Advances in understanding the predominance, phenotypes, and mechanisms of bacteria related to meat spoilage

Discovery of a temperature-dependent protease spoiling meat from Pseudomonas fragi: Target to myofibrillar and sarcoplasmic proteins rather than collagen

Chilled meat frequently suffered microbial spoilage because bacteria can secrete various proteases that break down the proteins. In this study, Pseudomonas fragi NMC 206 exhibited a temperature-dependent secretion pattern, with the ability to release the specific protease only below 25 °C. It was identified as alkaline protease AprA by LC-MS/MS, with the molecular weight of 50.4 kDa, belonging to the Serralysin family metalloprotease. Its significant potential for meat spoilage in situ resulted in alterations in meat color and sensory evaluation, as well as elevated pH, total volatile basic nitrogen (TVB-N) and the formation of volatile organic compounds (VOCs). The hydrolysis of meat proteins in vitro showed that AprA possessed a considerable proteolysis activity and degradation preferences on meat proteins, especially its ability to degrade myofibrillar and sarcoplasmic proteins, rather than collagen. These observations demonstrated temperatures regulated the secretion of AprA, which was closely related to chilled chicken spoilage caused by bacteria. These will provide a new basis for the preservation of meat products at low temperatures.

Effect of chilled storage period on the volatile organic compounds and bacterial community in goose meat

Storage time is considered to be one of the most important factors affecting the obnoxious odor and microbial spoilage of fresh meat. In this study, volatile organic compounds (VOCs) and bacterial community structure of chilled goose meat during storage were investigated. The results showed that numerous VOCs were produced during the fresh goose meat storage, including aldehydes (nonanal, (E)-2-octenal, hexanal, tetradecanal), alcohol (1-octen-3-ol), furan (2-pentylfuran), and carboxylic acids (methyl diethyldithiocarbamate), which might be a breakdown product during spoilage. In addition, there were slight fluctuations in fatty acid profiles and amino acid contents. Furthermore, bacterial community diversity decreased with prolonged storage. Also, Pseudomonas and Acinetobacter were the dominant spoilage bacteria contributing to nonanal and methyl diethyldithiocarbamate generation. Taken together, these data provide insights into the characterization of VOCs and the bacterial community of chilled goose meat, which will help to further control the microbial quality of chilled meat.

Revealing the spoilage characteristics of refrigerated prepared beef steak by advanced bioinformatics tools

BACKGROUND

Although microorganisms are the main cause of spoilage in prepared beef steaks, very few deep spoilage mechanisms have been reported so far. Aiming to unravel the mechanisms during 12 days of storage at 4 °C affecting the quality of prepared beef steak, the present study investigated the changes in microbial dynamic community using a combined high-throughput sequencing combined and bioinformatics. In addition, gas chromatography-mass spectrometry combined with multivariate statistical analysis was utilized to identify marker candidates for prepared steaks. Furthermore, cloud platform analysis was applied to determine prepared beef steak spoilage, including the relationship between microbiological and physicochemical indicators and volatile compounds.

RESULTS

The results showed that the dominant groups of Pseudomonas, Brochothrix thermosphacta, Lactobacillus and Lactococcus caused the spoilage of prepared beef steak, which are strongly associated with significant changes in physicochemical properties and volatile organic compounds (furan-2-pentyl-, pentanal, 1-octanol, 1-nonanol and dimethyl sulfide). Metabolic pathways were proposed, among which lipid metabolism and amino acid metabolism were most abundant.

CONCLUSION

The present study is helpful with respect to further understanding the relationship between spoilage microorganisms and the quality of prepared beef steak, and provides a reference for investigating the spoilage mechanism of dominant spoilage bacteria and how to extend the shelf life of meat products. © 2024 Society of Chemical Industry.

Monitoring of meat quality and change-point detection by a sensor array and profiling of bacterial communities

BACKGROUND

Real-time monitoring of food consumer quality remains challenging due to diverse bio-chemical processes taking place in the food matrices, and hence it requires accurate analytical methods. Thresholds to determine spoiled food are often difficult to set. The existing analytical methods are too complicated for rapid in situ screening of foodstuff.

RESULTS

We have studied the dynamics of meat spoilage by electronic nose (e-nose) for digitizing the smell associated with volatile spoilage markers of meat, comparing the results with changes in the microbiome composition of the spoiling meat samples. We apply the time series analysis to follow dynamic changes in the gas profile extracted from the e-nose responses and to identify the change-point window of the meat state. The obtained e-nose features correlate with changes in the microbiome composition such as increase in the proportion of Brochothrix and Pseudomonas spp. and disappearance of Mycoplasma spp., and with representative gas sensors towards hydrogen, ammonia, and alcohol vapors with R2 values of 0.98, 0.93, and 0.91, respectively. Integration of e-nose and computer vision into a single analytical panel improved the meat state identification accuracy up to 0.85, allowing for more reliable meat state assessment.

SIGNIFICANCE

Accurate identification of the change-point in the meat state achieved by digitalizing volatile spoilage markers from the e-nose unit holds promises for application of smart miniaturized devices in food industry.

Microbiological safety of dry-aged meat: a critical review of data gaps and research needs to define process hygiene and safety criteria

Dry-aged meat is gaining popularity among food business operators and private consumers. The process is carried out in aerobic conditions by hanging beef carcasses or placing subprimal or primal cuts in a dedicated cabinet for several weeks or even months while controlling the environment through the management of process parameters such as temperature, relative humidity, and airflow. In this review, we present a critical evaluation of the literature to evaluate tools to manage the process to guarantee food safety and identify critical control points, as well as good hygiene and manufacturing practices. In controlled aging conditions, only Listeria monocytogenes and Yersinia enterocolitica can multiply, while a reduction in the number of Salmonella spp. and Escherichia coli O157:H7 is generally reported. Enterobacteriaceae usually decrease on the surface of the meat during maturation; thus, for the purpose of the hygiene evaluation of the production process, a count no higher than that of unmatured meat is expected. Besides, various studies report that the total bacterial count and the spoilage microorganisms significantly increase on the surface of the meat, up to 5-6 Log10 CFU/g in the absence of visible spoilage. Bacteria of the Pseudomonas genus tend to progressively replace other microorganisms during maturation; thus, the total mesophilic or psychrophilic bacterial load is not a good indicator of process hygiene for matured meat. Critical parameters for the control of the process are temperature, relative humidity, and ventilation, which should be monitored during the process. For this reason, equipment designed and certified for dry-aging must be used, and the manufacturer must validate the process. Food business operators must apply general good manufacturing practices (GMP) and good hygiene practices (GHP) for meat processing and some GMP and GHP specific for dry-aging. Several research needs were identified, among them the evolution of the populations of L. monocytogenes and Y. enterocolitica and the microbiology of the inner parts of the dry-aged meat.

