Antibacterial Activity and Mechanism of Lauric Acid Against Staphylococcus aureus and Its Application in Infectious Cooked Chicken.

Staphylococcus aureus contamination and prevention has always been a major concern for food industry. This work investigated the antibacterial activity and mechanisms of lauric acid (LA) against S. aureus. Results revealed 156 µg/mL was the minimum inhibitory concentration (MIC) for LA and it retarded growth rate of S. aureus. The inhibitory effect was enhanced with LA concentration. After being treated with 2 MIC LA for 24 h, the number of S. aureus decreased by 3.56 log colony-forming unit (CFU)/mL. Scanning electron microscopy profiling revealed that LA resulted in altered morphology of S. aureus cells. In addition, propidium iodide staining of flow cytometry suggested that LA treatment disrupted the cell membrane integrity. Changes in 8-anilino-1-naphthalenesulfonic acid fluorescence indicated a depolarization change in cell membrane fluidity. For practical applications, LA also displayed an antimicrobial potential in cooked chicken food model system, with 1.25-5 g/L of LA prolonging shelf life by 2 days at 4°C. Moreover, it had no adverse effect on pH values, color in cooked chicken meat, and even reduced lipid oxidation. To sum up, LA has great antimicrobial properties and is a candidate preservative for cooked meat food.

Antibacterial Effect of Chrysanthemum Buds' Crude Extract Against Salmonella Typhimurium and Potential Application in Cooked Chicken.

The objective of this study was to clarify the antibacterial activity and mechanism of Chrysanthemum buds' crude extract (CBCE) against Salmonella Typhimurium, and explore the potential application in cooked chicken. The zone of inhibition (ZI), minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) were used to assess the in vitro antibacterial activity of CBCE against Salmonella Typhimurium. The antibacterial mechanism was elucidated by revealing the changes in intracellular adenosine 5'-triphosphate (ATP) concentration, membrane potential, content of biomacromolecule, and cell morphology. Furthermore, the effect of CBCE on the counts of Salmonella Typhimurium and color of cooked chicken during storage was studied. The results showed that the ZI, MIC, and MBC of CBCE against Salmonella Typhimurium were 12.9 ± 0.53-13.6 ± 0.14 mm, 40, and 80 mg/mL, respectively. In the process of inhibiting Salmonella Typhimurium by CBCE, the reduction of intracellular ATP concentration, cell membrane depolarization, leakage of protein and nucleic acid, and destruction of cell morphology were observed. Moreover, after treatments with CBCE, the growth of Salmonella Typhimurium in cooked chicken was significantly inhibited (p < 0.05) compared with the control group. No significant differences (p > 0.05) in lightness (L*), redness (a*), and yellowness (b*) values of cooked chicken were found between untreated and treated samples, as well as the color of cooked chicken treated with CBCE did not change significantly (p > 0.05) during the six days of storage. Overall, our findings suggested that CBCE exhibited the antibacterial effect against Salmonella Typhimurium, and had the potential to be used as a natural food preservative for the control of Salmonella Typhimurium in chicken products.

Selection and characterization, application of a DNA aptamer targeted to Streptococcus pyogenes in cooked chicken.

An aptamer against Streptococcus pyogenes was selected and identified, and a fluorescent method based on the reported aptamer was established to detect S. pyogenes in the cooked chicken. Through a twelve rounds of whole-bacterium SELEX (systematic evolution of ligands by exponential enrichment) selection in vitro, a set of aptamers binding to the whole cell of S. pyogenes were generated, harvesting a low-level dissociation constant (Kd) value of 44 ±â€¯5 nmol L-1 of aptamer S-12. Aptamer-based quantification of S. pyogenes in the cooked chicken sample was implemented in a fluorescence resonance energy transfer-based assay by using graphene oxide, resulting in a limit of detection of 70 cfu mL-1. The selected aptamer showed affinity and selectivity recognizing S. pyogenes; besides, more biosensors based on the selected aptamer as a molecular recognition element could be developed in the innovative determinations of S. pyogenes.

Antimicrobial efficacy of Syzygium antisepticum plant extract against Staphylococcus aureus and methicillin-resistant S. aureus and its application potential with cooked chicken.

