Ecofriendly green biosynthesis and characterization of novel bacteriocin-loaded bacterial cellulose nanofiber from Gluconobacter cerinus HDX-1

Characterization of nanosilver antibacterial bacterial cellulose composite membranes coated with montmorillonite and their potential application in food packaging

Bacterial cellulose (BC) is a natural, renewable polymer material with an ultrafine nanonetwork structure. However, BC has limited applications in food packaging and medical materials because of its lack of antibacterial properties. To expand the applications of BC, a new BC composite membrane was synthesized via an ex situ method. The BC membrane was first immersed in 100 mL of deionized water containing 3 mg of AgNO₃ for 24 h to incorporate silver nanoparticles (AgNPs). The BC-Ag composite was immersed in a 2 wt% montmorillonite (MMT) solution for 24 h to prepare the BC-Ag-MMT composite membrane. The structure and antibacterial properties of the composite were then examined. Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the successful synthesis of the BC-Ag-MMT composite membrane. The results revealed that the addition of AgNPs and MMT resulted in a significant decrease in porosity (13.23 ± 1.12 %), water vapor transmission rate (735.12 ± 12.55 g/(m2·day)), and oxygen permeability (2.28 ± 0.29 g/(s·m2Pa)) while increasing the membrane thickness (0.89 ± 0.08 mm). The incorporation of MMT into BC notably improved the thermal stability of the membrane and further influenced its porosity. The antibacterial activity was evaluated via the inhibition zone method. The BC-Ag-MMT composite membrane exhibited antibacterial activity against Salmonella paratyphi A, Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Salmonella enterica. These findings demonstrated that the BC-Ag-MMT composite membrane possesses exceptional physical and chemical properties, mechanical strength, and antibacterial efficacy. The composite membrane holds significant potential for applications in food packaging.

Zein-based nisin-loaded electrospun nanofibers as active packaging mats for control of Listeria monocytogenes on peach

Zein-based nanofibers (NFs) functionalized with nisin (NS), reinforced with montmorillonite nanoclay (nMMT) were fabricated by uniaxial electrospinning (ES) for the first time to preserve yellow peach. Spinnability/viscosity/conductivity optimizations generated porous (95.09%), bead-free, ultrathin (119 nm) NFs of low hydrophobicity (26.05°). Glutaraldehyde (GTA) crosslinking fostered positive outcomes of tensile strength (1.23 MPa), elongation (5.0%), hydrophobicity (99.46°), surface area (201.38 m2.g-1), pore size (2.88 nm), thermal stability (Tmax = 342 °C), antioxidant/cytotoxic activities in optimized NFs that released NS sustainably according to Korsmeyer-Peppas model indicating a Fickian diffusion mechanism with R2 = 0.9587. The novel NFs inhibited growth of Listeria monocytogenes/aerobic mesophilic populations in peach after 4 days of abusive storage, evincing their robustness in food contact applications. Simultaneously, quality parameters (moisture/texture/browning/total soluble solids/pH) and peach physical appearance were maintained for up to 8 days, endorsing the practical value of zein-based NFs as a non-thermal postharvest intervention for prolonging fruits storage life.

Characterization of exopolysaccharide/potato starch nanocomposite films loading g-C3N4 and Ag and their potential applications in food packaging

The interest in nanocomposite films incorporating edible ingredients and active nanoparticles has surged due to their potential to enhance food quality and prolong shelf-life. This research focused on developing innovative exopolysaccharides (EPS)/potato starch (PS) nanocomposite films integrated with g-C3N4 and AgNO3. Extensive analysis was conducted to assess the microstructure, physical attributes and antimicrobial properties of these films. Fourier transform infrared (FT-IR) analysis revealed electrostatic and hydrogen bonding interactions within the film components. X-ray diffraction (XRD) and X-ray photoelectron spectrometer (XPS) data indicated a high level of compatibility among EPS, PS, g-C3N4, and AgNO3, with no new absorption peaks or characteristic signals of C3N4 and Ag appearing in the nanocomposite films patterns. The thickness, water solubility and water vapor permeability (WVP) of the EPS-PS-C3N4-Ag nanocomposite film increased due to the addition of g-C3N4, reached 0.31 ± 0.03 nm, 36.61 ± 1.76 % and 1.42 ± 0.34 × 10-10 g-1 s-1 Pa-1, respectively. While transparency, swelling degree, and oxygen permeability (OP) significantly decreased, reached 26.18 ± 2.38 %, 63.01 ± 2.51 % and 41.98 ± 1.28 %, respectively. Scanning electron microscopy (SEM) and atomic force microscope (AFM) images depicted an augmented roughness and porosity on the film surface upon integration of g-C3N4 and AgNO3. Moreover, the EPS-PS-C3N4-Ag nanocomposite film displayed enhanced mechanical strength due to the presence of g-C3N4. The melting temperature (Tm) of EPS-PS-C3N4-Ag nanocomposite film was 313.3 °C, the removal rates of DPPH and ABTS was 66.11 ± 2.87 % and 45.09 ± 1.23 % respectively. Significant inhibition of microbial growth was observed in film containing g-C3N4 and AgNO3, which demonstrated no toxicity towards NIH-33 cells, suggesting their potential application as promising active packaging material for food preservation.