Deep Learning-Based Automated Cell Detection-Facilitated Meat Quality Evaluation

Meat consumption is increasing globally. The safety and quality of meat are considered important issues for human health. During evaluations of meat quality and freshness, microbiological parameters are often analyzed. Counts of indicator cells can provide important references for meat quality. In order to eliminate the error of manual operation and improve detection efficiency, this paper proposed a Convolutional Neural Network (CNN) with a backbone called Detect-Cells-Rapidly-Net (DCRNet), which can identify and count stained cells automatically. The DCRNet replaces the single channel of residual blocks with the aggregated residual blocks to learn more features with fewer parameters. The DCRNet combines the deformable convolution network to fit flexible shapes of stained animal cells. The proposed CNN with DCRNet is self-adaptive to different resolutions of images. The experimental results indicate that the proposed CNN with DCRNet achieves an Average Precision of 81.2% and is better than traditional neural networks for this task. The difference between the results of the proposed method and manual counting is less than 0.5% of the total number of cells. The results indicate that DCRNet is a promising solution for cell detection and can be equipped in future meat quality monitoring systems.

Recent advances in spoilage mechanisms and preservation technologies in beef quality: A review

Beef is a popular meat product that can spoil and lose quality during postharvest handling and storage. This review examines different preservation methods for beef, from conventional techniques like low-temperature preservation, irradiation, vacuum packing, and chemical preservatives, to novel approaches like bacteriocin, essential oil, and non-thermal technologies. It also discusses how these methods work and affect beef quality. The review shows that beef spoilage is mainly due to enzymatic and microbial activities that impact beef freshness, texture, and quality. Although traditional preservation methods can extend beef shelf life, they have some drawbacks and limitations. Therefore, innovative preservation methods have been created and tested to improve beef quality and safety. These methods have promising results and potential applications in the beef industry. However, more research is needed to overcome the challenges and barriers for their commercialization. This review gives a comprehensive and critical overview of the current and emerging preservation methods for beef and their implications for the beef supply chain.

Behavior of Spoilage Bacterial Communities in Different Cuts of Enshi Black Pork under Refrigerated Storage (4 °C)

The Enshi black pig is a Chinese native breed known for its rich nutrition content and high quality, which has notable traction in the consumer market. In this study, the potential impact of the main commercial cuts from Enshi black pork carcasses (ham, loin, and belly) on the bacteria community of spoiled meat under refrigerated storage (4 °C) was assessed by using a high-throughput sequencing method. Moreover, the spoilage potential of isolated strains from spoiled pork was investigated. The results demonstrated significant differences (p < 0.05) in bacterial community diversity and composition among spoiled ham, loin, and belly samples. Linear discriminant analysis effect size (LEfSe) analysis revealed a total of 20 significantly different potential bacterial biomarkers, with the dominant genera of Pseudomonas, Psychrobacter, Shewanella and Carnobacterium. Additionally, C. divergens THT1-5, isolated from spoiled ham samples, displayed cold adaptation and higher spoilage potential in Enshi black pork. These findings are helpful for identifying key factors contributing to spoilage in Enshi black pork and developing strategies to inhibit bacterial growth during preservation.

The antibacterial and inhibition effect of chitosan grafted gentisate acid derivatives against Pseudomonas fluorescens: Attacking multiple targets on structure, metabolism system, antioxidant system, and biofilm

This work aimed to investigate the antibacterial ability and potential mechanism of chitosan grafted gentisate acid derivatives (CS-g-GA) against Pseudomonas fluorescens. The results showed that CS-g-GA had a significant suppressive impact on the growth of Pseudomonas fluorescens, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were 0.64 mg/mL and 1.28 mg/mL, respectively. Results of scanning electron microscopy (SEM) and alkaline phosphatase (AKPase) confirmed that CS-g-GA destroyed the cell structure thereby causing the leakage of intracellular components. In addition, 1 × MIC of CS-g-GA could significantly inhibit the formation of biofilms, and 74.78 % mature biofilm and 86.21 % extracellular polysaccharide of Pseudomonas fluorescens were eradicated by CS-g-GA at 2 × MIC. The results on the respiratory energy metabolism system and antioxidant system demonstrated that CS-g-GA caused respiratory disturbance and energy limitation by influencing the key enzyme activities. It could also bind to DNA and affect genetic metabolism. From this, it could be seen that CS-g-GA had the potential to control foodborne contamination of Pseudomonas fluorescens by attacking multiple targets.

Research progress of chilled meat freshness detection based on nanozyme sensing systems

It is important to develop rapid, accurate, and portable technologies for detecting the freshness of chilled meat to meet the current demands of meat industry. This report introduces freshness indicators for monitoring the freshness changes of chilled meat, and systematically analyzes the current status of existing detection technologies which focus on the feasibility of using nanozyme for meat freshness sensing detection. Furthermore, it examines the limitations and foresees the future development trends of utilizing current nanozyme sensing systems in evaluating chilled meat freshness. Harmful chemicals are produced by food spoilage degradation, including biogenic amines, volatile amines, hydrogen sulfide, and xanthine, which have become new freshness indicators to evaluate the freshness of chilled meat. The recognition mechanisms are clarified based on the special chemical reaction with nanozyme or directly inducting the enzyme-like catalytic activity of nanozyme.

Pseudomonas weihenstephanensis through the iron metabolism pathway promotes in situ spoilage capacity of prepared beef steaks during cold storage

In this study, we evaluated the histomorphology, reactive oxygen species (ROS), protein degradation, and iron metabolism characteristics and differential expression analysis of genes for siderophores synthesis and protease secretion in prepared beef steaks inoculated alone or co-inoculated with P. weihenstephanensis, B. thermotrichothrix and M. caseolyticus at 4 °C for 12 days. The results showed that the P. weihenstephanensis was the key bacteria that degraded protein in the process of prepared beef steaks spoilage, which led to protein oxidation by promoting ferritin degradation to release free iron and inducing ROS accumulation. The highest expression of FpvA and AprE was detected in the P. weihenstephanensis group by comparing qRT-PCR of the different inoculation groups. Both qRT-PCR and Western blot revealed that ferritin heavy polypeptide and ferritin light chain polypeptide gene and protein expressions were significantly higher in the P. weihenstephanensis inoculation group compared to the other inoculation groups. Results suggested that FpvA and AprE might play roles in meat spoilage and were potential positional, physiological and functional candidate genes for improving the quality traits of prepared beef steaks. This work may provide insights on controlling food quality and safety by intervening in spoilage pathways targeting iron carrier biosynthesis or protease secretion genes.

Fully Biodegradable Packaging Films for Fresh Food Storage Based on Oil-Infused Bacterial Cellulose

Fully biodegradable packaging materials are demanded to resolve the issue of plastic pollution. However, the fresh food storage performance of biodegradable materials is generally much lower than that of plastics due to their high permeability, microbial friendliness, and limited stretchability and transparency. Here a biodegradable packaging material is reported with high fresh food storage performance based on an oil-infused bacterial cellulose (OBC) porous film. The oil infusion significantly improved cellulose's food-keeping performance by reducing its gas permeability, increasing its stretchability and transparency, and enabling the active release of green vapor-phase preservative molecules, while maintaining its intrinsically high degradability. Strawberries stored in a container with the OBC lid at 23 °C after 5 days exhibited a moldy rate of 0%, in contrast to the 100% moldy rate of those stored by poly(ethylene). Enhanced storage performance is also obtained on tomatoes, pork, and shrimp. The OBC film is naturally degraded after being buried in wet soil at 30 °C for 9 days, identical to the degradation rate of bacterial cellulose. The liquid seal strategy broadly applies to different celluloses, providing a general option for developing cellulose-based biodegradable packaging materials.

