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To achieve the control of foodborne pathogenic bacteria Clostridium perfringens by non-thermal technology, curcumin was used as the photosensitizer to explore its inhibitory mechanism on C. perfringens. The bactericidal effect of different curcumin concentrations on C. perfringens was investigated. The cell morphology after curcumin treatment was investigated through scan electron microscopy. The integrity of the cell membrane was analyzed by confocal laser scanning microscope and leakage of extracellular macromolecules. The oxidative damage of C. perfringens was determined by ROS analysis. The results indicated that curcumin showed a significantly (P

To investigate the effects of different packaging methods on microbial composition of chilled chicken during storage, the microbial diversity was analyzed by Illumina MiSeq high-throughput sequencing. The results showed that the modified atmosphere packaging (MAP), the vacuum packaging (VP) and the nitrogen-filled packaging (N2) could significantly reduce the number of microorganisms and volatile base nitrogen during refrigeration at 4 °C compared with the pallet packed (PP) group. High-throughput sequencing showed that the bacterial species richness of chilled chicken was high in the early stage of storage. The dominant bacteria of chilled chickens in PP group at the later stage of storage were Pseudomonas, Brochothrix, Acinetobacter and Shewanella. It indicated that they could tolerate lower temperatures. Compared with the PP group, the abundance of Pseudomonas and Acinetobacter in MAP group decreased by 14.8% and 9.2%, respectively, while nitrogen-filled packaging reduced the abundance of Acinetobacter and Shewanella. by 9.6% and 7.4%, respectively. The abundance of Acinetobacter and Brochothrix decreased significantly by 8% and 5.6% after vacuum packaging. Different packaging methods could have a greater impact on the flora in chilled chicken meat. All three types of packaging could inhibit the growth of Acinetobacter and MAP had a better inhibitory effect on Pseudomonas, while nitrogen-filled packaging and vacuum packaging had a better inhibitory effect on Shewanella and Brochothrix. This study also provides a theoretical basis for the future packaging methods used in chilled chicken meat.

The inhibitory and bactericidal activities of thyme oil against the foodborne multiple antibiotics-resistant Enterococcus faecalis biofilm were evaluated in this study. Gas chromatography-mass spectrometry revealed that more than 70% of the composition of thyme oil is thymol. Crystal violet staining assay showed that 128 and 256 μg/mL thyme oil significantly inhibited the biofilm formation of E. faecalis. The cell adherence of E. faecalis, as shown by its swimming and swarming motilities, was reduced by thyme oil. The exopolysaccharide (EPS) quantification assay showed that thyme oil inhibited the EPS synthesis in E. faecalis biofilms. The 3D-view observations through confocal laser scanning and scanning electron microscopy suggested that cell adherence and biofilm thickness were decreased in thyme oil–treated biofilms. Quantitative real-time analyses showed that the transcription of ebp and epa gene clusters, which were related to cell mobility and EPS production, was inhibited by thyme oil. Thus, thyme oil effectively inhibited the biofilm formation of E. faecalis by affecting cell adherence and EPS synthesis. Furthermore, 2,048 and 4,096 μg/mL thyme oil can effectively inactivate E. faecalis population in the mature E. faecalis biofilms by 5.75 and 7.20 log CFU/mL, respectively, after 30 min of treatment. Thus, thyme oil at different concentrations can be used as an effective antibiofilm or germicidal agent to control E. faecalis biofilms.

This study aimed to investigate the mechanism of different treatments, namely, ultrasound (US), chlorogenic acid (CA), and ultrasound combined with chlorogenic acid (US plus CA) on the inactivation of Staphylococcus aureus planktonic and biofilm cells. Results showed that the combined treatment of US and CA exhibited remarkable synergistic antibacterial and antibiofilm effects. Scanning electron microscopy images indicated that the combined treatment of US and CA caused the most serious damage to the cell morphology. Confocal laser scanning microscopy images revealed that the combined treatment led to sharp increase and severe damage to the permeability of the cell membrane, causing the release of ATP and nucleic acids and decreasing the exopolysaccharide contents in S. aureus biofilm. Finally, the combined treatment of US plus 1% CA for 60 min inactivated S. aureus cells by 1.13 lg CFU/g on mutton. Thus, the combined treatment of US and CA had synergistic effect against S. aureus under planktonic, biofilm, and food systems.

