Yasuyoshi Hayata

Development of TiO2 powder-coated food packaging film and its ability to inactivate Escherichia coli in vitro and in actual tests

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.

INACTIVATION OF ESCHERICHIA COLI BY CO2 MICROBUBBLES AT A LOWER PRESSURE AND NEAR ROOM TEMPERATURE

The ability of CO2 microbubbles (MB-CO2) to inactivate Escherichia coli suspended in a saline solution at a pressure lower than 2.0 MPa was investigated. A 6-log reduction in E. coli population occurred with MB-CO2 at 40°C and 2.0 MPa after 60 min treatment, and a slight reduction occurred with low-pressurized CO2 under the same conditions. The dissolved CO2 concentration in the solution with MB-CO2 was much higher than that with low-pressurized CO2. On the other hand, E. coli could not be inactivated with N2 microbubbles instead of CO2 under the same conditions. The ability of MB-CO2 to inactivate E. coli increased concomitant with increasing the CO2 feeding rate, pressure, and temperature. These results demonstrate that, with the experimental conditions and apparatus used in this study, MB-CO2 could very effectively inactivate E. coli at a temperature of 30°C to 40°C and at a pressure of 0.5 to 2.0 MPa.

Inactivation of Saccharomyces cerevisiae by CO2 Microbubbles at a Lower Pressure and Near Ambient Temperature

The ability of CO2 microbubbles (MB-CO2) to inactivate Saccharomyces cerevisiae suspended in a physiological saline solution at a pressure lower than 2.0 MPa was investigated. A 6-log reduction in the S. cerevisiae population was induced by MB-CO2 at 40°C and 2.0 MPa after a 50 min treatment in a physiological saline solution with 5.0% ethanol, and a 3-log reduction was induced by low-pressurized CO2 under the same conditions. Furthermore, the ability of MB-CO2 to inactivate S. cerevisiae increased concomitant with increasing the CO2 feeding rate, pressure, temperature, and ethanol concentration in a physiological saline solution. Additionally, the decimal reduction time (D value) in the inactivation of S. cerevisiae by the MB-CO2 treatment might depend on the saturation value of the dissolved CO2 concentration in the solution. These results suggested that MB-CO2 treatment could inactivate S. cerevisiae in a low-concentration ethanol solution at 40°C to 45°C and at a pressure of 1.0 to 2.0 MPa.

Chlorophenoxyacetic acid and chloropyridylphenylurea accelerate translocation of photoassimilates to parthenocarpic and seeded fruits of muskmelon (Cucumis melo).

We compared the effect of p-chlorophenoxyacetic acid (p-CPA) and 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU) on parthenocarpic and seeded muskmelon (Cucumis melo) fruits in regards to fruit development and the transport of photoassimilates from leaves exposed to ¹⁴CO₂ to the developing fruits. Ten days after anthesis (DAA), the fresh weight, total ¹⁴C-radioactivity and contents of ¹⁴C-sucrose and ¹⁴C-fructose were higher in the CPPU-induced parthenocarpic fruits than in seeded fruits. However, at 35 DAA, fresh weight and sucrose content in mesocarp, placenta and empty seeds of the parthenocarpic fruits were lower than in seeded fruits. Also, total ¹⁴C-radioactivity and ¹⁴C-sugar content of the parthenocarpic fruits were lower as well as the translocation rate of ¹⁴C-photoassimilates into these fruits. Application of p-CPA to the parthenocarpic fruits at 10 and 25 DAA increased fresh weight and sugar content. Moreover, these treatments elevated the total ¹⁴C-radioactivity, ¹⁴C-sucrose content and the translocation rate of ¹⁴C-photoassimilates. The ¹⁴C-radioactivity along the translocation pathway from leaf to petiole, stem, lateral shoot and peduncle showed a declining pattern but dramatically increased again in the fruits. These results suggest that the fruits sink strength was regulated by the seed and enhanced by the application of p-CPA.

Effect of jasmonates on ethylene biosynthesis and aroma volatile emission in Japanese apricot infected by a pathogen (Colletotrichum gloeosporioides).

The effects of the application of the jasmonic acid derivative n-propyl dihydrojasmonate (PDJ) on ethylene biosynthesis, volatile compounds, and endogenous jasmonic acid (JA) and methyl jasmonate (MeJA) were examined in Japanese apricot (Prunus mume Sieb.) infected by a pathogen (Colletotrichum gloeosporioides). The fruit were dipped into 0.4 mM PDJ solution before inoculation with the pathogen and stored at 25 °C for 6 days. The inoculation induced an increase in 1-aminocyclopropane-1-carboxylic acid (ACC), ethylene, JA, and MeJA. In contrast, PDJ application reduced the endogenous JA, MeJA, and ethylene production and expression of the ACC oxidase gene (PmACO1) caused by the pathogen infection. The lesion diameter with C. gloeosporioides decreased upon PDJ application. The alcohol, ester, ketone, and lactone concentrations and alcohol acyltransferase (AAT) activity increased in the pathogen-infected fruit, but were decreased by PDJ application. These results suggest that PDJ application might influence ethylene production through PmACO1 and that aroma volatile emissions affected by pathogen infection can be correlated with the ethylene production, which is mediated by the levels of jasmonates.