Chawengkijwanich Chamorn, Hayata Yasuyoshi
National Nanotechnology Center, National Science and Technology Development Agency, Thailand Science Park, Klong luang, Pathumthani 12120, Thailand.
Int J Food Microbiol. 2008 Apr 30;123(3):288-92. doi: 10.1016/j.ijfoodmicro.2007.12.017. Epub 2007 Dec 28.
Titanium dioxide (TiO2) has attracted a great deal of attention as a photocatalytic disinfecting material in the food and environmental industry. TiO2 has been used to inactivate a wide variety of microorganisms in many applications. In the present study, we aimed to develop a TiO2 powder-coated packaging film and clarify its ability to inactivate Escherichia coli both in vitro and in actual tests, using two different particle sizes and two types of illumination at different intensities. No inhibition effect of the testing method itself on the growth of E. coli was observed. The cells of E. coli were found to have decreased 3 log CFU/ml after 180 min of illumination by two 20 W black-light bulbs (wavelength of 300-400 nm) on TiO2-coated oriented-polypropylene (OPP) film, while E. coli decreased 1 log CFU/m with black-light illumination of uncoated OPP film. The results showed that both ultraviolet A (UVA; wavelength of 315-400 nm) alone and TiO2-coated OPP film combined with UVA reduced the number of E. coli cell in vitro, but that the reduction of E. coli cell numbers was greater by TiO2-coated OPP film combined with UVA. The antimicrobial effect of TiO2-coated film is dependent on the UVA light intensity (0, <0.05 and 1 mW/cm2) and the kind of artificial light (black-light and daylight fluorescent bulbs), but it is independent of the particle size of TiO2 coating on the surface of OPP film. The surviving cell numbers of E. coli on TiO2-coated film decreased 3 log and 0.35 log CFU/ml after 180 min of illumination by two 20 W black bulbs and two 20 W daylight fluorescent bulbs, respectively. Despite the lesser efficacy of the photocatalytic method with fluorescent lights, the survival of E. coli cells using this method was 50% of that using fluorescent lights alone. In the actual test, the number of E. coli cells from cut lettuce stored in a TiO2-coated film bag irradiated with UVA light decreased from 6.4 on Day 0 to 4.9 log CFU/g on Day 1, while that of an uncoated film bag irradiated with UVA light decreased from 6.4 to 6.1 log CFU/g after 1 day of storage. The result shows that the TiO2-coated film could reduce the microbial contamination on the surface of solid food products and thus reduce the risks of microbial growth on fresh-cut produce.
二氧化钛（TiO₂）作为食品和环境工业中的光催化消毒材料受到了广泛关注。在许多应用中，TiO₂已被用于灭活多种微生物。在本研究中，我们旨在开发一种涂覆有TiO₂粉末的包装薄膜，并通过使用两种不同粒径和两种不同强度光照的两种类型照明，阐明其在体外和实际测试中灭活大肠杆菌的能力。未观察到测试方法本身对大肠杆菌生长有抑制作用。在用两个20 W黑光灯（波长300 - 400 nm）照射涂覆有TiO₂的定向聚丙烯（OPP）薄膜180分钟后，发现大肠杆菌细胞数量减少了3 log CFU/ml，而用未涂覆的OPP薄膜进行黑光照射时，大肠杆菌减少了1 log CFU/ml。结果表明，单独的紫外线A（UVA；波长315 - 400 nm）以及涂覆有TiO₂的OPP薄膜与UVA结合在体外均能减少大肠杆菌细胞数量，但涂覆有TiO₂的OPP薄膜与UVA结合对大肠杆菌细胞数量的减少幅度更大。涂覆有TiO₂的薄膜的抗菌效果取决于UVA光强度（0、<0.05和1 mW/cm²）以及人工光的种类（黑光灯和日光荧光灯），但与OPP薄膜表面TiO₂涂层的粒径无关。在用两个20 W黑光灯和两个20 W日光荧光灯分别照射180分钟后，涂覆有TiO₂的薄膜上大肠杆菌的存活细胞数量分别减少了3 log和0.35 log CFU/ml。尽管使用荧光灯的光催化方法效果较差，但使用该方法时大肠杆菌细胞的存活率是仅使用荧光灯时的50%。在实际测试中，用UVA光照射储存在涂覆有TiO₂薄膜袋中的切生菜，大肠杆菌细胞数量从第0天的6.4 log CFU/g降至第1天的4.9 log CFU/g，而用UVA光照射未涂覆薄膜袋中的切生菜，储存1天后大肠杆菌细胞数量从6.4降至6.1 log CFU/g。结果表明，涂覆有TiO₂的薄膜可以减少固体食品表面的微生物污染，从而降低鲜切农产品上微生物生长的风险。