Pseudomonas aeruginosa is one of the foodborne pathogenic bacteria that greatly threatens human health. An ultrasensitive technology for P. aeruginosa detection is urgently demanded. Herein, based on the mechanism of aptamer-specific recognition, an electrochemical-colorimetric dual-mode ultrasensitive sensing strategy for P. aeruginosa is proposed. The vertices of DNA tetrahedral nanoprobes (DTNPs), that immobilized on the gold electrode were modified with P. aeruginosa aptamers. Furthermore, the G-quadruplex, which was conjugated with a P. aeruginosa aptamer, was synthesized via rolling circle amplification (RCA). Once P. aeruginosa is captured, a hemin/G-quadruplex, which possesses peroxidase-mimicking activity, will separate from the P. aeruginosa aptamer. Then, the exfoliated hemin/G-quadruplexes are collected for oxidation of the 3,3′,5′,5′-tetramethylbenzidine for colorimetric sensing. In the electrochemical mode, the hemin/G-quadruplex that is still bound to the aptamer catalyzes polyaniline (PANI) deposition and leads to a measurable electrochemical signal. The colorimetric and electrochemical channels demonstrated a good forward and reverse linear response for P. aeruginosa within the range of 1–108 CFU mL−1, respectively. Overall, compared with a traditional single-mode sensor for P. aeruginosa, the proposed dual-mode sensor featuring self-calibration not only avoids false positive results but also improves accuracy and sensitivity. Furthermore, the consistency of the electrochemical/colorimetric assay was verified in practical meat samples and showed great potential for applications in bioanalysis.

Spoilage bacteria play a remarkable role in the spoilage of chilled chicken. In this paper, a total of 42 isolates belonging to 16 species of four genera were isolated from chilled chicken and displayed different characterizations of psychrotrophic spoilage. Six isolates of J7, J8, Q20, Q23, R1, and R9 with differences in proteolytic capabilities were further characterized for in situ spoilage potential evaluation. Pseudomonas lundensis J8 exhibited the strongest spoilage potential in situ, displaying a fast growth rate, increased pH velocity, high total volatile basic nitrogen, and high peptide content in the chicken samples. The volatile flavor analysis of chicken samples via electronic nose indicated that the content of characteristic odors representing spoilage, including sulfides, organic sulfide, and hydride, increased during storage. Additionally, the principle component and correlation analyses revealed that the spoilage odors produced by different species of bacteria were significantly different and positively correlated with the results of protease activity in vitro. The characteristics of spoilage bacteria in chilled chicken provided a comprehensive insight into microbial assessment during storage.

Clostridium perfringens is a major pathogen causing foodborne illnesses. In this experiment, the inactivation effects of heat and lactic acid (LA) treatments on C. perfringens spores was investigated. Heat treatment (80 °C, 90 °C and 100 °C), LA (0.5% and 1%), and combined LA and heat treatments for 30 and 60 min were performed. Residual spore counts showed that the count of C. perfringens spores was below the detection limit within 30 min of treatment with 1% LA and heat treatment at 90 °C. Scanning electron microscopy and confocal scanning laser microscopy results showed that the surface morphology of the spores was severely disrupted by the co-treatment. The particle size of the spores was reduced to 202 nm and the zeta potential to −3.66 mv. The inner core of the spores was disrupted and the co-treatment resulted in the release of 77% of the nuclear contents 2,6-pyridinedicarboxylic acid. In addition, the hydrophobicity of spores was as low as 11% after co-treatment with LA relative to the control, indicating that the outer layer of spores was severely disrupted. Thus, synergistic heating and LA treatment were effective in inactivating C. perfringens spores.

The effects of modified atmosphere packaging (MAP) on the growth and spoilage characteristics of Pseudomonas lundensis LD1 and Shewanella putrefaciens SP1 in chilled chicken at 0–10 °C were studied. MAP inhibited microbial growth, TVB-N synthesis, and lipid oxidation. The inhibitory effect of MAP became more significant as the temperature decreased. The kinetic models to describe the growth of P. lundensis LD1 and S. putrefaciens SP1 at 0–10 °C were also established to fit the primary model Gompertz and the secondary model Ratkowsky. The models had a high degree of fit to describe the growth of dominant spoilage bacteria in chilled chicken. The observed numbers of P. lundensis LD1 and S. putrefaciens SP1 at 2 °C were compared with the predicted numbers, and the accuracy factor and bias factor ranged from 0.93 to 1.14. These results indicated that the two models could help predict the growth of P. lundensis and S. putrefaciens in chilled chicken at 0–10 °C. The analyzed models provide fast and cost-effective alternatives to replace traditional culturing methods to assess the influence of temperature and MAP on the shelf life of meat.

The aim of this study was to optimize and characterize Flavourzyme hydrolysis conditions for the preparation of antioxidant peptides from duck meat, using response surface methodology. The results indicated that optimal Flavourzyme hydrolysis conditions for preparation of antioxidant peptides from duck protein were a temperature of 50.19°C, pH 5.45, and a reaction time of 1.03 h. Compared to non-hydrolyzed duck meat, Flavourzyme hydrolysis significantly improved the hydroxyl-radical scavenging, DPPH radical-scavenging, ferrous ion-chelating, reducing, and ABTS radical cation-scavenging activities of duck meat. Therefore, Flavourzyme can be regarded as an effective hydrolytic enzyme for the preparation of antioxidant peptides from duck meat.

