Design, synthesis and characterization of lysozyme-gentisic acid dual-functional conjugates with antibacterial/antioxidant activities

Physiological and ecological responses of flue-cured tobacco to field chilling stress: insights from metabolomics and proteomics

Introduction

Currently, research on tobacco's response to chilling stress is mostly limited to laboratory simulations, where temperature is controlled to study physiological and molecular responses. However, laboratory conditions cannot fully replicate the complex environment of field chilling stress, so conducting research under field conditions is crucial for understanding the multi-level adaptive mechanisms of tobacco to chilling stress in natural environments.

Methods

This study aims to use field trials, starting from physiological responses, combined with proteomics and untargeted metabolomics, to systematically reveal the physiological and biochemical characteristics and key molecular mechanisms of tobacco leaves under chilling stress. It provides new insights into tobacco's adaptation strategies under chilling stress.

Results

The results showed that (1) chilling stress damages the appearance of tobacco leaves, reduces the chlorophyll content, increases H2O2 and malondialdehyde (MDA) levels in cold-injured tobacco leaves, and damages the plasma membrane system. Although catalase (CAT) activity increases to cope with the accumulation of reactive oxygen species (ROS), the activities of key antioxidant enzymes superoxide dismutase (SOD) and peroxidase (POD) significantly decrease, indicating that the antioxidant system of tobacco leaves fails in environments with sudden temperature drops. (2) Proteomics analysis indicated that 410 differentially expressed proteins were identified in cold-stressed tobacco leaves, with 176 upregulated and 234 downregulated. Tobacco leaves under chilling stress attempt to maintain energy supply and physiological stability by enhancing glycolysis, starch, and sucrose metabolism pathways. Concurrently, chilling stress triggers the expression of proteins related to cell wall reinforcement and antioxidant defense. However, due to impaired ribosomal function, protein synthesis is significantly inhibited, which aggravates damage to photosynthesis and cellular functions. (3) Metabolomics analysis revealed that the differential metabolites in cold-stressed tobacco leaves were mainly enriched in tyrosine metabolism, isoquinoline alkaloid biosynthesis, and fatty acid degradation pathways. This indicates that under chilling stress, tobacco leaves enhance adaptability by regulating energy metabolism, increasing antioxidant capacity, and stabilizing cell membrane structure.

Conclusions

Therefore, under chilling stress, tobacco leaves exhibit complex physiological adaptability through multiple regulatory mechanisms involving proteins and metabolites. The research results provide important insights into the metabolic regulatory mechanisms of tobacco in response to extreme environments and also enhance the theoretical foundation for addressing low-temperature stress in practical production.

Insights into the fabrication and antibacterial effect of fibrinogen hydrolysate-carrageenan loading apigenin and quercetin composite hydrogels

Escherichia coli and Staphylococcus aureus are the most prevalent pathogenic bacteria, often resulting in the foodborne disease outbreaks through food spoilage and foodborne infections. To prevent and control food spoilage and foodborne infections induced by Escherichia coli and Staphylococcus aureus, the antibacterial hydrogels were fabricated using fibrinogen hydrolysate-carrageenan (AHs-C) and flavonoids (apigenin and quercetin), and the antibacterial effect of the composite hydrogels against Escherichia coli and Staphylococcus aureus was further investigated. The results of mechanical property exhibited that the composite hydrogels with 0.2 % of apigenin and quercetin (AHs-C-Ap/Que) showed the highest hardness and swelling property compared with the separate addition of apigenin or quercetin. Scanning electron microscopy and atomic force microscopy showed that the dense networks were formed in the hydrogels of AHs-C-Ap/Que., and the average roughness of AHs-C-Ap/Que. significantly increased to 30.70 nm compared with AHs-C. 1H NMR and FTIR spectra demonstrated that apigenin and quercetin were bound to AHs-C by hydrogen bond, hydrophobic interaction and Schiff base, where the interactions between Ap/Que. and AHs-C was stronger compared with the separate addition of apigenin or quercetin. The hydrogels of AHs-C-Ap/Que. showed the highest antibacterial capacity and antibacterial adhesion against Escherichia coli and Staphylococcus aureus. The antibacterial adhesion assay showed that 99 % removal ratios for E. coli and S. aureus were observed in AHs-C-Ap/Que. hydrogels, which showed a great potential to prevent food spoilage and foodborne infections.

