A new targeted approach of postharvest accumulation of anthocyanin in fragrant leaves of Melissa officinalis L.

Postharvest accumulation of anthocyanin in aromatic herbs is not well studied but holds potential for diverse application. Lemon balm (Melissa officinalis L.)an aromatic herb known for its lemon fragrance is widely used in traditional medicine as well as in herbal tea. M. officinalis is typically propagated by stem cutting. While attempting to induce roots in water from detached leaf bases, temporal changes in leaf colouration from green to red was observed, indicative of anthocyanin accumulation. Quantitative distinction of colouration as well as from the L* a* b* values generated support change of leaf colour from green to red. The detached leaves were observed to retard senescence during the colour-changing phase for up to eight weeks. However, the time-course accumulation of anthocyanin was found to be strictly leaf size dependent; highest accumulation of anthocyanin (1156.72 ± 36.92 µg/g)noted 49 days after postharvest treatment using leaf size of 5 cm. High-performance liquid chromatographic analysis revealed the presence of cyanidin glycosides as the major anthocyanin that accumulate in detached leaves upon postharvest treatment; presence of cyanidin moiety was further confirmed by acid hydrolysis. Degradation of photosynthetic pigments were also observed during the postharvest treatment process. Moreover, the content of citral, the major terpene volatile remained unchanged while enhanced accumulation of the phenolic marker compound rosmarinic acid was observed during the process. These anthocyanic leaves (49 days postharvest treated)showed higher tyrosine and elastase inhibitory activities and enhanced free-radical scavenging capacities as compared with green leaves. This new, yet-so-simple technology for value addition in lemon balm leaves holds promise especially in traditional medicine, colourant and fragrance sectors.