Alanine and glutamate catabolism collaborate to ensure the success of Bacillus subtilis sporulation.

Sporulation as a typical bacterial differentiation process has been studied for decades. However, two crucial aspects of sporulation, (i) the energy sources supporting the process, and (ii) the maintenance of spore dormancy throughout sporulation, are scarcely explored. Here, we reported the crucial role of RocG-mediated glutamate catabolism in regulating mother cell lysis, a critical step for sporulation completion of Bacillus subtilis, likely by providing energy metabolite ATP. Notably, rocG overexpression resulted in an excessive ATP accumulation in sporulating cells, leading to adverse effects on future spore properties, e.g. increased germination efficiency, reduced DPA content, and lowered heat resistance. Additionally, we revealed that Ald-mediated alanine metabolism was highly related to the inhibition of premature germination and the maintenance of spore dormancy during sporulation, which might be achieved by decreasing the typical germinant L-alanine concentration in sporulating environment. Our data inferred that sporulation of B. subtilis was a highly orchestrated biological process requiring a delicate balance in diverse metabolic pathways, hence ensuring both the completion of sporulation and production of high-quality spores.

Hydrogen-rich saline upregulates the Sirt1/NF-κB signaling pathway and reduces vascular endothelial glycocalyx shedding in sepsis-induced acute kidney injury.

ABSTRACT: Sepsis causes dysfunction in different organs, but the pathophysiological mechanisms behind it are similar and mainly involve complex haemodynamic and cellular dysfunction. The importance of microcirculatory dysfunction in sepsis is becoming increasingly evident, in which endothelial dysfunction and glycocalyx degradation play a major role. This study aimed to investigate the effects of hydrogen-rich saline (HRS) on renal microcirculation in septic renal failure, and whether Sirt1 was involved in the renoprotective effects of HRS. Rats model of sepsis was established by cecal ligation and puncture, and septic rats were intraperitoneal injected with HRS (10 ml/kg). We found that in sepsis, the degree of glycocalyx shedding was directly proportional to the severity of sepsis. The seven-day survival rate of rats in the HRS + CLP group (70%) was higher than that of the CLP group (30%). HRS improved acidosis and renal function and reduced the release of inflammatory factors (TNF, IL-1ßand IL-6). The endothelial glycocalyx of capillaries in the HRS + CLP group (115 nm) was observed to be significantly thicker than that in the CLP group (44 nm) and EX527 (67.2 nm) groups by electron microscopy, and fewer glycocalyx metabolites (SDC-1, HS, HA, and MMP9) were found in the blood. Compared with the CLP group, HRS reduced renal apoptosis and upregulated Sirt1 expression, and inhibited the NF-κB/MMP9 signalling pathway. In addition, HRS did not damage immune function in septic rats as well. Generally speaking, our results suggest that HRS can alleviate the inflammatory response, inhibit glycocalyx shedding, improve septic kidney injury, and enhance survival rate.

Insight into the mechanism of high hydrostatic pressure effect on inhibitory efficiency of three natural inhibitors on polyphenol oxidase.

The development of natural inhibitors of polyphenol oxidase (PPO) is crucial in the prevention of enzymatic browning in fresh foods. However, few studies have focused on the effect of subsequent sterilization on their inhibition efficiency. This study investigated the influence and mechanism of high hydrostatic pressure (HHP) on the inhibition of PPO by epigallocatechin gallate (EGCG), cyanidin-3-O-glucoside (C3G), and ferulic acid. Results showed that under the conditions of 550 MPa/30 min, the activity of EGCG-PPO decreased to 55.92%, C3G-PPO decreased to 81.80%, whereas the activity of FA-PPO remained stable. Spectroscopic experiments displayed that HHP intensified the secondary structure transformation and fluorescence quenching of PPO. Molecular dynamics simulations revealed that at 550 MPa, the surface interaction between PPO with EGCG or C3G increased, potentially leading to a reduction in their activity. In contrast, FA-PPO demonstrated conformational stability. This study can provide a reference for the future industrial application of natural inhibitors.