For the past decades, there has been a growing demand for natural antimicrobials in the food industry. Plant extracts have attracted strong research interests due to their wide-spectrum antimicrobial activities, but only a limited number have been investigated thoroughly. The present study aimed at identifying a novel anti-staphylococcal plant extract, to validate its activity in a food model, and to investigate on its composition and antimicrobial mechanism. Four plant extracts were evaluated against Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) in vitro, with Syzygium antisepticum leaf extract showing the strongest antimicrobial activity (MIC = 0.125 mg/mL). Relatively high total phenolic content (276.3 mg GAE/g extract) and antioxidant activities (90.2-138.0 mg TE/g extract) were measured in S. antisepticum extract. Food validation study revealed that higher extract concentration (32 mg/mL) was able to inhibit or reduce staphylococcal growth in cooked chicken, but caused color change on meat surface. By GC-MS, ß-caryophyllene (12.76 area%) was identified as the dominant volatile compound in extract. Both crude extract and pure ß-caryophyllene induced membrane damages in S. aureus. These results suggested good anti-staphylococcal properties of S. antisepticum plant extract, identified its major volatile composition and its membrane-damaging antimicrobial mechanism.

Outbreak of Salmonella enteritidis phage type 1B associated with frozen pre-cooked chicken cubes, Finland 2012.

In August to October 2012, a nationwide outbreak of Salmonella enteritidis phase type (PT) 1B with 53 cases occurred in Finland. Hypothesis generating interviews pointed toward ready-to-eat chicken salad from a Finnish company and at the same time Estonian authorities informed of a S. enteritidis PT 1B outbreak linked to chicken wrap prepared at an Estonian restaurant. We found that chicken salad was associated with the infection (odds ratio (OR) 16·1, 95% confidence interval (CI) 1·7-148·7 for consumption and OR 17·5. 95% CI 4·0-76·0 for purchase). The frozen pre-cooked chicken cubes used in Finnish salad and in Estonian wraps were traced back to a production plant in China. Great Britain made two Rapid Alert Systems for Food and Feed notifications on chicken cubes imported to the UK from the same Chinese production plant. Microbiological investigation confirmed that the patient isolates in Estonia and in Finland were indistinguishable from the strains isolated from chicken cubes in Estonia and in the UK. We recommend that despite certificates for tested Salmonella, food items should be analyzed when Salmonella contamination in outbreak investigations is suspected. In outbreak investigations, electronically implemented case-case study saves time, effort, and money compared with case-control study.

Transcriptome analysis reveals the inhibitory mechanism of phloretin on virulence expression of Staphylococcus aureus and its application in cooked chicken.

Staphylococcus aureus (S. aureus) enterotoxins have aroused great concern to food safety owing to its increased risk of food poisoning. The current research aimed to investigate the anti-virulence mechanisms of phloretin against S. aureus in terms of toxin activity and gene expression. The results indicated that phloretin could effectively inhibit the production of hemolysins and enterotoxins, and its anti-virulence effect was exerted in a concentration-dependent manner. Transcriptome results indicated that phloretin could downregulate the transcription level of majority virulence factors related genes (68 %) of S. aureus, including the quorum sensing-related genes (agrB, agrC, agrA, sspA, splF, splD and others) and bacterial secretion system-related genes (secDF, secY2, and yidC). In addition, it was speculated that phloretin was most likely to bind to the AgrA DNA binding domain, thereby affecting the expression of downstream virulence genes (hla, seb, spa, rot, geh, etc) based on molecular docking. Finally, the application in cooked chicken indicated that phloretin could effectively decrease the content of enterotoxins and improve the storage quality of cooked chicken. These findings not only evidenced the feasible anti-virulence activity of phloretin, but also provided a new strategy to prevent S. aureus food poisoning in cooked meat preservation.

Characterization of aroma profiles of chinese four most famous traditional red-cooked chickens using GC-MS, GC-IMS, and E-nose.

The aroma profile of the four most popular types of red-cooked chickens in China was analyzed using a combination of gas chromatography-mass spectrometry (GC-MS), gas chromatography-ion mobility spectrometry (GC-IMS), and electronic nose (E-nose). Principal component analysis (PCA) demonstrated that the E-nose could successfully distinguish between the four types of red-cooked chickens. Additionally, a fingerprint was created using GC-IMS to examine the variations in volatile organic compounds (VOCs) distribution in the four chicken types. A total number of 84 and 62 VOCs were identified in the four types of red-cooked chickens using GC-MS and GC-IMS, respectively. Odor activity value (OAV) showed that 1-octen-3-ol, heptanal, hexanal, nonanal, octanal, eugenol, dimethyl trisulfide, anethole, anisaldehyde, estragole, and eucalyptol were the key volatile components in all samples. Furthermore, partial least squares-discriminant analysis (PLS-DA) demonstrated that (E, E)-2,4-decadienal, dimethyl trisulfide, octanal, eugenol, hexanal, (E)-2-nonenal, 1-octen-3-ol, butanal, ethyl acetate, ethyl acetate (D), nonanal, and heptanal could be used as markers to distinguish aroma of the four types of red-cooked chickens. Also, it is worth noting that levels of VOCs varied between chicken breast muscle and skin. The obtained results offer theoretical and technological support for flavor identification and control in red-cooked chickens to enhance their quality and encourage consumer consumption, which will be advantageous for the red-cooked chicken production chain.

