Harnessing oregano residues: Mechanistic insights into enhancing alfalfa silage fermentation

Oregano essential oil (OEO), primarily composed of carvacrol, serves as a significant bactericide and represents a promising alternative to antibiotics for use as feed additives worldwide. However, the extraction of OEO generates substantial solid residues that require proper treatment. We found that residues obtained after the distillation of high-yield carvacrol-type OEO (RDCO) still contain numerous active compounds, including non-volatile components such as flavonoids and phenolic acids, along with volatile compounds like thymoquinone and carvacrol. This study demonstrates that incorporating RDCO into Medicago sativa L. silage fermentation optimizes the microbial community by suppressing undesirable microorganisms (i.e., 18.17-fold reduction in Pseudomonas with 6 % RDCO vs . control) while promoting beneficial probiotics (i.e., 4.26-fold enrichment of Lactobacillus ). Also, 6 % RDCO addition significantly increased lactic acid production by 31 % vs . control. Furthermore, treated silages exhibited elevated levels of volatile and non-volatile secondary metabolites alongside enhanced fermentation quality. Metaproteomic analysis revealed that RDCO promoted lactic acid production by enhancing bacterial glycolysis/gluconeogenesis, pyruvate metabolism, and TCA cycle. This study establishes a scientific foundation for the sustainable utilization of plant essential oil extraction residues and explores new avenues for high-value applications of these industrial by-products, thus emphasizing the valorization and recycling of the waste residues.