High pressure processing plus technologies: Enhancing the inactivation of vegetative microorganisms.

High pressure processing (HPP) is a non-thermal technology that can ensure microbial safety without compromising food quality. However, the presence of pressure-resistant sub-populations, the revival of sub-lethally injured (SLI) cells, and the resuscitation of viable but non-culturable (VBNC) cells pose challenges for its further development. The combination of HPP with other methods such as moderate temperatures, low pH, and natural antimicrobials (e.g., bacteriocins, lactate, reuterin, endolysin, lactoferrin, lactoperoxidase system, chitosan, essential oils) or other non-thermal processes (e.g., CO2, UV-TiO2 photocatalysis, ultrasound, pulsed electric fields, ultrafiltration) offers feasible alternatives to enhance microbial inactivation, termed as "HPP plus" technologies. These combinations can effectively eliminate pressure-resistant sub-populations, reduce SLI or VBNC cell populations, and inhibit their revival or resuscitation. This review provides an updated overview of microbial inactivation by "HPP plus" technologies and elucidates possible inactivation mechanisms.

A review on fermented vegetables: Microbial community and potential upgrading strategy via inoculated fermentation.

Fermentation is a traditional method utilized for vegetable preservation, with microorganisms playing a crucial role in the process. Nowadays, traditional spontaneous fermentation methods are widely employed, which excessively depend on the microorganisms attached to the surface of raw materials, resulting in great difficulties in ideal control over the fermentation process. To achieve standardized production and improve product quality, it is essential to promote inoculated fermentation. In this way, starter cultures can dominate the fermentation processes successfully. Unfortunately, inoculated fermentation has not been thoroughly studied and applied. Therefore, this paper provides a systematic review of the potential upgrading strategy of vegetable fermentation technology. First, we disclose the microbial community structures and succession rules in some typical spontaneously fermented vegetables to comprehend the microbial fermentation processes well. Then, internal and external factors affecting microorganisms are explored to provide references for the selection of fermented materials and conditions. Besides, we widely summarize the potential starter candidates with various characteristics isolated from spontaneously fermented products. Subsequently, we exhibited the inoculated fermentation strategies with those isolations. To optimize the product quality, not only lactic acid bacteria that lead the fermentation, but also yeasts that contribute to aroma formation should be combined for inoculation. The inoculation order of the starter cultures also affects the microbial fermentation. It is equally important to choose a proper processing method to guarantee the activity and convenience of starter cultures. Only in this way can we achieve the transition from traditional spontaneous fermentation to modern inoculated fermentation.

Natural chlorophyll: a review of analysis methods, health benefits, and stabilization strategies.

Chlorophyll (Chl) is a natural pigment, widely distributed ranging from photosynthetic prokaryotes to higher plants, with an annual yield of up to 1.2 billion tons worldwide. Five types of Chls are observed in nature, that can be distinguished and identified using spectroscopy and mass spectrometry. Chl is also used in the food industry owing to its bioactivities, including obesity prevention, inflammation reduction, viral infection inhibition, anticancer effects, anti-oxidation, and immunostimulatory properties. It has great potential of being applied as a colorant and dietary supplement in the food industry. However, Chl is unstable under various enzymatic, acidic, heat, and light conditions, which limit its application. Although some strategies, such as aggregation with other food components, microencapsulation, and metal cation replacement, have been proposed to overcome these limitations, they are still not enough to facilitate its widespread application. Therefore, stabilization strategies and bioactivities of Chl need to be expected to expand its application in various fields, thereby aiding in the sustainable development of mankind.

Decoding the Effects of High Hydrostatic Pressure and High-Temperature Short-Time Sterilization on the Volatile Aroma Profile of Red Raspberry Juice.