Effects of chitosan-gentianic acid derivatives on the quality and shelf life of seabass (Lateolabrax maculatus) during refrigerated storage

Chitosan is a natural polymer material with antibacterial, biodegradable and biocompatibility. At present, the research is mainly to enhance the antibacterial and antioxidant activity of chitosan by grafting with phenolic acids to further expand its application in food. In this study, the effect of chitosan-g-gentisic acid graft copolymer (CS-g-GA) on the shelf life of refrigerated seabass (Lateolabrax maculatus) was investigated. The results of microbial analysis demonstrated that GA and CS-g-GA treatment could effectively inhibit the growth of microorganisms. In addition, physicochemical analysis showed that GA and CS-g-GA treatment could reduce the increase of pH value, thiobarbituric acid reactive substances (TBARS), total volatile base nitrogen (TVB-N) and K-value, delay water loss, maintain texture and color, and postpone the decrease of sensory score. Compared with the control sample, CS-g-GA could keep the quality of Lateolabrax japonicus and extend its shelf-life for another 9 days. In summary, CS-g-GA has good application and development prospects for the preservation of seabass.

Conjugation of Lysozyme and Epigallocatechin Gallate for Improving Antibacterial and Antioxidant Properties

One of the main interests in the food industry is the preservation of food from spoilage by microorganisms or lipid oxidation. A novel alternative is the development of additives of natural origin with dual activity. In the present study, a chemically modified lysozyme (Lys) with epigallocatechin gallate (EGCG) was developed to obtain a conjugate (Lys-EGCG) with antibacterial/antioxidant activity to improve its properties and increase its application potential. The modification reaction was carried out using a free radical grafting method for the Lys modification reaction, using ascorbic acid and hydrogen peroxide as radical initiators in an aqueous medium. The synthesis of Lys-EGCG conjugate was confirmed by spectroscopic (FT-IR, 1H-RMN, and XPS) and calorimetry differential scanning (DSC) analyses. The EGCG binding to the Lys biomolecule was quantified by the Folin-Ciocalteu method; the antibacterial activity was evaluated by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MCB) against Staphylococcus aureus and Pseudomonas fluorescens; the antioxidant activity was evaluated by ABTS, DPPH, and FRAP. The spectroscopic results showed that the Lys-EGCG conjugate was successfully obtained, and the DSC analysis revealed a 20 °C increase (P < 0.05) in the denaturation temperature of Lys due to EGCG modification. The EGCG concentration in Lys-EGCG was 97.97 ± 4.7 µmol of EGCG/g of sample. The antibacterial and antioxidant activity of the Lys-EGCG conjugate was higher (P < 0.05) than pure EGCG and Lys. The chemical modification of Lys with EGCG allows for the bioconjugate with a dual function (antibacterial/antioxidant), broadening the range of Lys and EGCG applications to different areas such as food, cosmetic, and pharmaceutical industries.

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

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

Antioxidant and anti-inflammatory function of Eupatorium adenophora Spreng leaves (EASL) on human intestinal Caco-2 cells treated with tert-butyl hydroperoxide

