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Abstract
Groundnut (Arachis hypogaea L.) is a vital food and oilseed crop in Nigeria, contributing significantly to dietary protein and economic livelihoods. However, long-term storage in sealed plastic or glass bottles applicable in a common household and small-scale trader practice creates a microaerobic, high-humidity environment conducive to fungal proliferation and aflatoxin contamination. This study aimed to evaluate the antifungal and antiaflatoxigenic efficacy of a ternary essential oil blend derived from cloves (Syzygium aromaticum), thyme (Thymus vulgaris) and bay leaves (Laurus nobilis) which are all Generally Recognized as Safe (GRAS) botanicals
against fungal isolates from heavily infested groundnut samples. Fungal enumeration on Potato Dextrose Agar revealed a mean contamination level of 1.42 × 10⁷ CFU/g (replicates: 1.38, 1.42,
1.46 × 10⁷ CFU/g), exceeding the International Commission on Microbiological Specifications for Foods (ICMSF) safety threshold (<10⁴ CFU/g) by 1,420-fold. Morphological and microscopic
characterization identified six fungal species, with Aspergillus parasiticus (30.6%), A. flavus (28.2%), and Emericella astellata (18.8%) dominating the mycoflora. Coconut Extract Agar (CEA) under UV 365 nm and Ammonia Vapor Test (AVT) confirmed 88.2% of isolates as aflatoxigenic, indicating high risk of B- and G-group aflatoxin synthesis. The methanol extract of the spice mixture exhibited strong, concentration-dependent antifungal activity in disc diffusion assays, producing inhibition zones of 7.7–23.2 mm across 25–100% concentrations, with maximum efficacy (23.2 mm) against E. astellata at 100%. The essential oil blend demonstrated complete fungicidal action, with minimum inhibitory concentrations (MIC) ranging from 1.0% (E. astellata) to 7.0% (A. parasiticus) and minimum fungicidal concentrations (MFC) from 3.0% to 9.0%. The MFC/MIC ratio (≤4) confirmed fungicidal rather than fungistatic activity. Mechanistically, the blend disrupts fungal cell membrane integrity, inhibits ergosterol biosynthesis, and suppresses aflatoxin pathway genes. The GRAS-compliant essential oil blend presents a promising, safe, and natural antifungal and antiaflatoxigenic agent for groundnut preservation. Future research should focus on in-situ validation and quantitative aflatoxin reduction using high-performance liquid chromatography (HPLC).
against fungal isolates from heavily infested groundnut samples. Fungal enumeration on Potato Dextrose Agar revealed a mean contamination level of 1.42 × 10⁷ CFU/g (replicates: 1.38, 1.42,
1.46 × 10⁷ CFU/g), exceeding the International Commission on Microbiological Specifications for Foods (ICMSF) safety threshold (<10⁴ CFU/g) by 1,420-fold. Morphological and microscopic
characterization identified six fungal species, with Aspergillus parasiticus (30.6%), A. flavus (28.2%), and Emericella astellata (18.8%) dominating the mycoflora. Coconut Extract Agar (CEA) under UV 365 nm and Ammonia Vapor Test (AVT) confirmed 88.2% of isolates as aflatoxigenic, indicating high risk of B- and G-group aflatoxin synthesis. The methanol extract of the spice mixture exhibited strong, concentration-dependent antifungal activity in disc diffusion assays, producing inhibition zones of 7.7–23.2 mm across 25–100% concentrations, with maximum efficacy (23.2 mm) against E. astellata at 100%. The essential oil blend demonstrated complete fungicidal action, with minimum inhibitory concentrations (MIC) ranging from 1.0% (E. astellata) to 7.0% (A. parasiticus) and minimum fungicidal concentrations (MFC) from 3.0% to 9.0%. The MFC/MIC ratio (≤4) confirmed fungicidal rather than fungistatic activity. Mechanistically, the blend disrupts fungal cell membrane integrity, inhibits ergosterol biosynthesis, and suppresses aflatoxin pathway genes. The GRAS-compliant essential oil blend presents a promising, safe, and natural antifungal and antiaflatoxigenic agent for groundnut preservation. Future research should focus on in-situ validation and quantitative aflatoxin reduction using high-performance liquid chromatography (HPLC).
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