ITS for early-stage spoilage of soybean residue

Soybean residue is byproduct of soybean processing, has been considered a valuable feed ingredient in livestock production. However, its high moisture content makes it highly perishable, leading to nutrient loss, microbial colonization, and mycotoxin contamination, which compromise feed efficiency and animal health. Despite its importance, systematic investigations into the early stages of soybean residue spoilage remain limited. This study characterized SR deterioration during storage (days 0, 1, 3, and 6) using physicochemical analyses, microbial profiling, quantitative PCR, metabolomics, and correlation networks. Rapid declines in soluble carbohydrates, starch, and organic matter were observed, together with reduced pH. Fungal proliferation intensified after day 3, with Fusarium and Candida emerging as dominant taxa. Correspondingly, concentrations of deoxynivalenol (DON) and zearalenone (ZEN) increased significantly. Metabolomic profiling revealed distinct clustering of samples across time points, with day 3 marking a clear inflection point for spoilage. Key metabolic pathways, including amino acid, carbohydrate, and purine metabolism, were enriched. Importantly, guanosine levels rose in parallel with DON accumulation, suggesting its potential as an early biomarker for spoilage risk. In conclusion, soybean residue spoilage becomes evident by day 3, driven by nutrient depletion, fungal succession, and metabolic reprogramming. The identification of guanosine as a biomarker links purine metabolism with toxin biosynthesis and provides a practical tool for early monitoring. These findings improve our understanding of SR deterioration and support the development of strategies to ensure the safe utilization of soybean residue in livestock production.