Inactivation rates of the microorganisms with LDPE film produced by extrusion without nanoparticles and with only ultraviolet (UV) irradiation, decreased compared to that for the TiO2-nanocomposite film with no UV exposure.
The results suggest that the TiO2 nanoparticles were responsible for the antimicrobial effect when exposed to ultraviolet A light illumination.
The higher antimicrobial activity of the composite films under UV light is due to the photocatalytic reaction of the TiO2 nanoparticles in the matrix, found Hojatollah Bodaghi et al.
The team used Pseudomonas spp. and Rhodotorula mucilaginosa to measure antimicrobial activity, as they represent the main microorganisms on fruit and vegetable crops, where previous studies have backed the process in E.coli, salmonella and listeria.
The viability of nano TiO2-treated cells was determined by plate counting before and after three hours of UVA irradiation.
Titanium Dioxide and UVA light combination
The researchers found the surviving number of bacteria under films without UVA irradiation did not decrease significantly, unlike results reported for E.coli, which proved that the nanocomposite film did not inactive the microorganisms without UVA light.
But after exposure to black light illumination, the TiO2 film exhibited photocatalytic inactivation, found the researchers.
“The number of surviving cell of the Pseudomonas spp. was decreased by 4 log CFU/ml and 1.35 log CFU/ml after three hours of UVA illumination on TiO2 nanocomposite thin film and LDPE thin film, respectively.
“The number of cells of R. mucilaginosa decreased by 2 log CFU/ml and 0.64 log CFU/ml on TiO2 nanocomposite thin film and LDPE thin film, respectively.”
The survival rate of Pseudomonas spp. on TiO2 nanocomposite film was 46.83%, while this ratio was 82% for LDPE film.
The survival rate of R. mucilaginosa on TiO2 nanocomposite film was 65%, while this ratio was 89% for LDPE film.
The presence of titanium dioxide nanoparticles in the structure of composite films gives them photocatalytic characteristics, which control the amount of ethylene production and microbial population in the packaging.
Test on pears
In a test on pears packaged in TiO2 nanocomposite film and stored under illumination by a fluorescent light lamp at 5°C for 17 days, the researchers found that the number of mesophilic bacteria and yeast cells decreased compared to samples stored in LDPE film.
“The cell loads of mesophilic bacteria from the pear fruit packaged in a TiO2 nanocomposite film decreased from 3.14 to less than 2 log CFU/g for a total storage period of 17 days, whereas the cell loads increased from 3.19 to 4.02 log CFU/g for fruit packaged in neat LDPE films.”
The results demonstrated that the TiO2 nanocomposite film under fluorescent lamp with UVA intensity of less than 0.05 mW/cm2 can reduce the contamination on the surface area of fruit products and prolong the shelf life of packaged fruit.
“These results are of industrial relevance because they present an effective technique for developing novel photocatalyst thin film as an active packaging system,” concluded the researchers.
Source: Food Science and Technology volume 50, Issue 2, March 2013, Pages 702-706
Published online ahead of print, doi: 10.1016/j.lwt.2012.07.027
“Evaluation of the photocatalytic antimicrobial effects of a TiO2 nanocomposite food packaging film by in vitro and in vivo tests”
Authors: Hojatollah Bodaghi, Younes Mostofi, Abdulrasoul Oromiehie, Zabihollah Zamani, Babak Ghanbarzadeh, Cristina Costa, Amalia Conte, Matteo Alessandro Del Nobile