Grinding-induced chemical shifts in clove (Syzygium aromaticum) essential oil differentially modulate antifungal and antibacterial activity

Abstract

Grinding is a common pretreatment before hydrodistillation of clove (Syzygium aromaticum) buds, but its effect on essential oil quality and bioactivity is not uniformly beneficial. This study compared ground essential oil (GEO) and unground essential oil (UEO) of clove bud for extraction yield, physicochemical properties, chemical composition (GC-MS), and antifungal and antibacterial activity. Grinding significantly increased extraction yield (1.19 ± 0.01% vs. 0.52 ± 0.02%, p < 0.001) and shifted the oil composition, raising the sesquiterpene fraction (6.96% vs. 3.39%) at the expense of phenylpropanoids (92.65% vs. 96.32%), while eugenol remained dominant in both oils (88.09% and 89.82%, respectively). This modest compositional shift produced a target-dependent, rather than uniform, effect on antifungal potency across three complementary assays. On disc diffusion, GEO gave larger inhibition zones against Alternaria sp. and Penicillium sp. II, whereas UEO was more active against Botrytis sp. and Geotrichum sp. UEO reached a low fungicidal concentration (≤ 25 µL/mL) against six of eight fungal species, versus three for GEO. In a volatile-phase (vapor) assay, however, GEO inhibited four species by vapor contact alone, while UEO was active only against Geotrichum sp. Antibacterial potency was unaffected by grinding for all five bacterial strains tested (p > 0.45), and both oils matched or exceeded tetracycline against Bacillus sp. and Pseudomonas sp. These results show that grinding does not uniformly enhance clove essential oil bioactivity: the appropriate processing choice depends on the target organism and the intended mode of application, whether by direct contact or fumigation.