Membrane Damage and Metabolic Disruption as the Mechanisms of Linalool against Pseudomonas fragi: An Amino Acid Metabolomics Study.

Pseudomonas fragi (P. fragi) is usually detected in low-temperature meat products, and seriously threatens food safety and human health. Therefore, the study investigated the antibacterial mechanism of linalool against P. fragi from membrane damage and metabolic disruption. Results from field-emission transmission electron microscopy (FETEM) and atomic force microscopy (AFM) showed that linalool damage membrane integrity increases surface shrinkage and roughness. According to Fourier transform infrared (FTIR) spectra results, the components in the membrane underwent significant changes, including nucleic acid leakage, carbohydrate production, protein denaturation and modification, and fatty acid content reduction. The data obtained from amino acid metabolomics indicated that linalool caused excessive synthesis and metabolism of specific amino acids, particularly tryptophan metabolism and arginine biosynthesis. The reduced activities of glucose 6-phosphate dehydrogenase (G6PDH), malate dehydrogenase (MDH), and phosphofructokinase (PFK) suggested that linalool impair the respiratory chain and energy metabolism. Meanwhile, genes encoding the above enzymes were differentially expressed, with pfkB overexpression and zwf and mqo downregulation. Furthermore, molecular docking revealed that linalool can interact with the amino acid residues of G6DPH, MDH and PFK through hydrogen bonds. Therefore, it is hypothesized that the mechanism of linalool against P. fragi may involve cell membrane damage (structure and morphology), disturbance of energy metabolism (TCA cycle, EMP and HMP pathway) and amino acid metabolism (cysteine, glutamic acid and citrulline). These findings contribute to the development of linalool as a promising antibacterial agent in response to the food security challenge.

Polysaccharides from Alpinia oxyphylla fruit prevent hyperuricemia by inhibiting uric acid synthesis, modulating intestinal flora and reducing renal inflammation.

Hyperuricemia (HUA) is one of the most common chronic diseases today, with a prevalence exceeding 14 % in both the United States and China. Current clinical treatments for HUA focus on promoting uric acid (UA) excretion and inhibiting UA production, but often neglect the strain on the liver and kidneys. The fruit of Alpinia oxyphylla (A. oxyphylla) is known to improve renal function, regulate metabolism, and exhibit anti-inflammatory effects; however, its effectiveness and mechanisms in treating HUA are not well understood. In this study, HUA mice induced by potassium oxonate and adenine were treated with A. oxyphylla polysaccharide (AFP) for 21 days. The levels associated with HUA were quantified using assay kits to evaluate the impact of AFP on HUA. Serum metabolomics and 16S rRNA sequencing were used to investigate the mechanisms by which AFP ameliorates HUA. The results showed that AFP treatment reduced abnormal biochemical levels, including UA, blood urea nitrogen, and creatinine, in HUA mice. AFP inhibited UA synthesis by regulating pyrimidine metabolism and the metabolism of alanine, aspartate and glutamate, reduced kidney inflammation, and promoted UA excretion by regulating intestinal flora. Thus, AFP appears to be an effective agent for alleviating HUA symptoms.

Disruption of Cell Membranes and Redox Homeostasis as an Antibacterial Mechanism of Dielectric Barrier Discharge Plasma against Fusarium oxysporum.

Direct barrier discharge (DBD) plasma is a potential antibacterial strategy for controlling Fusarium oxysporum (F. oxysporum) in the food industry. The aim of this study was to investigate the inhibitory effect and mechanism of action of DBD plasma on F. oxysporum. The result of the antibacterial effect curve shows that DBD plasma has a good inactivation effect on F. oxysporum. The DBD plasma treatment severely disrupted the cell membrane structure and resulted in the leakage of intracellular components. In addition, flow cytometry was used to observe intracellular reactive oxygen species (ROS) levels and mitochondrial membrane potential, and it was found that, after plasma treatment, intracellular ROS accumulation and mitochondrial damage were accompanied by a decrease in antioxidant enzyme activity. The results of free fatty acid metabolism indicate that the saturated fatty acid content increased and unsaturated fatty acid content decreased. Overall, the DBD plasma treatment led to the oxidation of unsaturated fatty acids, which altered the cell membrane fatty acid content, thereby inducing cell membrane damage. Meanwhile, DBD plasma-induced ROS penetrated the cell membrane and accumulated intracellularly, leading to the collapse of the antioxidant system and ultimately causing cell death. This study reveals the bactericidal effect and mechanism of the DBD treatment on F. oxysporum, which provides a possible strategy for the control of F. oxysporum.

