Unveiling thymol's antifungal action against Aspergillus niger via transcriptome analysis and its role in enhancing strawberry preservation
Aspergillus niger contamination in fruits and cereals threatens food safety, health, and economies, driving demand for eco-friendly antimicrobial solutions. Thymol's broad-spectrum antifungal activity and low toxicity make it an ideal candidate for antifungal agent synthesis. In this study, thymol was selected from six natural antibacterial substances based on its largest inhibition zone diameter (29.77+/-0.25 mm) in solid-phase antifungal test against A. niger. The minimum inhibitory concentration (MIC) of thymol to A. niger was 0.42 mg/mL. In addition, transcriptomic analysis was performed to investigate the cellular and molecular responses of A. niger to thymol treatment. Treatment with 1 MIC significantly altered 6255 genes (3159 up-regulated / 3096 down-regulated). Genes related to ergosterol synthesis, adenosine triphosphate (ATP) production and antioxidant activity were down-regulated, whereas apoptosis-related genes were up-regulated. Combined with comprehensive physiological and biochemical experiments including cell membrane potential measurements, cellular leakage assays, DNA gel electrophoresis, phosphatidylserine (PS) externalization detection, etc., this study indicated that thymol treatment triggers multifaceted cellular responses in A. niger: (1) membrane integrity disruption, (2) ROS accumulation and oxidative stress, (3) ATP depletion, and apoptosis-like cell death. Finally, an antifungal composite film containing thymol nano-emulsion was prepared. It could delay strawberry mold growth by 3 days under controlled conditions (25 deg C, 50% relative humidity). These findings highlight thymol's potential as a natural antifungal agent for developing active packaging to extend strawberry shelf life.