Preparation of self-assembling Litsea cubeba essential oil/ diphenylalanine peptide micro/nanotubes with enhanced antibacterial properties against Staphylococcus aureus biofilm

Fabrication and characterization of pullulan/tapioca starch-based antibacterial films incorporated with Litsea cubeba essential oil for meat preservation

Active packaging is a novel technology that utilizes active materials to interact with products and the environment, improving food shelf life. The purpose of this work was to fabricate a multifunctional film using Litsea cubeba essential oil (LC-EO) (1 %, 3 %, 5 %, and 7 %) as the active ingredient and pullulan(P)/tapioca starch (TS) as the carrier material. Adding essential oil improves the films properties, such as barrier ability, anti-oxidant, and antibacterial activity. However, tensile strength (TS) and elongation at break (EAB) were slightly reduced from 28.94 MPa to 11.29 MPa and 15.36 % to 12.19 %. The developed PTS3% films showed the best performance in mechanical properties, especially EAB (14.26 %), WVP (3.26 %) and OP (3.13 %), respectively. The inhibitory zone diameters in the agar-well diffusion test were 18.59 mm for Staphylococcus aureus and 17.32 mm for Escherichia coli. Further study was conducted to compare the preservation effects of film with low-density polyethylene bag (LDPE) on chilled beef. Remarkably, PTS3% film decreased the bacterial population in beef meat while maintaining the pH, color, texture, and TBARS levels within an acceptable range for ten days of storage at 4 °C rather than in a low-density polyethylene bag. The outcomes indicated the potential of PTS3% films in food packaging applications.

Gelation Behavior and Drug Sustained-Release Properties of a Helix Peptide Organohydrogel with pH Responsiveness

Based on the typical similar repeat units (abcdefg)n of α-helical structure, the peptide H was designed to self-assemble into an organohydrogel in response to pH. Depending on the different pH, the proportions of secondary structure, microstructure, and mechanical properties of the gel were investigated. Circular dichroism (CD) and Fourier transform infrared (FT-IR) showed that the proportion of α-helical structure gradually increased to become dominant with the increase of pH. Combining transmission electron microscopy (TEM) and atomic force microscopy (AFM), it was found that the increase of the ordered α-helix structure promoted fiber formation. The further increase in pH changed the intermolecular forces, resulting in an increase in the α-helix content and the enhancement of helix-helix interaction, causing the gel fibers to converge into thicker and more dense ones. The temperature test showed the stable rheological properties of the organohydrogel between 20-60 °C. Drug release and cytotoxicity showed that the DOX-loaded organohydrogel could have a better release in an acidic environment, indicating its potential application as a drug local delivery carrier.

Replacement of polyethylene oxide by peach gum to produce an active film using Litsea cubeba essential oil and its application in beef

This study evaluated the effects of adding various concentrations (0 %, 1 %, 2 %, and 3 %) of peach gum (PG) to films made from polyethylene oxide (PEO) combined with Litsea cubeba essential oil (LCEO) to be utilized as active packaging for food in the future. The findings showed that the film containing PG 2 % concentration had the best physic-mechanical properties. In films made with PG, the glass transition temperature was significantly improved. Combining PG and PEO resulted in films that were brighter in color, had lower WVP values, and had the lowest water activity. Furthermore, XRD demonstrated that PG additions were compatible with the film of PEO blended with LCEO. The PG films formulated with PG presented high antioxidant and antibacterial activity against Staphylococcus aureus and E. coli. Wrapping beef with P2G2 film led to maintaining its quality with suitable levels of pH, TBARS, and TVB-N. This also decreased the number of E. coli and S. aureus in beef throughout the storage period. The results indicate that adding PG to PEO films enhances their suitability for food preservation.

Solvent-dependent formation kinetics of L,L-diphenylalanine micro/nanotubes

Investigating the molecular mechanism underlying the aggregation process of amyloid fibers is of great importance both for its implications in several degenerative diseases and for the design of new materials based on self-assembly. In particular, micro/nanotubes of L,L-diphenylalanine have been investigated as a model of amyloid plaques in Alzheimer's disease and also for their broad range of physical properties, e.g., good thermo- and mechanical stability, semiconductivity, piezoelectricity and optical properties. It has been reported that the assembly/disassembly dynamics of L,L-diphenylalanine crystals is influenced by the solvent composition being triggered by evaporation of solvents. In fact the solvatomorphism of this peptide-based nanomaterial is complex and rich attracting great attention. Here we investigated the growing kinetics of the micro/nanotubes of L,L-diphenylalanine in samples prepared with toluene, ethanol, and acetic acid solvents by time-resolved Raman spectroscopy. Our results indicated that the self-assembly in this case competes with the water evaporation process contrary to what is reported by samples prepared with widely used solvent 1,1,1,3,3,3-hexafluoro-2-propanol. We note that exclusively tubular structures (being hollow for the toluene solvent case) were observed. Interestingly our results support the fact that for acetic acid, ethanol, and toluene the micro/nanotube formation process is autocatalytic instead of being nucleation-dominating as reported for samples prepared using solvent 1,1,1,3,3,3-hexafluoro-2-propanol.

