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Abstract
Flowers of Murraya paniculata were assessed for production of phenolic secondary metabolites and were found to yield temporally variable concentrations of total phenolics and flavonoids due to enzymatic regulation by L-phenylalanine ammonia lyase. Maximum yield of phenolics was obtained from partly open flowers, with esterified hydroxycinnamic acids (mainly ferulic acid) forming the major component. Scopoletin-a coumarin product of ferulic acid - was isolated consistently from senescent flowers by High Performance Liquid Chromatography (HPLC). Approximately 200 mg of fresh floral tissue extracted with one millilitre solvent (methanol:water :: 30:70) yielded up to 1.6 mg of ferulic acid and 40 μg of scopoletin from partly open (at 18:00 h) and senescent (at 06:00 h) blooms respectively. Along with other hydroxycinnamic acid and coumarin components of M. paniculata flowers detected by HPLC, o-coumaric acid and isoauraptene were identified by Gas Chromatography-Mass Spectrometry. Various free-radical scavenging assays revealed the ferulic acid fraction to have stronger antioxidant activities than the scopoletin fraction, but no antibiotic activity was detected for ferulic acid. Total antioxidant capacities of ferulic acid and scopoletin fractions were estimated to be 9% and 7.8% of that of ascorbic acid standard, respectively. Scopoletin fraction exhibited Minimum Inhibitory Concentrations at 0.585 mg.mL-1 against Bacillus subtilis and 1.372 mg.mL-1 against Escherichia coli. The high concentrations of these bioactive phenylpropanoids in such a common flower species presents potential application in low-risk crop protection and plant-based nutraceuticals.