Unraveling the Antibacterial Mechanism of Plasma-Activated Lactic Acid against Pseudomonas ludensis by Untargeted Metabolomics

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.

Blue Light for Inactivation of Meatborne Pathogens and Maintaining the Freshness of Beef

ABSTRACT

Beef is rich in various nutrients but easily spoils due to bacterial contamination; thus, a bactericidal method is needed to inactivate meatborne pathogens while maintaining the freshness of beef. The present study was conducted to investigate for the first time the bactericidal effect of blue light (BL) at 415 nm against four meatborne pathogens (methicillin-resistant Staphylococcus aureus, Escherichia coli, Salmonella Typhimurium, and Listeria monocytogenes) both in vitro and inoculated onto the surface of fresh beef. The populations of the four pathogens on the nonirradiated control beef did not change significantly (P > 0.05), whereas a dose-dependent inactivation effect was found for BL-treated beef both in vitro and in vivo. On the beef cuts, BL at 109.44 J/cm2 inactivated 90% of inoculated cells of the tested strains (P < 0.05), and this inactivation effect was sustained during 7 days of cold storage. Insignificant changes in lipid oxidation rate, water holding capacity, and cooking loss were found during storage between the control beef and the beef irradiated at 109.44 J/cm2 at the same time. BL had a minor and nonsignificant effect on surface color and free amino acid concentrations. The pH of the treated beef increased more slowly (P < 0.05) than did that of untreated beef. These results suggest that BL could be a novel bactericide and could help maintain the freshness of beef.

HIGHLIGHTS

Effect of Gaseous Chlorine Dioxide Treatment on the Quality Characteristics of Buckwheat-Based Composite Flour and Storage Stability of Fresh Noodles

In this study, the effects of gaseous chlorine dioxide treatment on the physicochemical properties of buckwheat-based composited flour (buckwheat-wheat-gluten) and shelf-life of fresh buckwheat noodles (FBNs), as well as the textural qualities and sensory properties of noodles were investigated. Chlorine dioxide treatment significantly reduced the total plate count (TPC) and the total flavonoids content in the mixed flour (p < 0.05), but the whiteness, development time and stability time were all increased. During storage, the microbial growth and darkening rate of FBNs made from chlorine dioxide treated buckwheat-based composite flour (CDBF) were delayed significantly, slowing the deterioration and improving storage stability of buckwheat noodles. In addition, chlorine dioxide treatment had no apparent adverse effect on the cooking loss and sensory characteristics during noodle storage. This finding would provide a new concept for the production of “low bacterial buckwheat-based flour” and have important consequences for the application of gaseous chlorine dioxide in food industry.