Combinations of pulsed white light and UV-C or mild heat treatment to inactivate conidia of Botrytis cinerea and Monilia fructigena.

The use of pulses of intense white light to inactivate conidia of the fungi Botrytis cinerea and Monilia fructigena, responsible for important economical losses during postharvest storage and transport of strawberries and sweet cherries, was investigated in this study. In the first stage, a light treatment applying pulses of 30 micros at a frequency of 15 Hz was investigated, resulting in a treatment duration varying from 1 to 250 s. The conidia of both fungi showed similar behaviour to pulsed light, with a maximal inactivation of 3 and 4 log units for B. cinerea and M. fructigena, respectively. The inactivation of the conidia increased with increasing treatment intensity, but no complete inactivation was achieved. The sigmoidal inactivation pattern obtained by the pulsed light treatment was described using a modification of the model of Geeraerd et al. [Int. J. Food Microbiol. 59 (2000) 185]. Hereto, the shoulder length was incorporated explicitly and relative values for the microbial populations were used. In the second stage, combinations of light pulses and ultraviolet-C or heat were applied. The UV light used in the experiments is the short-wave band or UV-C, running from 180 to 280 nm with a peak at 254 nm (UV-B runs from 280 to 320 nm and UV-A from 320 to 380 nm). The UV-C doses were 0.025, 0.05 and 0.10 J/cm(2), and the temperatures for the thermal treatment ranged from 35 to 45 degrees C during 3-15 min. When combining UV-C and light pulses, there was an increase in inactivation for both B. cinerea and M. fructigena, and synergism was observed. There was no effect of the order of the treatments. For the heat-light pulses combination, there was a difference between both fungi. The order of the treatments was highly significant for B. cinerea, but not for M. fructigena. Combining heat and light treatments improved the inactivation, and synergism between both methods was again observed. Complete inactivation of M. fructigena conidia was obtained after, e.g., a 40-s pulsed light treatment and 15 min at 41 degrees C, or after an 80-s light treatment and 10 min at 41 degrees C.

Inactivation of conidia of Botrytis cinerea and Monilinia fructigena using UV-C and heat treatment.

The effect of UV-C (lambda = 254 nm) and heat treatment was investigated on the inactivation of conidia of Botrytis cinerea and Monilinia fructigena, two major postharvest spoilage fungi of strawberries and cherries, respectively. Both fungi were grown at 21 degrees C in the dark and conidia were isolated after 1 week by washing the mycelium with a mild detergent solution. After filtration and resuspension in phosphate buffer to a titer of 10(5) to 10(6) cfu/ml, the conidia were subjected to different treatments. The applied UV-C doses varied from 0.01 to 1.50 J/cm2, and the conditions for the thermal treatment were 3, 5, 10, 15 and 20 min at temperatures ranging from 35 to 48 degrees C. Both techniques were applied individually and in combination. Spore inactivation increased with increasing intensity of single treatments. No surviving spores of B. cinerea were observed after 15 min at 45 degrees C or an UV-C treatment of 1.00 J/cm2. M. fructigena was more sensitive and a thermal treatment of 3 min at 45 degrees C or an UV-C treatment of 0.50 J/cm2 resulted in complete spore inactivation. Combination of both techniques reduced the required intensity of the treatment for inactivation of both fungi. The order of the applications had a significant effect on the degree of inactivation. The inactivation of B. cinerea conidia was greater when the heat treatment came first, and for M. fructigena, most inactivation was achieved when the heat treatment was preceded with an UV-C irradiation.

Comparison of exhaust emissions from Swedish environmental classified diesel fuel (MK1) and European Program on Emissions, Fuels and Engine Technologies (EPEFE) reference fuel: a chemical and biological characterization, with viewpoints on cancer risk.

