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.

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.

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.

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.

Comparative transcriptomics to reveal muscle-specific molecular differences in the early postmortem of Chinese Jinjiang yellow cattle.

Differences in the expression of functional genes between beef Longissimus Lumborum (LL) and Psoas Major (PM) are not well understood. The aim of present study is to reveal transcriptome changes of beef LL and PM during early postmortem by high-throughput Illumina Hiseq4000 Sequencing. Hierarchical clustering analysis indicated significant differences in transcriptome profiles between LL and PM as well as 1 h and 12 h postmortem. A total of 65 genes differentially expressed between LL and PM (fold change ≥3, and p < 0.05; 34 were up-regulated in LL and 31 in PM), and the majority of them (53 genes) occurred at 12 h postmortem. These differentially expressed genes mainly involved in energy production and conversion, nucleotide metabolic, posttranslational modification, and transcription. KEGG analysis revealed that oxidative phosphorylation was one of the important pathways. This study gave new perspectives to understand the underlying mechanisms associated with muscle-specific beef quality.

Enzymatic characteristics of polyphenoloxidase from shrimp (Penaeus vannamei) and its inhibition by a novel hydroxypyridinone derivative.

Melanosis developed in shrimp (Penaeus vannamei) is mainly initiated by polyphenoloxidase (PPO), thus understanding of the characteristics of PPO in shrimp is important for controlling the melanosis of shrimp. The shrimp cephalothorax turns black most rapidly amongst all the tissues during the chilled storage. Crude PPO extracted from this cephalothorax has an optimal pH of 6.0 and an optimal temperature of 50 °C. PPO is relatively stable under neutral and weak alkaline conditions (pH 5.5-9.0) and the temperature range of 25-35 °C. The kinetic parameters K m and V max were recorded as 3.02 mM and 54.3 U/mg of protein, respectively, using L-Dopa as a substrate. The molecular weight of PPO was estimated as 200-220 kDa by an activity staining test. A hydroxypyridinone derivative, 5-hydroxy-1-octyl-4-oxo-1,4-dihydropyridine-2-carbaldehyde O-ethyl oxime, was demonstrated to efficiently inhibit the PPO, indicating that this compound might find application as a shrimp preservative.

Targeted metabolomics to reveal muscle-specific energy metabolism between bovine longissimus lumborum and psoas major during early postmortem periods.

Targeted metabolomics was applied to elucidate energy metabolites in bovine (Chinese Jinjiang yellow cattle, n = 4) longissimuss lumborum (LL) and psoas major (PM) muscles during the early postmortem period (1 h, 6 h, 12 h, and 24 h). The a* value increased significantly (P < .05) in both of LL and PM within 24 h postmortem. Compared with PM, LL had higher area percentage of type IIB fibers (48.41% vs 30.60%, P < .001) and lower proportion of type I fibers (24.98% vs 46.16%, P < .001). A total of 22 energy metabolites were successfully detected by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The principal component and hierarchical cluster analyses of these metabolites exhibited clear distinctions between LL and PM samples from different postmortem periods. Enzymic activities (lactate dehydrogenase, malate dehydrogenase, and succinate dehydrogenase), contents of pyruvate and numbers of metabolites involved in tricarboxylic acid (TCA) cycle evidenced different changes in LL and PM, which indicated distinguished metabolic patterns between them.