Comparative Study of the Antibacterial Effects of S-Nitroso-N-acetylcysteine and Sodium Nitrite against Escherichia coli and Their Application in Beef Sausages.

This study investigated the antibacterial effects of S-nitroso-N-acetylcysteine (SNAC) and sodium nitrite (NaNO2) against Escherichia coli and their application in beef sausages. Both SNAC and NaNO2 demonstrated pH-responsive antibacterial activity, with SNAC showing greater efficacy than NaNO2 (p < 0.05) at the same pH (3, 5, and 7). The reactive oxygen species (ROS) and reactive nitrogen species (RNS) induced in E. coli by SNAC were significantly higher than those induced by NaNO2 (p < 0.05), and both ROS and RNS values increased as the pH decreased. In addition, a lower pH led to more pores on the E. coli cell surface and increased membrane permeability, resulting in a more pronounced inhibitory effect. When applied to a beef sausage, SNAC-treated sausages had significantly lower total colony counts and carbonyl content compared to NaNO2-treated ones (p < 0.05). Consequently, SNAC shows great potential as a replacement for NaNO2 in meat products.

Changes in stresses sensitivity of ohmic heating-induced sublethally injured Staphylococcus aureus during repair: Potential mechanisms at the cellular and molecular levels.

Ohmic heating (OH), an emerging food processing technology employed in the food processing industry, raises potential food safety concerns due to the recovery of sublethally injured pathogens such as Staphylococcus aureus (S. aureus). In the present study, sensitivity to various stress conditions and the changes in cellular-related factors of OH-injured S. aureus during repair were investigated. The results indicated that liquid media differences (nutrient broth (NB), phosphate-buffered saline (PBS), milk, and cucumber juice) affected the recovery process of injured cells. Nutrient enrichment determines the bacterial repair rate, and the rates of repair for these media were milk > NB > cucumber juice > PBS. The sensitivity of injured cells to various stressors, including different acids, temperature, nisin, simulated gastric fluid, and bile salt, increased during the injury phase and subsequently diminished upon repair. Additionally, the intracellular ATP content, enzyme activities (Na+/K+-ATPase, Ca2+/Mg2+-ATPase, and T-ATPase) and ion concentrations (Mg2+, K+, and Ca2+) gradually increased during repair. After 5 h of repair, the intracellular substances content of cell's was significantly higher than that of the injured bacteria without repair, while some indicators (e.g., Na+/K+-ATPase, K+, and Ca2+) were not restored to the untreated level. The results of this study indicated that OH-injured S. aureus exhibited strengthened resistance post-recovery, potentially due to the restoration of cellular structures. These findings have implications for optimizing food storage conditions and advancing OH processes in the food industry.

Inactivation of Bacillus cereus spores by ohmic heating: Efficiency and changes of spore biological properties.

Bacillus cereus spores pose a significant concern during food processing due to their high resistance to environmental stress. Ohmic heating (OH) is an emerging and alternative heating technology with potential for inactivating such spores. This study evaluated the inactivation effects and the biological property changes of Bacillus cereus spores during OH treatments. OH effectively inactivated spores in milk, orange juice, broth, rice soup, and buffer solution in less time than oil bath heating (OB). A decrease in NaCl content improved spore inactivation at the same temperature. Spores were more sensitive to acid at 80-85 °C with OH treatment. Furthermore, OH at 10 V/cm and 50 Hz could reduce the spore resistance and inhibit an increase in spore hydrophobicity and spore aggregation. Both heating methods resulted in significant dipicolinic acid (DPA) leakage and damage to the cortex and inner membranes of the spores. However, OH at 10 V/cm and 50 Hz had the lowest DPA leakage and inflicted the least damage to the inner membrane. The damage to the spore's inner membrane was considered the primary reason for inactivation by OB and OH treatments. Still, OH at 10 V/cm and 50 Hz might also block the germination or outgrowth of treated spores or cause damage to the spore core.

Effects of ohmic heating with different voltages on the quality and microbial diversity of cow milk during thermal treatment and subsequent cold storage.

Ohmic heating (OH), an innovative heating technology, presents potential applications in the pasteurization of liquid foods. Therefore, the study was conducted to evaluate the effect of OH at various voltage gradients (10 V/cm, 12.5 V/cm, and 15 V/cm) and water bath (WB) on microbial inactivation, physicochemical and sensory properties and microbial flora of pasteurized milk. Results indicated that OH with higher voltage could effectively inactivate microorganisms in milk, requiring less heating time and energy. Moreover, OH treatment at higher voltages could decelerate lipid oxidation and better maintain the sensory quality and essential amino acids content of milk. Additionally, all treatments significantly altered the microbial community, and during storage, the microbial community in milk treated with 10 V/cm and 12.5 V/cm OH remained relatively stable. OH treatments with voltage gradients exceeding 12.5 V/cm could effectively inactive microorganisms and maintain the quality attributes of milk.

