Chemical composition, antibacterial activity, and mechanism of action of essential oil from Litsea cubeba against foodborne bacteria

Study on Electrochemical Behaviors of Heat-Treated Escherichia coli and Staphylococcus aureus

Evaluating the bacterial activity effectively is critical to addressing the challenges posed by bacterial infections. Electrochemistry offers significant advantages in accuracy and cost efficiency compared with methods that are more time-consuming or require expensive instrumentation. This study initially established an electrochemical method for detecting bacterial activity using heat treatment as the pretreatment step. Subsequent optimization of the heat treatment and detection conditions further enhanced the method efficiency. The detection results of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) under different heating conditions showed that the peak current values of E. coli and S. aureus were the highest after heating at 50 °C for 15 min. The dynamic changes in the electrochemical signals from the heat-treated bacteria with alteration in heating conditions were indicated to be related to the effects of heating on the external structure and purine metabolism of the bacterial cells. Although heat-treated E. coli and S. aureus exhibited similar peak potentials, different substances were observed to have contributed to these potentials. A positive linear correlation was observed between the peak current and bacterial concentration. Compared to the plate counting method, the electrochemical method detected the activity changes in E. coli and S. aureus from the logarithmic to the stationary phase earlier. The findings support the broad application of electrochemical methods in microbial detection and provide valuable insights into the purine metabolism of heat-stressed bacteria.

Antibacterial Effect of Euryale ferox Seed Shell Polyphenol Extract on Salmonella Typhimurium

This study aimed to evaluate the effects of Euryale ferox Seed Shell Polyphenol Extract (EFSSPE) on a foodborne pathogenic bacterium. EFSSPE showed antimicrobial activity toward Salmonella Typhimurium CICC 22956; the minimum inhibitory concentration of EFSSPE was 1.25 mg/mL, the inhibition curve also reflected the inhibitory effect of EFSSPE on the growth of S. Typhimurium. Detection of alkaline phosphatase outside the cell revealed that EFSSPE treatment damaged the cell wall integrity of S. Typhimurium. EFSSPE also altered the membrane integrity, thereby causing leaching of 260-nm-absorbing material (bacterial proteins and DNA). Moreover, the activities of succinate dehydrogenase and malate dehydrogenase were inhibited by EFSSPE. The hydrophobicity and clustering ability of cells were affected by EFSSPE. Scanning electron microscopy showed that EFSSPE treatment damaged the morphology of the tested bacteria. These results indicate that EFSSPE can destroy the cell wall integrity and alter the permeability of the cell membrane of S. Typhimurium.

Litsea cubeba essential oil: Extraction, chemical composition, antioxidant and antimicrobial properties, and applications in the food industry

Litsea cubeba (Lour.) Pers. (Lauraceae) is a valuable industrial crop that produces essential oil. The essential oil extracted from L. cubeba (LCEO) has broad-spectrum antimicrobial activity and high antioxidant properties, with great potential for increased usage in the food industry. This literature review summarizes the extraction techniques, content and chemical composition, and antioxidant and antimicrobial activities of LCEO, with a focus on its usage in the food industry, which is an area of substantial recent research. The chemical composition of LCEO, which is affected by various factors, plays a key role in determining its bioactivity and usage in food. The potent antimicrobial activity of LCEO against various foodborne pathogens gives it potential for use in food packaging and preservation to extend shelf life. Future research challenges include the elucidation of the role and mechanism of individual chemical components of LCEO in inhibiting specific foodborne microorganisms; cultivar development to produce germplasm that yields essential oils of the desired chemical composition; and the development of commercial products that can be used in the food industry.

Antibacterial activity and mechanism of luteolin isolated from Lophatherum gracile Brongn. against multidrug-resistant Escherichia coli

Infections caused by multidrug-resistant (MDR) bacteria have become a major challenge for global healthcare systems. The search for antibacterial compounds from plants has received increasing attention in the fight against MDR bacteria. As a medicinal and edible plant, Lophatherum gracile Brongn. (L. gracile) has favorable antibacterial effect. However, the main antibacterial active compound and its antimicrobial mechanism are not clear. Here, our study first identified the key active compound from L. gracile as luteolin. Meanwhile, the antibacterial effect of luteolin was detected by using the broth microdilution method and time-kill curve analysis. Luteolin can also cause morphological structure degeneration and content leakage, cell wall/membrane damage, ATP synthesis reduction, and downregulation of mRNA expression levels of sulfonamide and quinolones resistance genes in multidrug-resistant Escherichia coli (MDR E. coli). Furthermore, untargeted UPLC/Q-TOF-MS-based metabolomics analysis of the bacterial metabolites revealed that luteolin significantly changed riboflavin energy metabolism, bacterial chemotaxis cell process and glycerophospholipid metabolism of MDR E. coli. This study suggests that luteolin could be a potential new food additive or preservative for controlling MDR E. coli infection and spread.

