Polyvinyl alcohol nanoparticles loaded with propolis extract: Fabrication, characterization and antimicrobial activity

Background and Purpose: Propolis has high potential beneficial bioactive properties such as anti-oxidative, anti­microbial, and anti-tumour activities. However, the bitter taste and the insolubility nature of propolis in water lead to some limitations in their usage in functional food applications. Experimental Approach: Herein, we evaluated the effects of nanoencapsulation of propolis at the different concentration levels (0, 0.4, 0.8, 1.0, and 1.2 %) into the polyvinyl alcohol (PVA) nanoparticles using the electrospraying method, on the structural, physical, antioxidant, antimicrobial and thermal properties. Key Results: The results revealed that the fabricated nanocapsules (PVA-NPs) obtained under optimal conditions had uniform size distribution and unstable particles with small particle size between 104-258 nm, a polydispersity index <0.317, and a zeta potential between -5 and +5 mV. The maximum encapsulation efficiency of PVA-NPs was about 25.32 % for 1 % of the initial propolis loading level. DSC thermal experiments showed an increase in the thermal stability of the propolis loaded PVA nanoparticles as compared to the neat PVA nanoparticles. The percent inhibition of DPPH radical scavenging activity of the nanocapsules was between 80 and 89 %. SEM analysis revealed that PVA-NPs had a spherical shape with a rough surface and were composed of long and thin fibres at nanometric diameters. FT-IR analysis showed that no indications of any chemical reactions were found between the constituents of the core and wall material due to their physical mixing. Antibacterial efficacy was evaluated by the Broth dilution method and PVA-NPs exhibited good inhibitory activity against S. aureus at low concentration ratios, whereas it had no inhibitory activity against E. coli O157:H7. Conclusion: PVA-NPs fabricated using the electrospraying technique can be used for the development of a new promising natural and bioactive agent in the food and pharmaceutical industry

Inactivation of non-toxigenic and toxigenic Escherichia coli O157:H7 inoculated on minimally processed tomatoes and cucumbers: Utilization of hydrosols of Lamiaceae spices as natural food sanitizers

Hydrosols obtained from three Lamiaceae plants (thyme, summer savory and oregano) were evaluated for their antibacterial activity against two Escherichia coli O157:H7 strains inoculated to fresh-cut tomato and cucumbers. Complete inhibitions of both E. coli O157:H7 strains on fresh-cut tomato and cucumber were achieved by all hydrosol treatments in varying treatment periods for low inoculation level (10(4) cfu/mL) while water wash (control) was inefficient to eliminate the bacterial populations. In the case of high inoculation (10(6) cfu/mL), hydrosol treatments reduced the populations to undetectable levels on cucumber cuts. Moreover, reductions in E. coli O157:H7 populations of fresh-cut tomato were always higher than 2.50 log cfu/g at this inoculation. The results suggested that hydrosols from Lamiaceae plants have the potential to be used as natural food sanitizers for fresh-cut tomatoes and cucumbers to provide their microbial safety without causing any sensorial defect on treated products or health problems in human. (C) 2012 Elsevier Ltd. All rights reserved