Inactivation of Listeria innocua in dairy fluids by pulsed electric fields: influence of electric parameters and food composition

• Published in: Innovative food science & emerging technologies 2002-12, Vol.3 (4), p.357-369
• Main Authors: Picart, Laëtitia, Dumay, Eliane, Cheftel, J.Claude
• Format: Article
• Language: English
• Subjects: Atomic force microscopy; Chemical and Process Engineering; Dairy cream; Electric pulses; Engineering Sciences; Food and Nutrition; Food engineering; Life Sciences; Listeria innocua; Microbial inactivation; Milk
• ISSN: 1466-8564; 1878-5522
• DOI: 10.1016/S1466-8564(02)00055-3

The inactivation of 3 strains of Listeria innocua (S1, S2, S3) by pulsed electric fields (PEF) in a batch treatment chamber (exponential decay pulses) was studied as a function of treatment time. In 16 mM Na phosphate buffer, pH 7.0, the resistance order of the strains to PEF (46 kV/cm, 1.1 Hz: S2>S1>S3) differed from that of heat resistance (60 °C: S1>S2>S3). Inactivation of L. innocua S2 (in the 16 mM phosphate buffer) increased with field strength (from 17 to 45 kV/cm) or treatment time. Increasing pulse repeat frequency from 1.1 to 100 Hz at 29 kV/cm markedly increased L. innocua S2 inactivation in whole milk (pH 6.6) (from 0.67 to 1.8 log cycles for 250 μs of cumulated treatment time), but less so in skim milk (pH 6.6). No influence of pulse repeat frequency on L. innocua S2 inactivation was observed in the 16 mM phosphate buffer (at 45–46 kV/cm), in 40 mM Na phosphate buffer (pH 6.6 at 29 kV/cm) or in liquid dairy cream (pH 6.7, at 30 or 37–38 kV/cm). Upon PEF processing in the 16 mM phosphate buffer at 36 or 45 kV/cm (100 Hz), the number of total survivors and of non-stressed survivors (able to grow on a selective medium) markedly decreased when the energy input to samples increased, most survivors becoming stressed. L. innocua S2 suspended in skim milk and subjected to PEF were observed by atomic force microscopy. 3D images revealed collapsed and/or segmented bacteria.