Fresh puffer fish (Takifugu obscurus) are susceptible to microbial contamination and have a very short shelf-life of chilled storage. Hence, this study aimed to evaluate the effects of plasma-activated lactic acid (PALA) on microbiota composition and quality attributes of puffer fish fillets during chilled storage. The results showed that PALA treatment effectively reduced the growth of bacteria and attenuated changes in physicochemical indicators (total volatile basic nitrogen, pH value, K value, and biogenic amines) of puffer fish fillets. Additionally, insignificant changes were observed in lipid oxidation during the first 8 days (p > 0.05). Illumina-MiSeq high-throughput sequencing revealed that PALA effectively inhibited the growth of Pseudomonas in puffer fish fillets and maintained the diverse characteristics of the microbial community. In combination with sensory analysis, PALA extended the shelf life of puffer fish fillets for 4 days, suggesting that PALA could be considered a potential fish fillet preservation method.
Plasma-activated liquid is a novel non-thermal antibacterial agent against a wide spectrum of foodborne bacteria, yet fewer studies focused on its disinfection of meat spoilage bacteria. In this study, the antibacterial properties of plasma-activated lactic acid (PALA) on Pseudomonas lundensis, isolated and identified from spoilage beef, were investigated. A plasma jet was used to treat lactic acid (0.05-0.20%) for 60-120 s. The results presented that the 0.2% LA solution treated with plasma for 120 s caused a 5.64 log reduction. Additionally, the surface morphology, membrane integrity and permeability were altered slightly and verified by scanning electron microscopy, double staining of SYTO-9 and propidium iodide, and a K+ test kit. The intracellular organization of the cells, observed by transmission electron microscopy, was damaged significantly. Increased intracellular reactive oxygen species (ROS) levels exceeded the antioxidant ability of glutathione (GSH), leading to a reduction in the activity of malate dehydrogenase (MDH), succinic dehydrogenase (SDH) and intracellular ATP levels. Metabolomics analysis indicated that the energy and synthesis of essential components, such as DNA and amino acid-related metabolic pathways, were disturbed. In conclusion, this research established a theoretical basis for the use of PALA in refrigerated beef preservation by shedding light on the bacteriostatic effect of PALA against Pseudomonas lundensis.
Fungal contamination imposes threats to agriculture and food production and human health. A method to safely and effectively restrict fungal contamination is still needed. Here, we report the effect and mode of action of ( E)-2-hexenal, one of the green leaf volatiles (GLVs), on the spore germination of Aspergillus flavus, which can contaminate a variety of crops. The EC50 value, minimum inhibitory concentration (MIC), and minimum fungicidal concentration (MFC) of ( E)-2-hexenal were 0.26, 1.0, and 4.0 μL/mL, respectively. As observed by scanning electron microscopy (SEM), the surface morphology of A. flavus spores did not change after treatment with the MIC of ( E)-2-hexenal, but the spores were shrunken and depressed upon treatment with the MFC of ( E)-2-hexenal. The MIC and MFC of ( E)-2-hexenal induced evident phosphatidylserine (PS) externalization of A. flavus spores as detected by double staining with Annexin V-FITC and propidium iodide, indicating that early apoptosis was potentially induced. Furthermore, sublethal doses of ( E)-2-hexenal disturbed pyruvate metabolism and reduced the intracellular soluble protein content of A. flavus spores during the early stage of germination, and MIC treatment decreased acetyl-CoA and ATP contents by 65.7 ± 3.7% and 53.9 ± 4.0% ( P < 0.05), respectively. Additionally, the activity of mitochondrial dehydrogenases was dramatically inhibited by 23.8 ± 2.2% ( P < 0.05) at the MIC of ( E)-2-hexenal. Therefore, the disruption of mitochondrial energy metabolism and the induction of early apoptosis are involved in the mechanism of action of ( E)-2-hexenal against A. flavus spore germination.
Salmonella enterica serovar Enteritidis (S. Enteritidis) is one of the most important causes of foodborne illness in the food industry. In this work, plasma-activated water (PAW) generated from the plasma jet was employed to reduce S. Enteritidis contamination. The antibacterial mechanism of PAW was revealed from biological changes, molecular docking, and transcriptomics. Results revealed that the addition of lactic acid could improve the antibacterial activity and efficiency of PAW, and confirmed the existence and antibacterial activity of free radicals (OH, 1O2, and NO) in PAW. Meanwhile, PAW treatment caused damage to characteristic functional groups of biomolecules, and led to the oxidation of lipids and degradation of DNA. Molecular docking results further suggested that the reactive species could interact with amino acid residues around key binding sites through hydrogen bonding, affecting the stability of structures. Furthermore, the transcriptomics results indicated that PAW is primarily active on bacterial proteins and to a lesser extent on membrane lipids and DNA. Overall, the action mechanism of PAW on biomacromolecules is comprehensively analyzed in this work, and it provides a theoretical basis for the broad application of plasma technology.
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