The loss of distinctive aromas due to sterilization significantly hinders efforts to enhance the sensory quality of fruit and vegetable juices. This study aimed to elucidate the impacts of high-hydrostatic pressure (HHP) and high-temperature short-time (HTST) sterilization methods on the loss of C6 aldehyde aroma-active compounds in red raspberry juice. External standard quantification and quantitative descriptive analysis (QDA) revealed a notable decline in the levels of hexanal and (Z)-3-hexenal following the HHP and HTST treatments (p < 0.05), resulting in a marked attenuation of the grassy aroma characteristic of red raspberry juice. Furthermore, a comprehensive examination of the precursors, pivotal enzymes, intermediates, and downstream aromas within the fatty acid metabolism pathway in different raspberry juice samples indicated that the C6 aldehydes loss induced by HHP and HTST sterilizations was primarily ascribed to the competitive inhibition of ß-oxidation and the hindered enzymatic oxidation of fatty acids. These insights suggest that modifying sterilization protocols and enhancing enzymatic stability may help preserve the aroma integrity of raspberry juice. Our findings offer practical guidance for optimizing juice processing techniques to maintain flavor.

Exploring high hydrostatic pressure effects on anthocyanin binding to serum albumin and food-derived transferrins.

This study investigated the effects of high hydrostatic pressure (HHP) on the binding interactions of cyanindin-3-O-glucoside (C3G) to bovine serum albumin, human serum albumin (HSA), bovine lactoferrin, and ovotransferrin. Fluorescence quenching revealed that HHP reduced C3G-binding affinity to HSA, while having a largely unaffected role for the other proteins. Notably, pretreating HSA at 500 MPa significantly increased its dissociation constant with C3G from 24.7 to 34.3 µM. Spectroscopic techniques suggested that HSA underwent relatively pronounced tertiary structural alterations after HHP treatments. The C3G-HSA binding mechanisms under pressure were further analyzed through molecular dynamics simulation. The localized structural changes in HSA under pressure might weaken its interaction with C3G, particularly polar interactions such as hydrogen bonds and electrostatic forces, consequently leading to a decreased binding affinity. Overall, the importance of pressure-induced structural alterations in proteins influencing their binding with anthocyanins was highlighted, contributing to optimizing HHP processing for anthocyanin-based products.

Semirational Design Based on Consensus Sequences to Balance the Enzyme Activity-Stability Trade-Off.

In this study, the phenomenon of the stability-activity trade-off, which is increasingly recognized in enzyme engineering, was explored. Typically, enhanced stability in enzymes correlates with diminished activity. Utilizing Rosa roxburghii copper-zinc superoxide dismutase (RrCuZnSOD) as a model, single-site mutations were introduced based on a semirational design derived from consensus sequences. The initial set of mutants was selected based on activity, followed by combinatorial mutation. This approach yielded two double-site mutants, D25/A115T (18,688 ± 206 U/mg) and A115T/S135P (18,095 ± 1556 U/mg), exhibiting superior enzymatic properties due to additive and synergistic effects. These mutants demonstrated increased half-lives (T1/2) at 80 °C by 1.2- and 1.6-fold, respectively, and their melting temperatures (Tm) rose by 3.4 and 2.5 °C, respectively, without any loss in activity relative to the wild type. Via an integration of structural analysis and molecular dynamics simulations, we elucidated the underlying mechanism facilitating the concurrent enhancement of both thermostability and enzymatic activity.

High hydrostatic pressure induced gastrointestinal digestion behaviors of quercetin-loaded casein delivery systems under different calcium concentration.

Casein micelle has a structure of outer hydrophilicity and inner hydrophobicity, its typical digestion characteristic is gastric coagulation. Based on calcium content as the key factor to control this process, high hydrostatic pressure (HHP) was firstly used to modify the micelle structure by mediating the tight connection between casein molecules themselves and with colloidal calcium, then the quercetin-loaded delivery systems were prepared. And in order to investigate the effect of exogenous calcium, calcium chloride was added for digestion. The results indicated that HHP broke the limitation of casein micelles as delivery carriers for hydrophobic components and increased the EE from 51.18 ± 3.07 % to 76.17 ± 3.41 %. During gastric digestion, higher pressure and exogenous calcium synergistically increased the clotting ability and inhibited the release of quercetin. In the small intestine, curds decomposed more slowly under higher pressure and calcium concentration, so the degradation of quercetin was effectively inhibited.

