melissa Officinalis L.)

Abstract

Here we investigated the effect of different LED light sources on the essential oil components and antioxidant activity of Melissa officinalis. Two genotypes of lemon balm (Ilam and Isfahan) were subjected to four artificial light treatments including white, red, blue, red + blue LEDs and greenhouse light as natural lighting. The LED lights significantly increased shoot fresh and dry weights and Leaf number in the two genotypes as compared to greenhouse condition. The results showed that the content and composition of essential oil in two genotypes was variable under different light treatments and the total amount of compounds in Ilam genotype was higher than the other genotype. The results of analysis of the essential oil by GC/MS indicated that the highest amount of monoterpenes in the genotypes was related to citronellal under red + blue LED lamps (15.3 and 17.2% in Ilam and Isfahan genotypes, respectively) but blue, white, and greenhouse condition had the most effect on sesquiterpenes content in both genotypes. Furthermore, the observed variation between the two genotypes in the essentials oil composition was related to the relative percentage of the constituents and not to the appearance or lack of a specific component. Red + blue lighting also caused the highest radical scavenging activity % in both genotypes (80.77 and 82.09% for Ilam and Isfahan genotypes, respectively). Based on principal component analyses (PCA), three main groups were identified regarding genotypes and all light treatments. Overall, results indicated that the essentials oil composition of two genotypes of lemon balm was affected both qualitatively and quantitatively by different LED light sources; hence, LED lights might be used to improve monoterpenes, sesquiterpenes and antioxidant activity in the selected genotypes.