Transcriptome Analysis of Protocatechualdehyde against Listeria monocytogenes and Its Effect on Chicken Quality Characteristics.

The development of natural antimicrobial agents offers new strategies for food preservation due to the health hazards associated with the spoilage of meat products caused by microbial contamination. In this paper, the inhibitory mechanism of protocatechualdehyde (PCA) on Listeria monocytogenes was described, and its effect on the preservation of cooked chicken breast was evaluated. The results showed that the minimal inhibitory concentration (MIC) of PCA on L. monocytogenes was 0.625 mg/mL. Secondly, PCA destroyed the integrity of the L. monocytogenes cell membrane, which was manifested as a decrease in membrane hyperpolarization, intracellular ATP level, and intracellular pH value. Field emission gun scanning electron microscopy (FEG-SEM) observed a cell membrane rupture. Transcriptome analysis showed that PCA may inhibit cell growth by affecting amino acid, nucleotide metabolism, energy metabolism, and the cell membrane of L. monocytogenes. Additionally, it was discovered that PCA enhanced the color and texture of cooked chicken breast meat while decreasing the level of thiobarbituric acid active substance (TBARS). In conclusion, PCA as a natural antibacterial agent has a certain reference value in extending the shelf life of cooked chicken breast.

Identification of novel biomarkers in chilled and frozen chicken using metabolomics profiling and its application.

Merchants used frozen chicken to pass it off as chilled chicken, resulting in Economically Motivated Adulteration incidents. Here in this work, firstly, we established OPLS-DA and OPLS-R models based on metabolomics to obtain differential metabolites in chilled and frozen chicken (with different storage times), the PLS-DA model based on above differential compounds could achieve accuracy of 91% (training) and 100% (testing) for the adulteration identification of uncooked chilled and frozen chicken. Secondly, cooking study was carried out to identify the discrepancy of the cooked chilled and frozen chicken. Higher nicotinamide, o-acetyl-l-carnitine, hypoxanthine, and IMP levels indicated better nutrition quality and more desirable flavor in chilled chicken nuggets, while higher bitter and sour peptides in frozen chicken nuggets indicated the loss of freshness.

The Microbiota of Modified-Atmosphere-Packaged Cooked Charcuterie Products throughout Their Shelf-Life Period, as Revealed by a Complementary Combination of Culture-Dependent and Culture-Independent Analysis.

Although refrigeration and modified-atmosphere packaging (MAP) allow for an extended shelf life of cooked charcuterie products, they are still susceptible to bacterial spoilage. To obtain better insights into factors that govern product deterioration, ample information is needed on the associated microbiota. In this study, sliced MAP cooked ham and cooked chicken samples were subjected to culture-dependent and culture-independent microbial analysis. In total, 683 bacterial isolates were obtained and identified from 60 samples collected throughout the storage period. For both charcuterie types, lactic acid bacteria (LAB) constituted the most abundant microbial group. In cooked ham, Brochothrix thermosphacta was highly abundant at the beginning of the shelf-life period, but was later overtaken by Leuconostoc carnosum and Lactococcus piscium. For cooked chicken products, Latilactobacillus sakei was most abundant throughout the entire period. Additionally, 13 cooked ham and 16 cooked chicken samples were analyzed using metabarcoding. Findings obtained with this method were generally in accordance with the results from the culture-dependent approach, yet they additionally demonstrated the presence of Photobacterium at the beginning of the shelf-life period in both product types. The results indicated that combining culture-dependent methods with metabarcoding can give complementary insights into the evolution of microorganisms in perishable foods.

Prediction of Thiol Group Changes in Minced Raw and Cooked Chicken Meat with Plant Extracts-Kinetic and Neural Network Approaches.