Co-encapsulation of Shirazi thyme (Zataria multiflora) essential oil and nisin using caffeic acid grafted chitosan nanogel and the effect of this nanogel as a bio-preservative in Iranian white cheese

The current study aims to co-encapsulate Shirazi thyme (Zataria multiflora) essential oil (ZEO) and nisin into chitosan nanogel as an antimicrobial and antioxidant agent to enhance the shelf-life of cheese. Chitosan-caffeic acid (CS-CA) nanogel was produced to co-encapsulate Zataria multiflora essential oil and nisin. This nanogel was characterized by dynamic light scattering (DLS), Fourier Transform Infrared (FTIR) spectroscopic analysis, X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM) images. The effect of free (TFZN) and encapsulated ZEO-nisin in chitosan nanogel (TCZN) on the chemical and microbiological properties of Iranian white cheese was assessed. The particle size, polydispersity index value (PDI), zeta potential, antioxidant activity, and encapsulation efficiency of the optimal chitosan-ZEO-nisin nanogel were 421.6 nm, 0.343, 34.0 mV, 71.06%-82.69%, and 41.3 ± 0.5%, 0.79 ± 0.06 mg/mL. respectively. FTIR and XRD approved ZEO and nisin entrapment within chitosan nanogel. The chitosan nanogel showed a highly porous surface with an irregular shape. The bioactive compounds of ZEO and nisin decreased the pH changes in cheese. On the 60th day of storage, the acidity of treated samples was significantly lower than that of control. Although the lowest anisidine index value was observed in samples treated with sodium nitrate (NaNO3) (TS), there was no significant difference between this sample and TCZN. The lowest microbial population was observed in TCZN and TS. After 60 days of ripening, Coliforms were not detected in the culture medium of TCZN and TS. The results can contribute to the development of a natural preservative with the potential for application in the dairy industry.

Biosynthesis and characterization of antibacterial bacterial cellulose composite membrane composed of montmorillonite and exopolysaccharides

Bacterial cellulose (BC), as a natural renewable polymer material, has the advantages of porous nanonetwork structure, high degree of polymerization, high purity, high crystallinity, excellent mechanical properties and biocompatibility. However, BC lacks antibacterial properties, which leads to the limitation of BC material in food packaging and medical materials. In this study, a new antibacterial material using the combination of montmorillonite (MMT), BC and exopolysaccharides (EPS) produced by Weissella confusa H2 was synthesized. Fourier infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analysis showed that BC-EPS, BC-MMT and BC-EPS-MMT composite membranes conformed to the typical type I cellulose structure. Compared to BC membrane, scanning electron microscopy (SEM) showed that the porosity of BC-EPS, BC-MMT and BC-EPS-MMT composite membranes was low and compact. The physical properties of BC-EPS, BC-MTT and BC-EPS-MTT composite membranes showed lower water vapor transmittance. The BC-MTT and BC-EPS-MTT composite membranes exhibit a lower swelling ratio in 120 min. The thermal properties show that BC-EPS, BC-MTT and BC-EPS-MTT composite membranes have higher thermal stability (352 °C, 310 °C, 314 °C). Additionally, both BC-MMT and BC-EPS-MMT demonstrated strong inhibitory effects against various bacterial strains, including Staphylococcus aureus, Escherichia coli, Salmonella paratyphi A, and Bacillus subtilis. The exceptional properties exhibited by composite membranes establishes them as a highly promising option in the field of food packaging and medical material applications.

New perspectives into Gluconobacter-catalysed biotransformations

Different from other aerobic microorganisms that oxidise carbon sources to water and carbon dioxide, Gluconobacter catalyses the incomplete oxidation of various substrates with regio- and stereoselectivity. This ability, as well as its capacity to release the resulting products into the reaction media, place Gluconobacter as a privileged member of a non-model microorganism class that may boost industrial biotechnology. Knowledge of new technologies applied to Gluconobacter has been piling up in recent years. Advancements in its genetic modification, application of immobilisation tools and careful designs of the transformations, have improved productivities and stabilities of Gluconobacter strains or enabled new bioconversions for the production of valuable marketable chemicals. In this work, the latest advancements applied to Gluconobacter-catalysed biotransformations are summarised with a special focus on recent available tools to improve them. From genetic and metabolic engineering to bioreactor design, the most recent works on the topic are analysed in depth to provide a comprehensive resource not only for scientists and technologists working on/with Gluconobacter, but for the general biotechnologist.

Characterization of antifungal cyclic dipeptides of Lacticaseibacillus paracasei ZX1231 and active packaging film prepared with its cell-free supernatant and bacterial nanocellulose

Fungal infection and/or spoilage are major concerns of crop and food security worldwide, prompting the developments and application of various antimicrobial agents. In this study, nine strains of lactic acid bacteria (LAB) with antifungal activities were isolated from the traditional Chinese fermented wort of Meigui rice vinegar, where fungi coexist. The cell-free supernatant (CFS) of Lacticaseibacillus paracasei ZX1231 exhibited significant inhibitory activities against Aspergillus niger, Penicillium citrinum, Penicillium polonicum, Zygosaccharomyces rouxii, Talaromyces rubrifaciens, and Candida albicans. Among the four cyclic dipeptides (CDPs) uncovered from the CFS, cyclo(Phe-Leu) and cyclo(Anthranily-Pro) were found in the family Lactobacillaceae for the first time, which inhibited the C. albicans filamentation by targeting upon RAS1-cAMP-PKA pathway. CFS antifungal activities were optimally combined with a bacterial nanocellulose (BNC) matrix to prepare the active quality packaging CFS-BNC films. The challenge tests confirmed that CFS-BNC films significantly inhibited the fungi growth and thus prolonged the shelf life of bread, beef, cheese and soy sauce. L. paracasei ZX1231, its CFS, and the CFS-BNC film may have extensive applications in food preservation and food packaging.