Investigation on the inactivation effect and mechanism of Listeria monocytogenes in fresh-cut cucumber during storage by ultrasound combined with sodium hypochlorite

Fresh agricultural products are frequently contaminated with Listeria monocytogenes (L. monocytogenes), which threatens consumer health. The mechanism of the inhibitory effect of ultrasound and sodium hypochlorite (US-NaClO) on L. monocytogenes on fresh-cut cucumber remains poorly understood. Therefore, the bactericidal ability and mechanism of US-NaClO treatment on L. monocytogenes were studied on fresh-cut cucumber during storage using various approaches such as determination of intracellular material leakage, scanning electron microscopy, flow cytometry, and expression analysis of virulence genes. The results showed that the number of L. monocytogenes on fresh-cut cucumber was significantly reduced after ultrasound treatment for 5 min in combined with 75 ppm sodium hypochlorite treatment(P < 0.05). The US-NaClO treatment affected cell morphology, impaired cell membrane integrity, increased cell membrane permeability, and reduced the concentration of K+, inorganic phosphate, ATP, proteins, and DNA in bacterial cells, leading to the inactivation of microorganisms. In addition, the US-NaClO treatment downregulated expression of the virulence genes actA, hly, inlA, mpl, pclA, and plcB, thus decreasing the pathogenicity of bacteria. It can avoid contamination by pathogenic bacteria during the production of fresh-cut cucumber, while providing safety assurance for production.

Emulsions containing composite (clove, oregano, and cinnamon) essential oils: Phase inversion preparation, physicochemical properties and antibacterial mechanism

Natural essential oils (EOs), especially those combining different individual EOs (also termed composite EOs) with enhanced performance, are becoming healthy, market-sought food preservatives/additives. This study aims to provide insights into the challenge regarding EOs processing due to their low solubility and the elusive mechanism under the enhanced bio-reactivity of composite EOs. A unique oil/water interacting network was created by phase-inversion processing, which enhances EO solubilization and emulsification to form composite EO formulations (EOFs) containing ordinary cinnamon, oregano and clove EOs. These EOFs mainly contained cinnamaldehyde, carvacrol and eugenol and exhibited excellent post-storage stability. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability of EOFs (at 15.880 μL/mL) was > 88%, and the Ferric reducing antioxidant power (FRAP) was 1.8 mM FeSO₄·7H₂O. The minimum inhibitory concentration (MIC) of EOFs against E. coli and S. aureus was ∼7.940 μL/mL. The EOFs could cause quick deterioration of bacterial structures, demonstrating high efficacy in bacteria-killing and anti-biofilm formation.

Atmospheric cold plasma: A potential technology to control Shewanella putrefaciens in stored shrimp

This work aimed to investigate the inactivation mechanism of atmospheric cold plasma (ACP) against Shewanella putrefaciens both in PBS and sterile shrimp juice (SSJ). Reductions in cell density, cell viability, and biofilm formation activity were observed after ACP treatment. ACP cyclical treatment (1 min, 5 times) was more efficient than a one-time treatment (5 min, 1 time). After ACP cyclical treatment, the cell counts and cell viability of S. putrefaciens in PBS were decreased by 3.41 log CFU/mL and 85.30 %, respectively. As for SSJ group, the antibacterial efficiency of ACP declined, but the antibacterial effect of ACP cyclical treatment was still stronger than that of ACP one-time treatment. The biofilm formation activity of S. putrefaciens in PBS was almost completely inhibited, while it gradually returned to normal level with the prolonged of storage time for the SSJ counterpart. The rapid decrease in AKP activity after ACP treatment indicated the damage to cell wall integrity, which was also demonstrated by TEM. In addition, cell membrane and DNA damage of the strain also occurred after ACP treatment. The ROS fluorescence intensity in PBS was higher for the one-time treatment group, while the cyclical treatment group exhibited higher and more stable ozone levels. It was also detected that the total nitric oxide concentration in bacterial suspension depended on the dose of ACP treatment time. ACP treatment (35 kV) for 5 min, especially cyclical treatment, displayed its antibacterial properties on packaged shrimp contaminated with high concentration of S. putrefaciens. ACP cyclical treatment reduced surface bacterial counts of whole shrimps by 0.52 log CFU/mL, while ACP one-time treatment only achieved a decrease of 0.18 log CFU/mL. Therefore, ACP treatment could be considered as a potential alternative to enhance microbial control in food processing.

