Inactivation of Escherichia coli, Saccharomyces cerevisiae, and Lactobacillus brevis in Low-fat Milk by Pulsed Electric Field Treatment: A Pilot-scale Study

Abstract

We investigated the effects of a pulsed electric field (PEF) treatment on microbial inactivation and the physical properties of low-fat milk. Milk inoculated with Escherichia coli, Saccharomyces cerevisiae, or Lactobacillus brevis was supplied to a pilot-scale PEF treatment system at a flow rate of 30 L/h. Pulses with an electric field strength of 10 kV/cm and a pulse width of 30 μs were applied to the milk with total pulse energies of 50-250 kJ/L achieved by varying the pulse frequency. The inactivation curves of the test microorganisms were biphasic with an initial lag phase (or shoulder) followed by a phase of rapid inactivation. PEF treatments with a total pulse energy of 200 kJ/L resulted in a 4.5-log reduction in E. coli, a 4.4-log reduction in L. brevis, and a 6.0-log reduction in S. cerevisiae. Total pulse energies of 200 and 250 kJ/L resulted in greater than 5-log reductions in microbial counts in stored PEF-treated milk, and the growth of surviving microorganisms was slow during storage for 15 d at 4℃. PEF treatment did not change milk physical properties such as pH, color, or particle-size distribution (p<0.05). These results indicate that a relatively low electric-field strength of 10 kV/cm can be used to pasteurize low-fat milk.

Impact of the pulsed electric field on physicochemical properties, fatty acid profiling, and metal migration of goat milk

“…These results are consistent with a study by Lee et al. (2015) which reported a non‐significant changes ( p > .05) in the FG size distribution of PEF‐treated (EFS: 10 kV/cm; pulse width: 10 µs) low‐fat milk.…”

“…Our result suggests that PEF treatment had non-significant change (p > .05) in the goat milk FGs and their agglomerates. These results are consistent with a study byLee et al (2015) which reported a non-significant changes (p > .05) in the FG size distribution of PEF-treated (EFS: 10 kV/cm; pulse width: 10 µs) low-fat milk. F I G U R E 1 Distribution pattern of untreated and PEF-treated goat milk fat globules at 20, 30, and 40 kV/cm for 5 µs (a) and 10 µs (b) micro-elements namely Fe, Cr, Ni, and Mn were analyzed in the present study.…”

“…Particle size distribution was determined through the method stated by Lee et al. (2015) with some modifications. A Mastersizer 2000 (Malvern Instrument, Malvern, United Kingdom) particle size analyzer equipped with a Hydro 2000MU dispersion unit was used with refractive indices of goat milk and dispersed phase were 1.40 and 1.33, respectively.…”

“…Lee et al. (2015) also demonstrated that PEF treatment at 10 kV/cm for 30 µs did not change the physical properties of commercial low‐fat bovine milk including pH, color, and particle size distribution. Sharma et al., (2018) also reported that the pH of PEF‐treated raw bovine whole milk did not change significantly ( p > .05) after treatment at 25.7 kV/cm for 34 µs.…”

“…Pasteurization is crucial to assure that the microbial load of goat milk is significantly reduced leading to the prolongation of its shelf life. However, conventional heat pasteurization affects the organoleptic properties of milk, which often produces cooked‐flavor due to the destruction of sulphydryl groups in sulphur‐containing amino acids (Lee et al., 2015). Thus, non‐thermal treatment such as pulsed electric field (PEF) has gained greater attention as a substitute for thermal pasteurization due to the rising demand for high nutritional value and fresh‐like characteristic of processed foods (Aadil et al., 2015; Aadil et al., 2018; Ahmad et al., 2019; Pankiewicz et al, 2019; Zhang et al., 2019).…”