Metal-free production of natural blue colorants through anthocyanin-protein interactions.

INTRODUCTION: The scarcity of naturally available sources for blue colorants has driven reliance on synthetic alternatives. Nevertheless, growing health concerns have prompted the development of naturally derived blue colorants, which remains challenging with limited success thus far. Anthocyanins (ACNs) are known for providing blue colors in plants, and metal complexation with acylated ACNs remains the primary strategy to generate stable blue hues. However, this approach can be costly and raise concerns regarding potential metal consumption risks. OBJECTIVES: Our study aims to introduce a metal-free approach to achieve blue coloration in commonly distributed non-acylated 3-glucoside ACNs by exploring their interactions with proteins and unveiling the underlying mechanisms. METHODS: Using human serum albumin (HSA) as a model protein, we investigated the structural influences of ACNs on their blue color generation using visible absorption spectroscopy, fluorescence quenching, and molecular simulations. Additionally, we examined the bluing effects of six proteins derived from milk and egg and identified the remarkable roles of bovine serum albumin (BSA) and lysozyme (LYS). RESULTS: Our findings highlighted the importance of two or more hydroxyl or methoxyl substituents in the B-ring of ACNs for generating blue colors. Cyanidin-, delphinidin- and petunidin-3-glucoside, featuring two neighboring hydroxyl groups in the B-ring, exhibited blue coloration when interacting with HSA or LYS, driven primarily by favorable enthalpy changes. In contrast, malvidin-3-glucoside, with two methoxyl substituents, achieved blue coloration through interactions with HSA or BSA, where entropy change played significant roles. CONCLUSION: Our work, for the first time, demonstrates the remarkable capability of widely distributed 3-glucoside ACNs to generate diverse blue shades through interactions with certain proteins. This offers a promising and straightforward strategy for the production of ACN-based blue colorants, stimulating further research in this field.

Association of specific gut microbiota with polyethylene microplastics caused gut dysbiosis and increased susceptibility to opportunistic pathogens in honeybees.

The emergence of microplastics as contaminants has raised concerns regarding their potential toxicity. Recent studies on microplastic pollution caused by food packaging have drawn attention to its impact on health. However, despite being used extensively in food packaging, there is little knowledge about the toxicity of polyethylene microplastics (PE-MPs). Here, we studied the toxicity of PE-MPs on the model animal honeybees using different particle sizes (1 µm, 10 µm, 100 µm in diameter). Oral exposure to 100-µm PE-MPs resulted in elevated honeybee mortality and increased their susceptibility to pathogens. This is likely due to the mechanical disruption and gut microbial dysbiosis by PE-MPs. Snodgrassella, a core functional gut bacteria, was specifically enriched on the surface of PE-MPs, which perturbs the gut microbial communities in honeybees. Furthermore, the increased mortality in challenge trials with the opportunistic pathogen Hafnia alvei for PE-MPs pre-exposed honeybees revealed a potential health risk. These findings provide fresh insights into evaluating the potential hazards associated with PE-MPs.

Analyzing the pressure resistant, sublethal injury and resuscitable viable but non-culturable state population of Escherichia coli, Staphylococcus aureus, Bacillus amyloliquefaciens and Lactiplantibacillus plantarum under high pressure processing.

