Moderate intensity Pulsed Electric Fields (PEF) as alternative mild preservation technology for fruit juice.

Moderate intensity Pulsed Electric Fields (PEF) was studied for microbial inactivation as an alternative to high intensity PEF or to classical thermal pasteurization. The process is characterized by the application of electric pulses, allowing an increase of the product temperature by the ohmic heat generated by the pulses. A systematic evaluation of the effect of parameters electric field strength (E) and pulse width (τ) on the inactivation of Escherichia coli, Listeria monocytogenes, Lactobacillus plantarum, Salmonella Senftenberg and Saccharomyces cerevisiae in orange juice was carried out in a continuous flow system. A wide range of conditions was evaluated, and both E and τ were shown to be important in the efficacy to inactivate micro-organisms. Remarkably, PEF conditions at E = 2.7 kV/cm and τ = 15-1000 µs showed to be more effective in microbial inactivation than at E = 10 kV/cm and τ = 2 µs. Inactivation kinetics of the tested PEF conditions were compared to an equivalent thermal process to disentangle non-thermal effects (electroporation) from thermal effects responsible for the microbial inactivation. At standard high intensity PEF treatment a non-thermal inactivation at E = 20 kV/cm and τ = 2 µs pulses was observed and attributed to electroporation. Non-thermal effects could also be resolved with moderate intensity PEF at E = 2.7 kV/cm and pulse width between τ = 15-1000 µs. Microbial inactivation at these moderate intensity PEF conditions was studied in more detail at different pH and medium conductivity for E. coli and L. monocytogenes in watermelon juice and coconut water. Under moderate intensity PEF conditions the effectiveness of treatment was independent of pH for all evaluated matrices in the pH range of 3.8-6.0, whereas under high intensity PEF conditions the pH of the product is a critical factor for microbial inactivation. This suggests that the inactivation proceeds through a different mechanism at moderate intensity PEF, and speculations for this mechanism are presented. In conclusion, moderate intensity PEF conditions at E = 2.7 kV/cm and pulse width of 15-1000 µs has potential for industrial processing for the preservation of fruit juices and pH neutral liquid food products.

Pulsed electric field processing of different fruit juices: impact of pH and temperature on inactivation of spoilage and pathogenic micro-organisms.

Pulsed electrical field (PEF) technology can be used for the inactivation of micro-organisms and therefore for preservation of food products. It is a mild technology compared to thermal pasteurization because a lower temperature is used during processing, leading to a better retention of the quality. In this study, pathogenic and spoilage micro-organisms relevant in refrigerated fruit juices were studied to determine the impact of process parameters and juice composition on the effectiveness of the PEF process to inactivate the micro-organisms. Experiments were performed using a continuous-flow PEF system at an electrical field strength of 20 kV/cm with variable frequencies to evaluate the inactivation of Salmonella Panama, Escherichia coli, Listeria monocytogenes and Saccharomyces cerevisiae in apple, orange and watermelon juices. Kinetic data showed that under the same conditions, S. cerevisiae was the most sensitive micro-organism, followed by S. Panama and E. coli, which displayed comparable inactivation kinetics. L. monocytogenes was the most resistant micro-organism towards the treatment conditions tested. A synergistic effect between temperature and electric pulses was observed at inlet temperatures above 35 °C, hence less energy for inactivation was required at higher temperatures. Different juice matrices resulted in a different degree of inactivation, predominantly determined by pH. The survival curves were nonlinear and could satisfactorily be modeled with the Weibull model.

Comparison of laboratory single species and field population-level effects of the pyrethroid insecticide lambda-cyhalothrin on freshwater invertebrates.

The toxicity of the pyrethroid insecticide lambda-cyhalothrin to freshwater invertebrates has been investigated using data from short-term laboratory toxicity tests and in situ bioassays and population-level effects in field microcosms. In laboratory tests, patterns of toxicity were consistent with previous data on pyrethroids. The midge Chaoborus obscuripes was most sensitive (48- and 96-h EC50 = 2.8 ng/L). Other insect larvae (Hemiptera, Ephemeroptera) and macrocrustacea (Amphipoda, Isopoda) were also relatively sensitive, with 48- and 96-h EC50 values between 10 and 100 ng/L. Generally, microcrustacea (Cladocera, Copepoda) and larvae of certain insect groups (Odonata and Chironomidae) were less sensitive, with 48-h EC50 values higher than 100 ng/L. Mollusca and Plathelminthes were insensitive and were unaffected at concentrations at and above the water solubility (5 microg/L). Generally, the EC50 values based on initial population responses in field enclosures were similar to values derived from laboratory tests with the same taxa. Also, the corresponding fifth and tenth percentile hazard concentrations (HC5 and HC10) were similar (laboratory HC5 = 2.7 ng/L and field HC5 = 4.1 ng/L; laboratory and field HC10 = 5.1 ng/L), at least when based on the same sensitive taxonomic groups (insects and crustaceans) and when a similar concentration range was taken into account. In the three field enclosure experiments and at a treatment level of 10 ng/L, consistent effects were observed for only one population (Chaoborus obscuripes), with recovery taking place within 3 to 6 weeks. The laboratory HC5 (2.7 ng/L) and HC10 (5.1 ng/L) based on acute EC50 values of all aquatic arthropod taxa were both lower than this 10 ng/L, a concentration that might represent the "regulatory acceptable concentration." The HC5 and HC10 values in this study in The Netherlands (based on static laboratory tests with freshwater arthropods) were very similar to those derived from a previous study in the United Kingdom (1.4 and 3.3 ng/L). This suggests that for pesticides like lambda-cyhalothrin, HC5 values based on static laboratory tests may provide a conservative estimate of the potential for community-level effects under field conditions. While these HC5 values are conservative for initial effects, they do not provide information on recovery potential, which may be important for regulatory decision-making.

Rate of bentazone transformation in four layers of a humic sandy soil profile with fluctuating water table.

The rate of transformation of a pesticide as a function of the depth in the soil is needed as an input into computations on the risk of residues leaching to groundwater. The herbicide bentazone was incubated at 15 degrees C in soil materials derived from four layers at depths of up to 2.5 m in a humic sandy soil profile with a fluctuating water table (0.8 to 1.4 m), while simulating the redox conditions existing in the field. Gamma-irradiation experiments indicated that bentazone is mainly transformed by microbial activity in the soil. The rate constant for transformation was highest in the humic sandy top layer; it decreased with depth in the sandy vadose subsoil. However, material from the top of the phreatic aquifer had a higher rate constant than that from the layers just above. The presence of fossil organic material in the fluviatile water-saturated sediment probably stimulated microbial activity and bentazone transformation. The changes in the transformation rate constant with depth showed the same trend as those in some soil factors, viz organic carbon content, water-extractable phosphorus and microbial density as measured by fluorescence counts. However, the (low) concentration of dissolved organic carbon (DOC) in the top of the aquifer did not fit the trend. The rate constant for bentazone transformation in the layers was higher at lower initial contents of the herbicide.