The aim of the study was to develop predictive models of thiol group (SH) level changes in minced raw and heat-treated chicken meat enriched with selected plant extracts (allspice, basil, bay leaf, black seed, cardamom, caraway, cloves, garlic, nutmeg, onion, oregano, rosemary, and thyme) during storage at different temperatures. Meat samples with extract addition were stored under various temperatures (4, 8, 12, 16, and 20 °C). SH changes were measured spectrophotometrically using Ellman's reagent. Samples stored at 12 °C were used as the external validation dataset. SH content decreased with storage time and temperature. The dependence of SH changes on temperature was adequately modeled by the Arrhenius equation with average high R2 coefficients for raw meat (R2 = 0.951) and heat-treated meat (R2 = 0.968). Kinetic models and artificial neural networks (ANNs) were used to build the predictive models of thiol group decay during meat storage. The obtained results demonstrate that both kinetic Arrhenius (R2 = 0.853 and 0.872 for raw and cooked meat, respectively) and ANN (R2 = 0.803) models can predict thiol group changes in raw and cooked ground chicken meat during storage.

Microbiological Quality of Cooked Chicken: Results of Monitoring in England (2013-17).

Results from monitoring of the microbiological quality of 2,721 samples of ready-to-eat cooked chicken collected between 2013 to 2017 in England were reviewed: 70% of samples were from retail, catering or manufacture and 30% were imported and collected at English ports. Samples were tested for a range of bacterial pathogens and indicator organisms. Six samples (<1%) had unsatisfactory levels of pathogens which were potentially injurious to health. Neither Salmonella nor Campylobacter were recovered from any sample. Two samples from catering settings contained either an unsatisfactory level of Bacillus cereus (5 x 10 6 CFU/g) or an unsatisfactory level of coagulase positive staphylococci (1.6 x 10 4 CFU/g). Listeria monocytogenes was recovered from 36 samples (one at manufacture, 26 at catering and nine at retail) and in four instances, unsatisfactory levels (≥10 2 CFU/g) were detected (three samples collected at catering and one at retail). For L. monocytogenes there were no significant differences between the rates of contamination with between the samples collected from ports, manufacture, retail supermarkets and other retailers (p = 0.288). There were no differences between the rates of contamination for other potential pathogens detected between samples from different settings. The prevalence of hygiene indicators ( Escherichia coli , Enterobacteriaceae and Aerobic Colony Counts) at import was significantly lower than in samples collected from manufacturers, retail or catering (p < 0.01). Samples collected from catering gave poorer results than all other settings. Regardless of the stage in the food chain, samples from Thailand and from other non-EU countries were of significantly better microbiological quality with respect to indicator organisms than those from the UK or from other EU countries (p = <0.001).

Listeria monocytogenes in Cooked Chicken: Detection of an Outbreak in the United Kingdom (2016 to 2017) and Analysis of L. monocytogenes from Unrelated Monitoring of Foods (2013 to 2017).

ABSTRACT: In England and Wales, Public Health England applies whole genome sequencing to cultures of Listeria monocytogenes recovered from human cases of listeriosis, foods, and food production environments. Following the routine inspection of a small retailer in February and March 2016, two unopened packs of cooked chicken produced by the same manufacturer were found to be contaminated with L. monocytogenes at levels of 340 and 20 CFU/g. A public recall of this product was issued in March 2016. Early in 2017, a less than five single-nucleotide polymorphism single-linkage cluster was detected between the L. monocytogenes isolates from the two cooked chicken products and cultures from five cases of human listeriosis in England and Scotland with onsets of illness between March 2016 and February 2017. Epidemiological data provided further supportive evidence that this cluster was an outbreak linked to a manufacturer of cooked chicken whose products were supplied to the small retailer that initiated the outbreak investigation. Unrelated to this outbreak, 34 L. monocytogenes isolates recovered from routine food monitoring of 2,007 samples of cooked chicken during 2013 to 2017 were analyzed by whole genome sequencing. Previously undetected fewer than five single-nucleotide polymorphism single-linkage clusters were identified between cultures from cooked chicken and with those from two clusters and two sporadic cases of human listeriosis that were consistent with foodborne transmission. This analysis identified linkage of L. monocytogenes clusters within specific food chains more readily than traditional manual tracing. Linking of data associated with L. monocytogenes cultures from cases of listeriosis with those from unrelated food testing is a unique source of information for communicable disease risk assessment, epidemiological studies, and disease prevention and control. This report provides further evidence that should act as a reminder of the association between cooked chicken consumption and human listeriosis.

Modeling for Predicting the Time to Detection of Staphylococcal Enterotoxin A in Cooked Chicken Product.