Chronic non-communicable diseases (CNCDs) pose a significant public health challenge. Addressing this issue, there has been a notable breakthrough in the prevention and mitigation of NCDs through the use of antioxidants and anti-inflammatory agents. In this study, we aim to explore the effectiveness of Eupatorium adenophora Spreng leaves (EASL) as an antioxidant and anti-inflammatory agent, and its potential applications. To construct a cellular model of oxidative damage and inflammation, Caco-2 cells were treated with tert-butyl hydroperoxide (t-BHP). The biocompatibility of EASL-AE with Caco-2 cells was assessed using the MTT assay, while compatibility was further verified by measuring LDH release and the protective effect against oxidative damage was also assessed using the MTT assay. Additionally, we measured intracellular oxidative stress indicators such as ROS and 8-OHdG, as well as inflammatory pathway signalling protein NFκB and inflammatory factors TNF-α and IL-1β using ELISA, to evaluate the antioxidant and anti-inflammatory capacity of EASL-AE. The scavenging capacity of EASL-AE against free radicals was determined through the DPPH Assay and ABTS Assay. Furthermore, we measured the total phenolic, total flavonoid, and total polysaccharide contents using common chemical methods. The chemical composition of EASL-AE was analyzed using the LC-MS/MS technique. Our findings demonstrate that EASL-AE is biocompatible with Caco-2 cells and non-toxic at experimental levels. Moreover, EASL-AE exhibits a significant protective effect on Caco-2 cells subjected to oxidative damage. The antioxidant effect of EASL-AE involves the scavenging of intracellular ROS, while its anti-inflammatory effect is achieved by down-regulation of the NFκB pathway. Which in turn reduces the release of inflammatory factors TNF-α and IL-1β. Through LC-MS/MS analysis, we identified 222 compounds in EASL-AE, among which gentianic acid, procaine and L-tyrosine were the compounds with high antioxidant capacity and may be the effective constituent for EASL-AE with antioxidant activity. These results suggest that EASL-AE is a natural and high-quality antioxidant and anti-inflammatory biomaterial that warrants further investigation. It holds great potential for applications in healthcare and other related fields.

Characteristics of hen egg white lysozyme, strategies to break through antibacterial limitation, and its application in food preservation: A review

Hen egg white lysozyme (HEWL) is used as a food additive in China due to its outstanding antibacterial properties. It is listed as GRAS grade (generally recognized as safe) by the United States Food and Drug Administration (FDA, US) and has been extensively researched and used in food preservation. And the industrial production of HEWL already been realized. Given the complex food system that can affect the antibacterial activity of HEWL, and the limitations of HEWL itself on Gram-negative bacteria. Based on the structure and main biological characteristics of HEWL, this paper focuses on reviewing methods to enhance the stability and antibacterial properties of HEWL. Immobilization tactics such as chemically driven self-assembly, embedding and adsorption address the restriction of poor HEWL antibacterial activity effected by external factors. Both intermolecular and intramolecular modification strategies break the bactericidal deficiencies of HEWL itself. It also comprehensively analyzes the current application status and future prospects of HEWL in the food preservation. There was limited research on the biological methods in modifying HEWL. If the HEWL is genetically engineered, it can broaden its antimicrobial spectrum, improve its other biological activities, so as to further expand its application in the food industry. At present, research on HEWL mainly focused on its antibacterial properties, whereas its application in anti-inflammatory and antioxidant effects also presented great potential.

3-Acyl-4-Pyranone as a Lysine Residue-Selective Bioconjugation Reagent for Peptide and Protein Modification

Chemoselective protein modification plays extremely important roles in various biological, medical, and pharmaceutical investigations. Mimicking the mechanism of the chemoselective reaction between natural azaphilones and primary amines, this work successfully simplified the azaphilone scaffold into much simpler 3-acyl-4-pyranones. Examinations confirmed that these slim-size mimics perfectly kept the unique reactivity for selective conjugation with the primary amines including lysine residues of peptides and proteins. The newly developed pyranone tool presents remarkably increased aqueous solubility and compatible second-order rate constant by comparison with the original azaphilone. Additional advantages also include the ease of biorthogonal combinative use with a copper-catalyzed azide-alkyne Click reaction, which was conveniently applied to decorate lysozyme with neutral-, positive- and negative-charged functionalities in parallel. Moderate-degree modification of lysozyme with positively charged quaternary ammoniums was revealed to increase the enzymatic activities.