Impact of Refrigerated Storage on Microbial Growth, Color Stability, and pH of Turkey Thigh Muscles

The quality of poultry meat offered to the consumer depends mainly on the level of hygiene during all stages of its production, storage time, and temperature. This study investigated the effect of refrigerated storage on the microbiological contamination, color, and pH of turkey thigh muscles stored at 1 °C over six days. Microbial growth, including total mesophilic aerobes, presumptive lactic acid bacteria, and Enterobacteriaceae, significantly increased, impacting the meat's sensory attributes and safety. On the 6th day of meat storage, the content of total mesophilic aerobes, presumptive lactic acid bacteria, and Enterobacteriaceae was 1.82 × 107 CFU/g, 1.00 × 104 CFU/g, and 1.87 × 105 CFU/g, respectively. The stability of color was assessed by quantifying the total heme pigments, comparing myoglobin, oxymyoglobin, and metmyoglobin concentrations, analyzing color parameters L*, a*, b*, and the sensory assessment of surface color, showing a decline in total heme pigments, three myoglobin forms, redness (a*) and lightness (L*). In contrast, yellowness (b*) increased. These changes were correlated with the growth of spoilage microorganisms that influenced the meat's pigmentation and pH, with a notable rise in pH associated with microbial metabolization. Based on the conducted research, it was found that the maximum storage time of turkey thigh muscles at a temperature of 1 °C is 4 days. On the 4th day of storage, the total mesophilic aerobe content was 3.5 × 105 CFU/g. This study underscores the critical need for maintaining controlled refrigeration conditions to mitigate spoilage, ensuring food safety, and preserving turkey meat's sensory and nutritional qualities. There is a need for further research to improve turkey meat storage techniques under specific temperature conditions by studying the impact of using varying packaging materials (with different barrier properties) or the application of natural preservatives. Additionally, future studies could focus on evaluating the effectiveness of cold chain management practices to ensure the quality and safety of turkey products during storage. By addressing these research gaps, practitioners and researchers can contribute to developing more efficient and sustainable turkey meat supply chains, which may help mitigate food wastage by safeguarding the quality and safety of the meat.

An Evaluation of the Sensitivity and Applicability of a Droplet Digital Polymerase Chain Reaction Assay to Simultaneously Detect Pseudomonas aeruginosa and Pseudomonas fragi in Foods

Achieving effective control over microbial contamination necessitates the precise and concurrent identification of numerous pathogens. As a common bacterium in the environment, Pseudomonas is rich in variety. It not only has pathogenic strains, but also spoilage bacteria that cause food spoilage. In this research, we devised a remarkably sensitive duplex droplet digital PCR (dddPCR) reaction system to simultaneously detect pathogenic Pseudomonas aeruginosa (P. aeruginosa) and spoilage Pseudomonas fragi (P. fragi). By employing comparative genomics, we identified four genes of P. fragi. Through a specific analysis, the RS22680 gene was selected as the detection target for P. fragi, and the lasR gene was chosen for P. aeruginosa, which were applied to construct a dddPCR reaction. In terms of specificity, sensitivity and anti-interference ability, the constructed dddPCR detection system was verified and analyzed. The assay showed excellent sensitivity and applicability, as evidenced by a limit of detection of 100 cfu/mL. When the concentration of natural background bacteria in milk or fresh meat was 100 times that of the target detection bacteria, the method was still capable of completing the absolute quantification. In the simulation of actual sample contamination, P. aeruginosa could be detected after 3 h of enrichment culture, and P. fragi could be detected after 6 h. The established dddPCR detection system exhibits exceptional performance, serving as a foundation for the simultaneous detection of various pathogenic bacteria in food products.

Meta-analysis of citrus-derived additives on chicken meat quality and safety: a comprehensive evaluation of acceptability, physicochemical properties, and microbial contamination

Citrus represents a valuable repository of antioxidant substances that possess the potential for the preservation of meat quality. This meta-analysis aimed to comprehensively assess the impact of citrus additives on the quality and safety of chicken meat. Adhering to the PRISMA protocol, we initially identified 103 relevant studies, from which 20 articles meeting specific criteria were selected for database construction. Through the amalgamation of diverse individual studies, this research provides a comprehensive overview of chicken meat quality and safety, with a specific focus on the influence of citrus-derived additives. Minimal alterations were observed in the nutritional quality of chicken meat concerning storage temperature and duration. The findings demonstrated a significant reduction in aerobic bacterial levels, with Citrus aurantiifolia exhibiting the highest efficacy (P < 0.01). Both extracted and nonextracted citrus components, applied through coating, curing, and marinating, effectively mitigated bacterial contamination. Notably, thiobarbituric acid reactive substances (TBARS) concentrations were significantly reduced, particularly with Citrus hystrix (P < 0.01). Total volatile base nitrogen (TVBN), an indicator of protein degradation, exhibited a decrease, with citrus extract displaying enhanced efficacy (P < 0.01). Chemical composition changes were marginal, except for a protein increase after storage (P < 0.01). Hedonic testing revealed varied preferences, indicating improvements in flavor, juiciness, and overall acceptability after storage (P < 0.01). The study underscores the effectiveness of citrus additives in preserving chicken meat quality, highlighting their antibacterial and antioxidant properties, despite some observed alterations in texture and chemical composition. Citrus additives have been proven successful in 1) mitigating adverse effects on chicken meat during storage, especially with Citrus hystrix exhibiting potent antimicrobial properties, and 2) enhancing the hedonic quality of chicken meat. This research strongly advocates for the application of citrus additives to uphold the quality and safety of chicken meat.

Changing Cinnamaldehyde Skeleton Achieves Antibacterial Nanoswitch

Changeable substituent groups of organic molecules can provide an opportunity to clarify the antibacterial mechanism of organic molecules by tuning the electron cloud density of their skeleton. However, understanding the antibacterial mechanism of organic molecules is challenging. Herein, we reported a molecular view strategy for clarifying the antibacterial switch mechanism by tuning electron cloud density of cinnamaldehyde molecule skeleton. The cinnamaldehyde and its derivatives were self-assembled into nanosheets with excellent water solubility, respectively. The experimental results show that α-bromocinnamaldehyde (BCA) nanosheets exhibits unprecedented antibacterial activity, but there is no antibacterial activity for α-methylcinnamaldehyde nanosheets. Therefore, the BCA nanosheets and α-methylcinnamaldehyde nanosheets achieve an antibacterial switch. Theoretical calculations further confirmed that the electron-withdrawing substituent of the bromine atom leads to a lower electron cloud density of the aldehyde group than that of the electron-donor substituent of the methyl group at the α-position of the cinnamaldehyde skeleton, which is a key point in elucidating the antimicrobial switch mechanism. The excellent biocompatibility of BCA nanosheets was confirmed by CCK-8. The mouse wound infection model, H&E staining, and the crawling ability of drosophila larvae show that as-prepared BCA nanosheets are safe and promising for wound healing. This study provides a new strategy for the synthesis of low-cost organic nanomaterials with good biocompatibility. It is expected to expand the application of natural organic small molecule materials in antimicrobial agents.