This study aimed to analyze and reduce the pressure resistance (PR), sublethal injury (SLI), and viable but non-culturable (VBNC) populations during HPP. Escherichia coli, Staphylococcus aureus, Bacillus amyloliquefaciens and Lactiplantibacillus plantarum were selected for evaluation of PR, SLI and VBNC cell counts and proportions during HPP. The results revealed that the bactericidal efficiency against these strains gradually improved as the processing pressure increased. However, viable bacteria could still be detected, suggesting that there may involve the presence of resistant population that difficult to be killed or revived from SLI. Further detecting the quantity and proportion of PR, SLI and VBNC bacteria found that these state of cells were present during whole HPP treatment. Additionally, the more resistant a bacterial species was to high pressure, the fewer SLI and more resuscitable VBNC (RVBNC) populations it generated, and vice versa. Therefore, correlation analysis was also employed to make the relationship between log reduction, SLI and RVBNC population ratios clearer. The results demonstrated that the log reduction was highly positive correlation with SLI population ratios, and negative correlation with RVBNC population within our detected species at 500 MPa. Furthermore, CO2 and Nisin were employed to combined with HPP to reduce these survivors. Comparing with 233, 218, 241 and 259 MPa for HPP treatment, it took 37, 89, 135 and 229 MPa for HPP + CO2, and 189, 161, 199 and 292 MPa for HPP + Nisin to the first decimal reduction for E. coli, S.aureus, B. amyloliquefaciens and L. plantarum, respectively. The results indicated that HPP combined with CO2 or Nisin could significantly reduce the quantity of PR, SLI, and RVBNC cells during HPP, and provide better bactericidal effects. In conclusion, we quantified the presence of PR, SLI, and VBNC bacteria after high pressure treatment and investigate the effectiveness of HPP combined with CO2 or Nisin to enhance the inactivation of bacteria and reduce the occurrence of PR, SLI, and RVBNC bacteria.

Effect of high pressure homogenization on the interaction between corn starch and cyanidin-3-O-glucoside.

The effects of high pressure homogenization (HPH) at different pressures (50, 100, 150 and 200 MPa) and temperatures (4, 20, 40, 60 and 80 °C) on the interaction between corn starch (CS) and cyanidin-3-O-glucoside (C3G) were investigated. Based on analyses of zeta potential, attenuated total reflection-flourier transformed infrared spectroscopy and binding rate after adding shielding agents, the main interaction force changed from electrostatic interaction to hydrogen bonds. In comparison, the interaction between CS and C3G exhibited greater strength at low temperatures and pressures. Especially, 4 °C/50 MPa HPH caused the most significant enhancement in binding rate and binding amount, from 9.56 % to 25.16 % and 0.96 µg/mg CS to 2.52 µg/mg CS, respectively. At this condition, the specific surface area of CS-C3G increased from 433.57 ± 0.91 m2/kg to 440.93 ± 1.01 m2/kg. Surface fluorescence reduction was observed by confocal laser scanning microscopy, further X-ray diffraction patterns indicated the retention of partial spatial structure. Therefore, HPH opened the entry channels, increased contact area and preserved steric hindrance, which increased hydrogen bonding sites. At high temperatures and high pressures (> 40 °C, > 100 MPa), the increasing free starch chains provided new hydrogen bonding sites. Overall, HPH was an effective method to enhance the interaction by affecting starch structure.

Research progress on the hypoglycemic activity and mechanisms of natural polysaccharides.

The incidence of diabetes, as a metabolic disease characterized by high blood sugar levels, is increasing every year. The predominantly western medicine treatment is associated with certain side effects, which has prompted people to turn their attention to natural active substances. Natural polysaccharide is a safe and low-toxic natural substance with various biological activities. Hypoglycemic activity is one of the important biological activities of natural polysaccharides, which has great potential for development. A systematic review of the latest research progress and possible molecular mechanisms of hypoglycemic activity of natural polysaccharides is of great significance for better understanding them. In this review, we systematically reviewed the relationship between the hypoglycemic activity of polysaccharides and their structure in terms of molecular weight, monosaccharide composition, and glycosidic bonds, and summarized underlying molecular mechanisms the hypoglycemic activity of natural polysaccharides. In addition, the potential mechanisms of natural polysaccharides improving the complications of diabetes were analyzed and discussed. This paper provides some valuable insights and important guidance for further research on the hypoglycemic mechanisms of natural polysaccharides.