Gallic acid-functionalized soy protein-based multiple cross-linked hydrogel: Mechanism analysis, physicochemical properties, and digestive characteristics

Herein, carbodiimide hydrochloride/N-hydroxysuccinimide was used to mediate the grafting of gallic acid (GA) (0.005, 0.0015, and 0.025 wt%) with soybean protein isolate (SPI) in the preparation of SPI-GA conjugates and hydrogels. The modified materials were primarily joined via the CN bonds and exhibited excellent antioxidant properties. In addition, spectral analysis revealed that the grafting of GA increased the flexibility of the SPI structure. The SPI-GA hydrogel is fabricated through covalent/non-covalent cross-linking mechanisms, including Schiff base, Michael addition, and hydrogen bonding. Furthermore, the microstructure, rheological properties, thermal stability, and textural properties of the hydrogel were affected by the amount of GA grafted. The SPI-GA hydrogel exhibited the best performance when the amount of GA graft was 0.015 wt%. Furthermore, the tightly cross-linked structure of SPI-GA prevented premature degradation of the protein by pepsin. In conclusion, these capabilities provide numerous possibilities for the development of multifunctional and active substance delivery carriers.

Poly(vinyl alcohol)/chitosan hydrogel incorporating chitooligosaccharide-gentisic acid conjugate with antioxidant and antibacterial properties as a potential wound dressing

The design and development of wound dressing with antioxidant and antibacterial properties to accelerate wound healing remain challenging. In this study, we synthesize a chitooligosaccharide-gentisic acid (COS-GSA) conjugate using the free-radical grafting method, and fabricate a poly(vinyl alcohol) (PVA)/chitosan (CH)/COS-GSA (PVA/CH/CG) hydrogel using a freeze-thaw method. We characterize the synthesized COS-GSA conjugates using through polyphenol assay, absorbance, and 1H NMR spectroscopy and evaluate their antioxidant properties. The COS-GSA conjugates are successfully synthesized and exhibit better antioxidant properties than pristine COSs. Subsequently, the fabricated hydrogel is characterized based on its morphological analysis, rheological properties, water contact angle, swelling, degradation, water retention properties, and COS-GSA release profiles. Finally, the biocompatibility of the fabricated hydrogel is evaluated on HDF and HaCaT cells through indirect and direct cytotoxicity. The PVA/CH/CG hydrogel exhibited significantly higher antioxidant properties (DPPH, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and hydrogen peroxide (H2O2) scavenging activities) and antibacterial activities (Staphylococcus aureus and Pseudomonas aeruginosa) compared to other fabricated hydrogels such as PVA, PVA/CH, and PVA/CH/COS (PVA/CH/C). These results provide evidence that PVA/CH/CG hydrogels with antioxidant, antibacterial, and non-cytotoxic properties have great potential for wound-dressing applications.

Lysozyme-phenolics bioconjugates with antioxidant and antibacterial bifunctionalities: Structural basis underlying the dual-function

This work aims at adopting an Electron Paramagnetic Resonance (EPR) spectroscopic technique to help understanding protein-phenolic conjugation and final functionalities relationship as well as the underlying structural basis of antioxidant and antibacterial dual functionalities. Specifically, lysozyme (Lys) was conjugated with two natural phenolic acids, i.e. rosmarinic acid (RA) and gentisic acid (GA, our previous work) with obviously different molecular features. Lys-RA displayed 8.6- and 4.0-times enhanced antioxidant stoichiometry compared to the native Lys and ones with GA, respectively, due to the stronger antioxidant activity of RA. However, RA conjugation mitigated both enzymatic and antibacterial activities of Lys-RA conjugates. Such inhibition effect is attributed to the greater structural and surface property changes of Lys upon conjugating with RA. Furthermore, the polyphenol conjugation related structural basis of disturbance, reactivity and selectivity were explored via site-directed spin labeling (SDSL)-EPR. A dynamic picture of reactivity and selectivity of phenolics conjugation on Lys was proposed.

