Short communicationDevelopment of TiO2 powder-coated food packaging film and its ability to inactivate Escherichia coli in vitro and in actual tests
Introduction
Titanium dioxide (TiO2) is a photocatalyst and widely utilized as a self-cleaning and self-disinfecting material for surface coatings in many applications (Fujishima et al., 1999, Fujishima et al., 2000). The photocatalytic reaction of TiO2 has been used to inactivate a wide spectrum of microorganisms (Matsunaga et al., 1988, Fujishima et al., 1999, Kim et al., 2003, Duffy et al., 2004, Maneerat and Hayata, 2006). The first work on the microbiocidal effect of TiO2 photocatalyst was carried out with Escherichia coli in water (Matsunaga et al., 1985). These authors reported that E. coli was killed by contact with a TiO2 photocatalyst upon illumination with light. Hydroxyl radicals (•OH) and reactive oxygen species (ROS) generated on the illuminated TiO2 surface play a role in inactivating microorganisms by oxidizing the polyunsaturated phospholipid component of the cell membrane of microbes (Saito et al., 1992, Fujishima et al., 1999, Maness et al., 1999, Huang et al., 2000, Kuhn et al., 2003, Cho et al., 2004). OH radicals are approximately one thousand or possibly ten thousand times more effective for E. coli inactivation than common disinfectants such as chlorine, ozone and chlorine dioxide (Cho et al., 2004).
TiO2 is non-toxic and has been approved by the American Food and Drug Administration (FDA) for use in human food, drugs, cosmetics and food contact materials. Currently there is considerable interest in the self-disinfecting property of TiO2 for meeting hygienic design requirements in food processing and packaging surfaces. Bactericidal and fungicidal effects of TiO2 on E. coli, Salmonella choleraesuis, Vibrio parahaemolyticus, Listeria monocytogenes, Pseudomonas aeruginosa, Stayphylococcus aureus, Diaporthe actinidiae and Penicillium expansum have been reported (Matsunaga et al., 1985, Matsunaga et al., 1988, Wei et al., 1994, Kikuchi et al., 1997, Horie et al., 1998, Sunada et al., 1998, Maness et al., 1999, Choi and Kim, 2000, Wist et al., 2002, Kim et al., 2003, Cho et al., 2004, Hur et al., 2005, Maneerat and Hayata, 2006). Application of TiO2 photocatalytic disinfection for drinking water production was investigated in Wist et al. (2002). The development of TiO2-coated or -incorporated food packaging and food preparing equipment has also received attention.
The aim of the present study was to develop TiO2-coated oriented-polypropylene (OPP) film, clarify its antimicrobial activity and causative factors and assess its potential use in food packaging. The TiO2-coated OPP packaging films were developed with two different particle sizes of TiO2 powder. The antimicrobial capacity of TiO2-coated packaging film against E. coli was examined both in vitro and in actual tests under two kinds of artificial light.
Section snippets
Preparation of TiO2-coated packaging film
Nanoparticle TiO2 powder (anatase-phase crystal structure with a 7-nm particle size) from Ishihara Sangyo Company, Ltd., Tokyo, Japan, and microparticle TiO2 powder (anatase-phase crystal structure with a 5-μm particle size) from Wako Pure Chemical Industries, Ltd., Tokyo, Japan, were used. An oriented-polypropyrene (OPP) plastic film with a thickness of 30 μm was obtained from Utsunomiya Pack Co., Ltd, Hiroshima, Japan. TiO2 powder was mixed with organic solvents (normally ethyl methyl ketone,
Results and discussion
The experiment on the antimicrobial activity of the TiO2-coated OPP film was carried out as shown in Fig. 1. The surviving number of E. coli cells on the surface of uncoated and TiO2-coated OPP film in the dark condition did not decrease after 3 h of experimental period (data not shown). This suggests that the antimicrobial testing method itself did not inactivate E. coli during the experiment. When exposed to black-light illumination, the TiO2-coated OPP film exhibited photocatalytic
Acknowledgments
This work was fully supported by the JSPS postdoctoral fellowship program for foreign researchers of the Japan Society for the Promotion of Science (JSPS). We are also grateful to the Utsunomiya Pack Company, Hiroshima, Japan, for the assistance in preparation of a TiO2-coated plastic film.
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