Improving the oxidative stability of poultry fat ethyl esters using clove essential oil (Syzygium aromaticum)

The utilisation of discarded broiler poultry fat for biodiesel production offers a sustainable waste-to-energy pathway; however, its practical application is hindered by poor oxidative stability. In this study, poultry fat ethyl esters (PFEE) were synthesised via base-catalysed transesterification, achieving a gravimetric yield of 90.33 ± 1.12%. GC-MS profiling revealed a high concentration of polyunsaturated ethyl linoleate (20.72%), which likely contributed to the pure PFEE's induction period (IP) being just 2.02 hours. To address this vulnerability, three botanical essential oils were screened as green bio-additives. Clove essential oil (CEO), predominantly composed of eugenol (80.12%), demonstrated the strongest antioxidant response compared to nutmeg and basil oils. Systematic evaluation identified 1.0% v/v CEO as the recommended practical concentration. At this formulation, the IP significantly extended to 21.46 hours—nearly three times the EN 14214 minimum requirement (≥ 8 h)—while keeping kinematic viscosity (4.46 cSt) and acid number (0.33 mg KOH/g) strictly within international standards. This marked improvement in oxidative stability is theoretically attributed to the well-established chain-breaking properties of eugenol, where its phenolic hydroxyl groups act as potent hydrogen donors to neutralize lipid peroxy radicals, followed by the resonance stabilisation of the resulting radicals. Ultimately, this study establishes the CEO as an efficient and sustainable bio-antioxidant for upgrading highly unsaturated waste-derived biofuels.