This study evaluated the effect of the combination of ultrasound and phenyllactic acid (PLA) on inactivating Staphylococcus aureus and Salmonella enteritidis biofilm cells and determined the possible antibiofilm mechanism. S. aureus and S. enteritidis biofilm cells were separately treated with ultrasound (US, 270 W), phenyllactic acid (PLA, 0.5% and 1%), and their combination (US + 0.5% PLA, and US + 1% PLA) for 5, 10, 20, 30, and 60 min. Biofilm inactivation, polysaccharide, and respiratory chain dehydrogenase assays were conducted. US and PLA had a synergistic effect on inactivating bacterial cells in S. aureus and S. enteritidis biofilms. The combination of US and PLA significantly decreased the contents of soluble and insoluble polysaccharides and the activity of respiratory chain dehydrogenase in the biofilm cells compared to the single treatment. Confocal laser scanning microscopy, scanning electron microscopy, and intracellular adenosine-triphosphate (ATP) analyses indicated that the combination of US and PLA seriously destroyed the cell membrane integrity of the S. aureus and S. enteritidis biofilms and caused the leakage of intracellular ATP. These findings demonstrated the synergistic antibiofilm effect of US combined with PLA and offered a research basis for its application in the food industry.

Perillaldehyde is a natural antibacterial agent extracted from perilla essential oil. In our methodology, five antibacterial nanofiber packaging films are prepared by loading different concentrations of perillaldehyde (P) into gelatin/zein (G/Z) polymers. Morphology observations show that the G/Z/P film had a good uniform microstructure and nano-diameter as the weight ratio of 5:1:0.02 (G/Z/P). Fourier transform infrared spectroscopy, and X-ray indicate that these three ingredients had good compatibility and strong interaction via hydrogen bonding. Water contact angle results show that the G/Z/P films gradually change from hydrophilic to hydrophobic with the increase of perillaldehyde. Thermal analysis indicates that the G/Z/P (5:1:0.02) film has good thermal stability. Antibacterial and storage analysis indicates that G/Z/P (5:1:0.02) film is effective to inactivate Staphylococcus aureus and Salmonella enteritidis, and obviously reduces the increasing rate of total bacteria counts and volatile basic nitrogen of chicken breasts. This study indicates that the G/Z/P (5:1:0.02) is a kind of potential antibacterial food packaging film.

Abstract SlpB, a surface layer protein isolated from Lactobacillus crispatus, has the potential to enhance the antimicrobial activity of nisin. Previous research indicated that, when combined with nisin, SlpB acted synergistically to inhibit Staphylococcus saprophyticus growth, thus extending the shelf life of chicken meat. In order to understand how SlpB enhances the antibacterial activity of nisin, electron microscopy, confocal laser scanning microscopy, flow cytometry and transmembrane electrical potential analysis were used to study cell wall organization and cell membrane integrity. No remarkable bacteriolytic effects were observed, indicating that cell death could not be attributed to cell lysis, although SlpB caused dramatic modifications of cell wall, thereby altering cell shape. The combination of SlpB and nisin also induced the release of ATP or UV-absorbing materials, as well as sudden dissipation of the transmembrane electrical potential by compromising membrane integrity. Considering that SlpB led to structural disorganization of the cell wall, and nisin access is enhanced to form a stable pore, cell death is a predictable outcome. SlpB significantly enhanced the effect of nisin at half of the minimum inhibitory concentration, which resulted in cell death by destroying the cell wall and cell membrane, therefore providing a new, feasible approach in food preservation.

Background: Photoautotrophic microalgae are a promising avenue for sustained biodiesel production, but are compromised by low yields of biomass and lipids at present. We are developing a chemical approach to improve microalgal accumulation of feedstock lipids as well as high-value alpha-linolenic acid which in turn might provide a driving force for biodiesel production. Results: We demonstrate the effectiveness of the small bioactive molecule "acetylcholine" on accumulation of biomass, total lipids, and alpha-linolenic acid in Chlorella sorokiniana. The effectiveness exists in different species of Chlorella. Moreover, the precursor and analogs of acetylcholine display increased effectiveness at higher applied doses, with maximal increases by 126, 80, and 60% over controls for biomass, total lipids, and alpha-linolenic acid, respectively. Production of calculated biodiesel was also improved by the precursor and analogs of acetylcholine. The biodiesel quality affected by changes in microalgal fatty acid composition was addressed. Conclusion: The chemical approach described here could improve the lipid yield and biodiesel production of photoautotrophic microalgae if combined with current genetic approaches. [ABSTRACT FROM AUTHOR]