Preparation of lemon essential oil nanoemulsion and its effect on the microbial community of pork patties.

The purpose of this study was to prepare an essential oil nanoemulsion and apply it to meat products to achieve antimicrobial effect. The nanoemulsion of lemon essential oil was produced by high power ultrasonication. The influences of ultrasonic power, ultrasonic time, and mass ratio of sodium caseinate to essential oil on the particle size were examined. The optimal conditions for preparing nanoemulsion were ultrasonic power 327 W, ultrasonic time 18 min, and sodium caseinate to essential oil mass ratio 4.23:1. Lower temperature was more conducive to the preservation of nanoemulsion. Compared to control and essential oil group, the nanoemulsion could decrease the total volatile basic nitrogen content and total bacterial colony in pork patties. When applied to pork patties, the nanoemulsion decreased the microbial diversity and inhibited the growth of a variety of microorganisms such as Bacillus, extending the storage time of pork patties. This study developed a novel and workable nanoemulsion for inhibiting bacteria of meat products.

Effects of vegetable oil and ethylcellulose on the oleogel properties and its application in Harbin red sausage.

The effects of ethylcellulose (EC) concentration (6-12 %) and types of vegetable oil (sunflower, peanut, corn, and flaxseed oils) on the color, hardness, oil loss, lipid oxidation, and rheology property of oleogels were investigated in this study. Peanut oil (PO) oleogel was selected to replace pork fat partially in Harbin red sausage. Meanwhile, the fatty acid profile, texture, and sensory attributes of the reformulated sausages were analyzed. Oleogels formulated with higher EC concentration had higher brightness and hardness, a higher degree of lipid oxidation, and greater storage (G') and loss (G'') moduli. Oleogels formulated with PO had lower oil loss, flaxseed oil oleogel had higher hardness. Corn oil and PO oleogels had a lower level of lipid oxidation. The texture, lipid oxidation, and sensory attributes of the reformulated sausages, in which 10-30 % pork fat was replaced with PO oleogel, did not significantly differ from those without oleogel replacement. Meanwhile, the reformulated sausages had a healthier fatty acids profile and higher nutritional value.

Sublethally injured microorganisms in food processing and preservation: Quantification, formation, detection, resuscitation and adaption.

Sublethally injured state has been recognized as a survival strategy for microorganisms suffering from stressful environments. Injured cells fail to grow on selective media but can normally grow on nonselective media. Numerous microorganism species can form sublethal injury in various food matrices during processing and preservation with different techniques. Injury rate was commonly used to evaluate sublethal injury, but mathematical models for the quantification and interpretation of sublethally injured microbial cells still require further study. Injured cells can repair themselves and regain viability on selective media under favorable conditions when stress is removed. Conventional culture methods might underestimate microbial counts or present a false negative result due to the presence of injured cells. Although the structural and functional components may be affected, the injured cells pose a great threat to food safety. This work comprehensively reviewed the quantification, formation, detection, resuscitation and adaption of sublethally injured microbial cells. Food processing techniques, microbial species, strains and food matrix all significantly affect the formation of sublethally injured cells. Culture-based methods, molecular biological methods, fluorescent staining and infrared spectroscopy have been developed to detect the injured cells. Cell membrane is often repaired first during resuscitation of injured cells, meanwhile, temperature, pH, media and additives remarkably influence the resuscitation. The adaption of injured cells negatively affects the microbial inactivation during food processing.

Inactivation effects and mechanism of ohmic heating on Bacillus cereus.

The inactivation effects and mechanism of ohmic heating (OH) on Bacillus cereus ATCC 11778 were investigated in this study, conventional heating (CH) was also carried out and served as control. All OH treatments (10 V/cm 50 Hz, 10 V/cm 500 Hz, 5 V/cm 50 Hz and 5 V/cm 500 Hz) could achieve a comparable inactivation effect with CH, while OH treatments significantly shortened the processing time. OH treated cells exhibited significantly higher leakage of metal ions (Mg2+ and K+) and biomacromolecules (nucleic acids and proteins) than those treated with CH when bacterial suspensions were heated to the same temperature. Moreover, OH treatment caused more damage on membrane structure, greatly decreased the cell membrane potential and endogenous enzyme activity than that of CH. The results of this study indicated that OH is more efficient in the inactivation of bacteria.