Rapid and non-destructive microbial quality prediction of fresh pork stored under modified atmospheres by using selected-ion flow-tube mass spectrometry and machine learning

Volatile organic compounds (VOCs) indicative of pork microbial spoilage can be quantified rapidly at trace levels using selected-ion flow-tube mass spectrometry (SIFT-MS). Packaging atmosphere is one of the factors influencing VOC production patterns during storage. On this basis, machine learning would help to process complex volatolomic data and predict pork microbial quality efficiently. This study focused on (1) investigating model generalizability based on different nested cross-validation settings, and (2) comparing the predictive power and feature importance of nine algorithms, including Artificial Neural Network (ANN), k-Nearest Neighbors, Support Vector Regression, Decision Tree, Partial Least Squares Regression, and four ensemble learning models. The datasets used contain 37 VOCs' concentrations (input) and total plate counts (TPC, output) of 350 pork samples with different storage times, including 225 pork loin samples stored under three high-O2 and three low-O2 conditions, and 125 commercially packaged products. An appropriate choice of cross-validation strategies resulted in trustworthy and relevant predictions. When trained on all possible selections of two high-O2 and two low-O2 conditions, ANNs produced satisfactory TPC predictions of unseen test scenarios (one high-O2 condition, one low-O2 condition, and the commercial products). ANN-based bagging outperformed other employed models, when TPC exceeded ca. 6 log CFU/g. VOCs including benzaldehyde, 3-methyl-1-butanol, ethanol and methyl mercaptan were identified with high feature importance. This elaborated case study illustrates great prospects of real-time detection techniques and machine learning in meat quality prediction. Further investigations on handling low VOC levels would enhance the model performance and decision making in commercial meat quality control.

Exploration of the shelf-life difference between chilled beef and pork with similar initial levels of bacterial contamination

This study compared the shelf-life of beef and pork longissimus lumborum muscles (loins) that had the same initial bacterial loads and were held under the same chilled storage conditions. To identify the underlying pathways, comparisons were conducted from the perspective of the spoilage indicators; protease/lipase activity, and the volatile organic compounds (VOC) generated over 28 d of chilled storage. The initial total viable microbial count (TVC) on Day 0 for both type of meat was 4.3 log10 CFU/g. It was found that the TVC of beef and pork did not differ throughout the total chilled storage period and both ultimately exceeded 7 log10 CFU/g after 28 d. Based on total volatile basic nitrogen (TVB-N) guidelines, pork was spoilt after 21 d of chilled storage and therefore 7 d earlier than beef. Changes in the concentration of VOC spoilage biomarkers, including 1-octen-3-ol, 1-octanol, nonanal, and others, confirmed that pork had a shorter shelf-life than beef. An important reason for the difference in shelf-life between the two types of meat was that pork had a higher protease activity, although the beef had higher levels of total lipase activity. These findings help us understand the differences in the spoilage process of raw meat from different species and explore specific measures to control the spoilage of beef or pork.

Levels of Indicator Bacteria and Characteristics of Foodborne Pathogens from Carcasses of Cattle Slaughterhouses in Korea

The initial microbial contamination of carcasses during slaughtering adversely affects spoilage and shelf life and is of global concern for food safety and meat quality. This study evaluated the hygiene and quality using the prevalence of foodborne pathogens and the level of indicator bacteria on 200 carcasses, collecting 10 from each of 20 cattle slaughterhouses in Korea. The distribution of aerobic bacterial count in carcasses was significantly highest at 2.0-3.0 log10 CFU/cm2 (34.1%), whereas the Escherichia coli count was significantly highest at under 1.0 log10 CFU/cm2 (94.0%) (P < 0.05). Clostridium perfringens was most prevalent (60.0% of slaughterhouses; 17.5% of carcasses), followed by Yersinia enterocolitica (30.0% of slaughterhouses; 6.5% of carcasses), Staphylococcus aureus (15.0% of slaughterhouses; 4.0% of carcasses), Listeria monocytogenes 1/2a (5.0% of slaughterhouses; 1.0% of carcasses), Salmonella enterica subsp. enterica serovar Infantis (5.0% of slaughterhouses; 1.0% of carcasses), and Shiga toxin-producing E. coli O:66 (5.0% of slaughterhouses; 0.5% of carcasses). Although 28 C. perfringens isolates from 11 slaughterhouses were divided into 21 pulsotypes, all isolates showed the same toxinotype as type A and only carried the cpa. Interestingly, 83.3% of isolates from two slaughterhouses located in the same province showed resistance to tetracycline. Furthermore, 13 Y. enterocolitica isolates from six slaughterhouses were divided into seven pulsotypes that were divided into biotypes 1A and 2 and serotypes O:5 and O:8, except for isolates that could not be typed. Twelve (92.3%) isolates only carried ystB, but one (7.7%) isolate carried ail and ystA. Moreover, 46.2% of Y. enterocolitica isolates showed multidrug resistance against ampicillin, cefoxitin, and amoxicillin/clavulanic acid. This study supports the need for continuous monitoring of slaughterhouses and hygiene management to improve the microbiological safety of carcasses.

Effect of chlorogenic acid grafted chitosan on microbiological compositions of sea bass (Lateolabrax japonicus) fillets: Dominant spoilage bacteria, inhibition activity and membrane damage mechanisms

This study investigated the effect of chlorogenic acid grafted chitosan (CS-g-CA) on the microbiota composition of sea bass (Lateolabrax japonicus), isolated and identified the specific spoilage organisms (SSOs) in the late stage of refrigerated fillets and evaluation of their spoilage potential. Moreover, antibacterial activity and membrane damage mechanism of CS-g-CA against spoilage bacteria was also investigated. Illumina-MiSeq high throughput sequencing results showed that CS-g-CA retarded the growth of Pseudomonas spp., which largely contributed to delaying the quality degradation of sea bass during storage. Then nine spoilage bacteria were isolated and identified from the fillets at the end of storage and inoculated into sterile fish fillets to determine their spoilage capacity. Results showed that fish fillets inoculated with spoilage bacteria exhibited a significant increase in TVB-N, TBA and putrescine content and decreased sensory quality during storage. Subsequently, the inhibitory activity of CS-g-CA against spoilage bacteria was investigated and strains that were more sensitive to the CS-g-CA with a strong spoilage capacity were selected for the study of the inhibition mechanism. Results suggested that CS-g-CA had strong inhibitory activity and led to bacterial death through the mechanism of membrane damage. Overall, this study analyzed the effect of CS-g-CA on the preservation of fish fillets from a microbiological point of view to provide a reference for the anti-bacterial preservation of aquatic products.

Volatile compounds produced in smoked bacon inoculated with potential spoilage bacteria

BACKGROUND

Volatile organic compounds (VOCs) produced during meat storage are mainly derived from the decomposition of meat components and the metabolism of spoilage bacteria. VOCs produced in sterile bacon model substrate inoculated or un-inoculated with spoilage bacteria, Staphylococcus xylosus (P2), Leuconostoc mesenteroides (P6), Carnobacterium maltaromaticum (P9), Leuconostoc gelidum (P16) and Serratia liquefaciens (P20), previously isolated, were identified by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). Furthermore, combinations of the strains (Pm) were also obtained.

RESULTS

In total, 54 volatile compounds, including aldehydes, alcohols, phenols, ketones, alkanes, alkanes, organic acids, esters and so forth, were determined after 45 days of storage in bacon inoculated with potential spoilage bacteria using the HS-SPME/GC-MS method. VOC concentrations of alcohols and organic acids in groups inoculated with bacteria were remarkably higher (P < 0.05) compared to that in control samples. Specifically, some VOCs are closely related to the metabolic activity of the inoculated bacterial strains; for example, 2,3-butanediol was associated with P2, P16 and P20, and acetic acid was mainly related to P6 and P9.

