Broad-spectrum antimicrobial activity of a citric acid–phenolic formulation in animal feed matrices

Microbial contamination in animal feed undermines livestock safety and storage stability, driving a critical demand for potent natural preservatives. This study investigated the antimicrobial efficacy of Alquermold Natural Plus L (AMNL), a formulation combining citric acid and bioactive monoterpenes, within compound feed and ground corn matrices. AMNL, applied at a dosage of 0.5 L/ton, was evaluated against a commercial benchmark at 2 L/ton. Both treatments were tested against key bacterial pathogens (Escherichia coli, Salmonella Typhimurium, and Pseudomonas aeruginosa) and fungal contaminants (Aspergillus niger, Fusarium oxysporum, and Rhizopus nigricans). Substrates were standardized to a contamination level of 106 CFU/g, with microbial reduction measured at 24 h and 7 days. The results revealed that AMNL consistently achieved greater reductions in bacterial and fungal populations than the competitor (a commercial feed preservative based primarily on organic acids), despite being applied at one-quarter of the inclusion rate. Antimicrobial performance improved over storage duration, particularly against bacterial taxa, while maintaining consistent efficacy across diverse microbial species and feed matrices. Linear mixed-effects modeling confirmed significant main effects for both treatment and time. These findings demonstrate that the formulation combining citric acid and monoterpenes provides effective microbial control, supporting its application as a high-performance natural alternative to conventional synthetic feed preservatives.