Supplements enhance antioxidant activity and improve the quality of whole-plant corn silage by altering secondary metabolic pathways and phenolic metabolite composition

Whole corn silage (WCS) is susceptible to deterioration during storage. However, suitable supplements can enhance active metabolites, which preserve silage quality and feeding value. This study compared the metabolic responses of WCS treated with Lactobacillus buchneri (LB), plant-derived melatonin (ME), and their combination (LB + ME) by evaluating fermentation quality, antioxidant indices, and active metabolites. Compared with that in the control (CK) treatment (348.43 U/g FW), superoxide dismutase (SOD) activity in the LB treatment significantly (p < 0.05) increased to 536.78 U/g FW. Meanwhile, the catalase activity in the ME treatment reached 34.90 nmol/min/g FW, which was significantly (p < 0.05) higher than that in the CK, LB, and LB + ME treatments. Furthermore, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacities increased to 7.89 and 7.36 μmol Trolox/g DM in the LB and ME treatments, respectively. Similarly, the ferric ion-reducing antioxidant power (FRAP) values increased to 10.50 and 9.30 μmol Trolox/g DM in the LB and ME treatments, respectively. Metabolomics analysis revealed 1449 secondary metabolites in WCS, with LB and ME promoting the synthesis of flavonoids, particularly sinapic acid, 1,2,5,7,8-pentahydroxy-3-methylanthracene-9,10-dione, and 2,4-dihydroxybenzoic acid. A positive correlation was observed between water-soluble carbohydrates, DPPH, FRAP, SOD, chrysoeriol, and kaempferide in LB-treated WCS. In conclusion, the LB treatment exhibited superior antioxidant activities, which ultimately promoted flavonoid synthesis. The findings of this study provide mechanistic insights into the influence of supplements on antioxidant pathways in WCS. The development of WCS additives also provides direction for the optimization of functional additive products.