CONCLUSION

The results of partial least squares regression indicated that there was a high correlation between the electronic nose sensors and VOCs of smoked inoculated potential spoilage bacteria. These compounds are potentially important for predicting deterioration of smoked bacon. © 2023 Society of Chemical Industry.

Spotlight on autochthonous microbiota, morpho-textural characteristics, and volatilome of a traditional Polish cold-smoked raw sausage

The aim of the present study was to obtain information on the bacterial diversity of traditional Polish cold-smoked raw sausages (Kiełbasa polska wędzona) manufactured by two artisanal producers using different selective growth media and a metataxonomic analysis. Physico-chemical and morpho-textural characteristics were also carried out, together with Microextraction-Gas Chromatography/Mass Spectrometry (HS-SPMEGC/MS) to study the volatile organic compounds (VOCs). The results overall obtained allowed a picture of the microbiota, the morpho-textural characteristics, and the volatilome of traditional Polish cold-smoked raw sausages (Kiełbasa polska wędzona) to be drawn for the first time. In more detail, viable counting revealed active populations of presumptive lactobacilli, enterococci, coagulase-negative cocci, and a few spoilage microorganisms typically occurring in raw meat products. The metataxonomic analysis revealed the dominance of Latilactobacillus sakei occurring with a relative frequency between 77% and 89%. Pediococcus pentosaceus, Weissella hellenica, and Leuconostoc carnosum were detected among the minority taxa. In the sausages herein studied, no histamine levels of concern were detected. The Principal Component Analysis (PCA) performed on the Amplicon Sequence Variants (ASVs) did not show significant differences in the microbiota composition among producers. The HS-SPMEGC/MS analysis allowed the detection and identification of more than 90 volatile components belonging to ten main classes, namely: aldehydes, ketones, esters and acetates, acids, alcohols, phenols, furans, sulphur compounds, terpenoids, and benzene derivatives. The detected VOCs originated from spices, smoke, and microbial metabolism. The PCA of volatile compounds allowed differences between the sausage samples of the two producers to be identified.

Intelligent food tag: A starch-anthocyanin-based pH-sensitive electrospun nanofiber mat for real-time food freshness monitoring

A starch-based nanofiber mat was prepared for real-time monitoring of food freshness for the first time. UV-vis results showed that roselle anthocyanins (RS) conferred a wide pH sensing range on the nanofiber mat. The prepared nanofiber mats demonstrated good color visibility (total color difference value (ΔE) increased to 56.4 ± 0.7) and a reversible response (within 120 s). Scanning electron microscopy and Fourier transform infrared spectroscopy results suggested that the nanofibers had smooth surfaces without beaded fibers and that RS was well embedded into the nanofibers. The introduction of RS improved the thermal stability of the nanofibers. Color stability tests revealed that the nanofibers exhibited excellent color stability (maximum change ΔE = 1.57 ± 0.03) after 14 days of storage. Pork and shrimp freshness tests verified that the nanofibers could effectively reflect the dynamic freshness of pork and shrimp. Nontoxic, degradable and responsive characteristics make the pH-sensitive nanofiber mat a smart food label with great application potential.

Zinc protoporphyrin IX generation by Leuconostoc strains isolated from bulged pasteurized vacuum sliced hams

The colour of meat typically fades as it decays. However, it has been observed that certain vacuum-packaged spoiled hams can maintain a pink colour even when the packaging is bulged. A large amount of Zinc protoporphyrin IX (ZnPP) was found in these hams, compared to fresh red hams or spoiled and grey hams. Combined with high-throughput sequencing and cultural isolation, the potential cultures of Leuconostoc mesenteroides S-13 (LM), Leuconostoc citreum OCLC11 (LC), and Leuconostoc mesenteroides subsp. IMAU:80679 (LS) were selected based on their ability to produce ZnPP. Subsequently, these cultures were introduced into a fermented sausage model to assess their effect on colour conversion. The analysis of absorption and fluorescent spectra showed that Nitrite sausages contained nitrosyl heme pigment, while bacteria-inoculated sausages were predominantly composed of ZnPP. In addition, the a* value of the LS sausage was close to the Nitrite group at the end of fermentation, significantly higher than control, indicating the effect of bacterial metabolism on the redness. Meanwhile, the Ferrochelatase (FECH) activity of LM, LC and LS groups were 140 ± 13, 113 ± 16 and 201 ± 20 U/g sausage, respectively, providing a potential method on compensating for nitrite/nitrate substitution based on the presence of ZnPP in meat products.

Applications of Prolamin-Based Edible Coatings in Food Preservation: A Review

Foods are susceptible to deterioration and sour due to external environmental influences during production and storage. Coating can form a layer of physical barrier on the surface of foods to achieve the purpose of food preservation. Because of its good barrier properties and biocompatibility, prolamin-based film has been valued as a new green and environment-friendly material in the application of food preservation. Single prolamin-based film has weaknesses of poor toughness and stability, and it is necessary to select appropriate modification methods to improve the performance of film according to the application requirements. The practical application effect of film is not only affected by the raw materials and the properties of the film itself, but also affected by the selection of preparation methods and processing techniques of film-forming liquid. In this review, the properties and selection of prolamins, the forming mechanisms and processes of prolamin-based coatings, the coating techniques, and the modifications of prolamin-based coatings were systematically introduced from the perspective of food coating applications. Moreover, the defects and deficiencies in the research and development of prolamin-based coatings were also reviewed in order to provide a reference for the follow-up research on the application of prolamin-based coatings in food preservation.

Shelf life estimation of refrigerated vacuum packed beef accounting for uncertainty

This study estimates the shelf life of vacuum packed beef meat (three muscles: striploin (longissimus thoracis et lumborum, LTL), tenderloin (psoas major, PM) and outside chuck (trapezius thoracis, TT)) at refrigeration temperatures (0 °C-10 °C) based on modelling the growth of two relevant groups of spoilage microorganisms: lactic acid bacteria (LAB) and Enterobacteriaceae. The growth models were developed combining a two-step and a one-step approach. The primary modelling was used to identify the parameters affecting the growth kinetics, guiding the definition of secondary growth models. For LAB, the secondary model included the effect of temperature and initial pH on the specific growth rate. On the other hand, the model for Enterobacteriaceae incorporated the effect of temperature on the specific growth rate and the lag phase; as well as the effect of the initial pH on the specific growth rate, the lag phase and the initial microbial count. We did not observe any significant effect of the type of muscle on the growth kinetics. Once the equations were defined, the models were fitted to the complete dataset using a one-step approach. Model validation was carried out by cross-validation, mitigating the impact of an arbitrary division between training and validation sets. The models were used to estimate the shelf life of the product, based on the maximum admissible microbial concentration (7 log CFU/g for LAB, 5 log CFU/g for Enterobacteriaceae). Although LAB was the dominant microbiota, in several cases, both LAB and Enterobacteriaceae reached the critical concentration practically at the same time. Furthermore, in some scenarios, the end of shelf life would be determined by Enterobacteriaceae, pointing at the potential importance of non-dominant microorganisms for product spoilage. These results can aid in the implementation of effective control measures in the meat processing industry.

