Optimization of Lactic Acid–Fermented Noni Juice as a Potential Functional Feed Additive for Poultry: Enhancement of Bioactive Compound Profiles and Antibacterial Efficacy In vitro

This study aimed to develop and optimize Lactiplantibacillus plantarum–fermented noni juice as a functional feed additive for poultry in vitro. A central composite design combined with response surface methodology was applied to optimize inoculum size, temperature, and fermentation time based on antioxidant activities (ABTS, DPPH, and FRAP), antibacterial activities against key poultry-associated gastrointestinal pathogens commonly implicated in foodborne transmission in poultry systems, including Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Salmonella Typhimurium, and physicochemical properties (total phenolic content, pH, and total titratable acidity). Optimal fermentation conditions were 9 × 10⁸ CFU/mL, 25 °C, and 18 days. The optimized product (OLP–FNJ) exhibited strong antioxidant capacity and high phenolic content. At the minimum inhibitory and bactericidal concentrations of 25% (v/v), OLP–FNJ exhibited broad-spectrum antibacterial activity against all tested pathogens while sparing beneficial L. plantarum. Scanning electron microscopy revealed pathogen membrane disruption and cell lysis. At sub-MIC levels, OLP–FNJ did not inhibit biofilm formation, pigment production, or quorum sensing, suggesting a membrane-targeted antibacterial mechanism rather than anti-virulence modulation. Cytotoxicity assays using Vero cells showed no toxicity up to 25%, and chemical and microbiological analyses supported its safety. Overall, OLP–FNJ represents a safe natural alternative to antibiotic feed additives in poultry production.