Enhancing rosmarinic acid production and regulating enzyme activity in Melissa officinalis L. using spectrally tunable light-emitting diodes

Melissa officinalis L. (lemon balm) is a renowned medical herb enriched with phenolic compounds, particularly rosmarinic acid (RA) which is known for its antimicrobial and antioxidant activities. This study aimed at improving the medicinal characteristics of M. officinalis by enhancing the production of the total phenolic content (TPC) and RA as well as evaluating the activities of RA-regulatory enzymes, following a series of light treatments, using i) three different spectrally tuned light treatments, ii) white light-emitting diode (LED), and iii) sunlight. Phytochemical analyses revealed that the blue-enriched light treatment (40% red, 35% blue, 15% green and 10% far-red) significantly elevated the TPC, RA, and antioxidant capacity of M. officinalis. Additionally, the application of spectrally tunable LEDs also induced the malondialdehyde level and sugar concentration with minimal effect on the chlorophyll content and antimicrobial activity. Increased activities of RA-regulatory enzymes, namely phenylalanine ammonia-lyase, tyrosine aminotransferase, and hydroxyphenylpyruvate reductase, were associated with RA production. These findings suggest that the elicitation based on spectrally tunable LEDs has promising potential for promoting phenolic compounds production in M. officinalis.

Automated summary

This study aimed to enhance the medicinal characteristics of Melissa officinalis by increasing the production of phenolic compounds, particularly rosmarinic acid (RA), and evaluating the activities of RA-regulatory enzymes using different light treatments. The results showed that a blue-enriched light treatment significantly increased the total phenolic content, RA, and antioxidant capacity of M. officinalis. The application of spectrally tunable LEDs also induced changes in malondialdehyde level and sugar concentration, with minimal effect on chlorophyll content and antimicrobial activity. The findings suggest that spectrally tunable LEDs have the potential to promote phenolic compounds production in M. officinalis.