Pulsed electric field for Escherichia coli inactivation in pumpkin juice and nectar

Abstract

In this study experiments were performed using a batch pulsed electric field (PEF) system at different electric field strengths with a voltage of 35 kV and pulse frequency of 3 Hz, at 20 and 40°C, with pulse width between 0.8 and 1.0 µs, to evaluate the inactivation of Escherichia coli in pumpkin juice and nectar. The performance of the PEF technology can vary as a function of several process parameters and the conditions and procedures applied. The physicochemical characteristics (pH, total soluble solids, electrical conductivity) of the pumpkin juice were also evaluated. The juice showed 5.01 ± 0.01 of pH, 10.70 ± 0.11 (mS cm^-1) of electric conductivity and 9.85 ± 0.07 of soluble solids while in nectar, these parameters were changed to 5.11 ± 0.01 of pH, 8.54 ± 0.21 of electric conductivity and 6.40 ± 0.12 of soluble solids.  The use of a temperature of 40°C and pumpkin nectar (70:30, juice: distilled water) showed no difference in the bacterial reduction compared to 20°C and using 100% pumpkin juice, since in non-thermal processes it is better to use lower temperatures for less energy expenditure and less possibility of changes in raw material. The data showed that the PEF treatment reduced the microbial load moderately in all experiments, by a maximum of approximately 2.5 - 3 log cycles with 80 J g^-1 of specific energy and above 26,000 V cm^-1 of field strength