Gram-negative Foodborne Pathogenic Bacteria Research Articles

Gelatin/poly(vinyl alcohol)-based dual functional composite films integrated with metal-organic frameworks and anthocyanin for active and intelligent food packaging

Innovative active and pH-colorimetric composite films were fabricated from gelatin/poly(vinyl alcohol) (Gel/PVA) integrated with copper-based metal-organic frameworks (Cu-MOFs) and red cabbage anthocyanin (RCA). The incorporation of Cu-MOFs improved the tensile strength, water resistance, and UV shielding properties of the developed composite films. The addition of anthocyanins and 3 wt% Cu-MOFs endowed the polymer matrix with excellent antioxidant (100 % against ABTS and DPPH radicals) and antibacterial (against Gram-positive and Gram-negative foodborne pathogenic bacteria) functions. The fabricated composite films exhibited significant color change at alkaline conditions of pH 7–12 and a marked color change upon exposure to ammonia. The designed indicator films used for shrimp freshness tracking and a visual color change from pink (for fresh shrimp) to green (for spoiled shrimp) was observed during storage at 28 °C for 24 h. The potential applications of the engineered composite films were studied by shrimp packaging, and the quality parameters of packaged samples were monitored during storage. The synergistic effects of adding anthocyanins and MOF nanostructures works for better product freshness preservation and responds well to shrimp spoilage level, introducing novel active and intelligent packaging options for practical smart packaging applications.

Carrageenan-based antimicrobial bionanocomposite films incorporated with ZnO nanoparticles stabilized by melanin

Zinc oxide nanoparticles (ZnONP) were prepared by reacting zinc acetate with KOH using melanin as a capping agent, and used for the preparation of antimicrobial carrageenan-based nanocomposite films. The ZnONP capped with melanin (mZnONP) was stable and flake-like, while the control ZnONP without capping was rod-like. ZnONPs, whether capped or not capped with melanin, were evenly dispersed in the carrageenan matrix to form smooth and flexible nanocomposite films. The mZnONP incorporated composite film (Carr/mZnONP) exhibited a higher UV-blocking property at the expense of less transparency than the control ZnONP incorporated nanocomposite film (Carr/ZnONP). The Carr/mZnONP composite film also exhibited higher thermal stability with increased mechanical and water vapor barrier properties than the Carr/ZnONP composite film. Both nanocomposite films exhibited strong antibacterial activity against Gram-negative foodborne pathogenic bacteria, E. coli, but slight antibacterial activity against Gram-positive bacteria, L. monocytogenes.

Prebiotic efficacy and mechanism of inulin combined with inulin-degrading Lactobacillus paracasei I321 in competition with Salmonella

Inulin efficacy was proven for raising anti-Salmonella activity of the inulin-degrading Lactobacillus paracasei I321 (infant isolate) through the mechanisms of antibacterial secretion and competitive adhesion. Inulin significantly promoted competitive adhesion of L. paracasei I321 against many Gram-negative foodborne pathogenic bacteria. Salmonella Typhimurium SA2093 was completely suppressed under highly competitive niche of fecal microflora when inulin, L. paracasei I321, and their synbiotic combination were applied. Inulin supplementation obviously alleviated nutrient limitation in the mimicked proximal colon leading to complete destruction of Salmonella. This was achieved through the manipulation of fecal bifidobacteria which subsequently altered antibacterial metabolites. Acetate was the major metabolite correlating to high number of fecal bifidobacteria in the presence of inulin, whereas lactate became dominant when L. paracasei I321 was coupled. This inulin-degrading strain was able to persist and dominate in the competitive environment of fecal microflora and functioned synergistically with inulin to completely destroy Salmonella.

Preparation, characterization, and antimicrobial activity of gelatin/ZnO nanocomposite films

Gelatin-based zinc oxide nanoparticle (ZnO NPs) nanocomposite films were prepared using various types of ZnO NPs, which were synthesized using two different zinc salts (zinc nitrate and zinc acetate) with or without capping agent (carboxymethyl cellulose). The ZnO NPs were in various shapes and sizes ranged from 200 to 400 nm depending on the preparation method. The gelatin/ZnO NPs nanocomposite films were characterized by UV–visible spectroscopy, FE-SEM, FT-IR, thermogravimetric analysis, and XRD. The influence of different types of ZnO NPs on the morphology, crystallization behavior, thermal stability, mechanical, water vapor barrier, water contact angle, and antibacterial properties of the gelatin-based nanocomposite films were investigated. Gelatin/ZnO NPs nanocomposite films exhibited three absorption peaks around 220–230, 270–280, and 360 nm. Apparent surface color and transmittance of gelatin film was greatly influenced by the types of ZnO NPs. FTIR spectra indicated interaction between ZnO NPs and N–H groups of gelatin. XRD data demonstrated the crystalline structure of ZnO NPs with dominant (100) facet in the gelatin/ZnO NPs nanocomposite films. ZnO NPs incorporated nanocomposite films exhibited enhanced thermal stability. Moisture content, water contact angle, water vapor permeability, and elongation at break of ZnO NPs incorporated films increased, while tensile strength and modulus of elasticity decreased compared with the control gelatin film. The gelatin/ZnO NPs nanocomposite films showed profound antibacterial activity against both Gram-positive and Gram-negative foodborne pathogenic bacteria. The nanocomposite film could be applied for the food preservation by controlling foodborne pathogens.