Combining the oxygen sensor based respirometry and 16S rRNA amplicon sequencing for the analysis of microbiota in commercial mince products

In this study, rapid respirometric microbial testing was combined with 16S rRNA amplicon sequencing, to assess the composition of microbiota in a total of 64 samples of commercial beef, turkey, lamb and pork mince. The O2 sensor-based respirometry system, while producing the anticipated total aerobic viable counts (TVC) data and patterns for most samples, also revealed unusual (linear) respiration profiles for some samples, mostly lamb and pork mince. The TVC values for beef mince, produced by respirometry and calculated using the available calibration equation, correlated well with the conventional plate counting method, ISO 4833-1:2013, 2013, while for the other species the correlation was less good. These effects, not observed in previous studies employing various food matrices, require further investigation. Using the same samples (crude homogenates) as in respirometry, the whole microbiome was also analysed by 16S rRNA amplicon sequencing for each mince-type. The sequencing showed an overall decrease in alpha diversity over shelf-life, with lamb and pork mince maintaining a proportion of rare taxa. Some taxa exhibited significant changes in abundance over shelf-life and after the respirometric analysis, with beef mince exhibiting a decrease in aerobic bacteria and an increase in facultative anaerobes. Beta diversity was also seen to depend on mince-type. Thus, the combined use of respirometry and sequencing techniques shows promise as a useful and unique analytical approach for food quality and safety evaluation, However, more data points and in-depth analysis are required to back up the findings of this initial study.

Biosurfactant from Pseudomonas fragi enhances the competitive advantage of Pseudomonas but reduces the overall spoilage ability of the microbial community in chilled meat

Biosurfactants from Pseudomonas spp. have been reported to exhibit antibacterial and anti-adhesive properties, but their role during meat spoilage remains unclear. In this study, the biosurfactant was isolated from an isolate of Pseudomonas fragi with strong spoilage potential, and its surface tension and emulsification ability were determined. The chemical and microbial characteristics of the biosurfactant-treated meat samples were periodically analyzed. The results demonstrated that the biosurfactant produced by P. fragi could reduce surface tension and showed good emulsification properties. For the in situ spoilage trials, biosurfactant from P. fragi changed the microbial diversity on meat, helping Pseudomonas establish a dominant position in the population. However, biosurfactant treatment caused chicken meat to exhibit a weaker spoilage state, as indicated by the growth of psychrophilic microorganisms, total volatile basic nitrogen (TVBN) and meat color. These results provide practical information for understanding the role of P. fragi biosurfactant during chilled meat storage.

Next-generation meat preservation: integrating nano-natural substances to tackle hurdles and opportunities

The increasing global meat demand raises concerns regarding the spoilage of meat caused by microbial invasion and oxidative decomposition. Natural substances, as a gift from nature to humanity, possess broad-spectrum bioactivity and have been utilized for meat preservation. However, their limited stability, solubility, and availability hinder their further development. To address this predicament, advanced organic nanocarriers provide an effective shelter for the formation of nano-natural substances (NNS). This review comprehensively presents various natural substances derived from plants, animals, and microorganisms, along with the challenges they face. Subsequently, the potential of organic nanocarriers is explored, highlighting their distinct features and applicability, in addressing these challenges. The review methodically examines the application of NNS in meat preservation, with a focus on their pathways of action and preservation mechanisms. Furthermore, the outlook and future trends for NNS applications in meat preservation are concluded. The theory and practice summary of NNS is expected to serve as a catalyst for advancements that enhance meat security, promote human health, and contribute to sustainable development.

Genomic Characterization of a Tetracycline-Resistant Strain of Brochothrix thermosphacta Highlights Plasmids Partially Shared between Various Strains

The Gram-positive bacterium Brochothrix thermosphacta is a spoilage agent commonly found on meat products. While the tet(L) gene, which confers resistance to tetracycline, has been identified in certain strains of B. thermosphacta, only a limited number of studies have investigated this gene and its potential presence on mobile DNA elements. This study aims to analyze the tetracycline-resistant strain B. thermosphacta BT469 at the genomic level to gain insight into the molecular determinants responsible for this resistance. Three plasmids have been identified in the strain: pBT469-1, which contains a tetR gene; pBT469-2, which harbours the tet(L) gene responsible for tetracycline resistance; and pBT469-3, which carries genes encoding for a thioredoxin and a phospholipase A2. Homology searches among sequences in public databases have revealed that the plasmid pBT469-2 is currently unique to the BT469 strain. However, the pBT469-1 plasmid is also found in three other strains of B. thermosphacta. Notably, sequences similar to pBT469-1 and pBT469-2 were also found in other bacterial genera, suggesting that these plasmids may be part of a diverse family present in several bacterial genera. Interestingly, sequences of various strains of B. thermosphacta show a high level of similarity with pBT469-3, suggesting that variants of this plasmid could be frequently found in this bacterium.

Self-assembled carboxymethyl chitosan/zinc alginate composite film with excellent water resistant and antimicrobial properties for chilled meat preservation

A major way to reduce meat waste is to extend the shelf life of chilled meat with appropriate packaging. However, most of the packaging film cannot keep meat fresh because of its poor antibacterial and water resistance performance. In this paper, a composite film for chilled meat packaging was synthesized by simple self-assembly of zinc ions with chelating carboxyl groups. Introducing zinc ions into the composite system endows excellent water resistance and antibacterial properties to the film, which are demonstrated by the water vapor permeability and Escherichia coli and Staphylococcus aureus antibacterial tests. The as-prepared composite film also showed enhanced mechanical properties due to the formation of chelation bonds between zinc ions and carboxyl groups. Moreover, the chilled meat preservation test demonstrated the as-prepared composite film can significantly extend the shelf life of pork by five days, indicating its outstanding freshness preservation property. This work demonstrated a facile method to synthesize water-resistant and antimicrobial composite film, which can appear as an effective packaging material for chilled meat and offer a new idea to solve its short shelf-life problem.

Degradation and evaluation of myofibril proteins induced by endogenous protease in aquatic products during storage: a review

Myofibril proteins degradation constitutes an important factor in quality deterioration, procedural activation or inhibition of endogenous protease potential regulates autolytic proteolysis-induced softening of post mortem fish muscle. Based on the brief introduction of myofibril proteins degradation in fish skeletal muscle, a detailed description of the main myofibril degradation properties and the distinct role played by endogenous proteases were proposed, which reflects the limitations and challenges of the current research on myofibril hydrolysis mechanisms based on the varied surrounding conditions. In addition, the latest researches on the evaluation method of myofibril proteins degradation were comprehensively reviewed. The potential use of label-free proteomics combined with bioinformatics was also emphasized and has become an important means to in-depth understand protein degradation mechanism.