Muscle fiber characteristics and apoptotic factor differences in beef Longissimus lumborum and Psoas major during early postmortem.

This study was conducted to study muscle fiber characteristics and apoptotic factor differences within 24 h postmortem of bovine longissimus lumborum (LL) and psoas major (PM). Compared to LL, PM had a higher proportion of type I fibers and lower proportion of type II fibers. PM also had higher ROS levels. For bcl-2 family proteins, anti-apoptotic BCL-2 level was lower and pro-apoptotic BAX level was higher in PM. For caspases, at 1 h postmortem, gene and protein expression level of caspase-3 and caspase-9 was higher in PM than that of LL. The levels of DNA damage apoptotic factors ABL1, AIF and ENDOG was higher in PM than in LL. The results suggested that apoptotic gene and protein expression were different in muscles with different fiber type composition. These findings provided insights into muscle fiber and apoptotic factor differences during early postmortem in bovine PM and LL.

Changes of mitochondrial lipid molecules, structure, cytochrome c and ROS of beef Longissimus lumborum and Psoas major during postmortem storage and their potential associations with beef quality.

This study investigated changes in mitochondrial lipid molecules and their potential associations with Longissimus lumborum (LL) and Psoas major (PM) quality during storage. A total of 1610 lipid species that matched with 36 lipid classes were identified from isolated mitochondria. PM had more key lipid molecules at storage d-1 including diacylglycerol and triacylglycerol (may play roles in membrane stability), phosphatidylethanolamine, acyl carnitine and cardiolipin (involved in energy metabolism), and cardiolipin and phosphatidylserine (important factors in apoptosis). Correspondingly, with extended storage time, mitochondrial structure, cytochrome c and reactive oxygen species (ROS) were changed, and muscle oxidation intensified. These changes have close associations with shear force and water holding capacity (WHC). Compared with LL, PM had higher content of lipid classes, more mitochondrial ROS, greater muscle oxidation, and lower shear force and WHC. These findings provided new insights into the effects of lipidome on mitochondrial structure, ROS and cytochrome c, and their potential associations with beef quality.

Employment of cold atmospheric plasma in chilled chicken breasts and the analysis of microbial diversity after the shelf-life storage.

Cold atmospheric plasma, featured as a non-thermal food processing technology has gained prominent attention for its practical application. The demand for chilled chicken has increased rapidly due to its nutritious value. However, chilled chicken often suffers from a short shelf life due to its susceptibility to spoilage. In this study, air- and nitrogen plasma were applied to investigate microbial inactivation effects and shelf-life extension of chilled chicken. Meanwhile, the microbial diversity of chicken breasts after air and nitrogen-CAP treatment and at the end of shelf-life was analyzed. Results illustrated that the inactivation effects of air plasma were more potent than that of nitrogen plasma, while nitrogen plasma could better maintain the sensory properties. Also, further investigation illustrated that air- and nitrogen-CAP could change the microbial community significantly. Both treatment time and working gases were essential experimental parameters that affected the microbial community composition.

Subcellular inactivation mechanisms of Pseudomonas aeruginosa treated by cold atmospheric plasma and application on chicken breasts.

As a novel microbe inactivation strategy, cold atmospheric plasma (CAP) technology has attracted great attractions in the past two decades. This study demonstrated that the CAP treatment was a robust inactivation approach for P. aeruginosa. Air and nitrogen-CAP achieved 100 % inactivation efficiency in 5 and 9 min, respectively. Furthermore, the inactivation mechanisms were explained by measuring several physicochemical indexes, including the characteristics of bacterial suspension, cell membrane integrity, cell viability, and the concentration of intracellular substances. The possible inactivation mechanisms might be that the RONS generated by air and nitrogen attacked the cell envelope, resulted in the leakage of intracellular substances; meanwhile, RONS also destroyed the intracellular anti-oxidative system, accelerated the oxidative stress and disrupted the intracellular redox homeostasis, subsequently the death of the cells. Moreover, the inactivation application in chicken breasts proved CAP could be a novel sanitizing process in practical industries.

Alteration of Mitochondrial Lipidome and Its Potential Effect on Apoptosis, Mitochondrial Reactive Oxygen Species Production, and Muscle Oxidation in Beef during Early Postmortem.