Comparison of the Main Metabolites in Different Maturation Stages of Camelliavietnamensis Huang Seeds

Camellia vietnamensis Huang is an important woody oil crop in China, which has attracted much attention because of its abundant nutritional components and pharmaceutical value. Its seeds undergo a complex series of physiological and biochemical changes during maturation, with consequent alterations in metabolites. In order to investigate the endogenous metabolism of C. vietnamensis on Hainan Island during seed development, in this study, ultra-high-performance liquid tandem chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC/Q-TOF-MS) and multivariate statistical analysis (MSA) were used to analyze the differences in the chemical compounds of C. vietnamensis seeds among the four maturation stages. A total of 293 metabolites were identified from the methanol extract of the seeds of C. vietnamensis. Five metabolites, belonging to benzene and substituted derivatives, 5′-deoxyribonucleosides and linear 1,3-diarylpropanoids, were found in all three comparison groups, with consistently down-regulated trends. The Kyoto Encyclopedia of Genes and Genomes (KEGG) results showed that phloretin and 5′-methylthioadenosine were the differentially expressed metabolites when seeds were in the growth periods of S2 and S3, and indole and L-tryptophan were the differentially expressed metabolites when seeds were in the growth periods of S3 and S4. In addition, 34 flavonoid metabolites were detected, of which 4 were differentially expressed. It was indicated that flavonoids dynamically change during all the oil-tea camellia seed development stages. The findings provide data for the better understanding of endogenous metabolic pathways during C. vietnamensis seed development.

Lysozyme and Its Application as Antibacterial Agent in Food Industry

Lysozymes are hydrolytic enzymes characterized by their ability to cleave the β-(1,4)-glycosidic bonds in peptidoglycan, a major structural component of the bacterial cell wall. This hydrolysis action compromises the integrity of the cell wall, causing the lysis of bacteria. For more than 80 years, its role of antibacterial defense in animals has been renowned, and it is also used as a preservative in foods and pharmaceuticals. In order to improve the antimicrobial efficacy of lysozyme, extensive research has been intended for its modifications. This manuscript reviews the natural antibiotic compound lysozyme with reference to its catalytic and non-catalytic mode of antibacterial action, lysozyme types, susceptibility and resistance of bacteria, modification of lysozyme molecules, and its applications in the food industry.

Self-assembly CuO-loaded nanocomposite involving functionalized DNA with dihydromyricetin for water-based efficient and controllable antibacterial action

With the antibiotic crisis intensifies, the defense and treatment of pathogen infections in safe and effective fashion has become a critical issue. Herein, we report a novel and advanced type of sterilization agent designed via the functionalization DNA nanocarriers based on dihydromyricetin and CuO-loaded nanoparticles (DNA/DMY-CuO). Firstly, a pure dihydromyricetin (DMY) isolated from Ampelopsis grossedentata is used as a bridge to the stimulate the construction of DNA cross-linking networks by hydrogen bonding. Subsequently, a 3D spherical CuO-loaded nanocomposite (204.39 nm) is customized using the DNA/DMY network as a biological template through a simple coordination-assisted self-assembly method, which exhibits a high dispersibility, water-solubility and physiological stability. The reversible physical interactions in nanocarriers allows the selective separation and automatic release of CuO NPs from DNA/DMY-CuO in neutral and wound exudate environments, thereby extending the survival period of CuO NPs by nearly 24 h. Meanwhile, the nanocarriers system relied on the strong binding ability of DMY to the outer membrane of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) achieves controlled drug delivery onto the pathogen wall. The advanced antibacterial action of DNA/DMY-CuO also reflected in membrane destruction, cytoplasmic constituent leakages and ATP synthetic pathway cessation, thereby halting cytosolic metalloregulatory mechanisms and minimizing drug-resistant bacteria. In summary, such multi-functional CuO-loaded nanocomposite provides a water-dispersibility, controllable, low cytotoxicity and long-effective platform to address the ever-growing threats of bacterial infections.