Dynamic interfacial adsorption and emulsifying performance of self-assembled coconut protein and fucoidan mixtures.

The functional properties of protein are affected by their aggregation behavior and morphology. In this study, the self-assembled coconut protein aggregates with specific morphology, including small amorphous aggregates (WLA), spherical-like aggregates (SLA) and rod-like aggregates (RLA), were regulated to form. The self-assembled process resulted in a decrease in fluorescence intensity and an increase in the surface hydrophobicity of coconut protein. Fucoidan was added to improve the stability of protein solutions, and the interfacial adsorption behavior was evaluated by dilatational rheology analysis. The results showed that the aggregation state of coconut protein affected its ability to reduce surface tension, and the interfacial layers mainly exhibited elastic property at oil-water interface (tanφ < 0.5). For macroscale analysis, the emulsions based on self-assembled coconut protein exhibited smaller droplet size, better rheological properties and centrifugal stability, especially WLA and RLA. This study may provide a reference to inspire the utilization of self-assembled coconut protein in the food industry.

Ultralong luminescence lifetime imaging of edible plant tissue for humidity sensing in food packaging by a smartphone.

The safety of luminescence sensors and probes used in food packaging should be seriously considered, while most luminescence sensors were artificially synthesized with unclear toxicity, and cannot be directly used as indicators that were in contact with food. To overcome this problem, a humidity indicator based on an edible plant tissue was developed without any chemical processing. We found that garlic bulbs could emit significant persistent luminescence after drying at room temperature. The luminescence lifetime decreases from hundreds of milliseconds to tens of milliseconds as humidity increases. The long-lived luminescence could easily be detected through smartphones without any sophisticated instruments. The edible garlic is expected to be used as a humidity indicator in food packaging without worrying about food safety. Furthermore, the interference of scattered light and short-lived fluorescence from foods and packages can be eliminated in time-resolved luminescence imaging, greatly increasing the signal-to-noise ratio.

Constructing artificial gap junctions to mediate intercellular signal and mass transport.

Natural gap junctions are a type of channel protein responsible for intercellular signalling and mass communication. However, the scope of applications for these proteins is limited as they cannot be prepared at a large scale and are unable to spontaneously insert into cell membranes in vitro. The construction of artificial gap junctions may provide an alternative strategy for preparing analogues of the natural proteins and bottom-up building blocks necessary for the synthesis of artificial cells. Here we show the construction of artificial gap junction channels from unimolecular tubular molecules consisting of alternately arranged positively and negatively charged pillar[5]arene motifs. These molecules feature a hydrophobic-hydrophilic-hydrophobic triblock structure that allows them to efficiently insert into two adjacent plasma membranes and stretch across the gap between the two membranes to form gap junctions. Similar to natural gap junction channels, the synthetic channels could mediate intercellular signal coupling and reactive oxygen species transmission, leading to cellular activity.

Mechanism for improving the in vitro digestive properties of coconut milk by modifying the structure and properties of coconut proteins with monosodium glutamate.

In this paper, the effect of monosodium glutamate (MSG) on coconut protein (CP) solubility, surface hydrophobicity, emulsification activity, ultraviolet spectroscopy and fluorescence spectroscopy was investigated. Meanwhile, the changes in the in vitro digestive properties of coconut milk were also further analyzed. MSG treatment altered the solubility and surface hydrophobicity of CP, thereby improving protein digestibility. Molecular docking showed that CP bound to pepsin and trypsin mainly through hydrogen bonds and salt bridges. And MSG increased the cleavable sites of pepsin and trypsin on CP, thus further improving the protein digestibility. In addition, MSG increased the Na+ concentration in coconut milk, promoted flocculation and aggregation between coconut milk droplets, which prevented the binding of lipase and oil droplets and inhibited lipid digestion. These findings may provide new ideas and insights to improve the digestive properties of plant-based milk.

