Continuous raw skim milk processing by pulsed electric field at non-lethal temperature: Effect on microbial inactivation and functional properties

Abstract

Pulsed electric field (PEF) is an emerging non-thermal processing technology used to inactivate microorganisms in liquid foods such as milk. The objective of this research was to study the effectiveness of continuous PEF equipment (square wave pulses) on total microorganisms of raw skim milk and on Salmonella enteritidis inactivation under moderate temperatures (T < 50°C). Processing parameters (electric field and pulse width) were chosen as follows: 45 kV·cm-1/500 ns and 55 kV·cm -1/250 ns, with increasing pulse frequencies from 40 to 120 Hz, that corresponds to an energy input varying from range 0-100 kJ·kg -1. In these conditions, the effectiveness of PEF processing on microbial inactivation was very limited: 1.4-log reduction of total microflora and S. enteritidis was the maximal inactivation ratio obtained. The effect of these PEF treatments on physicochemical and technological properties of the milk was also evaluated. These process conditions had an effect on proteinic components of milk such as casein micelles, since viscosity of PEF-treated milk decreased and coagulation properties were enhanced for high field levels (45-55 kV·cm-1) with 2.1 to 3.5 μs cumulated treatment time and square waves. This study demonstrated that, contrary to numerous previous studies, PEF treatments had an impact on some food constituents. © INRA, EDP Sciences, 2005.