Properties and characterization of agar/CuNP bionanocomposite films prepared with different copper salts and reducing agents

Various types of agar-based bio-nanocomposite (BNC) films were prepared by blending agar and six different copper nanoparticles (CuNPs) with different shapes and sizes obtained from three different sources of copper salts and two different reducing agents. The BNC films were characterized by UV–visible, FE-SEM, FT-IR, and XRD. The thermogravimetric study showed that the melting point of BNC films was increased when ascorbic acid was used as a reducing agent for CuNPs synthesis. Apparent surface color and transmittance of agar film was greatly influenced by the reinforcement of CuNPs. However, mechanical and water vapor barrier properties did not change significantly (p>0.05) by blending with CuNPs. Tensile modulus and tensile strength decreased slightly for all types of CuNPs reinforced while elongation at break slightly increased when CuNPs produced by ascorbic acid were blended. The agar bio-nanocomposite films showed profound antibacterial activity against both Gram-positive and Gram-negative food-borne pathogenic bacteria.

Composition of essential oil of Omani Juniperus excelsa fruit and antimicrobial activity against foodborne pathogenic bacteria

Juniperus excelas is an important flowering medicinal plant belonging to the Cupressaceae family. Essential oil was obtained from fresh fruit of J. excelas by hydro-distillation in a Clevenger apparatus and analysed by gas chromatography–mass spectrometry (GC–MS). The chemical constituents of the essential oil were identified by their mass spectra, retention time and retention indices. The yield was 0.27%. We identified 48 chemical compounds accounting for 89.74% of the composition. The major chemical components were α-terpinene (23.85%), limonene (23.42%), fenchene (6.57%), camphene (6%), δ-3-carene (4.17%), 4-terpineol (2.93%), germacrene B (2.21%), myrcene (1.96%), α-pinene (1.77%), β-pinene (1.53%) and abietatriene (1.13%). The antimicrobial activity of the essential oil of J. excelas was determined against one Gram-positive and two Gram-negative foodborne pathogenic bacteria, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. No activity was detected.

The antioxidative and antimicrobial properties of the blue honeysuckle (Lonicera caerulea L.), Siberian rhubarb (Rheum rhaponticum L.) and some other plants, compared to ascorbic acid and sodium nitrite

The aim of the present study was to evaluate the antioxidative and antimicrobial effects of the ethanol and buffered water infusions of six different plants grown in Estonia, namely Siberian rhubarb (Rheum rhaponticum L.), blue honeysuckle (Lonicera caerulea L.), tomato (Lycopersicon esculentum Mill.), bilberry (Vaccinium myrtillus L.), sea-buckthorn (Hippophae rhamnoides L.) and black currant (Ribes nigrum L.), compared to the food additives ascorbic acid (E300) and sodium nitrite (NaNO2, E250). Additionally, the content of vitamin C and the content of anthocyanins, flavonols and total polyphenols in the studied samples were estimated using High performance liquid chromatography (HPLC) method.Of the bacterial species used in present study, gram-positive bacteria were represented by Listeria monocytogenes, Kocuria rhizophila and Bacillus subtilis. Gram-negative foodborne pathogenic bacteria were represented by Escherichia coli and Campylobacter jejuni. Probiotic bacterial species, often used in dairy products, were represented by Bifidobacterium bifidum and Lactobacillus acidophilus.The studied plant infusions had both antioxidant and antimicrobial properties. The highest antioxidative effect in the buffered water infusion was found with the berries of blue honeysuckle. However, in the 30% ethanol infusions the antioxidative effect was the highest with the petioles of the Siberian rhubarb, exceeded only by the ascorbic acid solution with the concentration of 10 mg/ml. Among tested plant infusions, the roots of the Siberian rhubarb exhibited the highest antibacterial effect against all bacterial species assayed.