Antifungal mechanisms of phenyllactic acid against Mucor racemosus: Insights from spore growth suppression, and proteomic analysis

Mucor, a common mold, is a major cause of post-harvest spoilage in sweet cherries, leading to significant economic losses. While previous studies have demonstrated that phenyllactic acid (PLA) exhibits potent antifungal activity against Mucor, its underlying mechanism remains unclear. Here, we probed into the efficacy of PLA in inhibiting Mucor spore growth and explored its mechanisms of action. PLA treatment suppressed Mucor spore growth in a dose-dependent manner, with a minimum inhibitory concentration of 12 mmol/L. Morphological analysis revealed that PLA caused nuclear chromatin condensation, DNA fragmentation, and severe ultrastructural damage, including cell swelling, vacuolization, and separation of the cell wall from the membrane. Additionally, results of flow cytometry showed that PLA induced phosphatidylserine externalization, mitochondrial membrane potential depolarization, and intracellular reactive oxygen species accumulation in Mucor spore cells. Tandem Mass Tag (TMT)-based proteomic analysis identified 1248 differentially expressed proteins (DEPs; 616 upregulated and 632 downregulated) in Mucor spores treated with 24 mmol/L PLA, compared to the untreated control (p < 0.05). Bioinformatics analysis revealed that these DEPs were primarily involved in oxidative phosphorylation, glycolysis, the citrate cycle, and the biosynthesis and metabolism of carbon and amino acids. Overall, these findings elucidate the antifungal mechanisms of PLA against Mucor spores and provide valuable insights into the potential application of PLA in food preservation.