Studies on the Inhibition Mechanism of Linalyl Alcohol against the Spoilage Microorganism Brochothrix thermosphacta.

The aim of this study was to investigate the bacterial inhibitory ability and mechanism of action of linalyl alcohol against B. thermosphacta. Linalyl alcohol causes the leakage of intracellular material by disrupting the cell wall and exposing the hydrophobic phospholipid bilayer, which binds to bacterial membrane proteins and alters their structure. In addition, linalyl alcohol causes cell membrane damage by affecting fatty acids and proteins in the cell membrane. By inhibiting the synthesis of macromolecular proteins, the normal physiological functions of the bacteria are altered. Linalyl alcohol binds to DNA in both grooved and embedded modes, affecting the normal functioning of B. thermosphacta, as demonstrated through a DNA interaction analysis.

Photocatalytic inactivation mechanism of nano-BiPO4 against Vibrio parahaemolyticus and its application in abalone.

Vibrio parahaemolyticus (V. parahaemolyticus) is the main pathogenic bacteria in seafood that can cause serious food-borne illness. The annual incidence of V. parahaemolyticus infection in the United States exceeds 45,000 cases, indicating there are potential shortcomings in seafood sterilization techniques. Meanwhile, the ongoing emergence of antibiotic-resistant strains highlights the urgent need for novel bacteriostatic strategies to eliminate V. parahaemolyticus. Nano-BiPO4 is a semiconductor with high H2O2 production efficiency and has potential for photocatalytic bacterial inactivation. But the effectiveness and mechanism of BiPO4 photocatalytic inactivation of V. parahaemolyticus has not been reported. In this study, nano-BiPO4 synthesized in pure water (P1) was found to exhibit optimal H2O2 production efficiency (1203 µmol h-1g-1) and antibacterial activity (in 0.8 g/L). Under UV light irradiation, P1 induced alterations in bacterial cell morphology, elevation in intracellular levels of ROS, H2O2, O2-, GSSG and MDA, and reduction in GSH level. Meanwhile, metabolomic analysis revealed that P1 stimulates the arginine biosynthesis, TCA cycle and alanine, aspartate and glutamate metabolism. These abnormal changes in the oxidative stress indicators and metabolic pathways proved that the bacterial damage was related to the H2O2 produced by nano-BiPO4 photocatalysis. Moreover, sliced abalone and hemolysis assay were used to demonstrate the applicability and biosafety of P1. This study provides theoretical support for exploring nano-BiPO4 as a bacterial inhibitor against V. parahaemolyticus.

Effects of protein concentration, ionic strength, and heat treatment on the interfacial and emulsifying properties of coconut (Cocos nucifera L.) globulins.

This research aimed to investigate the effects of protein concentration (0.2 %-1.0 %), ionic strength (100-500 mM NaCl), and heat treatment (temperature: 80 and 90℃; time: 15 and 30 min) on the interfacial and emulsifying properties of coconut globulins (CG). When protein concentration was set at 0.2-0.6 %, the interfacial adsorption increased with the increasing of protein concentration. However, the lowest interfacial viscoelasticity was found when CG concentration was 0.6 %. When the protein concentration was higher than 0.6 %, the dilatational viscoelasticity increased with the increasing of protein concentration. The protein concentration showed positive effect on the emulsion stability of CG. The ionic strength showed positive effect on the interfacial adsorption but negative effects on the interfacial viscoelasticity and emulsion stability. Higher temperature and longer heating time brought worse interface behavior. The heated CG (90℃, 30 min) had the worst interfacial behavior but the best emulsion stability.

Effect of steam explosion on the morphological, textural, and compositional characteristics of betel nut.