Antibacterial Pattern of Rosa roxburghii Tratt Pomace Crude Extract Against Staphylococcus aureus and Its Application in Preservation of Cooked Beef

Staphylococcus aureus is a common foodborne pathogen and spoilage bacterium in meat products. To develop a natural preservative for meat products, this study revealed the antibacterial activity and mechanism of Rosa roxburghii Tratt pomace crude extract (RRPCE) against S. aureus, and applied RRPCE to the preservation of cooked beef. The diameter of inhibition zone, minimum inhibitory concentration (MIC), and minimum bactericide concentration of RRPCE against S. aureus were 15.85 ± 0.35 to 16.21 ± 0.29 mm, 1.5 mg/mL, and 3 mg/mL, respectively. The growth curve of S. aureus was completely stalled by treatment with RRPCE at 2 MIC. RRPCE results in the decrease of intracellular adenosine 5'-triphosphate (ATP) content, depolarization of cell membrane, leakage of cell fluid including nucleic acid and protein, and destruction of cell membrane integrity and cell morphology. During storage, RRPCE significantly reduced S. aureus viable counts, pH, and total volatile basic nitrogen of cooked beef compared with untreated samples (p < 0.05). In addition, RRPCE could significantly increase the redness (a*) value, decrease lightness (L*) and yellowness (b*) values, and slow down the color change of cooked beef (p < 0.05). These findings suggest that RRPCE can effectively inhibit S. aureus, and has the potential as a natural preservative for the preservation of cooked beef.

Bioassay-Guided Isolation and Identification of Antibacterial Components against Escherichia coli from Industrial Hemp Leaves

Industrial hemp leaves have raised much interest in nutraceuticals and functional foods areas. To expand its application ranges, the antibacterial activities of industrial hemp leaf extract on Escherichia coli, Staphylococcus aureus, and Bacillus cereus were evaluated and the active components were screened. As a result, the industrial hemp leaf extract was found to have strong bacteriostatic effects on E. coli and S. aureus. Bioassay-guided fractionation and isolation from fractions active against E. coli were conducted. Two compounds, cannabidivarinic acid and cannabidiolic acid, were firstly recognized by analytical HPLC by comparing the retention times and UV spectra with standards and later isolated using preparative HPLC. Moreover, the antibacterial mechanisms of cannabidivarinic acid and cannabidiolic acid were investigated by testing the alkaline phosphatase activity, β-galactosidase activity, conductivity, proteins leakage, nucleic acid leakage, and scanning electron microscope observation. The results demonstrated that cannabidivarinic acid and cannabidiolic acid could destroy the cell wall and membrane of E. coli, resulting in the inhibition of enzyme activity and leakage of contents. They could damage the bacteria cell envelope as well. Presented results pointed out cannabidivarinic acid and cannabidiolic acid as promising natural bacteriostatic agents for the food, pharmaceutical, and cosmetic industry.

Microbiological Quality of Deer Meat Treated with Essential Oil Litsea cubeba

Simple Summary

Consumers are increasingly turning to healthier and less environmentally harmful diet alternatives. Game is an ideal food from this point of view because it represents meat with a high protein content, low fat content, a favourable composition of fatty acids and minerals. Various types of packaging are often used to extend the shelf life of meats. Packaging can be combined with natural antimicrobials, such as various plant extracts and essential oils, for better effectiveness. Little is known about the microbial quality and preservation of deer meat. In the present study, deer meat was treated with essential oil from Litsea cubeba 0.5 and 1.0% concentration in rapeseed oil combined with aerobic and vacuum packaging. The meat was evaluated for microbiological quality (counts and microbiota identification) for 20 days under refrigerated storage. Our result show that Litsea cubeba essential oil is an effective natural agent against deer meat spoilage bacteria.

Abstract

The present study aimed to evaluate deer meat microbiological quality when treated with essential oil (EO) from Litsea cubeba (dissolved in rapeseed oil at concentrations 0.5 and 1%), in combination with vacuum packaging during 20 days of storage of meat at 4 °C. Total viable counts (TVC), coliforms bacteria (CB), lactic acid bacteria (LAB) and Pseudomonas spp. were analysed at day 0, 1, 5, 10, 15 and 20. MALDI-TOF MS Biotyper technology was applied to identify microorganisms isolated from meat. The highest number of TVC at the end of the experiment was 5.50 log CFU/g in the aerobically packaged control group and the lowest number of TVC was 5.17 log CFU/g in the samples treated with 1.0% Litsea cubeba EO. CB were not detected in the samples treated with 1.0% Litsea cubeba EO during the entire storage period. Bacteria of the genus Pseudomonas were detected only in the aerobically and vacuum packaged control group. The highest number of LAB was 2.06 log CFU/g in the aerobic control group, and the lowest number of LAB was 2.01 log CFU/g in the samples treated with 1.0% Litsea cubeba EO on day 20. The most frequently isolated bacteria from deer meat were Pseudomonas ludensis, Pseudomonas corrugata, Pseudomonas fragi, Bacillus cereus, Staphylococcus epidermidis and Sphingomonas leidyi.