Resuscitation of viable but nonculturable bacteria promoted by ATP-mediated NAD+ synthesis.

INTRODUCTION: Entry into the viable but nonculturable (VBNC) state is a survival strategy adopted by bacteria to survive harsh environment. Although VBNC cells still have metabolic activity, they lose the ability to form colonies on nonselective culture media. Thus, conventional bacterial detection methods, such as plate counting, are unable to detect the presence of VBNC cells. When the environmental conditions are appropriate, VBNC cells can initiate resuscitation, posing a great risk to the safety of public health. The study of the VBNC resuscitation mechanism could provide new insights into the prevention and control of VBNC resuscitation. OBJECTIVES: Uncovering the molecular mechanism of VBNC cell resuscitation by investigating the role of O-antigen ligase (RfaL) in inhibiting the resuscitation of Escherichia coli O157:H7 in the VBNC state. METHODS: RfaL was screened and verified as a resuscitation inhibitor of VBNC Escherichia coli O157:H7 by detecting resuscitation curve and time-lapse microscopy. The mechanism of RfaL impacts VBNC E. coli resuscitation was investigated by detecting the single cell ATP content, metabolomic changes, NAD(H) content and new protein biosynthesis of WT and ΔrfaL at different stage of resuscitation. RESULTS: Mutation of rfaL, which encoded an O-antigen ligase, markedly shortened the resuscitating lag phase. Further studies indicated that ΔrfaL VBNC cells contained higher ATP levels, and ATP consumption during the resuscitating lag phase was highly correlated with resuscitation efficiency. Metabolomic analysis revealed that ATP was utilized to activate the Handler and salvage pathways to synthesize NAD+, balancing redox reactions to recover cell activity and promote cell resuscitation. CONCLUSION: Our findings revealed a strategy employed by VBNC cells for revival, that is, using residual ATP to primarily recover metabolic activity, driving cells to exit dormancy. The synthesis pathway of lipopolysaccharide (LPS) in rfaL null mutant was inhibited and could supply more ATP to synthesis NAD+ and promote resuscitation.

Toward the bioactive potential of myricitrin in food production: state-of-the-art green extraction and trends in biosynthesis.

Myricitrin is a member of flavonols, natural phenolic compounds extracted from plant resources. It has gained great attention for various biological activities, such as anti-inflammatory, anti-cancer, anti-diabetic, as well as cardio-/neuro-/hepatoprotective activities. These effects have been demonstrated in both in vitro and in vivo models, making myricitrin a favorable candidate for the exploitation of novel functional foods with potential protective or preventive effects against diseases. This review summarized the health benefits of myricitrin and attempted to uncover its action mechanism, expecting to provide a theoretical basis for their application. Despite enormous bioactive potential of myricitrin, low production, high cost, and environmental damage caused by extracting it from plant resources greatly constrain its practical application. Fortunately, innovative, green, and sustainable extraction techniques are emerging to extract myricitrin, which function as alternatives to conventional techniques. Additionally, biosynthesis based on synthetic biology plays an essential role in industrial-scale manufacturing, which has not been reported for myricitrin exclusively. The construction of microbial cell factories is absolutely an appealing and competitive option to produce myricitrin in large-scale manufacturing. Consequently, state-of-the-art green extraction techniques and trends in biosynthesis were reviewed and discussed to endow an innovative perspective for the large-scale production of myricitrin.

The underlying mechanism of bacterial spore germination: An update review.