Lipid molecules are important participants in mitochondria-mediated apoptosis. This study explored the effect of mitochondrial lipids on mitochondria-mediated apoptosis, mitochondrial reactive oxygen species (ROS) production, and muscle oxidation of beef longissimus lumborum (LL, n = 6) and psoas major (PM, n = 6) during 24 h postmortem. A total of 432 lipid species matched with 21 lipid classes were identified. Remarkably, at 12 h postmortem, the levels of cardiolipin and phosphatidylserine in PM and ceramide, cardiolipin, phosphatidylserine, and sphingosine in LL increased significantly compared with 1 h postmortem, indicating that mitochondria-mediated apoptosis in beef muscle was accelerated during early postmortem. Moreover, PM had higher levels of cardiolipin and phosphatidylserine than LL, also suggesting a higher degree of apoptosis in PM during postmortem. Lipid molecules may assist the production of mitochondrial ROS and decrease the mitochondrial membrane potential (MMP) during postmortem apoptosis, resulting in muscle oxidation and the damage of antioxidant system. Notably, compared with LL, PM had higher abundance of apoptosis-related lipid molecules, a higher amount of ROS, faster diminishment in MMP, and then a higher degree of apoptosis. These findings provided new insights into the apoptosis and muscle biochemistry in beef during early postmortem.

Light activation of gold nanorods but not gold nanospheres enhance antibacterial effect through photodynamic and photothermal mechanisms.

Plasmonic nanomaterials of gold and silver have been reported to have antibacterial effect. In this study, three gold nanomaterials (NMs) of different aspect rations (Gold nanospheres (AuNSs, aspect ratio 1), and two gold nanorods (AuNRs636, aspect ratio 2.79; AuNRs772, aspect ratio 3.42)) and silver nanoparticles (AgNPs) were synthesized, characterized and the effect of incandescent light on their antibacterial properties were examined. Bacterial inactivation during photoinactivation of nanomaterials and antibacterial mechanisms (biotic ROS, membrane potential, membrane damage) were investigated using Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, Salmonella enterica serovar Typhimurium, and methicillin-resistant S. aureus. The results indicated that AuNSs had no antibacterial activity in the tested concentration (0.49-250 µg/mL), while AuNR636 and AuNRs772 showed significant bactericidal effect on all tested bacteria. Notably, AuNRs636 presented higher antibacterial effect than AuNRs772, which could result from higher surface reactivity of AuNRs636 owing to higher dangling bonds. Further studies showed that AuNRs but not AuNSs generated hydroxyl radicals (·OH) (photodynamic effect) and photothermal effect when exposed to incandescent light. The combined photodynamic and photothermal effect resulted in bacterial inactivation through cell membrane damage, lowering of cell membrane potential and DNA degradation. In summary, this investigation showed that Au NRs but not Au NSs exhibit photodynamic and photothermal effects suggesting the potential of fabricating material surfaces with Au NRs for photoactivated bacterial inactivation.

Recovery and virulence factors of sublethally injured Staphylococcus aureus after ohmic heating.

Ohmic heating (OH) is an alternative thermal processing technique, which is widely used to pasteurize or sterilize food. However, sublethally injured Staphylococcus aureus induced by OH is a great concern to food safety. The recovery of injured S. aureus by OH and virulence factor changes during recovery were investigated in this study. The liquid media (phosphate-buffered saline, buffered peptone water and nutrient broth (NB)), temperature (4, 25 and 37 °C) and pH (6.0, 7.2 and 8.0) influenced the recovery rate and the injured cells completely repaired in NB at 37 °C, pH 7.2 with the shortest time of 2 h. The biofilm formation ability, mannitol fermentation, hemolysis, and coagulase activities decreased in injured S. aureus and recovered during repair process. Quantitative real-time PCR showed the expression of sek, clfB and lukH involved in virulence factors increased during recovery. The results indicated that the virulence factors of injured S. aureus recovered after repair.

Comparative transcriptomic study of Escherichia coli O157:H7 in response to ohmic heating and conventional heating.

In this study, the high-throughput Illumina HiSeq 2000 mRNA sequencing technique was used to investigate the transcriptome response of Escherichia coli O157:H7 exposed to ohmic heating (OH) and water bath heating (WB). Compared to untreated samples, a total of 293, 516, and 498 genes showed differential expression after HVOH (high voltage short time ohmic heating), LVOH (low voltage long time ohmic heating), and WB, respectively. Therefore, LVOH had the potential to cause comparable effects on the transcriptome of E. coli O157:H7 as compared to WB, but not HVOH. These results indicated that additional non-thermal effects were not reflected on transcriptome of E. coli O157:H7 using both HVOH and LVOH, in particular the HVOH. Most of differentially expressed genes involved in information storage and processing, and cellular processes and signaling showed up-regulation whereas most of genes related to the metabolism were down-regulated after HVOH, LVOH, and WB. In addition, more attention needs to be paid to the up-regulation of a large number of virulence genes, which might increase the ability of surviving E. coli O157:H7 to infect host cells after HVOH, LVOH, and WB. This transcriptomic study on the response of E. coli O157:H7 to OH protomes the understanding of inactivation mechanism of OH on the molecular level and opens the door to future studies for OH.