To reduce the adverse physical effects on the oral mucosa caused by excessive hardness of betel nut fibers, steam explosion was used to soften betel nuts. The effect of three operating parameters (pressure holding time, explosion pressure, and initial moisture content) on the morphology, texture, and chemical composition of the betel nuts was investigated. The fiber hardness and Shore hardness decreased by 56.17%-89.28% and 7.03%-34.29%, respectively, and the transverse tensile strength and fiber tensile strength also decreased by up to 60.72% and 24.62%, respectively. Moreover, the coefficient of static friction and moisture content increased. After steam explosion, the betel nut increased in transverse diameter, became darker and more yellow-red in color, and showed a damaged microstructure. The contents of free phenol and alkaloids decreased after steam explosion treatment, with free phenols and total alkaloids decreasing from 34.32 mg(GAE)/g and 7.84 mg/g to 21.58 mg(GAE)/g and 6.50 mg/g, respectively, after the A-50 s treatment condition. The steam explosion increased the quantity of phenols, alkaloids, and soluble solids released from the betel nut under the same simulated release conditions of the texture analyzer. The research also showed that increased pressure holding time and explosion pressure enhanced the explosion efficiency, while the initial moisture content was reduced the explosion efficiency. Therefore, steam explosion is an effective pretreatment approach to soften betel nut and facilitate healthy development of the betel nut industry.

Proteomics reveals energy limitation and amino acid consumption as antibacterial mechanism of linalool against Shigella sonnei and its application in fresh beef preservation.

Meat is often contaminated by food-borne pathogens, resulting in significant economic losses. Linalool from plant essential oils (EOs) has been reported to have excellent antibacterial properties. Therefore, this study aims to elucidate the mechanism of linalool against Shigella sonnei (S. sonnei) based on proteomic and physiological indicators. The results indicated that linalool severely perturbed the expression levels of intracellular proteins, of which 208 were up-regulated and 49 were down-regulated. Moreover, linalool exerted its inhibitory effect mainly through the induction of amino acid limitation and insufficient energy levels based on the pathways involved in differential expressed proteins (DEPs). After 8 h, alkaline phosphatase (AKP) leakage increased 20.96 and 21.52-fold in the MIC and 2MIC groups while protein leakage increased 2.17 and 2.50-fold, respectively, which revealed the potential of linalool on cell structure damage combined with nucleic acid leakage. In addition, the ATP content decreased to 36.92% and 18.84% in the MIC and 2MIC groups, respectively when processed for 8 h. In particular, linalool could effectively control the quality change of fresh beef by measuring pH, total volatile basic nitrogen (TVB-N), total viable counts (TVC) while not affecting its sensory acceptability based on the result of sensory evaluation. This research provides theoretical insights for the development of linalool as a new natural antibacterial agent.

Substrate-Controlled Catalysis in the Ether Cross-Link-Forming Radical SAM Enzymes.

Darobactin is a heptapeptide antibiotic featuring an ether cross-link and a C-C cross-link, and both cross-links are installed by a radical S-adenosylmethionine (rSAM) enzyme DarE. How a single DarE enzyme affords the two chemically distinct cross-links remains largely obscure. Herein, by mapping the biosynthetic landscape for darobactin-like RiPP (daropeptide), we identified and characterized two novel daropeptides that lack the C-C cross-link present in darobactin and instead are solely composed of ether cross-links. Phylogenetic and mutagenesis analyses reveal that the daropeptide maturases possess intrinsic multifunctionality, catalyzing not only the formation of ether cross-link but also C-C cross-linking and Ser oxidation. Intriguingly, the different chemical outcomes are controlled by the exact substrate motifs. Our work not only provides a roadmap for the discovery of new daropeptide natural products but also offers insights into the regulatory mechanisms that govern these remarkably versatile ether cross-link-forming rSAM enzymes.

Unraveling the Antioxidant Activity of 2R,3R-dihydroquercetin.