Role of Litsea cubeba Essential Oil in Agricultural Products Safety: Antioxidant and Antimicrobial Applications

The essential oil from Litsea cubeba (LCEO) has good antioxidant, antimicrobial, anti-insect properties, which gives it the potential for use as a natural additive to food resources and food products in order to prevent spoilage and extend shelf life. In this study the biological activity related to food preservation was observed. The main volatile organic compounds were geranial (39.4%), neral (29.5%), and limonene (14.3%). Antioxidant activity was 30.9%, which was equal to 167.94 µg of Trolox per mL of sample. Antimicrobial activity showed the strongest inhibition against Serratia marcescens by disk diffusion method and minimum inhibitory concentrations MIC 50 and MIC 90 were the lowest for Micrococcus luteus with values 1.46 and 3.52 µL/mL, respectively. Antimicrobial activity of the LCEO vapor phase showed strong inhibition of microorganisms on apples, pears, potatoes, and kohlrabies. Over 50% of gram-positive and gram-negative bacteria and yeasts were inhibited by a concentration of 500 µL/mL. The inhibition of microorganisms was concentration dependent. Anti-insect activity was also strong, with 100% lethality of Pyrrhocoris apterus at a concentration of 25%. These results suggest that LCEO could be potentially used as a food preservative.

Evaluation of antibiotic combination of Litsea cubeba essential oil on Vibrio parahaemolyticus inhibition mechanism and anti-biofilm ability

Vibrio parahaemolyticus (V. parahaemolyticus) is a common pathogen in seafood. The use of antibiotics is a primary tool to prevent and control V. parahaemolyticus in the aquaculture industry. However, V. parahaemolyticus combats the damage caused by antibiotics by forming biofilms under certain conditions. In this study, we analyzed the antibacterial effect and the characteristics of V. parahaemolyticus by experimentally determining the minimum inhibitory concentration (MIC) and the fractional inhibitory concentration index (FICI) values of a combination of the Litsea cubeba essential oil (LCEO) and several commonly used V. parahaemolyticus antibiotics. The bactericidal effect of the essential oil alone and essential oil in combination with the antibiotics were evaluated with time-kill curves. The damage to cell membranes and cell walls were assessed by measuring the content of macromolecules and alkaline phosphatase (AKP) released into the supernatant using V. parahaemolyticus ATCC17802 as the experimental strain. The membrane structure was observed by transmission electron microscopy. The results showed that the MIC value of the LCEO was 1,024 μg/mL, and the LCEO FICI values in combination with tetracycline or oxytetracycline hydrochloride was 0.3125 and 0.75, respectively, indicating synergistic and additive effects. Moreover, LCEO inhibited the growth and promoted the removal of biofilms by reducing the content of hydrophobic and extracellular polysaccharides on the cell surface. This study provides a reference for studying the antibacterial activity of LCEO and the combination of antibiotics to prevent and control the formation of biofilms by V. parahaemolyticus.

Antibacterial Mode of Eucommia ulmoides Male Flower Extract Against Staphylococcus aureus and Its Application as a Natural Preservative in Cooked Beef

The research was conducted to elucidate the antibacterial performance and mode of action of Eucommia ulmoides male flower extract (EUMFE) against Staphylococcus aureus and its application as a natural preservative in cooked beef. The antibacterial activity was evaluated by determining the diameter of inhibition zone (DIZ), minimum inhibitory concentration (MIC), and minimum bactericide concentration (MBC). The changes in membrane potential, contents of bacterial DNA and protein, integrity and permeability of the cell membrane, and cell morphology were analyzed to reveal the possible mode of action. The effect of EUMFE on the counts of S. aureus, pH, color, total volatile basic nitrogen (TVB-N), and thiobarbituric acid reactive substances (TBARS) of the cooked beef stored at 4°C for 9 days were studied. The results showed that the DIZ, MIC, and MBC of EUMFE against S. aureus were 12.58 ± 0.23 mm, 40 mg/mL, and 80 mg/mL, respectively. The mode of action of EUMFE against S. aureus included hyperpolarization of cell membrane, decrease in bacterial DNA and protein contents, destruction of cell membrane integrity, increase in cell membrane permeability, and damage of cell morphology. After treatments with EUMFE, the growth of S. aureus and lipid oxidation in cooked beef were significantly inhibited (P < 0.05). The pH and TVB-N values of cooked beef treated with EUMFE were significantly reduced as compared to control group (P < 0.05). The color of cooked beef samples containing EUMFE showed decreased L* and b* values, and increased a* and ΔE* values. Therefore, our findings showed that EUMFE had a good antibacterial effect on S. aureus, and provided a theoretical basis for the application of EUMFE as a natural preservative in the preservation of cooked beef.