Potential of chitosan from mushroom waste to enhance quality and storability of fresh-cut melons.

The possibility of usage mushroom industry wastage, as a source of antimicrobial biopolymer chitosan to form active edible coatings was studied. It was found that the champignon stipe, an underutilized part of the mushroom, gave rise to a higher chitosan yield than caps (176 vs. 105 mg/g). Fungal chitosan caused a total growth inhibition of the Saccharomyces cerevisiae yeast and Escherichia coli bacteria at concentrations of 1% and 2%, respectively. The fungal chitosan-based edible coatings were applied on fresh-cut melons and found to enhance fruit firmness, inhibit off-flavors and reduce the microbial counts (up to 4 log CFU/g). Volatiles profile showed the coated melons have a higher content of esters responsible for fruit flavor (79.93% and 57.15% for fungal chitosan coated melon and uncoated melon, respectively). This study demonstrates that waste from the mushroom industry can be utilized for the production of non-animal sourced chitosan to form active edible coatings.

Polydiacetylene nanovesicles as carriers of natural phenylpropanoids for creating antimicrobial food-contact surfaces.

The ultimate goal of this study was developing antimicrobial food-contact materials based on natural phenolic compounds using nanotechnological approaches. Among the methyl-ß-cyclodextrin-encapsulated phenolics tested, curcumin showed by far the highest activity toward Escherichia coli with a minimum inhibitory concentration of 0.4 mM. Curcumin was enclosed in liposome-type polydiacetylene/phosholipid nanovesicles supplemented with N-hydroxysuccinimide and glucose. The fluorescence spectrum of the nanovesicles suggested that curcumin was located in their bilayer region. Free-suspended nanovesicles tended to bind to the bacterial surface and demonstrated bactericidal activity toward Gram-negative (E. coli) and vegetative cells of Gram-positive (Bacillus cereus) bacteria reducing their counts from 5 log CFU mL(-1) to an undetectable level within 8 h. The nanovesicles were covalently bound to silanized glass. Incubation of E. coli and B. cereus with nanovesicle-coated glass resulted in a 2.5 log reduction in their counts. After optimization this approach can be used for controlling microbial growth, cross-contamination, and biofilm formation on food-contacting surfaces.

High-Throughput Screening of Nanoparticle-Stabilizing Ligands: Application to Preparing Antimicrobial Curcumin Nanoparticles by Antisolvent Precipitation.

Water-dispersible curcumin nanoparticles were prepared by bottom-up antisolvent precipitation approach. A new high-throughput screening technique was developed for selecting appropriate ligands stabilizing the nanoparticles in aqueous medium and improving their performance. The initial set of twenty-eight potential stabilizing ligands was evaluated based on their capacity to improve curcumin dispersibility in aqueous medium. The performance of four promising ligands (amino acid proline, polyphenol tannic acid, polycation Polyquaternium 10, and neutral polymer polyvinylpyrrolidone) was tested in ultrasound-aided antisolvent precipitation trials. Using the selected stabilizing ligands diminished the average particle size from ca. 1,200 to 170-230 nm, reduced their dispersity, improved stability, and allowed reaching curcumin concentration of up to 1.4 mM in aqueous medium. Storage stability of the aqueous nanodispersions varied from 2 days to 2 weeks, depending on stabilizing ligand. Studying the effects of ionic strength and pH on size and ζ-potential of the particles suggested that electrostatic forces and hydrophobic interactions could be the major factors affecting their stability. The ligand-protected nanoparticles showed minimal inhibitory concentration of 400 or 500 µM toward Escherichia coli. We suggest that the presented screening approach may be useful for preparing nanoparticles of various poorly water-soluble bioactive materials.

Ultraviolet light stimulates flavonol accumulation in peeled onions and controls microorganisms on their surface.

The effects of ultraviolet (UV) light on flavonol content in peeled onions (Allium cepa L.) and on microbial survival on their surface were investigated. The content of phenolic compounds showed a gradient within the onion bulb, with the highest level in the external dry "skin" (tunic) and the lowest level in the center. Peeled bulbs were treated with UV light comprising the bands of UV-C (more than half of the total UV output), UV-A, and UV-B. The response to UV depended upon the position of the scales within the bulb. In the outer fleshy scales, the UV doses of 1.2-6 kJ m(-2) approximately doubled the accumulation of flavonols and the total antioxidant capacity. When mid-depth (5th from the outside) scales were exposed to UV, the lowest dose tested (1.2 kJ m(-2)) had no significant effect on flavonols accumulation, whereas the higher doses decreased their levels. The low-dose UV treatment reduced the count of Escherichia coli on artificially contaminated peeled onions by 1.5-3 logs and alleviated the decay of Penicillium-inoculated bulbs. The present study has demonstrated a potential of UV light for simultaneous decontamination of peeled onions and their enrichment in health-enhancing phytonutrients.