Staphylococcus aureus membrane-damaging activities of four phenolics.

The membrane-damaging activities of four phenolics chosen for their bactericidal activity against Staphylococcus aureus CNRZ3 were investigated: 5,7-dihydroxy-4-phenylcoumarin (DHPC), 5,8-dihydroxy-1,4-naphthoquinone (DHNQ), epigallocatechin gallate (EGCG) and isobutyl 4-hydroxybenzoate (IBHB). Staphylococcus aureus CNRZ3 cells, as well as model liposomes mimicking its membrane phospholipids composition, were treated with each phenolic at its minimal bactericidal concentration. Membrane integrity, intracellular pH and intracellular esterase activity were examined by flow cytometric analysis of S. aureus cells stained with propidium iodide and SYTO® 9, 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester, and 5(6)-carboxyfluorescein diacetate, respectively. While intracellular pH was affected by the foyr phenolics, only DHNQ and to a lesser extent EGCG, caused a loss of membrane integrity. Flow cytometric analysis of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and DPPC/POPG (2-oleoyl-1-palmitoyl-sn-glycero-3-phosphoglycerol) liposomes stained with Coumarin 6 (which penetrates the lipid bilayer) or 5-N(octadecanoyl)-amino-fluorescein (which binds to the liposome shell) suggested that only EGCG and DHNQ penetrated the bilayer of phospholipids of liposomes. Taken together, these findings support the hypothesis that EGCG and DHNQ bactericidal activity results from their accumulation in the phospholipid bilayer of S. aureus cells membrane causing its disruption.

Potential of Incorporation of Antimicrobial Plant Phenolics Into Polyolefin-Based Food Contact Materials to Produce Active Packaging by Melt-Blending: Proof of Concept With Isobutyl-4-Hydroxybenzoate.

There is an increasing interest for active food packaging incorporated with natural antimicrobial agents rather than synthetic preservatives. However, most of plastics for direct contact with food are made of polyolefins, usually processed by extrusion, injection, or blow-molding methods while most of natural antimicrobial molecules are thermolabile compounds (e.g., essential oils). Therefore, addition of plant phenolics (with low volatility) to different polyolefins might be promising to design active controlled release packaging processed by usual plastic compounding and used for direct contact with food products. Therefore, up to 2% (wt/wt) of isobutyl-4-hydroxybenzoate (IBHB) was mixed with 3 polyolefins: EVA poly(ethylene-co-vinyl acetate), LLDPE (Linear Low Density Polyethylene), and PP (PolyPropylene) by melt-blending from 75 to 170°C and then pelletized in order to prepare heat-pressed films. IBHB was chosen as an antibacterial phenolic active model molecule against Staphylococcus aureus to challenge the entire processing. Antibacterial activity of films against S. aureus (procedure adapted from ISO 22196 standard) were 4, 6, and 1 decimal reductions in 24 h for EVA, LLDPE, and PP films, respectively, demonstrating the preservation of the antibacterial activity after melt processing. For food contact materials, the efficacy of antimicrobial packaging depends on the release of the antimicrobial molecules. Therefore, the three types of films were placed at 23°C in 95% (v/v) ethanol and the release rates of IBHB were monitored: 101 ± 1%, 32 ± 7%, and 72 ± 9% at apparent equilibrium for EVA, LLDPE, and PP films, respectively. The apparent diffusion coefficients of IBHB in EVA and PP films were 2.8 ± 0.3 × 10-12 and 4.0 ± 1.0 × 10-16 m2s-1. For LLDPE films, IBHB crystals were observed on the surface of films by SEM (Scanning Electron Microscopy): this blooming effect was due the partial incompatibility of IBHB in LLDPE and its fast diffusion out of the polymer matrix onto the film surface. In conclusion, none of these three materials was suitable for a relevant controlled release packaging targeting the preservation of fresh food, but a combination of two of them is promising by the design of a multilayer packaging: the release could result from permeation through an inner PE layer combined with an EVA one acting as a reservoir.

Homogeneous acylation of Cellulose diacetate: Towards bioplastics with tuneable thermal and water transport properties.

In this study, we report a simple, non-degrading and efficient homogeneous acylation of cellulose diacetate (CDA) by using a large panel of commercially available acylating aliphatic moieties, differing in their structure (fatty, ramified, bulky, cycloaliphatic, aromatic, more or less spaced from the cellulose backbone), in view of generating a library of well-defined cellulose mixed esters with enhanced thermoplasticity. As reflected by a lowering of the glass temperature (Tg), the covalent grafting confers an improved mobility to the cellulose chains, by disrupting the initial H-bonds. In particular, it appears that the gain in free volume is tailored by the substituent structure and that acylating reagents consisting in a terminal bulky moieties spaced from CDA chains by a linear chain efficiently separate macromolecular chains without generating detrimental stiffening interactions (low Tg around 125 °C). Moreover, free-standing films easily prepared by solvent casting exhibit relevant water transport properties, which are closely dictated and tuned by the water solubility of the cellulose mixed ester.

Polybutylene succinate adipate/starch blends: a morphological study for the design of controlled release films.

Films made of plasticized starch (PLS)/poly(butylene succinate co-butylene adipate) (PBSA) blends were prepared by thermomechanical processing varying the PBSA proportions in blends to obtain biphasic materials with distinct morphologies. These morphologies were characterized by selective extraction of each phase, microscopic observations, and selective water/oxygen permeation properties. These experiments allowed identifying the blend compositions corresponding to the beginning of partial continuity (cluster partial percolation) until total continuity of each phases. This property was related to the controlled release of model molecule (fluorescein) previously dispersed in the PLS and revealed that its release depended on the tortuosity of the PLS phase tailored by the polymer blends composition and by the limited swelling of the PLS when entrapped in the PBSA phase. Future applications will focus on food preservatives dispersed in PBSA-PLS blends to obtain active antimicrobial packaging put in direct contact with intermediate to high moisture foods.