Preparation, characterization, and antifungal property of the inclusion complex of Litsea cubeba essential oil/hydroxypropyl-β-cyclodextrin and its application in preservation of Shatang mandarin

To explore the potential application of plant essential oil in the postharvest preservation of fruits, the inclusion complex (IC) of Litsea cubeba essential oil (LCEO) with hydroxypropyl-β-cyclodextrin (HPβCD), prepared by the saturated aqueous solution method, was studied. LCEO/HPβCD-IC was characterized by fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), particle size distribution, and thermogravimetric-differential scanning calorimetry (TG-DSC) analysis. The formation of LCEO/HPβCD-IC was confirmed, and the volume average particle diameter was 24.376 µm. Due to the inclusion of HPβCD, the volatility of LCEO was significantly reduced and the thermal stability was significantly improved. In addition, the antifungal activities of the LCEO ICs were compared, and LCEO/HPβCD-IC was more effective against the citrus postharvest pathogens (P. italicum and G. citri-aurantii). The effects of the LCEO ICs on the postharvest quality of Shatang mandarin were studied. Compared with the control group (CK) and LCEO/βCD-IC group, the LCEO/HPβCD-IC group showed a significant delay in the decrease of good fruit rate, hardness, total soluble solids (TSSs), and Vitamin C (Vc) content, with a lower weight loss rate of Shatang mandarin. Therefore, LCEO/HPβCD-IC is expected to be used as a green preservative for the storage and preservation of citrus fruits. PRACTICAL APPLICATION: In this study, LCEO was encapsulated in HPβCD by the saturated aqueous solution method and the prepared inclusion complex was characterized. The effects of LCEO/HPβCD-IC and LCEO/βCD-IC on postharvest preservation of Shatang mandarin were compared. This work offers valuable insights into the postharvest preservation of citrus fruit by essential oil inclusion complexes.

YAFAF-Based Hydrogel: Characterization, Mechanism, and Factors Influencing Micro-organization

The YAFAF-based hydrogel was a three-dimensional network cross-linked by grooved fiber bundles. The fiber bundles were formed by entanglement of fibrils with a diameter of 2 nm, and the surface of the fibrils also presented grooves. Spectroscopic analysis revealed that the main secondary structures were β-sheets and β-turns, which led to the grooved feature of fibrils. In comparison of the nuclear magnetic resonance spectra of peptide solutions at 313 and 277 K, the nuclear Overhauser effects can be clearly observed, indicating that hydrogen-bondings and π-π stacking interactions play important roles in self-assembly. The micro-organization of the self-assemblies was affected by the ratio of solvents (x_A) remarkably. Unexpectedly, x_A of 0.05 produced hollow spherical aggregates. The result of these investigations on the mechanism and organization of the YAFAF-based hydrogel can contribute to the development of strategies using hydrogels in the food industry.

Application of Xanthan-Gum-Based Edible Coating Incorporated with Litsea cubeba Essential Oil Nanoliposomes in Salmon Preservation

Salmon is prone to be contaminated by Vibrio parahaemolyticus (V. parahaemolyticus), leading to the deterioration of salmon quality and the occurrence of food-borne diseases. In this study, we aimed to develop a novel xanthan-gum-based edible coating embedded with nano-encapsulated Litsea cubeba essential oil (LC-EO) for salmon preservation at 4 °C. First, the results of the growth curves and scanning electron microscopy (SEM) showed that LC-EO displayed potent antibacterial activity against V. parahaemolyticus; the optimal concentration of LC-EO in the liposomes was 5 mg/mL, and the maximal encapsulation efficiency (EE) was 37.8%. The particle size, polydispersity coefficient (PDI), and zeta potential of the liposomes were 168.10 nm, 0.250, and −32.14 mV, respectively. The rheological test results of xanthan-gum-based edible coatings incorporating liposomes showed that the prepared coating was suitable for applying on food surfaces. The results in the challenge test at 4 °C demonstrated that the treatment of 1:3 (liposome: xanthan gum, v/v) coating performed the best preservative properties, the coating treatment delayed the oxidation of salmon, and controlled the growth of V. parahaemolyticus. These findings suggest that the coatings formulated in this study could be used as a promising approach to control V. parahaemolyticus contamination and maintain salmon quality.

Polymeric Nanomaterials for Efficient Delivery of Antimicrobial Agents

Bacterial infections have threatened the lives of human beings for thousands of years either as major diseases or complications. The elimination of bacterial infections has always occupied a pivotal position in our history. For a long period of time, people were devoted to finding natural antimicrobial agents such as antimicrobial peptides (AMPs), antibiotics and silver ions or synthetic active antimicrobial substances including antimicrobial peptoids, metal oxides and polymers to combat bacterial infections. However, with the emergence of multidrug resistance (MDR), bacterial infection has become one of the most urgent problems worldwide. The efficient delivery of antimicrobial agents to the site of infection precisely is a promising strategy for reducing bacterial resistance. Polymeric nanomaterials have been widely studied as carriers for constructing antimicrobial agent delivery systems and have shown advantages including high biocompatibility, sustained release, targeting and improved bioavailability. In this review, we will highlight recent advances in highly efficient delivery of antimicrobial agents by polymeric nanomaterials such as micelles, vesicles, dendrimers, nanogels, nanofibers and so forth. The biomedical applications of polymeric nanomaterial-based delivery systems in combating MDR bacteria, anti-biofilms, wound healing, tissue engineering and anticancer are demonstrated. Moreover, conclusions and future perspectives are also proposed.