Effect of low voltage electrostatic field combined with partial freezing on the quality and microbial community of large yellow croaker

The effect of low voltage electrostatic field combined with partial freezing (LVEF- PF) treatment on storage quality and microbial community of large yellow croaker was studied. Three different methods including chilled (C), partial freezing (PF) and 6 kV/m electrostatic field combined partial freezing storage were used to preserve large yellow croaker for 18 days. Total viable counts (TVC), sensory evaluation, and physiochemical index including pH, total volatile basic nitrogen (TVB-N), K value and centrifugal loss were examined. During storage, the large yellow croaker was susceptible to microbial growth and spoilage. However, LVEF-PF treatment was found to be effective in enhancing sensory quality, inhibiting microbial growth, and maintaining myofibril microstructure. Low field nuclear magnetic resonance showed that LVEF-PF treatment reduced the migration of immobilized water to free water. At 18th day, the TVC value of LVEF-PF, PF and chilled group were 3.56 log CFU/g, 5.11 log CFU/g, 7.73 log CFU/g, respectively. Therefore, from the results of TVB-N and TVC value, the shelf life of LVEF-PF group was at least 3 days longer than PF group, and 6 days longer than the chilled group. High-throughput sequencing showed that the microbial community diversity significantly decreased during storage. The predominant bacteria in chilled, PF, LVEF-PF group at 18th day were Pseudomonas, Psychrobacter and Shewanella, respectively, and the relative abundance of spoilage bacteria such as Pseudomonas and Psychrobacter were reduced by LVEF-PF treatment, that corresponding with lower values of TVB-N and TVC value. LVEF-PF treatment could be used as a new processing and storage method to delay deterioration and prolong shelf life of large yellow croaker.

The Application of Ultraviolet Treatment to Prolong the Shelf Life of Chilled Beef

This study simulated the storage conditions of chilled beef at retail or at home, and the sterilization and preservation effects of short-time ultraviolet irradiation were studied. The conditions of different irradiation distances (6 cm, 9 cm, and 12 cm) and irradiation times (6 s, 10 s, and 14 s) of ultraviolet (UV) sterilization in chilled beef were optimized, so as to maximally reduce the initial bacterial count, but not affect the quality of the chilled beef. Then, the preservation effect on the chilled beef after the optimized UV sterilization treatment during 0 ± 0.2 °C storage was investigated. The results showed that UV irradiation with parameters of 6 cm and 14 s formed the optimal UV sterilization conditions for the chilled beef, maximally reducing the number of microorganisms by 0.8 log CFU/g without affecting lipid oxidation or color change. The 6 cm and 14 s UV sterilization treatment of the chilled beef was able to reduce the initial microbial count, control the bacterial growth, and delay the increase in the TVB-N values during storage. Compared with the control group, the total bacterial count decreased by 0.56-1.51 log CFU/g and the TVB-N value decreased by 0.20-5.02 mg N/100 g in the UV-treated group. It was found that the TBARS value of the UV treatment group increased during late storage; on days 9-15 of storage, the TBARS values of the treatment group were 0.063-0.12 mg MDA/kg higher than those of the control group. However, UV treatment had no adverse impact on the pH, color, or sensory quality of chilled beef. These results prove that UV treatment can effectively reduce the microbial count on the surface of beef and improve its microbial safety, thus maintaining the quality of beef and prolonging its shelf life. This study could provide a theoretical basis for the preservation technology of chilled beef in small-space storage equipment.

Characterization of effector protein Hap determining meat spoilage process from meat-borne Aeromonas salmonicida

The spoilage roles of effector proteins secreted by dominant spoilage bacteria during food spoilage remained unknown. In this investigation, a hemagglutinin protease (Hap) belonging to the M4 family metallopeptidase was identified from Aeromonas salmonicida 29 isolate. It, has a molecular weight of 33.5 kDa, a V_max of 17.06 μg/mL/min, and a K_m of 2.46 mg/mL, and is conserved in various dominant spoilage bacteria. The stability testing demonstrated that Hap could maintain specific activity in the common environments (pH, temperature, and metal ions) of chilled meat. It exhibited high spoilage ability on meat in situ, increasing TVB-N, pH values, and the production of volatile organic compounds (VOCs), which was consistent with proteolytic activity analysis, completely confirming the determinant role of Hap for meat spoilage. These observations will enrich the spoilage theory and provide new insights into the control of food quality and safety.

Fortification of polysaccharide-based packaging films and coatings with essential oils: A review of their preparation and use in meat preservation

As the demand for botanical food additives and eco-friendly food packaging materials grows, the use of essential oils, edible biodegradable films and coatings are becoming more popular in packaging. In this review, we discussed the recent research trends in the use of natural essential oils, as well as polysaccharide-based coatings and films: from the composition of the substrates to preparing formulations for the production of film-forming technologies. Our review emphasized the functional properties of polysaccharide-based edible films that contain plant essential oils. The interactions between essential oils and other ingredients in edible films and coatings including polysaccharides, lipids, and proteins were discussed along with effects on film physical properties, essential oil release, their active role in meat preservation. We presented the opportunities and challenges related to edible films and coatings including essential oils to increase their industrial value and inform the development of edible biodegradable packaging, bio-based functional materials, and innovative food preservation technologies.

Selected-ion flow-tube mass spectrometry for the identification of volatile spoilage markers for fresh pork packaged under modified atmospheres

Microbial behavior during meat storage leads to the generation of volatile organic compounds (VOCs) and unpleasant off-odors. This study focused on a novel real-time analytical method, selected-ion flow-tube mass spectrometry (SIFT-MS), to monitor VOC quality and identify spoilage indicators for fresh pork stored under different packaging atmospheres (air, 70/0/30, 70/30/0, 5/30/65, 0/30/70 - v/v% O₂/CO₂/N₂) at 4 °C. A comprehensive selection methodology was used to identify compounds with good instrumental data quality as well as a strong relationship with microbial growth and olfactory rejection. Based on the volatolome quantified by SIFT-MS, storage periods and conditions can be discriminated using multivariate statistics. Acetoin (or ethyl acetate) represented a significant pork quality marker for high-O₂ conditions, whereas ethanol, 3-methylbutanal and sulfur compounds can indicate the anaerobic storage progress. Considering the applicability in monitoring different VOC profiles, SIFT-MS is expected to be promising in many storage scenarios to improve analytical efficiency and ensure reliability.

Replacement of polyethylene oxide by peach gum to produce an active film using Litsea cubeba essential oil and its application in beef

This study evaluated the effects of adding various concentrations (0 %, 1 %, 2 %, and 3 %) of peach gum (PG) to films made from polyethylene oxide (PEO) combined with Litsea cubeba essential oil (LCEO) to be utilized as active packaging for food in the future. The findings showed that the film containing PG 2 % concentration had the best physic-mechanical properties. In films made with PG, the glass transition temperature was significantly improved. Combining PG and PEO resulted in films that were brighter in color, had lower WVP values, and had the lowest water activity. Furthermore, XRD demonstrated that PG additions were compatible with the film of PEO blended with LCEO. The PG films formulated with PG presented high antioxidant and antibacterial activity against Staphylococcus aureus and E. coli. Wrapping beef with P2G2 film led to maintaining its quality with suitable levels of pH, TBARS, and TVB-N. This also decreased the number of E. coli and S. aureus in beef throughout the storage period. The results indicate that adding PG to PEO films enhances their suitability for food preservation.

White and honey Chlorella vulgaris: Sustainable ingredients with the potential to improve nutritional value of pork frankfurters without compromising quality

This study aimed to evaluate the effect of the chlorophyll-deficient microalgae mutants, honey (yellow) and white Chlorella vulgaris, (3%) on the nutritional, physicochemical, microbiological, and sensory characteristics of frankfurters. The presence of microalgae resulted in increased PUFA content and higher PUFA/SFA ratio, but lower n-6/n-3 ratio and lipid indices (P < 0.05). C. vulgaris inclusion in frankfurters increased (P < 0.05) Na, K, Ca, P, and Zn and improved the Na/K ratio, but lowered Mn, and in the case of white C. vulgaris, Cu content, compared to the control. The higher protein content decreased water release from emulsions elaborated with microalgae. White C. vulgaris inclusion decreased cohesiveness and springiness of the frankfurters. Due to the presence of pigment, microalgae inclusion led to a decrease in redness and an increase in yellowness of frankfurters. The presence of microalgae resulted in lower (P < 0.05) bacterial counts and did not affect TBARs during storage. The addition of microalgae in frankfurters produced acceptable sensory characteristics but resulted in lower scores compared to reference products.