Staphylococcal enterotoxins (SEs) produced by Staphylococcus aureus (S. aureus) are the cause of Saphylococcal food poisoning (SFP) outbreaks. Thus, estimation of the time to detection (TTD) of SEs, that is, the time required to reach the SEs detection limit, is essential for food preservation and quantitative risk assessment. This study was conducted to explore an appropriate method to predict the TTD of SEs in cooked chicken product under variable environmental conditions. An S. aureus strain that produces staphylococcal enterotoxin A (SEA) was inoculated into cooked chicken meat. Initial inoculating concentrations (approximately 102, 103, 104 CFU/g) of S. aureus and incubation temperatures (15 ± 1, 22 ± 1, 29 ± 1, and 36 ± 1°C) were chosen as environmental variables. The counting of S. aureus colonies and the detection of SEA were performed every 3 or 6 h during the incubation. The TTD of SEA was considered a response of S. aureus to environmental variables. Linear polynomial regression was used to model the effects of environmental variables on the TTD of SEA. Result showed that the correlation coefficient (R2) of the regressed equation is higher than 0.98, which means the obtained equation was reliable. Moreover, the minimum concentration of S. aureus for producing a detectable amount of SEA under various environmental conditions was approximately 6.32 log CFU/g, which was considered the threshold for S. aureus to produce SEA. Hence, the TTD of SEA could be obtained by calculating the time required to reach the threshold by using an established S. aureus growth predictive model. Both established methods were validated through internal and external validation. The results of graphical comparison, RMSE, SEP, Af , and Bf showed that the accuracy of both methods were acceptable, and linear polynomial regression method showed more accurately.

Effect of oregano oil and tannic acid combinations on the quality and sensory characteristics of cooked chicken meat.

The antioxidant effects of oregano essential oil and tannic acid combinations on ground chicken breast and thigh meats were studied. Six treatments, including: 1) control (none added), 2) 100 ppm oregano essential oil + 5 ppm tannic acid, 3) 100 ppm oregano essential oil + 10 ppm tannic acid, 4) 200 ppm oregano essential oil + 5 ppm tannic acid, 5) 200 ppm oregano essential oil + 10 ppm tannic acid, and 6) 5 ppm butylated hydroxyanisole (BHA) for breast or 14 ppm for thigh meat, were prepared. Cooked meat samples were individually vacuum-packaged in oxygen-impermeable vacuum bags and then cooked in-bag to an internal temperature of 75°C. After cooling to room temperature, the cooked meat was re-packaged in new oxygen-permeable bags and stored at 4°C for 7 days. Cooked ground chicken meats were analyzed for lipid and protein oxidation and volatiles at 0, 3, and 7 d of storage. The significant differences among the treatments were very clear in cooked meat samples: Thigh meat patties showed higher 2-thiobarbituric acid reactive substances (TBARS), total carbonyl, and volatiles content compared to the breast meat during storage. A combination of 200 ppm oregano oil with 10 ppm tannic acid showed the most significant effects (P < 0.05) on TBARS, total carbonyl, and off-odor volatile formation for both breast and thigh meats. Oregano oil (200 ppm) and 10 ppm tannic acid combination also showed positive effects on the sensory scores of chicken thigh meat. In conclusion, the combination of 200 ppm oregano oil and 10 ppm tannic acid could be a good replacement for the synthetic antioxidants in ground cooked chicken meat.

Effect of Oregano Essential Oil (Origanum vulgare subsp. hirtum) on the Storage Stability and Quality Parameters of Ground Chicken Breast Meat.

A study was conducted to investigate the effect of oregano essential oil on the oxidative stability and color of raw and cooked chicken breast meats. Five treatments, including (1) control (none added); (2) 100 ppm oregano essential oil; (3) 300 ppm oregano essential oil; (4) 400 ppm oregano essential oil; and (5) 5 ppm butylated hydroxyanisole (BHA), were prepared with ground boneless, skinless chicken breast meat and used for both raw and cooked meat studies. For raw meat study, samples were individually packaged in oxygen-permeable bags and stored in a cold room (4 °C) for 7 days. For cooked meat study, the raw meat samples were vacuum-packaged in oxygen-impermeable vacuum bags and then cooked in-bag to an internal temperature of 75 °C. After cooling to room temperature, the cooked meats were repackaged in new oxygen-permeable bags and then stored at 4 °C for 7 days. Both raw and cooked meats were analyzed for lipid and protein oxidation, volatiles, and color at 0, 3, and 7 days of storage. Oregano essential oil significantly reduced (p < 0.05) lipid and protein oxidation, and improved color stability of raw and cooked meat. However, oregano oil at 400 ppm showed the strongest effect for all these parameters. Hexanal was the major aldehyde, which was decreased significantly (p < 0.05) by oregano oil treatment, in cooked meat. Overall, oregano essential oil at 100-400 ppm levels could be a good preservative that can replace the synthetic antioxidant in chicken meat.