Guwahati: That zesty scent from citrus peels may be doing more than invigorating your senses. A new study has found that essential oils derived from citrus peels grown in Northeast India are rich in natural compounds with powerful antimicrobial and antioxidant properties.
Researchers from Tamil Nadu Agricultural University, Coimbatore, and Mizoram University analysed the chemical composition and biological activity of essential oils extracted from five citrus species collected across the northeastern hill states—including Arunachal Pradesh, Meghalaya, Manipur, Nagaland, and Mizoram. Their findings were recently published in ACS Agricultural Science & Technology.
Citrus fruits are among the most important horticultural crops worldwide, with the northeastern region of India recognised for its rich citrus biodiversity. However, peels—often discarded as waste by citrus processing industries—are a treasure trove of health-boosting compounds. Prior studies have shown that citrus peels contain abundant flavonoids and glycosides with anti-inflammatory, anticancer, and antimicrobial effects.
The essential oils are particularly rich in terpene-based compounds, especially D-limonene, a monoterpenoid known for its aromatic, nutritional, and bioactive properties. Using gas chromatography–mass spectrometry (GC-MS), the team confirmed that D-limonene was the dominant compound in all oil samples.
The highest concentration of D-limonene was found in Citrus reticulata from Arunachal Pradesh (84.14%), followed by the same species from Meghalaya (68.67%). In contrast, Citrus macroptera from Lunglei, Mizoram, had the lowest D-limonene content at 25.8%.
Other important compounds—including α-terpineol, β-myrcene, linalool, octanal, nonanal, decanal, and hexadecanoic acid—were common across all samples. Interestingly, citronellal, a typical citrus oil component, was absent in Citrus macroptera.
But the study didn’t stop at chemical profiling. The oils were tested for their antifungal activity against three major crop pathogens:
- Fusarium oxysporum f. sp. cubense (banana wilt)
- Macrophomina phaseolina (root rot)
- Colletotrichum gloeosporioides (fruit rot)
At 1000 ppm, Citrus reticulata oil from Manipur completely inhibited Fusarium, while Citrus macroptera oil from Mizoram inhibited it by 77.31%. Against Macrophomina, Citrus reticulata from Meghalaya showed 100% inhibition, followed by Manipur (96.85%) and Mizoram (92.96%). For Colletotrichum, Citrus macroptera from Mizoram was most effective, with a 98.89% inhibition rate.
The team also assessed the antioxidant potential of the oils using the DPPH method, where a lower IC₅₀ value indicates stronger antioxidant activity. Here, Citrus macroptera stood out again, showing the strongest antioxidant power (IC₅₀: 33.63 µg/mL). In comparison, Citrus reticulata from Meghalaya had the weakest activity (IC₅₀: 50.66 µg/mL).
The IC₅₀ value (short for Inhibitory Concentration 50%) is a commonly used measure in biology and pharmacology to assess how effective a substance is at inhibiting a specific biological or biochemical function.
IC₅₀ is the concentration of a substance (in this case, citrus essential oil) required to inhibit a given biological process, such as free radical activity, by 50%. It’s typically measured in units like µg/mL (micrograms per millilitre).
“D-limonene, a major component in these citrus oils, plays a vital role in antifungal activity by disrupting fungal membranes, inhibiting ergosterol synthesis, and interfering with cell metabolism,” the researchers explained.
They added that citrus essential oils hold strong potential as eco-friendly biopesticides, offering a sustainable alternative to synthetic chemicals. Their efficacy, minimal residue on food, and low toxicity to humans make them ideal for use in agriculture and public health.
The study further suggests that the oils’ antifungal action may be linked to their antioxidant strength, reinforcing their potential role in safeguarding both crops and ecosystems.
So next time you’re about to toss that orange or pomelo peel, think twice. It could be more than kitchen waste—it might be a natural protector with real scientific backing.
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