Effects of fat/oil type and ethylcellulose on the gel characteristic of pork batter.

The effects of fat/oil type (pork fat; sunflower seed, peanut, corn and flaxseed oils) and ethylcellulose (EC) concentration (8%, 10% and 12%) on the gel characteristic of pork batter were investigated in this study. Replacing pork fat in meat batter with organogels prepared with EC and vegetable oils obtained cooked batters with higher hardness, gumminess and chewiness, furthermore, increasing EC level in the organogels increased hardness, while cohesiveness and springiness showed no significant changes. Emulsion stability of all organogels groups was improved compared to pork fat group and the type of vegetable oil affected the emulsion stability. A shorter relaxation time T2 and a larger peak area P22 were observed for batters formulated with oraganogels, which indicated higher percentage of immobilized water. The batters prepared with pork fat displayed larger fat globules, lower L* value than those prepared with organogels, but the redness (a* values) had no significant difference.

Comparative analysis of quality and microbial safety of ohmic and water bath cooked pork batter during refrigerated storage.

In this study, the microbial safety, lipid and protein oxidation, and water characteristics of ohmic (OH) and water bath (WB) cooked pork batter during storage at 4 °C were investigated. The results indicated that the cooking time was much shorter for samples cooked to 72 °C by OH cooking (2 min) than WB cooking (41 min), but OH and WB cooked samples had no significant difference in total viable colony (TVC) at day 28. No significant differences were observed in thiobarbituric acid reactive substances (TBARS) and total sulfhydryl content between OH and WB cooked samples (P > 0.05), but the OH cooked samples had higher carbonyl content (P < 0.05). Although there were no significant differences for water content and drip loss between OH and WB cooked samples, the relaxation time T 22 of the OH cooked samples were longer than WB cooked ones (P < 0.05). On the whole, the qualities of the OH cooked samples were comparable to the WB cooked ones during the entire storage period, indicating that there was a great prospect for OH cooking to be applied in the meat product industry.

Mitochondria changes and metabolome differences of bovine longissimus lumborum and psoas major during 24 h postmortem.

This study was performed to reveal mitochondria changes and metabolome differences between bovine longissimus lumborum (LL) and psoas major (PM) muscles within the first 24 h postmortem. PM showed significant lower (P < .05) pH than LL at 6 h and 12 h postmortem. LL had significant higher (P < .05) mitochondrial membrane potential and lower mitochondrial reactive oxygen species levels than PM at 24 h postmortem. For metabolome, distinctive separation between LL and PM could be seen from principal component analysis and hierarchical clustering analysis. Carnosine, L-histidine and adenosine diphosphate were found with higher abundances in LL. Whereas higher abundances of inosine and hypoxanthine were detected in PM, which indicated distinct purine metabolism rate between muscle types. Higher abundances of glycerophospholipids in PM may increase risk of oxidation damage, and subsequently result in inferior meat quality during extended retail display. The results of this study provided an idea for further research regarding the muscle-specific mitochondrial ROS on meat quality.

Label free-based proteomic analysis of Escherichia coli O157:H7 subjected to ohmic heating.

To investigate the inactivation mechanism of ohmic heating (OH) on Escherichia coli O157:H7 at the same inactivation levels, a label-free quantitative proteomic approach was employed in this study. Quantification of 2633 proteins was obtained with high confidence. Compared to untreated samples (CT), a total of 169, 84, and 26 proteins showed significantly differential abundance after high voltage OH (HVOH, 10 V/cm), low voltage OH (LVOH, 5 V/cm), and water bath heating (WB), respectively. Glyoxylate and dicarboxylate metabolism, ABC transporters, biosynthesis of amino acids, glycerophospholipid metabolism, and ribosome pathway were the main KEGG pathways mediated by OH, but only ribosome pathway was greatly affected by WB. The significant differences in proteome changes of E. coli O157:H7 among HVOH, LVOH, and WB treatments, especially the greater number of differential proteins in HVOH, indicated that OH might exert additional effects on proteome of E. coli O157:H7 due to the electric current, particularly in HVOH with higher electric field. This result enriched our understanding of molecular changes of E. coli O157:H7 induced by OH and provided data reference for further research into the inactivation mechanism of OH.