Bacterial spores are highly resilient and universally present on earth and can irreversibly enter the food chain to cause food spoilage or foodborne illness once revived to resume vegetative growth. Traditionally, extensive thermal processing has been employed to efficiently kill spores; however, the relatively high thermal load adversely affects food quality attributes. In recent years, the germination-inactivation strategy has been developed to mildly kill spores based on the circumstance that germination can decrease spore-resilient properties. However, the failure to induce all spores to geminate, mainly owing to the heterogeneous germination behavior of spores, hampers the success of applying this strategy in the food industry. Undoubtedly, elucidating the detailed germination pathway and underlying mechanism can fill the gap in our understanding of germination heterogeneity, thereby facilitating the development of full-scale germination regimes to mildly kill spores. In this review, we comprehensively discuss the mechanisms of spore germination of Bacillus and Clostridium species, and update the molecular basis of the early germination events, for example, the activation of germination receptors, ion release, Ca-DPA release, and molecular events, combined with the latest research evidence. Moreover, high hydrostatic pressure (HHP), an advanced non-thermal food processing technology, can also trigger spore germination, providing a basis for the application of a germination-inactivation strategy in HHP processing. Here, we also summarize the diverse germination behaviors and mechanisms of spores of Bacillus and Clostridium species under HHP, with the aim of facilitating HHP as a mild processing technology with possible applications in food sterilization. Practical Application: This work provides fundamental basis for developing efficient killing strategies of bacterial spores in food industry.

Effect of preliminary stresses on the induction of viable but non-culturable Escherichia coli O157:H7 NCTC 12900 and Staphylococcus aureus ATCC 6538.

As a novel non-thermal pasteurization technology, high pressure carbon dioxide (HPCD) has been used in food processing. However, it could induce microorganisms into a viable but nonculturable (VBNC) state, posing a potential risk to food safety and public health. In this study, we attempted to investigate the effect of various preliminary stresses including cold, heat, osmosis, acidity and oxidation on HPCD-induced VBNC formation. The results indicated that there was no effect of preliminary stresses on VBNC Staphylococcus aureus induction. However, heat, acidity and long-term (24 h) cultivation preadaptation could significantly increase the VBNC E. coli production induced by HPCD. Transcriptome analysis revealed that genes involved in ATP production were significantly decreased in these three stress-treated cells, and further ATP levels determination revealed that the ATP levels of the cell were significantly decreased after heat, acidity and long-term cultivation preadaptation, implying the decrease of ATP level caused by these stresses might be the reason for increasing VBNC production. To further study the relationship between ATP level and VBNC cell ratios after preadaptation. We artificially decreased the ATP levels, and detect their VBNC ratios after HPCD treatment. We found that with the ATP concentration decreasing after exposure to carbonyl cyanide m-chlorophenyl hydrazine (CCCP), the VBNC ratios were increased after HPCD treatment, indicating that the ATP contents were highly negatively correlated with VBNC ratios. This study proved that the preadaptation of heat, acidity and long-term cultivation could promote VBNC induction by decreasing the intracellular ATP level. In general, the obtained result gave the instruction about the storage environment for food materials, helped to further develop and optimize the HPCD processing to prevent VBNC formation and accelerate the development of HPCD technology in food industry.

Influence of pressurization rate and mode on cell damage of Escherichia coli and Staphyloccocus aureus by high hydrostatic pressure.

As a non-thermal technology, high hydrostatic pressure (HHP) has been widely investigated for inactivating microorganisms in food. Few studies have been presented on the pressurization/depressurization rate and mode of microbial inactivation. In this study, effect of pressurization rate and mode on Escherichia coli and Staphylococcus aureus cell damage during HHP treatment was investigated. The results showed that fast pressurization + linear mode (FL) treatment has the best bactericidal effect on E. coli and S. aureus, followed by fast pressurization + stepwise mode (FS) and slow pressurization + stepwise mode (SS) treatments. FL treatment caused more morphological damage to the cell wall, cell membrane, and cytoplasmic components compared with FS and SS treatment detected by SEM and TEM. Additionally, the damage to membrane permeability of them was also enhanced after FL treatment. Therefore, our results indicated that FL treatment could be applied to enhance the bactericidal effect of HHP on bacteria by increasing the damage to cell morphological structure and membrane integrity.