Lacto-fermented garlic sauce improved the quality and extended the shelf life of lamb meat under the chilled condition

This study evaluated the potential of fermented garlic as a marinated lamb sauce ingredient to improve the quality and shelf life of chilled lamb. Garlic was subjected to Lacto-fermentation for 72 h at 37 °C using Lacticaseibacillus casei. The ¹H NMR metabolomics profile showed the presence of eight amino acids and five organic acids in fermented garlic, indicating the attribution to the antioxidant and antimicrobial activities. The FRAP and DPPH assays of fermented garlic revealed antioxidant activities of 0.45 ± 0.09 mmol/100 g DW and 93.85 ± 0.02 %, respectively. Meanwhile, fermented garlic inhibited the growth of Escherichia coli (95 %), Staphylococcus aureus (99 %) and Salmonella Typhimurium (98 %). When fermented garlic was added to the marinade sauce, it successfully reduced the microbial load of lamb meat by 0.5 log CFU/g after 3 days of storage. There were no significant differences in color between the control and marinated lamb after 3 days of marinating in a sauce formulated with fermented garlic. Furthermore, marinated lamb significantly improved water-holding capacity, texture, juiciness, and overall acceptance. These findings indicated a potential addition of fermented garlic in marinade lamb sauce recipes to improve the quality and safety of meat products.

Preliminary investigation into the prediction of indicators of beef spoilage using Raman and Fourier transform infrared spectroscopy

The objective of this study was to assess the potential to predict the microbial beef spoilage indicators by Raman and Fourier transform infrared (FT-IR) spectroscopies. Vacuum skin packaged (VSP) beef steaks were stored at 0 °C, 4 °C, 8 °C and under a dynamic temperature condition (0 °C ∼ 4 °C ∼ 8 °C, for 36 d). Total viable count (TVC) and total volatile basic nitrogen (TVB-N) were obtained during the storage period along with spectroscopic data. The Raman and FTIR spectra were baseline corrected, pre-processed using Savitzky-Golay smoothing and normalized. Subsequently partial least squares regression (PLSR) models of TVC and TVB-N were developed and evaluated. The root mean squared error (RMSE) ranged from 0.81 to1.59 (log CFU/g or mg/100 g) and the determination coefficient (R²) from 0.54 to 0.75. The performance of PLSR model based on data fusion (combination of Raman and FT-IR data) is better than that based on Raman spectra and similar to that of FT-IR. Overall, Raman spectroscopy, FT-IR spectroscopy, and a combination of both exhibited a potential for the prediction of the beef spoilage.

Effect of low temperature on the resistance of Listeria monocytogenes and Escherichia coli O157:H7 to acid electrolyzed water

Low temperature can affect the resistance of pathogenic bacteria to other external stress. The present study was envisaged to assess the tolerance of L. monocytogenes and E. coli O157:H7 to acidic electrolyzed water (AEW) under low temperature stress. AEW treatment caused a damage to cell membrane of the pathogenic bacteria, which led to protein leakage and DNA damage. Compared with the pathogenic bacteria cultured at 37 °C (pure culture), the L. monocytogenes and E. coli O157:H7 cells cultivated at low temperature presented a less damage and had a higher survival rate when exposed to AEW. Therefore, 4 °C or 10 °C grown bacteria were less susceptible to AEW than those cultured at 37 °C. And this phenomenon was verified when AEW was used to treat the pathogenic bacteria inoculated in salmon. In addition, transcriptomic sequencing technology (RNA-seq) was used to reveal the mechanism of AEW tolerance of L. monocytogenes under low temperature stress. Transcriptomic analysis showed the expression of the cold shock protein, regulation of DNA-templated transcription, ribosome pathway, phosphotransferase system (PTS), bacteria chemotaxis, SOS response and DNA repair were involved in the resistance of L. monocytogenes to AEW. We speculated that the direct modulation of the expression of cold shock protein CspD, the indirect effect on the expression of cspD by inhibiting the expression of Crp/Fnr family transcriptional regulator or enhancing the level of cAMP by regulating PTS could reduce the resistance of L. monocytogenes cultivated at 4 °C to AEW. Our study contributes to solving the problem of the reduced bacteriostatic effect in cold storage environment.

Antibacterial Activity and Mechanism of Oxidized Bacterial Nanocellulose with Different Carboxyl Content

Oxidized bacterial nanocellulose (OBC) is reported to prevent microbial growth, but its antibacterial characteristics and mechanism are still unclear. Here, the antibacterial mechanism of OBC is explored by detecting and assessing the interaction of OBC with different carboxyl content on Staphylococcus aureus and Escherichia coli. The results show that OBC has strong antibacterial activity and antibiofilm activity against S. aureus and E. coli, which is positively correlated with the carboxyl content of OBC. After OBC treatment, the bacteria adhesion is inhibited and the cell membrane is destroyed leading to increased permeability. Further investigation reveals that the concentration of cyclic diguanosine monophosphate (c-di-GMP) that induced biofilm formation is significantly decreased to 1.81 pmol mg^-1 after OBC treatment. In addition, OBC inactivates mature biofilms, with inactivation rates up to 79.3%. This study suggests that OBC has excellent antibacterial and antiadhesion properties, which can increase the cell membrane permeability and inhibit c-di-GMP formation. In addition, OBC also has a strong inactivation effect on mature biofilm, which can be used as an effective antibiofilm agent.

The biological effect of a beef-derived Latilactobacillus sakei on beef steaks during chilled storage

The aim of this study was to investigate the biological inhibiting effect of a beef-derived Latilactobacillus sakei (RS-25) on the spoilage of beef steaks in overwrapped packaging during the 12 days of storage at 4°C. Beef quality as well as microbial indicators were determined at different intervals during the storage after the inoculation of RS-25 at the 6 log CFU/g, and the high-throughput sequencing was applied to investigate the changes of microbial community structure during the storage. The inoculation of RS-25 on beef had no effect (p > .05) on pH, TBARS, and TVB-N during storage indicating the weak effect of such strain on the eat quality. Furthermore, the rise of L* and the delayed decline of a* and b* reveal the protection effect of RS-25 on the meat color. RS-25 reduced the re-contaminated Salmonella typhimurium by 1.16 log CFU/g (p < .01), and the growth of Brochothrix thermosphacta was also inhibited but no inhibition was found on the Pseudomonas spp. at the first 6 days of storage. The inhibiting effect of RS-25 was covered by the rapid growth of other microorganism during the following 6 days of storage. Consistent with the microbial counts results, high-throughput sequencing analysis confirmed that the inoculated L. sakei RS-25 was dominant at first 6 days, and then replaced by Pseudomonas spp. The findings obtained from the current study may provide basic information for the further application of bioprotective bacteria in preservation of beef steaks in the overwrapped packaging.