# Impact of gamma irradiation on lemongrass (Cymbopogon citratus): phytochemical content, antioxidant and antibacterial activity

## TL;DR

Gamma irradiation improves lemongrass essential oil's phytochemical content, antioxidant activity, and antibacterial properties.

## Contribution

Controlled gamma irradiation is shown to enhance the functional quality of lemongrass essential oil without chemical treatment.

## Key findings

- Gamma irradiation increased citral and geraniol content in lemongrass essential oil.
- Irradiation improved antioxidant activity and antibacterial efficacy against S. aureus and P. aeruginosa.
- Moderate doses (10–20 kGy) enriched oxygenated monoterpenes, phenolics, and flavonoids without degrading thermolabile compounds.

## Abstract

Gamma (γ) irradiation is a safe, non-chemical treatment used to decontaminate and enhance the biochemical quality of aromatic and medicinal plants. Cymbopogon citratus (lemongrass) essential oil (CCEO) is dominated by oxygenated monoterpenes such as citral and geraniol, compounds that confer notable antioxidant and antimicrobial activities. This study’s objective was to assess the effects of gamma irradiation on the phytochemical composition, antioxidant activity, and antibacterial efficacy of CCEO.

Fresh lemongrass leaves were hydrodistilled to obtain essential oil (EO) then exposed to γ-irradiation at 0, 5, 10, 15, and 20 kGy. GC‒MS analysis was conducted to assess the essential oil composition. Total phenolic compounds (TPC) and total flavonoid content (TFC) were quantified using Folin–Ciocalteu and AlCl3 colorimetric assays, respectively. Antioxidant activity was assessed by DPPH• radical scavenging. Antibacterial activity was evaluated against Staphylococcus aureus and Pseudomonas aeruginosa via the well-diffusion method. All analyses were performed in triplicate.

GC–MS analysis identified 22 constituents dominated by citral isomers. Citral A (geranial) increased from 38.72 to 40.06 %, citral B (neral) from 31.85 to 33.03 %, α-myrcene from 7.08 to 8.05 %, and geraniol from 4.40 to 5.02 % as irradiation increased to 20 kGy. TPC rose from 92.12 to 103.11 mg GAE/g oil (+11.9 %), and TFC from 109.25 to 208.47 mg QUE/g oil (+90.7 %). Antioxidant capacity improved, with IC₅₀ decreasing from 611.28 to 498.08 µg/mL and DPPH scavenging increased from 70.66 % to 75.15 % (at 1000 µg/mL). Antibacterial efficacy also strengthened: inhibition zones expanded from 10.2 mm to 21.4 mm (+110 %) for S. aureus and from 8.1 mm to 18.9 mm (+134 %) for P. aeruginosa. Moderate irradiation doses (10–20 kGy) produced the greatest enrichment in oxygenated monoterpenes, phenolics, flavonoids, and bioactivity, while avoiding degradation of thermolabile compounds.

Controlled γ-irradiation doses markedly enhanced the compositional and functional quality of CCEO by increasing citral and geraniol content, elevating phenolic and flavonoid contents, and improving antioxidant and antibacterial performance. Optimized irradiation up to 20 kGy represents a practical post-harvest strategy for augmenting the industrial and pharmacological value of CCEO.

γ-Irradiation at 5, 10, 15, and 20 kGy modified Cymbopogon citratus essential oil, increasing citral, geraniol, and β-myrcene levels.

Moderate doses (10-15 kGy) enhanced total phenolic (TPC) and flavonoid (TFC) contents.

Irradiated essential oils showed higher antioxidant activity (lower IC50 and stronger DPPH scavenging).

Improved antibacterial efficacy against Pseudomonas aeruginosa and Staphylococcus aureus.

Controlled γ-irradiation is a safe, green method to enhance the phytochemical quality and functional value of lemongrass essential oil.