Diesel fuels, classified as environmentally friendly, have been available on the Swedish market since 1991. The Swedish diesel fuel classification is based upon the specification of selected fuel composition and physical properties to reduce potential environmental and health effects from direct human exposure to exhaust. The objective of the present investigation was to compare the most stringent, environmentally classified Swedish diesel fuel (MK1) to the reference diesel fuel used in the "European Program on Emissions, Fuels and Engine Technologies" (EPEFE) program. The study compares measurements of regulated emissions, unregulated emissions, and biological tests from a Volvo truck using these fuels. The regulated emissions from these two fuels (MK1 vs EPEFE) were CO (-2.2%), HC (12%), NOx (-11%), and particulates (-11%). The emissions of aldehydes, alkenes, and carbon dioxide were basically equivalent. The emissions of particle-associated polycyclic aromatic hydrocarbons (PAHs) and 1-nitropyrene were 88% and 98% lower than those of the EPEFE fuel, respectively. The emissions of semi-volatile PAHs and 1-nitropyrene were 77% and 80% lower than those from the EPEFE fuel, respectively. The reduction in mutagenicity of the particle extract varied from -75 to -90%, depending on the tester strain. The reduction of mutagenicity of the semi-volatile extract varied between -40 and -60%. Furthermore, the dioxin receptor binding activity was a factor of 8 times lower in the particle extracts and a factor of 4 times lower in the semi-volatile extract than that of the EPEFE fuel. In conclusion, the MK1 fuel was found to be more environmentally friendly than the EPEFE fuel.

Kinetic analysis and modelling of combined high-pressure-temperature inactivation of the yeast Zygosaccharomyces bailii.

Eight foodborne yeasts were screened for sensitivity to high-pressure (HP) inactivation under a limited number of pressure-temperature combinations. The most resistant strains were Zygoascus hellenicus and Zygosaccharomyces bailii. The latter was taken for a detailed study of inactivation kinetics over a wide range of pressures (120-320 MPa) and temperatures (-5 to 45 degrees C). Isobaric and isothermal inactivation experiments were conducted in Tris-HCl buffer pH 6.5 for 48 different combinations of pressure and temperature. Inactivation was biphasic, with a first phase encompassing four to six decades and being described by first-order kinetics, followed by a tailing phase. Decimal reduction times (D) were calculated for the first-order inactivation phase and their temperature and pressure dependence was described. At constant temperature, D decreased with increasing pressure as expected. At constant pressure, D showed a maximum at around 20 degrees C, and decreased both at lower and at higher temperatures. A mathematical expression was developed to describe accurately the inactivation of Z. bailii as a function of pressure and temperature under the experimental conditions employed. A limited number of experiments in buffer at low pH (3-6) suggest that the model is, in principle, applicable at low pH. In apple and orange juice however, higher inactivation than predicted by the model was achieved.

Escherichia coli mutants resistant to inactivation by high hydrostatic pressure.

Alternating cycles of exposure to high pressure and outgrowth of surviving populations were used to select for highly pressure-resistant mutants of Escherichia coli MG1655. Three barotolerant mutants (LMM1010, LMM1020, and LMM1030) were isolated independently by using outgrowth temperatures of 30, 37, and 42 degrees C, respectively. Survival of these mutants after pressure treatment for 15 min at ambient temperature was 40 to 85% at 220 MPa and 0.5 to 1.5% at 800 MPa, while survival of the parent strain, MG1655, decreased from 15% at 220 MPa to 2 x 10(-8)% at 700 MPa. Heat resistance of mutants LMM1020 and LMM1030 was also altered, as evident by higher D values at 58 and 60 degrees C and reduced z values compared to those for the parent strain. D and z values for mutant LMM1010 were not significantly different from those for the parent strain. Pressure sensitivity of the mutants increased from 10 to 50 degrees C, as opposed to the parent strain, which showed a minimum around 40 degrees C. The ability of the mutants to grow at moderately elevated pressure (50 MPa) was reduced at temperatures above 37 degrees C, indicating that resistance to pressure inactivation is unrelated to barotolerant growth. The development of high levels of barotolerance as demonstrated in this work should cause concern about the safety of high-pressure food processing.