It has been reported that in an oxidative environment, the flavonoid 2R,3R-dihydroquercetin (2R,3R-DHQ) oxidizes into a product that rearranges to form quercetin. As quercetin is a very potent antioxidant, much better than 2R,3R-DHQ, this would be an intriguing form of targeting the antioxidant quercetin. The aim of the present study is to further elaborate on this targeting. We can confirm the previous observation that 2R,3R-DHQ is oxidized by horseradish peroxidase (HRP), with H2O2 as the oxidant. However, HPLC analysis revealed that no quercetin was formed, but instead an unstable oxidation product. The inclusion of glutathione (GSH) during the oxidation process resulted in the formation of a 2R,3R-DHQ-GSH adduct, as was identified using HPLC with IT-TOF/MS detection. GSH adducts appeared on the B-ring of the 2R,3R-DHQ quinone, indicating that during oxidation, the B-ring is oxidized from a catechol to form a quinone group. Ascorbate could reduce the quinone back to 2R,3R-DHQ. No 2S,3R-DHQ was detected after the reduction by ascorbate, indicating that a possible epimerization of 2R,3R-DHQ quinone to 2S,3R-DHQ quinone does not occur. The fact that no epimerization of the oxidized product of 2R,3R-DHQ is observed, and that GSH adducts the oxidized product of 2R,3R-DHQ on the B-ring, led us to conclude that the redox-modulating activity of 2R,3R-DHQ quinone resides in its B-ring. This could be confirmed by chemical calculation. Apparently, the administration of 2R,3R-DHQ in an oxidative environment does not result in 'biotargeting' quercetin.

Mechanism for improving coconut milk emulsions viscosity by modifying coconut protein structure and coconut milk properties with monosodium glutamate.

In this study, monosodium glutamate (MSG) was used to improve the viscosity of coconut milk and the underlying mechanism was explored by investigating the changes in structures of coconut milk protein and physicochemical properties of coconut milk. Firstly, the effect of MSG on the properties of coconut milk was studied. The results showed that MSG increased the pH and zeta potential, reduced the particle size, thus enhancing the droplet interaction and increasing the viscosity of coconut milk. Subsequently, the effects of MSG on the structure and properties of coconut proteins (CP) were investigated. FTIR spectroscopy and circular dichroism spectroscopy showed that MSG was able to change the secondary structure of CP. The results of SDS-PAGE showed that MSG was able to bind to CP to form a larger molecular weight protein, thus improving the viscosity of coconut milk. Moreover, MSG was also able to increase the water-binding capacity of CP. In addition, molecular docking and driving force analysis revealed that hydrogen bonds, electrostatic forces, disulfide bonds, and hydrophobic interactions are the main interactions between MSG and CP. Studying the effect of MSG on the viscosity of coconut milk provides theoretical support to improve the viscosity of other plant protein emulsions.

Sodium alginate emulsion loaded with linalool: Preparation, characterization and antibacterial mechanism against Shigella sonnei.

This study aimed to prepare sodium alginate-linalool emulsion (SA-LE) to overcome the low solubility of linalool and explore its inhibitory activity against Shigella sonnei. The results indicated that linalool significantly reduced the interfacial tension between SA and oil phase (p < 0.05). Droplet sizes of fresh emulsions were uniform with sizes from 2.54 to 2.58 µm. The ζ-potential was between -23.94 and -25.03 mV, and the viscosity distribution was 973.62 to 981.03 mPa·s at pH 5-8 (near neutral pH) without significant difference. In addition, linalool could be effectively released from SA-LE in accordance with the Peppas-Sahlin model, mainly described by Fickian diffusion. In particular, SA-LE can inhibit S. sonnei with a minimum inhibitory concentration of 3 mL/L, which was lower than free linalool. The mechanism can be described as damaging the membrane structure and inhibiting respiratory metabolism accompanied by oxidative stress based on FESEM, SDH activity, ATP and ROS content. These results suggest that SA is an effective encapsulation strategy to enhance the stability of linalool and its inhibitory effect on S. sonnei at near neutral pH. Moreover, the prepared SA-LE has the potential to be developed as a natural antibacterial agent to address the growing food safety challenges.

Forrestiacids E-K: Further [4 + 2]-Type Triterpene-Diterpene Hybrids as Potential ACL Inhibitors from the Vulnerable Conifer Pseudotsuga forrestii.

Seven [4 + 2]-type triterpene-diterpene hybrids derived from a rearranged or a normal lanostane unit (dienophile) and an abietane moiety (diene), forrestiacids E-K (1-7, respectively), were further isolated and characterized from Pseudotsuga forrestii (a vulnerable conifer endemic to China). The intriguing molecules were revealed with the guidance of an LC-MS/MS-based molecular ion networking strategy combined with conventional phytochemical procedures. Their chemical structures with absolute configurations were established by spectroscopic data, chemical transformation, electronic circular dichroism calculations, and single-crystal X-ray diffraction analysis. They all contain a rare bicyclo[2.2.2]octene motif. Both forrestiacids J (6) and K (7) represent the first examples of this unique class of [4 + 2]-type hybrids that arose from a normal lanostane-type dienophile. Some isolates remarkably inhibited ATP-citrate lyase (ACL), with IC50 values ranging from 1.8 to 11 µM. Docking studies corroborated the findings by highlighting the interactions between the bioactive compounds and the ACL enzyme (binding affinities: -9.9 to -10.7 kcal/mol). The above findings reveal the important role of protecting plant species diversity in support of chemical diversity and potential sources of new therapeutics.

Edible Quality Analysis of Different Areca Nuts: Compositions, Texture Characteristics and Flavor Release Behaviors.

The areca nut is one of the most important cash crops in the tropics and has substantial economic value. However, the research information about the edible quality of different areca nuts is still insufficient. This study compared the composition, texture characteristics and flavor release behaviors of four different areca nuts (AN1, AN2, AN3 and AN4) and two commercially dried areca nuts (CAN1 and CAN2). Results showed that AN1 had higher soluble fiber and lower lignin, which was the basis of its lower hardness. Meanwhile, the total soluble solid (TSS) of AN1 was the highest, which indicated that AN1 had a moister and more succulent mouthfeel. After the drying process, the lignification degree of AN1 was the lowest. Through textural analyses, the hardness of AN1 was relatively low compared to the other dried areca nuts. AN1, CAN1 and CAN2 had higher alkaline pectin content and viscosity, and better flavor retention, which indicated better edible quality. The present study revealed the differences of various areca nuts and provided vital information to further advance the study of areca nuts.

Development and Characterization of an Edible Zein/Shellac Composite Film Loaded with Curcumin.

The development of functional edible films is promising for the food industry, and improving the water barrier of edible films has been a research challenge in recent years. In this study, curcumin (Cur) was added to zein (Z) and shellac (S) to prepare an edible composite film with a strong water barrier and antioxidant properties. The addition of curcumin significantly reduced the water vapor permeability (WVP), water solubility (WS), and elongation at break (EB), and it clearly improved the tensile strength (TS), water contact angle (WCA), and optical properties of the composite film. The ZS-Cur films were characterized by SEM, FT-IR, XRD, DSC, and TGA; the results indicated that hydrogen bonds were formed among the curcumin, zein, and shellac, which changed the microstructure and improved the thermal stability of the film. A test of curcumin release behavior showed controlled release of curcumin from the film matrix. ZS-Cur films displayed remarkable pH responsiveness, strong antioxidant properties, and inhibitory effects on E. coli. Therefore, the insoluble active food packaging prepared in this study provides a new strategy for the development of functional edible films and also provides a possibility for the application of edible films to extend the shelf life of fresh food.

Respiratory depression driven by membrane damage as a mechanism for linalool to inhibit Pseudomonas lundensis and its preservation potential for beef.

AIMS: This study aimed to investigate the mechanism of linalool against Pseudomonas lundensis and its application on beef. METHODS AND RESULTS: Field emission scanning electron microscopy found that linalool exerted antibacterial activity with a minimum inhibitory concentration (MIC) of 1.5 ml l-1 by disrupting cell structure. Loss of cell membrane integrity was monitored due to leakage of nucleic acids and K+. In addition, respiratory depression appeared in Ps. lundensis based on inhibition of enzyme activities including hexokinase (HK), glucose 6-phosphate dehydrogenase (G6PDH), phosphofructokinase (PFK), pyruvate kinase (PK), pyruvate dehydrogenase (PDH), citrate synthase (CS), succinate dehydrogenase (SDH), and malate dehydrogenase (MDH). Subsequently, energy limitation also occurred according to the decrease in ATP content and ATPase activity. Molecular docking confirmed that linalool can combine with enzymes in cell wall (ddlB) and energy synthesis (AtpD) pathways to exert antibacterial effect. Of note, linalool has advantages for beef preservation by delaying quality changes including pH, total volatile basic nitrogen (TVB-N) and total viable count (TVC). CONCLUSIONS: Linalool has significant inhibitory effect on Ps. lundensis, and respiratory depression driven by membrane damage is the main inhibitory mechanism.